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Abstract Background In-vitro mechanical tests are commonly performed to assess pre-clinically the effect of implant design on the stability of hip endoprostheses. There is no standard protocol for these tests, and the forces applied vary between studies. This study examines the effect of the abductor force with and without application of the anterior-posterior hip contact force in the in-vitro assessment of cementless hip implant stability. Methods Cementless stems (VerSys Fiber Metal) were implanted in twelve composite femurs which were divided into two groups: group 1 (N = 6) was loaded with the hip contact force only, whereas group 2 (N = 6) was additionally subjected to an abductor force. Both groups were subjected to the same cranial-caudal hip contact force component, 2.3 times body weight (BW) and each specimen was subjected to three levels of anterior-posterior hip contact load: 0, -0.1 to 0.3 BW (walking), and -0.1 to 0.6 BW (stair climbing). The implant migration and micromotion relative to the femur was measured using a custom-built system comprised of 6 LVDT sensors. Results Substantially higher implant motion was observed when the anterior-posterior force was 0.6BW compared to the lower anterior-posterior load levels, particularly distally and in retroversion. The abductor load had little effect on implant motion when simulating walking, but resulted in significantly less motion than the hip contact force alone when simulating stair climbing. Conclusions The anterior-posterior component of the hip contact load has a significant effect on the axial motion of the stem relative to the bone. Inclusion of the abductor force had a stabilizing effect on the implant motion when simulating stair climbing.

Controlling voids to minimize the final porosity level is an important concern when processing advanced composite structures. In this study, the porosity evolution during processing of partially impregnated prepregs is investigated using interrupted cure cycles and optical microscopy. Laminates made of MTM 45-1/5HS carbon/epoxy prepreg subjected to different cure cycles, bagging conditions, and humidity levels were studied. Fiber tow geometry and gas permeability were measured to determine the amount of compaction and the interconnectivity of unsaturated zones in the laminates. Three types of voids were identified: inter-laminar, fiber tow and resin voids, all with different origins and evolution patterns. It is shown that gas transport (both in-plane and through-thickness), fiber bed compaction, and resin infiltration govern void evolution during processing. The results provide insights for development of representative transport models and to optimize processing cycles. [ABSTRACT FROM AUTHOR]

Partially-impregnated prepregs are three-phase systems consisting of fiber, resin, and gas. During processing, one of the main goals is to evacuate the gas and infiltrate the space left behind with liquid resin to minimize porosity. Most work in this area has focused on gas and resin transport independently, and the interaction between resin and gas transport in these systems is currently poorly understood. The current study examines this interaction by evaluating the resulting laminate porosity as a function of different bag and applied pressures during debulk and cure. Experimental results show that resin flow can promote gas evacuation without the need for hard vacuum under the bag. An explicitly-coupled gas–resin transport model is developed on the basis that fiber-bed porosity is a function of resin infiltration. The model extends previous work in the area and is shown to predict the experimentally measured porosity under different pressure situations with acceptable accuracy. [ABSTRACT FROM AUTHOR]

This article presents an experimental study of the effect of tool/consolidation temperature on dimensional fidelity and curved beam strength of thermoformed carbon/PEEK composites made of continuous fibers and random oriented strands (ROS). When processing continuous fiber carbon/PEEK composites, higher tool/consolidation temperatures give higher curved beam and inter‐ply strength and more repeatable process induced deformations. Spring‐in increases with tool temperature but the spring‐in is repeatable and flange warpage is reduced because of lower resin viscosity and increased material flow during consolidation. For the ROS material form, no increase in curved beam strength was observed with higher consolidation temperatures and failure was not governed by the inter‐ply strength of the laminate because of the shorter fibers. Lower tool/consolidation temperatures gave less spring‐in and flange warpage was not dependent on consolidation temperature. Spring‐in for both material forms was found to be thermo‐elastic with no effects from crystallization shrinkage. [ABSTRACT FROM AUTHOR]

Void characterization and porosity measurements of uncured and partially cured carbon/epoxy prepregs are challenging due to the soft nature of the matrix. If samples need to be cut from a larger laminate, the act of cutting and polishing can alter the void morphology. This paper presents a method to prepare samples for optical microscopy by infiltrating the pore space in the soft prepreg with a room-temperature curing low-viscosity resin to support the structure during cutting and polishing in preparation for optical microscopy. The methodology is validated by comparison with results obtained from porosity measurements using the ASTM D2734 standard density method. The paper also explores the use of thickness measurements to determine porosity. It is shown that thickness measurements can be used to estimate porosity for the no-bleed out-of-autoclave prepreg system used in the present study but that the accuracy is lower than using microscopy or density methods. [ABSTRACT FROM AUTHOR]

