Nanotopography reveals metabolites that maintain the immunomodulatory phenotype of mesenchymal stromal cells.

Mesenchymal stromal cells (MSCs) are multipotent progenitor cells that are of considerable clinical potential in transplantation and anti-inflammatory therapies due to their capacity for tissue repair and immunomodulation. However, MSCs rapidly differentiate once in culture, making their large-scale expansion for use in immunomodulatory therapies challenging. Although the differentiation mechanisms of MSCs have been extensively investigated using materials, little is known about how materials can influence paracrine activities of MSCs. Here, we show that nanotopography can control the immunomodulatory capacity of MSCs through decreased intracellular tension and increasing oxidative glycolysis. We use nanotopography to identify bioactive metabolites that modulate intracellular tension, growth and immunomodulatory phenotype of MSCs in standard culture and during larger scale cell manufacture. Our findings demonstrate an effective route to support large-scale expansion of functional MSCs for therapeutic purposes.

Nanopatterned Titanium Implants Accelerate Bone Formation In Vivo.

Accelerated de novo formation of bone is a highly desirable aim of implants targeting musculoskeletal injuries. To date, this has primarily been addressed by biologic factors. However, there is an unmet need for robust, highly reproducible yet economic alternative strategies that strongly induce an osteogenic cell response. Here, we present a surface engineering method of translating bioactive nanopatterns from polymeric in vitro studies to clinically relevant material for orthopedics: three-dimensional, large area metal. We use a titanium-based sol-gel whereby metal implants can be engineered to induce osteoinduction both in vitro and in vivo. We show that controlled disordered nanotopographies presented as pillars with 15-25 nm height and 100 nm diameter on titanium dioxide effectively induce osteogenesis when seeded with STRO-1-enriched human skeletal stem cells in vivo subcutaneous implantation in mice. After 28 days, samples were retrieved, which showed a 20-fold increase in osteogenic gene induction of nanopatterned substrates, indicating that the sol-gel nanopatterning method offers a promising route for translation to future clinical orthopedic implants.

Nanotopography controls cell cycle changes involved with skeletal stem cell self-renewal and multipotency.

In culture isolated bone marrow mesenchymal stem cells (more precisely termed skeletal stem cells, SSCs) spontaneously differentiate into fibroblasts, preventing the growth of large numbers of multipotent SSCs for use in regenerative medicine. However, the mechanisms that regulate the expansion of SSCs, while maintaining multipotency and preventing fibroblastic differentiation are poorly understood. Major hurdles to understanding how the maintenance of SSCs is regulated are (a) SSCs isolated from bone marrow are heterogeneous populations with different proliferative characteristics and (b) a lack of tools to investigate SSC number expansion and multipotency. Here, a nanotopographical surface is used as a tool that permits SSC proliferation while maintaining multipotency. It is demonstrated that retention of SSC phenotype in culture requires adjustments to the cell cycle that are linked to changes in the activation of the mitogen activated protein kinases. This demonstrates that biomaterials can offer cross-SSC culture tools and that the biological processes that determine whether SSCs retain multipotency or differentiate into fibroblasts are subtle, in terms of biochemical control, but are profound in terms of determining cell fate.

Dynamic Surfaces for the Study of Mesenchymal Stem Cell Growth through Adhesion Regulation.

Out of their niche environment, adult stem cells, such as mesenchymal stem cells (MSCs), spontaneously differentiate. This makes both studying these important regenerative cells and growing large numbers of stem cells for clinical use challenging. Traditional cell culture techniques have fallen short of meeting this challenge, but materials science offers hope. In this study, we have used emerging rules of managing adhesion/cytoskeletal balance to prolong MSC cultures by fabricating controllable nanoscale cell interfaces using immobilized peptides that may be enzymatically activated to change their function. The surfaces can be altered (activated) at will to tip adhesion/cytoskeletal balance and initiate differentiation, hence better informing biological mechanisms of stem cell growth. Tools that are able to investigate the stem cell phenotype are important. While large phenotypical differences, such as the difference between an adipocyte and an osteoblast, are now better understood, the far more subtle differences between fibroblasts and MSCs are much harder to dissect. The development of technologies able to dynamically navigate small differences in adhesion are critical in the race to provide regenerative strategies using stem cells.

Regulation of stem cell fate by nanomaterial substrates.

Stem cells are increasingly studied because of their potential to underpin a range of novel therapies, including regenerative strategies, cell type-specific therapy and tissue repair, among others. Bionanomaterials can mimic the stem cell environment and modulate stem cell differentiation and proliferation. New advances in these fields are presented in this review. This work highlights the importance of topography and elasticity of the nano-/micro-environment, or niche, for the initiation and induction of stem cell differentiation and proliferation.

Systems Biology Approaches Applied to Regenerative Medicine.

Systems biology is the creation of theoretical and mathematical models for the study of biological systems, as an engine for hypothesis generation and to provide context to experimental data. It is underpinned by the collection and analysis of complex datasets from different biological systems, including global gene, RNA, protein and metabolite profiles. Regenerative medicine seeks to replace or repair tissues with compromised function (for example, through injury, deficiency or pathology), in order to improve their functionality. In this paper, we will address the application of systems biology approaches to the study of regenerative medicine, with a particular focus on approaches to study modifications to the genome, transcripts and small RNAs, proteins and metabolites.

Nanotopography - potential relevance in the stem cell niche.

Understanding signals in the niche that regulate stem cell behaviours is important for applications such as tissue engineering, and limitations in ex vivo/in vitro recapitulation of some stem cell niches, particularly the bone marrow, have led researchers to attempt to delineate signalling mechanisms present in vivo using a reductionist approach. This is especially important as 'stemness' is not solely an intrinsic property of stem cells but a result of the reciprocal interactions between stem cells and their niches. Physical stimuli such as mechanical stiffness and topography are known to significantly impact stem cell behaviours; being translated through adhesions, intracellular tension and mechanotransduction, which can alter gene expression and thus cell fate. In this review general properties of the stem cell niche are initially described, using intestinal and bone marrow niches as examples. The lesser-described physical stimuli of nanotopography and the mechanisms by which stem cells respond and interact with it are described, including biochemical and physical mechanotrasduction, chemical and physical signal integration and adhesion mechanisms in both anchorage-dependent and -independent cells. Specific examples of nanotopographical influence over stem cell differentiation are highlighted and parallels drawn between the stem cell niche and these 'synthetic'in vitro observations. Ultimately if the complex stem cell niche is to be mimicked in vitro or stem cells exploited for medical applications the physical microenvironment, including nanotopography, must be optimised.

State of the art composites comprising electrospun fibres coupled with hydrogels: a review.

Research into scaffolds tailored for specific tissue engineering and biomaterial applications continues to develop as these structures are commonly impeded by their limitations. For example, electrospun fibres and hydrogels are commonly exploited because of their ability to mimic natural tissues; however, their clinical use remains restricted due to negligible cellular infiltration and poor mechanical properties, respectively. A small number of research groups are beginning to investigate composite scaffolds based on electrospun fibres and hydrogels in an attempt to overcome their individual shortcomings. This review paper discusses the various methodologies and approaches currently undertaken to create these novel composite structures and their intended applications. The combination of these two commonly used scaffold architectures to create synergistically superior structures is showing potential with regards to therapeutic use within the tissue engineering community. FROM THE CLINICAL EDITOR: This review discusses methodologies to create novel electrospun nanofibers and hydrogels, and their intended applications. The combination of these two scaffold architectures has important future clinical applications, although their use is currently limited to the experimental tissue engineering community.