Force-based engineering of gradients

Tissue engineering research has opened a new chapter in modern medicine since it emerged as a mainstream research field in the early 90s. Until now, however, effective strategies to fully emulate the complexity of natural tissue remain elusive. One of the key features in the development of complex tissue structures is the presence of morphogen gradients during development. In nature, from squid beaks to human teeth, gradients are preserved in many structures after evolution. In a living organism, gradients play an essential role in defining the physiological function. The formation of these gradients is often largely dictated by an anisotropic distribution of different morphogens present during development. The spatial difference in concentration of different morphogens results a spatial variance in cell signalling, patterning the development of tissue and leading to the formation of heterogeneous structure. Although these principles of development are well-established, the overwhelming majority of in vitro engineering strategies use uniform scaffolds and spatially invariant growth factor delivery to produce homogeneous tissue constructs. It is clear that more sophisticated fabrication processes are required to replicate the native complexity and fulfil the functional requirements of tissue grafts. A few material strategies have been developed that can heterogeneously deliver biological or mechanical cues; however, most of them are limited by complex fabrication procedures or restricted compatibility with different material systems. By establishing signaling factor gradients within tissue engineering scaffolds, the formation of heterogeneous tissue interfaces can be achieved. This thesis will demonstrate two gradient casting strategies to emulate physiological gradients, exploiting magnetism and buoyancy to distribute growth factors. These strategies are shown to be capable of establishing gradients in different materials, and are used to engineer osteochondral tissue. The strategies proposed in this research are designed to be widely applicable and easy to reproduce. It is hoped that these strategies may be adapted and tailored for wider use by the tissue engineering field, allowing development of complex, functional tissue by mimicking the processes used by nature.Open Acces

Glycosylated superparamagnetic nanoparticle gradients for osteochondral tissue engineering

In developmental biology, gradients of bioactive signals direct the formation of structural transitions in tissue that are key to physiological function. Failure to reproduce these native features in an in vitro setting can severely limit the success of bioengineered tissue constructs. In this report, we introduce a facile and rapid platform that uses magnetic field alignment of glycosylated superparamagnetic iron oxide nanoparticles, pre-loaded with growth factors, to pattern biochemical gradients into a range of biomaterial systems. Gradients of bone morphogenetic protein 2 in agarose hydrogels were used to spatially direct the osteogenesis of human mesenchymal stem cells and generate robust osteochondral tissue constructs exhibiting a clear mineral transition from bone to cartilage. Interestingly, the smooth gradients in growth factor concentration gave rise to biologically-relevant, emergent structural features, including a tidemark transition demarcating mineralized and non-mineralized tissue and an osteochondral interface rich in hypertrophic chondrocytes. This platform technology offers great versatility and provides an exciting new opportunity for overcoming a range of interfacial tissue engineering challenges

Kartogenin Enhances Chondrogenic Differentiation of MSCs in 3D Tri-Copolymer Scaffolds and the Self-Designed Bioreactor System

Human cartilage has relatively slow metabolism compared to other normal tissues. Cartilage damage is of great clinical consequence since cartilage has limited intrinsic healing potential. Cartilage tissue engineering is a rapidly emerging field that holds great promise for tissue function repair and artificial/engineered tissue substitutes. However, current clinical therapies for cartilage repair are less than satisfactory and rarely recover full function or return the diseased tissue to its native healthy state. Kartogenin (KGN), a small molecule, can promote chondrocyte differentiation both in vitro and in vivo. The purpose of this research is to optimize the chondrogenic process in mesenchymal stem cell (MSC)-based chondrogenic constructs with KGN for potential use in cartilage tissue engineering. In this study, we demonstrate that KGN treatment can promote MSC condensation and cell cluster formation within a tri-copolymer scaffold. Expression of Acan, Sox9, and Col2a1 was significantly up-regulated in three-dimensional (3D) culture conditions. The lacuna-like structure showed active deposition of type II collagen and aggrecan deposition. We expect these results will open new avenues for the use of small molecules in chondrogenic differentiation protocols in combination with scaffolds, which may yield better strategies for cartilage tissue engineering

Kartogenin Enhances Chondrogenic Differentiation of MSCs in 3D Tri-Copolymer Scaffolds and the Self-Designed Bioreactor System

Human cartilage has relatively slow metabolism compared to other normal tissues. Cartilage damage is of great clinical consequence since cartilage has limited intrinsic healing potential. Cartilage tissue engineering is a rapidly emerging field that holds great promise for tissue function repair and artificial/engineered tissue substitutes. However, current clinical therapies for cartilage repair are less than satisfactory and rarely recover full function or return the diseased tissue to its native healthy state. Kartogenin (KGN), a small molecule, can promote chondrocyte differentiation both in vitro and in vivo. The purpose of this research is to optimize the chondrogenic process in mesenchymal stem cell (MSC)-based chondrogenic constructs with KGN for potential use in cartilage tissue engineering. In this study, we demonstrate that KGN treatment can promote MSC condensation and cell cluster formation within a tri-copolymer scaffold. Expression of Acan, Sox9, and Col2a1 was significantly up-regulated in three-dimensional (3D) culture conditions. The lacuna-like structure showed active deposition of type II collagen and aggrecan deposition. We expect these results will open new avenues for the use of small molecules in chondrogenic differentiation protocols in combination with scaffolds, which may yield better strategies for cartilage tissue engineering