Scanning and Transmission Electron Microscopy, and Electron Probe Analysis of the Interface Between Implants and Host Bone

Bioinert materials (e.g., alumina implants) and bioactive ceramics (e.g., calcium phosphate ceramics, glass -ceramics) are now extensively used in dentistry. However, the physico-chemical interactions at the interfaces between the implant and the host bone are poorly understood. The purpose of this study was to define the interactions at these interfaces using a combination of analytical techniques: light microscopy, scanning and transmission electron microscopy, electron probe microanalysis, X-ray microradiography, X-ray diffraction, and infrared specstroscopy. Bioinert (pure titanium) and bioactive materials (hydroxyapatite, beta-tricalcium phosphate and biphasic calcium phosphate) were implanted in dogs, and the implants, recovered after various periods of implantation, were analyzed. The results demonstrated the following: the bioactive materials interact with the biological fluid and the living tissues in a specific manner. This process includes biodissolution/biodegradation, apatite crystal precipitation, and bone formation on the implant surface at the expense of the material. The results are discussed according to the limitations of the analytical techniques used. The medical and chemical word COALESCENCE is suggested to describe the specific interactions of bioactive materials and INTERACTION for the phenomenon of physical contact of the bioinert materials with the host bone

Osteoconductive properties of poly(96L/4D-lactide)/beta-tricalcium phosphate in long term animal model

The objective of this study was to determine the effect of calcium phosphate mineral content on the bone in-growth at the expense of composite of co-polylactide polymer charged with 2 different ratios of β-TCP granules (10 and 24 w-% of β-TCP). The evaluation was realized in a long term rabbit bone model. After 24, 48 and 76 weeks, the implants were examined by micro CT, scanning electron microscopy (SEM) using backscattered electron (BSE) and light microscopy (polarized and blue light microscopy). No foreign body reaction was detected during the 76 weeks follow-up in any of the test samples. Polymer hydrolysis began at approximately 24 weeks, by 76 weeks, the pure polymer implant had begun to release P(96L/4D)LA particles and show signs of peripheral localized bone resorption. A decrease in the amount of CaP was noticed between 24 and 76 weeks in both 10 wt-% and 24 wt-% β-TCP/P(96L/4D)LA composites. The study showed that the highest bone in-growth was with 24 wt-% β-TCP/P(96L/4D)LA composite. Bone in-growth and mineralization were evident for the composites associated with specific peripheral bone architecture. Fluorescent labelling demonstrated high bone in-growth and remodeling at the interface, while for pure co-polymer no bone remodeling or bone activity was maintained after 48 weeks. The study demonstrated the positive effect of calcium phosphate content into P(96L/4D)LA. This kind of composite is a suitable resorbable osteoconductive matrix, which provides long term stability required for ligament fixation device

Solution-Mediated Transformation of Octacalcium Phosphate (OCP) to Apatite

OCP crystals were hydrolyzed in solutions containing Ca2+, Mg2+, HPO42-, CO32-, F-, citrate or P2O7 ions. Products of hydrolysis were analyzed using scanning (SEM) and transmission (TEM) electron microscopy, infrared spectroscopy and x-ray diffraction. Results demonstrated that the OCP to Apatite (AP) transformation is influenced by: (1) types of ions in solution: inhibited by Mg2+, citrate or P2O74-; facilitated by F-, CO32-, HPO42- or Ca2+ ions; (2) ionic concentrations; (3) solution pH; (4) OCP crystal size. SEM showed needle-like micro-crystals on the surfaces and ends of OCP macrocrystals. TEM showed side-to-side and end-to-end arrangements and presence of central defects in the apatite crystals. IR spectra showed the incorporation of CO3, or HPO4, the HPO4 incorporation being least from F-containing solutions. These results suggest that OCP to AP transformation occurred by the process of dissolution of OCP and subsequent precipitation of Ca-deficient apatites, incorporating CO32-, HPO42- or F- present in solution. These results indicate that the observed stabilty of OCP in pathological calcifications may be due to the presence of Mg2+, citrate and/or P2O74- and/or low levels of CO32-, F-, Ca2+, HPO42- ions in the biological fluids

Beta-tricalcium phosphate ceramic triggers fast and robust bone formation by human mesenchymal stem cells

Due to their osteoconductive and inductive properties, a variety of calcium phosphate (CaP) scaffolds are commonly used in orthopaedics as graft material to heal bone defects. In this study, we have used two CaP scaffolds with different hydroxyapatite (HA) and \u3b2-tricalcium phosphate (\u3b2-TCP) ratios (MBCP\uae; 60/40 and MBCP+\uae; 20/80) to investigate their intrinsic capacity to favour human bone marrow stem cells (hBMSCs) osteogenic differentiation capacity. We report that MBCP+\uae showed in in vitro culture model a higher rate of calcium ion release in comparison with MBCP\uae. In two defined coculture systems, the hBMSC seeded onto MBCP+\uae presented an increased amount of VEGF secretion, resulting in an enhanced endothelial cell proliferation and capillary formation compared with hBMSC seeded onto MBCP\uae. When both ceramics combined with hBMSC were implanted in a nude mouse model, we observed a faster osteogenic differentiation and enhancement mature bone deposition sustained by the presence of a vast host vasculature within the MBCP+\uae ceramics. Bone formation was observed in samples highly positive to the activation of calcium sensing receptor protein (CaSr) on the surface of seeded hBMSC that also shown higher BMP-2 protein expression. With these data we provide valuable insights in the possible mechanisms of ossification and angiogenesis by hBMSC that we believe to be primed by calcium ions released from CaP scaffolds. Evidences could lead to an optimization of ceramic scaffolds to prime bone repair

