Teja Guda

Design and characterization of a novel chitosan/nanocrystalline calcium phosphate composite scaffold for bone regeneration

To meet the challenge of regenerating bone lost to disease or trauma, biodegradable scaffolds are being investigated as a way to regenerate bone without the need for an auto- or allograft. Here, we have developed a novel microsphere-based chitosan/nanocrystalline calcium phosphate (CaP) composite scaffold and investigated its potential compared to plain chitosan scaffolds to be used as a bone graft substitute. Composite and chitosan scaffolds were prepared by fusing microspheres of 500-900 microm in diameter, and porosity, degradation, compressive strength, and cell growth were examined. Both scaffolds had porosities of 33-35% and pore sizes between 100 and 800 . However, composite scaffolds were much rougher and, as a result, had 20 times more surface area/unit mass than chitosan scaffolds. The compressive modulus of hydrated composite scaffolds was significantly higher than chitosan scaffolds (9.29 +/- 0.8 MPa vs. 3.26 +/- 2.5 MPa), and composite scaffolds were tougher and more flexible than what has been reported for other chitosan-CaP composites or CaP scaffolds alone. Using X-ray diffraction, scaffolds were shown to contain partially crystalline hydroxyapatite with a crystallinity of 16.7% +/- 6.8% and crystallite size of 128 +/- 55 nm. Fibronection adsorption was increased on composite scaffolds, and cell attachment was higher on composite scaffolds after 30 min, although attachment rates were similar after 1 h. Osteoblast proliferation (based on dsDNA measurements) was significantly increased after 1 week of culture. These studies have demonstrated that composite scaffolds have mechanical properties and porosity sufficient to support ingrowth of new bone tissue, and cell attachment and proliferation data indicate composite scaffolds are promising for bone regeneration.

Current trends in dental implants.

Tooth loss is very a very common problem; therefore, the use of dental implants is also a common practice. Although research on dental implant designs, materials and techniques has increased in the past few years and is expected to expand in the future, there is still a lot of work involved in the use of better biomaterials, implant design, surface modification and functionalization of surfaces to improve the long-term outcomes of the treatment. This paper provides a brief history and evolution of dental implants. It also describes the types of implants that have been developed, and the parameters that are presently used in the design of dental implants. Finally, it describes the trends that are employed to improve dental implant surfaces, and current technologies used for the analysis and design of the implants.

Femoral suspension devices for anterior cruciate ligament reconstruction: Do adjustable loops lengthen?

Background: Cortical suspension devices are commonly used for femoral graft fixation during anterior cruciate ligament (ACL) reconstructive surgery. Adjustable-length fixation devices provide technical advantages over fixed-length loops but may be more susceptible to lengthening during cyclic loading. Hypothesis: Both fixed-length and adjustable-length femoral cortical suspension devices would withstand ultimate loads greater than those normally experienced by the native ACL and would prevent clinically significant lengthening during prolonged cyclic loading. Study Design: Controlled laboratory study. Methods: Mechanical testing was performed on 3 ACL graft cortical suspensory devices by use of an extended cyclic loading (4500 cycles at 10-250 N) and pull-to-failure protocol. Two adjustable-length devices were additionally tested with the free suture ends tied. Results: Total displacement after 4500 cycles of tensioning at variable loads (expressed as mean ± SD) was 42.45 mm (±7.01 mm) for the Arthrex TightRope RT, 5.76 mm (±0.35 mm) for the Biomet ToggleLoc, and 1.34 mm (±0.03 mm) for the Smith & Nephew EndoButton CL Ultra (P < .001). The Arthrex TightRope reached clinical failure of 3 mm lengthening after fewer cycles (1349 ± 316) than the Biomet ToggleLoc (2576 ± 73) (P < .001). The Smith & Nephew EndoButton did not reach clinical failure during cyclic testing. With the free suture ends tied, after 4500 cycles, the Arthrex TightRope had a significant decrease in lengthening to 13.36 ± 1.86 mm (P < .037) There was also a significant difference in ultimate load between the TightRope (809.11 ± 52.94 N) and the other 2 constructs (P < .001). Conclusion: The ultimate load of all graft-fixation devices exceeded the forces likely to be experienced in a patient’s knee during the early postoperative rehabilitation period. However, the adjustable-length fixation devices experienced a clinically significant increase in loop lengthening during cyclic testing. This lengthening is partially caused by suture slippage into the adjustable-length loop. Clinical Relevance: Adjustable-length ACL graft cortical suspension devices lengthen under cyclic loads because free suture ends are pulled into the adjustable loop. This may allow for graft-fixation device lengthening during the acute postoperative period.

