ABSTRACT
Calcium phosphate cements are brittle biomaterials of low bending strength. One promising approach to improve their mechanical properties is reinforcement with fibers. State of the art degradable reinforced composites contain fibers made of polymers, resorbable glass or whiskers of calcium minerals. We introduce a new class of composite that is reinforced with degradable magnesium alloy wires. Bending strength and ductility of the composites increased with aspect ratio and volume content of the reinforcements up to a maximal bending strength of 139±41MPa. Hybrid reinforcement with metal and polymer fibers (PLA) further improved the qualitative fracture behavior and gave indication of enhanced strength and ductility. Immersion tests of composites in SBF for seven weeks showed high corrosion stability of ZEK100 wires and slow degradation of the magnesium calcium phosphate cement by struvite dissolution. Finally, in vitro tests with the osteoblast-like cell line MG63 demonstrate cytocompatibility of the composite materials.
Subject(s)
Bone Cements/chemistry , Bone Cements/therapeutic use , Bone Substitutes/chemical synthesis , Bone Substitutes/toxicity , Osteoblasts/drug effects , Phosphates/chemistry , Phosphates/toxicity , Adhesiveness , Cell Line , Cell Survival/drug effects , Compressive Strength , Humans , Magnesium , Materials Testing , Osteoblasts/cytology , Stress, Mechanical , Weight-BearingABSTRACT
Calcium phosphate cements (CPC) are well-established materials for the repair of bone defects with excellent biocompatibility and bioactivity. However, brittleness and low flexural/tensile strength so far restrict their application to non-load bearing areas. Reinforcement of CPC with fibers can substantially improve its strength and toughness and has been one major strategy to overcome the present mechanical limitations of CPC. Fiber reinforced calcium phosphate cements (FRCPC) thus bear the potential to facilitate the use of degradable bone substitutes in load bearing applications. This review recapitulates the state of the art of FRCPC research with focus on their mechanical properties and their biological evaluation in vitro and in vivo, including the clinical data that has been generated so far. After an overview on FRCPC constitutes and processing, some general aspects of fracture mechanics of reinforced cementitious composites are introduced, and their importance for the mechanical properties of FRCPC are highlighted. So far, fiber reinforcement leads to a toughness increase of up to two orders of magnitude. FRCPC have extensively been examined in vitro and in vivo with generally good results. While first clinical products focus on the improved performance of FRCPC with regard to secondary processing after injection such as fixation of screws and plates, first animal studies in load bearing applications show improved performance as compared to pure CPCs. Aside of the accomplished results, FRCPC bear a great potential for future development and optimization. Future research will have to focus on the selection and tailoring of FRCPC components, fiber-matrix compatibilization, integral composite design and the adjusted degradation behavior of the composite components to ensure successful long term behavior and make the composites strong enough for application in load bearing defects.
Subject(s)
Biocompatible Materials/chemistry , Bone Cements/chemistry , Bone Substitutes/chemistry , Calcium Phosphates/chemistry , Materials Testing , Animals , Humans , Weight-BearingABSTRACT
Using the sol-gel process, Nd-Mn-doped PZT fibers were produced. The PZT was doped with 2 mol% neodymium and 1.1 mol% manganese. For characterization, the fibers were embedded in a polymer. The resulting 1-3 composites were poled with constant electric field. Strain and polarization were measured by applying a bipolar sinusoidal voltage of high amplitude. Instead of the expected shifted butterfly-shaped strain hysteresis, an asymmetric strain-field relation was observed. It is characterized by a rather linear region in direction of the poling field and an inflated region without strain switching for reversed polarity. Within the temperature range from room temperature to 80 degrees C, the strain switching seems to be suppressed. Measurements of the piezoelectric coefficient at superimposed electric field prove the blocking of strain switching. Cyclation experiments with sesquipolar load show a pronounced linearity of the strain loops that declines after more than 2 x 10(4) cycles.
