Ian L. Chin

Modulating how macrophages sense mechanical cues offers a novel strategy to control fibrosis around implanted biomaterials. We term this approach ‘mechano-immunotherapy’, which involves the desensitization of immune mechanosensory pathways to control the host response. Here, we use RN-1734 (RN), a model small molecule to demonstrate the proof-of-concept that pharmacologically disrupting macrophage mechanosensation can mitigate fibrosis. In vitro, RN reduced calcium influx and pro-inflammatory cytokine secretion in J774. a2 macrophages. These effects were strictly context-dependent with efficacy observed only in macrophages on high-stiffness (10% w/v) GelMA hydrogels, with no significant impact on those in softer (5% w/v) hydrogels. In vivo, RN selectively attenuated fibrotic capsule formation around implanted electrospun scaffolds but not smooth hydrogels. Notably, despite hydrogels releasing ∼6-fold more drug than scaffolds, fibrosis was reduced only in the scaffold group, suggesting that therapeutic efficacy is driven by the inhibition of high mechanosensory input rather than the loaded drug concentration alone. Spatial transcriptomics revealed that macrophages acted as the primary mechanosensors at the tissue-implant interface. Unsupervised global principal component analysis revealed that RN acted predominantly on early day 3 macrophages. The strongest effect was observed in surface-adhered mechanosensitive macrophages, where RN treatment enhanced their M2-like phenotype and promoted their dispersal from clustered aggregates into broader distribution within the scaffold. This redistribution was accompanied by a marked reduction in the recruitment of interstitial macrophages from the surrounding tissue, which were enriched for matrix-forming gene signatures. Together, these findings suggest that pharmacological desensitization of immune mechanosensors may represent a promising, context-specific approach to improve biomaterial integration.

In obstructive airway diseases such as asthma and chronic obstructive pulmonary disease (COPD), the extracellular matrix (ECM) protein amount and composition of the airway smooth muscle (ASM) is often remodelled, likely altering tissue stiffness. The underlying mechanism of how human ASM cell (hASMC) mechanosenses the aberrant microenvironment is not well understood. Physiological stiffnesses of the ASM were measured by uniaxial compression tester using porcine ASM layers under 0, 5 and 10% longitudinal stretch above in situ length. Linear stiffness gradient hydrogels (230 kPa range) were fabricated and functionalized with ECM proteins, collagen I (ColI), fibronectin (Fn) and laminin (Ln), to recapitulate the above‐measured range of stiffnesses. Overall, hASMC mechanosensation exhibited a clear correlation with the underlying hydrogel stiffness. Cell size, nuclear size and contractile marker alpha‐smooth muscle actin (αSMA) expression showed a strong correlation to substrate stiffness. Mechanosensation, assessed by Lamin‐A intensity and nuc/cyto YAP, exhibited stiffness‐mediated behaviour only on ColI and Fn‐coated hydrogels. Inhibition studies using blebbistatin or Y27632 attenuated most mechanotransduction‐derived cell morphological responses, αSMA and Lamin‐A expression and nuc/cyto YAP (blebbistatin only). This study highlights the interplay and complexities between stiffness and ECM protein type on hASMC mechanosensation, relevant to airway remodelling in obstructive airway diseases.

Correction for ‘Interrogating cardiac muscle cell mechanobiology on stiffness gradient hydrogels’ by Ian L. Chin et al., Biomater. Sci., 2021, 9, 6795–6806, https://doi.org/10.1039/D1BM01061A.

Present understandings of cardiomyocyte mechanobiology have primarily been developed using 2‐dimensional, monocellular cell cultures, however the emergence of 3‐dimensional (3D) multicellular cardiac constructs has enabled us to develop more sophisticated recapitulations of the cardiac microenvironment. Several of these strategies have illustrated that incorporating elements of the extracellular matrix (ECM) can promote greater maturation and enhance desirable cardiac functions, such as contractility, but the responses of these cardiac constructs to biophysically aberrant conditions, such as in the post‐infarct heart, has remained relatively unexplored. In our study, we employ a stiffness gradient gelatin methacryloyl (GelMA) hydrogel platform to unpack the mechanobiology of cardiac spheroids. We encapsulated neonatal rat cardiac cell spheroids in a 4.4–18.7 kPa linear stiffness gradient up to 120 h. We found the proportion of viable cells within the spheroids increased over time, but the cell number per spheroid decreased. Spheroids expand more in softer matrices while stiffer matrices promote larger nuclei without changing nuclei shape. Volume expansion came primarily from cells expressing vimentin. We did not observe any correlations between stiffness and mechanomarker expression, however we found that after 120 h post‐encapsulation, the localization of YAP, the localization of MRTF‐A and the expression of Lamin‐A was correlated with spheroid morphology. The same trends were not observed 24 h post‐encapsulation, indicating that volume adaptation can take a relatively long time. Our data demonstrates that cardiac spheroids are mechanosensitive and that their capacity to respond to ECM‐based cues depends on their capacity to adapt their volume with a 3D microenvironment.

Mechanobiology of H9C2 cells and neonatal cardiomyocytes mapped using stiffness gradient hydrogels with a range of extracellular matrix coatings, revealing stiffness-driven trends in cell morphology, YAP and MRTF-A expression.

We present a series of synthetic polymer hydrogels which break the traditional correlation between pore size and mechanical properties.