Immobilized Candida antarctica Lipase B (N435) catalysis in-bulk leads to higher molecular weight poly(glycerol sebacate), PGS, than self-catalyzed condensation polymerization. Then, poly(glycerol-1,8-octanediol-sebacate), PGOS, copolymers with low-level substitution of O for G units (G/O ratios 1:1, 2:1, 3:1, 4:1, and 10:1), were prepared in bulk by immobilized Candida antarctica Lipase B (N435) catalysis. The central question explored was the extent that exchanging less than half of PGS glycerol units with 1,8-octanediol can be used as a strategy to fine-tune biomaterial properties. Synthesized copolymers having G/O ratios of 2:1, 3:1, 4:1, and 10:1 have similar molecular weights where Mw varied from 52,800-63,800, Mn varied from 5,100 to 6,450, and dispersity values were also similar (8.4-11.4). All the copolymers were branched, and dendritic glycerol units reached 11% for PGOS-0.91:0.09:1.0. Over the copolymer compositional range studied herein, Tm and ΔHf values varied from 5.3 to 21.1 °C and 8.0 to 23.1 J/g, respectively. Stress-strain curves of PGOS copolymers cured at 140 °C for 48 h exhibited either a unimodal, bimodal, or trimodal response to tensile loading. Varying G/O from 10:1-to-2:1 resulted in significant increases in the peak stress (0.26 to 4.01 Mpa), pre-yield modulus (0.65 Mpa to 62.59 Mpa), failure to strain (64% to 110%), and failure toughness (0.1 Mpa to 0.56 Mpa). This demonstrates that, altering the G/O ratio over a narrow compositional range provides biomaterials with widely different yet tunable mechanical properties. Further investigation of PGOS-0.75:0.25:1.0 films revealed that, by varying the cure conditions from 120 to 160 °C for periods of 24 to 72 h, provides access to biomaterials with a failure strain range from 15% to 224% and Young's modulus from 1.17 to 10.85 Mpa. Hence, using the dual variables of compositional variation and changes in cure conditions provides an exciting platform of PGS-analogues to optimize material-tissue interactions.

Lipase catalyzed poly(glycerol-sebacate) and poly(glycerol-1,8-octanediol-sebacate): combining compositional and crosslinking variables to engineer biomaterial properties

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