JP3586815B2 - Manufacturing method of cell structure - Google Patents

Description

【００４６】
【表２】

【００４７】
ポリマー溶液の調製に用いる混合溶媒は、前記の溶剤と非溶剤の体積比率が一般に１０：１〜１０：１０であればセル構造体を得ることができる。これよりも溶剤の比率が大きいと、溶媒の気散終了時までポリマーの溶解が続き、セル壁の沈殿が生ぜず、溶媒の気散後に気泡を介在しない透明なポリマー塊ができるのみである。一方、溶剤の比率が小さいと、僅かの溶剤が気散しただけでポリマーが一挙に沈殿するため、セル間の溶着が不完全となり、セル間の物理的つながりのない脆いセル構造体が出来上がったり、型の形状とは全く異なった収縮、変形したものができるので良くない。三次元空間的にセルが連結してしっかりした形状の安定なセル構造体が構築されるにふさわしい比率の範囲は、溶媒組成によって異なるが、１０：１〜１０：７である。
【００４８】
本発明の製造方法は、溶剤と非溶剤が上記の体積比率に混合された溶媒にポリマーを溶解して調製したポリマー溶液を型内に充填し、溶剤の沸点より低い温度、好ましくは２０℃以下の温度で常圧又は減圧下に溶媒を気散させる工程から成っている。溶剤の沸点以上で溶媒を気散させると、溶剤が沸騰してセル壁を破壊し、溶着するので、良質のセル構造体を得ることはできない。
【００４９】
この工程を密閉された装置の中で行えば、気散した溶媒は回収されるので何度も繰り返して使用することができ、また操作中にも吸入することがないので安全かつ省資源的である。
【００５０】
また、ポリマー溶液の粘度を上げてセル壁の固定化を図る目的で、溶媒を気散させる前に約１０℃以下の低温に冷却して増粘し、減圧下に気散させる操作を採用することも望ましい。この操作は肉厚のシート状や異形状のセル構造体をつくるのに有効である。
【００５１】
本発明の方法によれば、数１００μｍ以下の厚さのフィルム状やシート状のセル構造体であれば、型内にポリマー溶液を薄く充填して室温、常圧で自然に溶媒を気散させだけで容易に見ている間の短時間にセル構造体を得ることができる。完全に溶媒を除去するには更に減圧下に乾燥すればよく、この操作により残留溶媒のない生体材料として用いることのできるセル構造体が得られる。
【００５２】
また、より肉厚の（１ｍｍ以上の厚さの）プレート状の厚さの一定したセル構造体などは、比較的濃厚なポリマー溶液を型内に充填して溶媒を気散させた後、更にその上にポリマー溶液を同様に充填して溶媒を気散させる操作を複数回繰り返すことによって得ることができる。
【００５３】
更に、肉厚の異形状に成形されたセル構造体は、ポリマー溶液を異形状の型内に充填して、前記のように溶媒を気散させることにより、少し長い時間を要するが容易に得ることができる。このとき溶剤が型の全面から均等に急速に気散できるように、前記ポリマーを通過させないが溶媒を通過させる微細な通気孔を無数に有する多孔質の型、例えば素焼きの陶器製の型などを使用するのが好ましい。そして、この場合も、溶媒の気散を速めることと、成形体内部のポリマー溶液の未沈殿部分への陥没と変形を避けて形状を保つことを目的として、ポリマー溶液を約１０℃以下の低温にて増粘し、減圧下に溶媒を強制的に気散させる操作を採ることも一つの方法である。このようにすれば、５ｃｍ以上の厚さをもつブロック状あるいは異形状に成形されたセル構造体を得ることができる。
【００５４】
セル構造体の発泡倍率を決定する要因は、ポリマー溶液の粘度、ポリマー濃度、混合溶媒の組成比、および溶媒の気散の速度であるが、ポリマー溶液が沈殿してセル構造体を形成する原理からすれば、ポリマー濃度が最も重要な要因の一つである。発泡倍率は肉厚の程度や気孔の大きさにも依存するが、数倍から数１０倍のものまで得ることができる。
【００５５】
本発明の方法によって得られる前述の生体内分解吸収性の脂肪族ポリエステル系ポリマーのセル構造体は、生体の損傷部治癒のための足場、薬物放出のための担体を主なる用途とする生体材料として使うことができる。このような生体材料としてのセル構造体を製造する場合は、損傷あるいは切除部位の治療や再建を速める目的で、生体活性物質、薬物、細胞の増殖因子などを含有させたポリマー溶液を調製して、これらの物質や薬物を含んだセル構造体とすることが望ましく、その厚さが１ｍｍ以上で、発泡倍率が３倍以上となるようにセル構造体をつくることが望ましい。
【００５６】
セル構造体に含ませる硬組織の治癒、再建のための生体活性物質としては、骨を誘導し、骨と結合が可能な生体活性ガラスやガラスセラミックス、例えば、Ｂｉｏｇｌａｓｓ（４５Ｓ５）、Ｃｅｒａｖｉｔａｌ（ＫＧＳ）、Ａ−Ｗ ｇｌａｓｓ ｃｅｒａｍｉｃｓ、ＢＩＯＶＥＲＩＴ−１、Ｉｍｐｌａｓｔｏ−Ｌ１などの顆粒、微粒子が挙げられる。そして、骨の増殖因子としては、表３に例示のものが挙げられる。また、薬物としては、骨組織治療薬であるカルシトニン、ビタミンＤ、女性ホルモン、ビスホスホネート（ｂｉｓｐｈｏｓｐｈｏｎａｔｅ）、ビタミンＫなどの硬組織関係の薬物以外にも、例えば抗癌剤（特に固形癌のように特定部位に設置埋入して治療する場合に有効）や抗菌剤、各種ホルモン、生理活性物質、各種サイトカインなど、種々の治療薬を含ませることができる。
【００５７】
【表３】

【００５８】
本発明の製造方法は凍結乾燥法とは異なり、セル壁のポリマー内部に上記の物質や薬物が大部分包埋された状態のセル構造体が得られるので、ポリマーの分解と併行した薬物の徐放性を正しくコントロールできる。しかも、本発明の製造方法は、生体の損傷部位の複雑な三次元空間を形状的にあてはめることができるように成形されたセル構造体を得ることができるので、そのように成形されたセル構造体の中に上記の物質等が含まれていると、細胞、組織の誘導が要求される生体の立体的形状に沿って生成されるので形を再建できる理想的な足場となる。
【００５９】
また、本発明の製造方法によって得られるセル構造体は、先述したように基本的に連続気泡体であり、発泡倍率が比較的高い場合は極めて大きな表面積を有する。表面積の大きさは見掛けの分解速度を大きくするので、発泡倍率の調節により分解速度（薬剤の徐放速度）をコントロールすることもできる。そして、孔の比率が大きいことは、周囲の細胞、組織の浸入を速めることになり、発泡倍率が大きいことは、セル構造体の重量が非発泡体である元の個体の１／発泡倍率であるから、極めて少ない重量の分解・吸収性ポリマーを生体内に埋入すればよいことになる。従って、分解・吸収過程で組織反応を生ずる原因となる分解細片の量もまた少なくなるので、異物反応の機会が極めて少なくなるという生体材料として重要な多くの性質を付与するものである。また、Ｔｇ（ガラス転移点）が体温以上、１００℃以下の比較的低温であるＰＬＡ（ポリ乳酸）などのセル構造体は、生体への埋入直前に加熱して、自由に変形させることが可能であるから、埋入部位の形状に密着した足場や製剤をつくるのに有利である。
【００６０】
更に、本発明の製造方法を応用すれば、薬物等の濃度が内側と表側で異なる濃度勾配をもったセル構造体や、他の材料と複合化させた高強度のセル構造体を得ることもできる。すなわち、前者の濃度勾配をもつセル構造体は、例えば、薬物等の濃度が異なる数種類のポリマー溶液を調製し、薬物濃度が高いポリマー溶液から、または薬物濃度が低いポリマー溶液から、順々に型内に充填して溶媒を気散させる操作を繰り返すことによって得られる。また、後者の複合化セル構造体は、例えば、生体内分解吸収性あるいは生体不活性な繊維でできた織物、不織布などの補強材料を型内に入れ、ポリマー溶液を型内に充填して溶媒を気散させることにより得られる。
【００６１】
【作用】
本発明の製造方法のように、有機合成ポリマーを溶剤と該溶剤より高沸点の非溶剤との混合溶媒に溶解してポリマー溶液を調製し、このポリマー溶液を型内に充填して、溶剤の沸点より低い温度で混合溶媒を気散させると、既述したように、沸点の低い溶剤が優先的に気散して沸点の高い非溶剤の比率が次第に上昇し、溶剤と非溶剤がある比率に達すると、溶媒はポリマーを溶解することができなくなって、ポリマーが急激に沈殿し、収縮、固化して固定化され、ポリマーの連結した薄いセル壁に溶媒が内包された状態のセル構造が形成される。そして、残りの溶剤がセル壁の一部分を破壊しながら細孔をつくって気散し、沸点の高い非溶剤も気散して、セル壁に包まれていた溶媒の溜め跡が気孔として固定して残り、基本的に気孔が連結した連続気泡のセル構造体が得られる。
【００６２】
【実施例】
以下、本発明の実施例を説明する。
【００６３】
［実施例１］
溶剤に塩化メチレン（ＣＨ_２Ｃｌ_２）、非溶剤（沈殿剤）にエタノール（Ｃ_２Ｈ_５ＯＨ）を使用し、溶剤と非溶剤の体積比（溶剤／非溶剤）を１０／０、１０／１、１０／３、１０／５、１０／７、１０／９に変化させた６種類の混合溶媒に、粘度平均分子量が約３０万（分子量分布；分散度Ｍｗ／Ｍｎ＝２．５）のポリ−Ｌ−乳酸を４ｇ／ｄｌの濃度に溶解してポリマー溶液を調製した。
【００６４】
これらのポリマー溶液を、直径が１０ｃｍのシャーレに液面が１３ｍｍの高さとなるように注入し、そのまま室温（１０〜２０℃）で大気圧下に静置してセル構造体をつくった。２４時間後にはポリマー溶液の溶媒は蒸散しており、溶媒の組成比（溶剤／非溶剤）が１０／７と１０／９のもののみが僅かにエタノール臭を残しているに過ぎなかった。その後、減圧乾燥すると、ガスクロマトグラフで溶媒を検知できなくなった。得られたセル構造体の性状等を下記の表４にまとめて示す。
【００６５】
【表４】

【００６６】
以上の結果からすれば、塩化メチレンとエタノールの混合溶媒の場合は、溶媒の組成比（塩化メチレン／エタノール）が１０／１〜１０／６で比較的良好なセル構造体が得られる。この範囲の溶媒組成比のポリマー溶液は、低沸点（４０℃）、高蒸気圧（３４８．９ｍｍＨｇ／２０℃）の塩化メチレンが優先的に蒸散するので、残留溶媒中の高沸点（７８．３℃）、低蒸気圧（４４ｍｍＨｇ／２０℃）のエタノールの比率が上昇して、溶液はポリマーを外気と接している溶液表面から内部の方向に徐々に白濁、沈殿させる。このとき残留溶媒を内在した連続気泡壁（ｐｏｒｅ ｉｎｔｅｒｃｏｎｎｅｃｔｉｏｎ）が形成され、更なる溶媒の気散とともに最終的に全面にセル構造体が形成される。
