No abstract

The level of integration present among organismal traits is thought to influence evolutionary potential, and this potential should be affected by the type or types of integration displayed (e.g., functional, developmental, or genetic). Morphological integration is generally high among functionally related traits, but whether this is predominantly determined by genetic architecture, or is instead a result of biomechanical remodeling during development remains poorly understood. We examine this question in Lake Malawi cichlid fishes by combining a finite-element analysis (FEA) of bite force transmission with quantitative genetic analyses of skull morphology in order to test the hypothesis that functionally coupled traits share a common genetic basis. FEA modeling indicates that the profile of the neurocranium affects its ability to resist forces transmitted from the jaws during biting, and suggests a novel role for skull shape in fish feeding mechanics. Quantitative trait loci mapping demonstrates that the functional integration between jaw and neurocranial shape has a genetic basis, and that this association is being driven by alleles inherited from the specialized biting species. Notably, the co-inheritance of these two functionally related traits in our F 2 matches patterns of covariation within and between Lake Malawi cichlid species. Across species, jaw and neurocranial shapes covary, but the trend appears strongest among biting species. Similarly, within populations of biting species, the dimensions of the jaw and neurocranium are tightly linked, whereas this correlation disappears within populations of omnivorous and suction feeding fish. These data suggest (1) that either pleiotropy, or physical linkage maintained by selection, underlies the phenotypic integration of these two functionally related traits, and (2) that this pattern of integration may have influenced the radiation of craniofacial morphology in Lake Malawi cichlids.Keywords Modularity Á Evolvability Á Adaptive radiation Á FEA Á QTL Á Lake Malawi cichlids Integration and EvolvabilityIntegration refers to the structure of covariation among traits, and the manifestation of phenotypic covariation is typically attributed to underlying functional, developmental, and/or genetic organization (

Understanding the surface micromechanical properties of ultra-high-molecular-weight polyethylene (UHMWPE) may allow for improvement in its wear characteristics. Microtomed sections of two UHMWPE tibial bearings, one that had been irradiation sterilized and shelf-aged, and the other irradiation sterilized and used in a patient, were subjected to depth sensing indentation testing. The microtomed sections exhibited a white band in the subsurface region that is characteristic of oxidation, and the indentation testing, followed by FTIR analysis at the same testing locations, was performed across this region and into the bulk of the material. Indentation testing yielded data leading to hardness, modulus, and energy dissipation factor (EDF). FTIR profiling generated information about oxidation; oxidation indices were calculated by taking a ratio of peak heights at 1,716 cm(-1) (ketone) to 2,022 cm(-1) (methylene). The mechanical properties showed a strong linear correlation with oxidation index above a minimum thickness. Modulus, hardness, and EDF all increased with increasing oxidation. The appropriate thickness-to-indentation-depth ratio was determined by two methods and was found to be approximately 20:1. The mechanical properties through the oxidized region were seen to vary with depth into the sample in a profile similar to the oxidation profile. The differing aging environments of the tibial bearings are hypothesized to have had an effect on both the mechanical and oxidation profiles. The retrieved bearing exhibited a narrower oxidation profile with peaks closer to the surface, and oxidation indices of lower magnitude. The mechanical properties proved similar, with less intense and narrower readings for the retrieved sample. This research is consistent with much of the literature.

Wear of ultra high molecular weight polyethylene (UHMWPE) is a limiting factor in longevity of joint replacements. Therefore, there is a desire to create new materials and enhance processing conditions associated with current materials to reduce wear. This requires understanding the effects of processing on performance of implants and of micron-scale wear mechanisms ongoing. Our goal is to generate detailed understanding of the micron-scale deformation-structure-properties relationships associated with UHMWPE subject to asperity wear processes and ultimately to be predictive of material success, in vivo. In this work, a surface strain analysis technique is developed and used to measure permanent strain from asperity deformations on the nano and micro scales. Deformation was applied to four material types (GUR 1050, GUR 1020, Hylamer, and Marathon) varying in molecular weight, crystallinity, and crosslinking. Surface strains were determined by mapping surface deformation fields and were compared across loading conditions and spatial scale, with variations in tip geometry and size, contact load, and material. Surface strains increased with asperity load for a fixed tip and were dependent on UHMWPE material, with a highly crystalline form exhibiting the most plastic strain and a crosslinked form exhibiting the least. Different asperity geometry [spherical microindenters with radius of 20 and 1500 mum, and a nanoindenter (Berkovich-type)] resulted in different surface strains (e.g., Berkovich vs. spherical were not similar) even when the nominal contact stress was similar. Finally, the extent of deformation during asperity wear correlates to the level of viscoelastic recovery of the materials observed after indentation testing.

The suitability of grafted vitamin-E highly crosslinked polyethylene (VE-HXPE) for use in posterior stabilized (PS) and constrained condylar knee (CCK) applications has not been explored. We hypothesized that VE-HXPE performs better than conventional and crosslinked polyethylene under clinically relevant conditions. PS tibial post fracture resistance under adverse shear loading conditions, CCK tibial post resistance to torsional fatigue, delamination resistance under high stress, and wear resistance were evaluated. Grafted VE-HXPE exhibits (1) 10% and 57% improved PS post fatigue strength compared to conventional PE (CPE) and remelted HXPE; (2) 45% improved CCK post fatigue strength compared to CPE; (3) Greater than 36× the delamination resistance of CPE; and (4) 96% and 73% wear reduction compared to CPE and HXPE. VE-HXPE performed well under clinically relevant in vitro conditions. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1789-1798, 2017.