Recent advances in tissue engineering have made progress towards the development of biomaterials with the capability for delivery of growth factors to promote enhanced tissue repair. However, controlling the release of these growth factors is a major challenge and the associated high costs and side effects of uncontrolled delivery of has proved increasingly problematic in clinical orthopaedics. Gene therapy might be a valuable tool to avoid these limitations. While non-viral vectors are typically inefficient at transfecting cells, our group have had significant success in this area using a scaffold-mediated gene therapy approach for regenerative applications. These gene activated scaffold platforms not only act as a template for cell infiltration and tissue formation, but also as a ‘factory’ to provoke autologous host cells to take up specific genes and then engineer therapeutic proteins in a sustained but eventually transient fashion. Alternatively, scaffold-mediated delivery of siRNAs and miRNAs can be used to silence specific genes associated with pathological states in orthopaedics. This presentation will provide an overview of some of this research with a particular focus on gene-activated biomaterials for promoting stable cartilage formation in joint repair and on scaffold-based delivery of therapeutics for enhancing vascularization & bone repair.

Side-effects associated to the use of bone morphogenetic proteins into scaffold-based devices for bone repair highlight the necessity for identifying new therapeutic targets that potentially improve bone healing in adults. In this sense, we recently demonstrated the age-associated decrease in the mechanosensitivity of bone marrow mesenchymal stromal/stem cells (MSCs) and identified c-Jun N-terminal kinase 3 (JNK3) as a mechanically-activated modulator of the superior osteogenic potential of MSCs derived from children (C-MSCs) in comparison to adults (A-MSCs). Building on this work, the aim of this study was to design a JNK3-activated collagen-nanohydroxyapatite (coll-nHA) scaffold that restore the child bone healing capacity in adults. Results revealed that JNK3 activator (JNK3*) enhanced A-MSC’ alkaline phosphatase (ALP) activity to the same extent of C-MSCs by facilitating the activation of JNK3. Moreover, A-MSCs cultured on the coll-JNK3* scaffold (collagen-scaffold containing JNK3*) showed positive uptake of the JNK3*, upregulation of early osteogenic markers as well as increased ALP activity and mineralization. More importantly, rat critical calvarial defects treated with coll-JNK3* for 28 days showed a significantly higher 18.07 % bone volume fraction in comparison to rats treated with Coll-nHA −6.04%- and empty defects −2.58%. Which correlated with the presence of a larger amount of blood vessels and mineralized tissue in samples treated with coll-JNK3* when compared with coll-nHA and empty defects. In conclusion, the coll-JNK3* capacity to enhance osteogenesis and bone healing by activating JNK3 highlights how by understanding the stem cell mechanobiology we can improve the development of next generation therapeutics for tissue repair.

Damage to articular cartilage is difficult to treat, as it has a low capacity to regenerate. Biomimetic natural polymer scaffolds can potentially be used to regenerate cartilage. Collagen hyaluronic acid (CHyA) scaffolds have been developed in our laboratory to promote cell infiltration and repair of articular cartilage. However, the low mechanical properties of such scaffolds potentially limit their use to the treatment of small cartilage defects. 3D-printed polymers can provide a reinforcing framework in these scaffolds, thus allowing their application in the treatment of larger defects. The aim of this study was to create mechanically functional biomaterial scaffolds by incorporating a CHyA matrix into 3D-printed polymer meshes resulting in an integrated porous material composite with improved mechanical properties for repair of large cartilage defects. 3D-printed meshes were developed to facilitate an architecture suitable for nutrient flow, cell infiltration, and even CHyA incorporation. And the meshes were freeze dried in custom made moulds to create a pore structure suitable for chondrogenesis. Uniaxial compressive testing of the scaffolds revealed improved mechanical properties following reinforcement with printed meshes, with the compressive modulus increasing from 0.8kPa (alone) to 0.5MPa (reinforced structure). The reinforced scaffolds maintained interconnected pores with the mean pore diameter increasing from 130 to 175µm. The reinforcement had no negative impact on MSC viability, with 90.1% viability in reinforced scaffolds at day 7. The compressive modulus of the reinforced CHyA scaffold is close to native articular cartilage, suggesting that this approach can be used for treatment of large cartilage defects.

The bone infection osteomyelitis (typically Staphylococcus aureus) requires a multistep treatment process including: surgical debridement, long-term systemic high-dose antibiotics, and often bone grafting. With antibiotic resistance becoming increasingly concerning, alternative approaches are urgently needed. Herein, we develop a one-step treatment for osteomyelitis that combines local, controlled release of non-antibiotic antibacterials (copper) within a proven regenerative scaffold. To maximise efficacy we utilised bioactive glass – an established material with immense osteogenic capacity – as a copper ion delivery reservoir. Copper ions have also been shown to stimulate angiogenesis and induce MSC differentiation down an osteogenic lineage. To eliminate grafting requirements, the copper-doped BG was incorporated into our previously developed collagen scaffolds to produce multifunctional antibacterial, osteogenic, and angiogenic scaffolds. Scaffolds were fabricated by freeze-drying a co-suspension of collagen and bioactive glass particles (+/− copper doping, referred to as CuBG and BG, respectively) at a range of different concentrations (0–300% w/w bioactive glass/collagen). Scaffolds demonstrated a 2.7-fold increase in compressive modulus (300% CuBG vs. 0%; p≤0.01), whilst maintaining >98% porosity. The 300% CuBG scaffolds showed significant antibacterial activity against Staphylococcus aureus (p≤0.001). In terms of osteogenesis, both 100% and 300% CuBG scaffolds increased cell-mediated calcium deposition on the scaffolds at day 14 and 28 (p≤0.05 and p≤0.001), as confirmed by alizarin red staining. 100% CuBG scaffolds significantly enhanced angiogenesis by increased tubule formation (p≤0.01) and VEGF protein production (p≤0.001) (all ≥n=3). In summary, this single-stage, off-the-shelf treatment for osteomyelitis shows potential to minimise bone grafting and antibiotic dependence, while reducing hospital stays and costs.

Purpose

Traditionally, the gold standard for bone grafting has been either autografts or allografts. Whilst autografts are still widely used, drawbacks such as donor site morbidity are shifting the market rapidly toward the use of orthobiologic bone graft substitutes. This study investigated the in vivo performance of a novel (W02008096334) collagen-hydroxyapatite (CHA) bone graft substitute material as an osteoinductive tissue engineering scaffold. This highly porous CHA scaffold offers significantly increased mechanical strength over collagen-only scaffolds while still exhibiting an extremely high porosity (≈ 99%), and an osteoinductive hydroxyapatite phase [1]. This study assessed the ability of the CHA scaffolds to heal critical-sized (15 mm) long bone segmental defects in vivo, as a viable alternative to autologous bone grafts.