Mechanical forces direct stem cell behaviour in development and regeneration.

Stem cells and their local microenvironment, or niche, communicate through mechanical cues to regulate cell fate and cell behaviour and to guide developmental processes. During embryonic development, mechanical forces are involved in patterning and organogenesis. The physical environment of pluripotent stem cells regulates their self-renewal and differentiation. Mechanical and physical cues are also important in adult tissues, where adult stem cells require physical interactions with the extracellular matrix to maintain their potency. In vitro, synthetic models of the stem cell niche can be used to precisely control and manipulate the biophysical and biochemical properties of the stem cell microenvironment and to examine how the mode and magnitude of mechanical cues, such as matrix stiffness or applied forces, direct stem cell differentiation and function. Fundamental insights into the mechanobiology of stem cells also inform the design of artificial niches to support stem cells for regenerative therapies.

A vaccine targeting resistant tumours by dual T cell plus NK cell attack.

Most cancer vaccines target peptide antigens, necessitating personalization owing to the vast inter-individual diversity in major histocompatibility complex (MHC) molecules that present peptides to T cells. Furthermore, tumours frequently escape T cell-mediated immunity through mechanisms that interfere with peptide presentation1. Here we report a cancer vaccine that induces a coordinated attack by diverse T cell and natural killer (NK) cell populations. The vaccine targets the MICA and MICB (MICA/B) stress proteins expressed by many human cancers as a result of DNA damage2. MICA/B serve as ligands for the activating NKG2D receptor on T cells and NK cells, but tumours evade immune recognition by proteolytic MICA/B cleavage3,4. Vaccine-induced antibodies increase the density of MICA/B proteins on the surface of tumour cells by inhibiting proteolytic shedding, enhance presentation of tumour antigens by dendritic cells to T cells and augment the cytotoxic function of NK cells. Notably, this vaccine maintains efficacy against MHC class I-deficient tumours resistant to cytotoxic T cells through the coordinated action of NK cells and CD4+ T cells. The vaccine is also efficacious in a clinically important setting: immunization following surgical removal of primary, highly metastatic tumours inhibits the later outgrowth of metastases. This vaccine design enables protective immunity even against tumours with common escape mutations.

The CLEC-2-podoplanin axis controls the contractility of fibroblastic reticular cells and lymph node microarchitecture.

In lymph nodes, fibroblastic reticular cells (FRCs) form a collagen-based reticular network that supports migratory dendritic cells (DCs) and T cells and transports lymph. A hallmark of FRCs is their propensity to contract collagen, yet this function is poorly understood. Here we demonstrate that podoplanin (PDPN) regulates actomyosin contractility in FRCs. Under resting conditions, when FRCs are unlikely to encounter mature DCs expressing the PDPN receptor CLEC-2, PDPN endowed FRCs with contractile function and exerted tension within the reticulum. Upon inflammation, CLEC-2 on mature DCs potently attenuated PDPN-mediated contractility, which resulted in FRC relaxation and reduced tissue stiffness. Disrupting PDPN function altered the homeostasis and spacing of FRCs and T cells, which resulted in an expanded reticular network and enhanced immunity.

Instant tough adhesion of polymer networks.

Generating strong rapid adhesion between hydrogels has the potential to advance the capabilities of modern medicine and surgery. Current hydrogel adhesion technologies rely primarily on liquid-based diffusion mechanisms and the formation of covalent bonds, requiring prolonged time to generate adhesion. Here, we present a simple and versatile strategy using dry chitosan polymer films to generate instant adhesion between hydrogel-hydrogel and hydrogel-elastomer surfaces. Using this approach we can achieve extremely high adhesive energies (>3,000 J/m2), which are governed by pH change and non-covalent interactions including H-bonding, Van der Waals forces, and bridging polymer entanglement. Potential examples of biomedical applications are presented, including local tissue cooling, vascular sealing, prevention of surgical adhesions, and prevention of hydrogel dehydration. We expect these findings and the simplicity of this approach to have broad implications for adhesion strategies and hydrogel design.

Materials-Based Approaches for Cancer Vaccination.

