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To design a carrier for chondrocytes that emulates the critical aspects of native cartilage tissue, hydrogels were formulated from a synthetic component based on poly(vinyl alcohol) (PVA) and from a natural component, negatively charged chondroitin sulfate (ChSA, a main component of proteoglycans). The synthesis of photoreactive and crosslinkable macromers based on PVA and ChSA is described in detail. A range of macroscopic hydrogel properties was obtained by varying the macromer molecular weight, concentration, and functionality prior to photoinitiated polymerization. Depending on the formulation, the PVA homopolymer gels had compressive moduli (K) ranging from 5 to 1680 kPa with equilibrium mass swelling ratios (q) of 2.4 to 15. Similar variations in pure ChSA gels produced networks with K's from 10 to 2600 kPa and q's from 5.9 to 27.5. Copolymer networks containing both ChSA and PVA had increased mechanics and increased swelling as compared to the homopolymer gels. An additional benefit to incorporating ChSA was the creation of enzymatically degradable gels. By use of chondroitinase ABC, the degradation kinetics of various homo- and copolymer networks were investigated. Finally, preliminary histological results indicate that these copolymer gels can support chondrogenesis of photoencapsulated cells.

FTIR was used to investigate the effects of thermal annealing on the hydrogen-bonding properties of a poly(urethane urea) copolymer. The copolymer was based on ethylene oxide-capped poly(propylene oxide) diol, 4,4‘-diphenylmethane diisocyanate (MDI), and 3,5-diethyltoluenediamine (DETDA). The result showed that thermal annealing caused the rise of the number of free urethane groups and the ordering of urea groups. The ordered urea hydrogen bonds were not destroyed below the melting point of the DETDA−MDI hard domain.

Microfluidic devices are commonly fabricated in silicon or glass using micromachining technology or elastomers using soft lithography methods; however, invariable bulk material properties, limited surface modification methods and difficulty in fabricating high aspect ratio devices prevent these materials from being utilized in numerous applications and/or lead to high fabrication costs. Contact Liquid Photolithographic Polymerization (CLiPP) was developed as an alternative microfabrication approach that uniquely exploits living radical photopolymerization chemistry to facilitate surface modification of device components, fabrication of high aspect ratio structures from many different materials with numerous covalently-adhered layers and facile construction of three-dimensional devices. This contribution describes CLiPP and demonstrates unique advantages of this new technology for microfabrication of polymeric microdevices. Specifically, the procedure for fabricating devices with CLiPP is presented, the living radical photopolymerization chemistry which enables this technology is described, and examples of devices made using CLiPP are shown.

A polymer patterning technology based on photografting polymerization mediated by photoiniferter chemistry is presented as a simple microlithographic technique that affords flexibility in fabricating and subsequently modifying polymer substrates with various chemistries. In principle, the technique relies upon the design and synthesis of a methacrylated photoiniferter, (methacryloyl ethylenedioxycarbonyl) benzyl N,N-diethyldithiocarbamate (HEMA-E-In). This photoiniferter allows the production of micropatterned polymer substrates with surface or internally grafted chemical modifications. The ability to modify surfaces with covalently bound polymer is demonstrated where the thickness of the layer depends on the exposure time. Furthermore, patterning chemical surface modifications was achieved by combining this process with photomasks to produce micron-sized features (approximately 20 µm). The method is quite diverse and enables spatially controlled internal modification of polymer networks as demonstrated herein. The developed techniques should be very useful for the facile development of 2-D and 3-D patterned and surface-modified polymers for microfluidic and biomaterial applications.

Grafting efficiency and graft conversion have been investigated for poly(ethylene glycol) methyl ether methacrylate (m-PEGMA) polymerized on the surface of diethyldithiocarbamate-containing polymer substrates. The substrate is prepared by copolymerization of a mixture of methacrylic monomers with a methacrylic diethyldithiocarbamate molecule, which serves as a photoiniferter that is chemically anchored on the surface of and throughout the substrate. Surface initiation was revealed by FTIR measurements of m-PEG200MA monomer conversion for two different monomer layer thicknesses; however, side reactions including chain transfer to PEG units affect surface-initiated polymerization of m-PEG200MA monomer significantly. Chain transfer causes a sharp decrease in the measured grafting efficiency at the beginning of this surface-mediated polymerization. Addition of N,N,N′,N′-tetraethylthiuram disulfide (TED), which suppresses chain transfer to PEG units, and the use of octyl methacrylate as the grafting monomer result in an increase in graft efficiency at early stages of the polymerization. Specific polymerization events that relate the chain transfer of PEG units to the graft properties of the photoiniferter-mediated polymerization are discussed.

Methacryloyl ethylenedioxycarbonyl) benzyl N,N-diethyldithiocarbamate (HEMA-E-In) was synthesized and used as a monomer iniferter to develop a novel, photopatternable grafting technology. This molecule functions as both a methacrylic monomer and a photoiniferter (photoinitiator-transfer agent-terminator). The structure of HEMA-E-In was characterized by 1 H NMR, Fourier transform infrared, and ultraviolet-visible spectroscopies. In the presence of the monomer iniferter, methyl methacrylate was polymerized by exposure to 365-nm ultraviolet radiation, confirming the initiation capability of HEMA-E-In. After the copolymerization of HEMA-E-In into a methacrylate-based polymer, attenuated total reflectance Fourier transform infrared spectra revealed that the photoiniferter functionality was present at the surface of this polymeric substrate. Photografting of poly(ethylene glycol) monomethacrylate monomer from the surface caused a significant change in the hydrophobicity of the surface as demonstrated by contact angle measurements. The novel monomer photoiniferter HEMA-E-In initiates the polymerization of bulk monomer and provides a reactive functionality that facilitates further initiation and polymer modification by the polymerization of different monomers.

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