Shining a light on extracellular matrix dynamics in vivo

Engineering cell-derived extracellular matrix for peripheral nerve regeneration

Extracellular matrices (ECMs) play a key role in nerve repair and are recognized as the natural source of biomaterials. In parallel to extensively studied tissue-derived ECMs (ts-ECMs), cell-derived ECMs (cd-ECMs) also have the capability to partially recapitulate the complicated regenerative microenvironment of native nerve tissues. Notably, cd-ECMs can avoid the shortcomings of ts-ECMs. Cd-ECMs can be prepared by culturing various cells or even autologous cells in vitro under pathogen-free conditions. And mild decellularization can achieve efficient removal of immunogenic components in cd-ECMs. Moreover, cd-ECMs are more readily customizable to achieve the desired functional properties. These advantages have garnered significant attention for the potential of cd-ECMs in neuroregenerative medicine. As promising biomaterials, cd-ECMs bring new hope for the effective treatment of peripheral nerve injuries. Herein, this review comprehensively examines current knowledge about the functional characteristics of cd-ECMs and their mechanisms of interaction with cells in nerve regeneration, with a particular focus on the preparation, engineering optimization, and scalability of cd-ECMs. The applications of cd-ECMs from distinct cell sources reported in peripheral nerve tissue engineering are highlighted and summarized. Furthermore, current limitations that should be addressed and outlooks related to clinical translation are put forward as well.

Dry and wet wrinkling of a silk fibroin biopolymer by a shape-memory material with insight into mechanical effects on secondary structures in the silk network

Surface wrinkling provides an approach to modify the surfaces of biomedical devices to better mimic features of the extracellular matrix and guide cell attachment, proliferation, and differentiation. Biopolymer wrinkling on active materials holds promise but is poorly explored. Here we report a mechanically actuated assembly process to generate uniaxial micro-and nanosized silk fibroin (SF) wrinkles on a thermo-responsive shape-memory polymer (SMP) substrate, with wrinkling demonstrated under both dry and hydrated (cell compatible) conditions. By systematically investigating the influence of SMP programmed strain magnitude, film thickness, and aqueous media on wrinkle stability and morphology, we reveal how to control the wrinkle sizes on the micron and sub-micron length scale. Furthermore, as a parameter fundamental to SMPs, we demonstrate that the temperature during the recovery process can also affect the wrinkle characteristics and the secondary structures in the silk network. We find that with increasing SMP programmed strain magnitude, silk wrinkled topographies with increasing wavelengths and amplitudes are achieved. Furthermore, silk wrinkling is found to increase β-sheet content, with spectroscopic analysis suggesting that the effect may be due primarily to tensile (e.g., Poisson effect and high-curvature wrinkle) loading modes in the SF, despite the compressive bulk deformation (uniaxial contraction) used to produce wrinkles. Silk wrinkles fabricated from sufficiently thick films (roughly 250 nm) persist after 24 h in cell culture medium. Using a fibroblast cell line, analysis of cellular response to the wrinkled topographies reveals high viability and attachment. These findings demonstrate use of wrinkled SF films under physiologically relevant conditions and suggest the potential for biopolymer wrinkles on biomaterials surfaces to find application in cell mechanobiology, wound healing, and tissue engineering.

Collective cell migration during optic cup formation features changing cell-matrix interactions linked to matrix topology

Cell migration is crucial for organismal development and shapes organisms in health and disease. Although a lot of research has revealed the role of intracellular components and extracellular signaling in driving single and collective cell migration, the influence of physical properties of the tissue and the environment on migration phenomena in vivo remains less explored. In particular, the role of the extracellular matrix (ECM), which many cells move upon, is currently unclear. To overcome this gap, we use zebrafish optic cup formation, and by combining novel transgenic lines and image analysis pipelines, we study how ECM properties influence cell migration in vivo. We show that collectively migrating rim cells actively move over an immobile extracellular matrix. These cell movements require cryptic lamellipodia that are extended in the direction of migration. Quantitative analysis of matrix properties revealed that the topology of the matrix changes along the migration path. These changes in matrix topologies are accompanied by changes in the dynamics of cell-matrix interactions. Experiments and theoretical modeling suggest that matrix porosity could be linked to efficient migration. Indeed, interfering with matrix topology by increasing its porosity results in a loss of cryptic lamellipodia, less-directed cell-matrix interactions, and overall inefficient migration. Thus, matrix topology is linked to the dynamics of cell-matrix interactions and the efficiency of directed collective rim cell migration during vertebrate optic cup morphogenesis.

Immuno-modulatory biomaterials as anti-inflammatory therapeutics

Biocompatible and biodegradable biomaterials are used extensively in regenerative medicine and serve as a tool for tissue replacement, as a platform for regeneration of injured tissue, and as a vehicle for delivery of drugs. One of the key factors that must be addressed in developing successful biomaterial-based therapeutics is inflammation. Whilst inflammation is initially essential for wound healing; bringing about clearance of debris and infection, prolonged inflammation can result in delayed wound healing, rejection of the biomaterial, further tissue damage and increased scarring and fibrosis. In this context, the choice of biomaterial must be considered carefully to minimise further induction of inflammation. Here we address the ability of the biomaterials themselves to modulate inflammatory responses and outline how the physico-chemical properties of the materials impact on their pro and anti-inflammatory properties (Fig. 1).