Jess Gerrit Snedeker

PIEZO mechanoreceptors play critical roles in fundamental physiological processes such as proprioception or musculoskeletal biomechanics. However, their complex gating mechanisms and downstream signaling are still not completely understood, mainly due to the lack of effective probing tools. Here, we combine molecular imprinting and magnetic concepts to develop tailor-made nanoswitches enabling wireless targeted actuation of PIEZO1. Two epitopes selected in silico from distinct domains of PIEZO1 were used as templates for synthesizing magnetically responsive molecularly imprinted nanoparticles. These nanoswitches showed sub-nanomolar affinity for their respective epitope and recognized PIEZO1 in endothelial cells, similarly to antibodies. Applying magnetic fields to actuate PIEZO1 through nanoswitches led to increased calcium signaling, Yes-associated protein (YAP) nuclear translocation, and significant changes in the expression of genes related to PIEZO1 activity, implying that they can transduce the stimulus into intracellular signaling effects. Finally, this wireless actuation system proved to be effective in differentially modulating the behavior of mesenchymal stem cells. Remarkably, the selective targeting of each epitope led to contrasting downstream signaling cascades, implying distinct roles for each superstructure domain in the sophisticated function of these channels. Overall, this technology constitutes a promising tool for studying PIEZO-mediated mechanobiology, opening perspectives for harnessing its potential toward therapeutic approaches.

Fibrosis arises from aberrant tissue repair in systemic sclerosis and is characterized by progressive stiffening across multiple tissues, including tendons. How altered tissue mechanics sustain fibrotic remodeling remains poorly understood, in part because of limited experimental models that capture key biophysical features of fibrosis. Here we develop a modular cantilever-based mechano-culture platform that enables tendon-like constructs to be maintained under controlled static tension. We show that elevated matrix tension induces fibroblast-to-myofibroblast activation and scar-like phenotypes in vitro. Analysis of preclinical and clinical models of systemic sclerosis reveals that increased three-dimensional matrix stiffness inversely correlates with transcription of major profibrotic collagens, while positively regulating genes associated with stromal–immune interactions. Co-culture with bone marrow–derived macrophages overrides tension-dependent suppression of matrix gene expression, suggesting that immune cues can supersede mechanical checkpoints. These findings demonstrate how tissue mechanics orchestrates reciprocal interactions between stromal and immune compartments to drive progressive fibrosis, and establish a reductionist platform for dissecting mechano-regulatory pathways in fibrotic diseases.

The aim of this study was to investigate changes in hamstring architecture and size over a 4-year period, explore sex-specific differences, and examine associations with biological maturation in adolescent competitive alpine skiers. 59 competitive alpine skiers (27 females, 32 males; baseline age: 14.9 ± 0.7 years) competing at regional to national level were examined at baseline and follow-up. BMI was calculated and biological maturation estimated using the sex-specific Mirwald equation. Ultrasound imaging assessed biceps femoris long head architecture and maximal anatomical cross-sectional area (ACSA_max) of all hamstring muscles. ACL injuries were retrospectively recorded and verified using medical records and MRI. Participants were grouped as uninjured (n = 53) and ACL-injured (n = 6). Mixed ANOVA revealed significant main and interaction effects for hamstring muscle size, but not for architecture. Post hoc analyses showed that hamstring muscle size increased in both sexes (all p < 0.001), except for the semitendinosus in females (p = 0.499). Biological maturation was associated with changes in femur length (R² = 0.32, p < 0.001) and total hamstring muscle size (R² = 0.52, p < 0.001). As a secondary observation, female skiers who later sustained an ACL injury (n = 5) descriptively showed smaller semitendinosus size across both time points. This study provides new insights into hamstring development in adolescent alpine skiers and highlights the role of biological maturation. Hamstring size increased, with greater hypertrophy in males. The smaller semitendinosus size in ACL-injured females may be relevant for injury prevention.

