Experimental parameters which are critical for producing small diameter (i.e. 100-300 μm) polymer... more Experimental parameters which are critical for producing small diameter (i.e. 100-300 μm) polymer microbeads, using electrostatic droplet generation, were investigated with three types of electrodes; a parallel plate, a positively charged needle and a grounded needle with alginate as the polymer. Electrode spacing was a critical factor controlling microbead size, but only for the parallel plate set-up. While the applied potential affected droplet size in all three set-ups, the smallest droplet size was produced with the positively charged needle. In some experiments needle oscillation was observed resulting in even smaller microbeads (i.e. < 100 μm). Calculated microbead diameters agreed well with experimental values.Des paramètres expérimentaux critiques pour la production de microbilles de polymère de petits diamètres (p.ex. 100-300 μm), par la génération de gouttelettes électrostatiques, ont été étudiés avec trois types d'électrodes: un plateau parallèle, une aiguille char...
Camptothecin is an example of a potent drug with a short half-life that would benefit from a loca... more Camptothecin is an example of a potent drug with a short half-life that would benefit from a localized drug depot system that maintains its stability prior to being released. For this reason, a thermoplastic, biodegradable polymer drug depot was prepared and characterized, and the in vitro release of camptothecin examined. e-Caprolactone oligomers were prepared by ring-opening polymerization initiated by various alcohols. The polymers were characterized via differential scanning calorimeter (DSC) for thermal transitions, and via a parallel plate rheometer for melt viscosity. Camptothecin was loaded into the oligomers and released into PBS buffer. The viscosity of the oligomers was alterable by the initiator used. The oligomers were semi-crystalline with melting points between 37 and 458C. Camptothecin was released from the oligomers in a diffusion-controlled manner, with the release rate increasing as the melt viscosity of the oligomer decreased. The unreleased camptothecin remained in its active lactone form for a period of up to 16 weeks. ß
... Anne Hsiehab, Tasneem Zahira, Yakov Lapitskya, Brian Amsdenc, Wankei Wand and Molly S. Shoic... more ... Anne Hsiehab, Tasneem Zahira, Yakov Lapitskya, Brian Amsdenc, Wankei Wand and Molly S. Shoichet*abe. a Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario, Canada M5S 3E5. ...
Purpose. The aim of the study is to determine whether a biodegradable elastomeric device that use... more Purpose. The aim of the study is to determine whether a biodegradable elastomeric device that uses an osmotic pressure delivery mechanism can release different therapeutic proteins at a nearly constant rate in nanomolar concentrations with high bioactivity, given the same formulation conditions. Vascular endothelial growth factor (VEGF) and interleukin-2 (IL-2) were embedded in the device as sample therapeutic proteins, and their release and bioactivity were compared to that achieved previously with interferon-g (IFN-g). Methods. A photo-cross-linkable biodegradable macromer consisting of acrylated star((-caprolactoneco-D,L-lactide) was prepared. VEGF, IL-2, and IFN-g were co-lyophilized with serum albumin and trehalose at different ratios and were then embedded into the elastomer by photo-cross-linking the lyophilized particles in a macromer solution. The protein mass and the bioactivity in the release supernatant were measured by enzyme-linked immunosorbent and cell-based assays. Results. VEGF, IL-2, and IFN-g were released at the same, nearly constant rate of 25.4 ng/day for over 18 days. Using the optimum elastomer formulation, the release profiles of the proteins were essentially identical, and their rates were linear and constant. Cell-based bioactivity assays showed that 70 and 88% of the released VEGF and IL-2, respectively, were bioactive. The rate of protein release can be adjusted by changing the trehalose loading concentration in the elastomer matrix without altering the linear nature of the protein release kinetics. The elastomeric device degraded in PBS buffer within 85 days.
Objective: Harvesting osteochondral grafts results in a zone of chondrocyte death (ZCD) in and ar... more Objective: Harvesting osteochondral grafts results in a zone of chondrocyte death (ZCD) in and around the periphery of the graft, creating a barrier for chondrocytes to migrate to the graft periphery, thus limiting cartilage-to-cartilage healing. The purpose of this study was to repopulate the induced ZCD through the combined effects of collagenase treatment and delivery of a chemotactic agent. Design: In bovine cartilage, the ZCD induced by the OATSÔ osteochondral harvesting system was determined, followed by a corresponding collagenase treatment to penetrate the developed ZCD. The chemotactic potential of platelet derived growth factor (PDGF-bb), insulin-like growth factor I (IGF-I), and basic fibroblast growth factor (bFGF) (2.5e100 ng/mL) was then assessed using a modified Boyden chamber assay to select an appropriate agent to induce chondrocyte migration. Afterwards, the combined effects of collagenase treatment and chondrocyte chemotaxis on the repopulation of an induced ZCD were examined in cartilage explants over a 4-week-period.