Therapeutic cancer vaccines offer the promise of stimulating the immune system to specifically eradicate tumor cells and establish long-term memory to prevent tumor recurrence. However, despite showing benign safety profiles and the ability to generate Ag-specific cellular responses, cancer vaccines have been hampered by modest clinical efficacy. Lessons learned from these studies have led to the emergence of innovative materials-based strategies that aim to boost the clinical activity of cancer vaccines. In this Brief Review, we provide an overview of the key elements needed for an effective vaccine-induced antitumor response, categorize current approaches to therapeutic cancer vaccination, and explore recent advances in materials-based strategies to potentiate cancer vaccines.

Effects of extracellular matrix viscoelasticity on cellular behaviour.

Substantial research over the past two decades has established that extracellular matrix (ECM) elasticity, or stiffness, affects fundamental cellular processes, including spreading, growth, proliferation, migration, differentiation and organoid formation. Linearly elastic polyacrylamide hydrogels and polydimethylsiloxane (PDMS) elastomers coated with ECM proteins are widely used to assess the role of stiffness, and results from such experiments are often assumed to reproduce the effect of the mechanical environment experienced by cells in vivo. However, tissues and ECMs are not linearly elastic materials-they exhibit far more complex mechanical behaviours, including viscoelasticity (a time-dependent response to loading or deformation), as well as mechanical plasticity and nonlinear elasticity. Here we review the complex mechanical behaviours of tissues and ECMs, discuss the effect of ECM viscoelasticity on cells, and describe the potential use of viscoelastic biomaterials in regenerative medicine. Recent work has revealed that matrix viscoelasticity regulates these same fundamental cell processes, and can promote behaviours that are not observed with elastic hydrogels in both two- and three-dimensional culture microenvironments. These findings have provided insights into cell-matrix interactions and how these interactions differentially modulate mechano-sensitive molecular pathways in cells. Moreover, these results suggest design guidelines for the next generation of biomaterials, with the goal of matching tissue and ECM mechanics for in vitro tissue models and applications in regenerative medicine.

Cytokine conjugation to enhance T cell therapy.

Adoptive T cell transfer (ACT) therapies suffer from a number of limitations (e.g., poor control of solid tumors), and while combining ACT with cytokine therapy can enhance effectiveness, this also results in significant side effects. Here, we describe a nanotechnology approach to improve the efficacy of ACT therapies by metabolically labeling T cells with unnatural sugar nanoparticles, allowing direct conjugation of antitumor cytokines onto the T cell surface during the manufacturing process. This allows local, concentrated activity of otherwise toxic cytokines. This approach increases T cell infiltration into solid tumors, activates the host immune system toward a Type 1 response, encourages antigen spreading, and improves control of aggressive solid tumors and achieves complete blood cancer regression with otherwise noncurative doses of CAR-T cells. Overall, this method provides an effective and easily integrated approach to the current ACT manufacturing process to increase efficacy in various settings.

Perivascular CLICK-gelatin delivery of thrombospondin-2 small interfering RNA decreases development of intimal hyperplasia after arterial injury.

Bypass graft failure occurs in 20%-50% of coronary and lower extremity bypasses within the first-year due to intimal hyperplasia (IH). TSP-2 is a key regulatory protein that has been implicated in the development of IH following vessel injury. In this study, we developed a biodegradable CLICK-chemistry gelatin-based hydrogel to achieve sustained perivascular delivery of TSP-2 siRNA to rat carotid arteries following endothelial denudation injury. At 21 days, perivascular application of TSP-2 siRNA embedded hydrogels significantly downregulated TSP-2 gene expression, cellular proliferation, as well as other associated mediators of IH including MMP-9 and VEGF-R2, ultimately resulting in a significant decrease in IH. Our data illustrates the ability of perivascular CLICK-gelatin delivery of TSP-2 siRNA to mitigate IH following arterial injury.

Self-Healing Injectable Hydrogels for Tissue Regeneration.

