Application of Multi-Arm Poly (Ethylene Glycol) -Polylactide Copolymers as Biodegradable Soft Biomaterials

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To explore the potential of a star-shaped 8-arms poly(ethylene glycol)35K-b-poly(L-lactide)37K (8-arms PEG35K-b-PLLA37K: M_n of PEG=35,000, M_n of PLLA=37,000) film as a novel bioabsorbable adhesion-prevention membrane, water structure, surface contact angle, protein adsorption, and cell and platelet anti-adhesion properties of such a hydrated film were investigated. Based on these results, it was found that the 8-arms PEG35K-b-PLLA37K film exhibited a biologically inert surface, which was the result of a large number of PEG chains and a free water layer on the film surface. This led to a reduction in protein absorption and cell and platelet adhesion onto the film surface. This implies the star-shaped 8-arms PEG35K-b-PLLA37K film can be utilized as a novel bioabsorbable adhesion-prevention membrane.Partially cholesterol-substituted 8-arm poly(ethylene glycol)-block-poly(L-lactide) (8-arm PEG-b-PLLA-cholesterol) was prepared as a novel star-shaped, biodegradable copolymer derivative. The amphiphilic 8-arm PEG-b-PLLA-cholesterol aqueous solution (polymer concentration, above 3 wt%) exhibited instantaneous temperature-induced gelation at 34℃, but the virgin 8-arm PEG-b-PLLA did not, irrespective of concentration. Moreover, we successfully created an extracellular matrix (ECM)-like micrometer-scale network structure with favorable porosity for 3D proliferation of cells inside the hydrogel. This network structure was mainly attributed to specific self-assembly between cholesterol groups. The 10 and 20 wt% hydrogels were eroded gradually in PBS at 37℃ over the course of a month, and the gel became completely dissociated. Moreover, the L929 cells encapsulated into the hydrogel were viable and proliferated 3-dimensionally inside the hydrogels as a result of the ECM-like network structure. Thus, in vitro cell culture studies demonstrated that 8-arm PEG-b-PLLA-cholesterol is a promising candidate as a novel injectable cell scaffold.