Villi Inspired Elastomeric Interlocking Device for Intestinal Retentive Applications

<b>Achieving prolonged retention of medical devices in the small intestine while mitigating tissue trauma remains a significant clinical challenge. Tissue-piercing microneedles harm intestinal epithelium inducing inflammation while reactive mucoadhesives are susceptible to fouling.</b><br/><b>Inspired by morphology of the intestinal villi, a mechanical interlocker laminated with high-aspect-ratio elastomeric microposts, that mimic dimensions of the villi, is investigated to develop intestinal retentive platforms. Effectiveness of the interlockers to resist peristalsis is characterized by performing mechanical simulations on Autodesk Fusion 360 and by determining the resistive force applied by villus when it collides with mobile micropost using Euler-Bernoulli beam theory for large deflections. </b><br/><b>The interlocking properties are optimized by studying two simulation models that investigate the influence of device material properties (50kPa &lt; <i>E</i>_m &lt; 1GPa, Poisson’s ratio = 0.49), micropost pitch ( 20,16,12,9 microposts per mm²), arrangement (cubic/hexagonal) and tip geometry (round/cubic) on the resistive force as the microposts interaction with villi under peristaltic shear (0.01N/cm²) and contraction (2666.45Pa). </b><br/><b>Digital Light Processing (DLP) 3D printing in tandem with a multi-step replica molding technique is used to fabricate the microposts and artificial villi (<i>E</i>_v= 50kPa). Dimensions of the microposts are optimized to address shrinkage post UV curing to achieve desired aspect ratio of ~5:1 (length = 1500um) and scanning electron microscopy is used to characterize the microposts (surface roughness = 20um). Work of interlocking between fabricated microposts and villi under varying preload and drag velocity is then evaluated through in vitro lap-shear tests performed on customized equipment to validate simulation results. </b><br/><b>It is demonstrated that the ability of individual villus to resist movement of a mobile micropost is directly proportional to the elastic modulus of the micropost and preload (<i>F</i>_sim upto 812uN, <i>E</i>_m = 10MPa). In vitro studies comply with simulation results permitting use of computational approach for future study of elastomeric mechanical interlocking systems (<i>F</i>_sim/<i>F</i>_exp= 1.06, <i>E</i>_m = 2.05MPa, degree of overlap = 95%). Additionally, interlockers seating 20 round tipped microposts per mm² arranged hexagonally can effortlessly consolidate within villi (&gt;95% degree of overlap) through peristaltic contraction thereby eliminating the need for external stimulation and optimally resist peristaltic shear via mechanical interlocking (Experimental Work of Interlocking = 64uJ per mm²). </b><br/><b>These interlockers present a compliant non-penetrative method to develop minimally invasive intestinal retentive platforms for applications in gut diagnostics by indwelling sensors, neuromodulation and oral drug delivery. </b>