Reduction of peritendinous adhesions by hydrogel containing biocompatible phospholipid polymer MPC for tendon repair

Background: Peritendinous adhesions are serious complications after surgical repair of tendons. As an anti-adhesion material, we focused on 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer, our original biocompatible polymer, and prepared an aqueous solution of MPC-containing polymer called poly(2-methacryloyloxyethyl phosphorylcholine-co-nbutyl methacrylate-co-p-vinylphenylboronic acid) (PMBV), which can be formed into hydrogel properties by mixture with another aqueous polymer, poly(vinyl alcohol) (PVA). The objective of the present study was to examine the possible application of the MPC hydrogel for the reduction of peritendinous adhesions. Methods: The effects of the hydrogel on peritendinous adhesions and tendon healing were examined by means of histological and mechanical analyses in a rat Achilles tendon model and a rabbit flexor digitorum profundus tendon model. Cell migration and viability were examined with use of fibroblastic NIH3T3 cells cultured in a double chamber dish. Results: Among the concentrations examined, 2.5% and 5.0% PMBV formed hydrogel properties immediately after mixing with 2.5% PVA and maintained a honeycomb microstructure with nanometer-scaled pores for three weeks after implantation. In animal models, the hydrogel formed from 5.0% PMBV remained at the sutured site during the critical period up to three weeks and disappeared by six weeks. The MPC hydrogel reduced the peritendinous adhesions histologically and mechanically by >25% at three weeks, without impairing tendon healing as determined with mechanical analyses. In the cell culture, cell migration was reduced by the MPC hydrogel, although cell viability was unaffected, indicating physical prevention, rather than cytotoxicity, to be the anti-adhesion mechanism. Conclusions: The MPC hydrogel that was formed by a local injection and mixture of two aqueous solutions, 5.0% PMBV and 2.5% PVA, reduced peritendinous adhesions without impairing tendon healing. This effect may be due to its excellent biocompatibility without a foreign-body reaction and the formation of a microstructure that physically prevents passage of cells but allows cytokines and growth factors to pass for healing. Clinical Relevance: This nanotechnology could potentially improve the quality of surgical repair of tendon, especially the zone-II area of the digital flexor tendon.