Cylindrical elastomers were prepared through the UV-initiated crosslinking of terminally acrylate... more Cylindrical elastomers were prepared through the UV-initiated crosslinking of terminally acrylated, 8,000 Da star-poly(trimethylene carbonate-co-ε-caprolactone) and star-poly(trimethylene carbonate-co-D,L-lactide). These elastomers were implanted intramuscularly into the hind legs of male Wistar rats to determine the influence of the comonomer on the weight loss, tissue response, and change in mechanical properties of the elastomer. The elastomers exhibited only a mild inflammatory response that subsided after the first week; the response was greater for the stiffer D,L-lactide-containing elastomers. The elastomers exhibited weight loss and sol content changes consistent with a bulk degradation mechanism. The D,L-lactide-containing elastomers displayed a nearly zeroorder change in Young's modulus and stress at break over the 30 week degradation time, while the ε-caprolactone-containing elastomers exhibited little change in modulus or stress at break.
Journal of Polymer Science Part A: Polymer Chemistry, 2008
The use of aliphatic polyesters for biomedical applications is limited by the lack of functionali... more The use of aliphatic polyesters for biomedical applications is limited by the lack of functionality of their backbones. The aim of the following study was to develop a novel elastic scaffold material containing functional groups to be used for future derivatization to tether peptide ligands to support cell adhesion, migration, and differentiation. The elastomer was based on three-arm star copolymers composed of e-caprolactone and a functionalized e-caprolactone, 2-oxepane-1,5-dione, and end-terminated with acrylate groups. The elastomer thus contains a ketone and two approaches were examined for obtaining a photocrosslinkable elastomer containing functional groups: crosslinking followed by ketone reduction using sodium borohydride to generate pendant hydroxyl groups, and reaction of the ketone with hydrazines. Reduction of the ketone lead to degradation of the elastomer through transesterification and ethanolate mediated cleavage of the polymer backbone. Reaction with hydrazines did not degrade the polymer and resulted in efficient functionalization of the elastomer. V V C 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8191-8199, 2008
0 A polymeric delayed-release protein delivery system was investigated with albumin as a model dr... more 0 A polymeric delayed-release protein delivery system was investigated with albumin as a model drug. The polysaccharide chtosan was reacted with sodium alginate in the presence of calcium chloride to form microcapsules with a polyelectrolyte complex membrane. Variables believed to be important for membrane formation were examined; these included reaction time, chitosan molecular weight, alginate concentration, chitosan concentration, and solution pH. An alginate-chitosan reaction time, in the range of 10 to 45 min, had no
The feasibility of generating an extended period of linear release of therapeutic proteins from p... more The feasibility of generating an extended period of linear release of therapeutic proteins from photo-cross-linked, biodegradable elastomer monolithic devices in vitro has been previously demonstrated. The release is driven primarily by the osmotic pressure generated upon the dissolution of the encapsulated particles within the polymer. The osmotic pressure is provided by co-incorporation into the particle of trehalose as an osmotigen. Herein, we demonstrate that the release rate of a therapeutic protein, vascular endothelial growth factor (VEGF), by this osmotic pressure mechanism is the same in vivo as found in vitro. 125 I-VEGF was colyophilized with trehalose and serum albumin and distributed as particles throughout a photo-cross-linked elastomer composed of trimethylene carbonate, g-caprolactone, and D,Llactide. The release of VEGF from the device was monitored by measuring the decrease in radioactivity within the devices in vitro and within explanted devices that had been implanted subcutaneously in the dorsal area of Wistar rats. The released VEGF remained bioactive in vivo, inducing the formation of blood vessels that contained red blood cells. Furthermore, the released trehalose was well tolerated by the surrounding tissue.
... in the capsule core to be partially sealed off by the slowly dissolving enteric polymer; henc... more ... in the capsule core to be partially sealed off by the slowly dissolving enteric polymer; hence, the ... a core would manifest greater microvoids, even in the dry state, and hence higher protein diffusion ... A good way that was found to counteract this effect was to mix alginate with the pH ...
