Increased Skeletal Muscle Cell and Osteoblast Numbers on Hydrothermally-Treated Nano-Hydroxyapatite/Collagen Type I Composites for Entheses Applications

The long-term success of certain orthopedic biomaterials necessitates the re-establishment of an implant-tendon entheses (or a soft-hard tissue attachment region). In the body, a fibrocartilaginous entheses is composed of four zones: pure dense fibrous connective tissue, uncalcified fibrocartilage, calcified fibrocartilage, and bone. Mimicking a natural entheses for orthopedic applications requires the creation of a mechanical transition zone or calcified zone to dissipate stress from the hard-soft tissue into soft tissue and/or the implant. Importantly, mineralization of bone and the formation of tendons occur at the nano-scale (10⁻⁹ m). Despite this fact, current approaches in formulating the next generation of entheses materials have not centered on the use of nanoscale materials. In this context, the objective of this in vitro study was to create entheses materials by calcifying collagenous materials (specifically, collagen type I, collagen rich porcine small intestine sub-mucosa (SIS) and gelatin A from porcine skin) with highly dispersed nanometer-sized hydroxyapatite (HA) particles. Results showed the best uniform coverage of current titanium (Ti) metallic implants with aqua-sonicated hydrothermally-prepared HA nanoparticles. Moreover, compared to any other material studied here, results demonstrated higher in vitro human skeletal muscle cell and human osteoblast cell numbers (two cell types important for entheses applications) on collage type I alone and collagen type I mixed with hydrothermally-prepared HA nanoparticles either with or without aqua-sonication. Thus, to achieve the most stable and successful coating on an orthopedic metallic implant for entheses applications, collective results from this study suggest the use of collagen type I mixed with aqua-sonicated, hydrothermally-treated, HA nanoparticles.