Angiogenic and inflammatory response to biodegradable scaffolds in dorsal skinfold chambers of mice

Quick layer-by-layer assembly of aligned multilayers of vascular smooth muscle cells in deep microchannels

One of the main challenges in vascular tissue engineering has been mimicking the complex native three-dimensional (3D) architecture of smooth muscle cells (SMCs). In the current study, we performed layer-by-layer (LBL) seeding of SMCs in a microchanneled scaffold, with or without interleaving a thin layer of collagen type I hydrogel, toward fabricating the 3D microarchitecture. This LBL process avoids the "steric hindrance" effect observed in direct 3D culture of SMCs in collagen hydrogel. More importantly, the LBL process enables the building up of multilayers of aligned and confluent SMCs. Within each layer, the SMCs as well as the SMC F-actin and alpha-actin filaments align along the direction of the scaffold microchannels, which would potentially improve the tensile and contractile strength of the tissue engineered construct, desirable properties for an engineered vasculature. In addition, rapid two-dimensional (2D) patterning of SMCs is possible with high seeding density, which makes the LBL method feasible for fabrication of multilayered structures in a short time, rendering it useful in clinical therapeutic applications.

In vitro and in vivo effects of deoxyribonucleic acid-based coatings funtionalized with vascular endothelial growth factor

Vascularization is important in wound healing and essential for tissue ingrowth into porous tissue-engineering matrices. Furthermore, peri-implant tissue vascularization is known to be important for the functionality of subcutaneously implanted biosensors (e.g., glucose sensors). As a first exploration of the use of deoxyribonucleic acid (DNA)-based coatings for the optimization of biosensor functionality, this study focused on the effect of DNA-based coatings functionalized with vascular endothelial growth factor (VEGF) on in vitro endothelial cell behavior and vascularization of the peri-implant tissue in vivo. To that end, DNA-based coatings consisting of poly-D-lysine and DNA were functionalized with different amounts of VEGF (25 and 250 ng) and compared to non-coated controls and non-functionalized DNA-based coatings. The results demonstrated the superiority of VEGF-functionalized DNA-based coatings in increasing endothelial cell proliferation and migration in vitro over non-coated controls and non-functionalized DNA-based coatings. In vivo, a significant increase in vascularization of the peri-implant area was observed for VEGF-functionalized DNA-based coatings. Because no dosage-dependent effects were observed, future experiments should focus on optimizing VEGF concentration for this purpose. Additionally, the administration of VEGF in combination with other (pro-angiogenic) factors should be considered.

Comparison of Hydrogels in theIn VivoFormation of Tissue-Engineered Bone Using Mesenchymal Stem Cells and Beta-Tricalcium Phosphate

Availability of grafts and morbidity at the donor site limit autologous transplantation in patients requiring bone reconstruction. A tissue-engineering approach can overcome these limitations by producing bone-like tissue of custom shape and size from isolated cells. Several hydrogels facilitate osteogenesis on porous scaffolds; however, the relative suitability of various hydrogels has not been rigorously assessed. Fibrin glue, alginate, and collagen I hydrogels were mixed with swine bone marrow-derived differentiated mesenchymal stem cells (MSCs), applied to 3-dimensionally printed porous beta-tricalcium phosphate (beta-TCP) scaffolds and implanted subcutaneously in nude mice. Although noninvasive assessment of osteogenesis in 3 dimensions is desirable for monitoring new bone formation in vivo, correlations with traditional histological and mechanical testing need to be established. High-resolution volumetric computed tomography (VCT) scanning, histological examination, biomechanical compression testing, and osteonectin (ON) expression were performed on excised scaffolds after 1, 2, 4, and 6 weeks of subcutaneous implantation in mice. Statistical correlation analyses were performed between radiological density, stiffness, and ON expression. Use of collagen I as a hydrogel carrier produced superior bone formation at 6 weeks, as demonstrated using VCT scanning with densities similar to native bone and the highest compression values. Continued contribution of the seeded MSCs was demonstrated using swine-specific messenger ribonucleic acid probes. Radiological density values correlated closely with the results of histological and biomechanical testing and ON expression. High-resolution VCT is a promising method for monitoring osteogenesis.