Journal of Materials Science: Materials in Medicine, 2008
A synthetic peptide fragment of human collagen type I (BCSP TM -1) was linked to the surface of a... more A synthetic peptide fragment of human collagen type I (BCSP TM -1) was linked to the surface of a commercially available ceramic in an effort to improve the properties of the bone graft substitute to accelerate local healing. BCSP TM -1 was covalently immobilized on the surface of the ceramic via the linkers 3-aminopropyltriethoxysilane (APTES) and suberic acid bis-N-hydroxysuccinimide ester (DSS). The chosen chemistry was non-cytotoxic. A rat calvaria cell assay using alkaline phosphatase (ALP) as an osteoblast differentiation marker, showed that modifying the surface of the ceramic was enough to enhance ALP activity, although the total cell population on the surface decreased. A significant increase in ALP activity/cell was noted with serum albumin bound to the surface, however, the BCSP TM -1 bound surface exhibited an even greater ALP activity that showed a surface concentration dependent trend. An optimal BCSP TM -1 surface density in the range of 0.87-2.24 nmol/cm 2 elicited the maximum ALP activity/cell at day 6 of culture. The peptide bound ceramic generated an ALP activity/cell that was roughly 3-fold higher than the non-modified ceramic and 2-fold higher than the APTES-grafted ceramic.
The ability of trimethylene carbonate (TMC) based elastomers to release bioactive vascular endoth... more The ability of trimethylene carbonate (TMC) based elastomers to release bioactive vascular endothelial growth factor (VEGF 165 ) and hepatocyte growth factor (HGF) separately and in combined and sequential fashions using an osmotic release mechanism was investigated. A TMC-based elastomer was chosen since TMC degrades without producing potentially harmful acidic degradation products, and its mechanical properties can be tailored by copolymerizing with D,L-lactide (DLLA) and ε-caprolactone (ε-CL) and by controlling the cross-link density. The bioactivities of released VEGF 165 and HGF were assessed using the proliferation of human aortic endothelial (HAEC) and CCL 208 monkey lung epithelial cell lines. VEGF 165 and HGF were lyophilized separately or together with trehalose, rat serum albumin (RSA) and NaCl. No significant elastomer degradation occurred over the initial 8 weeks, during which the bulk of the embedded growth factors were released. The presence of a low concentration of NaCl in the release media did not affect the viability of HAEC and CCL 208 cells. The TMC-based elastomer was able to provide a sustained release of highly bioactive VEGF 165 and HGF for more than 10 days. When released in combination from the same device, VEGF 165 and HGF were released at similar rates. By preparing a dual-layered cylinder, in which VEGF 165 was in the outer layer and HGF in the inner layer, a constant release of VEGF alone was first obtained, followed by overlapping and constant release of the two growth factors after a period of 4 days. This study demonstrates the potential of TMC-based elastomers combined with an osmotic mechanism to release acid-sensitive growth factors in bioactive form alone and in combination, in controlled rates and sequences.
The purpose of this study was to examine the potential of low molecular weight poly(trimethylene ... more The purpose of this study was to examine the potential of low molecular weight poly(trimethylene carbonate) for localized vascular endothelial growth factor (VEGF) delivery. Poly(trimethylene carbonate) of various molecular weights was prepared by ring-opening polymerization initiated by 1-octanol. The resultant polymers were liquid at room temperature with low glass transition temperatures and viscosities at 37°C that permitted their injection through an 18 ½ G 1.5″ needle. Particles consisting of VEGF colyophilized with trehalose were mixed into the polymers and the rate of release of VEGF was assessed in vitro. With a 1% particle loading, VEGF was released from the polymer at a rate of 20 ng/day over a period of 3 weeks. This release behavior was independent of the molecular weight of polymer used. Increasing the VEGF content in the lyophilized particles did not increase the VEGF release rate, an effect attributed to the solubility limit of VEGF in the solution formed upon dissolution of the particles. The VEGF released retained its bioactivity at greater than 95% of that of as-lyophilized VEGF, as assessed using a human aortic endothelial cell proliferation assay. This high bioactivity was supported by in vivo release experiments, wherein VEGF containing polymer implants induced the generation of significantly greater numbers of blood vessels towards the polymer implant than controls. The blood vessels did not remain stable and were reduced in number by three weeks, due to the unsustained and low concentration of VEGF released. This formulation approach, of using a low viscosity polymer delivery vehicle, is potentially useful for localized delivery of acidsensitive proteins, such as VEGF.