Biomaterials with the ability to self-heal and recover their structural integrity offer many advantages for applications in biomedicine. The past decade has witnessed the rapid emergence of a new class of self-healing biomaterials commonly termed injectable, or printable in the context of 3D printing. These self-healing injectable biomaterials, mostly hydrogels and other soft condensed matter based on reversible chemistry, are able to temporarily fluidize under shear stress and subsequently recover their original mechanical properties. Self-healing injectable hydrogels offer distinct advantages compared to traditional biomaterials. Most notably, they can be administered in a locally targeted and minimally invasive manner through a narrow syringe without the need for invasive surgery. Their moldability allows for a patient-specific intervention and shows great prospects for personalized medicine. Injected hydrogels can facilitate tissue regeneration in multiple ways owing to their viscoelastic and diffusive nature, ranging from simple mechanical support, spatiotemporally controlled delivery of cells or therapeutics, to local recruitment and modulation of host cells to promote tissue regeneration. Consequently, self-healing injectable hydrogels have been at the forefront of many cutting-edge tissue regeneration strategies. This study provides a critical review of the current state of self-healing injectable hydrogels for tissue regeneration. As key challenges toward further maturation of this exciting research field, we identify (i) the trade-off between the self-healing and injectability of hydrogels vs their physical stability, (ii) the lack of consensus on rheological characterization and quantitative benchmarks for self-healing injectable hydrogels, particularly regarding the capillary flow in syringes, and (iii) practical limitations regarding translation toward therapeutically effective formulations for regeneration of specific tissues. Hence, here we (i) review chemical and physical design strategies for self-healing injectable hydrogels, (ii) provide a practical guide for their rheological analysis, and (iii) showcase their applicability for regeneration of various tissues and 3D printing of complex tissues and organoids.

STING activation promotes robust immune response and NK cell-mediated tumor regression in glioblastoma models.

Immunotherapy has had a tremendous impact on cancer treatment in the past decade, with hitherto unseen responses at advanced and metastatic stages of the disease. However, the aggressive brain tumor glioblastoma (GBM) is highly immunosuppressive and remains largely refractory to current immunotherapeutic approaches. The stimulator of interferon genes (STING) DNA sensing pathway has emerged as a next-generation immunotherapy target with potent local immune stimulatory properties. Here, we investigated the status of the STING pathway in GBM and the modulation of the brain tumor microenvironment (TME) with the STING agonist ADU-S100. Our data reveal the presence of STING in human GBM specimens, where it stains strongly in the tumor vasculature. We show that human GBM explants can respond to STING agonist treatment by secretion of inflammatory cytokines. In murine GBM models, we show a profound shift in the tumor immune landscape after STING agonist treatment, with massive infiltration of the tumor-bearing hemisphere with innate immune cells including inflammatory macrophages, neutrophils, and natural killer (NK) populations. Treatment of established murine intracranial GL261 and CT-2A tumors by biodegradable ADU-S100-loaded intracranial implants demonstrated a significant increase in survival in both models and long-term survival with immune memory in GL261. Responses to treatment were abolished by NK cell depletion. This study reveals therapeutic potential and deep remodeling of the TME by STING activation in GBM and warrants further examination of STING agonists alone or in combination with other immunotherapies such as cancer vaccines, chimeric antigen receptor T cells, NK therapies, and immune checkpoint blockade.

Active tissue adhesive activates mechanosensors and prevents muscle atrophy.

While mechanical stimulation is known to regulate a wide range of biological processes at the cellular and tissue levels, its medical use for tissue regeneration and rehabilitation has been limited by the availability of suitable devices. Here we present a mechanically active gel-elastomer-nitinol tissue adhesive (MAGENTA) that generates and delivers muscle-contraction-mimicking stimulation to a target tissue with programmed strength and frequency. MAGENTA consists of a shape memory alloy spring that enables actuation up to 40% strain, and an adhesive that efficiently transmits the actuation to the underlying tissue. MAGENTA activates mechanosensing pathways involving yes-associated protein and myocardin-related transcription factor A, and increases the rate of muscle protein synthesis. Disuse muscles treated with MAGENTA exhibit greater size and weight, and generate higher forces compared to untreated muscles, demonstrating the prevention of atrophy. MAGENTA thus has promising applications in the treatment of muscle atrophy and regenerative medicine.

Matrix viscoelasticity controls spatiotemporal tissue organization.

