Effects of the length of crosslink chain on poly(2- hydroxyethyl methacrylate) (pHEMA) swelling and biomechanical properties G. Mabilleau, 1 I.C.Stancu, 1,2 T. Honore´, 3 G. Legeay, 3 C. Cincu, 1,2 M.F.Basle´, 1 D. Chappard 1 1 INSERM,EMI 0335–LHEA, ANGERS,F-49045 France 2 Department of Macromolecular Chemistry, Industrial Chemistry Faculty, University Politehnica, Bucharest, RO-71101 Romania 3 CTTM,Le Mans, F-72000 France Received 3 May 2005; revised 1 September 2005; accepted 6 September 2005 Published online 12 December 2005 in Wiley InterScience (www.interscience.wiley.com). DOI:10.1002/jbm.a.30618 Abstract: Polymers are widely used in medicine for vascular prostheses, bone substitutes, and devices for con- trolled release. Among these polymers, poly(2-hydroxyethyl methacrylate) (pHEMA) is the mostemployed.To confer particular properties, pHEMA can be copolymerized with other monomers or in the presenceof plasticizersor crosslinking agents. The influence of the length of crosslink chains on swelling, surface rugosity, hardness, and stiffness of crosslinked pHEMA were studied by several techniques, including fractal analysis and AFM. Four crosslinking agents (divinyl benzene, DVB; ethylene glycol dimethacry- late,EGDMA;tetraethylene glycol diacrylate, TEGDA;and polyethylene glycol diacrylate, PEGDA) were added to the bulk polymerization mixture.Only linear and PEGDA– pHEMA presented a significant decrease in surface rough- ness confirmed by fractal analysis. Differences in hardness and biomechanicalpropertieswere evidenced on dried polymersbut the highestdifferenceswere exhibited for hydrated pHEMA.Correlations between the length of the crosslink chain and hardness or stiffness of hydrated crosslinked pHEMA were evidenced. TEGDA and PEGDA appeared to be the two most suitable crosslinking agents for controlled release of bioactive molecules in bone. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res 77A: 35– 42, 2006 Key words: poly(2-hydroxyethyl methacrylate); cross-link chain length; biomechanics; hardness; swelling INTRODUCTION Polymersare widely used in medicine to make medical devices, prostheses, cements or coatings, mi- crobeads, and in encapsulation of cells and controlled release of active compounds. 1 Different types of poly- mers are usable, but according to their physico-chem- ical properties,they can be proposed for specific tissular purposes. For vascular prostheses, poly(tetra- fluoroethylene)(PFTE)and poly(ethylene terephta- late) (PET) are often used. 2 For bone substitutes, poly- (methyl methacrylate) (pMMA), poly(2-hydroxyethyl methacrylate)(pHEMA), poly(l-lactic acid) (PLA), poly(l-glycolic acid)(PGA), and poly(ethylene) (PE) are widely used. 3–7 For the controlled release, hydro- gels [poly(vinyl alcohol) (PVA), poly(N-vinyl-2-pyrro- lidone) (PVP),and pHEMA],which have the capaci- ties to swell, are employed. 8 –12 Hydrogels are divided in two groups: (1) highly swollen hydrogels, including cellulose derivatives, PVA, PVP among others and (2) moderately and poorly swollen hydrogels, including pHEMA and many of its derivatives. 13 In general,a hydrophilic monomer can be polymerized with other more or less hydrophilic monomers to achieve desired swelling properties. Other ways to improve hydrogel properties are the use of plasticizers and crosslinking agents; they can confer mechanical properties compat- ible with the desired properties required at the im- plantation sites. 14 A plasticizer is defined as any chem- ical agent added to a synthetic resin in order to impart flexibility,workability,stretchability,or a related property to the synthetic resin. 15 Crosslinking agents can be incorporated into linear polymers to improve such properties as stiffness, surface hardness, and re- sistance to temperature and solvent attack. 16 pHEMA may be formulated to develop bone sub- stitutes or devices for the controlled release of drugs while maintaining mechanical and biological proper- Correspondence to: D. Chappard, INSERM, EMI 0335 –LHEA, Faculty of Medicine, 49045 Angers, France;e-mail:daniel. chappard@univ-angers.fr © 2005 Wiley Periodicals, Inc.