Search

Hydroxyapatite (HA) reinforced collagen scaffolds have shown promise for synthetic bone graft substitutes and tissue engineering scaffolds. Freeze-dried HA–collagen scaffolds are readily fabricated and have exhibited osteogenicity in vivo , but are limited by an inherent scaffold architecture that results in a relatively small pore size and weak mechanical properties. In order to overcome these limitations, HA–collagen scaffolds were prepared by compression molding HA reinforcements and paraffin microspheres within a suspension of concentrated collagen fibrils (∼180 mg/mL), cross-linking the collagen matrix, and leaching the paraffin porogen. HA–collagen scaffolds exhibited an architecture with high porosity (85–90%), interconnected pores ∼300–400 μm in size, and struts ∼3–100 μm in thickness containing 0–80 vol% HA whisker or powder reinforcements. HA reinforcement enabled a compressive modulus of up to ∼1 MPa, which was an order of magnitude greater than unreinforced collagen scaffolds. The compressive modulus was also at least one order of magnitude greater than comparable freeze-dried HA–collagen scaffolds and two orders of magnitude greater than absorbable collagen sponges used clinically. Moreover, scaffolds reinforced with up to 60 vol% HA exhibited fully recoverable elastic deformation upon loading to 50% compressive strain for at least 100,000 cycles. Thus, the scaffold mechanical properties were well-suited for surgical handling, fixation, and bearing osteogenic loads during bone regeneration. The scaffold architecture, permeability, and composition were shown to be conducive to the infiltration and differentiation of adipose-derive stromal cells in vitro . Acellular scaffolds were demonstrated to induce angiogenesis and osteogenesis after subcutaneous ectopic implantation by recruiting endogenous cell populations, suggesting that the scaffolds were osteoinductive. [ABSTRACT FROM AUTHOR]

Abstract: Freeze-dried collagen scaffolds reinforced with hydroxyapatite (HA) are of clinical interest for synthetic bone graft substitutes and tissue engineering scaffolds, but a systematic evaluation of the effects of the HA reinforcement weight fraction and morphology on the mechanical properties is lacking. Therefore, freeze-dried collagen scaffolds were reinforced with either HA whiskers or an equiaxed HA powder at 1:1, 1:2, or 1:4 collagen:HA by weight (which corresponded to approximately 28, 44, and 61 vol% HA, respectively) to investigate the effects of the HA reinforcement weight fraction and morphology on the architecture and compressive mechanical properties. All scaffolds exhibited a highly elongated linear pore structure containing 90%–96% porosity, which decreased with increased HA content, and a pore width of ∼50 μm. HA reinforcement resulted in up to a ten-fold increase in compressive modulus at high reinforcement levels (∼200 kPa at 1:4 collagen:HA by weight) compared to scaffolds with no reinforcement or low reinforcement levels (∼20 kPa at 1:1 collagen:HA by weight). This effect could not be explained by the concomitant decrease in the scaffold porosity (from 95% to 90%) with HA reinforcement, which could only account for up to a two-fold increase in compressive modulus. At moderate reinforcement levels (1:2 collagen:HA by weight), HA whisker reinforced scaffolds exhibited a nearly four-fold greater modulus compared to the equiaxed HA powder, while there were no differences with the HA reinforcement morphology at high and low reinforcement levels. Therefore, the elongated morphology of HA whiskers enabled a reinforcing effect at a lower level of reinforcement compared to a conventional, equiaxed HA powder. [Copyright &y& Elsevier]

Abstract: Poly(methyl methacrylate) (PMMA) bone cements have a long and successful history of use for implant fixation, but suffer from a relatively low fracture and fatigue resistance which can result in failure of the cement and the implant. Fiber or particulate reinforcement has been used to improve mechanical properties, but typically at the expense of the pre-cured cement viscosity, which is critical for successful integration with peri-implant bone tissue. Therefore, the objective of this study was to investigate the effects of zirconia fiber reinforcement on the fatigue life of acrylic bone cements while maintaining a relatively low pre-cured cement viscosity. Sintered straight or variable diameter fibers (VDFs) were added to a PMMA cement and tested in fully reversed uniaxial fatigue until failure. The mean fatigue life of cements reinforced with 15 and 20 vol% straight zirconia fibers was significantly increased by ∼40-fold, on average, compared to a commercial benchmark (Osteobond™) and cements reinforced with 0–10 vol% straight zirconia fibers. The mean fatigue life of a cement reinforced with 10 vol% VDFs was an order of magnitude greater than the same cement reinforced with 10 vol% straight fibers. The time-dependent viscosity of cements reinforced with 10 and 15 vol% straight fibers was comparable to the commercial benchmark during curing. Therefore, the addition of relatively small amounts of straight and variable diameter zirconia fibers was able to substantially improve the fatigue resistance of acrylic bone cement while exhibiting similar handling characteristics compared to current commercial products. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this study was to examine the effects of the hydroxyapatite (HA) reinforcement morphology and content on the fatigue behavior of HA reinforced high density polyethylene (HDPE). To this end, HDPE was reinforced with 20 and 40 vol% of either HA whiskers or an equiaxed HA powder, and tested in four-point bending fatigue under simulated physiological conditions. The fatigue life, mechanical property degradation and failure surfaces were compared between experimental groups. HDPE reinforced with HA whiskers exhibited a four- to five-fold increase (, T-test) in fatigue life compared to an equiaxed powder for either the 20 and 40 vol% reinforcement level. Composites containing 40 vol% HA exhibited decreased fatigue life compared to those with 20 vol% HA for either reinforcement morphology (, ANOVA). HA whisker reinforced HDPE exhibited less stiffness loss, permanent deformation (creep) and energy dissipation at a given number of cycles compared to HA powder. Thus, HA whisker reinforced HDPE was more tolerant of fatigue damage due to either microcracking or polymer plasticity. Scanning electron microscopy of failure surfaces and surface microcracks showed evidence of toughening by uncracked ligaments, crack tip plasticity, polymer fibril bridging and HA whisker pullout. The results of this study suggest that the use of HA whiskers, in place of HA powder, is a straightforward means to improve the fatigue life and damage tolerance of HA reinforced polymers for synthetic bone substitutes. [Copyright &y& Elsevier]

The article discusses the role of courts and legal professionals in the determination of risks involved with criminal offenders. A model of violence reconstruction is recommended via a criminal responsibility examination as a template. Expert witness can be practicable to courts when decisions need to be exercised that evolve around a possible and future dangerousness of a person. Post-release programs may be developed by correctional systems to complement pre-release programs for former inmates who have wrapped up their sentences, especially those with mental illness.