Biomolecular and physical cues of the extracellular matrix environment regulate collective cell dynamics and tissue patterning. Nonetheless, how the viscoelastic properties of the matrix regulate collective cell spatial and temporal organization is not fully understood. Here we show that the passive viscoelastic properties of the matrix encapsulating a spheroidal tissue of breast epithelial cells guide tissue proliferation in space and in time. Matrix viscoelasticity prompts symmetry breaking of the spheroid, leading to the formation of invading finger-like protrusions, YAP nuclear translocation and epithelial-to-mesenchymal transition both in vitro and in vivo in a Arp2/3-complex-dependent manner. Computational modelling of these observations allows us to establish a phase diagram relating morphological stability with matrix viscoelasticity, tissue viscosity, cell motility and cell division rate, which is experimentally validated by biochemical assays and in vitro experiments with an intestinal organoid. Altogether, this work highlights the role of stress relaxation mechanisms in tissue growth dynamics, a fundamental process in morphogenesis and oncogenesis.

Antiplatelet therapy for Staphylococcus aureus bacteremia: Will it stick?

Staphylococcus aureus bacteremia (SAB) remains a clinically challenging infection despite extensive investigation. Repurposing medications approved for other indications is appealing as clinical safety profiles have already been established. Ticagrelor, a reversible adenosine diphosphate receptor antagonist that prevents platelet aggregation, is indicated for patients suffering from acute coronary syndrome (ACS). However, some clinical data suggest that patients treated with ticagrelor are less likely to have poor outcomes due to S. aureus infection. There are several potential mechanisms by which ticagrelor may affect S. aureus virulence. These include direct antibacterial activity, up-regulation of the innate immune system through boosting platelet-mediated S. aureus killing, and prevention of S. aureus adhesion to host tissues. In this Pearl, we review the clinical data surrounding ticagrelor and infection as well as explore the evidence surrounding these proposed mechanisms of action. While more evidence is needed before antiplatelet medications formally become part of the arsenal against S. aureus infection, these potential mechanisms represent exciting pathways to target in the host/pathogen interface.

Transcriptional profiling of stroma from inflamed and resting lymph nodes defines immunological hallmarks.

Lymph node stromal cells (LNSCs) closely regulate immunity and self-tolerance, yet key aspects of their biology remain poorly elucidated. Here, comparative transcriptomic analyses of mouse LNSC subsets demonstrated the expression of important immune mediators, growth factors and previously unknown structural components. Pairwise analyses of ligands and cognate receptors across hematopoietic and stromal subsets suggested a complex web of crosstalk. Fibroblastic reticular cells (FRCs) showed enrichment for higher expression of genes relevant to cytokine signaling, relative to their expression in skin and thymic fibroblasts. LNSCs from inflamed lymph nodes upregulated expression of genes encoding chemokines and molecules involved in the acute-phase response and the antigen-processing and antigen-presentation machinery. Poorly studied podoplanin (gp38)-negative CD31(-) LNSCs showed similarities to FRCs but lacked expression of interleukin 7 (IL-7) and were identified as myofibroblastic pericytes that expressed integrin α(7). Together our data comprehensively describe the transcriptional characteristics of LNSC subsets.

Implementation of a Global Pediatric Trauma Course in an Upper Middle-Income Country: A Pilot Study.

