Mineralization of gellan gum hydrogels with calcium and magnesium carbonates by alternate soaking in solutions of calcium/magnesium and carbonate ion solutions.

Mineralization of hydrogels is desirable prior to applications in bone regeneration. CaCO3 is a widely used bone regeneration material, and Mg, when used as a component of calcium phosphate biomaterials, has promoted bone-forming cell adhesion and proliferation and bone regeneration. In this study, gellan gum hydrogels were mineralized with carbonates containing different amounts of calcium (Ca) and magnesium (Mg) by alternate soaking in, firstly, a calcium and/or magnesium ion solution and, secondly, a carbonate ion solution. This alternate soaking cycle was repeated five times. Five different calcium and/or magnesium ion solutions, containing different molar ratios of Ca to Mg ranging from Mg free to Ca free were compared. Carbonate mineral formed in all sample groups subjected to the alternate soaking cycle. Ca : Mg elemental ratio in the mineral formed was higher than in the respective mineralizing solution. Mineral formed in the absence of Mg was predominantly CaCO3 in the form of a mixture of calcite and vaterite. Increasing the Mg content in the mineral formed led to the formation of magnesian calcite and decreased the total amount of the mineral formed and its crystallinity. Hydrogel mineralization and increasing Mg content in mineral formed did not obviously improve proliferation of MC3T3-E1 osteoblast-like cells or differentiation after 7 days.

Performance of ß-tricalcium phosphate granules and putty, bone grafting materials after bilateral sinus floor augmentation in humans.

Sinus floor augmentation (SFA) using bone grafting materials, and in particular calcium phosphates (CaP), is a well-established pre-implantology procedure. The use of CaP simplifies SFA procedures. ß-tricalcium phosphate (ß-TCP) is amply used for SFA. This study evaluated the clinical and osteogenic performance of ß-TCP granules (TCP-G) and a ß-TCP putty (TCP-P) bone graft material. TCP-P consisted of TCP-G in a hyaluronic acid (HyA) carrier. Bone formation, volume stability and osteogenic marker expression after bilateral SFA in patients was assessed. Eight patients were selected for a split-mouth design. Biopsies obtained six months after SFA, were processed for immunohistochemical analysis of collagen type I (Col I), alkaline phosphatase (ALP), osteocalcin (OC) and bone sialoprotein (BSP). Histomorphometric analysis determined bone, grafting material and marrow space percentages. Cone-beam computed tomography was used to calculate the graft volume and its stability. Both materials allowed excellent bone regeneration and volume stability. TCP-P displayed better surgical handling properties, greater bone formation, higher expression of Col I, ALP, OC and BSP; as well as significantly lower grafting volume reduction values. HyA had no adverse effect on TCP-P performance. Due to its clinical and osteogenic performance, TCP-P can be regarded as excellent bone grafting material for SFA.

Processing and in vivo evaluation of multiphasic calcium phosphate cements with dual tricalcium phosphate phases.

Calcium phosphate cements (CPCs) use the simultaneous presence of several calcium phosphates phases. This is done to generate specific bulk and in vivo properties. This work has processed and evaluated novel multiphasic CPCs containing dual tricalcium phosphate (TCPs) phases. Dual TCPs containing α- and ß-TCP phases were obtained by thermal treatment. Standard CPC (S-CPC) was composed of α-TCP, anhydrous dicalcium phosphate and precipitated hydroxyapatite, while modified CPC (DT-CPC) included both α- and ß-TCP. Physicochemical characterization of these CPCs was based on scanning electron microscopy, X-ray diffraction, specific surface area (SSA) and particle size (PS) analysis and mechanical properties. This characterization allowed the selection of one DT-CPC for setting time, cohesion and biological assessment compared with S-CPC. Biological assessment was carried out using a tibial intramedullary cavity model and subcutaneous pouches in guinea pigs. Differences in the surface morphology and crystalline phases of the treated TCPs were detected, although PS analysis of the milled CPC powders produced similar results. SSA analysis was significantly higher for DT-CPC with α-TCP treated at 1100°C for 5h. Poorer mechanical properties were found for DT-CPC with α-TCP treated at 1000°C. Setting time and cohesion, as well as the in vivo performance, were similar in the selected DT-CPC and the S-CPC. Both CPCs created the desired host reactions in vivo.

Bone formation analysis: effect of quantification procedures on the study outcome.

