A Newly Developed Chemically Crosslinked Dextran–Poly(Ethylene Glycol) Hydrogel for Cartilage Tissue Engineering Jojanneke M. Jukes, M.Sc., 1 Leonardus J. van der Aa, M.Sc., 2 Christine Hiemstra, Ph.D., 2 Theun van Veen, B.Sc., 1 Pieter J. Dijkstra, Ph.D., 2,3 Zhiyuan Zhong, Ph.D., 3 Jan Feijen, Ph.D., 2 Clemens A. van Blitterswijk, Ph.D., 1 and Jan de Boer, Ph.D. 1 Cartilage tissue engineering, in which chondrogenic cells are combined with a scaffold, is a cell-based approach to regenerate damaged cartilage. Various scaffold materials have been investigated, among which are hydrogels. Previously, we have developed dextran-based hydrogels that form under physiological conditions via a Michael- type addition reaction. Hydrogels can be formed in situ by mixing a thiol-functionalized dextran with a tetra-acrylated star poly(ethylene glycol) solution. In this article we describe how the degradation time of dextran– poly(ethylene glycol) hydrogels can be varied from 3 to 7 weeks by changing the degree of substitution of thiol groups on dextran. The degradation times increased slightly after encapsulation of chondrocytes in the gels. The effect of the gelation reaction on cell viability and cartilage formation in the hydrogels was investigated. Chon- drocytes or embryonic stem cells were mixed in the aqueous dextran solution, and we confirmed that the cells survived gelation. After a 3-week culturing period, chondrocytes and embryonic stem cell–derived embryoid bodies were still viable and both cell types produced cartilaginous tissue. Our data demonstrate the potential of dextran hydrogels for cartilage tissue engineering strategies. Introduction B ecause of the poor self-healing capacity of carti- lage, surgical intervention is generally required when the tissue is damaged or diseased. Some techniques rely on the formation of fibrocartilage, such as microfracturing or subchondral bone drilling; other techniques use grafts to replace the damaged cartilage, such as mosaicplasty. How- ever, the fibrocartilage has poor mechanical properties and only results in temporary relief and there is a limited avail- ability of chondral autografts. 1,2 Cartilage tissue engineering is a cell-based therapy aimed at regenerating the damaged articular cartilage. Chondrocytes can be combined with a scaffold material, such as a hydrogel, to achieve high cell density and homogeneous seeding and to retain the cells in the defect. Hydrogels are hydrated networks of crosslinked hydro- philic polymers. Due to their high water content, many hy- drogels are compatible with cells and proteins. Cells can be combined with the hydrogel precursors before gelation, and functional groups or growth factors, such as transforming growth factor, 3,4 can be incorporated into the hydrogel to enhance tissue formation. A wide variety of hydrogels based on natural materials and synthetic polymers 5–9 have been developed and studied in recent years. The aqueous polymer solution can be turned into a gel by physical or chemical crosslinks. 10 The noncovalent bonds of physically crosslinked hydrogels, for example, in stereo- complexed hydrogels, 11 result in mechanically weak hydro- gels. The physical interactions are reversible, resulting in disruption of the gel upon a change in, for example, tem- perature or pH. An advantage is that these gels can generally be formed under mild conditions. Chemical crosslinking re- sults in more stable hydrogels due to the covalent bonds formed. The properties of chemically crosslinked hydrogels can be varied by the amount of crosslinks introduced and the hydrophilic–hydrophobic ratio. Further customization can be achieved by varying the concentration of polymer and the polymer length. Reactive crosslinkers or initiators, or cross- linking conditions can be toxic for included cells or may lead to modification of biological compounds. Examples of che- mical crosslinking methods include photopolymerization of Departments of 1 Tissue Regeneration and 2 Polymer Chemistry and Biomaterials, MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, The Netherlands. 3 Biomedical Polymers Laboratory and Jiangsu Key Laboratory of Organic Chemistry, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou, P.R. China. TISSUE ENGINEERING: Part A Volume 16, Number 2, 2010 ª Mary Ann Liebert, Inc. DOI: 10.1089=ten.tea.2009.0173 565 Downloaded by 34.228.24.229 from www.liebertpub.com at 05/21/20. For personal use only.