Experimental parameters which are critical for producing small diameter (i.e. 100-300 μm) polymer... more Experimental parameters which are critical for producing small diameter (i.e. 100-300 μm) polymer microbeads, using electrostatic droplet generation, were investigated with three types of electrodes; a parallel plate, a positively charged needle and a grounded needle with alginate as the polymer. Electrode spacing was a critical factor controlling microbead size, but only for the parallel plate set-up. While the applied potential affected droplet size in all three set-ups, the smallest droplet size was produced with the positively charged needle. In some experiments needle oscillation was observed resulting in even smaller microbeads (i.e. < 100 μm). Calculated microbead diameters agreed well with experimental values.Des paramètres expérimentaux critiques pour la production de microbilles de polymère de petits diamètres (p.ex. 100-300 μm), par la génération de gouttelettes électrostatiques, ont été étudiés avec trois types d'électrodes: un plateau parallèle, une aiguille char...
Camptothecin is an example of a potent drug with a short half-life that would benefit from a loca... more Camptothecin is an example of a potent drug with a short half-life that would benefit from a localized drug depot system that maintains its stability prior to being released. For this reason, a thermoplastic, biodegradable polymer drug depot was prepared and characterized, and the in vitro release of camptothecin examined. e-Caprolactone oligomers were prepared by ring-opening polymerization initiated by various alcohols. The polymers were characterized via differential scanning calorimeter (DSC) for thermal transitions, and via a parallel plate rheometer for melt viscosity. Camptothecin was loaded into the oligomers and released into PBS buffer. The viscosity of the oligomers was alterable by the initiator used. The oligomers were semi-crystalline with melting points between 37 and 458C. Camptothecin was released from the oligomers in a diffusion-controlled manner, with the release rate increasing as the melt viscosity of the oligomer decreased. The unreleased camptothecin remained in its active lactone form for a period of up to 16 weeks. ß
... Anne Hsiehab, Tasneem Zahira, Yakov Lapitskya, Brian Amsdenc, Wankei Wand and Molly S. Shoic... more ... Anne Hsiehab, Tasneem Zahira, Yakov Lapitskya, Brian Amsdenc, Wankei Wand and Molly S. Shoichet*abe. a Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario, Canada M5S 3E5. ...
Purpose. The aim of the study is to determine whether a biodegradable elastomeric device that use... more Purpose. The aim of the study is to determine whether a biodegradable elastomeric device that uses an osmotic pressure delivery mechanism can release different therapeutic proteins at a nearly constant rate in nanomolar concentrations with high bioactivity, given the same formulation conditions. Vascular endothelial growth factor (VEGF) and interleukin-2 (IL-2) were embedded in the device as sample therapeutic proteins, and their release and bioactivity were compared to that achieved previously with interferon-g (IFN-g). Methods. A photo-cross-linkable biodegradable macromer consisting of acrylated star((-caprolactoneco-D,L-lactide) was prepared. VEGF, IL-2, and IFN-g were co-lyophilized with serum albumin and trehalose at different ratios and were then embedded into the elastomer by photo-cross-linking the lyophilized particles in a macromer solution. The protein mass and the bioactivity in the release supernatant were measured by enzyme-linked immunosorbent and cell-based assays. Results. VEGF, IL-2, and IFN-g were released at the same, nearly constant rate of 25.4 ng/day for over 18 days. Using the optimum elastomer formulation, the release profiles of the proteins were essentially identical, and their rates were linear and constant. Cell-based bioactivity assays showed that 70 and 88% of the released VEGF and IL-2, respectively, were bioactive. The rate of protein release can be adjusted by changing the trehalose loading concentration in the elastomer matrix without altering the linear nature of the protein release kinetics. The elastomeric device degraded in PBS buffer within 85 days.
Objective: Harvesting osteochondral grafts results in a zone of chondrocyte death (ZCD) in and ar... more Objective: Harvesting osteochondral grafts results in a zone of chondrocyte death (ZCD) in and around the periphery of the graft, creating a barrier for chondrocytes to migrate to the graft periphery, thus limiting cartilage-to-cartilage healing. The purpose of this study was to repopulate the induced ZCD through the combined effects of collagenase treatment and delivery of a chemotactic agent. Design: In bovine cartilage, the ZCD induced by the OATSÔ osteochondral harvesting system was determined, followed by a corresponding collagenase treatment to penetrate the developed ZCD. The chemotactic potential of platelet derived growth factor (PDGF-bb), insulin-like growth factor I (IGF-I), and basic fibroblast growth factor (bFGF) (2.5e100 ng/mL) was then assessed using a modified Boyden chamber assay to select an appropriate agent to induce chondrocyte migration. Afterwards, the combined effects of collagenase treatment and chondrocyte chemotaxis on the repopulation of an induced ZCD were examined in cartilage explants over a 4-week-period.
