Water absorbing and quick degradable PLLA/PEG multiblock copolymers reduce the encapsulation and inflammatory cytokine production

Biomaterials that contact with soft tissues such as postoperative adhesion prevention membrane or tissue-regenerative scaffolds should possess specific features such as hydrophilicity, mild to no immunogenicity, and quick degradability. The inflammation reaction to multiblock copolymers of poly(l-lactic acid) (PLLA) and poly(ethylene glycol), named as Multi, which we developed as a good adhesion prevention materials with a very high degradation rate were investigated and compared with usual PLLA, non-degradable polyethylene (PE), and acellular collagenous tissue (COL). Tissue encapsulation, inflammatory cell recruitment, and expression of four cytokines (IL-1β, IL-6, IL-10, and TGFβ) affecting the promotion or inhibition of inflammation and wound healing were evaluated. The thick encapsulation for PE might have related to high expression of TGFβ, and it was largely reduced in the cases of PLLA and Multi. The cytokine expression pattern in PE was dominantly alternatively activated macrophage (M2) type, while expression patterns to Multi were classically activated macrophage (M1)-type dominant, as with the COL specimen. Thus, multi is a tissue compatible material in spite of the large degradability. By introducing low molecular weight PEG into PLLA as multiblock-type sequence, we successfully prepared biocompatible PLLA derivatives with high molecular weight, large degradation rate, and mild tissue responses.