Effect of Morphological Features and Surface Area of Hydroxyapatite on the Fatigue Behavior of Hydroxyapatite−Polyethylene Composites

Estimating Low- and High-Cyclic Fatigue of Polyimide-CF-PTFE Composite through Variation of Mechanical Hysteresis Loops

The fatigue properties of neat polyimide and the “polyimide + 10 wt.% milled carbon fibers + 10 wt.% polytetrafluoroethylene” composite were investigated under various cyclic loading conditions. In contrast to most of the reported studies, constructing of hysteresis loops was performed through the strain assessment using the non-contact 2D Digital Image Correlation method. The accumulation of cyclic damage was analyzed by calculating parameters of mechanical hysteresis loops. They were: (i) the energy losses (hysteresis loop area), (ii) the dynamic modulus (proportional to the compliance/stiffness of the material) and (iii) the damping capacity (calculated through the dissipated and total mechanical energies). On average, the reduction in energy losses reached 10–18% at the onset of fracture, whereas the modulus variation did not exceed 2.5% of the nominal value. The energy losses decreased from 20 down to 18 J/m3 (10%) for the composite, whereas they reduced from 30 down to 25 J/m3 (17%) for neat PI in the low-cycle fatigue mode. For high-cycle fatigue, energy losses decreased from 10 to 9 J/m3 (10%) and from 17 to 14 J/m3 (18%) for neat PI and composite, respectively. For this reason, the changes of the energy losses due to hysteresis are of prospects for the characterization of both neat PI and the reinforced PI-based composites.

Injection-molded hydroxyapatite/polyethylene bone-analogue biocomposites via structure manipulation

By means of an OSIM technique, anisotropic biomimetic, high-performance HA/HDPE biocomposites were obtained.

Surface characterization for ultrahigh molecular weight polyethylene/hydroxyapatite gradient composites prepared by the gelation/crystallization method

To establish implant longevity of hip prosthesis in orthopedics, a new approach was proposed to improve dramatically the wear resistance and to reduce the surface friction of the acetabular cup as a bearing material in the femoral head. To do so, ultrahigh molecular weight polyethylene (UHMWPE) and hydroxyapatite (HA) composites with four amounts of HA content were prepared by a sol-gel process, and the four composites were hot-molded to make a composite with HA gradient content. When the resultant UHMWPE/HA agglomerates by the sol-gel method were molded in the narrow temperature range of 145-153 °C, the (110) planes with highest density of atoms in the PE crystal unit were oriented predominantly parallel to the resultant film surface. Such an unusual planar orientation contributed excellent wear resistance and low friction on the surface. Polarized light-scattering patterns, SEM images, and FTIR spectra of the specimens with such unusual planar orientation supported that the narrow molding temperature range achieves good dispersion of HA particles and high crystallinity of the UHMWPE matrix on the surface layer. Negative complex Poisson's ratio reduced from complex tensile and shear moduli was attributed to spongy-like tissue formation under crystallization of UHMWPE chains on the HA particle surface. The gradient composite molded maintained the spongy-like structure, which played an important role to avoid the cracking under bending stress.

Effect of long-term in vitro testing on the properties of bioactive glass-polysulfone composites

The combination of bioactive ceramics and polymers can allow the preparation of composites with tailorable mechanical properties and bioactive behavior. In these composites, bioactive ceramics can act as a source of both reinforcement and bioactivity, while the polymer matrix can add toughness and processability to the material. On the other hand, the effect of using a highly dimensional unstable phase as a reinforcing agent on the long-term properties of the composite is a major concern regarding the lifetime of possible applications. In this work, a bioactive glass-polysulfone particulate composite was prepared by hot-pressing at 215 degrees C a mixture of polysulfone and different concentrations of bioactive glass particles (Bioglass 45S5, particle size range: 125-106 microm) to yield composites having 20 and 40 vol % of bioactive glass particles. The obtained composites were exposed to a simulated body fluid at 37 degrees C for different periods of time ranging from 1 h to 60 days. After the test, the mechanical properties of the composites were investigated by a four-point bending test, while DMS (dynamic mechanical spectroscopy) was used to identify the effect of water on the structure and behavior of the composite. The interface between glass particles and the polymer was also investigated by SEM/EDX and diffuse reflection infrared spectroscopy. The results showed that a decay in the mechanical properties of the composites within the first 20 h of test can occur. Otherwise, after this initial decay, no more pronounced reduction in properties could be noted. The analyses of the fracture surface of composites tested in vitro indicated the hydration of the surface of the particles. Therefore, it was concluded that water migration through the interface of the composite causes surface dissolution of glass particles and formation of voids, which were responsible for the observed decay in mechanical properties. Composites with modified interfaces revealed less damaged fracture surfaces than composites with untreated interfaces.

Bioactive ceramic-reinforced composites for bone augmentation

Biomaterials have been used to repair the human body for millennia, but it is only since the 1970s that man-made composites have been used. Hydroxyapatite (HA)-reinforced polyethylene (PE) is the first of the 'second-generation' biomaterials that have been developed to be bioactive rather than bioinert. The mechanical properties have been characterized using quasi-static, fatigue, creep and fracture toughness testing, and these studies have allowed optimization of the production method. The in vitro and in vivo biological properties have been investigated with a range of filler content and have shown that the presence of sufficient bioactive filler leads to a bioactive composite. Finally, the material has been applied clinically, initially in the orbital floor and later in the middle ear. From this initial combination of HA in PE other bioactive ceramic polymer composites have been developed.

Effect of filler surface morphology on the impact behaviour of hydroxyapatite reinforced high density polyethylene composites

Instrumented falling weight impact tests have been carried out to characterize the impact behaviour of hydroxyapatite reinforced high-density polyethylene composite (HA-HDPE) in order to use this biomaterial in skull implants. The effects of HA filler surface morphology and volume fraction on the fracture toughness were studied, and fracture mechanism investigated. Impact resistance was found to be markedly improved by using a sintered grade HA filler with smooth particle surface instead of spray dried grade HA with rough surface. SEM examination of impacted fracture surfaces revealed that the improvement of impact resistance was due to the stronger interfacial bonding between smooth HA particles and HDPE polymer matrix compared with that between rough HA and HDPE, which results in more energy absorption during impact and hence better fracture resistance.