Structural phase formation and in vitro bioactivity evaluations of strontium phosphosilicate for orthopedic applications

A Comparative Study on Physicochemical Properties and In Vitro Biocompatibility of Sr-Substituted and Sr Ranelate-Loaded Hydroxyapatite Nanoparticles

Synthetic hydroxyapatite nanoparticles (nHAp) possess compositional and structural similarities to those of bone minerals and play a key role in bone regenerative medicine. Functionalization of calcium phosphate biomaterials with Sr, i.e., bone extracellular matrix trace element, has been proven to be an effective biomaterial-based strategy for promoting osteogenesis in vitro and in vivo. Functionalizing nHAp with Sr2+ ions or strontium ranelate (SrRAN) can provide favorable bone tissue regeneration by locally delivering bioactive molecules to the bone defect microenvironment. Moreover, administering an antiosteoporotic drug, SrRAN, directly into site-specific bone defects could significantly reduce the necessary drug dosage and the risk of possible side effects. Our study evaluated the impact of the Sr source (Sr2+ ions and SrRAN) used to functionalize nHAp by wet precipitation on its in vitro cellular activities. The systematic comparison of physicochemical properties, in vitro Sr2+ and Ca2+ ion release, and their effect on in vitro cellular activities of the developed Sr-functionalized nHAp was performed. The ion release tests in TRIS-HCl demonstrated a 21-day slow and continuous release of the Sr2+ and Ca2+ ions from both Sr-substituted nHAp and SrRAN-loaded HAp. Also, SrRAN and Sr2+ ion release kinetics were evaluated in DMEM to understand their correlation with in vitro cellular effects in the same time frame. Relatively low concentration (up to 2 wt %) of Sr in the nHAp led to an increase in the alkaline phosphatase activity in preosteoblasts and expression of collagen I and osteocalcin in osteoblasts, demonstrating their ability to boost bone formation.

Fabrication and In Vitro Drug Delivery Evaluation of Cephalexin Monohydrate-Loaded PLA:PVA/HAP:TiO2 Fibrous Scaffolds for Bone Regeneration

Owing to the excellent osteoconductive property of hydroxyapatite, we aimed to design a cephalexin monohydrate-loaded PLA:PVA/HAP:TiO₂ nanofibrous scaffold to improve the drug delivery efficiency toward bone regenerative applications. In this study, HAP:TiO₂ (anatase and rutile phases) samples were prepared by a coprecipitation method, which were later blended with PLA:PVA polymeric solution (with and without the drug) to fabricate a nanofibrous matrix via the electrospinning technique. All the prepared samples were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, contact angle, porosity, and tensile strength tests. Further, in vitro biodegradation and the drug-releasing ability were examined by varying the concentration of cephalexin monohydrate in the composite matrix. Deposition of the apatite layer on the scaffolds was examined after incubation in simulated body fluid solution to confirm the bioactivity of the prepared nanofibers. Biocompatibility by the MTT assay and osteogenic differentiation by ARS staining were evaluated by culturing MG63 cells on PLA:PVA/HAP:TiO₂ nanofibers, which could ensue better support for cell proliferation. Consequently, the sustained release profile and better biocompatibility of the scaffolds revealed a strong potential use in bone regenerative applications.

Electroplating of HAp-brushite coating on metallic bioimplants with advanced hemocompatibility and osteocompatibility properties

In cases of severe bone tissue injuries, the use of metallic bioimplants is quite widespread due to their high strength, high fracture toughness, hardness, and corrosion resistance. However, they lack adequate biocompatibility and show poor metal-tissue integration during the post-operative phase. To mitigate this drawback, it is beneficial to add a biocompatible polymer layer to ensure a quick growth of cell or tissue over the surface of metallic bioimplant material. Furthermore, this additional layer should possess good adherence with the underlying material and also accompany a rapid bonding between the tissue and the implant material, in order to reduce the recovery time for the patient. Therefore, in this work, we report a novel green electroplating route for growing porous hydroxyapatite-brushite coatings on a stainless steel surface. The malic acid used for the production of hydroxyapatite-brushite coatings has been obtained from an extract of locally available apple fruit (Malus domestica). We demonstrate the effect of electroplating parameters on the structural morphology of the electroplated composite layer via XRD, SEM with EDS, and FTIR characterization techniques and report an optimized set of electroplating parameters that will yield the best composite coating in terms of thickness, adherence to substrate and speed. The hemocompatibility and osteocompatibility studies on the electroplated composites coating show this technology's effectiveness and potential applicability in biomedical applications. Compared to other routes reported in the literature, this electroplating route is quicker and yields better composite coatings with faster bone tissue growth potential.

Development of sea urchin type silica stabilised zirconia nanospheres with enhanced antimicrobial and osteoactivity properties

Zirconia based ceramics are giving new hope in hard tissues replacement and implants application. Among the three forms of zirconia (ZrO2), tetragonal form ( t-ZrO2) possess high mechanical stability in comparison with the other two which makes it suitable for fabricating biomedical implants with enhanced osteo activity. Here, tetragonal phase nanospheres consisting of silica stabilised zirconia (1:1) were prepared via sol gel method. The nanospheres exhibit sea urchin type morphology as observed from FESEM analysis. XRD patterns confirm the formation of t -SiO2-ZrO2 binary phase after high temperature calcination at 650°C. The immersion studies in SBF help in the formation of a layer of apatite in a gradual manner over the pallets for the period of 7, 14, 21 and 28 days which was confirmed by XRD, FTIR analysis. Moreover, t- SiO2 – ZrO2 samples were subjected to cytotoxicity tests through MTT assay on MG-63 cell lines. Antibacterial properties were investigated quantitatively using colony forming unit method against both gram positive as well as gram-negative bacteria.

Synthesis and characterization of silver substituted strontium phosphate silicate apatite using solid-state reaction for osteoregenerative applications

Strontium phosphosilicate is one of the fastest-growing apatite in bone regeneration application due to the presence of strontium and silica components in the parent materials. However, bacterial infections cause setbacks to the bone regeneration process often leading to surgical revisions, and is a big issue that needs to be addressed. Silver on this front has proven to be a great substituent as seen in the case of calcium phosphate-based ceramics that addresses the bactericidal properties of a biomaterial. Apatite strontium phosphosilicate substituted with a stoichiometric amount of silver as a dopant was synthesized using a high-temperature solid-state reaction. The phase formation was characterized by XRD and FT-IR coupled with morphological features visualized using Electron Microscopy. Antibacterial properties were investigated quantitatively using Colony-forming unit method against both Gram-positive as well as Gram-negative bacteria. Cytotoxicity assay was performed against MG-63 Cell lines and it showed excellent biocompatibility at 25ug/ml with optimal doping of 2% silver. Further, apatite seeding and formation were characterized after immersion in simulated body fluid solution which showed apatite phase formation initiated after 4 days of treatment characterized by XRD and FT-IR studies. This apatite formation was also visualized and confirmed using SEM.