Silica-calcium Phosphate Nanocomposite Research Articles

Morphology, Crystal Size and Crystallinity Degree of Silica-Calcium Phosphate Composite (S) and Apatite Cement Formulation - <i>In Vitro</i> Bioactivity Test

Silica-calcium phosphate nanocomposite (SCPC) is a porous bioactive resorbable bioactive ceramics. Incorporating apatite bone cement (AC) formulation of tetracalcium phosphate-dicalcium phosphate dihydrate and SCPC has contributed to the higher mechanical strength of a new prototype apatite cement formulation. This in-vitro experiment aims to investigate the bioactivity of AC formulation using simulated body fluid (SBF). The samples consist of two groups of AC formulations (n=4). The first group, AC with 10% SCPC and the second group AC without SCPC, was immersed in the SBF for 14 days. The samples before and after immersion were analyzed by X-Ray Diffraction (XRD), Energy Dispersive X-ray Spectroscopy (EDS), and Scanning Electron Microscope (SEM). The samples' size and degree of crystallinity were analyzed statistically using Shapiro-Wilk, Levene, and Mann-Whitney test. As a result, there was no significant difference in the crystal size and the degree of the crystallinity of both samples. The surface morphology of all samples were coated with hydroxyapatite after immersing in the SBF solution. Both AC formulations with and without SCPC have bioactivity as the bone substitute materials. Combining AC with SCPC50 is a promising method to improve the bioactivity and mechanical strength of calcium phosphate bone cement.

Assessment of the effect of silica calcium phosphate nanocomposite on mesenchymal stromal cell differentiation and bone regeneration in critical size defect

ObjectiveThe research was designed to assess silica calcium phosphate nanocomposite (SCPC) biocompatibility and bioactivity as an osteoinductive scaffold and cell carrier. Consequently, the ability of cell seeded SCPC implant to regenerate a critical size defect in rat calvarium. Materials and MethodsThe study was conducted in two parts. A series of in vitro experiments on bone marrow stromal cells (MSCs) seeded in the SCPC scaffold evaluated cell attachment, proliferation and osteogenic differentiation. In the second part, a cell seeded SCPC construct was implanted in rat calvarium and bone regeneration was assessed by histological examination to evaluate the newly formed bone quality and the residual graft volume. ResultsIn vitro experimentation revealed that MSCs cultured on SCPC maintained viability and proliferation when seeded into the SCPC. Scanning electron microscopy demonstrated cell adhesion and calcium appetite formation, MSCs differentiated towards the osteogenic lineage as indicated by the upregulation of RUNX2, ALP, Col1a1 markers. Histological examination showed regeneration from the periphery and core of the defect with new bone formation at different stages of maturation. ConclusionRegenerative medicine delivers promising solutions and technologies for application in craniofacial reconstruction. SCPC scaffold has the potential to be used as a cell carrier to achieve stem cell-based bone regeneration, which provides a viable alternative for treatment of challenging critical size defect.

Setting Time, Handling Property and Mechanical Strength Evaluation of SCPC50 and Apatite Cement Mixture in Various Combinations

Apatite cement is ideal self-setting cement for bone substitute material, however its use is limited only to areas that receive minimum load bearing because mechanical strength of apatite cement is low. Silica-calcium phosphate nanocomposite (SCPC50) is material having good mechanical strength and has an important role in bone remodeling (bone metabolism), mineralization, synthesis of cartilage, collagen production, proliferation and differentiation of bone cells. However, the unsetting and granule’s physical shape of SCPC50 limits the application. The purpose of this study is to determine the effect of various mixtures of SCPC50 and apatite cement to manipulative index (setting time and handling property), and mechanical properties. The experimental results show that the setting time of apatite cement mixture with 5% and 10% SCPC50 was 40% higher (p<0.05). The mechanical strength evaluated by Diametral Tensile Strength showed that the addition of both 5% silica and 10% SCPC50 composition to apatite cement mixture increased the mechanical strength of apatite cement mixture (p<0.1). The handling property of cement paste was significantly increased between the apatite cement without SCPC50 and apatite cement with both 5% SCPC50 and 10% SCPC50 (p<0.05). It is concluded that the addition of SCPC50 to apatite cement mixture could improve the mechanical properties and it is expected to improve its bioactivity.

