Development of three-dimensional printed scaffold prototypes as dressings and implants intended for the treatment of skin tissue regenerative-related pathologies

Abstract

Tissue engineering is a more and more maturing field of medicine, needing increasingly automated manufacturing processes for the creation of tissue repair solutions. Herein this thesis, design and development of biocompatible materials as well as 3D printing (3DP) technology were focused and deepened in particular for the realization of hydrogel-based advanced medication prototypes, mostly dedicated to the skin regeneration but also suitable for dentistry purposes rather than for further applications. In brief, overall pre and post-3D printing process parameters were investigated, in terms of correct material processing through the developed instrumentation, as well as chemico-physical features characterizing the hydrogels. Biocompatibility, cell proliferation enhancement were also probed by inoculating human fibroblasts and/or keratinocytes and measuring their viability, distribution and morphology. In vivo experimental on diabetic ulcerated rats was assessed to prove their validity as wound dressing prototypes in comparison to a commercial patch, selected as model, and spontaneous healing. Further, alternative antimicrobial compounds to antibiotics were included in hydrogel constructs, studied in this case like controlled drug delivery systems for the treatment of infected wounds.

Development and functionalization of polymer hydrogels can boost tissue regeneration, in this work, film materials for dentistry were doped with fibronectin and its engineered binding aptamer for bone reconstruction or epithelial repair. A Further functionalization, by collagen coating, was instead adjusted for 3D printed chitosan scaffolds; several characterizations and assays were performed in order to explore their potentiality for the purpose targeted. Moreover, an analytical approach based on mass spectrometry, defined as hydrogen/deuterium exchange (HDX-MS), was tuned to better evaluate proper material functionalization with fibronectin.

Sterilization of developed prototype materials is not trivial for potentially marketable hydrogels, gamma irradiation was assessed and preliminary studied as promising suitable procedure. The 3DP overall process was retained innovative in terms of obtainable hydrogel forms, furthermore, their general technical features seemed to be prone to favor cell growth through the 3D polymer structures. In vivo trials even more efficiently demonstrated their effectiveness as medications for ameliorating tissue regeneration, proved in particular by histological staining and microscopical analysis conducted. In vitro antimicrobial activity of silver sulfadiazine-loaded scaffolds was fully achieved on P. aeruginosa and S. aureus, very common wound bed infecting pathogens. The functionalization of these hydrogel materials for dentistry aims resulted particularly effective in terms of in vitro osteoblast and epithelial cells growth enhancement as well as for those cultured on 3D printed chitosan-collagen scaffolds. Moreover, the HDX-MS analysis confirmed fibronectin could selectively recognize the aptamer, indicating an efficient docking of the complex on the biomaterial. Mass spectrometry was used also for the determination of collagen composition of decellularized rat thyroid matrixes, revealing which matrix preparation protocol was more appropriate for scaffold re-colonization. Gamma rays sterilization procedure seems in a preliminary way to be feasible, but further technical investigations are required. A step forward in the research on biocompatible materials intended for several purposes particularly focusing on wound dressings as well as their processing through additive manufacturing has been made, giving a small but hopefully significant contribute for the prototyping of hydrogels-based three-dimensional scaffolds. As additional application, resourcefulness of 3DP was exploited also for the production of biocompatible wastewaters filtering system models for detoxification from amoxicillin as pollutant pharmaceutical. TiO2 was included in form of powder in the material ad hoc developed for the purpose as drug photocatalytic agent. Characterizations and utilization tests were conducted in order to assay the feasibility of the idea. The formulation and 3D development of models of wastewaters filters surprised for its effectiveness and re-usability, further tests on other drugs are running to finely ameliorate the promising system.