Evaluation of bone matrix and demineralized bone matrix incorporated PLGA matrices for bone repair

The aim of this study was to evaluate the composite matrices prepared using Poly(lactic-co-glycolic acid)- PLGA (85:15) by incorporating human bone matrix (BM) powder or demineralized bone matrix (DBM) powder with the weight ratio of polymer: BM or DBM (75:25) to apply for bone repair. Murine Bone Marrow Stromal Cell (BMSC) attachment was studied with different time points at 30 min, 1 h, 2 h, 4 h, and 6 h for BM/PLGA, DBM/PLGA and PLGA control matrices. All types of matrices were linearly increased the BMSC attachment with the increase of time. Significantly higher number of BMSCs was attached to the both BM/PLGA and DBM/PLGA matrices after 2 h compared to the controls. If BM or DBM is incorporated into biodegradable PLGA matrices and cultured with BMSCs, those composite matrices could be potentially used for bone tissue engineering applications. In addition, particle migration and handling difficulties in DBM powder in clinical applications eliminate using a PLGA matrix. Furthermore, we have observed that DBM/PLGA matrices were structurally stronger compared to the BM/PLGA or control PLGA matrices when they exposed to physiological environment for 72 days.     

Enhanced osteoinductive capacity and decreased variability by enrichment of demineralized bone matrix with a bone protein extract

Osteoinductive capacity of demineralized bone matrix (DBM) is sometimes insufficient or shows high variability between different batches of DBM. Here, we tried to improve its osteoinductive activity by alkali-urea or trypsin treatment but this strategy was unsuccessful. Then, we tested the enrichment of DBM with a bone protein extract (BPE) containing osteogenic growth factors comparing two sources: cortical bone powder and DBM. The osteoinductive capacity (alkaline phosphatase activity) of the obtained BPEs was evaluated in vitro in C2C12 cells. Specific protein levels present in the different BPE was determined by enzyme-linked immunosorbent assay or by a multiplex assay. BPE from cortical bone powder showed a lack of osteoinductive effect, in agreement with the low content on osteoinductive factors. In contrast, BPE from DBM showed osteoinductive activity but also high variability among donors. Thus, we decided to enrich DBM with BPE obtained from a pool of DBM from different donors. Following this strategy, we achieved increased osteoinductive activity and lower variability among donors. In conclusion, the use of a BPE obtained from a pool of demineralized bone to enrich DBM could be used to increase its osteoinductive effect and normalize the differences between donors.

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Loading of VEGF to the heparin cross-linked demineralized bone matrix improves vascularization of the scaffold

Deficient vascularization is one of the prominent shortcomings of porous tissue-engineering scaffolds, which results in insufficient oxygen and nutrients transportation. Here, heparin cross-linked demineralized bone matrices (HC-DBM) pre-loaded with vascular endothelial growth factor (VEGF) were designed to promote cells and new microvessels invasion into the matrices. After being chemical crosslinked with heparin by N-hydroxysuccinimide and N-(3-di-methylaminopropyl)-N’-ethylcarbodiimide, the scaffold could bind more VEGF than the non-crosslinked one and achieve localized and sustained delivery. The biological activity of VEGF binding on heparinized collagen was demonstrated by promoting endothelial cells proliferation. Evaluation of the angiogenic potential of heparinized DBM loaded with VEGF was further investigated by subcutaneous implantation. Improved angiogenesis of heparinized DBM loaded with VEGF was observed from haematoxylin-eosin staining and immunohistochemistry examination. The results demonstrated that heparin cross-linked DBM binding VEGF could be a useful strategy to stimulate cells and blood vessels invasion into the scaffolds.     

Restoration of mandibular bone defects with demineralized bone matrix combined with three-dimensional cultured bone marrow-derived mesenchymal stem cells in minipig models

Mandibular defects, caused by congenital, pathological or iatrogenic insults, can significantly affect patient quality of life. The reconstruction of mandible has recently gained the interest of clinical and tissue engineering researchers. The purpose of this study was to evaluate the effectiveness of three-dimensional (3-D) cultured autologous grafts prepared using bone marrow-derived mesenchymal stem cells (BMSCs) combined with demineralized bone matrix (DBM) scaffolds for the restoration of mandibular defects. Cylindrical defects were created in the mandibular body of minipigs and filled with 3D-cultured BMSCs/DBM autografts, 2D-cultured BMSCs/DBM autografts, DBM material (without cells), or were left unfilled (blank). Using computed tomographic (CT) imaging and histological staining, we found that treatment of mandibular defects using 3-D cultured BMSCs/DBM autografts offered improvements in bone formation over both 2-D cultured autografts and cell-free DBM scaffolds. We found increased osteoid formation in 3D and 2D cultures, with more osteogenic cells present in the 3D constructs. We suggest that 3-D cultured homograft BMSCs combined with DBM scaffolds represents a new strategy for bone reconstruction, with potential future clinical applicability.     

