Self-limiting atomic layer deposition of barium oxide and barium titanate thin fi lms using a nov... more Self-limiting atomic layer deposition of barium oxide and barium titanate thin fi lms using a novel pyrrole based precursor Using a novel barium precursor (py-Ba), the fi rst ever self-limiting, high quality atomic layer deposition of barium oxide has been achieved which conformally coats a high aspect ratio substrate. Intermixing BaO and TiO 2 depositions, amorphous barium titanate thin fi lms exhibiting high dielectric constant have been obtained.
The lack of efficient water-soluble two-photon absorption (TPA) photoinitiators has been a critic... more The lack of efficient water-soluble two-photon absorption (TPA) photoinitiators has been a critical obstruction for three dimensional hydrogel microfabrications with high water load by two-photon induced polymerization (TPIP). In this paper, a series of cyclic benzylidene ketone-based two-photon initiators, containing carboxylic acid sodium salts to improve water solubility, were synthesized via classical aldol condensation reactions. The cytotoxicity of cyclopentanone-based photoinitiators is as low as that of the well-known biocompatible photoinitiator Irgacure 2959 as assessed in the dark with MG63 cell line. In z-scan measurement, the TPA cross sections of the investigated initiators are only moderate in water, while the TPA values for hydrophobic analogues measured in chloroform were much higher. All novel initiators exhibited broad processing windows in TPIP tests using hydrophilic photopolymers with up to 50 wt% of water. Impressively, microfabrication of hydrogels with excellent precision was possible at a writing speed as high as 100 mm s 21 .
Journal of Polymer Science Part A Polymer Chemistry
Designing 3D hydrogels with user-defined geometries can facilitate a variety of basic research in... more Designing 3D hydrogels with user-defined geometries can facilitate a variety of basic research in biomaterials science and tissue engineering. In their article on page 4799, R. Liska, X.-H. Qin, and coworkers report the direct assembly of 3D hydrogel structures with free-transport properties via two-photon thiolene lithography. This study reports the first biomacromolecule with pendant, low cytotoxic vinyl ester groups and subsequent copolymerization with free cysteines donated by reduced albumin. The cover image shows a 3D hydrogel construct (480 × 580 × 75 μm3) consisting of three layers of packed cylinders with a hexagonal arrangement. This method may lead researchers to better understand how cells detect and respond to their micro-environmental signals.
A reproducible method is needed to fabricate 3D scaffold constructs that results in periodic and ... more A reproducible method is needed to fabricate 3D scaffold constructs that results in periodic and uniform structures with precise control at sub-micrometer and micrometer length scales. In this study, fabrication of scaffolds by two-photon polymerization (2PP) of a biodegradable urethane and acrylate-based photoelastomer is demonstrated. This material supports 2PP processing with sub-micrometer spatial resolution. The high photoreactivity of the biophotoelastomer permits 2PP processing at a scanning speed of 1000 mm s(-1) , facilitating rapid fabrication of relatively large structures (>5 mm(3) ). These structures are custom printed for in vitro assay screening in 96-well plates and are sufficiently flexible to enable facile handling and transplantation. These results indicate that stable scaffolds with porosities of greater than 60% can be produced using 2PP. Human bone marrow stromal cells grown on 3D scaffolds exhibit increased growth and proliferation compared to smooth 2D sca...
Two-photon induced polymerization (TPIP) allows greatly improved spatial resolution relative to t... more Two-photon induced polymerization (TPIP) allows greatly improved spatial resolution relative to traditional one-photon polymerization. The main limiting factors of the technology are the high cost of pulsed lasers, slow writing speeds, and poor reactivity of traditional initiators. We address the third issue through synthesis of a series of benzylidene ketones with both high two-photon absorbance and good initiating efficiency. As a result, sub-micrometer structures are produced both faster and with lower required laser intensity.
2012): Design, physical prototyping and initial characterisation of 'lockyballs', Virtual and Phy... more 2012): Design, physical prototyping and initial characterisation of 'lockyballs', Virtual and Physical Prototyping, 7:4, 287-301 To link to this article: http://dx.
