Neo-Natal Castration Leads to Subtle Differences in Porcine Anterior Cruciate Ligament Morphology and Function in Adolescence.

Female adolescent athletes are at a higher risk of tearing their anterior cruciate ligament (ACL) than male counterparts. While most work related to hormones has focused on the effects of estrogen to understand the increased risk of ACL injury, there are other understudied factors, including testosterone. The purpose of this study was to determine how surgical castration in the male porcine model influences ACL size and function across skeletal growth. Thirty-six male Yorkshire crossbreed pigs were raised to 3 (juvenile), 4.5 (early adolescent), and 6 months (adolescent) of age. Animals were either castrated (barrows) within 2 weeks after birth or were left intact (boars). Posteuthanasia, joint and ACL size were assessed via MRI, and biomechanics were assessed via a robotic testing system. Joint size increased throughout age, yet barrows had smaller joints than boars. ACL cross-sectional area (CSA), length, volume, and in situ stiffness increased with age, as did the percent contribution of the ACL anteromedial (AM) bundle to resisting loads. Boar ACL, AM bundle, and PL bundle volumes were 19%, 25%, and 15% larger than barrows across ages. However, ACL CSA, in situ stiffness, and bundle contribution were similar between boars and barrows. The barrows had smaller temporal increases in AM bundle function than boars, but these data were highly variable. Early and sustained loss in testosterone leads to subtle differences in ACL morphology but may not influence measures associated with increased injury risk, such as CSA or bundle forces in response to applied loads.

Photopolymerization Parameters Influence Mechanical, Microstructural, and Cell Loading Properties of Rapidly Fabricated Cell Scaffolds.

Engineered scaffolds are commonly used to assist in cellular transplantations, providing crucial support and specific architecture for a variety of tissue engineering applications. Photopolymerization as a fabrication technique for cell scaffolds enables precise spatial and temporal control of properties and structure. One simple technique to achieve a two-dimensional structure is the use of a patterned photomask, which results in regionally selective photo-cross-linking. However, the relationships between photopolymerization parameters like light intensity and exposure time and outcomes like structural fidelity and mechanical properties are not well-established. In this work, we used photopolymerization to generate degradable polycaprolactone triacrylate (PCLTA) scaffolds with a defined microstructure. We examined the impact of light intensity and exposure time on scaffold properties such as shear modulus and micropore structure. To assess feasibility in a specific application and determine the relationship between parameter-driven properties and cell loading, we cultured retinal progenitor cells on the PCLTA scaffolds. We found that light intensity and polymerization time directly impact the scaffold stiffness and micropore structure, which in turn influenced the cell loading capacity of the scaffold. Because material stiffness and topography are known to impact cell viability and fate, understanding the effect of scaffold fabrication parameters on mechanical and structural properties is critical to optimizing cell scaffolds for specific applications.

Neo-natal castration leads to subtle differences in porcine anterior cruciate ligament morphology and function in adolescence.

Female adolescent athletes are at a higher risk of tearing their anterior cruciate ligament (ACL) than male counterparts. While most work related to hormones has focused on the effects of estrogen to understand the increased risk of ACL injury, there are other understudied factors, including testosterone. The purpose of this study was to determine how surgical castration in the male porcine model influences ACL size and function across skeletal growth. Thirty-six male Yorkshire crossbreed pigs were raised to 3 (juvenile), 4.5 (early adolescent), and 6 months (adolescent) of age. Animals were either castrated (barrows) within 1-2 weeks after birth or were left intact (boars). Post-euthanasia, joint and ACL size were assessed via MRI, and biomechanics were assessed via a robotic testing system. Joint size increased throughout age, yet barrows had smaller joints than boars (p<0.001 for all measures). ACL cross-sectional area (CSA), length, volume, and stiffness increased with age (p<0.0001), as did ACL anteromedial (AM) bundle percent contribution to resisting loads (p=0.012). Boar ACL, AM bundle, and PL bundle volumes were 19% (p=0.002), 25% (p=0.003), and 15% (p=0.04) larger than barrows across ages. However, CSA, stiffness, and bundle contribution were similar between boars and barrows (p>0.05). The barrows had smaller temporal increases in AM bundle percent function than boars, but these data were highly variable. Thus, early and sustained loss in testosterone leads to subtle differences in ACL morphology, but may not influence measures associated with increased injury risk, such as CSA or bundle forces in response to applied loads.

Critical scaling near the yielding transition in granular media.

We show that the yielding transition in granular media displays second-order critical-point scaling behavior. We carry out discrete element simulations in the low-inertial-number limit for frictionless, purely repulsive spherical grains undergoing simple shear at fixed nondimensional shear stress Σ in two and three spatial dimensions. To find a mechanically stable (MS) packing that can support the applied Σ, isotropically prepared states with size L must undergo a total strain γ_{ms}(Σ,L). The number density of MS packings (∝γ_{ms}^{-1}) vanishes for Σ>Σ_{c}≈0.11 according to a critical scaling form with a length scale ξ∝|Σ-Σ_{c}|^{-ν}, where ν≈1.7-1.8. Above the yield stress (Σ>Σ_{c}), no MS packings that can support Σ exist in the large-system limit L/ξ≫1. MS packings generated via shear possess anisotropic force and contact networks, suggesting that Σ_{c} is associated with an upper limit in the degree to which these networks can be deformed away from those for isotropic packings.

Meaning of biodistance statistics: a test case using adult monozygotic twins.

Anthropometry, historically one of the primary research techniques in physical anthropology, has been widely utilized in biodistance studies. The complex genetic and environmental interaction that governs the expression of anthropometric dimensions, together with concerns over measurement error, have sometimes clouded the interpretation of biodistances based upon anthropometry. In this study, 51 pairs of adult monozygotic twins were analysed using discriminant analysis and Mahalanobis' generalized distance. Both male and female twins, grouped by first- versus second-born, displayed very small, statistically insignificant distances between groups. When literature estimates of intra-observer measurement errors were used as a frame of reference, the average absolute differences between the twin pairs were approximately twice the size of the measurement error estimates. The results of this study suggest that, first, the environmental effect upon the genetically influenced traits measured by anthropometry is not large enough to bring about significant multivariate differences between identical twin pairs; and, second, biodistance studies based upon anthropometry can be reliable so long as measurement error is minimized.