【００６７】
溶媒組成比が１０／５で発泡倍率１２．７倍という高い値のセル構造体が得られ、発泡倍率とともにセル構造体が厚くなった。これは溶液の外気と接触している表面からポリマーが溶剤の気散により直ちに沈殿、固化し、セル壁を形成して固定化したために厚みが維持されたためと考えられる。この事実は、ある発泡倍率のある厚みのセル構造体を要求するときは、溶媒の組成比とポリマー溶液の濃度を調節すればよいことを示唆している。
【００６８】
溶剤のみの場合は、溶剤が気散完了するまでポリマーを溶解しながら気散するので、溶剤の抜けがらの孔は溶着して孔として残らない。そのために、ポリマー本来の透明なシートが形成された。
【００６９】
溶剤の比率が高い場合は、溶剤の気散により体積が減少し、その分だけ厚みが低下したところで沈殿、固化してセル壁の固定化がなされるために、セル構造体の厚みと発泡倍率が低下したと考えられる。逆に初期の非溶剤（沈殿剤）の比率が高い場合は、溶剤のわずかな気散によって直ちに非溶剤の沈殿剤としての効果が発現され、沈殿が一気に生成する。このとき、ポリマーを溶解して連続したセル壁を形成するだけの量の溶剤が残っていないので、孔が生成するときに大きく収縮したり、沈殿したポリマーの粒子が単に溶着して連結体を形成し、それが気孔を介在したような一種の焼結体のごときセル構造体を形成すると考えられる。実際に、溶媒組成比が１０／７では沈殿、固化するときの収縮が厳しく、表面に多くの皺のある変形したセル構造体が得られ、溶媒組成比が１０／９では脆くて粒子が容易に脱落するセル構造体が得られた。しかし、セル構造体を形成する比率の上限は１０／１０と考えられる。この事実は本発明のセル構造の生成機構を良く裏付けている。
【００７０】
このように、本発明の極めて簡便な方法は、従来の凍結乾燥法や溶出法のように長時間を要して、なおかつフィルム、シートなどの薄物、低発泡倍率の多孔体しか得られない方法とは明らかに異なり、肉薄、低発泡倍率のセル構造体は勿論のこと、肉厚の高発泡倍率のセル構造体まで得ることができるものであることを実証している。更に、本発明の方法によれば異形状の成形体も容易につくることができる。それは異形状の型内にポリマー溶液を充填するか、できたセル構造体を後に熱変形（ｐｏｓｔ−ｔｈｅｒｍｏｔｒａｎｓｆｏｒｍｉｎｇ）する方法に依ればよい。
【００７１】
［実施例２］
溶媒の組成比（ＣＨ_２Ｃｌ_２／Ｃ_２Ｈ_５ＯＨ）を１０／５に固定し、実施例１のポリ−Ｌ−乳酸の濃度を１．０、２．０、３．０、４．０、５．０、７．０ｇ／ｄｌに変えてポリマー溶液を調製した。そして、これらのポリマー溶液を実施例１と同形のシャーレに充填し、同様にしてセル構造体を得た。得られたセル構造体の性状を下記表５にまとめて示す。
【００７２】
【表５】

【００７３】
この結果から、発泡倍率が濃度に比例的に依存することが明らかである。
【００７４】
［実施例３］
実施例で用いたポリ−Ｌ−乳酸を、塩化メチレンとエタノールと水の混合溶媒（ＣＨ_２Ｃｌ_２／Ｃ_２Ｈ_５ＯＨ／Ｈ_２Ｏ＝１０／５／０．３）に４ｇ／ｄｌの濃度で溶解してポリマー溶液を調製した。
【００７５】
このポリマー溶液を、型内に液面が８ｃｍの高さとなるまで充填し、５日間、室温、常圧下に静置した。その結果、厚さが３．１ｃｍ、発泡倍率が約１０倍のセル構造体が得られた。このセル構造体は実施例１の溶媒組成比が１０／１の場合のそれよりも硬かった。これは水の影響によりポリマーの沈殿、固化が急激であり、結晶化度がやや高くなったこと、およびセル壁の固定が強固になったためと考えられる。
【００７６】
以上の実施例１〜３で得られたセル構造体は、生体内分解吸収性の生体材料（医用材料）として有用である。例えば、これらのセル構造体は生体の損傷部位の一時的な充填材として機能する組織置換のための足場や、三次元空間への細胞培養を目的とする多孔性基材などに有用である。また、ポリ乳酸のようにガラス転移点が６５℃付近であり、体温より高い場合は、６５℃以上の熱水中で暖めた後、生体部位の形状に合わせて任意に後熱変形（ｐｏｓｔ−ｔｈｅｒｍｏｔｒａｎｓｆｏｒａｍｉｎｇ）できるので、損傷した生体の複雑な欠損部をもとの形状に誘導復元させるための基材として用いることができる。
【００７７】
［実施例４］
グリコール酸（ＧＡ）とＬ−乳酸（ＬＡ）の共重合体（ＧＡ／ＬＡ＝５０／５０、モル比、重量平均分子量Ｍｗ：７．１万、メディソーブテクニーク製）を、クロロホルム／イソプロピルアルコール＝１０／３（体積比）の混合溶媒に４ｇ／ｄｌの濃度で溶解し、実施例１と同様の溶液沈殿法によって、厚さが約３．４ｍｍ、発泡倍率が約６倍の連続気泡のセル構造体を得た。これはＧＡ／ＬＡの共重合体であるために実施例１のものと比較すると軟らかい発泡体であった。このセル構造体は約３ケ月以内に生体内で分解吸収する生体材料（医用材料）として有用である。
【００７８】
［実施例５］
ポリカプロラクトン（ＰＣＬ）（プラクセルＨ−７、重量平均分子量Ｍｗ：７万、ダイセル化学工業（株）製）を、クロロホルム／１−プロパノール＝１０／４（体積比）の混合溶媒に８ｇ／ｄｌの濃度で溶解し、実施例１と同じ溶液沈殿法によって、ガラス転移点が−６０℃の軟質のセル構造体を得た。このものは厚さ７ｍｍ、発泡倍率が約７倍であった。このセル構造体は、自然界で生分解する製品として有用である。
【００７９】
［実施例６］
微生物がつくるポリエステル樹脂である３−ヒドロキシブチレートと４−ヒドロキシブチレートの共重合体［Ｐ（３ＨＢ−４ＨＢ），４ＨＢ含有率約１０モル％と５０モル％、数平均分子量Ｍｎ：約１０万、三菱化成（株）製］を、クロロホルム／エタノール＝１０／５（体積比）の混合溶媒に３ｇ／ｄｌの濃度で溶解し、実施例１と同様にして溶液沈殿法により、厚さ約１１ｍｍ、発泡倍率約１２倍の連続気泡のセル構造体を得た。
【００８０】
４ＨＢ含有率が約１０モル％のポリマーのセル構造体はやや硬く、ポリプロピレンフォームとよく似た風合いであった。また、４ＨＢ含有率が約５０モル％のポリマーのセル構造体はやや軟らかくポリエチレンフォームとよく似た風合いであった。このポリマーは１７５℃以上で熱分解し溶融粘度が低下するが、本溶液沈殿法では常温でセル構造体を生成するのでポリマーの劣化の危惧は全くなく、初めのポリマーの性質がそのままセル構造体に転化されている。そのため、このセル構造体は自然環境下で分解される生分解性と、生体内で分解吸収される生体内吸収性の両方をそなえている。ポリヒドロキシブチレート（ＰＨＢ）のホモポリマーは結晶性が高く（約８０％）、融点（１７６℃）と熱分解温度（２００℃）が接近しており、実用上の物性と加工面に問題があるが、生体への適合性がある。本方法は加熱を要しないため、ＰＨＢのホモポリマーであっても本来の性質を変えることなく加工できるので、ＤＤＳ（Ｄｒｕｇ Ｄｅｌｉｖｅｒｙ Ｓｙｓｔｅｍ）の担体として医療用途への展開を可能にする。
【００８１】
［実施例７］
バイオポリエステルである３−ヒドロキシブチレートと３−ヒドロキシバレレート［Ｐ（３ＨＢ−ＨＶ）、ＨＶのモル比５％（バイオポールＤ３００Ｇ）と１２％（バイオポールＤ６００Ｇ）、重量平均分子量Ｍｗ：７０万、ゼネカ株式会社製］を、塩化メチレン／エタノール＝１０／５（体積比）の混合溶媒に７ｇ／ｄｌの濃度で溶解し、溶液沈殿法により厚さ１０〜１２ｍｍ、発泡倍率１０〜１２倍の連続気泡のセル構造体を得た。
【００８２】
バイオポールＤ３００Ｇのセル構造体はポリプロピレンフォームに似た風合いであり、バイオポールＤ６００Ｇのセル構造体はポリエチレンと酢酸ビニルの共重合体（ＥＶＡ）によく似た風合いであった。これらは好気、嫌気の両方の自然環境下で微生物分解され、その速度は非発泡体の個体より速いので自然に還元するのに有利である。
【００８３】
［実施例８］
生分解性の熱可塑性脂肪族ポリエステルであるポリエチレンサクシネート（重量平均分子量Ｍｗ：１６．４×１０^４ 、ビオーレ＃１０００、昭和高分子（株）製）と、ポリブチレンサクシネート（重量平均分子量Ｍｗ：２２．７×１０^４ 、ビオーレ＃３０００、昭和高分子（株）製）を、塩化メチレン／イソプロピルアルコール＝１０／３（体積比）の混合溶媒に１０ｇ／ｄｌの濃度で溶解した。このポリマー溶液を深さ４０ｍｍの容器に一杯に満たし、溶液沈殿法により、４日間乾燥させて連続気泡のセル構造体を得た。その厚さは１８〜２２ｍｍ、発泡倍率は８〜１２倍であり、＃１０００のセル構造体は＃３０００のセル構造体よりもやや硬い風合いを示し、＃３０００のセル構造体は中密度ポリエチレンフォーム程度の風合いを示した。これらは微生物の存在する湿った土中、活性汚泥水中あるいは海水中などで、微生物によって非発泡体の固体よりも速く分解される。
【００８４】
［実施例９］
粘度平均分子量が２０万（分子量分布；分散度Ｍｗ／Ｍｎ＝３．７）のポリ−Ｌ−乳酸を、塩化メチレン／エタノール／水＝１０／３／０．２（体積比）の混合溶媒に１２ｇ／ｄｌの濃度で溶解し、高粘度のポリマー溶液を調製した。これに平均粒径が数１０μｍ以下の生体活性ガラスセラミック（Ａ−Ｗ ｇｌａｓｓｃｅｒａｍｉｃｓ、日本電気ガラス（株）製）を５重量％混合してよく撹拌した。この混合溶液は多くの細かい気泡を含んでいた。
【００８５】
次に、これを縦×横×高さ＝５ｃｍ×５ｃｍ×５ｃｍの素焼きの陶器の中に高さ３ｃｍまで充填した後、減圧乾燥器の中に入れ、１０℃、６００ｍｍＨｇにて３０分間減圧したのち室温、常圧下に一昼夜静置した。その後１０ｍｍＨｇにて数時間減圧乾燥して残留溶媒を除去して得られたセル構造体は、３００μｍ以上の比較的大きな孔径と数１０μｍ以下の細かな孔径を介在する厚さ約２．５ｃｍ、発泡倍率約８．０倍の連続気泡体であった。走査型電子顕微鏡によって、Ａ−Ｗガラスセラミックはそのほとんどがポリマーのセル壁中に存在していたが、一部はセル壁の表面や孔内部に存在したり、セル壁から露出していることが観察された。
【００８６】