Analysis of bovine-derived demineralized bone extracts

Demineralized bone factors are capable of stimulating bone regeneration through an osteoinductive mechanism and thus it has been recognized as a good bone graft. In this study, a kind of demineralized bone extracts (DBX) derived from bovine tibia by a chemical route. The extracts thus obtained were analyzed for their bio-chemical and physical properties using various techniques and results provided quite interesting insights into the demineralization process. There is no significant evidence of mineral phase associated with the connective tissue detected during chemical as well as physical testing, indicating the formation of DBX. This kind of bone extracts may used as a bone graft material and as a substrate for the growth of biomimetic apatites.     

Propagation of ultrasonic waves through demineralized cancellous bone

Ultrasonic velocity is determined in a number of bovine cancellous (spongy) bone samples by using a double-probe-through-transmission ultrasonic pulse technique. The ultrasonic velocity, total mineral content, bone density, and solid volume fraction of the specimen were determined. The relation between fast velocity and each of the other parameters was examined to explore the best correlation using linear, logarithmic, power, and exponential relationships. There is a strong positive relationship between ultrasonic velocity and each of the other parameters. The exponential model fits the data better than the linear model, logarithmic model, and power model. Biot's theory also is used to predict the velocity of ultrasound in the demineralized bone. It is shown that the transmission of ultrasonic pulses in the cancellous bone samples can be adequately described using Biot's theory. The different parameters occurring in the Biot theory have been measured independently, and the calculation has been compared with measured velocity of water-saturated bone samples. The correlation coefficients for regression analysis between the experimental velocities and those predicted by Biot's theory are greater than 0.86.     

Repair of rabbit femoral condyle bone defects with injectable nanohydroxyapatite/chitosan composites

Repair of massive bone loss remains a challenge to the orthopaedic surgeons. Autologous and allogenic bone grafts are choice for bone reconstructive surgery, but limited availability, risks of transmittable diseases and inconsistent clinical performances have prompted the development of tissue engineering. In the present work, the bone regeneration potential of nanohydroxyapatite/chitosan composite scaffolds were compared with pure chitosan scaffolds when implanted into segmental bone defects in rabbits. Critical size bone defects (6 mm diameter, 10 mm length) were created in the left femoral condyles of 43 adult New Zealand white rabbits. The femoral condyle bone defects were repaired by nanohydroxyapatite/chitosan compositions, pure chitosan or left empty separately. Defect-bridging was detected by plain radiograph and quantitative computer tomography at eight and 12 weeks after surgery. Tissue samples were collected for gross view and histological examination to determine the extent of new bone formation. Eight weeks after surgery, more irregular osteon formation was observed in the group treated with nanohydroxyapatite/chitosan composites compared with those treated with pure chitosan. 12 weeks after surgery, complete healing of the segmental bone defect was observed in the nanohydroxyapatite/chitosan-group, while the defect was still visible in the chitosan-group, although the depth of the defect had diminished. These observations suggest that the injectable nanohydroxyapatite/chitosan scaffolds are potential candidate materials for regeneration of bone loss.     

Tribological performance of the biological components of synovial fluid in artificial joint implants

Abstract

The concentration of biological components of synovial fluid (such as albumin, globulin, hyaluronic acid, and lubricin) varies between healthy persons and osteoarthritis (OA) patients. The aim of the present study is to compare the effects of such variation on tribological performance in a simulated hip joint model. The study was carried out experimentally by utilizing a pin-on-disk simulator on ceramic-on-ceramic (CoC) and ceramic-on-polyethylene (CoP) hip joint implants. The experimental results show that both friction and wear of artificial joints fluctuate with the concentration level of biological components. Moreover, the performance also varies between material combinations. Wear debris sizes and shapes produced by ceramic and polyethylene were diverse. We conclude that the biological components of synovial fluid and their concentrations should be considered in order to select an artificial hip joint to best suit that patient.     

