Nano-hydroxyapatite–thermally denatured small intestine sub-mucosa composites for entheses applications

The objective of the present in vitro study was to estimate the adhesion strength of nanometer crystalline hydroxyapatite (HA)–small intestine sub-mucosa (SIS) composites on model implant surfaces. Techniques of thermal denaturation (60°C, 20 min) of SIS were used to enhance the adhesion strength of entheses materials to underlying implants. Specifically, results indicated that the adhesion strength of thermally denatured SIS was 2–3 times higher than that for normal unheated SIS. In addition, aqua-sonicated, hydrothermally treated nano-HA dispersions enhanced the adhesion strength of SIS on implant surfaces. Importantly, results of the present study demonstrated that human skeletal muscle cell (hSkMC) numbers were not affected by thermally denaturing SIS in nano-HA composite coatings; however, they increased on aqua-sonicated nano-HA/SIS composites compared with SIS alone. Interestingly, thermally denatured SIS that contained aqua-sonicated, hydrothermally treated nano-HA decreased human osteoblasts (hOBs) numbers compared with respective unheated composites; all other composites when thermally denatured did not influence hOB numbers. Results also showed that the number of hOBs increased on nano-HA/SIS composites compared with SIS composites alone. Human mesenchymal stem cell (hMSC) numbers were not affected by the presence of nano-HA in SIS composites. For these reasons, the collective results of this in vitro study demonstrated a technique to increase the coating strength of entheses coatings on implant surfaces (using thermally denatured SIS and aqua-sonicated, hydrothermally prepared nano-HA) while, at the same time, supporting cell functions important for entheses regeneration.