この実施例のように生体内吸収性ポリマー中に骨との結合能を有し、骨形成を誘導する種々の生体活性な無機材料（ｂｉｏａｃｔｉｖｅ ｃｅｒａｍｉｃｓ）を充填したセル構造体は、孔内に存在したり、孔壁に露出している一部分の該セラミック、あるいは吸収性ポリマーが生体内で加水分解して劣化する過程で露出した生体活性セラミックによって骨の形成が誘導、促進される。また、２００μｍ以上の孔径を多く有する連続気泡体の場合は、周囲組織の細胞の浸入が容易であることが知られているので、ポリマーの吸収に伴い組織との置換がなされる足場（ｓｃａｆｆｏｌｄ）として有用である。本実施例は生体活性なセラミック粉末を混合するものであるが、リン酸四カルシウム（Ｃａ_４（ＰＯ_４）_２Ｏ）と第二リン酸カルシウム二水塩（ＣａＨＰＯ_４・２Ｈ_２Ｏ）の粉末を混ぜてポリマーに混合する方法をとれば、ポリマーが分解した部分でこの粉末が体液と接触するので、両者が反応して水酸化アパタイトを生成して固まる。つまり自己固定（ｓｅｌｆ−ｓｅｔｔｉｎｇ）による骨との結合もまた可能である。この場合、ポリマー溶液を充填する型の形状を生体の損傷部位に合わせてつくれば、三次元方向に骨の誘導、形成が可能な足場をつくることができる。生体の損傷部位を三次元空間方向に形状的に復元することは、従来からの形成、再建外科（Ｐｌａｓｔｉｃ ａｎｄ Ｓｕｒｇｅｒｙ）および整形外科（Ｏｒｔｈｏｐａｅｄｉｃ Ｓｕｒｇｅｒｙ）の一つの未解決の重要課題であったが、本実施例はかかる生体材料を提供できることを示唆している。また、この際、骨の生長因子である各種のＢＭＰ（Ｂｏｎｅ Ｍｏｒｐｈｏｇｅｎｅｔｉｃ Ｐｒｏｔｅｉｎ）を混合することにより、より骨の欠損部の回復が確実なものとなる。ここで、ＰＬＡの分子量の分散度を本実施例のように大きくとれば、分子量の大きいものは吸収までに時間を要し、低分子量のものは埋入後の短時間に分解吸収されるので、混合された生体活性材料が露出あるいは放出する速度をコントロールできるという利点がある。
【００８７】
また、本実施例のポリマー溶液を型に注入するときに型内に超高分子量ポリエチレンあるいはポリ−Ｌ−乳酸の糸で織った織物あるいは不織布を内在させて溶液沈殿法によりセル構造体をつくれば、高強度の生体不活性繊維あるいは生体内吸収性繊維で補強されたセル構造体を得ることができる。これは、それぞれ永続的あるいは一時的に強度を有する生体の損傷部位の組織置換の足場として有効に使用できる。この場合、該繊維を三次元織組織もしくは編組織またはこれらを組合わせた複合組織からなる力学的生体適合性を備えたバルク状の構造体（特願平６−２５４５１５号）を該ポリマー溶液に内在させて、溶液沈殿法によりセル構造体をつくれば、三次元空間方向に周囲組織と結合できて、力学的適合性を充足した足場と補綴材の両方の機能をもつ生体材料が得られる。
【００８８】
以上の方法は骨、軟骨などの硬組織に限らず、平均分子量１０万程度の低分子量ＰＬＡやＬＡ／ＧＡ共重合体などの比較的柔軟なセル構造体の場合は軟組織の欠損部の足場として用いることができる。その場合は線維芽細胞増殖因子（ＦＧＦ）、上皮増殖因子（ＥＧＦ）、インシュリン様増殖因子（ＩＧＦ）などの増殖因子、あるいはトランスフォーミング成長因子−β（ＴＧＦ−β）などの増殖抑制因子である各種のサイトカインを内含させてもよい。
【００８９】
［実施例１０］
グリコール酸（ＧＡ）とＤ，Ｌ−乳酸（ＬＡ）の共重合体（ＧＡ／ＬＡ＝２０／８０、モル比、重量平均分子量Ｍｗ：１７万）を、塩化メチレン／エタノール＝１０／５（体積比）の混合溶媒に４ｇ／ｄｌの濃度で溶解した。このポリマー溶液３ｇに抗癌剤であるアドレアマイシン（Ａｄｒｉａｍｙｃｉｎｅ：ＡＤＭ）の４０ｍｇをマイクロホモジナイザーを用いて溶解した。次に、この溶液を縦１．０ｃｍ、横１．０ｃｍの型に充填して、実施例１と同じ条件の溶液沈殿法により、縦×横×高さ＝１．０×１．０×１．０ｃｍの発泡倍率が約１０倍のＡＤＭの色である紅色に着色した連続気泡のセル構造体を得た。このブロックを縦×横×高さ＝０．５×０．５×０．５ｃｍの四つのブロックに切断し、その一個を３７℃のリン酸緩衝液（ＰＢＳ：Ｐｈｏｓｐｈａｔｅ Ｂｕｆｆｅｒ Ｓｏｌｕｔｉｏｎ）に浸漬してＡＤＭの放出の推移を調べた。放出はほぼ０次オーダーで進行し、セル構造体は約３．５ケ月後には形状を留めないまでに崩壊し、ＰＢＳ中に溶解し、ＡＤＭは全て放出された。
【００９０】
一般に発泡体の骨格を形成するセル壁の膜厚は数１０μｍ以下の薄いフィルム程度の厚さしかない。従って、セル壁の膜内に存在する薬が分子レベルで分散（溶解）していても、微粒子で分散していても、膜からの放出は本質的にフィルムの表面からの放出と異なるものではない。しかも連続気泡体（特に高い発泡倍率）の場合は、薄膜が三次元空間的に凹凸をもって密な連結孔を形成しているので、単位空間当たりの膜の表面積は平坦なフィルム表面比べると極めて大きい。従って、このようなセル壁から放出される薬剤の量は多いので、限定された量の薬物しか充填できない劇薬を高濃度に徐放することを求められる抗癌剤などの徐放性製剤の担体として有効である。生体内分解吸収性ポリマーの分解速度は体液と接触する面積がおおきい程、分解の機会が多いので見掛けの分解速度が速くなる。従って、高倍率体ほど分解が速くなる。本発明で得られる生体内分解吸収性セル構造体を徐放性製剤の担体として用いて有効な薬剤は、抗菌剤、抗癌剤、各種ホルモン、生理活性物質、各種サイトカインなど多くの種類があるが、放出量に見合ったポリマーと発泡倍率を選択する必要がある。
【００９１】
【発明の効果】
以上の説明から理解できるように、本発明のセル構造体の製造方法は極めて簡便であり、フィルム状やシート状の薄肉のセル構造体から、数ｃｍ以上の厚い異形状のセル構造体まで容易に製造することができ、発泡倍率や気孔が小さなものから大きいものまで製造することができる。
【００９２】
しかも、本発明の製造方法は、加熱や加水分解によってポリマーが劣化する工程がないので、生分解性の環境に還元する無公害のセル構造体を元のポリマーの物性を損なうことなく製造できる。また、セル構造体中に残存する添加物なども使用しないので、ポリ乳酸などの脂肪族ポリエステル系ポリマーを使用すれば、該ポリマー本来の生体安全性、生体適合性などをそのまま保持した生体内分解吸収性のセル構造体を得ることができる。そして、薬物や生体活性物質などを配合したポリマー溶液を使用すると、セル壁中に薬物などの大部分が包含され、ポリマーの分解に相応して薬物などを正確に放出制御できるセル構造体を得ることができる。
【００９３】
更に、本発明の製造方法によれば、ポリマー溶液を型内に充填することによって、生体の損傷部位の複雑な三次元空間を形状的に任意にあてはめることができるように成形された、三次元的足場の構築と周囲組織の浸入に有利なセル構造体を得ることができ、また、ポリマーとしてガラス転移点が体温以上、１００℃以下の比較的低温であるポリ乳酸などを用いる場合は、生体への埋入直前に加熱変形が可能で埋入部位の形状に密着した理想的な足場を形成できるセル構造体を得ることができる。[0001]
[Industrial applications]
The present invention relates to a novel method for producing a cellular material of an organic synthetic polymer, that is, a novel production method that can be referred to as a solution-precipitating technique (SPT) of the polymer.
[0002]
In particular, the production method of the present invention is an extremely effective method for producing a biodegradable cell structure that can be reduced to the environment and a biodegradable and absorbable cell structure expected to be used as a biomaterial. is there.
[0003]
[Prior art]
Recently, research on biodegradable or biodegradable and absorbable polymers and development of uses thereof have been actively pursued. The biodegradable polymer performs its function until use, and then gradually decomposes by environmental light, air, water, microorganisms, etc. ₂ , H ₂ It has been developed for the purpose of one of pollution-free plastic products that avoids environmental pollution by returning to O or the like. Above all, a biodegradable foam can reduce the amount of material, and is therefore significant from the viewpoint of resource saving. Attempts have been made to apply conventional foaming methods to these polymers, but this is not sufficient, and there is a need for a method that is simpler and truly suitable for these polymers.
