Engineering Vascularized Bone Grafts by Integrating a Biomimetic Periosteum and β-TCP Scaffold

Abstract

Treatment of large bone defects using synthetic scaffolds remain a challenge mainly due to insufficient vascularization. This study is to engineer a vascularized bone graft by integrating a vascularized biomimetic cell-sheet-engineered periosteum (CSEP) and a biodegradable macroporous beta-tricalcium phosphate (β-TCP) scaffold. We first cultured human mesenchymal stem cells (hMSCs) to form cell sheet and human umbilical vascular endothelial cells (HUVECs) were then seeded on the undifferentiated hMSCs sheet to form vascularized cell sheet for mimicking the fibrous layer of native periosteum. A mineralized hMSCs sheet was cultured to mimic the cambium layer of native periosteum. This mineralized hMSCs sheet was first wrapped onto a cylindrical β-TCP scaffold followed by wrapping the vascularized HUVEC/hMSC sheet, thus generating a biomimetic CSEP on the β-TCP scaffold. A nonperiosteum structural cell sheets-covered β-TCP and plain β-TCP were used as controls. In vitro studies indicate that the undifferentiated hMSCs sheet facilitated HUVECs to form rich capillary-like networks. In vivo studies indicate that the biomimetic CSEP enhanced angiogenesis and functional anastomosis between the in vitro preformed human capillary networks and the mouse host vasculature. MicroCT analysis and osteocalcin staining show that the biomimetic CSEP/β-TCP graft formed more bone matrix compared to the other groups. These results suggest that the CSEP that mimics the cellular components and spatial configuration of periosteum plays a critical role in vascularization and osteogenesis. Our studies suggest that a biomimetic periosteum-covered β-TCP graft is a promising approach for bone regeneration.

Vascularization in Bone Tissue Engineering Constructs

“…84, 123 Numerous studies have been performed on cell mono- or co-cultures in scaffolds for improved vascular formation. 1, 20, 44, 70 Even though cells in scaffolds can promote the formation of microvascular networks, it usually takes a relatively long period, from days to weeks, to develop functional vasculature in vitro and in vivo , 7, 43, 44 so ischemia could set in before this process is sufficiently developed to restore blood perfusion. 55 As a result, cellularized constructs have met with limited implementation in clinical practice due to long-term loss of viability and adverse host responses.…”

“…Collectively, spatiotemporal control of cell and signal presentation has been investigated as a strategy to facilitate tissue formation and scaffold remodeling. 88 One promising scheme is to mimic biological cascades by sequential delivery of growth factors 50, 68 or cells 39, 44, 78, 92 to enhance tissue regeneration as compared to approaches involving simultaneous GF release 68 or uniform cell loading. 39 …”

Bone Tissue Engineering with Multilayered Scaffolds—Part I: An Approach for Vascularizing Engineered Constructs In Vivo

“…[1][2][3][4] Several approaches are being investigated to achieve functional vascularization in engineered tissues similar to that seen in vivo. [4][5][6][7][8] However, less than optimal scaffold architecture remains as one of the crucial factors, which affect the depth, rate of vascular ingrowth, and spatial distribution of vessels in the engineered construct. [9][10][11][12] Both angiogenesis, where the development of new vessels occurs from pre-existing blood vessels, and vasculogenesis, where blood vessels are formed through the de novo differentiation of stem cells into endothelial cells and/or their progenitors, have been studied by researchers to overcome the problem of inadequate vascularization of tissue-engineered constructs.…”

Pre-vascularization Enhances Therapeutic Effects of Human Mesenchymal Stem Cell Sheets in Full Thickness Skin Wound Repair

“…For example, a pre-vascularized bone graft implanted subcutaneously in nude mice demonstrated a much higher density of microvessels in vivo than a non-vascularized bone graft. In addition, more bone matrix was found in the pre-vascularized samples 20. A pre-vascularized cardiac patch grafted to a rat heart showed an increased number of new patent blood vessels than its avascular counterpart.…”