Evaluation of four biodegradable, injectable bone cements in an experimental drill hole model in sheep.

Four cement applications were tested in this investigation. Two dicalcium phosphate dihydrate (DCPD-brushite) hydraulic cements, an apatite hydraulic fiber loaded cement, and a calcium sulfate cement (Plaster of Paris) were implanted in epiphyseal and metaphyseal cylindrical bone defects in sheep. The in vivo study was performed to assess the biocompatibility and bone remodeling of four cement formulations. After time periods of 2, 4, and 6 months, the cement samples were clinically and histologically evaluated. Histomorphometrically, the amount of new bone formation, fibrous tissue, and bone marrow and the area of remaining cement were measured. In all specimens, no signs of inflammation were detectable either macroscopically or microscopically. Cements differed mainly in their resorption time. Calcium sulfate was already completely resorbed at 2 months and showed a variable amount of new bone formation and/or fibrous tissue in the original drill hole over all time periods. The two DCPD cements in contrast were degraded to a large amount at 6 months, whereas the apatite was almost unchanged over all time periods.

Fiber-reinforced calcium phosphate cement formulations for cranioplasty applications: a 52-week duration preclinical rabbit calvaria study.

The in vivo tissue response to a newly developed fiber-reinforced calcium phosphate cement (CPC) formulation was assessed using a well-established rabbit calvarial defect model. Bilateral subcritical sized (8-mm diameter) defects were surgically created in the parietal bones of each rabbit (a total of 48 rabbits), and randomized to be filled with either the new fiber-reinforced formulation, a conventional CPC (positive control), or left unfilled (negative control). The implant sites were subsequently retrieved after 12, 24, and 52 weeks postsurgery. Each specimen, including the parietal bone craniotomy and underlying brain, were recovered at necropsy and the tissue responses were assessed by histology. The resulting histological slides indicated that there was no evidence of severe inflammatory responses or osteolysis. The data showed new dural and pericranial bone formation along the implants, as well as excellent bone-to-implant interfaces in all of the CPC-filled defects. These results suggest that the biologic response to the new fiber-reinforced CPC formulations and conventional nonreinforced CPC are very similar, and both demonstrate excellent biocompatibility as well as an overall osteophylic response.

Bone healing response to an injectable calcium phosphate cement with enhanced radiopacity.

The aim of this study was to determine the impact of barium sulfate on remodeling and regeneration in standard tibial defects in rabbits treated with the Norian skeletal repair system (SRS). Two formulations of SRS (with and without barium sulfate) were injected into the medullary canal of the tibia of New Zealand white rabbits. Animals were sacrificed at 6 weeks, 6 months, 1 year, and 2 years. Over the 2-year duration of the study, standard SRS and SRS with barium sulfate appeared to be biocompatible and osteoconductive with no evidence of either inflammation or fibrous tissue around the implant materials or at the bone-material interfaces. This outcome underscores the osteophilic property of the SRS. A difference we observed between the standard SRS and the SRS with barium sulfate was the appearance of acellular material contiguous to the SRS with barium sulfate. Energy dispersive X-ray spectroscopy (EDX) analysis was conducted and confirmed that the acellular material was barium sulfate. Pathological examination of additional tissues including regional lymph nodes revealed neither dissemination of calcium phosphate nor barium sulfate. We concluded that the residual barium sulfate detected by EDX was localized to the intramedullary canal of the tibia.

Measurements of the solubilities and dissolution rates of several hydroxyapatites.

Calcium phosphate based materials, such as apatites, are increasingly being developed and used in implants for orthopedic and dental applications. Previous investigation of various calcium phosphate ceramics has demonstrated great variability in the solubility characteristics in solution between materials with similar stoichiometric composition. Therefore, in this study, the solubility and rate of dissolution of three apatite sources, BoneSource, Norian cranial repair system (CRS), and a sintered hydroxyapatite (Calcitite) are evaluated in a thermodynamically closed system. The measured solubility under physiological conditions (tris buffer solution, pH 7.4, 37 degrees C) of BoneSource, Norian CRS and Calcitite is 7.5, 7.4 and 1.4 ppm, respectively. Initial dissolution rates at 10 min of BoneSource, CRS, and Calcitite were 0.0465, 0.1589, and essentially 0 mg/min respectively. Solubility product constants at 37 degrees C were calculated to be 1.49 x 10(-35) for CRS, 1.19 x 10(-35) for BoneSource, and 2.92 x 10(-42) for Calcitite. The increased solubility of the BoneSource and Norian CRS materials over that of Calcitite is related to their poor crystallinity compared to sintered hydroxyapatite.