[0004]
The biodegradable polymer is firstly degraded by an extracellular secretory enzyme, metabolized by microorganisms, and completely degraded. Many biodegradable plastics have been developed to date, but those that have reached the market are classified into the following three types.
(1) Water-soluble polymer (polyvinyl alcohol, acrylic polymer, polyethylene oxide blend polymer, etc.),
{Circle around (2)} starch-based polymer (a mixture of 60% corn starch based on a thermoplastic polymer, a starch-based polymer);
(3) Aliphatic polyesters (PCL: polycaprolactone, PLA: polylactide, P (HB / VL): hydroxybutyrate / valerate copolymer, PESU: polyethylene succinate, PBSU: polybutylene succinate).
[0005]
Polymers belonging to (3) are a) PCL, PLA, PESU, PBSU produced by an artificial synthesis method, and b) PHB: polyhydroxybutyrate, P (3HB-co-3HV) produced by microbial synthesis. : A copolymer of 3-hydroxybutyrate and 3-hydroxyvalerate (a polymer obtained by improving PHB in which hydroxyvaleric acid units (HV) are randomly incorporated in HB in an HV molar ratio of 5 to 20%), P ( 3HB-4HB): Copolymer of 3HB and 4-hydroxybutyrate, P (3HB-3HP): Copolymer of 3HB and 4-hydroxypropionate, etc. are produced. Among these aliphatic polyesters, PCL and PLA are also biodegradable bioabsorbable polymers meaning that they degrade in vivo. In particular, PLA has been practically used as a bioabsorbable material whose safety and biocompatibility have been confirmed in vivo, and as a fracture fixing material and a carrier for drug release / release products at present.
[0006]
By the way, the following bioabsorbable materials that have been used for medical purposes or are under research and development are as follows.
(1) Organic polymer material
(A) Natural polymer i) Protein: collagen (natural, regenerated), gelatin (crosslinked), fibrin, albumin (denatured), ii) polysaccharide: cellulose (oxide), starch (crosslinked), chitin, Chitosan, hyaluronic acid (cross-linked), etc.
(B) Synthetic polymer: polyglycolic acid (PGA), polylactic acid (PLA) (L-form, DL-form), LA / GA copolymer, polylactic acid-polyethylene glycol (PLA / PEG) copolymer, polylactic acid -Polypropylene glycol (PLA / PPG) copolymer, polycaprolactone (PCL), lactic acid-caprolactone copolymer P (LA / CL), glycolic acid-carbonate copolymer, polydioxanone (PDS), cyanoacrylate polymer, synthesis Such as polypeptides,
(2) Inorganic materials i) Phosphoric acid type: hydroxyapatite (HA), tricalcium phosphate (TCP), ii) Carbonic acid type: calcium carbonate, etc.
[0007]
Among them, (b) PGA, PLA, PLA / PGA, PCL, P (LA / CL), PDS, PLA / PEG and PLA / PPG are various aspects related to safety (toxicity) and metabolism in vivo. From the viewpoint of the physical properties of these materials, and are being actively studied with the aim of using various biomaterials. Among the biodegradable aliphatic polymers described above, PHB-based polymers that are finally decomposed into CO2 and H2O by in-vivo decomposition are considered to be safe in vivo. Could be used as a biomaterial in the near future.
[0008]
By the way, the purpose of use of the absorbable biomaterial is 1) surgery assistance (blood stasis, fixation, lumen retention, vascular occlusion, etc.), 2) wound healing (wound healing, tissue growth, organ regeneration, etc.), 3) drug Release (cancer treatment, wound healing promotion, thrombus prevention, infection prevention, etc.). Of these, 2) and 3) are medical applications that are highly promising for absorbable materials in the future, and research is being actively conducted on biomaterials for implants and sustained-release preparations of drugs.
[0009]
The living body has a very strong self-healing ability, and for example, connective tissues such as bones and muscles and internal organs such as the liver self-heal even if damaged. Reconstruction of the injured part becomes easier if there is a scaffold where cells can easily proliferate at the time of injury or a partition that prevents invasion of other tissues. After healing, they are absorbed and disappear, which is advantageous because there is no danger of causing a foreign body reaction with long-term implantation as with non-absorbable materials. At this time, if various factors such as peptidic factors that promote cell growth and differentiation and bioceramics capable of inducing bone tissue are included in the resorbable material, the loss of tissues and organs can be reduced. Since the reconstruction can be performed more quickly, which is ideal, transplantation research for that purpose is active. However, it is not easy to incorporate various growth factors of a polypeptide into an absorbent material without decomposing or denaturing them. In addition, these various growth factors continue to be gradually released to the injured area as the absorbent material is decomposed, and the living body absorbs the remaining absorbent material early after the release is completed. Controlling extinction is also not technically easy.
[0010]
In the same way, many kinds of drugs such as anti-cancer drugs, anti-thrombotic drugs, antibacterial drugs, physiologically active substances, cytokines, etc. are made into preparations in which biodegradable and absorbable polymers are supported, and they are effective for the target biological part. Research on a therapeutic system (DDS: Drug Delivery System) that releases the drug while controlling the concentration continuously or intermittently is also active. In this case, too, it is not easy to control the rate of polymer decomposition / absorption and release control. At present, the shapes of artificial implants and preparations being studied for the purpose of healing of the injured site and drug release are mainly those of relatively non-foamed solid films, sheets, rods (tablets) and the like. Although the thickness is small, many studies have been made on DDS in which a drug is included in fine particles such as microcapsules.
[0011]
By the way, in the process of decomposing / absorbing a biodegradable / absorbable polymer having a certain shape, foreign body reaction of the living body due to debris generated by decomposition, which is not found in non-absorbable materials (forebody body reaction). ) Often occurs, which may result in an intermittent inflammation reaction. This process can be explained as follows. For example, when a PLA having a viscosity-average molecular weight of 100,000 or more and having a certain shape is implanted into a certain part of a living body with relatively good blood flow, hydrolysis starts from its surface layer first. The surface whitens, which gradually evolves over time into the inner transparent layer. At this time, cracks begin to be formed in the surface layer, so that breakage easily occurs with a small force. The molecular weight of the surface is considerably reduced and the surroundings are covered with fibrous connective tissues. As the hydrolysis (molecular weight reduction) proceeds further, the disintegration proceeds into finer fragments. Generally, when a very large number of small pieces of about 20 to 30 μm are formed, a foreign substance reaction occurs in surrounding tissues. However, inflammation is less likely to occur unless the strips are concentrated in a single period and generated in large quantities. However, transient inflammation develops and continues until it occurs in large quantities and exceeds the amount eaten poorly. The tissue reaction at this stage is a phenomenon that supports the process in which a small piece of 2 to 3 μm or less is phagocytosed by cells such as multinucleate giant cells and macrophages, and is metabolized into lactic acid.
[0012]
There are various factors that determine the decomposition. When the chemical conditions (molecular structure, molecular weight, molecular weight distribution) of the implantation site and the material are the same, the speed of the decomposition is determined by the size (thickness, It depends mainly on the shape), morphology (whether crystalline, amorphous or porous) or the degree of surface roughness. Since hydrolysis (enzymatic degradation) proceeds from the contact surface of the material, the larger the surface area, the faster the initial degradation. In that regard, foams with a large surface area (especially open cells) are advantageous for speeding up decomposition. Also, if it is desired that a large amount of locally degraded debris cannot be obtained, a foam with a thin material reduces the possibility of generating a tissue reaction. In addition, when the pores are connected to each other with a size of 200 μm or more that allows cells to penetrate into the interior before the decomposition as in the case of an open-cell body, the invasion of the surrounding tissue is easy and the replacement is quick. At one time while the foam maintains its strength, it may be advantageous to provide a bond by entanglement with surrounding tissue.
[0013]
Based on the above facts, the advantage of using a cell structure (foam) as a biodegradable / absorbable material is mainly
(1) Increase the speed up to total decomposition and absorption,
(2) Reduce the amount of material, reduce foreign body reaction with tissue,
(3) To facilitate infiltration of surrounding tissues,
The advantage of (1) is also an effective factor for controlling the release rate and adjusting the efficiency when used as a carrier for sustained release of a drug.
[0014]
In view of these advantages, various attempts have been made in recent years to develop biomaterials made of bioabsorbable foams for tissue reconstruction and sustained-release preparations of drugs. Here, a conventional method for producing a foam will be described.
[0015]
The conventional methods for producing foams (cell structures) are classified based on the principle of bubble generation, as follows: 1) gas mixing method, 2) blowing agent decomposition method, 3) solvent diffusion method, 4) chemical reaction method, 5) sintering method, 6) elution method, 7) other (freeze-drying method, etc.).
[0016]
In addition, from a different viewpoint, when classified based on the foaming technology, a) a normal pressure heating method, b) an extrusion foaming method, c) a pressure (press) foaming method, d) an injection foaming method, e) a bead foaming method, f ) Two-component mixing method, g) Urethane foaming method, h) Sintering method, i) Elution method, j) Others.
[0017]
The principles are summarized as follows.
[0018]
Gas mixing method: foams due to the expansion of air or inert gas mixed into the material,
Foaming agent decomposition method: foaming by generated gas of decomposition type foaming agent that generates gas by thermal decomposition or chemical reaction,
Solvent gas diffusion method: foams by vaporization and expansion of water or a low boiling point organic solvent (evaporating foaming agent).
Chemical reaction method: foaming by gas generated in the polymerization process of material
Sintering method: powder obtained by sintering powdery and granular materials, and forming voids between particles as bubbles,
Elution method (extraction method): Elutes (extracts) and removes soluble substances mixed in the material, leaving the traces as pores.
Others: In the freeze-drying method, a solvent that crystallizes at a low temperature is mixed, and the crystal is sublimated under reduced pressure in a frozen state, and the mark is made a hole. There is also a method of mixing hollow microspheres.
[0019]
Of the above methods, except for the chemical reaction method, if the difference in difficulty and the quality of the resulting foam are ignored, it is in principle impossible to make a foam of a biodegradable or biodegradable and absorbable polymer. I can do it. However, a method requiring heating in steps such as mixing and foaming is not suitable for a biodegradable or biodegradable and absorbable polymer since hydrolysis is promoted only by a small amount of water. In addition, the decomposition method of the blowing agent, in which the decomposition residue of the blowing agent remains in the cell structure, or the resin modification method that requires the use of a thickener or a cross-linking agent to adjust the viscosity of the polymer, is based on the safety of the polymer itself. In the case of a biodegradable absorbent polymer, it should be avoided because the risk of waste is high.
[0020]
At present, the above-described methods for producing a cell structure which are being studied for the purpose of a biomaterial include the following methods that do not involve heating.
