Recent reports of adverse health effects (e.g., capsular contracture, lymphoma) linked to the absence or presence of texture on soft-tissue implants (e.g., breast implants) suggest surface topography may have pathological impact(s). We propose that surface texture influences the transfer of displacements, experienced by an implant undergoing micromotion, to surrounding interfacial extracellular matrix, which in turn impacts the activity of the resident cells and is based on degree of tissue integration. We hypothesize that transfer of displacements due to micromotion promotes interstitial fluid movement that imposes hydrodynamic stresses (pressures, shear stresses) on cells residing in the interfacial tissues and impacts their activity. To address this, we developed a computer simulation to approximate hydrodynamic stresses in the interstitial environment of saturated poroelastic tissues (model soft-tissue implantation sites) generated from oscillatory implant micromotion as a function of the magnitude of translational displacement, direction of motion, degree of tissue integration, and surface roughness of the implant. Highly integrated implants were predicted to generate the highest fluid shear stresses within model tissues, with oscillatory fluid shear stresses up to 80 dyn/cm2 for a 20-μm displacement. Notably, application of oscillatory 80 dyn/cm2 shear stress to cultured human fibroblasts elicited cell death after 20 h compared to cells maintained under static conditions or exposed to 80 dyn/cm2 steady, unidirectional shear. These results indicate that oscillatory interstitial fluid stresses generated by micromotion of an integrated implant may influence the activity of the surrounding cells and play a role in the body's fibrotic response to textured soft-tissue implants.
Keywords: Computational model; Fibrotic capsule; Foreign body response; In vitro model; Mechanotransduction; Medical device; Shear stress.
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