Tendons are sparsely vascularized connective tissues that link muscles to bones, withstanding some of the highest mechanical stresses in the body. Mechanical overloading and tissue hypervascularity are implicated in tendinopathy, a common musculoskeletal disorder, yet their mechanistic roles remain unclear. Here, we identify hypoxia-inducible factor 1α (HIF1α) as not only a marker but also a driver of tendinopathy. Histological and multiomics evaluation of human tendinopathic samples revealed extensive extracellular matrix remodeling, including pathological collagen cross-linking coinciding with active hypoxic signaling. Hypothesizing a causal contribution of hypoxia signaling, we generated mice with tenocyte-targeted deletions of the von Hippel–Lindau ( Vhl ) gene, which controls hypoxia signaling by regulating HIFα degradation. Vhl inactivation was sufficient to induce pathological hallmarks of tendinopathy, such as collagen matrix disorganization, cross-linking, altered mechanics, and neurovascular ingrowth. This phenotype was HIF1α dependent given that codeleting HIF1α rescued tendon morphology and mechanics. Moreover, deleting vascular endothelial growth factor A ( Vegfa ) alongside VHL effectively suppressed neovascularization but failed to rescue extracellular matrix abnormalities or restore mechanical function, emphasizing a direct role of HIF1α in driving tendon disease independently of angiogenesis. Mechanistically, we found that HIF1α activation was strain dependent in primary cultured human tendon cells and induced by mechanical overload in murine tendon explants. Furthermore, genetically removing Hif1 α from tenocytes prevented aberrant tendon remodeling in response to chronic overload. These findings position HIF1α signaling as a central driver of tendinopathy that acts through a maladaptive tissue response to chronic overload, providing mechanistic insights that could be leveraged for therapeutic approaches.

Tendinopathy is a complex, painful condition that affects up to 5% of the general population in their lifetime. Antibiotic treatment with fluoroquinolones has been associated with the onset of tendinopathy and tendon rupture. The mechanisms behind fluoroquinolone induced tendinopathy remain unclear. To probe activation of potentially causative pathways, we treated juvenile mice with ciprofloxacin in drinking water for 4 weeks and performed RNA sequencing on tail tendons. We discovered that ciprofloxacin‐treated mice had upregulated genes relating to nerve development. Additionally, treated mice showed downregulation of genes associated with extracellular matrix (ECM) processes. We further explored ECM changes using histological and mechanical testing methods on patellar tendons. We found that ciprofloxacin treatment led to altered cell morphology and proteoglycan density. These changes translated to a decrease in mechanical properties of the patellar tendons. Furthermore, ciprofloxacin‐treated mice had a higher percentage of apoptotic cells, and we confirmed increased presence of nerve cells (Plexin B1 ⁺ ) in the patellar tendons compared to controls. Taken together, we showed that ciprofloxacin treatment in juvenile mice induces structural and biological phenotypes commonly associated with fluoroquinolone‐induced tendinopathy and identify the axis of pathological neural activation as a promising area for further exploration. Clinical significance: Oral administration of ciprofloxacin in mice presents a clinically relevant model for studying mechanisms of tendinopathy in humans.

Biohybrid actuators leveraging living muscle tissue offer the potential to replicate natural motion for biomedical and robotic applications. However, challenges such as limited force output and inefficient force transfer at tissue interfaces persist. The myotendinous junction, a specialized interface connecting muscle to the tendon, plays a critical role in efficient force transmission for movement. Engineering muscle-tendon units in vitro is essential for replicating native musculoskeletal functions in biohybrid actuators. Here, we present a three-dimensionally bioprinted system integrating skeletal muscle tissue with tendon-mimicking anchors containing fibroblasts, forming a biomimetic interdigitated myotendinous junction. Using computational models, we optimized muscle geometries to enhance deformation and force generation. The engineered system improved mechanical stability, myofiber maturation, and force transmission, generating contractile forces of up to 350 micronewtons over a 3-month period. This work highlights how biomimetic designs and mechanical optimization can advance bioactuator technologies for applications in medicine and robotics.

Tendon ruptures have recently reached incidences of 18–35 cases/100,000 and often lead to adhesion formation during healing. Furthermore, scar formation may result in inferior biomechanics and often leads to re-ruptures. To address these problems, we cultivated rabbit adipose-derived stem cells in a co-culture with rabbit Achilles tenocytes and harvested their secretome. Following a cell-free approach, we incorporated such secretome into an electrospun tube via emulsion electrospinning. These novel implants were characterized by SEM, the WCA, and FTIR. Then, they were implanted in the rabbit Achilles tendon full transection model with an additional injection of secretome, and the adhesion extent as well as the biomechanics of extracted tendons were assessed three weeks postoperatively. The fiber thickness was around 3–5 μm, the pore size 11–13 μm, and the tube wall thickness approximately 265 μm. The WCA indicated slightly hydrophilic surfaces in the secretome-containing layer, with values of 80–90°. In vivo experiments revealed a significant reduction in adhesion formation (−22%) when secretome-treated tendons were compared to DegraPol^® (DP) tube-treated tendons (no secretome). Furthermore, the cross-sectional area was significantly smaller in secretome-treated tendons compared to DP tube-treated ones (−32%). The peak load and stiffness of secretome-treated tendons were not significantly different from native tendons, while tendons treated with pure DP tubes exhibited significantly lower values. We concluded that secretome treatment supports tendon healing, with anti-adhesion effects and improved biomechanics at 3 weeks, making this approach interesting for clinical application.

