Analysis of the osteoinductive capacity and angiogenicity of an in vitro generated extracellular matrix.

Item does not contain fulltextIn this study, the osteoinductive potential of an in vitro generated extracellular matrix (ECM) deposited by marrow stromal cells seeded onto titanium fiber mesh scaffolds and cultured in a flow perfusion bioreactor was investigated. Culture periods of 8, 12, and 16 days were selected to allow for different amounts of ECM deposition by the cells as well as ECM with varying degrees of maturity (Ti/ECM/d8, Ti/ECM/d12, and Ti/ECM/d16, respectively). These ECM-containing constructs were implanted intramuscularly in a rat animal model. After 56 days, histologic analysis of retrieved constructs revealed no bone formation in any of the implants. Surrounding many of the implants was a fibrous capsule, which was often interspersed with fat cells. Within the pore spaces, the predominant tissue response was the presence of blood vessels and young fibroblasts or fat cells. The number of blood vessels on a per area basis calculated from a histomorphometric analysis increased as a function of the amount of ECM within the implanted constructs, with a significant difference between Ti/ECM/d16 and plain Ti constructs. These results indicate that although an in vitro generated ECM alone may not induce bone formation at an ectopic site, its use may enhance the vascularization of implanted constructs

Methods: a comparative analysis of radiography, microcomputed tomography, and histology for bone tissue engineering.

Contains fulltext : 48806.pdf (publisher's version ) (Open Access)This study focused on the assessment of radiography, microcomputed tomography, and histology for the evaluation of bone formation in a 15.0-mm defect in the rabbit radius after the implantation of a tissue-engineered construct. Radiography was found to be useful as a noninvasive method for obtaining images of calcified tissue throughout the time course of the experiment. With this method, however, image quality was low, making it difficult to obtain precise information about the location and quantity of the bone formed. Microcomputed tomography was used to create three-dimensional reconstructions of the bone (25-microm resolution). These reconstructions allowed for greater spatial resolution than the radiography, but did not allow for imaging of the implanted scaffold material or the surrounding, nonmineralized tissue. To visualize all materials within the defect area at the cellular level, histology was used. Histological analysis, however, is a destructive technique that did not allow for any further analysis of the samples. Each technique examined here has its own advantages and limitations, but each yields unique information regarding bone regeneration. It is only through the use of all three techniques that complete characterization of the bone growth and tissue/construct responses after implantation in vivo

High Doses of Bone Morphogenetic Protein 2 Induce Structurally Abnormal Bone and Inflammation In Vivo

The major Food and Drug Association–approved osteoinductive factors in wide clinical use are bone morphogenetic proteins (BMPs). Although BMPs can promote robust bone formation, they also induce adverse clinical effects, including cyst-like bone formation and significant soft tissue swelling. In this study, we evaluated multiple BMP2 doses in a rat femoral segmental defect model and in a minimally traumatic rat femoral onlay model to determine its dose-dependent effects. Results of our femoral segmental defect model established a low BMP2 concentration range (5 and 10 μg/mL, total dose 0.375 and 0.75 μg in 75 μg total volume) unable to induce defect fusion, a mid-range BMP2 concentration range able to fuse the defect without adverse effects (30 μg/mL, total dose 2.25 μg in 75 μg total volume), and a high BMP2 concentration range (150, 300, and 600 μg/mL, total dose 11.25, 22.5, and 45 μg in 75 μg total volume) able to fuse the defect, but with formation of cyst-like bony shells filled with histologically confirmed adipose tissue. In addition, compared to control, 4 mg/mL BMP2 also induced significant tissue inflammatory infiltrates and exudates in the femoral onlay model that was accompanied by increased numbers of osteoclast-like cells at 3, 7, and 14 days. Overall, we consistently reproduced BMP2 side effects of cyst-like bone and soft tissue swelling using high BMP2 concentration approaching the typical human 1500 μg/mL

Novel osteoinductive biomimetic scaffolds stimulate human osteoprogenitor activity: implications for skeletal repair

The development of new bone formation strategies offers tremendous therapeutic implications in a variety of musculoskeletal diseases. One approach involves harnessing the regenerative capacity of osteoprogenitor bone cells in combination with biomimetic scaffolds generated from appropriate scaffold matrices and osteoinductive factors. The aims of our study were to test the efficacy of two innovative osteoinductive agents: the osteoblast stimulating factor-1 (osf-1), an extracellular matrix-associated protein, and osteoinductive extracts of Saos-2 cells on human osteoprogenitor cells. Saos-2 extracted osteoinductive factors significantly stimulated alkaline phosphatase specific activity in basal and osteogenic conditions. Osf-1 significantly stimulated chemotaxis, total colony formation, alkaline phosphatase-positive colony formation, and alkaline phosphatase specific activity at concentrations as low as 10 pg/ml compared with control cultures. Osteoinductive factors present in Saos-2 cell extracts and osf-1 promoted adhesion, migration, expansion, and differentiation of human osteoprogenitor cells on 3-D scaffolds. The successful generation of 3-D biomimetic structures incorporating osf-1 or osteoinductive factors from Saos-2 cells indicates their potential for de novo bone formation that exploits cell-matrix interactions