Quantification of the amount of newly formed bone is an essential part of bone regeneration studies. Histomorphometry, based on histological sections of plastic-embedded specimens, is the most frequently applied technique in this assessment. Before performing image analysis, a specific region of interest (ROI) has to be determined. Based on the histological procedure, different areas within the ROI can be discriminated and assigned to relevant tissue structures. However, in literature not much attention is paid to the effect of the histological procedures on the final outcome of the histomorphometrical measurements on bone regeneration. In this study, the histomorphometrical bone formation of the intramedullary cavity of the guinea pig tibia, filled with calcium phosphate cement, was quantified in plastic-embedded and paraffin-embedded specimens and in specimens analyzed with scanning electron microscopy in the backscattering mode (SEM-BS). The data showed that the histological procedure significantly affected the measured bone amount. Therefore, it is recommended that scaffold characteristics are carefully considered in selecting a proper technique for the analysis of bone formation in bone tissue engineering studies. The results of this study identified high-resolution SEM-BS and elastic van Gieson staining of decalcified histological sections as recommendable techniques for evaluating bone formation.

Influence of the pore generator on the evolution of the mechanical properties and the porosity and interconnectivity of a calcium phosphate cement.

Porosity and interconnectivity are important properties of calcium phosphate cements (CPCs) and bone-replacement materials. Porosity of CPCs can be achieved by adding polymeric biodegradable pore-generating particles (porogens), which can add porosity to the CPC and can also be used as a drug-delivery system. Porosity affects the mechanical properties of CPCs, and hence is of relevance for clinical application of these cements. The current study focused on the effect of combinations of polymeric mesoporous porogens on the properties of a CPC, such as specific surface area, porosity and interconnectivity and the development of mechanical properties. CPC powder was mixed with different amounts of PLGA porogens of various molecular weights and porogen sizes. The major factors affecting the properties of the CPC were related to the amount of porogen loaded and the porogen size; the molecular weight did not show a significant effect per se. A minimal porogen size of 40 µm in 30 wt.% seems to produce a CPC with mechanical properties, porosity and interconnectivity suitable for clinical applications. The properties studied here, and induced by the porogen and CPC, can be used as a guide to evoke a specific host-response to maintain CPC integrity and to generate an explicit bone ingrowth.

An injectable calcium phosphate cement for the local delivery of paclitaxel to bone.

Bone metastases are usually treated by surgical removal, fixation and chemotherapeutic treatment. Bone cement is used to fill the resection voids. The aim of this study was to develop a local drug delivery system using a calcium phosphate cement (CPC) as carrier for chemotherapeutic agents. CPC consisted of alpha-tricalcium phosphate, calcium phosphate dibasic and precipitated hydroxyapatite powders and a 2% Na(2)HPO(4) hardening solution. Scanning electron microscopy (SEM) was used to observe CPC morphology. X-ray diffraction (XRD) was used to follow CPC transformation. The loading/release capacity of the CPC was studied by a bovine serum albumin-loading model. Release/retention was measured by high performance liquid chromatography and X-ray photoelectron spectrometry. For chemotherapeutic loading, paclitaxel (PX) was loaded onto the CPC discs by absorption. Viability of osteosarcoma U2OS and metastatic breast cancer MDA-MB-231 cells was measured by an AlamarBlue assay. Results of SEM and XRD showed changes in CPC due to its transformation. The loading model indicated a high retention behavior by the CPC composition. Cell viability tests indicated a PX minimal lethal dose of 90 µg/ml. PX released from CPC remained active to influence cell viability. In conclusion, this study demonstrated that CPC is a feasible delivery vector for chemotherapeutic agents.

Rapid prototyped porous titanium coated with calcium phosphate as a scaffold for bone tissue engineering.

High strength porous scaffolds and mesenchymal stem cells are required for bone tissue engineering applications. Porous titanium scaffolds (TiS) with a regular array of interconnected pores of 1000 microm in diameter and a porosity of 50% were produced using a rapid prototyping technique. A calcium phosphate (CaP) coating was applied to these titanium (Ti) scaffolds with an electrodeposition method. Raman spectroscopy and energy dispersive X-ray analysis showed that the coating consisted of carbonated hydroxyapatite. Cross-sectioned observations by scanning electron microscopy indicated that the coating evenly covered the entire structure with a thickness of approximately 25 microm. The bonding strength of the coating to the substrate was evaluated to be around 25 MPa. Rat bone marrow cells (RBMC) were seeded and cultured on the Ti scaffolds with or without coating. The Alamar Blue assay provided a low initial cell attachment (40%) and cell numbers were similar on both the uncoated and coated Ti scaffolds after 3 days. The Ti scaffolds were subsequently implanted subcutaneously for 4 weeks in syngenic rats. Histology revealed the presence of a mineralized collagen tissue in contact with the implants, but no bone formation. This study demonstrated that porous Ti scaffolds with high strength and defined geometry may be evenly coated with CaP layers and cultured mesenchymal stem cells for bone tissue engineering.