Purpose: Adjacent segment degeneration (ASDeg) and disease (ASDis) remain significant challenges following lumbar spinal fusion surgery, with reported incidences of 36% for ASDeg and 11% for ASDis within two to seven years post-operation. However, the mechanisms leading to the development of ASDeg are still poorly understood. This comprehensive review aims to elucidate the multifactorial etiology of ASDeg by examining important iatrogenic alterations associated with spinal fusion. Methods: A systematic review following PRISMA guidelines was conducted to identify clinical studies quantifying the occurrence of ASDeg and ASDis after lumbar fusion surgery. An EMBASE and citation search up to April 2023 yielded 378 articles. Data extracted encompassed study design, fusion type, sample size, patient age, and incidence of ASDeg and ASDis. A total of 87 publications were analyzed in the context of iatrogenic alterations caused by surgical access (muscle damage, ligament damage, facet joint damage) and instrumentation (fusion angle, immobilization). Results: Ligament damage emerged as the most impactful iatrogenic factor promoting ASDeg and ASDis development. Similarly, muscle damage had a significant impact on long-term musculoskeletal health, with muscle-sparing approaches potentially reducing ASDis rates. Immobilization led to compensatory increased motion at adjacent segments; however, the causal link to degeneration remains inconclusive. Fusion angle showed low evidence for a strong impact due to inconsistent findings across studies. Facet joint violations were likely contributing factors but not primary initiators of ASDeg. Conclusion: Based on the analyzed literature, ligament and muscle damage are the most impactful iatrogenic factors contributing to ASDeg and ASDis development. Minimally invasive techniques, careful retractor placement, and ligament-preserving decompression may help mitigate these effects by reducing undue muscle and ligament trauma. Although it is not possible to definitively advocate for one or more techniques, the principle of selecting the most tissue-sparing approach needs to be scaled across surgical planning and execution. Further research is necessary to fully elucidate these mechanisms and inform surgical practices to mitigate ASDeg risk.

One hallmark of healthy tendon tissue is the high confinement of tenocytes between tightly packed, highly aligned collagen fibers. During tendinopathy, this organization becomes dysregulated, leading to cells with round-shaped morphology and collagen fibers which exhibit crimping and misalignment. The elongated nuclei in healthy tendons are linked to matrix homeostasis through distinct mechanotransduction pathways, and it is believed that the loss of nuclear confinement could upregulate genes associated with abnormal matrix remodeling. Replicating the cell and nuclear morphology of healthy and diseased states of tendon, however, remains a significant challenge for engineered in vitro tendon models. Here we report on a high throughput biofabrication of mini-tendons that mimick the tendon core compartment based on the filamented light (FLight) approach. Each mini-tendon, with a length of 4 mm, was composed of parallel hydrogel microfilaments (2–5 µm diameter) and microchannels (2–10 µm diameter) that confined the cells. We generated four distinct matrices with varying stiffness (7–40 kPa) and microchannel dimensions. After 14 d of culture, 29% of tenocytes in the softest matrix with the largest microchannel diameter were aligned, exhibiting an average nuclear aspect ratio (nAR) of 2.1. In contrast, 84% of tenocytes in the stiffest matrix with the smallest microchannel diameter were highly aligned, with a mean nAR of 3.4. When tenocytes were cultured on the FLight hydrogels (2D) as opposed to within the hydrogels three-dimensional (3D), the mean nAR was less than 1.9, indicating that nuclear morphology is significantly more confined in 3D environments. By tuning the stiffness and microarchitecture of the FLight matrix, we demonstrated that mechanical confinement can be modulated to exert control over the extent of nuclear confinement. This high-throughput, tunable platform offers a promising approach for studying the mechanobiology of healthy and diseased tendons and for eventual testing of drug compounds against tendinopathy.