Key Engineering Materials Vols. 396-398

Abstract: We have developed a novel macroporous calcium phosphate cement MCPC® that sets to poorly crystalline apatite after mixing the powder component with an aqueous solution and has interconnective macroporosity We performed cranioplasty on rat model by injecting the new macroporous calcium phosphate cement MCPC®. The mechanical property of the cement is about 12MPa after 24 hours (compression test). The cement matrix is totally transformed into poorly crystalline apatite in 48 hours. This study demonstrates that MCPC® cement was suitable and efficient for parietal bone reconstruction. Its injectability and moldability allows to be used in bone reconstruction surgery and its mechanical properties are compatible to support calvarial reconstruction. In addition, a bone ingrowth onto the BCP granules occurred on time.

Abstract: The aim of this study was verify the biological efficacy of the use of a xenograft for bone loss therapy. Blood clot, particulate autogenous bone or anorganic bovine xenograft filled critical size defects (CSD) in rat calvaria (8mm diameter). After 0, 7, 30 and 90 days the animals were killed and macroscopic, radiographic and histopathological analysis were conducted. Although no treatment promoted the total closure of bone defect, autogenous bone group had better bone repair after 90 days, followed by xenograft group that exhibited direct bone neoformation onto, and around, the particles confirming its osteoconductivity. In conclusion, the xenograft tested in vivo showed biocompatibility, biodegradability and osteoconductive properties in rat calvaria CSD.

Abstract: Spherical beta-tricalcium phosphate (b-TCP) granules synthesized using a unique dropping slurry method expressed good osteoconductivity with prominent bone apposition and bioresorbability when implanted into the rat femur (Gonda et al., Key Eng. Mater. 361-363:1013-1016, 2008). The spherical b-TCP granules were implanted into the bone defect created in the distal end of the right femur of each 8-week-old female Wistar rat. To analyze performance of the spherical b-TCP granules as bone substitute in the bone with reduction in osteogenic potential, the right sciatic neurectomy was performed after implantation and the right hind limb was kept unloaded for 2 weeks before euthanization. Four weeks after implantation, some spherical b-TCP granules with resorption in part were surrounded by newly formed bone. Eight and 12 weeks after implantation, most of the residual b-TCP granules were embedded in newly formed bone, and total volume of the implant and newly formed bone was more than the other portions of the bone or the bone of control animals. Osteoclast activity in the implanted area was also higher than the other portions of the bone or the bone of control animals. Replacement of the intraosseous residual b-TCP granules for bone progressed at 12 weeks after implantation compared to those at 8 weeks after implantation. These data suggested that the spherical b-TCP granules stimulated osteogenesis and osteoclast activity of the unloaded bone.

Abstract: The aim of this study was to evaluate the capacity of the association of calcium phosphate cement with collagen membrane for large segmental bone defect. Six adult beagle dog underwent defect creation in the ulna and was reconstructed with combination of macroporous calcium phosphate cement MCPC® and resorbable collagen membrane EZ Cure®. After 6 months of implantation, the samples were analyzed with Micro CT, light microscopy and SEM using BSE. Bridging of the defect with a lamellar and well organized bone was achieved in all animals. MCPC granules resorption was increased at the extremities of the implant. Collagen membrane at the expense of the implant was replaced by periosteum-like formation. The results demonstrate the ability of the composite to reconstruct large segmental and critical size defect in long bone.

Abstract: Bioactive ceramics such as bioactive glasses, calcium carbonate and sintered hydroxyapatite are widely used in biomaterials field because of their high biocompatibility. In this study, natural hydroxyapatite (N-HA) and synthetic Hydroxyapatite (S-HA) were heat treated at 800°C and studied using “in vitro” experiments. Several physicochemical methods like: SRD, FTIR, SEM and ICP-OES were employed to evaluate the effects of the thermal treatment and to compare their behaviour after soaking in the Simulated Body Fluid SBF at different times. The formation of TCP has favours the formation of new phase. Obtained results show that the dissolution occurred more in N-HA than in S-HA and consequently the precipitation of new phosphate phase is more important in N-HA. This is due to the presence of Mg, Sr and Zn in N-HA with concentration higher to that in S-HA.