Assessment of bone augmentation using silica calcium phosphate nanocomposite (SCPC)versus hydroxyapatite in open sinus lift Surgeries(A Scanning Electron Microscope, Cone Beam Computerized Tomography and histological study)

ObjectivesMaxillary sinus pneumatization and extraction of posterior maxillary teeth are among the most common factors attributing to the diminished alveolar process. Implants placed in posterior region of maxilla showed the highest failure rates due to poor bone density in addition to insufficient remaining bone volume needed for implant primary stability. Materials and methodsTen patients were selected from out patient clinic with partially or fully edentulous maxilla missing premolars or molars with residual alveolar bone height less than 6 mm, both groups received open sinus lift surgery with different grafting material group1 (control group) received hydroxyapatite (HA)in a disc form, group 2(Study group) received silica calcium phosphate nanocomposite (SCPC) in a disc form. Clinical evaluation, Cone Beam Computerized Tomography (CBCT) (Pre-operative, 0 & 4 months postoperatively), Scanning Electron Microscopy (SEM) (4 months postoperatively) and histological study (4 months postoperatively)were performed for both groups as follow-up following either stages of surgery. Resultsall patients had uneventful wound healing, and none experienced excessive postsurgical edema. Following surgical stage II (implant placement) all patients exhibited proper dental implant osseointegration, and all were properly restored by fixed prosthodontics. For radio graphical results the bone height and bone width showed statistically significant increase in both groups; The histopathological results of both groups revealed new bone formation in the histological sections attained from the core bone biopsies over 4 months postoperatively. While the analysis of the SEM images revealed that in the control group (HA), the new bone exhibited an irregular and porous appearance In the study group (SCPC), the bone appeared as a continuous plate with nearly homogenous surface. Conclusionwithin the limitations of the present study, the present data support the fact that both HA and SCPC can be used, successfully, in sinus augmentation procedures. Moreover, the suggested technique in combination with grafts in the form of discs, and using piezoelectric surgical units are simpler and safer approaches to lateral sinus lift augmentation procedures.

Regeneration of Critical-Size Canine Calvarial Defect by Silica-Calcium Phosphate-Composite (SCPC) and Human Adipose Derived Stem Cells

Reconstruction of large maxillofacial bone defects remains challenging even with diverse current treatment modalities. Silica-calcium phosphate nano composite (SCPC) is a resorbable bioactive bone graft material with a strong stimulatory effect on osteogenic gene expression of osteoblasts and mineralized tissue formation. In a prospective experimental study we investigated the ability of SCPC scaffold seeded with human adipose derived stem cells (ADSCs) to regenerate bone in a critical-size canine calvarial defect. Porous SCPC discs were prepared by powder metallurgy method. ADSCs were isolated from human breast adipose tissue, expanded in vitro and differentiated along osteogenic lineage. Bilateral critical-sized defects, 2.5 cm in diameter each, were made in the calvaria of 12 adult dogs. One calvarial defect was filled by either SCPC disc alone (Group I) or SCPC disc seeded with 2.5 x106 osteoblast-like cells (Group II) while other defect was left empty (ungrafted). Bone tissue regeneration and graft material resorption was evaluated 3 and 6 months postoperative using CT and histology. Calvarial defects grafted with SCPC alone or SCPC-Cell construct were grossly repaired while control ungrafted defect did not repair. Microscopically the newly formed bone in the grafted defects was compact and integrated with the surrounding host tissues. Near complete resorption of the graft material was observed. Histomorphometric analysis demonstrated higher bone surface area and more graft material resorption in defects grafted with SCPC-cell hybrid compared to SCPC alone.

Early osteoblast responses to orthopedic implants: Synergy of surface roughness and chemistry of bioactive ceramic coating.

