Andreas Moser

Tough and degradable photopolymers derived from alkyne monomers for 3D printing of biomedical materials

This contribution deals with the synthesis and exploration of alkyne carbonate derivatives as biocompatible building blocks in the thiol–yne photopolymerisation reaction with the aim to facilitate the fabrication of tailor made medical devices by UV based additive manufacturing technologies. It turned out that the investigated alkyne carbonates offer curing rates similar to comparable acrylates, while providing much higher conversion and lower monomer cytotoxicity. Curing the synthesized building blocks in combination with the commercially available thiol pentaerythritol tetra(3-mercaptopropionate) (PETMP) leads to networks that degrade in aqueous alkaline and acidic media in a surface erosion manner. Additionally, a selective adjustment of the degradability is feasible by the choice and content of thiol monomers. Notably, monomers containing a tricyclo[5.2.1.02,6]decane-4,8-dimethanol backbone provide decent thermo-mechanical properties and appropriate impact strengths similar to polylactic acid (PLA). Most importantly, selected thiol–yne formulations were printed successfully with an accuracy of 40 × 40 μm, which seems to be sufficiently high to prints medical devices in appropriate resolution.

Exploring Network Formation of Tough and Biocompatible Thiol-yne Based Photopolymers.

This work deals with the in-depth investigation of thiol-yne based network formation and its effect on thermomechanical properties and impact strength. The results show that the bifunctional alkyne monomer di(but-1-yne-4-yl)carbonate (DBC) provides significantly lower cytotoxicity than the comparable acrylate, 1,4-butanediol diacrylate (BDA). Real-time near infrared photorheology measurements reveal that gel formation is shifted to higher conversions for DBC/thiol resins leading to lower shrinkage stress and higher overall monomer conversion than BDA. Glass transition temperature (Tg ), shrinkage stress, as well as network density determined by double quantum solid state NMR, increase proportionally with the thiol functionality. Most importantly, highly cross-linked DBC/dipentaerythritol hexa(3-mercaptopropionate) networks (Tg ≈ 61 °C) provide a 5.3 times higher impact strength than BDA, which is explained by the unique network homogeneity of thiol-yne photopolymers.

Photo-responsive thiol–ene networks for the design of switchable polymer patterns

This study highlights the photo-patternable degradation of thiol–ene networks by combining the photoisomerization of o-nitrobenzyl ester (o-NBE) groups with the advantages of a photo-induced “click” reaction. Photo-responsive alkene monomers with o-NBE links are synthesized and crosslinked with selected multi-functional thiols via radical-mediated thiol–ene chemistry. By pursuing an initiation with visible light (λ > 400 nm), fast and efficient photopolymerization of the monomers is obtained under mild conditions without inducing the photocleavage of the o-NBE links. The UV induced (λ < 400 nm) photo-degradation involving a cleavage of covalent links is controlled by the functionality of the thiol crosslinker and evidenced by sol–gel analysis. The wavelength dependent changes in solubility are then applied for the design of polymer patterns which are inscribed in thin polymer films by photolithographic processes and characterized by microscopy techniques. Negative tone patterns are achieved by the radical-mediated photopolymerization of the monomers upon visible light exposure. Subsequent UV irradiation allows switching to positive tone patterns by spatially controlled photodegradation of the thiol–ene networks and surface relief patterns with a resolution of 4 μm are accomplished.

Data on synthesis and thermo-mechanical properties of stimuli-responsive rubber materials bearing pendant anthracene groups

The photo-reversible [4πs+4πs] cycloaddition reaction of pendant anthracene moieties represents a convenient strategy to impart wavelength dependent properties into hydrogenated carboxylated nitrile butadiene rubber (HXNBR) networks. The present article provides the 1H NMR data on the reaction kinetics of the side chain functionalization of HXNBR. 2-(Anthracene-9-yl)oxirane with reactive epoxy groups is covalently attached to the polymer side chain of HXNBR via ring opening reaction between the epoxy and the carboxylic groups. Along with the identification, 1H NMR data on the quantification of the attached functional groups are shown in dependence on reaction time and concentration of 2-(anthracene-9-yl)oxirane. Changes in the modification yield are reflected in the mechanical properties and DMA data of photo-responsive elastomers are illustrated in dependence on the number of attached anthracene groups. DMA curves over repeated cycles of UV induced crosslinking (λ>300 nm) and UV induced cleavage (λ=254 nm) are further depicted, demonstrating the photo-reversibility of the thermo-mechanical properties. Interpretation and discussion of the data are provided in “Design and application of photo-reversible elastomer networks by using the [4πs+4πs] cycloaddition reaction of pendant anthracene groups” (Manhart et al., 2016) [1].