Repair of the dura mater with processed collagen devices.

BACKGROUND: We evaluated in a canine duraplasty model how specific differences in device physicomechanical properties, porosity, and crosslinking influenced the biological performance of three processed collagen dural substitutes. METHODS: Three collagen dural substitutes were studied: Dura-Guard, DuraGen, and Durepair. The initial strength, stiffness, and suture retention force were measured using standard mechanical test methods. The relative pore sizes of each device were assessed with a scanning electron microscope. Differential scanning calorimetry was used to measure their respective collagen denaturation temperatures. The biologic response and performance of the materials were evaluated via an acute (1 month) and long-term (3 and 6 months) canine bilateral duraplasty study. RESULTS: The mechanical properties of Dura-Guard and Durepair were similar to native dura. We could not quantify the mechanical properties of DuraGen because of its fragile nature. The denaturation temperature of DuraGen and Dura-Guard differed significantly from that reported for native collagens. The denaturation temperature of Durepair was comparable with the values reported for native collagens. All three materials were tolerated well by the animals. DuraGen did not maintain its structural integrity beyond 1 month. Dura-Guard and Durepair persisted for 6 months. Durepair was populated by fibroblasts and blood vessels, whereas Dura-Guard was not. CONCLUSIONS: The three dural substitutes tested were found to be safe and effective in healing surgically created defects in the dura mater. Although each of these dura substitutes are composed of collagen, differences in the collagen source and processing influenced device physicomechanical properties, porosity, and the nativity of the collagen polymer. These measured differences influenced device intraoperative handling and installation as well as the post-operative biological response, where differences in device resorption, cell penetration, vascularization, and collagen remodeling were observed.

Linear poroelastic cancellous bone anisotropy: trabecular solid elastic and fluid transport properties.

The mechanical performance of cancellous bone is characterized using experiments which apply linear poroelasticity theory. It is hypothesized that the anisotropic organization of the solid and pore volumes of cancellous bone can be physically characterized separately (no deformable boundary interactive effects) within the same bone sample. Due to its spongy construction, the in vivo mechanical function of cancellous or trabecular bone is dependent upon fluid and solid materials which may interact in a hydraulic, convective fashion during functional loading. This project provides insight into the organization of the tissue, ie., the trabecular connectivity, by defining the separate nature of this biphasic performance. Previous fluid flow experiments [Kohles et al., 2001, Journal of Biomechanics, 34(11), pp. 1197-1202] describe the pore space via orthotropic permeability. Ultrasonic wave propagation through the trabecular network is used to describe the solid component via orthotropic elastic moduli and material stiffness coefficients. The linear poroelastic nature of the tissue is further described by relating transport (fluid flow) and elasticity (trabecular load transmission) during regression analysis. In addition, an empirical relationship between permeability and porosity is applied to the collected data. Mean parameters in the superior-inferior (SI) orientation of cubic samples (n=20) harvested from a single bovine distal femur were the largest (p<0.05) in comparison to medial-lateral (ML) and anterior-posterior (AP) orientations: Apparent elastic modulus (2,139 MPa), permeability (4.65x10(-10) m2), and material stiffness coefficient (13.6 GPa). A negative correlation between permeability as a predictor of structural elastic modulus supported a parametric relationship in the ML (R2=0.4793), AP (R2=0.3018), and SI (R2=0.6445) directions (p<0.05).