Biology subjects

Burdis, R.

Publications and source records attributed to Burdis, R..

4 recordsLinked to original sources

bioRxiv2026

Integrating vascular and hypertrophic cartilage microtissues to fabricatescaled-up grafts for endochondral bone tissue engineering

ABSTRACTThe repair of large bone defects remains a major clinical challenge, in part due to inadequate vascularization and poor integration of graft materials. Tissue engineering strategies that recapitulate the developmental process of endochondral ossification, whereby a cartilage template remodels into bone, have shown significant potential in pre-clinical models of large bone defect healing. However, successfully scaling these approaches to clinically relevant sizes will require the development of strategies to support the rapid vascularization of the graft following implantation in vivo. Here, mechanically reinforced templates were first fabricated by integrating hypertrophic cartilage microtissues derived from human mesenchymal stem/stromal cells (MSCs) within an osteoconductive 3D-printed polycaprolactone (PCL) framework coated with nano-hydroxyapatite (nanoHA). In vitro the cartilage microtissues fused and generated an extracellular matrix rich in sulphated glycosaminoglycans and collagen. To prevascularize these constructs, vascular microtissues derived from a co-culture of endothelial cells and MSCs were incorporated into a central channel within the construct, which generated a microvascular network within the graft in vitro. Following subcutaneous implantation, hypertrophic cartilage templates with ( vascular-channel group) and without ( empty-channel group) this central vascularized channel supported endochondral bone formation. Quantitative microCT and histological analyses revealed significantly greater remaining bone in the empty-channel group, whereas the vascular-channel group supported enhanced vascularization and remodeling of the graft in vivo. These findings support the continued development and testing of a modular biofabrication strategy that combine self-organizing hypertrophic cartilage and vascular microtissues with osteoconductive 3D-printed architectures to generate scalable, prevascularised hypertrophic cartilage templates for endochondral bone repair. Key-words: spheroids, microtissues, hypertrophic cartilage, vascularization, endochondral ossification, bone tissue engineering.

bioengineering↗

bioRxiv2026

An injectable soft implant for long-acting, reversible, ultra-stable release of therapeutics

Providing long-term (>6 months) zero-order drug release from easily administered formulations is a key challenge in improving patient adherence and facilitating access. Herein, we report the design and development of an injectable, biodegradable, long-acting polymeric microparticle-embedded hydrogel platform for prolonged, zero-order release of therapeutics. This "soft implant" is injectable for ease of administration and can be retrieved via a small incision, allowing for discontinuation of therapy if desired. Central to the platform are surface-eroding poly(orthoester) (POE) microparticles, which were molecularly tailored to tune zero-order drug release across a wide range of timeframes. We demonstrate the clinical potential of the "soft implant" using levonorgestrel, a contraceptive agent requiring sustained dosing. In vitro, we observed zero-order release for 300 days, projected for >12 months, with behavior consistent with surface erosion further supported through Raman chemical mapping. In vivo studies confirmed zero-order release for six months, projected to 12 months, from a subcutaneous injection in rats. We envision that our platform could transform therapies that require long-term, regular drug dosing, significantly improving compliance and therapy outcomes.

bioengineering↗

bioRxiv2022

Temporal enzymatic treatment to enhance the remodelling of multiple cartilage microtissues into a structurally organised tissue

Scaffold-free tissue engineering strategies aim to recapitulate key aspects of normal developmental processes as a means of generating highly biomimetic grafts. Cartilage and fibrocartilaginous tissues have successfully been engineered by bringing together large numbers of cells, cellular aggregates or microtissues and allowing them to self-assemble or self-organize into a functional graft. Despite the promise of such approaches, considerable challenges still remain, such as engineering scaled-up tissues with predefined geometries, ensuring robust fusion between adjacent cellular aggregates or microtissues, and directing the (re)modelling of such biological building blocks into a unified scaled-up graft with hierarchical matrix organisation mimetic of the native tissue. In this study, we first demonstrate the benefits of engineering cartilage via the fusion of multiple cartilage microtissues compared to conventional scaffold-free approaches where (millions of) individual cells are allowed to aggregate and generate a cartilaginous graft. Key advantages include the engineering of a tissue with a richer extracellular matrix, a more hyaline-like cartilage phenotype and a final graft which better matched the intended geometry. A major drawback associated with this approach is that individual microtissues did not completely (re)model and remnants of their initial architectures where still evident throughout the macrotissue. In an attempt to address this limitation, the enzyme chondroitinase ABC (cABC) was employed to accelerate structural (re)modelling of the engineered tissue. Temporal enzymatic treatment supported robust fusion between adjacent microtissues, enhanced microtissue (re)modelling and supported the development of a more biomimetic tissue with a zonally organised collagen architecture. Additionally, we observed that cABC treatment modulated matrix composition (rebalancing the collagen:glycosaminoglycans ratio), tissue phenotype, and to a lesser extent, tissue mechanics. Ultimately, this work demonstrates that microtissue self-organisation is an effective method for engineering scaled-up cartilage grafts with a pre-defined geometry and near-native levels of ECM accumulation. Importantly we have demonstrated that key limitations associated with tissue engineering using multiple cellular aggregates, microtissues or organoids can be alleviated by temporal enzymatic treatment during graft development.

bioengineering↗

bioRxiv2022

Engineering High-Quality Cartilage Microtissues using Hydrocortisone Functionalised Microwells

Engineering clinically-relevant musculoskeletal tissues at a human scale is a considerable challenge. Developmentally-inspired scaffold-free approaches for engineering cartilage tissues have shown great promise in recent years, enabling the generation of highly biomimetic tissues. Despite the relative success of these approaches, the absence of a supporting scaffold or hydrogel creates challenges in the development of large scale tissues. Combining numerous scaled-down tissue units (herein termed microtissues) into a larger macrotissue represents a promising strategy to address this challenge. The overall success of such approaches, however, relies on the development of strategies to support the robust and consistent chondrogenic differentiation of clinically relevant cell sources such as mesenchymal stem/stromal cells (MSCs) within microwell arrays to biofabricate numerous microtissues rich in cartilage-specific extracellular matrix components. In this paper, we first describe a simple method to manufacture cartilage microtissues at various scales using novel microwell array stamps. This system allows the rapid and reliable generation of cartilage microtissues, and can be used as a platform to study microtissue phenotype and development. Based on the unexpected discovery that Endothelial Growth Medium (EGM) enhanced MSC aggregation and chondrogenic capacity within the microwell arrays, this work also sought to identify soluble factors within the media capable of supporting robust differentiation using heterogeneous MSC populations. Hydrocortisone was found to be the key factor within EGM that enhanced the chondrogenic capacity of MSCs within these microwell arrays. This strategy represents a promising means of generating large numbers of high-quality, scaffold-free cartilage microtissues for diverse biofabrication applications.

bioengineering↗