Biomaterials 24 (2003) 3969–3980 Synthesis and characterization of a novel degradable phosphate-containing hydrogel $ Dong-an Wang, Christopher G. Williams, Qiang Li, Blanka Sharma, Jennifer H. Elisseeff* Department of Biomedical Engineering, Johns Hopkins University, 3400 North Charles Street/Clark Hall 106, Baltimore, MD 21218, USA Received 3 December 2002; accepted 8 April 2003 Abstract A phosphate-containing and photocrosslinkable polymer, poly(ethylene glycol) di-[ethyl phosphatidyl (ethylene glycol) methacrylate], ‘‘PhosPEG-dMA’’, was synthesized. As a water-soluble macromer, PhosPEG-dMA is suitable for in situ injection and cell-encapsulation by light-induced gelation to produce a novel biocompatible and biodegradable hydrogel for application to cartilage and bone tissue engineering. 1 H-NMR, MALDI-TOF mass spectrometry, and elemental analysis were performed to characterize the macromer. Fifteen and 20% (w/v) PhosPEG gels were photopolymerized using UV light with 0.05% photoinitiator. The swelling and water content of the hydrogels was studied and the crosslinking efficiency (density) of the macromers was simulated based on the Peppas-Merrill model. Torsional mechanical analysis of the gels demonstrated a viscoelastic characteristic with high elasticity. The results indicated that, with the fixed PEG-segment size, the greater strength and water-content of the gels depend on the higher crosslinking density. Degradation experiments revealed a linear dry-weight loss of 22.88% and 16.08% from 15% and 20% PhosPEG gels after 9 weeks. The 31 P-NMR detected the signals of both phosphate and phosphoric acid in the degrading systems (the gel bulks and the supernatants). Finally, human mesenchymal stem cells (hMSC) were encapsulated into PhosPEG Gel constructs and remained viable as qualitatively demonstrated by ‘‘Live/Dead’’ cell staining assay and MTT assay. The cell-encapsulation efficiency was determined by the characterization of DNA content in each gel construct and the semi-quantitative analysis of the cell viability was also performed by the DNA assay combined with MTT assay. r 2003 Elsevier Science Ltd. All rights reserved. Keywords: Hydrogel; Degradation; Tissue engineering; Phosphate; Photopolymerization; Macromer 1. Introduction Hydrogels are a class of biomaterials that have shown great promise as a scaffold for tissue engineering. These materials have tissue-like water contents, may be formed in situ for ease in implantation, and can encapsulate cells as they crosslink. Photopolymerization is one method to crosslink a liquid, macromer solution to form a hydrogel with significant temporal and spatial control [1–5]. Previous research investigated the application of photo- polymerizing hydrogels to cartilage tissue engineering. Cartilage-like tissue was formed after encapsulation of bovine chondrocytes in a poly(ethylene glycol)-based photopolymerizing hydrogel and incubation both in vitro and in vivo [6,7]. Others have investigated tissue engineering bone in poly(vinyl alcohol)-based and novel poly(propylene fumarate) photopolymerizing hydrogels [8–10]. The physical and biological properties of the hydrogel scaffold play an important role in the development of engineered tissues. For example, Anseth and colleagues demonstrated enhanced cartilage tissue development in hydrogels that were degradable and had an increased pore size [6,7]. A hydrogel scaffold must initially be strong to survive the in vivo environment and protect encapsulated cells and nascent tissue while eventually degrading to increase pore size and allow for full functional tissue formation. Anseth and Hubbell in- vestigated addition of degradable polyester linkages in photopolymerizing poly(ethylene glycol)- and poly (vinyl alcohol)-based photopolymerizing gels [11–16]. Polyesters have a significant history as a degradable polymer in multiple biomedical applications, including tissue engineering, making them a logical choice for ARTICLE IN PRESS $ Abstract submitted to the 29th Annual Meeting of Society for Biomaterials, Reno, Nevada, 2003. *Corresponding author. Tel.: +1-410-516-4915; fax: +1-410-516- 8152. E-mail address: jhe@bme.jhu.edu (J.H. Elisseeff). 0142-9612/03/$-see front matter r 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0142-9612(03)00280-1