[0021]
1) Elution method: The polymer is dissolved in chloroform as a solvent, and fine particles of NaCl, starch, and sodium citrate sieved to a predetermined size are added thereto and mixed. This solution is cast on a glass plate and the solvent is diffused to obtain a film or sheet. Thereafter, the particles are immersed in water to elute fine particles soluble in water, and the elution traces are used as pores. This sample preparation method is a common means of making porous films that are commonly found in the scientific literature (eg, Journal of Materials Science in Medicine 5 (1994) 181-189, Journal of Applied Biomaterials 665-68).
[0022]
2) Freeze-drying method: The polymer is dissolved (about 5%) in a solvent such as dioxane (mp 11 ° C.) and cast on a support plate. Upon cooling to below the melting point of dioxane, dioxane is crystallized, which is then sublimated with dioxane under reduced pressure vacuum. The traces of the dioxane crystals become pores. However, there is also a method in which 1) and 2) in which the fine particles of 1) are mixed in a dioxane solution of a polymer are combined. This freeze-drying method has already been used in various fields, and a method using a benzene solution is described in US Pat. No. 4,181,983. The solvent is not only 1,4-dioxane but also hexafluoroisopropanol or 1,4-dioxane and C ₂ ~ C ₅ It is intended to use a mixed solvent of acetic acid ester of alcohol and a fibrous reinforcing element and soluble particles to be eluted, followed by freeze-drying to obtain an open cell, which is used for an implant. A description of the technique is found in JP-A-63-255068.
[0023]
3) Solvent diffusion method: a method in which P (3HB-4HB) is dissolved in a solvent such as chloroform, dichloromethane, acetone, or the like, and the solution is cast to adjust the scattering speed of the solvent to obtain a porous film. And JP-A-4-326932. Another solvent diffusion method is to contact a liquid in a supercritical state under pressure, impregnate the polymer with the liquid, and then reduce the pressure below the critical pressure to obtain a porous matrix. However, this does not essentially fall outside the scope of solvent diffusion, which is one of the conventional foaming methods. Also, CO ₂ The device when using as a supercritical fluid is far from simple.
[0024]
The above method has the following disadvantages.
[0025]
B) Both the elution method and the freeze-drying method are methods for producing a porous body having a film or sheet thickness of several hundred μm or less, and are suitable for producing plates or rods having a greater thickness or a molded article having a different shape. Not.
[0026]
B) In the elution method, it takes time to elute the fine particles, and in some cases, over 10 days. Still worry about complete elution.
[0027]
C) Since freeze-drying is a method of sublimating a solid at a low temperature, it takes a long time for sublimation, and there is concern about safety due to residual solvent. Therefore, this method can be applied only to thin films and sheets. In addition, the proportion of solvent crystals in the matrix is high (80% or more in some cases). When a drug or bioceramic is dissolved or mixed in the solvent, most of it is present in the pores from which the solvent has escaped, In the case where the porous body is used as a sustained-release preparation or as a scaffold for a damaged site containing a growth factor, the drug simply escapes from this hole because only the remainder is present. Cannot be precisely controlled.
[0028]
D) In these methods, a foam (cell structure) having a high expansion ratio and a high porosity cannot be obtained.
[0029]
[Problems to be solved by the invention]
An object of the present invention is to solve the problems of the above method. That is
1) The polymer is simple, has no process of deteriorating by heating and hydrolysis, and does not use additives remaining in the final product. If it has biocompatibility, it is a method for producing a cell structure that can be kept as it is,
2) It is a manufacturing method capable of producing not only a thin cell structure such as a film and a sheet but also a cell structure having a thick shape of several cm or more and a high expansion ratio. thing,
3) a production method capable of producing a cell structure having uniform and fine bubbles to a large cell structure having uniform bubbles;
4) The polymer matrix (cell wall) can contain not only a drug compatible with the polymer but also an incompatible drug or an inorganic substance such as bioceramic, and accurately releases the drug in accordance with the decomposition of the polymer. A manufacturing method capable of obtaining a controllable cell structure,
5) A cell structure formed so that a complicated three-dimensional space of a damaged part of a living body can be arbitrarily fitted in shape, functioning as a three-dimensional scaffolding construction and a temporary prosthetic material, By a permeation of the surrounding tissue, it is a manufacturing method capable of obtaining a cell structure capable of reconstructing a three-dimensional damaged site,
6) During surgery, it can be heated and deformed according to the shape of the defect in the living body to be implanted, and can be tightly packed to induce a three-dimensional shape not only for hard tissues such as bone and cartilage but also for damaged parts of soft tissues. It is a manufacturing method capable of obtaining a hard or soft cell structure to be an ideal scaffold that can be,
And so on.
[0030]
[Means for Solving the Problems]
In order to achieve the above object, the method for producing a cell structure of the present invention is characterized in that the organic synthetic polymer is compatible with each other, a solvent capable of dissolving the polymer, and a solvent having a higher boiling point than the solvent and cannot dissolve the polymer. A polymer solution is prepared by dissolving in a mixed solvent with a non-solvent, the polymer solution is filled into a mold, and the polymer is precipitated by evaporating the mixed solvent at a temperature lower than the boiling point of the solvent. I do.
[0031]
Here, the cell structure refers to a porous material having a low porosity of 0 to 30% such as a sintered body and including a small cavity, as well as a lightweight material having a porosity of 75% or more. Up to and including. The latter can be regarded as a cell, which is one structural unit together with individual pores and solids surrounding the pores, and thus can be defined as cellular solids. The cell structure is a solid consisting of a network of cell walls joined together. In this specification, the cell structure may be expressed as a foam or a porous body, but basically means the same. The term “precipitation” refers to a phenomenon in which a solid phase of a polymer formed in a polymer solution sinks and stagnates over the entire area of the solution to form a distinct heterogeneous phase.
[0032]
The principle of cell structure formation by the method of the present invention can be considered as follows.
[0033]
Now, methylene chloride (bp 40 ° C., vp: vapor pressure 248.9 mmHgat 20 ° C.) is used as a solvent, and isopropyl alcohol (bp 82.4 ° C., v.p. 32. Using 4 mmHg at 20 ° C.), a polymer solution was prepared by dissolving PLA (viscosity average molecular weight: 200,000) in a mixed solvent in which both were mixed so that the volume ratio was 10: 5, and this was filled into a mold. The case where the mixed solvent is diffused at 1 atm and 20 ° C. is considered.
[0034]
First, of the mixed solvents, low boiling methylene chloride, which is a solvent for PLA, is preferentially diffused. Then, the ratio of the non-solvent isopropyl alcohol having a high boiling point gradually increases. When the non-solvent to solvent ratio reaches a certain ratio, the solvent can no longer dissolve the PLA, and the dissolved PLA precipitates rapidly. That is, the non-solvent functions as a precipitant. At this time, a cell structure is formed in which the solvent (isopropyl alcohol as the main component and the remaining low ratio of methylene chloride which has been diffused) is contained in the thin wall of the PLA. In other words, the PLA forms a form in which cell walls are connected. This connection occurs because PLA is dissolved in a solvent, precipitates when the ratio of non-solvent is increased, and is rapidly contracted, solidified, and fixed. After that, when the mixture is further left, the remaining solvent evaporates, and at the same time, the non-solvent having a higher boiling point than the solvent evaporates. After they evaporate, traces of the solvent wrapped in the cell remain fixed as pores. At this time, the solvent destroys a part of the cell wall to form pores, and plays a role in efficiently dispersing the solvent from the surface layer of the cell structure to the outside of the cell structure. Accordingly, the formed cell structure is basically an open cell in which pore cores are connected. However, a closed cell in which a cell is independent may partially exist depending on factors such as a solvent composition, a viscosity of a polymer solution, and a polymer concentration. In any case, a cell structure having micropores having various thicknesses and connected to pore walls made of a thin film of a polymer arranged in a random space is formed.
[0035]
As described above, since the polymer solution sequentially precipitates from the surface in contact with the outside air to form cells, the method of the present invention can be referred to as a solution precipitation method (SPT: Solution-Precipitating Technique).
[0036]
The method of the present invention involves impregnating a polymer with a low-boiling solvent, which evaporates at a low temperature, under pressure, and then depressurizes and heats the solvent under heating, as in the solvent gas diffusion method, which is one of the conventional foaming methods. This is different from the method in which a cell structure is formed by utilizing the force of expansion and expansion. In other words, the solvent of the polymer is used to dissolve the polymer, the non-solvent is used to precipitate the polymer, and the ratio of the solvent and the non-solvent of the initially dissolved polymer solution changes due to the gas diffusion, This is a porous method in which a polymer is precipitated to form a cell structure by increasing the ratio of a non-solvent. This method does not require heating for mixing and expansion of the blowing agent, and also differs from the conventional method in that point.
[0037]
As described above, the method of the present invention is simple, and furthermore, there is no step of deterioration due to heating or hydrolysis, and no additives remaining in the cell structure are used. If the material has biosafety and biocompatibility, the biosafety and biocompatibility can be maintained as it is, which is extremely useful for producing a cell structure as a biomaterial.
[0038]
Hereinafter, the production method of the present invention will be described in more detail.
[0039]
The organic synthetic polymer used in the present invention is not particularly limited as long as the above method can be applied. However, when obtaining a biodegradable cell structure that ultimately reduces to the environment, the aforementioned biodegradable aliphatic polyester is preferably used. In order to obtain a cell structure expected to be used as a biomaterial, the biodegradable and absorbable aliphatic polyester-based polymer described above is suitably used, and among them, biosafety and biocompatibility are preferred. Polylactic acid (PLA) and various PLA copolymers, such as a copolymer of lactic acid and glycolic acid, a copolymer of lactic acid and caprolactone, and a copolymer of polylactic acid and polyethylene glycol Polymers, copolymers of polylactic acid and polypropylene, etc. are optimal.
[0040]
Here, the biological material, A non-viable material used in a medical device, is defined as intended to interact with biological systems (Progress in Biomedical Engineering, 4 Definitions in Biomaterials Edited by D.F.Williams, Elsevier Amsterdam- Oxford-New York-Tokyo 1987). In addition, biodegradability refers to the property of being degraded by the biological action of enzymes and simply hydrolyzed by water, and has the meaning of both biological degradation and degradation in vivo. .
[0041]
The solvent used in the present invention is a solvent capable of dissolving the organic synthetic polymer, and a solvent having a low boiling point, which easily diffuses at a temperature slightly higher than room temperature, is suitable. For example, when the organic synthetic polymer is an aliphatic polyester polymer, methylene chloride (CH ₂ Cl ₂ ), Chloroform (CHCl ₃ ), 1,1-dichloroethane (CH ₃ CHCl ₂ ) Can be used. Among them, low-toxicity methylene chloride having the lowest boiling point and the highest vapor pressure is most suitable, and chloroform is also preferable. Fluorocarbon solvents (Freon) are also effective, but are excluded because they destroy the ozone layer. Monochloroethane is also effective, but is undesirable because of its relatively high toxicity.