The development of practical two-photon absorption photoinitiators (TPA PIs) has been slow due to... more The development of practical two-photon absorption photoinitiators (TPA PIs) has been slow due to their complicated syntheses often reliant on expensive catalysts. These shortcomings have been a critical obstruction for further advances in the promising field of two-photon-induced photopolymerization (TPIP) technology. This paper describes a series of linear and cyclic benzylidene ketone-based two-photon initiators containing double bonds and dialkylamino groups synthesized in one step via classical aldol condensation reactions. Systematic investigations of structure−activity relationships were conducted via quantum-chemical calculations and experimental tests. These results showed that the size of the central ring significantly affected the excited state energetics and emission quantum yields as well as the two-photon initiation efficiency. In the TPIP tests the 4-methylcyclohexanone-based initiator displayed much broader ideal processing windows than its counterparts with a central five-membered ring and previously described highly active TPA PIs. Surprisingly, a writing speed as high as 80 mm/s was obtained for the microfabrication of complex 3D structures employing acrylate-based formulations. These highly active TPA PIs also exhibit excellent thermal stability and remain inert to one-photon excitation. Straightforward synthesis combined with high TPA initiation efficiency makes these novel initiators promising candidates for commercialization.
The two-photon polymerization (2PP) of photosensitive gelatin in the presence of living cells is ... more The two-photon polymerization (2PP) of photosensitive gelatin in the presence of living cells is reported. The 2PP technique is based on the localized cross-linking of photopolymers induced by femtosecond laser pulses. The availability of water-soluble photoinitiators (PI) suitable for 2PP is crucial for applying this method to cell-containing materials. Novel PIs developed by our group allow 2PP of formulations with up to 80% cell culture medium. The cytocompatibility of these PIs was evaluated by an MTT assay. The results of cell encapsulation by 2PP show the occurrence of cell damage within the laser-exposed regions. However, some cells located in the immediate vicinity and even within the 2PP-produced structures remain viable and can further proliferate. The control experiments demonstrate that the laser radiation itself does not damage the cells at the parameters used for 2PP. On the basis of these findings and the reports by other groups, we conclude that such localized cell damage is of a chemical origin and can be attributed to reactive species generated during 2PP. The viable cells trapped within the 2PP structures but not exposed to laser radiation continued to proliferate. The live/dead staining after 3 weeks revealed viable cells occupying most of the space available within the 3D hydrogel constructs. While some of the questions raised by this study remain open, the presented results indicate the general practicability of 2PP for 3D processing of cell-containing materials. The potential applications of this highly versatile approach span from precise engineering of 3D tissue models to the fabrication of cellular microarrays.
Journal of Polymer Science Part A: Polymer Chemistry, 2013
Engineering three-dimensional (3D) hydrogels with well-defined architectures has become increasin... more Engineering three-dimensional (3D) hydrogels with well-defined architectures has become increasingly important for tissue engineering and basic research in biomaterials science. To fabricate 3D hydrogels with (sub)cellular-scale features, two-photon polymerization (2PP) shows great promise although the technique is limited by the selection of appropriate hydrogel precursors. In this study, we report the synthesis of gelatin hydrolysate vinyl esters (GH-VE) and its copolymerization with reduced derivatives of bovine serum albumin (acting as macrothiols). Photorheology of the thiol-ene copolymerization shows a much more rapid onset of polymerization and a higher end modulus in reference to neat GH-VE. This allowed 2PP to provide well-defined and stable hydrogel microstructures. Efficiency of the radical-mediated thiol-vinyl ester photopolymerization allows high 2PP writing speed (as high as 50 mm s 21 ) with low laser power (as low as 20 mW). MTT assays indicate negligible cytotoxicities of the GH-VE macromers and of the thiol-ene hydrogel pellets. Osteosarcoma cells seeded onto GH-VE/BSA hydrogels with different macromer relative ratios showed a preference for hydrogels with higher percentage of GH-VE. This can be attributed both to a favorable modulus and preferable protein environment since gelatin favors cell adhesion and albumin incurs nonspecific binding.