Pro-osteogenic stimulation of bone cells by bioactive ceramic-coated orthopedic implants is influenced by both surface roughness and material chemistry; however, their concomitant impact on osteoblast behavior is not well understood. The aim of this study is to investigate the effects of nano-scale roughness and chemistry of bioactive silica-calcium phosphate nanocomposite (SCPC50) coated Ti-6Al-4V on modulating early bone cell responses. Cell attachment was higher on SCPC50-coated substrates compared to the uncoated controls; however, cells on the uncoated substrate exhibited greater spreading and superior quality of F-actin filaments than cells on the SCPC50-coated substrates. The poor F-actin filament organization on SCPC50-coated substrates is thought to be due to the enhanced calcium uptake by the ceramic surface. Dissolution analyses showed that an increase in surface roughness was accompanied by increased calcium uptake, and increased phosphorous and silicon release, all of which appear to interfere with F-actin assembly and osteoblast morphology. Moreover, cell attachment onto the SCPC50-coated substrates correlated with the known adsorption of fibronectin, and was independent of surface roughness. High-throughput genome sequencing showed enhanced expression of extracellular matrix and cell differentiation related genes. These results demonstrate a synergistic relationship between bioactive ceramic coating roughness and material chemistry resulting in a phenotype that leads to early osteoblast differentiation.

Tissue engineering scaffold for sequential release of vancomycin and rhBMP2 to treat bone infections

The ability of silica calcium phosphate nanocomposite (SCPC75) for the controlled sequential delivery of vancomycin (Vanc) and rhBMP2 was evaluated. Fourier transform infrared spectroscopy analyses of the SCPC75 showed an increase in the bond energy of the PO4 (-3) due to the interactions with negatively charged moieties of Vanc. Furthermore, a decrease in the bond energy of the Si-O-Si functional groups was observed after rhBMP2 adsorption. In conjunction with the differences in bond site and bond energy at the ceramic/drug interface, significant differences in drug release kinetics and bioceramic dissolution rate were found. UV-vis spectrometry showed a burst release of Vanc in the first 8 h followed by a sustained release stage for up to 28 days. ELISA showed first-order release kinetics of rhBMP2 without burst release. The rhBMP2 release from SCPC75 was associated with a significantly lower rate of Ca and a higher rate of Si dissolutions when compared with Vanc release over identical time periods. Differences in the release kinetic profiles of Vanc and rhBMP2 from the SCPC75-Vanc/SCPC75-rhBMP2 scaffolds at 70/30, 50/50, or 20/80 ratios allowed for sequential drug release profiles that could be exploited to customize doses and release duration of each drug. The released rhBMP2 significantly upregulated MC3T3-E1 expression of collagen type I, osteopontin, and osteocalcin mRNA by 12.6-, 3.3-, and 2.4-fold, respectively. The released Vanc demonstrated bactericidal effects on Staphylococcus aureus in vitro. These results suggest the potential of SCPC75-Vanc-rhBMP2 scaffolds in the treatment of damaged and/or infected bone.

Mechanical properties and cytotoxicity of a resorbable bioactive implant prepared by rapid prototyping technique

Bioceramic processing using rapid prototyping technique (RPT) results in a fragile device that requires thermal treatment to improve the mechanical properties. This investigation evaluates the effect of thermal treatment on the mechanical, porosity, and bioactivity properties as well as the cytotoxicity of a porous silica-calcium phosphate nanocomposite (SCPC) implant prepared by RPT. Porous SCPC implant was subject to 3-h treatment at 800°C, 850°C, or 900°C. The compressive strength (s) and modulus of elasticity (E) were doubled when the sintering temperature is raised from 850 to 900°C measuring (s = 15.326 ± 2.95 MPa and E = 1095 ± 164 MPa) after the later treatment. The significant increase in mechanical properties takes place with minimal changes in the surface area and the percentage of pores in the range 1-356 μm. The SCPC implant prepared at 900°C was loaded with rh-BMP-2 and grafted into a segmental defect in the rabbit ulna. Histology analyses showed highly vascularized bone formation inside the defect. Histopathological analyses of the liver, spleen, kidney, heart, and the lung of rabbits grafted with and without SCPC demonstrated healthy tissues with no signs of toxicity or morphology alterations. Results of the study suggest that it is possible to engineering the mechanical properties of the SCPC implant without compromising its bioactivity. The enhanced bone formation inside the porous SCPC facilitated cell-mediated graft resorption and prohibited any accumulation of the material in the body organs.