[0042]
On the other hand, non-solvents are those that cannot dissolve the organic synthetic polymer and must have a higher boiling point than the above-mentioned solvents. The solvent and the non-solvent must be compatible and must be well-mixed. When a non-solvent having poor compatibility is used, it is difficult to obtain a cell structure having high porosity and uniform and fine pores. The upper limit of the boiling point of the non-solvent is up to around 110 ° C., and it is preferable that the boiling point is considerably higher than the boiling point of the solvent. If the non-solvent has a boiling point higher than 110 ° C., the vapor pressure at room temperature is low and the air diffusion at room temperature is too slow, so it takes time to manufacture the cell structure, and the non-solvent remains in the cell. Easier to do. If the difference in boiling point between the non-solvent and the solvent is less than about 15 ° C., the solvent is likely to evaporate together with the non-solvent, so that the function of the non-solvent as a precipitant is reduced.
[0043]
Specific examples of the non-solvent include monohydric alcohols which are compatible with the above-mentioned solvents such as methylene chloride and have a boiling point in the range of 60 ° C. to 110 ° C. (under 1 atm), for example, methanol, ethanol, 1-propanol. , 2-propanol (isopropyl alcohol), 2-butanol, ter-butanol, ter-pentanol, etc., and ethanol, 1-propanol, and 2-propanol are particularly preferably used in view of toxicity and odor. Is done. Non-solvents obtained by adding a small amount of water to these monohydric alcohols are also preferably used. Water acts as a stronger precipitant than alcohol and promotes the precipitation of the polymer.
[0044]
Table 1 lists preferred solvents and non-solvents, and shows the respective boiling points and vapor pressures at 20 ° C. Table 2 shows the difference in boiling point and the difference in vapor pressure between methylene chloride and chloroform and each non-solvent. The combination of the solvent and the non-solvent of the mixed solvent may be appropriately selected in consideration of the boiling point and the vapor pressure in Table 1, but when methylene chloride or chloroform is selected as the solvent, the combination of the boiling point difference shown in Table 2 and A preferable polymer solution may be prepared by judging the vapor pressure difference and the viscosity of the polymer solution.
[0045]
[Table 1]

[0046]
[Table 2]

[0047]
When the mixed solvent used for preparing the polymer solution has a volume ratio of the above-mentioned solvent and non-solvent generally of 10: 1 to 10:10, a cell structure can be obtained. If the ratio of the solvent is larger than this, the dissolution of the polymer continues until the end of the solvent diffusion, and no precipitation of the cell wall occurs, and only a transparent polymer mass without bubbles is formed after the solvent diffusion. On the other hand, if the ratio of the solvent is small, the polymer precipitates at once with only a small amount of solvent evaporating, so that the welding between the cells is incomplete, and a brittle cell structure without physical connection between the cells may be produced. However, it is not good because a contracted or deformed product completely different from the shape of the mold can be formed. The range of the ratio suitable for constructing a stable cell structure having a firm shape by connecting cells in a three-dimensional space is 10: 1 to 10: 7, depending on the solvent composition.
[0048]
The production method of the present invention is a method in which a polymer solution prepared by dissolving a polymer in a solvent in which a solvent and a non-solvent are mixed in the above volume ratio is filled in a mold, and a temperature lower than the boiling point of the solvent, preferably 20 ° C. or lower. And evaporating the solvent under normal pressure or reduced pressure. If the solvent is diffused at a temperature higher than the boiling point of the solvent, the solvent will boil and break the cell walls, thereby welding, so that a high-quality cell structure cannot be obtained.
[0049]
If this step is carried out in a sealed device, the gaseous solvent is recovered and can be used over and over again, and it is safe and resource saving because it is not inhaled during operation. is there.
[0050]
In addition, in order to increase the viscosity of the polymer solution and fix the cell walls, an operation of increasing the viscosity by cooling to a low temperature of about 10 ° C. or less before dispersing the solvent, and dispersing the solvent under reduced pressure is adopted. It is also desirable. This operation is effective for producing a thick sheet-like or irregularly shaped cell structure.
[0051]
According to the method of the present invention, in the case of a film-like or sheet-like cell structure having a thickness of several hundreds μm or less, a polymer solution is thinly filled in a mold, and the solvent is spontaneously diffused at room temperature and normal pressure. The cell structure can be easily obtained in a short time while viewing. In order to completely remove the solvent, drying may be further performed under reduced pressure. By this operation, a cell structure which can be used as a biomaterial having no residual solvent is obtained.
[0052]
In addition, a thicker (eg, 1 mm or more) plate-shaped cell structure having a constant thickness is filled with a relatively thick polymer solution in a mold, and then the solvent is diffused. It can be obtained by repeating the operation of similarly filling the polymer solution thereon and evaporating the solvent a plurality of times.
[0053]
Further, the cell structure molded into the irregular shape with a thick wall can be easily obtained by filling the polymer solution into the irregular shape mold and evaporating the solvent as described above, although it takes a little longer time. be able to. At this time, so that the solvent can be quickly and evenly diffused from the entire surface of the mold, a porous mold having a myriad of fine vents that do not allow the polymer to pass but allow the solvent to pass therethrough, such as an unglazed pottery mold. It is preferred to use. In this case, too, the polymer solution is kept at a low temperature of about 10 ° C. or less for the purpose of accelerating the diffusion of the solvent and maintaining the shape by avoiding the depression and deformation of the polymer solution in the unprecipitated portion inside the molded body. It is also one method to employ an operation of increasing the viscosity by forcibly and forcibly evaporating the solvent under reduced pressure. In this way, it is possible to obtain a block-shaped or irregularly shaped cell structure having a thickness of 5 cm or more.
[0054]
The factors that determine the expansion ratio of the cell structure are the viscosity of the polymer solution, the polymer concentration, the composition ratio of the mixed solvent, and the rate of gas diffusion.The principle that the polymer solution precipitates to form the cell structure For that reason, polymer concentration is one of the most important factors. The expansion ratio depends on the thickness and the size of the pores, but can be several times to several tens times.
[0055]
The biodegradable and absorbable aliphatic polyester polymer cell structure obtained by the method of the present invention is a scaffold for healing a damaged part of a living body, and a biomaterial mainly used as a carrier for drug release. Can be used as When producing such a cell structure as a biomaterial, a polymer solution containing a bioactive substance, a drug, a cell growth factor, or the like is prepared for the purpose of speeding up treatment or reconstruction of a damaged or excised site. It is desirable to form a cell structure containing these substances and drugs, and to form the cell structure so that its thickness is 1 mm or more and the expansion ratio is 3 times or more.
[0056]
As a bioactive substance for healing and reconstructing hard tissue contained in the cell structure, a bioactive glass or a glass ceramic capable of inducing bone and binding with bone, for example, Bioglass (45S5), Ceravital (KGS) , A-W glass ceramics, BIOVERIT-1, Implasto-L1 and the like. Table 3 shows examples of bone growth factors. In addition, as a drug, besides a hard tissue-related drug such as calcitonin, vitamin D, a female hormone, bisphosphonate, and vitamin K which are bone tissue therapeutics, for example, an anticancer drug (particularly, a specific site such as solid cancer). Various therapeutic agents such as antimicrobial agents, various hormones, physiologically active substances, and various cytokines.
[0057]
[Table 3]

[0058]
Unlike the freeze-drying method, the production method of the present invention provides a cell structure in which most of the above substances and drugs are embedded inside the polymer on the cell wall. Release can be controlled correctly. In addition, the manufacturing method of the present invention can obtain a cell structure molded so that a complicated three-dimensional space of a damaged part of a living body can be formally applied. When the above substances and the like are contained in the body, they are generated in accordance with the three-dimensional shape of the living body, which requires the induction of cells and tissues, and thus become an ideal scaffold that can reconstruct the shape.
[0059]
Further, the cell structure obtained by the production method of the present invention is basically an open-cell body as described above, and has an extremely large surface area when the expansion ratio is relatively high. Since the size of the surface area increases the apparent decomposition rate, the decomposition rate (the sustained release rate of the drug) can be controlled by adjusting the expansion ratio. A large ratio of pores speeds up the infiltration of surrounding cells and tissues, and a large foaming ratio means that the weight of the cell structure is 1 / foaming ratio of the original non-foamed individual. Therefore, it is only necessary to implant a very small amount of the degradable / absorbable polymer into the living body. Therefore, the amount of decomposed debris that causes a tissue reaction in the decomposing / absorbing process is also reduced, thereby giving many important properties as a biomaterial that the chance of foreign substance reaction is extremely reduced. In addition, a cell structure such as PLA (polylactic acid) having a relatively low Tg (glass transition point) of not lower than body temperature and not higher than 100 ° C. can be freely deformed by heating immediately before implantation into a living body. Since it is possible, it is advantageous for making a scaffold or a preparation closely adhered to the shape of the implantation site.
[0060]
Furthermore, by applying the production method of the present invention, it is also possible to obtain a cell structure having a concentration gradient in which the concentration of a drug or the like is different between the inside and the front side, and a high-strength cell structure that is composited with another material. it can. That is, for the former cell structure having a concentration gradient, for example, several types of polymer solutions having different concentrations of a drug or the like are prepared, and a polymer solution having a high drug concentration or a polymer solution having a low drug concentration is sequentially formed from a polymer solution. It is obtained by repeating the operation of filling the inside and evaporating the solvent. Further, the latter composite cell structure is, for example, a reinforcing material such as a woven or non-woven fabric made of biodegradable or bio-inactive fibers is placed in a mold, and a polymer solution is filled in the mold to form a solvent. Is obtained by dispersing.
[0061]
[Action]
As in the production method of the present invention, an organic synthetic polymer is dissolved in a mixed solvent of a solvent and a non-solvent having a higher boiling point than the solvent to prepare a polymer solution. When the mixed solvent is diffused at a temperature lower than the boiling point, as described above, the solvent having a low boiling point is preferentially gasified and the ratio of the non-solvent having a high boiling point gradually increases. When the solvent reaches the point where the solvent cannot dissolve the polymer, the polymer precipitates rapidly, shrinks, solidifies and becomes immobilized, and the cell structure in which the solvent is encapsulated in the thin cell walls connected with the polymer is formed. It is formed. The remaining solvent destroys a part of the cell wall and creates pores and diffuses, and the non-solvent with a high boiling point also diffuses and the solvent traces wrapped in the cell wall are fixed as pores. Thus, an open-cell cell structure in which pores are basically connected is obtained.
[0062]
【Example】
Hereinafter, examples of the present invention will be described.
