Surgical failure, mainly caused by loosening implants, causes great mental and physical trauma to patients. Improving the physicochemical properties of implants to achieve favourable osseointegration will continue to be the focus of future research. Strontium (Sr), a trace element, is often incorporated into hydroxyapatite (HA) to improve its osteogenic activity. Our previous studies have shown that miR-21 can promote the osteogenic differentiation of mesenchymal stem cells by the PI3K/β-catenin pathway. The aim of this study is to fabricate a SrHA and miR-21 composite coating and it is expected to have a favorable bone healing capability.

Ti discs (20 mm diameter and one mm thickness for the in vitro section) and rods (four mm diameter and seven mm length for the in vivo section) were prepared by machining pure Ti. The Ti cylinders were placed in a Teflon-lined stainless-steel autoclave for treating at 150°C for 24 h to form SrHA layer. The miR-21 was encapsulated in nanocapsules. The miR-21 nanocapsules were mixed with CMCS powder to form a gel-like sample and uniformly coated on the SrHA modifed Ti. Osteoblast-like MG63 cells were cultured on SrHA and miR-21 modified Ti, Cell proliferation activity and osteogenesis-related gene expression were evaluated. A bone defect model was established with mature New Zealand to evaluate the osseointegration. Cylindrical holes (four mm in diameter) were created at the distal femur and tibial plateau. Each rabbit was implanted with four of the aforementioned rods (distal femur and tibial plateau of the hind legs). After implantation for one, two and three months, the rabbits were observed by X-ray and scanned using u-CT. Histological and Immunohistochemical analysis were performed to examine the osteogenic markers. A biomechanical push-in test was used to assess the bone-implant bonding strength.

Both SrHA nanoparticles with good superhydrophilicity and miR-21 nanocapsules with uniform sizes were distributed evenly on the surface of the Ti. In vitro experiments revealed that the composite coating was beneficial to osteoblast proliferation, differentiation and mineralization. In vivo evaluations demonstrated that this coating could not only promote the expression of angiogenic factor CD31 but also enhance the expression of osteoblastic genes to facilitate angio-osteogenesis. In addition, the composite coating also showed a decreased RANKL expression compared with the miR-21 coating. As a result, the SrHA/miR-21 composite coating promoted new bone formation and mineralization and thus enhanced osseointegration and bone-implant bonding strength.

A homogeneous SrHA and miR-21 composite coating was fabricated by generating pure Ti through a hydrothermal process, followed by adhering miR-21 nanocapsules. This coating combined the favorable physicochemical properties of SrHA and miR-21 that synergistically promoted angiogenesis, osteogenesis, osseointegration, bone mineralization and thus bone-implant bonding strength. This study provided a new strategy for surface modification of biomedical implants.

Purpose: High levels of the chitinase 3-like protein HC-gp39 (human cartilage glycoprotein 39) have been found in the synovial fluid and sera of patients with arthritis. Although the function of this protein is unclear, in chondrocytes at least it appears to limit catabolic responses to cytokines such as Il-1b. Here we have investigated secretion of this protein by intervertebral disc cells and determined if its production is influenced by extracellular osmolarity.

Methods: Cells were isolated from bovine caudal discs by enzyme digestion and cultured in DMEM in alginate beads for 6 days. Medium osmolarity was increased in the physiological range by sodium/potassium addition. Supernatants were collected every 2 days and replaced with fresh media. At the end of experiment the supernatants were used for lactate determination and for detection of GP-39 by western blotting. Beads were assayed for glycosaminoglycans, cell viability and cell density.

Results: GP-39 was a major protein secreted by disc cells. It was evident on day 2 at low osmolarities. By day 4 concentrations in the medium had increased significantly and the protein was present mainly in fragmented form, particularly at high osmolarities. Osmolarity had no effect on cell density or viability. Rates of lactate production and GAG accumulation were greatest at high osmolarities.

Discussion: Changes in osmolarity, equivalent to those experienced by disc cells during the diurnal loss and regain of fluid content, had significant effects on cell metabolism and influenced production of GP-39. Osmotic changes might thus influence responses of disc cells to inflammatory signals.