4D Printing Self-Deploying Bio-Based Structure for the Non-Invasive Treatment of Intestinal Ulcers

Ulcers are a breach in the membrane of the stomach or intestine caused by inflamed necrotic tissue. When they develop in the ileum and jejunum, ulcers represent a burden clinical challenge, since they are not accessible through regular colon- or gastroscopy. Here, we envision the design and fabrication via 4D printing of a self-deployable microfabricated and multi-layered structure, physically programmed to reach a mild bleeding chronic ulcer, wirelessly communicate, and locally promote the tissue regeneration, thanks to bio-enabled materials processed via 4D printing (i.e. the fabrication via additive manufacturing of active structure characterized by a programmed change, over time, under a predefined stimulus) for the non-invasive treatment of ulcers.<br/>The self-deploying over time can be achieved through the differential swelling properties of a bilayer C-shaped cylindrical structure. The swelling mismatch creates a deformation gradient in the structure that drives its deploy when hydrated. The two layer of the structure are made of the same bulk material, i.e., (3-Glycidoxypropyl) methyldiethoxysilane crosslinked gelatin in PBS (GPTMS-GEL), and the swelling behavior was tuned through the material concentration.<br/>Finite element modeling has been exploited to study the interactions between structural mechanics and the hygroscopic swelling, and to predict the humidity-triggered shape change of the structure according to its geometry, properties and arrangement of materials. Preliminary models shown that the aforementioned difference in swelling lead to the desired self-deploying of the structure when the materials are properly arranged in space.<br/>Then, we fabricated a proof of concept of the self-deployable structure (i.e., C-shape with an internal Ø of 12 mm and a length of 20 mm) using a custom 3D printer equipped with a piston driven extruder and a rotating spindle. The inner layer of the structure was made by the high swelling solution, extruded on a spindle, purposely fabricated via stereolithography, to form 2.4 mm spaced lines with a width of 1.6 mm. The second layer was made of low swelling material and was deposited on the previous one to create a continuous layer. The structure was then dried for 48h, removed from the spindle, and finally its humidity-triggered self-deploying was analyzed by dipping the structure into a PBS 1X solution. Those tests showed the structure ability to self-deploy in a water-based solutions, in around 100 sec., thus enlarging its surface and potentially cover an ulcer.<br/>Finally, we designed and fabricated a sacrificial spindle to be used as printing support, able to degrade once hydrating, thus realizing the 4D printed structure. This sacrificial spindle (internal Ø = 3mm, external Ø = 6mm, length = 20 mm) was fabricated via fused deposition modeling in Polyvinyl alcohol (PVA) using a spiral vise slicing approach. Its degradation profile was evaluated at different pH (i.e., 7.4 and 6.2), that represents the pH range encountered in the intestinal tract of interest. Those tests showed that the PVA spindle is able to completely dissolve in around 110 minutes, in both tested solutions.<br/>We are currently optimizing the inclusion of peptides-enriched regenerated silk into the gelatin-based solution to allow the localization and adhesion of the structure to a bleeding ulcer and to promote tissue regeneration. In this context, infrared spectroscopy will be used to assess the role of the folding of the secondary structures on the swelling properties of the gelatin-based structure and the citotoxicity of structure <i>in vitro </i>by Caco2 culture<i>. </i>Moreover, we are miniaturizing the device to be easily swallowable, and we are implementing the addition of an external gastro-resistant layer (e.g., alginate) to cover the smart structure and protect it from the acid pH of the stomach, thus enabling the administration of the device orally.