Hydrogels are polymeric materials with water contents similar to that of soft tissues. Due to the... more Hydrogels are polymeric materials with water contents similar to that of soft tissues. Due to their biomimetic properties, they have been extensively used in various biomedical applications including cell encapsulation for tissue engineering. The utilization of photopolymers provides a possibility for the temporal and spatial controlling of hydrogel cross-links. We produced three-dimensional (3-D) hydrogel scaffolds by means of the two-photon polymerization (2PP) technique. Using a highly efficient water-soluble initiator, photopolymers with up to 80 wt.% water were processed with high precision and reproducibility at a writing speed of 10 mm∕s. The biocompatibility of the applied materials was verified using Caenorhabditis elegans as living test organisms. Furthermore, these living organisms were successfully embedded within a 200 × 200 × 35 μm 3 hydrogel scaffold. As most biologic tissues exhibit a window of transparency at the wavelength of the applied femtosecond laser, it is suggested that 2PP is promising for an in situ approach. Our results demonstrate the feasibility of and potential for bio-fabricating 3-D tissue constructs in the micrometre-range via near-infrared lasers in direct contact with a living organism.
Two-Photon-Polymerization (2PP) is a fast developing method for the micro-and nanostructuring of ... more Two-Photon-Polymerization (2PP) is a fast developing method for the micro-and nanostructuring of three-dimensional parts. The manufacturing of biocompatible structures using this technique is a promising field as it fulfills the demands for parts with high feature resolution. This paper reports the fabrication of scaffolds using photopolymers with embedded living organisms (Caenorhabditis elegans). The structuring was performed with a pulsed near-infrared laser with a wavelength of 810nm and adjustable power up to 160mW. Using a 20x magnification microscope objective with a numerical aperture of 0.4, a high resolution scaffold with a base area of 300x300µm and a height of 80µm could be fabricated. Taking advantage of high laser intensities (writing speed: 300µm/s) the structuring process took only 12 minutes.
Utilization of multiphoton absorption has led to important advances in microscopy and photofabric... more Utilization of multiphoton absorption has led to important advances in microscopy and photofabrication. Herein, our recent results on precise immobilization of molecules within 3D polymeric matrices by means of multiphoton grafting are presented. Assessment of nonlinear absorption properties of difunctional aromatic azide, selected for this purpose was performed by the Z-scan technique. It indicates that a three-photon absorption process is responsible for photolysis of this compound. Successful photografting for production of 3D patterns with lateral resolution down to 4 µm was achieved. Our results demonstrate the potential of the developed three-photon grafting method for precise 3D site-specific functionalization of different materials.
Self-limiting atomic layer deposition of barium oxide and barium titanate thin fi lms using a nov... more Self-limiting atomic layer deposition of barium oxide and barium titanate thin fi lms using a novel pyrrole based precursor Using a novel barium precursor (py-Ba), the fi rst ever self-limiting, high quality atomic layer deposition of barium oxide has been achieved which conformally coats a high aspect ratio substrate. Intermixing BaO and TiO 2 depositions, amorphous barium titanate thin fi lms exhibiting high dielectric constant have been obtained.
The lack of efficient water-soluble two-photon absorption (TPA) photoinitiators has been a critic... more The lack of efficient water-soluble two-photon absorption (TPA) photoinitiators has been a critical obstruction for three dimensional hydrogel microfabrications with high water load by two-photon induced polymerization (TPIP). In this paper, a series of cyclic benzylidene ketone-based two-photon initiators, containing carboxylic acid sodium salts to improve water solubility, were synthesized via classical aldol condensation reactions. The cytotoxicity of cyclopentanone-based photoinitiators is as low as that of the well-known biocompatible photoinitiator Irgacure 2959 as assessed in the dark with MG63 cell line. In z-scan measurement, the TPA cross sections of the investigated initiators are only moderate in water, while the TPA values for hydrophobic analogues measured in chloroform were much higher. All novel initiators exhibited broad processing windows in TPIP tests using hydrophilic photopolymers with up to 50 wt% of water. Impressively, microfabrication of hydrogels with excellent precision was possible at a writing speed as high as 100 mm s 21 .
Journal of Polymer Science Part A Polymer Chemistry
Designing 3D hydrogels with user-defined geometries can facilitate a variety of basic research in... more Designing 3D hydrogels with user-defined geometries can facilitate a variety of basic research in biomaterials science and tissue engineering. In their article on page 4799, R. Liska, X.-H. Qin, and coworkers report the direct assembly of 3D hydrogel structures with free-transport properties via two-photon thiolene lithography. This study reports the first biomacromolecule with pendant, low cytotoxic vinyl ester groups and subsequent copolymerization with free cysteines donated by reduced albumin. The cover image shows a 3D hydrogel construct (480 × 580 × 75 μm3) consisting of three layers of packed cylinders with a hexagonal arrangement. This method may lead researchers to better understand how cells detect and respond to their micro-environmental signals.
