Preliminary report of in vitro reconstruction of a vascularized tendonlike structure: a novel application for adipose-derived stem cells.

INTRODUCTION: A greater supply of tendinous tissue can be obtained through tissue engineering technology with increasing application of adult stem cells. It is well known that adipose-derived stem cells (ADSCs), found in abundance in adipose tissue, have the same differentiating capacity as mesenchymal stem cells yet have the advantage of being easily isolated. In the present study, we combined the great facility of ADSCs to differentiate with the application of an external mechanical stimulus to successfully create an in vitro reconstructed tendonlike structure with a microcapillary network. MATERIALS AND METHODS: Hyalonect meshes (Fidia Advanced Biopolymers, Abano Terme, Padova, Italy) were used as scaffold. Human ADSCs were seeded onto the biomaterials, and the cell/scaffold constructs were cultured under mechanical stress for up to 15 days. Human tenocytes were used in the same conditions as control. Performance was assessed by histology, immunochemistry, ultrastructure, and biomolecular analysis. RESULTS: Adipose-derived stem cells seeded onto Hyalonect adhered and differentiated along the entire surface of the biomaterial and began to infiltrate within its structure. Subsequently, endothelial cells migrated, forming a capillary in the new extracellular matrix. CONCLUSIONS: This technique allowed for the creation of a vascularized tendon equivalent that could easily be detached from the bioreactor, thus facilitating its implant at the lesion site. These results highlight the biologic performance of biodegradable hyaluronic acid-based (HYAFF-11) scaffolds, which were shown to be suitable for deposition of the autologous extracellular matrix critical for ADSCs differentiation.

Tissue engineering approaches for the construction of a completely autologous tendon substitute.

Tissue engineering is a multidisciplinary field that involves the application of the principles and methods of engineering and life sciences towards i) the fundamental understanding of structure-function relationships in normal and pathological mammalian tissues and ii) the development of biological substitutes that restore, maintain or improve tissue function. The goal of tissue engineering is to surpass the limitations of conventional treatments based on organ transplantation and biomaterial implantation. The field of tendon tissue engineering is relatively unexplored due to the difficulty in in vitro preservation of tenocyte phenotype. Only recently has mechanobiology allowed us to gain a better understanding of the fundamental role of in vitro mechanical stimuli in maintaining the phenotype of tendinous tissue. This review analyzes the techniques used so far for in vitro regeneration of tendinous tissue.

In vivo regeneration of small-diameter (2 mm) arteries using a polymer scaffold.

The difficulty of obtaining significant long-term patency and good wall mechanical strength in vivo has been a significant obstacle in achieving small-diameter vascular prostheses. The aim of the present study was to develop a prosthetic graft that could perform as a small-diameter vascular conduit. Tubular structures of hyaluronan (HYAFF-11 tubules, 2 mm diameter, 1 cm length) were grafted in the abdominal aorta of 30 rats as temporary absorbable guides to promote regeneration of vascular structures. Performance was assessed by histology, immunohistochemistry, and ultra-structural analysis. These experiments resulted in three novel findings: 1) complete endothelialization of the tube's luminal surface occurred; 2) sequential regeneration of vascular components led to complete vascular wall regeneration 15 days after surgery; and 3) the biomaterial used created the ideal environment for the delicate regeneration process during the critical initial phases, yet its biodegradability allowed for complete degradation of the construct four months after implantation, at which time, a new artery remained to connect the artery stumps. This study assesses the feasibility to create a completely biodegradable vascular regeneration guide in vivo, able to sequentially orchestrate vascular regeneration events needed for very small artery reconstruction.

In vitro reconstruction of an endothelialized skin substitute provided with a microcapillary network using biopolymer scaffolds.

Successful in vitro reconstruction of skin requires the inclusion of several cell types that give rise in coculture to the specific elements present in native skin, and the appropriate scaffolding structure to house and support these cells. In addition to the two main structural components, epidermis and dermis, one critical apparatus of the skin is a capillary network that guarantees adequate perfusion of nutrients and oxygen. The aim of the present study was to develop an in vitro coculture system that assumed the human dermal-epidermal architecture and included a microcapillary network in a three-dimensional biomaterial that guaranteed ease of handling in a clinical setting. Endothelialized skin (ES) was prepared by coculturing three human cell types: keratinocytes, fibroblasts, and endothelial cells, obtained from human full-thickness skin samples, in scaffolds produced from modified hyaluronic acid. Results were evaluated by histological and immunohistochemical analyses at different time points. In vitro, engineered skin obtained with this composite culture developed into a well-differentiated upper layer of stratified keratinocytes lining a dermal-like structure, in which fibroblasts, extracellular matrix and a microvascular network were present. Furthermore, the biodegradable fabric produced from hyaluronic acid and used as the scaffolding support for this in vitro constructed skin graft greatly facilitated handling in the perioperative period.