3D printing for biomedical applications: Hybrid nanoparticle reinforced hydrogels for soft tissue regeneration and bone flaps for cranial reconstruction

Abstract

This dissertation focuses on the quantitative insights into process v science behind the development of tissue-engineered grafts using additive manufacturing (AM) technology. Additive manufacturing, commonly referred to as 3D printing, is a highly versatile process that enables the fabrication of complex structures by depositing material in a layer-bylayer manner according to a pre-defined digital model. Here, AM process is employed to fabricate soft, polymeric hydrogel scaffolds designed to support tissue regeneration. Hydrogels are three-dimensional polymeric networks capable of absorbing and retaining substantial amounts of water, which imbues them with viscoelastic properties that closely mimic those of natural tissues. Due to their high-water content and biocompatibility, hydrogels are widely used in tissue engineering applications. In this study, gelatin-based hydrogels were extruded via 3D printing to fabricate patient-specific scaffolds. Gelatin, a biopolymer derived from the partial hydrolysis of collagen, is particularly advantageous due to the presence of RGD sequence for the reconstruction of biological tissues. The experimental focus of this dissertation was to develop and optimize a series of hydrogel compositions for use in tissue-engineered scaffolds, while also investigating their interactions with biological systems, in vivo (study conducted in whole organism). To assess the biocompatibility and functional integration of these 3D-printed scaffolds, the hydrogel scaffolds were implanted subcutaneously in experimental rats, and their degradation, inflammatory response, and regenerative potential were evaluated over time. The results demonstrated that the hydrogel scaffolds underwent gradual degradation postimplantation, a desirable characteristic for the scaffolds in tissue engineering. The initial stages of degradation were accompanied by a transient inflammatory response, as expected when foreign materials are introduced into a biological system. However, the inflammation progressively diminished, with significant reduction observed by the end of the 30-day study period. These findings indicate that the scaffold materials were well-tolerated by the host tissue over time, with a favourable immune response that suggests long-term biocompatibility. The vi scaffolds exhibited properties conducive to the promotion of vascularization and tissue regeneration, including structural integrity, porosity, and biodegradability, which are critical parameters for scaffolds intended for clinical applications. The scientific evidence presented in this dissertation underscores the potential of these 3Dprinted hydrogel scaffolds as viable candidates for use in tissue engineering. However, further preclinical testing is required to fully establish their safety and efficacy before advancing to human clinical trials. Larger animal models, such as pigs or sheep, could be employed in future studies to better simulate human physiology and provide more robust data on the fabricated scaffold performance in vivo. Once validated in these models, the hydrogel scaffolds could progress to human clinical trials, where their therapeutic potential for tissue regeneration in various clinical contexts can be evaluated. In conclusion, this research contributes to the growing body of knowledge on biofabrication techniques and their application to tissue engineering. The development of 3D-printed, patientspecific hydrogel scaffolds represents a significant advancement in the field, offering a promising alternative to traditional autologous grafting techniques. By leveraging the precision of additive manufacturing and the regenerative properties of hydrogels, these scaffolds hold the potential to improve surgical outcomes, minimize complications, and facilitate personalized treatment strategies in modern healthcare. With continued research and development, these innovations may soon become integral components of clinical practice, contributing to the realization of personalized medicine and improving patient outcomes across a wide range of medical applications.