Engineering microfluidic-assisted 3D bioprinting platforms for skeletal tissue engineering and disease modelling

Tissue engineering is a rapidly evolving field that both seeks to address the limitations of traditional medical treatments by regenerating or replacing damaged tissues [1,2] and involves in developing biological models to mimic the physiologic behaviour of tissue [3–5]. This multidisciplinary field combines principles from biology, materials science, and engineering to develop functional tissue constructs that can mimic the structure and function of native tissues. The core of the tissue engineering and regenerative medicine (TERM) field is the fabrication of scaffolds that perform as temporary frameworks for supporting proliferation [6,7], and differentiation [8–10], while simultaneously guiding tissue regeneration [11–13]. Thus, the properties of the scaffolds can be divided into two main categories: microscopic and macroscopic properties. Microscopic properties involve the into structural and biomolecular details at the cellular level, such as surface topography and material composition. These characteristics play a key role in regulating cell adhesion, proliferation, and differentiation [14–16]. For example, a scaffold with different surface roughness or chemical composition can influence cellular responses, such as cells spread and proliferation [14,17,18], and biomolecular diffusion or retention [19–21]. On the other hand, macroscopic properties include the overall shape, size, and porosity of the scaffold. These characteristics determine the ability of the constructs to mimic the native tissue architecture and how well the scaffold integrates with the surrounding tissue. The macroscopic geometry is essential for ensuring that the scaffold fits the anatomical shape of the mimicked tissue [22–24]. Additionally, the size pore affects fluid perfusion, oxygen supply and waste removal, which are essential to sustaining cellular activity and promoting tissue regeneration [25,26]. Ultimately, both microscopic and macroscopic properties must be carefully engineered to create scaffolds that support the needs of tissue regeneration. To date, a number of studies have exclusively focused on the microscopic properties of scaffolds, neglecting the importance of replicating also the macroscopic properties, such us both the influence of the overall shape and the reproduction of irregularities of tissues, which are essential for future implantation and tissue regeneration. TERM approach continues to face several technological limitations, as only a few devices can address both the microscopic and macroscopic properties simultaneously [27–29]. Many devices struggle to produce constructs that not only meet high standards of microscopic fidelity but also successfully reproduce the complex, irregular shapes of native tissues. Furthermore, devices that can achieve both are often prohibitively expensive, making them inaccessible to many research institutions limiting the research in tissue engineering field. This thesis work aims to tackle these challenges by developing new strategies, devices, methodologies, and printing strategies to fabricate non-standard, complex, and irregular scaffold taking care of microscopy scaffold properties simultaneously. These innovations address the significant gap in traditional TERM techniques, utilizing custom-made and accessible instrumentations to bridge the divide between affordability and advanced functionality. This summary covers the key developments in scaffold production with both macroscopic and microscopic properties, using advanced materials. A number of innovative approaches have been explored to advance the field of TERM. A custom-made bioprinting platform was created to fabricate complex tissue models for effective bone tissue applications enabling a precise spatial patterning and controlled drug release. Subsequently, the fabrication of cylindrical vascular constructs is 0 approached developing an advanced deposition methods and achieving both mechanical integrity and biological functionality. Finally, non-planar bioprinting technique was developed using a robotic arm and custom software to fabricate constructs which can replicate irregular tissue shapes.