Abstract: Polymeric calcium phosphate cements (PCPC) derived from biodegradable poly-g-glutamic acid (g-PGA) were prepared in an attempt to improve the mechanical strength of calcium phosphate cement (CPC). The characteristics of the PCPCs were compared to those of cement incorporated with citric acid. The diametral tensile and compressive strengths of the CPC incorporated with g-PGA were significantly higher than that of cement incorporated with citric acid at equivalent concentrations (p<0.05). The maximal diametral tensile and compressive strengths of the CPC incubated for 1 week in physiological saline solution were approximately 18.0 and 50.0 MPa, respectively. However, the initial setting time of the PCPC was much slower than that of CPC incorporated with citric acid. The formation of ionic complexes between calcium ions and g-PGA was observed using FT-IR spectroscopy. Hydroxyapatite (HA) formation was retarded by g-PGA incorporation according to scanning electronic microscopy (SEM) and powder X-ray diffraction (XRD) observations.

Abstract: Non metallic materials like polyurethane has been successfully used for bone reconstruction in general and specifically in craniofacial and in mandible surgeries as an implantable material. However, any polymer alone cannot be universally successful as a medical device or structural implant because the eventual lack of well defined porous geometry, inherent interconnected porosity, the non dispensable need for a combined mechanical behavior with biological interaction and manufacturing feasibility. In this work, a bioactive material composite with high mechanical strength was designed using a castor oil polyurethane (PU) structure with a functional gradient having a dense core and a porous bioactive surface. The models and replicas for the implants were processed with Rapid Prototyping (RP) techniques and their application (case studies) were fulfilled according to the SUS (Brazilian Health Service) with the support of Santa Tereza Hospital, Petropolis, RJ.

Abstract: In the coming decades, the need for reconstructive surgery of bones is predicted to increase with the ageing of the population as well as the increase of injuries needing traumatologic treatments. Therefore, there is still a constant search for tissue engineering and bone substitute materials. Xenografts, synthetic hydroxyapatitite, bioactive glasses and other bone substitutes have widely been studied. When bone defects are filled using bioceramics in granules, their utilization is limited to small size defects, because the injected granules do not give immediate support against the biomechanical loading of the bone. The aim of this study was to evaluate the preliminary biomineralization and the compression strength of experimental injectable bone cements modified with calcium ceramics. Our studies have focused on the development of injectable composites of bone cements, i.e. in situ curable resin systems containing impregnated Ca ceramics. The polymerized bone cement composites aspire to simulate as closely as possible the mechanical and structural properties properties of bone. The present compressive strength of our inorganic-organic bone cements are >65 up to ~180 MPa. These cements are slightly porous from their outermost surface and showed preliminarily osteoconductivity of some degree.

Abstract: The incorporation of magnesium in the synthetic apatite has been associated with biomineralization process and osteoporosis therapy in human and animals. Magnesium easily replaces calcium in the apatite lattice and influences or controls the hydroxyapatite crystallization processes. In this work, Mg-substituted calcium deficient apatite, with Mg/Ca ratio = 0.1, 0.15 and 0.2 were synthesized by precipitation method. Then, sintered at 1000 oC and compared with a commercial product labeled as tricalcium phosphate sintered at the 1000 oC. The sintered products showed tricalcium phosphate (β-TCP) structure. The Mg2+ substitution in the Ca(4) and Ca(5) sites of β-TCP and the lattice parameter changes were estimated using the Rietveld method. Using this method, the formulas Ca2.73(Mg0.27)(PO4)2, Ca2.71(Mg0.29)(PO4)2 and Ca2.70(Mg0.23Mg0.07)(PO4)2 were calculated for the samples with Mg/Ca ratio = 0.1, 0.15 and 0.2 respectively.

Abstract: Single-component, self-setting and injectable calcium phosphate cement (CPC) based on amorphization process of dicalcium phosphate dehydrate (DCPD) is proposed. After preparation of DCPD by wet chemistry, the material was dry milled in an Attritor high energy process (at 400 RPM) during 20 minutes. Experiments were also conducted using a regular ball milling process at 15 and 30h residence time. Amorphization of DCPD confirmed using FTIR, XRD and 31 P solid-states NMR (cross-polarization and decoupling). Upon hydration of amorphized DCPD powder with saline (0.55 ml/g), putty-like consistency produced. The paste hardened in 30 minutes at 37°C and reached a compressive strength of about 20 MPa. The final product was a low crystalline calcium deficient apatite, similar to the composition and structure of bone mineral.