Promotion of pro‐osteogenic responses by a bioactive ceramic coating

The objective of this study was to analyze the responses of bone-forming osteoblasts to Ti-6Al-4V implant material coated with silica-calcium phosphate nanocomposite (SCPC50). Osteoblast differentiation at the interface with SCPC50-coated Ti-6Al-4V was correlated to the adsorption of high amount of serum proteins, high surface affinity to fibronectin, Ca uptake from and P and Si release into the medium. SCPC50-coated Ti-6Al-4V adsorbed significantly more serum protein (p < 0.05) than control uncoated substrates. Moreover, Western blot analysis showed that the SCPC50 coating had a high affinity for serum fibronectin. Protein conformation analyses by FTIR showed that the ratio of the area under the peak for amide I/amide II bands was significantly higher (p < 0.05) on the surface of SCPC50-coated substrates than that on the surface of the control uncoated substrates. Moreover, ICP - OES analyses indicated that SCPC50-coated substrates withdrew Ca ions from, and released P and Si ions into, the tissue culture medium, respectively. In conjunction with the favorable protein adsorption and modifications in medium composition, MC3T3-E1 osteoblast-like cells attached to SCPC50-coated substrates expressed 10-fold higher level of mRNA encoding osteocalcin and had significantly higher production of osteopontin and osteocalcin proteins than cells attached to the uncoated Ti-6A1-4V substrates. In addition, osteoblast-like cells attached to the SCPC50-coated substrates produced significantly lower levels of the inflammatory and osteoclastogenic cytokines, IL-6, IL-12p40, and RANKL than those attached to uncoated Ti-6Al-4V substrates. These results suggest that SCPC50 coating could enhance bone integration with orthopedic and maxillofacial implants while minimizing the induction of inflammatory bone cell responses.

Machining of a bioactive nanocomposite orthopedic fixation device

Bioactive ceramics bond to bone and enhance bone formation. However, they have poor mechanical properties which restrict their machinability as well as their application as load bearing implants. The goal of this study was to machine bioactive fixation screws using a silica-calcium phosphate nanocomposite (SCPC50). The effect of compact pressure, holding time, and thermal treatment on the microstructure, machinability, and mechanical properties of SCPC50 cylinders were investigated. Samples prepared by powder metallurgy technique at compact pressure range of 100-300 MPa and treated at 900°C/1 h scored a poor machinability rating of (1/5) due to the significant formation of amorphous silicate phase at the grain boundaries. On the other hand, lowering of compact pressure and sintering temperature to 30 MPa/3 h and 700°C/2 h, respectively, minimized the formation of the amorphous phase and raised the machinability rating to (5/5). The modulus of elasticity and ultimate strength of machinable SCPC50 were 10.8 ± 2.0 GPa and 72.8 ± 22.8 MPa, respectively, which are comparable to the corresponding values for adult human cortical bone. qRT-PCR analyses showed that bone cells attached to SCPC50 significantly upregulated osteocalcin mRNA expression as compared to the cells on Ti-6Al-4V. Moreover, cells attached to SCPC50 produced mineralized bone-like tissue within 8 days. On the other hand, cells attached to Ti-6Al-4V failed to produce bone mineral under the same experimental conditions. Results of the study suggest that machinable SCPC50 has the potential to serve as an attractive new material for orthopedic fixation devices.

Evaluation of a bioresorbable drug delivery system for the treatment of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) represents a major global health burden. Typically HCC responds poorly to chemotherapy, and such approaches to treat HCC are commonly associated with severe hepatic and/or systemic toxicity. The aim of this study was to evaluate a porous resorbable silica-calcium phosphate nanocomposite (SCPC) as a controlled release vehicle for cisplatin. Particles of two different formulations--SCPC50 and SCPC75, containing 19.49 and 32.9 mol % silica, respectively--were loaded with cisplatin by immersion treatment and pressed into discs. In vitro release kinetics studies of cisplatin from SCPC50 and SCPC75 demonstrated an initial burst release of 0.39 ± 0.04 mg (of the 1.49 mg total loaded) and 0.87 ± 0.07 mg (of the 2.34 mg total loaded), respectively. Over the following 44-day period. SCPC75-cisplatin hybrid produced a significantly higher sustained cisplatin release than that released from SCPC50. Cisplatin release correlated well with the surface area, and silica dissolution kinetics of the SCPC carrier. Treatment of rat HCC cells (H4IIE) with cisplatin released from SCPC-cisplatin hybrids induced apoptotic cell death in H4IIE cells in vitro. Results of this study suggest that SCPC composites may be of potential use for the treatment of HCC in vivo.

