Faculty Bibliography

Various calcium phosphate based coatings have been evaluated for better bony integration of metallic implants and are currently being investigated to improve the surface bioactivity of polymeric scaffolds. The aim of this study was to evaluate the role of calcium phosphate coating and simultaneous delivery of recombinant human bone morphogenetic protein-2 (rhBMP-2) on the in vivo bone regeneration capacity of biodegradable, porous poly(propylene fumarate) (PPF) scaffolds. PPF scaffolds were coated with three different calcium phosphate formulations: magnesium-substituted beta-tricalcium phosphate (beta-TCMP), carbonated hydroxyapatite (synthetic bone mineral, SBM) and biphasic calcium phosphate (BCP). In vivo bone regeneration was evaluated by implantation of scaffolds in a critical-sized rabbit calvarial defect loaded with different doses of rhBMP-2. Our data demonstrated that scaffolds with each of the calcium phosphate coatings were capable of sustaining rhBMP-2 release and retained an open porous structure. After 6weeks of implantation, micro-computed tomography revealed that the rhBMP-2 dose had a significant effect on bone formation within the scaffolds and that the SBM-coated scaffolds regenerated significantly greater bone than BCP-coated scaffolds. Mechanical testing of the defects also indicated restoration of strength in the SBM and beta-TCMP with rhBMP-2 delivery. Histology results demonstrated bone growth immediately adjacent to the scaffold surface, indicating good osteointegration and osteoconductivity for coated scaffolds. The results obtained in this study suggest that the coated scaffold platform demonstrated a synergistic effect between calcium phosphate coatings and rhBMP-2 delivery and may provide a promising platform for the functional restoration of large bone defects.

Objectives: This study aimed to determine the efficacy of experimental calcium phosphate-based solutions (sCaP) containing fluoride (F), with and without zinc (Zn) ions on reducing susceptibility to acid dissolution and Streptococcus mutans (S. mutans) colonization of dentin surfaces. Methods: Dentin sections were treated with double distilled water (control) and with sCaP solutions differing in pH and in F(-) and/or Zn(2+) ion concentrations. Solutions A (pH 7); B, C, and D (pH 5.5); solution C, twice Zn(2+) and F(-) ion concentration compared to B; solution D is similar to C but without Zn(2+). The dentin surfaces were characterized using scanning electron microscopy (SEM), x-ray diffraction, and Fourier Transform Infrared spectroscopy. Dissolution was determined in acidic buffer. Bacterial (S. mutans) attachment and growth were evaluated using SEM and Bioquant. Statistical analyses applied analysis of variance (ANOVA) and Duncan's multiple Range test. Results: Compared to control, dentin surfaces treated with sCaP solutions showed: (a) occluded dentin tubules; (b)reduced susceptibility to acid dissolution; and (c) Zn(2+) ions were more effective than F(-) ions in inhibiting bacterial colonization. Significance: Acidic sCaP containing both F and Zn ions have mineralizing, acid resistance, and antibacterial effects and may be potentially useful as a strategy against dentin caries formation and progression.

The objective of this research was to develop a calcium phosphate-based synthetic bone mineral (SBM) that will have a potential for osteoporosis therapy and prevention. The goal of this study was to test the efficacy of SBM in preventing loss of strength in long bones of osteoporotic sheep. The animals were divided into four groups: sham-operated; ovariectomized (OVX); OVX supplemented with SBM without fluoride; OVX supplemented with SBM containing fluoride. The bones were scanned by CT and tested mechanically in 4-point-bending from which the mechanical properties and fracture behavior were evaluated. The load at 1mm deformation for the OVX sheep tibias was significantly lower than the sham operated group and groups with special diets. The sheep given the SBM (+F) showed the highest load carrying capacity. Similarly, the stiffness and energy to fracture of the OVX sheep was also significantly lower than the group given SBM (+F). The ultimate stress and the elastic modulus did not show any statistically significant difference among the four groups. SBM was partially successful at preventing loss of bone strength in osteoporotic sheep

