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Due to their nature as tissue composites, skeletal joints pose an additional challenge in terms of evaluating the functional significance of morphological variation in their bony and cartilaginous components in response to altered loading conditions. Arguably, this complexity requires more direct means of investigating joint plasticity and performance than typically employed to analyze macro- and micro-anatomical phenomena. To address a significant gap in our understanding of the plasticity of the mammalian temporomandibular joint (TMJ), we investigated the histology and mechanical properties of condylar articular cartilage in rabbits subjected to long-term variation in diet-induced masticatory stresses, specifically cyclical loading. Three cohorts of male weanlings were raised for six months on different diets until adulthood. Following euthanasia, the TMJ condyles on one side were dissected away, fixed, decalcified, dehydrated, embedded and sectioned. Safranin O staining was employed to identify variation in proteoglycan content, which in turn was used to predict patterns of articular cartilage stiffness in contralateral condylar specimens for each treatment group. Hematoxylin and eosin staining was used to quantify diet-induced changes in chondrocyte hypertrophy and cellularity. Mechanical tests document significant decreases in articular cartilage stiffness corresponding to patterns of extracellular matrix relative protein abundance in rabbits subjected to greater cyclical loading. This indicates that TMJs routinely subjected to higher masticatory stresses due to a challenging diet eventually develop postnatal decreases in the ability to counter compressive loads during postcanine biting and chewing. These findings provide novel information regarding TMJ performance, with broader implications about the costs and benefits of phenotypic plasticity as well as implications for how such biological processes affect connective tissue mechanobiology and pathobiology. [ABSTRACT FROM AUTHOR]

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: The present study tested the relationships between macro-level violence and birthweight in structurally disadvantaged communities in the District of Columbia. The study hypothesized that both rates of violence and violence “uncertainty” (the latter was operationalized as within-census tract residual change scores in violence), should be inversely associated with birthweight among all live singleton births in DC from 2000 to 2002. Using mixed models, the study found that (1) patterns of violence and violence uncertainty were significantly associated with birthweight among mothers residing in structurally disadvantaged communities, and (2) these findings held for Black and Hispanic, but not white, mothers. The study argues that urban ecological researchers should begin to consider not just how rates (or levels) of violence influence health and other social outcomes in communities, but also the effects of violence uncertainty as a source of unpredictable risk and territorial disruption. [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 authors compared the association of several personality traits, drug of choice, and polysubstance involvement in 325 individuals (44% male) receiving treatment for substance dependence on heroin, cocaine, and/or alcohol. Measures included the Structured Clinical Interview for DSM-III-R, the MacAndrew Alcoholism Scale (MAC), the socialization scale of the California Psychological Inventory (CPI-Soc), the novelty seeking dimension of the Temperament and Character Inventory (TCI-NS), and the conscientiousness domain of the NEO Five-Factor Inventory (NEO-C). Analyses adjusted for demographic covariates, affective and antisocial personality disorder, and substance dependence severity. Although scant evidence supported the hypothesis that these personality traits were associated with substance choice, CPI-Soc and MAC were associated linearly with the extent of polysubstance involvement. Also, patients who were dependent on two or more substances displayed higher levels of TCI-NS, CPI-Soc, and MAC. Findings implicate an association between behavioral disinhibition and a continuum of addiction defined primarily in terms of polysubstance involvement. [Copyright &y& Elsevier]

Explores the arrest patterns of police officers in domestic violence events for a stratified random sample of domestic violence incidents in two police districts in Boston, Massachusetts in 1993. Indication that risk to the victim is the most important decision-making criterion for officers; Evolving police response to domestic violence.