[0063]
[Example 1]
Methylene chloride (CH ₂ Cl ₂ ), Ethanol (C ₂ H ₅ OH) and changing the volume ratio of solvent and non-solvent (solvent / non-solvent) to 10/0, 10/1, 10/3, 10/5, 10/7, 10/9. Poly-L-lactic acid having a viscosity average molecular weight of about 300,000 (molecular weight distribution; dispersity Mw / Mn = 2.5) was dissolved in a mixed solvent at a concentration of 4 g / dl to prepare a polymer solution.
[0064]
These polymer solutions were poured into a Petri dish having a diameter of 10 cm so that the liquid level was 13 mm, and allowed to stand at room temperature (10 to 20 ° C.) under atmospheric pressure to form a cell structure. After 24 hours, the solvent of the polymer solution had evaporated, and only those having a solvent composition ratio (solvent / non-solvent) of 10/7 and 10/9 had a slight ethanol odor. Thereafter, when the solvent was dried under reduced pressure, the solvent could not be detected by gas chromatography. The properties and the like of the obtained cell structure are shown in Table 4 below.
[0065]
[Table 4]

[0066]
According to the above results, in the case of a mixed solvent of methylene chloride and ethanol, a relatively good cell structure can be obtained with a solvent composition ratio (methylene chloride / ethanol) of 10/1 to 10/6. In the polymer solution having a solvent composition ratio in this range, methylene chloride having a low boiling point (40 ° C.) and a high vapor pressure (348.9 mmHg / 20 ° C.) evaporate preferentially, and thus the high boiling point (78.3) in the residual solvent is used. ° C) and the ratio of ethanol having a low vapor pressure (44 mmHg / 20 ° C) increases, and the solution gradually becomes cloudy and precipitates from the surface of the solution in contact with the outside air toward the inside. At this time, a pore interconnect (pore interconnection) containing the residual solvent is formed, and the cell structure is finally formed on the entire surface with further diffusion of the solvent.
[0067]
A cell structure having a solvent composition ratio of 10/5 and a high expansion ratio of 12.7 times was obtained, and the cell structure became thicker with the expansion ratio. This is presumably because the polymer immediately precipitated and solidified from the surface of the solution in contact with the outside air due to the diffusion of the solvent, and the thickness was maintained because the cell wall was formed and fixed. This fact suggests that when a cell structure having a certain expansion ratio and a certain thickness is required, the composition ratio of the solvent and the concentration of the polymer solution may be adjusted.
[0068]
When only the solvent is used, the polymer is dissolved and vaporized until the solvent is completely vaporized, so that the pores from which the solvent is removed do not remain as pores. This resulted in the formation of a polymer transparent sheet.
[0069]
When the ratio of the solvent is high, the volume is reduced due to the diffusion of the solvent, and when the thickness is reduced by that amount, precipitation and solidification are performed to fix the cell walls. Is considered to have decreased. Conversely, when the initial ratio of the non-solvent (precipitating agent) is high, the effect of the non-solvent as a precipitating agent is immediately exerted by slight gas diffusion of the solvent, and a precipitate is generated at once. At this time, there is not enough solvent left to dissolve the polymer and form a continuous cell wall, so that when the pores are generated, the polymer shrinks greatly, or the precipitated polymer particles simply weld to form the connected body. It is considered to form a cell structure such as a kind of sintered body having pores interposed. Actually, when the solvent composition ratio is 10/7, shrinkage during precipitation and solidification is severe, and a deformed cell structure having many wrinkles on the surface is obtained. When the solvent composition ratio is 10/9, the particles are brittle and particles are easily formed. Was obtained. However, the upper limit of the ratio for forming the cell structure is considered to be 10/10. This fact supports the generation mechanism of the cell structure of the present invention.
[0070]
As described above, the extremely simple method of the present invention requires a long time as in the conventional freeze-drying method and the elution method, and is a method in which only a thin material such as a film or a sheet or a porous material having a low expansion ratio can be obtained. This clearly demonstrates that it is possible to obtain not only a thin and low expansion ratio cell structure but also a thick and high expansion ratio cell structure. Further, according to the method of the present invention, a molded article having a different shape can be easily produced. It may depend on the method of filling the polymer solution into the irregularly shaped mold or post-thermotransforming the resulting cell structure.
[0071]
[Example 2]
Solvent composition ratio (CH ₂ Cl ₂ / C ₂ H ₅ OH) was fixed at 10/5, and the concentration of poly-L-lactic acid in Example 1 was changed to 1.0, 2.0, 3.0, 4.0, 5.0, and 7.0 g / dl. A polymer solution was prepared. Then, these polymer solutions were filled in a Petri dish having the same shape as in Example 1, and a cell structure was obtained in the same manner. The properties of the obtained cell structure are summarized in Table 5 below.
[0072]
[Table 5]

[0073]
From this result, it is clear that the expansion ratio is proportional to the concentration.
[0074]
[Example 3]
The poly-L-lactic acid used in Examples was converted to a mixed solvent of methylene chloride, ethanol and water (CH ₂ Cl ₂ / C ₂ H ₅ OH / H ₂ O = 10/5 / 0.3) at a concentration of 4 g / dl to prepare a polymer solution.
[0075]
This polymer solution was filled in a mold until the liquid surface reached a height of 8 cm, and was allowed to stand at room temperature and normal pressure for 5 days. As a result, a cell structure having a thickness of 3.1 cm and an expansion ratio of about 10 was obtained. This cell structure was harder than that of Example 1 when the solvent composition ratio was 10/1. This is considered to be because the precipitation and solidification of the polymer were sharply affected by the water, the crystallinity was slightly increased, and the fixation of the cell wall was strengthened.
[0076]
The cell structures obtained in the above Examples 1 to 3 are useful as biomaterials (medical materials) capable of decomposing and absorbing in vivo. For example, these cell structures are useful as scaffolds for tissue replacement functioning as temporary fillers for injured sites in living bodies, porous substrates for cell culture in three-dimensional space, and the like. Further, when the glass transition point is around 65 ° C. and is higher than the body temperature, such as polylactic acid, after warming in hot water at 65 ° C. or higher, post-heat deformation (post- Since it can be thermotransformed, it can be used as a base material for guiding and restoring a complex defect of a damaged living body to its original shape.
[0077]
[Example 4]
A copolymer of glycolic acid (GA) and L-lactic acid (LA) (GA / LA = 50/50, molar ratio, weight average molecular weight Mw: 71,000, manufactured by Medisorb Technik) was converted into chloroform / isopropyl alcohol = Dissolved in a mixed solvent of 10/3 (volume ratio) at a concentration of 4 g / dl, and by the same solution precipitation method as in Example 1, an open cell cell having a thickness of about 3.4 mm and an expansion ratio of about 6 times. A structure was obtained. Since this was a GA / LA copolymer, it was a soft foam as compared with that of Example 1. This cell structure is useful as a biomaterial (medical material) that decomposes and absorbs in vivo within about 3 months.
[0078]
[Example 5]
Polycaprolactone (PCL) (Praccel H-7, weight average molecular weight Mw: 70,000, manufactured by Daicel Chemical Industries, Ltd.) was added to a mixed solvent of chloroform / 1-propanol = 10/4 (volume ratio) at 8 g / dl. By dissolving at a concentration, a soft cell structure having a glass transition point of −60 ° C. was obtained by the same solution precipitation method as in Example 1. This had a thickness of 7 mm and an expansion ratio of about 7 times. This cell structure is useful as a biodegradable product in nature.
[0079]
[Example 6]
Copolymer of 3-hydroxybutyrate and 4-hydroxybutyrate, which are polyester resins produced by microorganisms [P (3HB-4HB), 4HB content: about 10 mol% and 50 mol%, number average molecular weight Mn: about 100,000 , Manufactured by Mitsubishi Kasei Co., Ltd.] in a mixed solvent of chloroform / ethanol = 10/5 (volume ratio) at a concentration of 3 g / dl, and a thickness of about 11 mm was obtained by a solution precipitation method in the same manner as in Example 1. As a result, an open cell structure having an expansion ratio of about 12 was obtained.
[0080]
The cell structure of the polymer having a 4HB content of about 10 mol% was slightly hard and had a texture very similar to that of the polypropylene foam. The cell structure of the polymer having a 4HB content of about 50 mol% was slightly soft and had a texture very similar to that of polyethylene foam. This polymer is thermally decomposed at 175 ° C. or higher, and its melt viscosity is reduced. However, in this solution precipitation method, the cell structure is formed at room temperature, so there is no fear of deterioration of the polymer, and the properties of the initial polymer remain unchanged. Has been converted to Therefore, this cell structure has both biodegradability, which is degraded in a natural environment, and in vivo absorbability, which is decomposed and absorbed in vivo. The homopolymer of polyhydroxybutyrate (PHB) has high crystallinity (about 80%), and its melting point (176 ° C) and thermal decomposition temperature (200 ° C) are close to each other. Yes, but compatible with living organisms. Since this method does not require heating, even a homopolymer of PHB can be processed without changing its original properties, so that it can be developed as a DDS (Drug Delivery System) carrier for medical applications.
[0081]
[Example 7]
Biopolyester 3-hydroxybutyrate and 3-hydroxyvalerate [P (3HB-HV), HV molar ratio of 5% (Biopol D300G) and 12% (Biopol D600G), weight average molecular weight Mw: 700,000 , Manufactured by Zeneca Co., Ltd.] in a mixed solvent of methylene chloride / ethanol = 10/5 (volume ratio) at a concentration of 7 g / dl, and a solution having a thickness of 10 to 12 mm and an expansion ratio of 10 to 12 times by a solution precipitation method. An open cell structure was obtained.
[0082]
The cell structure of Biopol D300G had a texture similar to that of polypropylene foam, and the cell structure of Biopol D600G had a texture very similar to a copolymer of polyethylene and vinyl acetate (EVA). They are biodegraded in both aerobic and anaerobic natural environments, and their rate is faster than that of non-foamed individuals, which is advantageous for natural reduction.
[0083]
Example 8
Polyethylene succinate which is a biodegradable thermoplastic aliphatic polyester (weight average molecular weight Mw: 16.4 × 10 ⁴ , Biole # 1000, manufactured by Showa High Polymer Co., Ltd.) and polybutylene succinate (weight average molecular weight Mw: 22.7 × 10 ⁴ , Biore # 3000, manufactured by Showa Polymer Co., Ltd.) was dissolved in a mixed solvent of methylene chloride / isopropyl alcohol = 10/3 (volume ratio) at a concentration of 10 g / dl. The container having a depth of 40 mm was completely filled with the polymer solution and dried for 4 days by a solution precipitation method to obtain an open-cell cell structure. The thickness is 18-22 mm, the expansion ratio is 8-12 times, the cell structure of # 1000 shows a slightly harder texture than the cell structure of # 3000, and the cell structure of # 3000 is medium density polyethylene foam. The texture was moderate. They are degraded faster by microorganisms than in non-foamed solids in moist soil, activated sludge water or seawater where microorganisms are present.