Osteoporosis affects the craniofacial and oral structures and has been associated with periodontal bone loss, tooth loss and reduced jaw bone mass. OBJECTIVE: This study aimed to test the therapeutic efficacy of synthetic bone mineral (SBM) in minimizing alveolar bone loss induced by mineral deficiency in a rat model. SBM consists of a calcium carbonate apatite (similar to bone apatite) matrix incorporating magnesium, zinc, and fluoride ions. DESIGN: Thirty female Sprague Dawley rats (2 months old) were randomly distributed into 3 groups (10 rats per group): GA (control), on basic diet; GB, on mineral deficient (MD) diet; and GC, on MD+SBM. The rats were sacrificed after 3 months, the jawbones were isolated and the soft tissues removed. Bone density was determined using X-ray radiography (Faxitron); mandibular cortical width, panoramic mandibular index, and alveolar resorption degree (M/M ratio) using BioquantOsteo; and bone micro-architecture micro-computed tomography and scanning electron microscopy. RESULTS: Compared to control (GA), the rats on MD diet (GB) experienced significant mandibular bone loss while the rats on MD+SBM diet (GC) experienced significantly less bone loss compared to the GB group. CONCLUSION: SBM, administered orally, may have the potential as an osteoporosis therapeutic agent in minimizing or preventing alveolar bone loss induced by mineral deficiency.

The use of biomaterials to replace lost bone has been a common practice for decades. More recently, the demands for bone repair and regeneration have pushed research into the use of cultured cells and growth factors in association with these materials. Here we report a novel approach to engineer new bone using a transient cartilage scaffold to induce endochondral ossification. Chondrocyte/chitosan scaffolds (both a transient cartilage scaffold-experimental-and a permanent cartilage scaffold-control) were prepared and implanted subcutaneously in nude mice. Bone formation was evaluated over a period of 5 months. Mineralization was assessed by Faxitron, micro computed tomography, backscatter electrons, and Fourier transform infrared spectroscopy analyses. Histological analysis provided further information on tissue changes in and around the implanted scaffolds. The deposition of ectopic bone was detected in the surface of the experimental implants as early as 1 month after implantation. After 3 months, bone trabeculae and bone marrow cavities were formed inside the scaffolds. The bone deposited was similar to the bone of the mice vertebra. Interestingly, no bone formation was observed in control implants. In conclusion, an engineered transient cartilage template carries all the signals necessary to induce endochondral bone formation in vivo.

Osteoporosis is a 'silent' disease characterized by thinning cortical bone and disorganized trabecular architecture causing bone fragility leading to fracture. Osteoporosis results when the rate of bone resorption far exceeds the rate of bone formation. Current pharmaceutical interventions (estrogen therapy, bisphosphonate-based drugs) focus on inhibiting bone resorption. However, some of these therapies have serious side effects (e.g., cancer risk from estrogen therapy; osteonecrosis of the jaw and delayed fracture healing from bisphosphonate-based drugs). The long term objective of the study was to develop a novel material for potential osteoporosis therapy, prevention and fracture repair. This novel material MZF-CaP or synthetic bone mineral, SBM) incorporates Mg, Zn and F ions in a calcium phosphate matrix. Separately, magnesium (Mg), zinc (Zn) and fluoride (F) ions have been associated with biomineralization and osteoporosis therapy in human and in animals. MZF-CaP or SBM was prepared by a modified hydrolysis method previously described and characterized using x-ray diffraction, FT-IR spectroscopy, inductive coupled plasma and dissolution in acidic buffer. Separately, male and female Sprague-Dawley rats were randomly assigned to the following groups depending on the diet: GA: normal on basic diets; GB: on mineral deficient diets (md); GC: on md + Mg-CaP; GD: on md + Zn-CaP; GE: md+F-CaP; and GF: md+MZF-CaP. The rats were sacrificed after 3 months and the femur bones separated, cleaned of extraneous soft tissues and stored until needed for analyses. Femur bones were analyzed using microradiography (Faxitron), scanning electron microscopy (SEM) and microCT. Results: SEM, Faxitron and microCT analyses showed thinning of cortical bone and disorganized trabecular bone architecture I, or osteoporotic rats on mineral deficient diet (GB) and prevention of bone loss in rats receiving the supplemented diets (GC,GD,GE,GF). Conclusion: These results indicate that the novel material, MZF-CaP or SBM had a potential for osteoporosis therapy and prevention. Studies to demonstrate the use of SBM in reversing (recovering) bone loss are in progress.

