Swelling of acrylate hydrogels filled with brushite and octacalcium phosphate
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Swelling of acrylate hydrogels filled with brushite and octacalcium phosphate* I. I. Preobrazhensky,a A. A. Tikhonov,a E. S. Klimashina,a,b P. V. Evdokimov,a,b and V. I. Putlyaeva,b aDepartment
of Materials Science, M. V. Lomonosov State University, Building 73, 1 Leninskie Gory, 119991 Moscow, Russian Federation. E-mail: [email protected] bDepartment of Chemistry, M. V. Lomonosov State University, Building 73, 1 Leninskie Gory, 119991 Moscow, Russian Federation
Hydrogels filled with СаНРО4•2Н2О and Са8(НРО4)2(РО4)4•5Н2О were synthesized from the acrylate derivatives of poly(ethylene glycol) by the photopolymerization method. The swelling behaviour of the filled and unfilled hydrogels in water was studied. The solubility of the photoinitiator in water and in the monomers was estimated. Key words: hydrogels, poly(ethylene glycol) acrylates, photopolymerization, swelling, octacalcium phosphate.
Hydrogels based on acrylate derivatives of poly(ethylene glycol) (PEG) are promising materials for bone tissue regeneration due to a combination of the elastic properties, biocompatibility, and capability to swell.1,2 The hydrogels based on PEG are capable of degrading in a medium of the organism, and their functional properties can be tuned by modifying the composition.3,4 The application of photopolymerization for gel formation makes it possible to use stereolithographic 3D printing for preparing hydrogel materials with a complex architecture providing the osteoconductive properties of the implant.5,6 The photoinitiator (PI) is chosen based on the series of key characteristics, in particular, solubility in water,7 and the choice significantly determines toxicity of the hydrogel.8,9 One of the methods for controlling the properties of the hydrogel (including swelling) is the filling of the hydrogels with the inorganic phase, mainly calcium phosphates, which are biocompatible and bioactive components.10,11 Hydroxyapatite is used most frequently for this purpose,12 but the highest solubility and layered morphology of the crystals make brushite (dicalcium phosphate dihydrate (DCPD) СаНРО4•2H2O)13 and octacalcium phosphate (Са8(НРО4)2(РО4)6•5Н2О (OCP))14 perspective fillers. The purpose of this work is to study swelling of the hydrogels based on PEG methacrylate (PEGMA) and PEG diacrylate (PEGDA) filled with DCPD and OCP. Irgacure®819 based on phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide was used as the PI.
Experimental The monomers PEGMA (Mw = 350) and PEGDA (Mw = 575) (both Sigma Aldrich, Germany) and PI Irgacure®819 (BASF, Germany) were used for the synthesis of hydrogels. Photopolymerization was carried out using a UV lamp ( = 365 nm, power 5 mW cm–2). The polymerization time (10 min for PEGMA and 5 min for PEGDA) was determined from the dependence of the polymerization depth on the radiation dose according to the Jacobs equation.15 The filler DCPD was synthesized by precipitation from aqueous solutions,16 and OCP was synthesized by the hydrolysis of DCPD in an acetate buffer17 at pH 5.75 and Т = 60 С. X-ray diffracti
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