Electrophoretic deposition of bioactive silica‐calcium phosphate nanocomposite on Ti‐6Al‐4V orthopedic implant

Bioactive silica-calcium phosphate nanocomposite (SCPC) has been coated on Ti-6Al-4V implant employing an electrophoretic deposition (EPD) technique. The effects of composition and pH of the suspending medium on the zeta potential of three different SCPC formulations; SCPC25, SCPC50 and SCPC75 were analyzed. The average zeta potential of SCPC50 in pure ethanol was more negative than that of SCPC25 or SCPC75; however, the difference was not statistically significant. Discs of Ti-6Al-4V were passivated, coated with SCPC50 (200 nm-10 μm) and thermally treated at 600-800°C to produce a coating thickness in the range of 43.1 ± 5.7 to 30.1 ± 4.6 μm. After treatment at 600, 700, and 800°C, the adhesion strength at the SCPC50/Ti-6Al-4V interface was 42.6 ± 3.6, 44.7 ± 8.7, and 47.2 ± 4.3 MPa, respectively. SEM-EDX analyses of SCPC50-coated Ti-6Al-4V preimmersed in PBS for 7 days showed the formation of a Ca-deficient hydroxyapatite surface layer. ICP-OES analyses of the immersing solution (n = 6) showed an increase in the ionic concentration of Si from 3.3 ± 0.9 to 5.0 ± 1.2 ppm between days 1 and 4; after which no significant change in the Si concentration was measured. Bone marrow mesenchymal stem cells attached to the SCPC50-coated implants expressed significantly higher (p < 0.05) alkaline phosphatase activity (82.4 ± 25.6 nmoles p-NP/mg protein/min) than that expressed by cells attached to HA-coated or uncoated implants. Results of the study suggest that bioactive SCPC50 can efficiently be coated on Ti-6Al-4V using EPD. The SCPC50 coating has the potential to enhance bone integration with the orthopedic implant.

A ceramic-based anticancer drug delivery system to treat breast cancer

Drug delivery systems offer the advantage of sustained targeted release with minimal side effect. In the present study, the therapeutic efficacy of a porous silica-calcium phosphate nanocomposite (SCPC) as a new delivery system for 5-Fluorouracil (5-FU) was evaluated in vitro and in vivo. In vitro studies showed that two formulations; SCPC50/5-FU and SCPC75/5-FU hybrids were very cytotoxic for 4T1 mammary tumor cells. In contrast, control SCPCs without drug did not show any measurable toxic effect. Release kinetics studies showed that SCPC75/5-FU hybrid provided a burst release of 5-FU in the first 24 h followed by a sustained release of a therapeutic dose (30.7 microg/day) of the drug for up to 32 days. Moreover, subcutaneous implantation of SCPC75/5-FU hybrid disk in an immunocompetent murine model of breast cancer stopped 4T1 tumor growth. Blood analyses showed comparable concentrations of Ca, P and Si in animals implanted with or without SCPC75 disks. These results strongly suggest that SCPC/5-FU hybrids can provide an effective treatment for solid tumors with minimal side effects.

Effect of processing parameters on the microstructure and mechanical behavior of silica-calcium phosphate nanocomposite

Silica-calcium phosphate nanocomposite (SCPC) is a bioactive ceramic characterized by superior bone regenerative capacity and resorbability when compared to traditional bioactive ceramics. The aim of the present study is to evaluate the effect of processing parameters on the microstructure and mechanical properties of SCPC. Cylinders were prepared by pressing the ceramic powder at 200, 300 or 400 MPa and sintering at 900, 1000 or 1100 degrees C for 3 h, respectively. XRD results indicate that the crystalline structure of the material is made of beta-NaCaPO(4) and alpha-cristobalite solid solutions. The increase in sintering temperature results in an increase in the grain size and the formation of a melting phase that coats the grains. TEM analyses reveal that the melting phase is amorphous and rich in silicon. The mechanical properties of SCPC cylinders are dependent on the content of the melting phase and the microstructure of the material. The ranges of compressive strength and modulus of elasticity of the SCPC are 62-204 MPa and 6-14 GPa, respectively, which are comparable to those of cortical bone. The results suggest that the interaction between crystalline and amorphous phases modulated the mechanical behavior of SCPC. It is possible to engineer the mechanical properties of SCPC by controlling the processing parameters to synthesize various fixation devices for orthopedic and cranio-maxillofacial applications.

