Two- and three-piece implants to boost data generation in preclinical in vivo research-A short technical report.

The purpose of this technical report is to present two novel experimental implant designs to boost data generation in preclinical in vivo research. Specifically, the report describes the rationale and the components of (1) a two-piece experimental implant suitable for a small animal platform (e.g., the rabbit femur/tibial epiphysis model), consisting of a threaded apical- and a coronal cylindrical piece, which is intended for collecting two types of biomechanical data, and (2) a three-piece experimental implant suitable for a large animal platform (e.g., the mini-pig mandible model), consisting of an apical "wound chamber", which allows the collection of histological/histomorphometrical data, and a middle threaded and coronal cylindrical piece, which also allow the collection of two types of biomechanical data. The increased volume of information generated from a single experiment in a small animal platform, using the proposed two-piece implant design, may assist in a more qualified decision-making process, on whether it is relevant to proceed to further assessment using a large animal platform. Furthermore, the increased volume of information generated in a single animal experiment either in a small or large animal platform, using the proposed two- and three-piece implants, respectively, likely decreases the number of animals otherwise needed for collecting the same information with standard one-piece implants and, thus, contributes to the reduction/refinement elements of the 3R principle.

Strontium enhances proliferation and osteogenic behavior of periodontal ligament cells in vitro.

BACKGROUND AND OBJECTIVE: Strontium (Sr) enhances osteogenic differentiation of certain multipotent cells. Periodontal ligament cells (PDLCs) are known to be multipotent, and Sr might be useful in periodontal bone tissue engineering. This study investigates the effect of high concentration of Sr on the proliferation and osteogenic behavior of PDLCs in vitro. MATERIAL AND METHODS: Primary human PDLCs were cultured in MEM + 10% FBS without (Ctrl) or with Sr in four diverse concentrations: Sr1, 11.3 × 10-3  mg/L, human serum physiological level; Sr2, 13 mg/L, typical human serum level after strontium ranelate treatment; Sr3, 130 mg/L, and Sr4, 360 mg/L. The spreading area (2, 4, 6, 24 hours), proliferation rate (1, 3, 7 days), osteogenic behavior (alkaline phosphatase - ALP activity, 7 and 14 days; expression of osteogenic genes, ALP, Runt-related transcription factor 2 - RUNX2, osteopontin - OPN, osteocalcin - OCN, and osteoprotegerin -OPG, 1, 3, 7, 14, 21 days), and formation of mineralized nodules (14 and 21 days) of the PDLCs were assessed. Data were compared group- and period-wise using ANOVA tests. RESULTS: Periodontal ligament cells cultured with Sr4 showed increased spreading area (after 4 hours), proliferation rate (from 3 days), and OCN and OPN (from 7 days) gene expression as compared to Ctrl, Sr1, Sr2, and Sr3. Sr4 also led to lower ALP activity (from 7 days), ALP (from 3 days), and RUNX2 (at 7 and 14 days) gene expression, together with more evident formation of mineralized nodules, compared to Ctrl, Sr1, Sr2, and Sr3. CONCLUSION: Periodontal ligament cells responded to Sr4 with increased cellular proliferation and osteogenic behavior in vitro.

A comparative in vivo study of strontium-functionalized and SLActive™ implant surfaces in early bone healing.

PURPOSE: Studies have shown that strontium-doped medical applications benefit bone metabolism leading to improved bone healing and osseointegration. Based on this knowledge, the aim of the study was to evaluate the performance of an implant surface, functionalized by a physical vapor deposition (PVD) coating (Ti-Sr-O), designed to yield predictable release of strontium. The Ti-Sr-O functionalized surface is compared to a routinely used, commercially available surface (SLActive™) with respect to bone-to-implant contact (BIC%) and new bone formation (BF%) in two defined regions of interest (ROI-I and ROI-II, respectively). MATERIALS AND METHODS: Ti-Sr-O functionalized, SLActive, and Grade 4 titanium implants were inserted in the femoral condyle of adult male New Zealand White rabbits. The PVD magnetron-sputtered Ti-Sr-O surface coating was characterized using scanning electron microscopy (SEM) for morphology and coating thickness. Strontium release and mechanical stability of the coating, under simulated insertion conditions, were evaluated. Furthermore, histomorphometrical BIC and BF were carried out 2 weeks after insertion. RESULTS: Histomorphometry revealed increased bone formation of Ti-Sr-O with significant differences compared to SLActive and Grade 4 titanium in both regions of interest, ROI-I and ROI-II, at 0-250 µm and 250-500 µm distance from the implant surfaces. Analogous results of bone-to-implant contact were observed for the two modified surfaces. CONCLUSION: The results show that a nanopatterned Ti-Sr-O functionalized titanium surface, with sustained release of strontium, increases peri-implant bone volume and could potentially contribute to enhancement of bone anchorage of osseointegrated implants.

