Michael Shin

In Vivo Bone Tissue Engineering Using Mesenchymal Stem Cells on a Novel Electrospun Nanofibrous Scaffold

The objective of this study was to assess bone formation from mesenchymal stem cells (MSCs) on a novel nanofibrous scaffold in a rat model. A highly porous, degradable poly(epsilon-caprolactone) (PCL) scaffold with an extracellular matrix-like topography was produced by electrostatic fiber spinning. MSCs derived from the bone marrow of neonatal rats were cultured, expanded, and seeded on the scaffolds. The cell-polymer constructs were cultured with osteogenic supplements in a rotating bioreactor for 4 weeks, and subsequently implanted in the omenta of rats for 4 weeks. The constructs were explanted and characterized by histology, immunohistochemistry, and scanning electron microscopy. The constructs maintained the size and shape of the original scaffolds. Morphologically, the constructs were rigid and had a bone-like appearance. Cells and extracellular matrix (ECM) formation were observed throughout the constructs. In addition, mineralization and type I collagen were also detected. This study establishes the ability to develop bone grafts on electrospun nanofibrous scaffolds in a well-vascularized site using MSCs.

Endothelialized networks with a vascular geometry in microfabricated poly(dimethyl siloxane).

One key challenge in regenerating vital organs is the survival of transplanted cells. To meet their metabolic requirements, transport by diffusion is insufficient, and a convective pathway, i.e., a vasculature, is required. Our laboratory pioneered the concept of engineering a vasculature using microfabrication in silicon and Pyrex. Here we report the extension of this concept and the development of a methodology to create an endothelialized network with a vascular geometry in a biocompatible polymer, poly(dimethyl siloxane) (PDMS). High-resolution PDMS templates were produced by replica-molding from micromachined silicon wafers. Closed channels were formed by bonding the patterned PDMS templates to flat PDMS sheets using an oxygen plasma. Human microvascular endothelial cells (HMEC-1) were cultured for 2 weeks in PDMS networks under dynamic flow. The HMEC-1 cells proliferated well in these confined geometries (channel widths ranging from 35 μm to 5 mm) and became confluent after four days. The HMEC-1 cells lined the channels as a monolayer and expressed markers for CD31 and von Willebrand factor (vWF). These results demonstrate that endothelial cells can be cultured in confined geometries, which is an important step towards developing an in vitro vasculature for tissue-engineered organs.

A tissue-engineered stomach as a replacement of the native stomach.

Background. Despite recent advances in reconstruction techniques, total gastrectomy is still accompanied by various complications. As an alternative treatment, we propose a tissue‐engineered stomach that replaces the mechanical and metabolic functions of a normal stomach. The objective of this study was to demonstrate the function of a tissue‐engineered stomach as a replacement of the native stomach. Methods. Tissue‐engineered stomachs were formed in recipient rats from stomach epithelium organoid units isolated from neonatal donor rats. After 12 weeks, the animals underwent a second operation for replacement of the native stomachs. Results. Tissue‐engineered stomachs were successfully used as a substitute of the native stomach in a rat model. An upper gastrointestinal tract study revealed no evidence of bowel stenosis or obstruction at both anastomosis sites. Histologically, the tissue‐engineered stomachs had well‐developed vascularized tissue with a neomucosa continuously lining the lumen and stratified smooth muscle layers. Immunohistochemical staining for &agr;‐actin smooth muscle showed that the smooth muscle layers were arranged in a regular fashion. Scanning electron microscopy showed that the surface topography of the tissue‐engineered stomachs resembled that of native stomachs. Conclusions. It has been demonstrated that a tissueengineered stomach can replace a native stomach in a rat model. Replacement of the native stomach by a tissue‐engineered stomach had beneficial effects on the formation of neomucosa and smooth muscle layers in the tissue‐engineered stomach.