Abstract
Dual setting cements composed of an in situ forming hydrogel and a reactive mineral phase combine high compressive strength of the cement with sufficient ductility and bending strength of the polymeric network. Previous studies were focused on the modification with non-degradable hydrogels based on 2-hydroxyethyl methacrylate (HEMA). Here, we describe the synthesis of suitable triblock degradable poly(ethylene glycol)-poly(lactide) (PEG-PLLA) cross-linker to improve the resorption capacity of such composites. A study with four different formulations was established. As reference, pure hydroxyapatite (HA) cements and composites with 40 wt% HEMA in the liquid cement phase were produced. Furthermore, HEMA was modified with 10 wt% of PEG-PLLA cross-linker or a test series containing only 25% cross-linker was chosen for composites with a fully degradable polymeric phase. Hence, we developed suitable systems with increased elasticity and 5–6 times higher toughness values in comparison to pure inorganic cement matrix. Furthermore, conversion rate from α-tricalcium phosphate (α-TCP) to HA was still about 90% for all composite formulations, whereas crystal size decreased. Based on this material development and advancement for a dual setting system, we managed to overcome the drawback of brittleness for pure calcium phosphate cements.
Highlights
Bone is often described as natural miracle due to its impressive mechanical properties
It has a very high load-capacity of ~90–190 MPa [1] for cortical bone, while at the same time it provides elastic and ductile properties with a high fracture resistance. This high stability is based on its structural composition, as natural bone is a composite mainly consisting of apatite, collagen, and water [2,3]. This leads to the idea to mimic bone structure in synthetic materials by combining an inorganic phase based on calcium phosphate cements (CPCs) with an organic polymeric matrix
H40P10 and P25, that were produced with the synthesized monomer, resulted in an even faster setting that only took halve of the time than the formulation with 40 wt% hydroxyethyl methacrylate (HEMA) (H40) alone
Summary
Bone is often described as natural miracle due to its impressive mechanical properties. It has a very high load-capacity of ~90–190 MPa [1] for cortical bone, while at the same time it provides elastic and ductile properties with a high fracture resistance This high stability is based on its structural composition, as natural bone is a composite mainly consisting of apatite, collagen, and water [2,3]. According to the chosen pH-values during setting reaction as well as different solubility products constants Ksp , one can distinguish between brushite (DCPD, CaHPO4 ·2H2 O; pH ≤ ~4.2) and hydroxyapatite (HA, Ca5 (PO4 ) OH; pH ≥ ~4.2) forming cements The latter one is clinically a very well established system due to its outstanding properties like bioactivity, osteoconductivity [5] and stochiometric similarity to mineral components present in bone and teeth [6]. Bohner [7] describes an “excellent”
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