Background: In-vitro mechanical tests are commonly performed to assess pre-clinically the effect of implant design on the stability of hip endoprostheses. There is no standard protocol for these tests, and the forces applied vary between studies. This study examines the effect of the abductor force with and without application of the anteriorposterior hip contact force in the in-vitro assessment of cementless hip implant stability. Methods: Cementless stems (VerSys Fiber Metal) were implanted in twelve composite femurs which were divided into two groups: group 1 (N = 6) was loaded with the hip contact force only, whereas group 2 (N = 6) was additionally subjected to an abductor force. Both groups were subjected to the same cranial-caudal hip contact force component, 2.3 times body weight (BW) and each specimen was subjected to three levels of anterior-posterior hip contact load: 0, -0.1 to 0.3 BW (walking), and -0.1 to 0.6 BW (stair climbing). The implant migration and micromotion relative to the femur was measured using a custom-built system comprised of 6 LVDT sensors. Results: Substantially higher implant motion was observed when the anterior-posterior force was 0.6BW compared to the lower anterior-posterior load levels, particularly distally and in retroversion. The abductor load had little effect on implant motion when simulating walking, but resulted in significantly less motion than the hip contact force alone when simulating stair climbing. Conclusions: The anterior-posterior component of the hip contact load has a significant effect on the axial motion of the stem relative to the bone. Inclusion of the abductor force had a stabilizing effect on the implant motion when simulating stair climbing. [ABSTRACT FROM AUTHOR]

Revision total hip replacement with impaction allografting has an attractive potential for restoring bone stock, however, fractures and implant migration remain problematic. Postoperative graft deformation is believed to contribute to migration. Under compressive loading, the fluid in the graft takes up the load initially through fluid pressure that dissipates over time. Given the short duration of an impaction, we proposed two novel graft compaction techniques that allow more time for fluid flow: holding a compression force constant for 90 s (creep technique), and cycles of compressing the graft to a given force and then holding the displacement constant (cyclic relaxation technique). This study examined the effect of the impaction force on the density and mechanical characteristics of the graft, and explored the potential benefit of the proposed alternative compaction techniques. Increasing the impaction force from "low" to "high" increased graft density by 41%, and this translated to stiffness and shear strength increases of 93 and 164%, respectively. The creep technique improved the stiffness and shear strength by 14 and 16%, respectively, when compared with impaction, while the cyclic relaxation technique did not improve the mechanical properties. Although the creep technique could potentially provide a lower risk of intraoperative fracture over the use of larger impaction forces, any clinical benefit of the creep technique warrants further investigation. Our results point to the importance of maximizing impaction forces in impaction allografting surgery. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008 [ABSTRACT FROM AUTHOR]

Marrow stromal cells (MSCs) are ideally suited for tissue engineered bone grafts since they have the potential to regenerate bone, but may also maintain the homeostasis of the repaired tissue through their ability for self-renewal. An ideal bone graft substitute should support MSC self-renewal as well as differentiation to ensure complete bone defect regeneration and maintenance. The purpose of this investigation was to determine the effect of different substrate materials on MSC expansion and differentiation. Calcium polyphosphate (CPP), bone and hydroxyapatite/tricalcium phosphate (HA/TCP) were seeded with rat MSCs and maintained in culture conditions that promote cell expansion. At 0, 3, 7, 14, and 21 days cell numbers were determined by measuring their metabolic activity using a MTT assay and the frequency of cycling cells by 24 hr BrdU incorporation. Osteogenic, chondrogenic, and adipogenic marker expression in these cultures was measured by qRT-PCR. An initial drop in cell numbers was observed on all substrates. CPP and bone, but not HA/TCP supported an increase in proliferating cells at day 14 and 21. In addition, no upregulation of mature bone markers was observed in cells cultured on CPP and bone, which suggests that these substrates support the expansion of undifferentiated MSCs. In contrast, cell numbers on HA/TCP decreased with time and only rare BrdU positive cells were observed. This decrease in proliferation correlated with the down regulation of osteogenic progenitor markers and the substantial increase in mature osteocyte markers, indicating that HA/TCP favors MSC differentiation and maturation along the osteogenic lineage., ((c) 2010 Wiley Periodicals, Inc.)