Search

Autologous fat grafting offers significant promise for the repair of soft tissue deformities; however, high resorption rates indicate that engineered solutions are required to improve adipose tissue (AT) survival. Advances in material development and biofabrication have laid the foundation for the generation of functional AT constructs; however, a balance needs to be struck between clinically feasible delivery and improved structural integrity of the grafts. A new approach combining the objectives from both the clinical and research communities will assist in developing morphologically and genetically mature AT constructs, with controlled spatial arrangement and increased potential for neovascularization. In a rapidly progressing field, this review addresses research in both the preclinical and bioengineering domains and assesses their ability to resolve functional challenges.

Tissue engineering approaches for bone repair have rapidly evolved due to the development of novel biofabrication technologies, providing an opportunity to fabricate anatomically-accurate living implants with precise placement of specific cell types. However, limited availability of biomaterial inks, that can be 3D-printed with high resolution, while providing high structural support and the potential to direct cell differentiation and maturation towards the osteogenic phenotype, remains an ongoing challenge. Aiming towards a multifunctional biomaterial ink with high physical stability and biological functionality, this work describes the development of a nanocomposite biomaterial ink (Mg-PCL) comprising of magnesium hydroxide nanoparticles (Mg) and polycaprolactone (PCL) thermoplastic for 3D printing of strong and bioactive bone regenerative scaffolds. We characterised the Mg nanoparticle system and systematically investigated the cytotoxic and osteogenic effects of Mg supplementation to human mesenchymal stromal cells (hMSCs) 2D-cultures. Next, we prepared Mg-PCL biomaterial ink using a solvent casting method, and studied the effect of Mg over mechanical properties, printability and scaffold degradation. Furthermore, we delivered MSCs within Mg-PCL scaffolds using a gelatin-methacryloyl (GelMA) matrix, and evaluated the effect of Mg over cell viability and osteogenic differentiation. Nanocomposite Mg-PCL could be printed with high fidelity at 20 wt% of Mg content, and generated a mechanical reinforcement between 30%–400% depending on the construct internal geometry. We show that Mg-PCL degrades faster than standard PCL in an accelerated-degradation assay, which has positive implications towards in vivo implant degradation and bone regeneration. Mg-PCL did not affect MSCs viability, but enhanced osteogenic differentiation and bone-specific matrix deposition, as demonstrated by higher ALP/DNA levels and Alizarin Red calcium staining. Finally, we present proof of concept of Mg-PCL being utilised in combination with a bone-specific bioink (Sr-GelMA) in a coordinated-extrusion bioprinting strategy for fabrication of hybrid constructs with high stability and synergistic biological functionality. Mg-PCL further enhanced the osteogenic differentiation of encapsulated MSCs and supported bone ECM deposition within the bioink component of the hybrid construct, evidenced by mineralised nodule formation, osteocalcin (OCN) and collagen type-I (Col I) expression within the bioink filaments. This study demonstrated that magnesium-based nanocomposite bioink material optimised for extrusion-based 3D printing of bone regenerative scaffolds provide enhanced mechanical stability and bone-related bioactivity with promising potential for skeletal tissue regeneration.

Human bone marrow stromal cells (hBMSCs) have been extensively utilised for bone tissue engineering applications. However, they are associated with limitations that hinder their clinical utility for bone regeneration. Cell fate can be modulated via altering their epigenetic functionality. Inhibiting histone deacetylase (HDAC) enzymes have been reported to promote osteogenic differentiation, with HDAC3 activity shown to be causatively associated with osteogenesis. Therefore, this study aimed to investigate the potential of using an HDAC2 & 3 selective inhibitor - MI192 to induce epigenetic reprogramming of hBMSCs and enhance its therapeutic efficacy for bone formation. Treatment with MI192 caused a time-dose dependant reduction in hBMSCs viability. MI192 was also found to substantially alter hBMSCs epigenetic function through reduced HDAC activity and increased histone acetylation. hBMSCs were pre-treated with MI192 (50 μM) for 48 h prior to osteogenic induction. MI192 pre-treatment significantly upregulated osteoblast-related gene/protein expression (Runx2, ALP, Col1a and OCN) and enhanced alkaline phosphatase specific activity (ALPSA) (1.43-fold) (P ≤ 0.001). Moreover, MI192 substantially increased hBMSCs extracellular matrix calcium deposition (1.4-fold) (P ≤ 0.001) and mineralisation when compared to the untreated control. In 3D microtissue culture, MI192 significantly promoted hBMSCs osteoblast-related gene expression and ALPSA (> 2.41-fold) (P ≤ 0.001). Importantly, MI192 substantially enhanced extracellular matrix deposition (ALP, Col1a, OCN) and mineralisation (1.67-fold) (P ≤ 0.001) within the bioassembled-microtissue (BMT) construct. Following 8-week intraperitoneal implantation within nude mice, MI192 treated hBMSCs exhibited enhanced extracellular matrix deposition and mineralisation (2.39-fold) (P ≤ 0.001) within the BMT when compared to the untreated BMT construct. Taken together, these results demonstrate that MI192 effectively altered hBMSCs epigenetic functionality and is capable of promoting hBMSCs osteogenic differentiation in vitro and in vivo, indicating the potential of using epigenetic reprogramming to enhance the therapeutic efficacy of hBMSCs for bone augmentation strategies.

