Carefully Controlled Photo-catalyzed Thiol-ene Networks of Poly(lactic acid)

PLA is researched for TE scaffolds, drug delivery, implants, and environmentally safe plastics. Bulk PLA has a tensile and flexural modulus of 3.5 and 6 GPa respectively and a Rockwell hardness of 88; thus despite bioabsorbable advantages, it is weak compared to metal implants. Additionally, a uniform degradation rate, which needs to be tuned to match tissue growth and regulate drug delivery, requires minimal molecular variability. Crosslinkable PLA would not only improve mechanical properties, but offer tunability via crosslink density. Further, catalysis by cell safe light and orthogonality of crosslinkable groups allow in-vivo crosslinking, minimizing implant procedures. Bis alpha, omega –ene functionalized PLA oligomers for use with thiolene chemistry were synthesized with polydispersities around 1.3 using organic catalysts. Ordered networks were photo-catalyzed with a multi-arm thiol. End functionalities allow crosslink density to be controlled by oligomer length, and the ordered network minimizes molecular variabiliy. Crosslinked samples prepared with the same oligomer consistenly show identical characterizations as analyzed by DSC, NMR, FTIR, and nano-indentation. Lastly, stress-strain curves exhibited a singular linear elastic regime.