A reproducible method is needed to fabricate 3D scaffold constructs that results in periodic and ... more A reproducible method is needed to fabricate 3D scaffold constructs that results in periodic and uniform structures with precise control at sub-micrometer and micrometer length scales. In this study, fabrication of scaffolds by two-photon polymerization (2PP) of a biodegradable urethane and acrylate-based photoelastomer is demonstrated. This material supports 2PP processing with sub-micrometer spatial resolution. The high photoreactivity of the biophotoelastomer permits 2PP processing at a scanning speed of 1000 mm s(-1) , facilitating rapid fabrication of relatively large structures (>5 mm(3) ). These structures are custom printed for in vitro assay screening in 96-well plates and are sufficiently flexible to enable facile handling and transplantation. These results indicate that stable scaffolds with porosities of greater than 60% can be produced using 2PP. Human bone marrow stromal cells grown on 3D scaffolds exhibit increased growth and proliferation compared to smooth 2D sca...
Two-photon induced polymerization (TPIP) allows greatly improved spatial resolution relative to t... more Two-photon induced polymerization (TPIP) allows greatly improved spatial resolution relative to traditional one-photon polymerization. The main limiting factors of the technology are the high cost of pulsed lasers, slow writing speeds, and poor reactivity of traditional initiators. We address the third issue through synthesis of a series of benzylidene ketones with both high two-photon absorbance and good initiating efficiency. As a result, sub-micrometer structures are produced both faster and with lower required laser intensity.
2012): Design, physical prototyping and initial characterisation of 'lockyballs', Virtual and Phy... more 2012): Design, physical prototyping and initial characterisation of 'lockyballs', Virtual and Physical Prototyping, 7:4, 287-301 To link to this article: http://dx.
The development of practical two-photon absorption photoinitiators (TPA PIs) has been slow due to... more The development of practical two-photon absorption photoinitiators (TPA PIs) has been slow due to their complicated syntheses often reliant on expensive catalysts. These shortcomings have been a critical obstruction for further advances in the promising field of two-photon-induced photopolymerization (TPIP) technology. This paper describes a series of linear and cyclic benzylidene ketone-based two-photon initiators containing double bonds and dialkylamino groups synthesized in one step via classical aldol condensation reactions. Systematic investigations of structure−activity relationships were conducted via quantum-chemical calculations and experimental tests. These results showed that the size of the central ring significantly affected the excited state energetics and emission quantum yields as well as the two-photon initiation efficiency. In the TPIP tests the 4-methylcyclohexanone-based initiator displayed much broader ideal processing windows than its counterparts with a central five-membered ring and previously described highly active TPA PIs. Surprisingly, a writing speed as high as 80 mm/s was obtained for the microfabrication of complex 3D structures employing acrylate-based formulations. These highly active TPA PIs also exhibit excellent thermal stability and remain inert to one-photon excitation. Straightforward synthesis combined with high TPA initiation efficiency makes these novel initiators promising candidates for commercialization.
The two-photon polymerization (2PP) of photosensitive gelatin in the presence of living cells is ... more The two-photon polymerization (2PP) of photosensitive gelatin in the presence of living cells is reported. The 2PP technique is based on the localized cross-linking of photopolymers induced by femtosecond laser pulses. The availability of water-soluble photoinitiators (PI) suitable for 2PP is crucial for applying this method to cell-containing materials. Novel PIs developed by our group allow 2PP of formulations with up to 80% cell culture medium. The cytocompatibility of these PIs was evaluated by an MTT assay. The results of cell encapsulation by 2PP show the occurrence of cell damage within the laser-exposed regions. However, some cells located in the immediate vicinity and even within the 2PP-produced structures remain viable and can further proliferate. The control experiments demonstrate that the laser radiation itself does not damage the cells at the parameters used for 2PP. On the basis of these findings and the reports by other groups, we conclude that such localized cell damage is of a chemical origin and can be attributed to reactive species generated during 2PP. The viable cells trapped within the 2PP structures but not exposed to laser radiation continued to proliferate. The live/dead staining after 3 weeks revealed viable cells occupying most of the space available within the 3D hydrogel constructs. While some of the questions raised by this study remain open, the presented results indicate the general practicability of 2PP for 3D processing of cell-containing materials. The potential applications of this highly versatile approach span from precise engineering of 3D tissue models to the fabrication of cellular microarrays.