Comparing the effect of strontium-functionalized and fluoride-modified surfaces on early osseointegration.

BACKGROUND: Studies have shown that medical devices comprising strontium contribute to bone healing and osseointegration. The aim of this study was to evaluate the in vivo performance of surface-functionalized implants (Ti-Sr-O) showing predictable release characteristics of strontium and compare it to performance a commercially available fluoride-modified surface. METHODS: Ti-Sr-O functionalized, fluoride-modified,  Grade 4 titanium implants were inserted in the femoral condyle of adult male New Zealand white rabbits. Atomic absorption spectrometry (AAS) was utilized to monitor strontium blood serum levels. Two weeks after insertion, histomorphometric evaluation was performed with respect to bone-to-implant contact (BIC%) and bone formation (BF%) using defined regions of interest. RESULTS: Mean values for BIC% showed a comparable degree of osseointegration for Ti-Sr-O and the fluoride-modified surface, while BF% revealed a significant difference in increased BF with Ti-Sr-O. AAS measurements did not indicate any influence of the Ti-Sr-O modified implants on the strontium blood serum concentrations. CONCLUSIONS: Within the limitations of this study, it was shown that the Ti-Sr-O coating, with sustained release characteristics of strontium, enhanced bone apposition and, thus, could find practical applications, e.g., within the field of medical implantology.

Effect of strontium surface-functionalized implants on early and late osseointegration: A histological, spectrometric and tomographic evaluation.

Numerous in vivo, in vitro and clinical studies report on beneficial effects of strontium with respect to increased bone growth. Based on this knowledge the aim of this study was to evaluate early and late osseointegration stages of functionalized titanium implants showing sustained release of strontium (Sr) and further investigate its potential systemic effect. Strontium functionalized (Ti-Sr-O) and Grade 4 (Control) titanium implants were inserted in the femoral condyle of New Zealand White rabbits. The Ti-Sr-O coating was characterized using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectrometry (EDX) for structure, coating thickness and chemical composition. Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) was used to evaluate released strontium in vitro while Atomic Absorption Spectrometry (AAS) was utilized to monitor serum levels of strontium and calcium. Additionally, histological and tomographic analysis of bone-to-implant contact (BIC%) and bone formation (BF%) was performed, following implantation periods of two or twelve weeks, respectively. Median values for BIC% for Ti-Sr-O revealed significant differences within the two- and twelve-week observation periods, while exceeding BF% was discovered especially after twelve weeks when performing the histological evaluation. The results from the micro-computed tomography (µ-CT) showed no significant differences, when comparing the experimental groups. AAS measurements did not indicate a systemic effect by the local strontium release. Within the limitations of the study, it was shown that a Ti-Sr-O coating with sustained release characteristics of strontium, accelerates bone apposition and represents a potential potent surface modification for endosseous medical implant devices. STATEMENT OF SIGNIFICANCE: This study presents first data with respect to early and late in vivo response on a strontium functionalized titanium surface comprising a nanotopography manufactured by a magnetron sputtering process. We investigated different osseointegration stages of screw-shaped implants with dental implant geometries in a rabbit femur model observing beneficial effects of the functionalized surface on bone-to-implant contact and bone formation caused by tailored release of the bone anabolic strontium. Histomorphometrical data revealed that a functionalized titanium surface with controlled liberation of strontium accelerates osseointegration while spectrometry measurements did not indicate a potential systemic effect of this osteoinductive agent and could thus have impact on modifications of medical implant devices.

Accelerated bone ingrowth by local delivery of strontium from surface functionalized titanium implants.

Studies have indicated systemic treatment with strontium (Sr) as a potential route to increase bone quality and formation around osseointegrating implants. However, adverse effects are linked to such treatment. In this study we present a surface modification method designed for sustained local release of Sr from implants. The four groups used were prepared by a magnetron co-sputtering process and selected on the basis of Sr release data. The composition, morphology and mechanical stability of the coatings were analyzed and the Sr release profiles were investigated in vitro by washout experiments. Mesenchymal stem cells were cultured on the different coatings to evaluate potential cytotoxic effects and the effect on cellular proliferation. No indication of toxicity was found. A rodent study demonstrated a significant increase in direct bone-to-implant contact and peri-implant bone volume, for several of the groups, four weeks after implantation when compared to a Grade 4 titanium reference group. Median values of bone-to-implant contact and new bone formation was found to be 19% and 53%, respectively, for the best group compared to 0% for both parameters with respect to the Grade 4 titanium reference. The results indicate that this method may have applications within the orthopedic and dental industry.