Large bone defects represent a significant challenge for clinicians and surgeons. Tissue engineering for bone regeneration represents an innovative solution for this dilemma and may yield attractive alternate bone substitutes. Three-dimensional (3D) printing with inexpensive desktop printers shows promise in generating high-resolution structures mimicking native tissues using biocompatible, biodegradable, and cost-effective thermoplastics, which are already FDA-approved for food use, drug delivery, and many medical devices. Microporous 3D-printed polylactic acid scaffolds, with different pore sizes (500, 750, and 1000 μm), were designed and manufactured using an inexpensive desktop 3D printer, and the mechanical properties were assessed. The scaffolds were compared for cell growth, activity, and bone-like tissue formation using primary human osteoblasts. Osteoblasts showed high proliferation, metabolic activity, and osteogenic matrix protein production, in which 750 μm pore-size scaffolds showed superiority. Further experimentation using human mesenchymal stem cells on 750 μm pore scaffolds showed their ability in supporting osteogenic differentiation. These findings suggest that even in the absence of any surface modifications, low-cost 750 μm pore-size 3D-printed scaffolds may be suitable as a bone substitute for repair of large bone defects.

Numerous studies show promise for cell-based tissue engineering strategies aiming to repair painful intervertebral disc (IVD) degeneration. However, clinical translation to human IVD repair is slow. In the present study, the regenerative potential of an autologous nucleus pulposus (NP)-cell-seeded thermoresponsive hyaluronic acid hydrogel in human lumbar IVDs was assessed under physiological conditions. First, agaroseencased in vitro constructs were developed, showing greater than 90 % NP cell viability and high proteoglycan deposition within HA-pNIPAM hydrogels following 3 weeks of dynamic loading. Second, a bovine-induced IVD degeneration model was used to optimise and validate T1ρ magnetic resonance imaging (MRI) for detection of changes in proteoglycan content in isolated intact IVDs. Finally, isolated intact human lumbar IVDs were pre-scanned using the established MRI sequence. Then, IVDs were injected with HA-pNIPAM hydrogel alone or autologous NP-cell-seeded. Next, the treated IVDs were cultured under cyclic dynamic loading for 5 weeks. Post-treatment T1ρ values were significantly higher as compared to pre-treatment scans within the same IVD and region of interest. Histological evaluation of treated human IVDs showed that the implanted hydrogel alone accumulated proteoglycans, while those that contained NP cells also displayed neo-matrix-surrounded cells within the gel. The study indicated a clinical potential for repairing early degenerative human IVDs using autologous cells/hydrogel suspensions. This unique IVD culture setup, combined with the long-term physiological culture of intact human IVDs, allowed for a more clinically relevant evaluation of human tissue repair and regeneration, which otherwise could not be replicated using the available in vitro and in vivo models.

Scaffold porosity plays an important role in bone tissue engineering as macropores promote cell migration and micropores promote protein adsorption and cell adhesion. Currently, most methods use complex, multi-step processes to create dual-scale porosity in composite scaffolds, and no studies evaluate the effect of microporosity on the bioactivity of composite scaffolds with dual porosity. To fill this gap, a simple solvent casting and porogen leaching technique using paraffin microspheres as a porogen and CitriSolv as the leaching solvent to prepare macroporous Bioglass-poly(lactic-co-glycolic acid) (Bg-PLGA) scaffolds with intrinsic micropores (1-10 μm) in the PLGA matrix is proposed, and the effect of microporosity on the bioactivity of the scaffolds is analyzed. PLGA matrix microporosity induces larger apatite deposition upon immersion in simulated body fluid, as well as enhanced protein adsorption upon contact with serum, compared to non-microporous scaffolds. Also, mesenchymal cells cultured on the microporous scaffolds show extensive matrix deposition. These results highlight this method as a simple and effective technique to produce dual-porosity scaffolds that are excellent candidates for bone tissue engineering, as their enhanced bioactivity, protein adsorption, and the extensive matrix deposition observed in-vitro are good indicators of fast bone integration upon implantation.