We synthesized two series of well-defined comb-dendritic tri-block copolymers consisting of a linear poly(ethylene glycol) (PEG) center block and poly(L-lactide) (PLLA) or poly(ε-caprolactone) (PCL) dendrons with various PCL or PLLA arm molecular weights of 1150-28500 g/mol. The first step was the divergent synthesis of dendritic PEG with 32 hydroxyl groups using acetonide-protected anhydride derivative of 2,2-bis(hydroxymethyl)propionic acid. Then dendritic PEG was used to initiate the ring-opening polymerization of ε-caprolactone or L-lactide. Different PLLA or PCL arm molecular weights in the copolymers were obtained by controlling the feed ratio of the monomer to the hydroxyl group. The chemical structures and molecular weights of these copolymers were confirmed by using 1H NMR, FTIR, and GPC. Differential Scanning Calorimetrical measurements showed that the glass transition temperature (Tg), melting temperature (Tm), and the degree of crystallinity (χc) of the PLLA-containing copolymers (CoPLLA) increased with increasing the PLLA arm molecular weight. For the PCL-containing copolymers (CoPCL), the Tm increased with increasing the PCL arm molecular weight but χc first increased when the PCL arm molecular weight increased from 1150 to 17200 g/mol and then decreased when it was 28500 g/mol. Tensile modulus increased with the increase of the arm molecular weight for both series of copolymers. Water contact angle measurements showed that the copolymer hydrophilicity decreased when the PCL or PLLA arm molecular weight was higher. Polarized optical microscopic images showed that the copolymer spherulites were smaller at lower Tc and crystalline cracks and ring-banded structure were observed in CoPLLA. The growth rate of copolymer spherulites was accelerated with the decrease of the crystallization temperature (Tc). Atomic force microscopic characterization showed that the surface roughness was larger for the copolymers crystallized at a higher Tc. Grazing incidence X-ray diffraction study on the copolymer films indicated that the crystallite size, lattice constants, and crystallinity of the copolymers increased with the depth from the top surface. Mouse pre-osteoblastic MC3T3-E1 cells were cultured on the copolymer spherulites and their attachment and proliferation were regulated by the copolymer hydrophilicity. On both CoPCL and CoPLLA, cells reached the maximum values when the arm molecular weight was 4500 g/mol.

Biodegradable comb-dendritic tri-block copolymers consisting of poly(ethylene glycol) and poly(L-lactide) or poly(ε-caprolactone) and pre-osteoblastic cellular response to the spherulitic surfaces

249th National Meeting (2015)

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