Dual-Purpose Bone Grafts Improve Healing and Reduce Infection

Objective: To determine if a dual-purpose bone graft can regenerate bone and reduce infection in highly contaminated bone critical size defects in rats. Methods: Biodegradable polyurethane (PUR) scaffolds were loaded with recombinant human bone morphogenetic protein-2 (BMP-2) and vancomycin (Vanc). The release kinetics of the BMP-2 were tuned to take advantage of its mechanism of action (ie, an initial burst to recruit cells and sustained release to induce differentiation of the migrating cells). The Vanc release kinetics were designed to protect the graft from contamination until it is vascularized by having a burst for a week and remaining well over the minimum inhibitory concentration for Staphylococcus aureus for 2 months. The bone regeneration and infection reduction capability of these dual-purpose grafts (PUR???2) were compared with collagen sponges loaded with BMP-2 (collagen?2) and PUR?2 in infected critical size rat femoral segmental defects. Results: The dual-delivery approach resulted in substantially more new bone formation and a modest improvement in infection than PUR?2 and collagen?2 treatments. Conclusions: The PUR bone graft is injectable, provides a more sustained release of BMP-2 than the collagen sponge, and can release antibiotics for more than 8 weeks. Thus, the dual-delivery approach may improve patient outcomes of open fractures by protecting the osteoinductive graft from colonization until vascularization occurs. In addition, the more optimal release kinetics of BMP-2 may reduce nonunions and the amount of growth factor required.

Development of Composite Scaffolds for Load-Bearing Segmental Bone Defects

The need for a suitable tissue-engineered scaffold that can be used to heal load-bearing segmental bone defects (SBDs) is both immediate and increasing. During the past 30 years, various ceramic and polymer scaffolds have been investigated for this application. More recently, while composite scaffolds built using a combination of ceramics and polymeric materials are being investigated in a greater number, very few products have progressed from laboratory benchtop studies to preclinical testing in animals. This review is based on an exhaustive literature search of various composite scaffolds designed to serve as bone regenerative therapies. We analyzed the benefits and drawbacks of different composite scaffold manufacturing techniques, the properties of commonly used ceramics and polymers, and the properties of currently investigated synthetic composite grafts. To follow, a comprehensive review of in vivo models used to test composite scaffolds in SBDs is detailed to serve as a guide to design appropriate translational studies and to identify the challenges that need to be overcome in scaffold design for successful translation. This includes selecting the animal type, determining the anatomical location within the animals, choosing the correct study duration, and finally, an overview of scaffold performance assessment.

Probabilistic analysis of preload in the abutment screw of a dental implant complex

STATEMENT OF PROBLEM Screw loosening is a problem for a percentage of implants. A probabilistic analysis to determine the cumulative probability distribution of the preload, the probability of obtaining an optimal preload, and the probabilistic sensitivities identifying important variables is lacking. PURPOSE The purpose of this study was to examine the inherent variability of material properties, surface interactions, and applied torque in an implant system to determine the probability of obtaining desired preload values and to identify the significant variables that affect the preload. MATERIAL AND METHODS Using software programs, an abutment screw was subjected to a tightening torque and the preload was determined from finite element (FE) analysis. The FE model was integrated with probabilistic analysis software. Two probabilistic analysis methods (advanced mean value and Monte Carlo sampling) were applied to determine the cumulative distribution function (CDF) of preload. The coefficient of friction, elastic moduli, Poissons ratios, and applied torque were modeled as random variables and defined by probability distributions. Separate probability distributions were determined for the coefficient of friction in well-lubricated and dry environments. The probabilistic analyses were performed and the cumulative distribution of preload was determined for each environment. RESULTS A distinct difference was seen between the preload probability distributions generated in a dry environment (normal distribution, mean (SD): 347 (61.9) N) compared to a well-lubricated environment (normal distribution, mean (SD): 616 (92.2) N). The probability of obtaining a preload value within the target range was approximately 54% for the well-lubricated environment and only 0.02% for the dry environment. The preload is predominately affected by the applied torque and coefficient of friction between the screw threads and implant bore at lower and middle values of the preload CDF, and by the applied torque and the elastic modulus of the abutment screw at high values of the preload CDF. CONCLUSIONS Lubrication at the threaded surfaces between the abutment screw and implant bore affects the preload developed in the implant complex. For the well-lubricated surfaces, only approximately 50% of implants will have preload values within the generally accepted range. This probability can be improved by applying a higher torque than normally recommended or a more closely controlled torque than typically achieved. It is also suggested that materials with higher elastic moduli be used in the manufacture of the abutment screw to achieve a higher preload.

Injectable reactive biocomposites for bone healing in critical-size rabbit calvarial defects

Craniofacial injuries can result from trauma, tumor ablation, or infection and may require multiple surgical revisions. To address the challenges associated with treating craniofacial bone defects, an ideal material should have the ability to fit complex defects (i.e. be conformable), provide temporary protection to the brain until the bone heals, and enhance tissue regeneration with the delivery of biologics. In this study, we evaluated the ability of injectable lysine-derived polyurethane (PUR)/allograft biocomposites to promote bone healing in critical-size rabbit calvarial defects. The biocomposites exhibited favorable injectability, characterized by a low yield stress to initiate flow of the material and a high initial viscosity to minimize the adverse phenomena of extravasation and filter pressing. After injection, the materials cured within 10-12 min to form a tough, elastomeric solid that maintained mechanical integrity during the healing process. When injected into a critical-size calvarial defect in rabbits, the biocomposites supported ingrowth of new bone. The addition of 80 µg mL(-1) recombinant human bone morphogenetic protein-2 (rhBMP-2) enhanced new bone formation in the interior of the defect, as well as bridging of the defect with new bone. These observations suggest that injectable reactive PUR/allograft biocomposites are a promising approach for healing calvarial defects by providing both mechanical stability as well as local delivery of rhBMP-2.