INTRODUCTION: Over 90% of pediatric trauma deaths occur in low- and middle-income countries (LMICs), yet pediatric trauma-focused training remains unstandardized and inaccessible, especially in LMICs. In Brazil, where trauma is the leading cause of death for children over age 1, we piloted the first global adaptation of the Trauma Resuscitation in Kids (TRIK) course and assessed its feasibility. METHODS: A 2-day simulation-based global TRIK course was hosted in Belo Horizonte in October 2022, led by one Brazilian and four Canadian instructors. The enrollment fee was $200 USD, and course registration sold out in 4 d. We administered a knowledge test before and after the course and a postcourse self-evaluation. We recorded each simulation to assess participants' performance, reflected in a team performance score. Groups received numerical scores for these three areas, which were equally weighted to calculate a final performance score. The scores given by the two evaluators were then averaged. As groups performed the specific simulations in varying orders, the simulations were grouped into four time blocks for analysis of performance over time. Statistical analysis utilized a combination of descriptive analysis, Wilcoxon signed-rank tests, Kruskal-Wallis tests, and Wilcoxon rank-sum tests. RESULTS: Twenty-one surgeons (19 pediatric, one trauma, one general) representing four of five regions in Brazil consented to study participation. Women comprised 76% (16/21) of participants. Overall, participants scored higher on the knowledge assessment after the course (68% versus 76%; z = 3.046, P < 0.001). Participants reported improved knowledge for all tested components of trauma management (P < 0.001). The average simulation performance score increased from 66% on day 1% to 73% on day 2, although this increase was not statistically significant. All participants reported they were more confident managing pediatric trauma after the course and would recommend the course to others. CONCLUSIONS: Completion of global TRIK improved surgeons' confidence, knowledge, and clinical decision-making skills in managing pediatric trauma, suggesting a standardized course may improve pediatric trauma care and outcomes in LMICs. We plan to more closely address cost, language, and resource barriers to implementing protocolized trauma training in LMICs with the aim to improve patient outcomes and equity in trauma care globally.

Perceived Impact of Coronavirus Disease 2019 on Surgical Training: A Brazilian Survey.

INTRODUCTION: Recent studies revealed that coronavirus disease 2019 (COVID-19) negatively impacted residency programs worldwide, particularly procedure-based programs. However, most studies are from high-income countries, with scarce data from low- and middle-income countries. Pandemic effects on surgical training were likely worse in strictly apprenticeship models relying heavily on surgical volume as opposed to competency-based programs. Notably, training programs in Brazil and other low- and middle-income countries follow these strict apprenticeship style frameworks. In this study, we aimed to evaluate the trainees' perceptions of the impact of COVID-19 on their Brazilian surgical programs. METHODS: A cross-sectional study was performed using an anonymous survey in Portuguese, distributed via social media platforms to surgical residents enrolled in Brazilian surgery programs. Data collection took place from August 2021 to May 2022. The survey contained 30 questions on the perception of the impact of COVID-19 on surgical training. RESULTS: One-hundred sixty-two residents from 17 different surgical specialties and all five regions of Brazil responded to the survey. Of 162 residents, 145 (89%) believed the pandemic negatively impacted their surgical training. Furthermore, of 162 residents, 153 (94%) reported that elective surgical volume decreased during the pandemic and 91 (56%) were redeployed to assist with COVID-19 management. As a result, 102 of 162 (63%) residents believed their surgical skills were negatively impacted by COVID-19. Yet, 95 of 162 (59%) residents reported their residency programs did not offer resources to mitigate the pandemic's impact on training. Of 162 residents, 57 (35%) reported they did not feel on track for graduation, with no statistical difference between responses by year of residency (P = 0.083). Additionally, 124 of 162 (77%) residents reported that the pandemic negatively affected their mental health, most commonly related to stress at work, stress about transmitting COVID-19, and loss in surgical training. CONCLUSIONS: Most of the surveyed Brazilian surgical residents felt the COVID-19 pandemic negatively impacted their training. This leads to believe that the detrimental impacts of the pandemic exposed preexisting weaknesses in the Brazilian surgical training model's dependence on a strict apprenticeship model. Our findings suggest a crucial need to redesign surgical education programs to make residency programs more prepared for changes in surgical volume, evolve the apprenticeship model to competency-based approaches, and unify surgical training standards in low- and middle-income countries.

Uncovering gaps in women's authorship: A big data analysis in academic surgery.