Cylindrical elastomers were prepared through the UV-initiated crosslinking of terminally acrylate... more Cylindrical elastomers were prepared through the UV-initiated crosslinking of terminally acrylated, 8,000 Da star-poly(trimethylene carbonate-co-ε-caprolactone) and star-poly(trimethylene carbonate-co-D,L-lactide). These elastomers were implanted intramuscularly into the hind legs of male Wistar rats to determine the influence of the comonomer on the weight loss, tissue response, and change in mechanical properties of the elastomer. The elastomers exhibited only a mild inflammatory response that subsided after the first week; the response was greater for the stiffer D,L-lactide-containing elastomers. The elastomers exhibited weight loss and sol content changes consistent with a bulk degradation mechanism. The D,L-lactide-containing elastomers displayed a nearly zeroorder change in Young's modulus and stress at break over the 30 week degradation time, while the ε-caprolactone-containing elastomers exhibited little change in modulus or stress at break.
Journal of Polymer Science Part A: Polymer Chemistry, 2008
The use of aliphatic polyesters for biomedical applications is limited by the lack of functionali... more The use of aliphatic polyesters for biomedical applications is limited by the lack of functionality of their backbones. The aim of the following study was to develop a novel elastic scaffold material containing functional groups to be used for future derivatization to tether peptide ligands to support cell adhesion, migration, and differentiation. The elastomer was based on three-arm star copolymers composed of e-caprolactone and a functionalized e-caprolactone, 2-oxepane-1,5-dione, and end-terminated with acrylate groups. The elastomer thus contains a ketone and two approaches were examined for obtaining a photocrosslinkable elastomer containing functional groups: crosslinking followed by ketone reduction using sodium borohydride to generate pendant hydroxyl groups, and reaction of the ketone with hydrazines. Reduction of the ketone lead to degradation of the elastomer through transesterification and ethanolate mediated cleavage of the polymer backbone. Reaction with hydrazines did not degrade the polymer and resulted in efficient functionalization of the elastomer. V V C 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8191-8199, 2008
0 A polymeric delayed-release protein delivery system was investigated with albumin as a model dr... more 0 A polymeric delayed-release protein delivery system was investigated with albumin as a model drug. The polysaccharide chtosan was reacted with sodium alginate in the presence of calcium chloride to form microcapsules with a polyelectrolyte complex membrane. Variables believed to be important for membrane formation were examined; these included reaction time, chitosan molecular weight, alginate concentration, chitosan concentration, and solution pH. An alginate-chitosan reaction time, in the range of 10 to 45 min, had no
The feasibility of generating an extended period of linear release of therapeutic proteins from p... more The feasibility of generating an extended period of linear release of therapeutic proteins from photo-cross-linked, biodegradable elastomer monolithic devices in vitro has been previously demonstrated. The release is driven primarily by the osmotic pressure generated upon the dissolution of the encapsulated particles within the polymer. The osmotic pressure is provided by co-incorporation into the particle of trehalose as an osmotigen. Herein, we demonstrate that the release rate of a therapeutic protein, vascular endothelial growth factor (VEGF), by this osmotic pressure mechanism is the same in vivo as found in vitro. 125 I-VEGF was colyophilized with trehalose and serum albumin and distributed as particles throughout a photo-cross-linked elastomer composed of trimethylene carbonate, g-caprolactone, and D,Llactide. The release of VEGF from the device was monitored by measuring the decrease in radioactivity within the devices in vitro and within explanted devices that had been implanted subcutaneously in the dorsal area of Wistar rats. The released VEGF remained bioactive in vivo, inducing the formation of blood vessels that contained red blood cells. Furthermore, the released trehalose was well tolerated by the surrounding tissue.
... in the capsule core to be partially sealed off by the slowly dissolving enteric polymer; henc... more ... in the capsule core to be partially sealed off by the slowly dissolving enteric polymer; hence, the ... a core would manifest greater microvoids, even in the dry state, and hence higher protein diffusion ... A good way that was found to counteract this effect was to mix alginate with the pH ...
