The use of injectable, thermosensitive poly(organophosphazene)-RGD conjugates for the enhancement of mesenchymal stem cell osteogenic differentiation.

An injectable and thermosensitive poly(organophosphazene)-RGD conjugate to enhance functionality was synthesized by a covalent amide linkage between a cell adhesion peptide, GRGDS and carboxylic acid-terminated poly(organophosphazene). The aqueous solutions of synthesized poly(organophosphazene)-GRGDS conjugates existed in an injectable fluid state at room temperature and immediately formed a hydrogel at body temperature. The rabbit mesenchymal stem cells (rMSCs) on the polymer-GRGDS conjugate (conjugate 1-2, 0.05 mol fraction as GRGDS) hydrogel constructs using an injection method into a nude mouse were proved to express markers at mRNA level for all stages towards osteogenesis and mainly a sharp increase of osteocalcin (OCN, a typical late osteogenic differentiation marker) levels at 4th week post-induction indicated that the maturation process has started within this period. By histological and immunohistochemical evaluations, significantly high mineralization level by calcium contents was detected qualitatively and collagen type I (Col I), a major characteristic marker protein, was mainly and highly expressed by the rMSCs cultivated in the polymer-GRGDS conjugate hydrogel constructs formed into the nude mouse. The results suggest that the poly(organophosphazene)-GRGDS conjugate to enhance biofunctionality hold a promise for cell delivery material to induce osteogenic differentiation of MSC for enhancing ectopic bone formation.