INTRODUCTION: Women are underrepresented in surgical authorship. Using big data analyses, we aimed to investigate women's representation as first and last authors in surgical publications worldwide and identify underlying predictors. METHODS: We retrieved eligible surgical journals using Scimago Journal & Country Rank 2021. We queried articles indexed in PubMed from selected journals published between January 2018 and April 2022. We used the EDirect tool to extract bibliometric data, including first and last authors' names, primary affiliation country, and publication year. Countries and dependent territories were classified following World Bank income levels and regions. Women's representation was predicted from forenames using the Gender-API software. Citations were included if gender accuracy was ≥80%. RESULTS: We analyzed 210,853 citations containing both first and last authors' forenames, representing 158 countries and 14 territories. Women constituted 23.8% (50,161/210,853) of the first and 14.7% (31,069/210,853) of the last authors. High-income economies had more women as first authors than other income categories (p < 0.001), but fewer women as last authors than upper-middle- and lower-middle-income economies (p < 0.001). The odds of the first author being a woman were more than three times higher when the last author was also a woman (OR 3.21, 95% CI 3.13-3.30) and vice versa (OR 3.25, 95% CI 3.16-3.34) after adjusting for income level and publication year. CONCLUSIONS: Women remain globally underrepresented in surgical authorship. Our findings urge concerted global efforts to overcome identified disparities.

Mechanical checkpoint regulates monocyte differentiation in fibrotic niches.

Myelofibrosis is a progressive bone marrow malignancy associated with monocytosis, and is believed to promote the pathological remodelling of the extracellular matrix. Here we show that the mechanical properties of myelofibrosis, namely the liquid-to-solid properties (viscoelasticity) of the bone marrow, contribute to aberrant differentiation of monocytes. Human monocytes cultured in stiff, elastic hydrogels show proinflammatory polarization and differentiation towards dendritic cells, as opposed to those cultured in a viscoelastic matrix. This mechanically induced cell differentiation is blocked by inhibiting a myeloid-specific isoform of phosphoinositide 3-kinase, PI3K-γ. We further show that murine bone marrow with myelofibrosis has a significantly increased stiffness and unveil a positive correlation between myelofibrosis grading and viscoelasticity. Treatment with a PI3K-γ inhibitor in vivo reduced frequencies of monocyte and dendritic cell populations in murine bone marrow with myelofibrosis. Moreover, transcriptional changes driven by viscoelasticity are consistent with transcriptional profiles of myeloid cells in other human fibrotic diseases. These results demonstrate that a fibrotic bone marrow niche can physically promote a proinflammatory microenvironment.

Polymeric Tissue Adhesives.

Polymeric tissue adhesives provide versatile materials for wound management and are widely used in a variety of medical settings ranging from minor to life-threatening tissue injuries. Compared to the traditional methods of wound closure (i.e., suturing and stapling), they are relatively easy to use, enable rapid application, and introduce minimal tissue damage. Furthermore, they can act as hemostats to control bleeding and provide a tissue-healing environment at the wound site. Despite their numerous current applications, tissue adhesives still face several limitations and unresolved challenges (e.g., weak adhesion strength and poor mechanical properties) that limit their use, leaving ample room for future improvements. Successful development of next-generation adhesives will likely require a holistic understanding of the chemical and physical properties of the tissue-adhesive interface, fundamental mechanisms of tissue adhesion, and requirements for specific clinical applications. In this review, we discuss a set of rational guidelines for design of adhesives, recent progress in the field along with examples of commercially available adhesives and those under development, tissue-specific considerations, and finally potential functions for future adhesives. Advances in tissue adhesives will open new avenues for wound care and potentially provide potent therapeutics for various medical applications.

Extracellular matrix plasticity as a driver of cell spreading.

Mammalian cell morphology has been linked to the viscoelastic properties of the adhesion substrate, which is particularly relevant in biological processes such as wound repair and embryonic development where cell spreading and migration are critical. Plastic deformation, degradation, and relaxation of stress are typically coupled in biomaterial systems used to explore these effects, making it unclear which variable drives cell behavior. Here we present a nondegradable polymer architecture that specifically decouples irreversible creep from stress relaxation and modulus. We demonstrate that network plasticity independently controls mesenchymal stem cell spreading through a biphasic relationship dependent on cell-intrinsic forces, and this relationship can be shifted by inhibiting actomyosin contractility. Kinetic Monte Carlo simulations also show strong correlation with experimental cell spreading data as a function of the extracellular matrix (ECM) plasticity. Furthermore, plasticity regulates many ECM adhesion and remodeling genes. Altogether, these findings confirm a key role for matrix plasticity in stem cell biophysics, and we anticipate this will have ramifications in the design of biomaterials to enhance therapeutic applications of stem cells.