Design and Fabrication of a Biomimetic Scaffold via Fused Deposition Modeling for Bone-on-Chip microfluidic devices

In order to optimize therapies aimed at tissue regeneration, it is essential to have access to e predictive and reliable in vitro models. Such models enable effective preclinical testing in accordance with the 3Rs principle, overcoming the limitation of 2D cell cultures and animal testing. 3D cell culture is a promising alternative to the current state-of-the-art, enabling the creation of more reliable 3D in vitro tissue models. Nowadays, advancements in microfluidics have led to platforms known as organ-on-a-chip, aimed at the in vitro study of engineered tissue models. According to the scaffold-based model of tissue engineering, these constructs have the aim to create a temporary structure that physically supports cells during tissue formation, providing biological and chemical cues. Following the structural characteristics of the target tissue, the design features of the scaffold such as the chosen biomaterials and the fabrication method are essential to achieve the desired cellular behaviour. Imbalances of the bone remodelling process are widespread, leading to diseases such as osteoporosis, which result in a significant loss of bone mass. These conditions, associated with aging, are challenging to characterize and have generated interest in developing innovative approaches to study the physio-pathological conditions of bone tissue. Researching efforts is also focused on the creation of an in vitro bone tissue model capable of mimicking the complex biocomposite material of bone tissue, characterized by a hierarchical structure at the micro and nano scale. In this work, composite scaffold constructs (PLA/nano-hydroxyapatite) have been developed for bone tissue modeling. Polylactic acid (PLA) is a biocompatible and biodegradable polymer, frequently used for bone tissue engineering. Hydroxyapatite (HA), the natural inorganic phase component of bone, provides greater mechanical strength and is naturally present at the bone site. PLA scaffolds were obtained by casting or manufactured with fused deposition modelling (FDM). Subsequently, the combination of the two materials occurred through surface functionalization, utilizing a mussel-inspired coating approach based on 3,4-dihydroxy-DL-phenylalanine (DOPA) polymerization to graft nHA onto PLA films and scaffolds. Two different coating techniques were utilized and compared, a layer-wise and a hybrid coating method. Scaffolds were characterized by morphological analysis through Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) analysis. To assess the functionalization with the DOPA coating, FTIR, WCA, and mechanical compression tests were performed. In vitro degradation studies were also conducted to demonstrate stability. Finally, preliminary studies with cells were carried out to assess the biocompatibility of the developed construct. The optimized construct will subsequently be integrated into a multi-compartment microchip for biological validation.