Journal of Materials Science: Materials in Medicine, 2008
A synthetic peptide fragment of human collagen type I (BCSP TM -1) was linked to the surface of a... more A synthetic peptide fragment of human collagen type I (BCSP TM -1) was linked to the surface of a commercially available ceramic in an effort to improve the properties of the bone graft substitute to accelerate local healing. BCSP TM -1 was covalently immobilized on the surface of the ceramic via the linkers 3-aminopropyltriethoxysilane (APTES) and suberic acid bis-N-hydroxysuccinimide ester (DSS). The chosen chemistry was non-cytotoxic. A rat calvaria cell assay using alkaline phosphatase (ALP) as an osteoblast differentiation marker, showed that modifying the surface of the ceramic was enough to enhance ALP activity, although the total cell population on the surface decreased. A significant increase in ALP activity/cell was noted with serum albumin bound to the surface, however, the BCSP TM -1 bound surface exhibited an even greater ALP activity that showed a surface concentration dependent trend. An optimal BCSP TM -1 surface density in the range of 0.87-2.24 nmol/cm 2 elicited the maximum ALP activity/cell at day 6 of culture. The peptide bound ceramic generated an ALP activity/cell that was roughly 3-fold higher than the non-modified ceramic and 2-fold higher than the APTES-grafted ceramic.
The ability of trimethylene carbonate (TMC) based elastomers to release bioactive vascular endoth... more The ability of trimethylene carbonate (TMC) based elastomers to release bioactive vascular endothelial growth factor (VEGF 165 ) and hepatocyte growth factor (HGF) separately and in combined and sequential fashions using an osmotic release mechanism was investigated. A TMC-based elastomer was chosen since TMC degrades without producing potentially harmful acidic degradation products, and its mechanical properties can be tailored by copolymerizing with D,L-lactide (DLLA) and ε-caprolactone (ε-CL) and by controlling the cross-link density. The bioactivities of released VEGF 165 and HGF were assessed using the proliferation of human aortic endothelial (HAEC) and CCL 208 monkey lung epithelial cell lines. VEGF 165 and HGF were lyophilized separately or together with trehalose, rat serum albumin (RSA) and NaCl. No significant elastomer degradation occurred over the initial 8 weeks, during which the bulk of the embedded growth factors were released. The presence of a low concentration of NaCl in the release media did not affect the viability of HAEC and CCL 208 cells. The TMC-based elastomer was able to provide a sustained release of highly bioactive VEGF 165 and HGF for more than 10 days. When released in combination from the same device, VEGF 165 and HGF were released at similar rates. By preparing a dual-layered cylinder, in which VEGF 165 was in the outer layer and HGF in the inner layer, a constant release of VEGF alone was first obtained, followed by overlapping and constant release of the two growth factors after a period of 4 days. This study demonstrates the potential of TMC-based elastomers combined with an osmotic mechanism to release acid-sensitive growth factors in bioactive form alone and in combination, in controlled rates and sequences.
The purpose of this study was to examine the potential of low molecular weight poly(trimethylene ... more The purpose of this study was to examine the potential of low molecular weight poly(trimethylene carbonate) for localized vascular endothelial growth factor (VEGF) delivery. Poly(trimethylene carbonate) of various molecular weights was prepared by ring-opening polymerization initiated by 1-octanol. The resultant polymers were liquid at room temperature with low glass transition temperatures and viscosities at 37°C that permitted their injection through an 18 ½ G 1.5″ needle. Particles consisting of VEGF colyophilized with trehalose were mixed into the polymers and the rate of release of VEGF was assessed in vitro. With a 1% particle loading, VEGF was released from the polymer at a rate of 20 ng/day over a period of 3 weeks. This release behavior was independent of the molecular weight of polymer used. Increasing the VEGF content in the lyophilized particles did not increase the VEGF release rate, an effect attributed to the solubility limit of VEGF in the solution formed upon dissolution of the particles. The VEGF released retained its bioactivity at greater than 95% of that of as-lyophilized VEGF, as assessed using a human aortic endothelial cell proliferation assay. This high bioactivity was supported by in vivo release experiments, wherein VEGF containing polymer implants induced the generation of significantly greater numbers of blood vessels towards the polymer implant than controls. The blood vessels did not remain stable and were reduced in number by three weeks, due to the unsustained and low concentration of VEGF released. This formulation approach, of using a low viscosity polymer delivery vehicle, is potentially useful for localized delivery of acidsensitive proteins, such as VEGF.
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Papers by Brian Amsden