The impact of various scaffold components on vascularized bone constructs

Influence of Xenogeneic and Alloplastic Carriers for Bone Augmentation on Human Unrestricted Somatic Stem Cells

Alloplastic and xenogeneic bone grafting materials are frequently used for bone augmentation. The effect of these materials on precursor cells for bone augmentation is yet to be determined. The aim of this study was to ascertain, in vitro, how augmentation materials influence the growth rates and viability of human unrestricted somatic stem cells. The biocompatibility of two xenogeneic and one alloplastic bone graft was tested using human unrestricted somatic stem cells (USSCs). Proliferation, growth, survival and attachment of unrestricted somatic stem cells were monitored after 24 h, 48 h and 7 days. Furthermore, cell shape and morphology were evaluated by SEM. Scaffolds were assessed for their physical properties by Micro-CT imaging. USSCs showed distinct proliferation on the different carriers. Greatest proliferation was observed on the xenogeneic carriers along with improved viability of the cells. Pore sizes of the scaffolds varied significantly, with the xenogeneic materials providing greater pore sizes than the synthetic inorganic material. Unrestricted somatic stem cells in combination with a bovine collagenous bone block seem to be very compatible. A scaffold’s surface morphology, pore size and bioactive characteristics influence the proliferation, attachment and viability of USSCs.

Endothelialized microrods for minimally invasive in situ neovascularization

Despite the significant advancements in fabricating various scaffolding systems over the past decades, generation of functional tissues towards vascularization remains challenging for the currently available biofabrication approaches. On the other hand, the applicability of traditional surgical transplantation of vascularized tissue constructs is sometimes limited due to the sophisticated surgical procedures, which are invasive, leading to increased risks of scar formation and infection. Considering these facts, we present an innovative platform, the angiogenic microrods composed of sodium alginate/gelatin harboring proliferating endothelial cells using a specially designed double T-junction microfluidic device with an expansion chamber, for achieving minimally invasive neovascularization in situ. Such vessel-like microarchitectures could be derived through controlled penetration of the crosslinker genepin for the gelatin phase, ensuing differential degrees in crosslinking of peripheral and central portions of the microstructures, thus resulting in the formation of vascular lumen-like hollow cavities via endothelial cell migration and proliferation during culture in vitro. Furthermore, in vivo performance of the microrods was explored. We believe that the development of these modular microrods for minimally invasive delivery is of great interest and offers a convenient approach for vascularization in situ.

Bone physiology as inspiration for tissue regenerative therapies

The development, maintenance of healthy bone and regeneration of injured tissue in the human body comprise a set of intricate and finely coordinated processes. However, an analysis of current bone regeneration strategies shows that only a small fraction of well-reported bone biology aspects has been used as inspiration and transposed into the development of therapeutic products. Specific topics that include inter-scale bone structural organization, developmental aspects of bone morphogenesis, bone repair mechanisms, role of specific cells and heterotypic cell contact in the bone niche (including vascularization networks and immune system cells), cell-cell direct and soluble-mediated contact, extracellular matrix composition (with particular focus on the non-soluble fraction of proteins), as well as mechanical aspects of native bone will be the main reviewed topics. In this Review we suggest a systematic parallelization of (i) fundamental well-established biology of bone, (ii) updated and recent advances on the understanding of biological phenomena occurring in native and injured tissue, and (iii) critical discussion of how those individual aspects have been translated into tissue regeneration strategies using biomaterials and other tissue engineering approaches. We aim at presenting a perspective on unexplored aspects of bone physiology and how they could be translated into innovative regeneration-driven concepts.

Vascularization in Craniofacial Bone Tissue Engineering

Craniofacial bones, separate from the appendicular skeleton, bear a significant amount of strain and stress generated from mastication-related muscles. Current research on the regeneration of craniofacial bone focuses on the reestablishment of an elaborate vascular network. In this review, current challenges and efforts particularly in advances of scaffold properties and techniques for vascularization remodeling in craniofacial bone tissue engineering will be discussed. A microenvironment of ischemia and hypoxia in the biomaterial core drives propagation and reorganization of endothelial progenitor cells (EPCs) to assemble into a primitive microvascular framework. Co-culture strategies and delivery of vasculogenic molecules enhance EPCs' differentiation and stimulate the host regenerative response to promote vessel sprouting and strength. To optimize structural and vascular integration, well-designed microstructures of scaffolds are biologically considered. Proper porous structures, matrix stiffness, and surface morphology of scaffolds have a profound influence on cell behaviors and thus affect revascularization. In addition, advanced techniques facilitating angiogenesis and vaculogenesis have also been discussed. Oxygen delivery biomaterials, scaffold-free cell sheet techniques, and arteriovenous loop-induced axial vascularization strategies bring us new understanding and powerful strategies to manage revascularization of large craniofacial bone defects. Although promising histological results have been achieved, the efficient perfusion and functionalization of newly formed vessels are still challenging.