Abstract
Porous microspheres have the potential for use as injectable bone fillers to obviate the need for open surgery. Successful bone fillers must be able to support vascularisation since tissue engineering scaffolds often cease functioning soon after implantation due to a failure to vascularise rapidly. Here, we test the angiogenic potential of a tissue engineered bone filler based on a photocurable acrylate-based high internal phase emulsion (HIPE). Highly porous microspheres were fabricated via two processes, which were compared. One was taken forward and investigated for its ability to support human mesenchymal progenitor cells and angiogenesis in a chorioallantoic membrane (CAM) assay. Porous microspheres with either a narrow or broad size distribution were prepared via a T-junction microfluidic device or by a controlled stirred-tank reactor of the HIPE water in oil in water (w/o/w), respectively. Culture of human embryonic stem cell-derived mesenchymal progenitor (hES-MP) cells showed proliferation over 11 days and formation of cell-microsphere aggregates. In-vitro, hES-MP cells were found to migrate into microspheres through their surface pores over time. The presence of osteoblasts, differentiated from the hES-MP cells, was evidenced through the presence of collagen and calcium after 30 days. Microspheres pre-cultured with cells were implanted into CAM for 7 days and compared with control microspheres without pre-cultured cells. The hES-MP seeded microspheres supported greater angiogenesis, as measured by the number of blood vessels and bifurcations, while the empty scaffolds attracted host chick cell ingrowth. This investigation shows that controlled fabrication of porous microspheres has the potential to create an angiogenic, bone filling material for use as a cell delivery vehicle.
Highlights
An important target for tissue engineering large defects is bone, where critical size defects can be treated with synthetic bone fillers, normally putties or pastes that are potentially injectable
The internal porosity of the polyHIPE can be controlled via the high internal phase emulsion (HIPE) pre-processing conditions
The stirring rate and temperature used during the formation of the primary emulsion, or water in oil (w/o) emulsion, had a direct effect on the pore size distribution of the resulting polyHIPE
Summary
An important target for tissue engineering large defects is bone, where critical size defects can be treated with synthetic bone fillers, normally putties or pastes that are potentially injectable. To support rapid cell ingrowth and allow vascularisation, an injectable bone filler should ideally be highly porous, and in this study, we investigate highly porous microspheres to achieve both. These porous microspheres can be used for many applications in tissue engineering such as microcarriers for cell expansion, cell implantation, delivery of bioactive agents, and building blocks for (self-assembled) scaffolds.. If the continuous phase is composed of suitable monomers and cross-linkers, a highly porous foam (polyHIPE) can be produced upon curing.26 This technique is referred to as the controlled stirred-tank reactor (CSTR) method. The aim of this study was to identify an controllable manufacturing method for highly porous microsphere scaffolds capable of supporting mesenchymal stem cell (MSC)-like cells and to measure their vascularisation potential using a chorioallantoic membrane (CAM) assay
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