Resorbable bioactive ceramic for treatment of bone infection

Polymethylmethacrylate (PMMA) beads have been widely used in the treatment of bone infection over the last three decades. Although PMMA does offer a mechanism to quickly and effectively administer a localized dose of antibiotic to the site of infection, its efficacy is limited by its nonresorbability and nonbioactivity. Resorbable bioactive silica-calcium phosphate nanocomposite (SCPC75) was investigated as a novel controlled release carrier of vancomycin for the treatment of osteomyelitis. SCPC75 particles adsorbed significantly higher amount of vancomycin compared with PMMA. Moreover, SCPC75 provided a sustained release kinetics of therapeutic dose of vancomycin up to 35 days. The novel resorbable ceramic was able to release 95.5% of the adsorbed drug in an average dose of 12 microg/mL/day over 480 h (35 days). In conjunction with the sustained drug release, a controlled dissolution rate that led to 40% mass loss of SCPC75 was observed. On the other hand, PMMA provided a sustained release of a therapeutic dose of vancomycin for 14 days after which minimal concentration of the drug was detected. Moreover, PMMA retained 32% of the drug adsorbed onto its surface. The SCPC-vancomycin implant can serve a dual function: provide a sustained therapeutic dose of antibiotic to eradicate infection and stimulate bone cell differentiation and new bone formation. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.

A Novel Bioactive Ceramic Coating for Improved Fixation of Orthopedic Implant

AbstractElectrophoretic deposition (EPD) coating of medical grade Ti-6Al-4V substrate with a novel silica-calcium phosphate nano-composite (SCPC) in the particle size range 50 nm-5 μm has been described. The influence of EPD parameters and thermal treatment on the coating homogeneity, thickness and adhesion strength has been studied. SEM analyses showed that EPD carried out in 5% (w/v) SCPC/ethanol suspension at 50 V produced a homogeneous coating on passivated Ti alloy discs. Tensile tests carried out to evaluate the adhesion strength at the ceramic/metal interface showed that the SCPC coating layer developed adhesion strength of 47 ± 4 MPa with Ti alloy after thermal treatment at 800 °C for 1 hr. SEM – EDX analyses of the fracture surface revealed that the presence of SCPC layer on the surface of the Ti alloy indicating high interfacial stability. Upon immersion of the SCPC-coated Ti alloy substrate in PBS, a surface biological hydroxyapatite layer was deposited suggesting bone bonding ability. The successful coating of SCPC on the Ti-6Al-4V has the potential to stimulate rapid fixation and lower stress shielding by enhancing the bone bonding ability of the implant.

Peptides as potent antimicrobials tethered to a solid surface: Implications for medical devices

AbstractMedical devices are an integral part of therapeutic management; despite their importance, they carry a significant risk of microbial infection. Bacterial attachment to a medical device is established by a single, multiplying organism, leading to subsequent biofilm formation. To date, no preventative measures have impacted the incidence of device-related infection. We report the bidirectional covalent coupling of an engineered cationic antimicrobial peptide (eCAP), WLBU2, to various biological surfaces is accomplished. These surfaces included (i) a carbohydrate-based gel matrix, (ii) a complex polymeric plastic bead, and (iii) a silica-calcium phosphate nanocomposite associated with bone reconstruction. WLBU2-conjugated surfaces are shown to retain potent antimicrobial activity related to bacterial surface adhesion. This study provides proof of principle that covalently coating laboratory and bone-regenerating materials with eCAPs has the potential for decreasing infection rates of implanted devices. These findings have important consequences to the patient management component of our current health care technology.