Journal of Polymer Science Part A: Polymer Chemistry, 2013
Engineering three-dimensional (3D) hydrogels with well-defined architectures has become increasin... more Engineering three-dimensional (3D) hydrogels with well-defined architectures has become increasingly important for tissue engineering and basic research in biomaterials science. To fabricate 3D hydrogels with (sub)cellular-scale features, two-photon polymerization (2PP) shows great promise although the technique is limited by the selection of appropriate hydrogel precursors. In this study, we report the synthesis of gelatin hydrolysate vinyl esters (GH-VE) and its copolymerization with reduced derivatives of bovine serum albumin (acting as macrothiols). Photorheology of the thiol-ene copolymerization shows a much more rapid onset of polymerization and a higher end modulus in reference to neat GH-VE. This allowed 2PP to provide well-defined and stable hydrogel microstructures. Efficiency of the radical-mediated thiol-vinyl ester photopolymerization allows high 2PP writing speed (as high as 50 mm s 21 ) with low laser power (as low as 20 mW). MTT assays indicate negligible cytotoxicities of the GH-VE macromers and of the thiol-ene hydrogel pellets. Osteosarcoma cells seeded onto GH-VE/BSA hydrogels with different macromer relative ratios showed a preference for hydrogels with higher percentage of GH-VE. This can be attributed both to a favorable modulus and preferable protein environment since gelatin favors cell adhesion and albumin incurs nonspecific binding.
Hydrogels are polymeric materials with water contents similar to that of soft tissues. Due to the... more Hydrogels are polymeric materials with water contents similar to that of soft tissues. Due to their biomimetic properties, they have been extensively used in various biomedical applications including cell encapsulation for tissue engineering. The utilization of photopolymers provides a possibility for the temporal and spatial controlling of hydrogel cross-links. We produced three-dimensional (3-D) hydrogel scaffolds by means of the two-photon polymerization (2PP) technique. Using a highly efficient water-soluble initiator, photopolymers with up to 80 wt.% water were processed with high precision and reproducibility at a writing speed of 10 mm∕s. The biocompatibility of the applied materials was verified using Caenorhabditis elegans as living test organisms. Furthermore, these living organisms were successfully embedded within a 200 × 200 × 35 μm 3 hydrogel scaffold. As most biologic tissues exhibit a window of transparency at the wavelength of the applied femtosecond laser, it is suggested that 2PP is promising for an in situ approach. Our results demonstrate the feasibility of and potential for bio-fabricating 3-D tissue constructs in the micrometre-range via near-infrared lasers in direct contact with a living organism.
Two-Photon-Polymerization (2PP) is a fast developing method for the micro-and nanostructuring of ... more Two-Photon-Polymerization (2PP) is a fast developing method for the micro-and nanostructuring of three-dimensional parts. The manufacturing of biocompatible structures using this technique is a promising field as it fulfills the demands for parts with high feature resolution. This paper reports the fabrication of scaffolds using photopolymers with embedded living organisms (Caenorhabditis elegans). The structuring was performed with a pulsed near-infrared laser with a wavelength of 810nm and adjustable power up to 160mW. Using a 20x magnification microscope objective with a numerical aperture of 0.4, a high resolution scaffold with a base area of 300x300µm and a height of 80µm could be fabricated. Taking advantage of high laser intensities (writing speed: 300µm/s) the structuring process took only 12 minutes.
Utilization of multiphoton absorption has led to important advances in microscopy and photofabric... more Utilization of multiphoton absorption has led to important advances in microscopy and photofabrication. Herein, our recent results on precise immobilization of molecules within 3D polymeric matrices by means of multiphoton grafting are presented. Assessment of nonlinear absorption properties of difunctional aromatic azide, selected for this purpose was performed by the Z-scan technique. It indicates that a three-photon absorption process is responsible for photolysis of this compound. Successful photografting for production of 3D patterns with lateral resolution down to 4 µm was achieved. Our results demonstrate the potential of the developed three-photon grafting method for precise 3D site-specific functionalization of different materials.
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Papers by Jan Torgersen