The osteoconductive property of calcium phosphate (CaP) biomaterials allow attachment, proliferation, migration, and phenotypic expression of bone cells leading to formation of new bone. The purpose of research is to develop new method of mineralizing commercial GBR membranes with calcium phosphate (CaP) and determine cell response. Resolut Adapt LT (Gore-tex) composed of co-polymer PGA/TMC and Biomend Extend (Zimmer) composed of bovine collagen were used. Membranes were mineralized with CaP using precipitation and new microwave methods. The mineralized and non-mineralized membranes were characterized using SEM, EDS, XRD, FT-IR, and TGA. Cell response to mineralized and non-mineralized membranes was determined using human osteoblast-like cells (MG-63). Microwave method was more efficient in terms of amount of minerals incorporated with membranes and time required. SEM. EDS, and FT-IR identified carbonate apatite in the mineralized membranes. No significant difference in cell proliferation was observed between mineralized and non-mineralized membranes. Greater production of type I collagen was observed with CaP mineralized membranes.

Fluoride, when incorporated in the apatite, stabilizes the structure. The purpose of this study was to determine the consequences of fluoride (F) substitution on the physico-chemical properties of apatites. F-containing apatites were prepared by precipitation or by hydrolysis of CaHPO4 in solutions containing different F concentrations and characterized using x-ray diffraction, FT-IR spectroscopy, scanning electron microscopy, thermogravimetry and chemical analyses. Results showed that F incorporation have the following effects: (a) decrease in a-axis dimension, (b) increase in crystal size and thickness, (c) decrease in calcium deficiency, and (d) lower solubility

Our earlier studies showed that several ions inhibit the crystal growth of apatite and promote the formation of amorphous calcium phosphates (ACP). These ions include: magnesium (Mg), zinc (Zn), stannous (Sn), ferrous (Fe), carbonate (CO3), pyrophosphate (P2O7). The purpose of this study was to investigate the effect of combination of these ions (e.g., Mg & CO3, Mg & P2O7, Mg & Zn, etc) on the formation and stability of ACP. ACP compounds containing the different ions were prepared at 25 and 37 degrees C according to the method we previously described. Chemical stability was investigated by suspending the different ACP preparations in solutions with or without inhibitory ions. Thermal stability was determined by sintering the ACP at different temperatures. Dissolution properties were determined in acidic buffer. The ACP before and after chemical or thermal treatment were analyzed using X-ray diffraction, infrared spectroscopy, and thermogravimetry. Results showed synergistic effects of inhibitory ions on the formation of ACP. ACP materials, regardless of their composition, remained amorphous even after heat treatment at 400 degrees C. Transformation of ACP to other calcium phosphate phases depended on the pH and on the solution composition

Plasma-sprayed HA coating combines the strength of the metal and the bioactivity of the HA. However, this method has several disadvantages. Alternatives to the plasma-spray method such as electrochemical deposition (ECD) and biomimetic or precipitation methods are being explored. The purpose of this study was to develop an ECD method for coating Ti alloy substrate with different calcium phosphates (octacalcium phosphate, calcium deficient apatite, carbonate-substituted apatite, fluoride-substituted apatite). Pairs of Ti6Al4V plates that have been mechanically polished, ultrasonically cleaned, acid etched, rinsed and dried were used as anodes and cathodes. ECD was carried out using programmed pulse time electric fields. Results showed that uniform coating with only the desired calcium phosphate can be obtained using metastable calcium phosphate solutions at different pH and temperature conditions and different electrolyte concentrations. Coating thickness varied with the duration of coating deposition. Crystal size varied with other ECD conditions (e.g., pulse time, current density). This method can be used to obtain uniform coating of the desired calcium phosphate composition at low temperatures (25 to 80 degrees C) on substrates of any type of geometry