Sca!olds in tissue engineering bone and cartilage
Dietmar W. Hutmacher
Laboratory for Biomedical Engineering, Institute of Engineering Science, Department of Orthopedic Surgery, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260, Singapore
Abstract Musculoskeletal tissue, bone and cartilage are under extensive investigation in tissue engineering research. A number of biodegradable and bioresorbable materials, as well as sca!old designs, have been experimentally and/or clinically studied. Ideally, a sca!old should have the following characteristics: (i) three-dimensional and highly porous with an interconnected pore network for cell growth and #ow transport of nutrients and metabolic waste; (ii) biocompatible and bioresorbable with a controllable degradation and resorption rate to match cell/tissue growth in vitro and/or in vivo; (iii) suitable surface chemistry for cell attachment, proliferation, and di!erentation and (iv) mechanical properties to match those of the tissues at the site of implantation. This paper reviews research 2000 Elsevier Science Ltd. All rights on the tissue engineering of bone and cartilage from the polymeric sca!old point of view. reserved. Keywords: Tissue engineering of bone and cartilage; Design and fabrication of 3-D sca!old; Biodegradable and bioresorbable polymers
1. 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 sca!old that will slowly degrade and resorb as the tissue structures grow in vitro and/or in vivo . The sca!old or three-dimensional (3-D) construct provides the necessary support for cells to proliferate and maintain their di!erentiated function, and its architecture de"nes the ultimate shape of the new bone and cartilage. Several sca!old materials have been investigated for tissue engineering bone and cartilage including hydroxyapatite (HA), poly( -hydroxyesters), and natural polymers such as collagen and chitin. Several reviews have been published on the general properties and design features of biodegradable and bioresorbable polymers and sca!olds [4}12]. The aim of this paper is to complete the information collected so far, with special emphasis on the evaluation of the material and design characteristics which are of speci"c interest in tissue engineering the mesenchymal tissues bone and cartilage.
The currently applied sca!old fabrication technologies, with special emphasis on the so-called solid-free form fabrication technologies, will also be bench marked. Finally, the paper discusses the author's research on the design and fabrication of 3-D sca!olds for tissue engineering an osteochondral transplant.
2. Polymer-based sca4old materials The meaning and de"nition of the words biodegradable, bioerodable, bioresorbable and bioabsorbable (Table 1)*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 sca!olds. In this paper, the polymer properties are based on the de"nitions given by Vert . The tissue engineering program for bone and cartilage in the author's multidisciplinary research curriculum has been classi"ed into six phases (Table 2). Each tissue engineering phase must be understood in an integrated manner across the research program*from the polymer material properties, to the sca!old micro- and macroarchitecture, to the cell, to the tissue-engineered transplant, to the host tissue. Hence, the research objectives in each phase are cross-disciplinary and...