Bone Engineering of the Rabbit Ulna

The purpose of the present preliminary study is to show that a novel 3-dimensional porous silica-calcium phosphate nanocomposite (SCPC) can provide a controlled release of rhBMP-2 and regenerate bone in a load-bearing segmental defect. A bone replica of the rabbit ulna was created from SCPC powder using rapid prototyping technology. The ceramic bone replica was coated with rhBMP-2 and then implanted into a 10-mm segmental defect created in a rabbit ulna and fixated with a 1-mm titanium adaptation plate. Bone healing was evaluated using computed tomography (CT) scan, histomorphometry, and biomechanical techniques. The release kinetics of rhBMP-2 and the dissolution kinetics were also determined in vitro. Statistical analysis was performed to compare the biomechanical strength of the grafted bone with the contralateral unoperated ulna. After 4 weeks, CT scans showed that the critical size defect had been replaced by newly formed bone. Torsional testing of the ulna after 12 weeks showed restoration of maximum torque and angle at failure. Histological evaluation showed that the regenerated bone had the morphological characteristics of mature bone. SCPC provided a sustained release profile of an effective dose of rhBMP-2 for 14 days. The SCPC-rhBMP-2 hybrid enhanced bone regeneration in a load-bearing segmental defect in a rabbit ulna. The regenerated bone acquired morphology and mechanical strength typical for natural bone. The enhanced bone formation correlates well with the surface bioactivity and effective release profile of rhBMP-2. The present preliminary study shows the proof of principles that porous, resorbable, bioactive SCPC-rhBMP-2 tissue engineering hybrid can serve as a substitute for autologous bone in load-bearing applications.

Dissolution kinetics of a Si‐rich nanocomposite and its effect on osteoblast gene expression

Silica-calcium phosphate nanocomposite (SCPC) has recently been proposed as a novel resorbable, bioactive, and mechanically compatible template for bone reconstruction. The effect of the physicochemical properties on the surface reactivity and dissolution kinetics of SCPC immersed in simulated body fluid (SBF) was investigated and compared to that of bioactive glass (BG). Moreover, the stimulatory effect on osteoblast gene expression of SCPC was determined using quantitative real-time polymerase chain reaction (qRT-PCR), and compared to that of hydroxyapatite (HA-200). Mercury porosimetry revealed that surface areas of SCPC particles containing 10 (SCPC10), 30 (SCPC30), and 50 (SCPC50) wt % Si-content were 14-, 18-, and 32-times higher than that of BG. Inductively coupled plasma analysis showed that after 192 h of immersion, Si-rich SCPC50 exhibited controlled bulk-dissolution and released 43.1 ppm Si, which was sixfold higher than that released from BG (7.7 ppm). Moreover, SCPC50 showed a rapid Ca-uptake from SBF and developed a surface apatite layer after only 2 h, whereas a similar layer was detected on BG after 8 days of immersion under the same experimental conditions. qRT-PCR revealed that osteopontin and osteocalcin mRNA expression by osteoblast-like cells attached to Si-rich SCPC50 was significantly higher than that on HA-200 or polystyrene after 2 days in culture. This suggested a role of dissolved Si in stimulating the differentiation and mineralization of osteoblast precursor cells. The favorable physiochemical and bioactivity properties of Si-rich SCPC nanocomposite indicate that SCPC can have wide applications as a synthetic bone graft for cell delivery applications in tissue engineering.

Enhancement of osteoblast gene expression by mechanically compatible porous Si‐rich nanocomposite

Synthesis of a porous bioactive ceramic implant for load bearing applications is a challenging task in maxillofacial and orthopedic surgeries. A novel bioactive resorbable silica-calcium phosphate nanocomposite (SCPC) has recently been introduced as a potential bone graft. In the present study, we employed SCPC to develop a resorbable porous scaffold and analyzed the effects of composition and porosity on the mechanical properties. The ranges of compressive strength and modulus of elasticity of SCPC containing 32-56% porosity were 1.5-50 MPa and 0.14-2.1 GPa, respectively, which matched the corresponding values for trabecular bone. The compressive strength of dense SCPC was dependent on the Si content and acquired values (93-285 MPa) comparable to that of cortical bone. The superior mechanical properties of SCPC are attributed to the intricate interactions at the boundaries of the nanograins and to the homogenous distribution of hierarchical pore-structure throughout the material volume. X-ray computed tomography and mercury porosimetry analyses revealed high interconnectivity of the pores in the size range 3 nm to 650 microm. Quantitative real-time PCR analyses showed that neonatal rat calvarial osteoblasts attached to Si-rich SCPC expressed 5- and 26-fold higher osteocalcin mRNA levels compared to cells attached to ProOsteon hydroxyapatite disks and tissue culture polystyrene plates respectively, after four days in culture. Results of the present study strongly suggest that porous, bioactive resorbable SCPCs can serve as tissue engineering scaffolds for cell delivery to treat load-bearing bone defects in orthopedic and maxillofacial surgeries.