A Cellular Perspective to Bioceramic Scaffolds for Bone Tissue Engineering: the State of the Art

A vast number of manufacturing techniques have been employed in the last five years to manufacture three dimensional (3D) calcium phosphate (CaP) scaffolds, with the intention to replicate the architecture of native bone as well as to repair and restore bone function. Design features such as architectural control and sintering temperature and their impact on scaffold performance is presented in this review. In vitro cell responses to bioceramic scaffolds and their in vivo performances have been enhanced. Current frontiers of active research on HA scaffolds have included the relationship between fluid flow and mechanotransduction as well as cell signaling pathways that induce endothelial cell recruitment and angiogenesis. Additionally, current research has focused on a better understanding of cell signaling and its environmental cues. The availability of non-invasive and non-destructive quantitative imaging modalities has also become critical in aiding the characterization of scaffolds and predicting scaffold performance. It is thus anticipated that further knowledge gained from this research will allow the overall advancement of scaffolds that can be clinically used to restore large bone defects.

Connexin 43 Channels Are Essential for Normal Bone Structure and Osteocyte Viability

Connexin (Cx) 43 serves important roles in bone function and development. Targeted deletion of Cx43 in osteoblasts or osteocytes leads to increased osteocyte apoptosis, osteoclast recruitment, and reduced biomechanical properties. Cx43 forms both gap junction channels and hemichannels, which mediate the communication between adjacent cells or between cell and extracellular environments, respectively. Two transgenic mouse models driven by a DMP1 promoter with the overexpression of dominant negative Cx43 mutants were generated to dissect the functional contribution of Cx43 gap junction channels and hemichannels in osteocytes. The R76W mutant blocks the gap junction channel, but not the hemichannel function, and the Δ130‐136 mutant inhibits activity of both types of channels. Δ130‐136 mice showed a significant increase in bone mineral density compared to wild‐type (WT) and R76W mice. Micro–computed tomography (µCT) analyses revealed a significant increase in total tissue and bone area in midshaft cortical bone of Δ130‐136 mice. The bone marrow cavity was expanded, whereas the cortical thickness was increased and associated with increased bone formation along the periosteal area. However, there is no significant alteration in the structure of trabecular bone. Histologic sections of the midshaft showed increased apoptotic osteocytes in Δ130‐136, but not in WT and R76W, mice which correlated with altered biomechanical and estimated bone material properties. Osteoclasts were increased along the endocortical surface in both transgenic mice with a greater effect in Δ130‐136 mice that likely contributed to the increased marrow cavity. Interestingly, the overall expression of serum bone formation and resorption markers were higher in R76W mice. These findings suggest that osteocytic Cx43 channels play distinctive roles in the bone; hemichannels play a dominant role in regulating osteocyte survival, endocortical bone resorption, and periosteal apposition, and gap junction communication is involved in the process of bone remodeling.

Novel osteoinductive photo-cross-linkable chitosan-lactide-fibrinogen hydrogels enhance bone regeneration in critical size segmental bone defects

The purpose of this study was to develop and characterize a novel photo-cross-linkable chitosan-lactide-fibrinogen (CLF) hydrogel and evaluate the efficacy of bone morphogenetic protein-2 (BMP-2) containing a CLF hydrogel for osteogenesis in vitro and in vivo. We synthesized the CLF hydrogels and characterized their chemical structure, degradation rate, compressive modulus and in vitro BMP-2 release kinetics. We evaluated bioactivities of the BMP-2 containing CLF hydrogels (0, 50, 100 and 500ngml(-1)) in vitro using W-20-17 preosteoblast mouse bone marrow stromal cells and C2C12 mouse myoblast cells. The effect of BMP-2 containing CLF gels (0, 0.5, 1, 2 and 5μg) on bone formation was evaluated using rat critical size segmental bone defects for 4weeks. Fourier transform infrared spectroscopy spectra and scanning electron microscopy images showed chemical and structural changes by the addition of fibrinogen into the chitosan-lactide copolymer. The incorporation of fibrinogen molecules significantly increased the compressive modulus of the hydrogels. The in vitro BMP-2 release study showed initial burst releases from the CLF hydrogels followed by sustained releases, regardless of the concentration of the BMP-2 over 4weeks. Cells in all groups were viable in the presence of the hydrogels regardless of BMP-2 doses, indicating non-cytotoxicity of hydrogels. Alkaline phosphate activity and mineralization of cells exhibited dose dependence on BMP-2 containing CLF hydrogels. Radiography, microcomputed tomography and histology confirmed that the BMP-2 containing CLF hydrogels prompted neo-osteogenesis and accelerated healing of the defects in a dose-dependent manner. Thus the CLF hydrogel is a promising delivery system of growth factors for bone regeneration.