3D bioprinting of constructs for tissue engineering and regenerative medicine has steadily gained attention due to its potential to fabricate anatomically-precise living constructs, localise specific cell types and enable the regeneration of functional tissues in a clinical setting. However, the limited availability of bioinks that can be successfully 3D bioprinted with high fidelity and simultaneously provide encapsulated cells with a tailored, low-stiffness microenvironment supporting functional tissue formation remains an unmet challenge. To address both the physical and biological limitations of available bioinks, this study aimed to develop a nanocomposite bioink (Sr-GelMA) comprising of strontium-carbonate (Sr) nanoparticles and low concentration (5 w/v%) gelatin-methacryloyl (GelMA) hydrogel for extrusion-based 3D bioprinting of low-stiffness cell-laden scaffolds with high shape fidelity and bone-specific cell signalling factors. We systematically investigated the effect of Sr incorporation on hydrogel physico-chemical properties, print fidelity, scaffold shape retention, as well as cell viability, osteogenic differentiation and in vitro bone formation. Nanocomposite Sr-GelMA hydrogels retained their physical and mechanical properties, while rheological studies revealed a significant increase in viscosity profiles that led to notably enhanced printability compared to GelMA alone. Moreover, bioprinted Sr-GelMA scaffolds exhibited excellent shape fidelity evidenced by a defined pore geometry on the x-y-z axis, resulting in an interconnected bioink filament and pore network that was maintained even after long-term culture and osteogenic differentiation (28 days) of human mesenchymal stromal cells (hMSCs). The presence of clustered Sr nanoparticles in the cell-laden bioink allowed high quality bioprinting combined with high hMSC viability (>95%) post-fabrication. Furthermore, Sr addition resulted in enhanced osteogenic differentiation of hMSCs as revealed by higher alkaline phosphatase (ALP) levels, osteocalcin (OCN) and collagen type-I (Col I) expression, with mineralised nodule formation distributed homogenously throughout the bioprinted construct. This study demonstrated that strontium-based nanocomposite bioinks optimised for extrusion-based 3D bioprinting of osteoconductive scaffolds support long-term shape retention with promising potential for bone tissue regeneration.

The development of high-resolution neuroprosthetics has driven the need for better electrode materials. Approaches to achieve both electrical and mechanical improvements have included the development of hydrogel and conducting polymer composites. However, these composites have limited biological interaction, as they are often composed of synthetic polymers or non-ideal biological polymers, which lack the required elements for biorecognition. This study explores the covalent incorporation of bioactive molecules within a conducting hydrogel (CH). The CH was formed from the biosynthetic co-hydrogel poly(vinyl alcohol)–heparin and the conductive polymer (CP), poly(3,4-ethylene dioxythiophene). Adhesive biomolecules sericin and gelatin were covalently incorporated via methacrylate crosslinking within the CH. Electrical properties of the bioactive CH were assessed, and it was shown that the polar biomolecules improved charge transfer. The bioactivity of heparin within the hybrid assessed by examining stimulation of B-lymphocyte (BaF3) proliferation showed that bioactivity was retained after electropolymerization of the CP through the hydrogel. Similarly, incorporation of sericin and gelatin in the CH promoted neural cell adhesion and proliferation, with only small percentages (⩽2 wt.%) required to achieve optimal results. Sericin provided the best support for the outgrowth of neural processes, and 1 wt.% was sufficient to facilitate adhesion and differentiation of neurons. The drug delivery capability of CH was shown through incorporation of nerve growth factor during polymer fabrication. NGF was delivered to the target cells, resulting in outgrowth of neural processes. The CH system is a flexible technology platform, which can be tailored to covalently incorporate bioactive protein sequences and deliver mobile water-soluble drug molecules.