TISSUE ENGINEERING SCAFFODS

Tissue Engineering Scaffolds

Tissue Engineering Scaffolds

Introduction

Bone and cartilage generation by autogenous cell/tissue transplantation is one of the most promising techniques in orthopedic surgery and biomedical engineering . Treatment concepts based on those techniques would eliminate problems of donor site scarcity, immune rejection and pathogen transfer . Osteoblasts, chondrocytes and mesenchymal stem cells obtained from the patient's hard and soft tissues can be expanded in culture and seeded onto a scaffold that will slowly degrade and resorb as the tissue structures grow in vitro and/or in vivo . The scaffold or three-dimensional (3-D) construct provides the necessary support for cells to proliferate and maintain their differentiated function, and its architecture defines the ultimate shape of the new bone and cartilage.(Agrawal,1995)

However, the available evidence indicates that the results vary considerably among the individuals, and that the tissues formed using these treatment regimes do not duplicate the composition, structure, and mechanical properties of normal articular cartilage . In addition, none of those matrix designs could be securely fixed under load-bearing conditions to the osteochondral bone which is a conditio sine qua non from a biomechanical and clinical point of view.(Pachence,1997)

Discussion

In general, the scaffold should be fabricated from a highly biocompatible material which does not have the potential to elicit an immunological or clinically detectable primary or secondary foreign body reaction . Furthermore, a polymer scaffold material has to be chosen that will degrade and resorb at a controlled rate at the same time as the specific tissue cells seeded into the 3-D construct attach, spread and increase in quantity (number of cells/per void volume) as well as in quality. Currently, the design and fabrication of scaffolds in tissue engineering research is driven by three material categories: I. Regulatory approved biodegradable and bioresorbable polymers , such as collagen, polyglycolide (PGA), polylactides (PLLA, PDLA), polycaprolactone (PCL), etc. II. A number of non-approved polymers, such as polyorthoester (POE), polyanhydrides, etc. which are also under investigation. III. The synthesis of entrepreneurial polymeric biomaterials, such as poly (lactic acid-co-lysine), etc., which can selectively shepherd specific cell phenotypes and guide the differentiation and proliferation into the targeted functional premature and/or mature tissue.(Pachence,1997)

The first stage of tissue engineering bone or cartilage begins with the design and fabrication of a porous 3-D scaffold, the main topic of this review paper.(Hutmacher,1996)

The meaning and definition of the words biodegradable, bioerodable, bioresorbable and bioabsorbable which are often used misleadingly in the tissue engineering literature—are of importance to discuss the rationale, function as well as chemical and physical properties of polymer-based scaffolds. In this paper, the polymer properties are based on the definitions given by Vert.(Naughton,1995)

The tissue engineering program for bone and cartilage in the author's multidisciplinary research curriculum has been classified into six phases . Each tissue engineering phase must be understood in an integrated manner across the research program—from the polymer material properties, to the scaffold micro- and macro- architecture, to the cell, to the tissue-engineered transplant, to the host tissue. Hence, the research objectives in each phase are cross-disciplinary and the sub-projects ...