Light-based 3D bioprinting is now employed widely to fabricate geometrically complex constructs for various biomedical applications. However, the inherent light scattering defect creates significant challenges in patterning dilute hydrogels to form high-fidelity structures with fine-scale features. Herein, we introduce a photoinhibiting approach that can effectively suppress the light scattering effect via a mechanism of simultaneous photoabsorption and free-radical reaction. This biocompatible approach significantly improves the printing resolution (~1.2 - ~2.1 pixels depending on swelling) and shape fidelity (geometric error less than 5%), while minimising the costly trial-and-error procedures. The capability in patterning 3D complex constructs using different hydrogels is demonstrated by manufacturing various scaffolds featuring intricate multi-sized channels and thin-walled networks. Importantly, cellularised gyroid scaffolds (HepG2) are fabricated successfully, exhibiting high cell proliferation and functionality. The strategy established in this study promotes the printability and operability of light-based 3D bioprinting systems, allowing numerous new applications for tissue engineering.

This paper demonstrates the essential and efficient methods to design, and fabricate optimal vascular network for tissue engineering structures based on their physiological conditions. Comprehensive physiological requirements in both micro and macro scales were considered in developing the optimisation design for complex vascular vessels. The optimised design was then manufactured by stereolithography process using materials that are biocompatible, elastic and surface bio-coatable. The materials are self-developed photocurable resin consist of BPA-ethoxylated-diacrylate, lauryl acrylate and isobornylacrylate with Irgacure® 184, the photoinitiator. The optimised vascular vessel offers many advantages: 1) it provides the maximum nutrient supply; 2) it minimises the recirculation areas and 3) it allows the wall shear stress on the vessel in a healthy range. The stereolithography manufactured vascular vessels were then embedded in the hydrogel seeded with cells. The results of in vitro studies show that the optimised vascular network has the lowest cell death rate compared with a pure hydrogel scaffold and a hydrogel scaffold embedded within a single tube in day seven. Consequently, these design and manufacture routes were shown to be viable for exploring and developing a high range complex and specialised artificial vascular networks.

3D-printed scaffolds that forge a new path for regenerative medicine are widely used in breast reconstruction due to their personalized shape and adjustable mechanical properties. However, the elastic modulus of present breast scaffolds is significantly higher than that of native breast tissue, leading to insufficient stimulation for cell differentiation and tissue formation. In addition, the lack of a tissue-like environment results in breast scaffolds being difficult to promote cell growth. This paper presents a geometrically new scaffold, featuring a triply periodic minimal surface (TPMS) that ensures structural stability and multiple parallel channels that can modulate elastic modulus as required. The geometrical parameters for TPMS and parallel channels were optimized to obtain ideal elastic modulus and permeability through numerical simulations. The topologically optimized scaffold integrated with two types of structures was then fabricated using fused deposition modeling. Finally, the poly (ethylene glycol) diacrylate/gelatin methacrylate hydrogel loaded with human adipose-derived stem cells was incorporated into the scaffold by perfusion and ultraviolet curing for improvement of the cell growth environment. Compressive experiments were also performed to verify the mechanical performance of the scaffold, demonstrating high structural stability, appropriate tissue-like elastic modulus (0.2 – 0.83 MPa), and rebound capability (80% of the original height). In addition, the scaffold exhibited a wide energy absorption window, offering reliable load buffering capability. The biocompatibility was also confirmed by cell live/dead staining assay.

The low bioavailability of orally administered drugs as a result of the instability in the gastrointestinal tract environment creates significant challenges to developing site-targeted drug delivery systems. This study proposes a novel hydrogel drug carrier using pH-responsive materials assisted with semi-solid extrusion 3D printing technology, enabling site-targeted drug release and customisation of temporal release profiles. The effects of material parameters on the pH-responsive behaviours of printed tablets were analysed thoroughly by investigating the swelling properties under both artificial gastric and intestinal fluids. It has been shown that high swelling rates at either acidic or alkaline conditions can be achieved by adjusting the mass ratio between sodium alginate and carboxymethyl chitosan, enabling site-targeted release. The drug release experiments reveal that gastric drug release can be achieved with a mass ratio of 1:3, whilst a ratio of 3:1 allows for intestinal release. Furthermore, controlled release is realised by tuning the infill density of the printing process. The method proposed in this study can not only significantly improve the bioavailability of oral drugs, but also offer the potential that each component of a compound drug tablet can be released in a controlled manner at a target location.