[0084]
[Example 9]
Poly-L-lactic acid having a viscosity average molecular weight of 200,000 (molecular weight distribution; dispersity Mw / Mn = 3.7) is converted into a mixed solvent of methylene chloride / ethanol / water = 10/3 / 0.2 (volume ratio). The polymer was dissolved at a concentration of 12 g / dl to prepare a high viscosity polymer solution. 5% by weight of a bioactive glass ceramic (AW glassceramics, manufactured by Nippon Electric Glass Co., Ltd.) having an average particle diameter of several tens of μm or less was mixed with the mixture and stirred well. This mixed solution contained many fine bubbles.
[0085]
Next, after filling this into unglazed pottery of length × width × height = 5 cm × 5 cm × 5 cm to a height of 3 cm, it was placed in a reduced pressure drier and reduced in pressure at 10 ° C. and 600 mmHg for 30 minutes. After that, it was allowed to stand at room temperature and normal pressure all day and night. Thereafter, the cell structure obtained by drying under reduced pressure at 10 mmHg for several hours to remove the residual solvent has a thickness of about 2.5 cm with a relatively large pore diameter of 300 μm or more and a fine pore diameter of several tens μm or less, and foaming. It was an open cell with a magnification of about 8.0. According to the scanning electron microscope, most of the AW glass ceramic was present in the cell wall of the polymer, but a part thereof was present on the surface of the cell wall, inside the pores, or was exposed from the cell wall. Was observed.
[0086]
As in this example, a cell structure filled with various bioactive inorganic materials (bioactive ceramics) having a binding property to bone and inducing bone formation in a bioabsorbable polymer exists in pores. Bone formation is induced and promoted by a part of the ceramic exposed to the pore wall or the bioactive ceramic exposed in the process of hydrolyzing and degrading the resorbable polymer in vivo. In the case of an open-cell body having a large pore diameter of 200 μm or more, it is known that cells in the surrounding tissue can easily enter the scaffold, and the scaffold is replaced with the tissue as the polymer is absorbed. Useful as In this embodiment, a bioactive ceramic powder is mixed, but tetracalcium phosphate (Ca) is used. ₄ (PO ₄ ) ₂ O) and dicalcium phosphate dihydrate (CaHPO) ₄ ・ 2H ₂ If the method of mixing the powder of O) and mixing with the polymer is adopted, this powder comes into contact with the body fluid at the portion where the polymer is decomposed, so that both react to form hydroxide apatite and solidify. That is, the connection with the bone by self-setting is also possible. In this case, if the shape of the mold to be filled with the polymer solution is made according to the injured part of the living body, a scaffold capable of guiding and forming bone in a three-dimensional direction can be made. Restoring the damaged area of a living body in a three-dimensional spatial direction has been one of the important unsolved problems of conventional plastic surgery and plastic surgery, and orthopedic surgery. This example suggests that such a biomaterial can be provided. At this time, by mixing various bone morphogenetic proteins (BMP), which are bone growth factors, it is possible to more reliably recover the bone defect. Here, if the degree of dispersion of the molecular weight of PLA is set to be large as in this example, those having a large molecular weight require a long time to absorb, and those having a low molecular weight are decomposed and absorbed in a short time after implantation. The advantage is that the rate of exposure or release of the mixed bioactive material can be controlled.
[0087]
Further, when the polymer solution of the present example is poured into a mold, a woven or non-woven fabric woven with ultra-high molecular weight polyethylene or poly-L-lactic acid yarn is embedded in the mold to form a cell structure by a solution precipitation method. Thus, a cell structure reinforced with high-strength bio-inert fibers or bio-absorbable fibers can be obtained. This can be effectively used as a scaffold for tissue replacement at a damaged site in a living body, which has permanent or temporary strength. In this case, a mechanically biocompatible bulk structure (Japanese Patent Application No. 6-254515) consisting of a three-dimensional woven or knitted fabric or a composite structure obtained by combining these fibers is added to the polymer solution. If the cell structure is formed internally by the solution precipitation method and can be connected to the surrounding tissue in the three-dimensional spatial direction, a biomaterial having both functions of a scaffold and a prosthetic material satisfying mechanical compatibility can be obtained.
[0088]
The above method is not limited to hard tissue such as bone and cartilage, and a relatively flexible cell structure such as low molecular weight PLA or LA / GA copolymer having an average molecular weight of about 100,000 can be used as a scaffold for a defective portion of soft tissue. Can be used. In that case, it is a growth factor such as fibroblast growth factor (FGF), epidermal growth factor (EGF), insulin-like growth factor (IGF), or a growth inhibitory factor such as transforming growth factor-β (TGF-β). Various cytokines may be included.
[0089]
[Example 10]
A copolymer of glycolic acid (GA) and D, L-lactic acid (LA) (GA / LA = 20/80, molar ratio, weight average molecular weight Mw: 170,000) was converted into methylene chloride / ethanol = 10/5 (volume). Ratio) in a mixed solvent of 4 g / dl. In 3 g of this polymer solution, 40 mg of adreamycin (ADM) as an anticancer drug was dissolved using a microhomogenizer. Next, this solution was filled in a mold having a length of 1.0 cm and a width of 1.0 cm, and was subjected to a solution precipitation method under the same conditions as in Example 1 so that the height × width × height = 1.0 × 1.0 × 1. An open-cell cell structure colored red was obtained, which is an ADM having an expansion ratio of about 10 cm and a foaming ratio of about 10 times. This block is cut into four blocks of length × width × height = 0.5 × 0.5 × 0.5 cm, and one of the blocks is immersed in a phosphate buffer solution (PBS: Phosphate Buffer Solution) at 37 ° C. The transition of ADM release was examined. Release proceeded on the order of zero order, and after about 3.5 months the cell structure collapsed until it did not retain its shape, dissolved in PBS, and all ADM was released.
[0090]
Generally, the thickness of the cell wall forming the skeleton of the foam is only as thin as several tens μm or less. Therefore, regardless of whether the drug present in the cell wall membrane is dispersed (dissolved) at the molecular level or dispersed in fine particles, the release from the membrane is essentially different from the release from the film surface. Absent. In addition, in the case of an open-cell body (especially a high expansion ratio), the thin film forms a dense connection hole with three-dimensional spatial irregularities, so that the surface area of the film per unit space is extremely large as compared with a flat film surface. . Therefore, since the amount of drug released from such a cell wall is large, it is effective as a carrier for a sustained-release preparation such as an anticancer drug that requires a high-concentration sustained release of a powerful drug capable of filling only a limited amount of drug. It is. As for the decomposition rate of the biodegradable and absorbable polymer, the larger the area in contact with the body fluid, the greater the chance of decomposition, so the apparent decomposition rate becomes faster. Accordingly, the higher the magnification, the faster the decomposition. Drugs that are effective using the biodegradable and absorbable cell structure obtained in the present invention as a carrier of a sustained-release preparation include many types such as antibacterial agents, anticancer agents, various hormones, physiologically active substances, and various cytokines. It is necessary to select a polymer and an expansion ratio appropriate for the amount of release.
[0091]
【The invention's effect】
As can be understood from the above description, the manufacturing method of the cell structure of the present invention is extremely simple, and can be easily performed from a thin cell structure having a film shape or a sheet shape to a cell structure having a large thickness of several cm or more. It can be manufactured from small to large foaming ratios and pores.
[0092]
In addition, since the production method of the present invention has no step of deteriorating the polymer by heating or hydrolysis, a pollution-free cell structure that reduces to a biodegradable environment can be produced without impairing the physical properties of the original polymer. In addition, since additives remaining in the cell structure are not used, if an aliphatic polyester-based polymer such as polylactic acid is used, biodegradation while maintaining the original biosafety and biocompatibility of the polymer as it is. An absorbent cell structure can be obtained. When a polymer solution containing a drug or a bioactive substance is used, most of the drug or the like is contained in the cell wall, and a cell structure capable of accurately controlling the release of the drug or the like in accordance with the decomposition of the polymer is obtained. be able to.
[0093]
Furthermore, according to the production method of the present invention, by filling a polymer solution into a mold, a three-dimensional shape formed so that a complex three-dimensional space of a damaged part of a living body can be arbitrarily applied to the shape. Cell structure advantageous for the construction of a target scaffold and the infiltration of surrounding tissues can be obtained. In addition, when polylactic acid or the like having a relatively low glass transition point of not lower than body temperature and not higher than 100 ° C. is used as a polymer, It is possible to obtain a cell structure that can be heated and deformed immediately before embedding into a cell and can form an ideal scaffold that is in close contact with the shape of the embedding site.

Claims (8)

As organic synthetic polymers , biodegradable and absorbable polylactic acid, copolymer of lactic acid and glycolic acid, copolymer of lactic acid and caprolactone, copolymer of polylactic acid and polyethylene glycol, copolymer of polylactic acid and polypropylene glycol one of the polymer, and methylene chloride as a solvent for the polymer, monohydric alcohol or unable dissolve the polymer has a boiling point within the range of the higher 60 ° C. than methylene chloride to 110 ° C. (under 1 atm) this A polymer solution is prepared by dissolving in a mixed solvent of a non-solvent consisting of alcohol and water, and the polymer solution is filled in a mold and cooled to a low temperature of 10 ° C. or lower, which is lower than the boiling point of methylene chloride, to increase the viscosity. A method for producing an open-cell cell structure , comprising precipitating a polymer by evaporating a mixed solvent under reduced pressure . After filling the polymer solution in a film-like or sheet-like thickness into the mold and dispersing the mixed solvent at a temperature lower than the boiling point of the solvent, the polymer solution is further filled thereon in the same manner. 2. The method according to claim 1, wherein an operation of similarly diffusing the mixed solution is repeated a plurality of times to manufacture a thick cell structure. 3. 3. The method according to claim 1, wherein a volume ratio of the solvent and the non-solvent of the mixed solvent is 10: 1 to 10:10. 4. 4. The mold for filling the polymer solution is a porous mold having a myriad of fine vents that do not allow the polymer to pass therethrough but allow only the mixed solvent to pass therethrough. The production method according to any one of the above. The method according to any one of claims 1 to 4, wherein the polymer solution contains a bioactive substance. The method according to any one of claims 1 to 4, wherein the polymer solution contains a drug. Cell structure of the continuous air bubbles, a thickness of 1mm or more, and wherein the expansion ratio is 3 times or more, the production method according to any one of claims 1 to 6. The method according to claim 7, wherein the open-celled cell structure serves as a scaffold or partition for healing and reconstructing a damaged part of a living body, or as a carrier for drug release.