Multibaseline InSAR height estimation through joint covariance matrix fitting

A new joint processing method based on joint covariance matrix fitting is presented for the multibaseline synthetic aperture radar interferometry. This method can make full use of the interferometric information embedded in the joint covariance matrix to estimate the terrain height without eigendecomposition and eigenspace division, and is insensitive to the rank variation of the joint signal subspace. By fitting the sample joint covariance matrix tapered with the coherence matrix, this method can work robustly with a finite sample support, which also makes it possible to recover the detail of terrain profile with a small neighbouring sample support. The results of numerical simulations demonstrate the validation of the proposed method.     

The effects of bovine trabecular bone matrix particulates on cortical bone repair

This paper reports the effects of a synthetic bone substitute and bone allograft on cortical bone repair in an experimental model. To test the hypothesis that bovine trabecular bone matrix, BBM, can enhance the repair rate of cortical bone, osteotomies were created in the rabbit fibula and filled with either allograft or BBM particulates or left empty as controls. At five weeks post-surgery, mechanical tests and histological evaluations were performed. No significant differences were observed in the mechanical properties of the healing bone in the three animal groups (n=6). Histologically, the medullary cavity was obstructed and the cross-sectional area ratio of the osteotomies to intact bone was approximately 3 : 1. Highly significant area differences were observed between the intact bone group and both the BBM and the allograft groups . At the junction between the original bone and the newly formed bone, both woven and lamellar bone microstructures were prevalent. However, in the BBM filled defects, the woven bone microstructure was not ostentatious. It is concluded that failure to demonstrate significantly differences between the treatments were due to the small sample sizes and or the efficacy of the tensile analysis.     

Misleading signals in joint schemes for the mean vector and covariance matrix

In multivariate statistical process control, it is recommendable to run two individual charts: one for the process mean vector and another one for the covariance matrix. The resulting joint scheme provides a way to satisfy Shewhart's dictum that proper process control implies monitoring both process location and spread. The multivariate quality characteristic is deemed to be out of control whenever a signal is triggered by either individual chart of the joint scheme. Consequently, a shift in the mean vector can be misinterpreted as a shift in the covariance matrix and vice versa. Compelling results are provided to give the quality control practitioner an idea of how joint schemes for the mean vector and covariance matrix are prone to trigger misleading signals that will likely lead to a incorrect diagnostic of which parameter has changed.     

Optothermophysical properties of demineralized human dental enamel determined using photothermally generated diffuse photon density and thermal-wave fields

Noninvasive dental diagnostics is a growing discipline since it has been established that early detection and quantification of tooth mineral loss can reverse caries lesions in their incipient state. A theoretical coupled diffuse photon density and thermal-wave model was developed and applied to photothermal radiometric frequency responses, fitted to experimental data using a multiparameter simplex downhill minimization algorithm for the extraction of optothermophysical properties from artificially demineralized human enamel. The aim of this study was to evaluate the reliability and robustness of the advanced fitting algorithm. The results showed a select group of optical and thermal transport parameters and thicknesses were reliably extracted from the computational fitting algorithm. Theoretically derived thicknesses were accurately predicted, within about 20% error, while the estimated error in the optical and thermal property evaluation was within the values determined from early studies using destructive analyses. The high fidelity of the theoretical model illustrates its efficacy, reliability, and applicability toward the nondestructive characterization of depthwise inhomogeneous sound enamel and complex enamel caries lesions.     

SAW and pseudo-SAW properties using matrix methods

Pseudo-surface-waves (PSAW's), or leaky SAW's, were first recognized over 25 years ago and the phase velocity (v(p)) and attenuation per wavelength (alphalambda) of PSAW modes for nonpiezoelectrics were calculated soon after. Since the seventies progress has been made in exploiting the higher velocities and electromechanical coupling constants (K(2)=2Deltav/v) achievable with PSAW's for piezoelectric device applications; this has stimulated new interest in the search for piezoelectric materials with orientations which have low alphalambda, high K(2), high v (p). Procedures for calculating the PSAW properties (v(p ), alphalambda, and K(2)) are not very explicitly given. In light of the preceding we present in this paper a review of the basic features of SAW and PseudoSAW's using the matrix method. In this paper: the mechanically free open-circuited and short-circuited surface wave boundary value problems for piezoelectrics are formulated using the matrix method; two types of modes (SAW and PSAW) are described; and a number of computationally simple, frequency independent analytical functions are derived, from which alphalambda, v(p ), and K(2) are calculated for any direction on any material plane using commercially available PC software. The relationship of these functions to the effective permittivity concept, favoured by many researchers, is demonstrated and illustrative numerical examples for the PSAW's reveals that low-loss orientations are quite sensitive to material constant values.