Reconstruction of irradiated bone segmental defects with a biomaterial associating MBCP+®, microstructured collagen membrane and total bone marrow grafting: An experimental study in rabbits

The bone tissue engineering models used today are still a long way from any oncologic application as immediate postimplantation irradiation would decrease their osteoinductive potential. The aim of this study was to reconstruct a segmental critical size defect in a weight-bearing bone irradiated after implantation. Six white New Zealand rabbits were immediately implanted with a biomaterial associating resorbable collagen membrane EZ® filled and micro-macroporous biphasic calcium phosphate granules (MBCP+®). After a daily schedule of radiation delivery, and within 4 weeks, a total autologous bone marrow (BM) graft was injected percutaneously into the center of the implant. All the animals were sacrificed at 16 weeks. Successful osseous colonization was found to have bridged the entire length of the defects. Identical distribution of bone ingrowth and residual ceramics at the different levels of the implant suggests that the BM graft plays an osteoinductive role in the center of the defect. Periosteum-like formation was observed at the periphery, with the collagen membrane most likely playing a role. This model succeeded in bridging a large segmental defect in weight-bearing bone with immediate postimplantation fractionated radiation delivery. This has significant implications for the bone tissue engineering approach to patients with cancer-related bone defects

Mandibular Segmental Defect Regenerated With Macroporous Biphasic Calcium Phosphate, Collagen Membrane, and Bone Marrow Graft in Dogs

OBJECTIVE: To reconstruct segmental mandibulectomy using calcium phosphate ceramics and collagen membrane with a delayed bone marrow grafting in experimental animals. DESIGN: Defects of segmental mandibulectomy were filled with calcium phosphate granules and wrapped with a collagen membrane in 4 dogs and left empty as a control in 2 dogs. Two months later, a bone marrow graft was injected into the center of the implants. Animals were humanely killed after a 16-week delay. SUBJECTS: Six adult beagles were included in this study. INTERVENTION: Segmental mandibulectomy. MAIN OUTCOME MEASURE: Bone ingrowth and material resorption in the reconstructed segment. RESULTS: Successful osseous colonization bridged the whole length of the defects. The good new bone formation at the center and the periosteum-like formation at the periphery suggest the osteoinductive role of the bone marrow graft and the healing scaffold role of the membrane. CONCLUSIONS: This model succeeded in regenerating a large segmental defect in the mandible. An investigation with a postimplantation radiation delivery schedule is required with the use of this model, which should be considered as a preclinical study for a bone tissue engineering approach in patients with cancer-related bone defects

Low temperature method for the production of calcium phosphate fillers

BACKGROUND: Calcium phosphate manufactured samples, prepared with hydroxyapatite, are used as either spacers or fillers in orthopedic surgery, but these implants have never been used under conditions of mechanical stress. Similar conditions also apply with cements. Many authors have postulated that cements are a useful substitute material when implanted in vivo. The aim of this research is to develop a low cristalline material similar to bone in porosity and cristallinity. METHODS: Commercial hydroxyapatite (HAp) and monetite (M) powders are mixed with water and compacted to produce cylindrical samples. The material is processed at a temperature of 37–120 degrees C in saturated steam to obtain samples that are osteoconductive. The samples are studied by X-ray powder diffraction (XRD), Vickers hardness test (HV), scanning electron microscopy (SEM), and porosity evaluation. RESULTS: The X-ray diffractions of powders from the samples show patterns typical of HAp and M powders. After thermal treatment, no new crystal phase is formed and no increase of the relative intensity of the peaks is obtained. Vicker hardness data do not show any relationship with treatment temperature. The total porosity decreases by 50–60% according to the specific thermal treatment. Scanning electron microscopy of the surfaces of the samples with either HAp 80%-M 20% (c) or Hap 50%-M 50% (f), show cohesion of the powder grains. CONCLUSIONS: The dissolution-reprecipitation process is more intesive in manufactured samples (c) and (f), according to Vickers hardness data. The process occurs in a steam saturated environment between 37 degrees and 120 degrees C. (c) (f) manufactured samples show pore dimension distributions useful to cellular repopulation in living tissues

Toward osteogenic differentiation of marrow stromal cells and in vitro production of mineralized extracellular matrix onto natural scaffolds

Uncorrected proofTissue engineering has emerged as a new interdisciplinary field for the repair of various tissues, restoring their functions by using scaffolds, cells, and/or bioactive factors. A temporary scaffold acts as an extracellular matrix analog to culture cells and guide the development of new tissue. In this chapter, we discuss the preparation of naturally derived scaffolds of polysaccharide origin, the osteogenic differentiation of mesenchymal stem cells cultured on biomimetic calcium phosphate coatings, and the delivery of biomolecules associated with extracellular matrix mineralization