Mechanical properties of whole-body soft human tissues: a review

Processing and properties of graphene-reinforced polylactic acid nanocomposites for bioelectronic and tissue regenerative functions

An in-situ polymer-solution-processing approach enables the efficient production of uniform graphene-reinforced polylactic acid (G-PLA) nanocomposites with notable physical and biomedical properties. The approach effectively enhances the interfacial bonding between graphene and PLA by creating graphene dangling bonds and defects during exfoliation. As a result, an 182 % increase in Young's modulus and an 85 % increase in tensile strength can be achieved in G-PLA. Only 0.5 wt% graphene addition can reduce the contact angle of the composite from 75.3 to 70.4 and reduce its oxygen permeability by 23 %. The improved hydrophilicity, hermeticity, and mechanical properties make G-PLA an excellent encapsulation material for implantable bioelectronics. Moreover, the composite surface attributes and cell behaviors at the material-tissue interface are investigated histologically through the culture of stem cells on as-synthesized G-PLA. G-PLA composites can significantly boost cell proliferation and regulate cell differentiation towards vascular endothelium, offering tissue regeneration at the surface of implants to recover the injured tissues. The degradation rate of G-PLA nanocomposite can also be regulated since the graphene slows down the autocatalytic chain splitting induced by the terminal carboxylic acid groups of PLA. Therefore, such G-PLA nanocomposites with physical and biomedical properties regulated by graphene loading enable the development of next-generation implantable electronic systems providing both sensing and tissue engineering functions for complicated applications such as implanted sensors monitoring the healing of fractured bones or intracranial pressure.

Tailoring the mechanical properties of macro-porous PVA hydrogels for biomedical applications

Polyvinyl alcohol (PVA) is a biocompatible biopolymer with superior dimensional and mechanical stability when compared to naturally available biomaterials such as collagen and gelatin. Furthermore, PVA in hydrogel form behaves non-linearly during mechanical loading, generating a response like soft biological tissues. Generally, PVA hydrogels are fabricated using freeze-thaw cycles (FTCs) and changing the number of FTCs gives control over its mechanical properties. Porosity of the hydrogel is another important factor which determines its mechanical properties and is also evident in biological soft tissues. Incorporating macro-pores in PVA hydrogels substantially reduces the stiffness of the material and can mimic some porous tissues such as lung, liver, bone marrow, kidneys, and penile tissues (corpus cavernosa and spongiosum). Within this study, we developed macro-porous PVA hydrogels using the freeze-thaw process followed by particulate leaching of sacrificial 3D-printed and milled PVA (m-PVA) filler particles. This fabrication method enables control over the porosity in macro-porous PVA hydrogels, which is crucial not only for tuning mechanical properties but also for mimicking the structure of spongy tissues, such as liver tissue and corpus cavernosum in the penis, for example. We investigated the level of porosity in the specimen using optical microscopy to understand the distribution of the pores and the pore size. The tunability of the mechanical properties of PVA hydrogels is a key finding of this study and is achieved using three factors: (i) weight percentage of sacrificial fillers, (ii) number of FTCs and (iii) concentration of PVA. These macro-porous PVA specimens have wide ranging biomedical applications as biological soft tissue analogues, or tissue engineering scaffolds, where the PVA hydrogel can be tuned to match the mechanical properties of these soft biological tissues.

Pre-Clinical Assessment of Bupivacaine-Loaded Poly(ester urea) Thin Films for Controlled Drug Release and Effective Pain Management After Surgery

Safe, effective pain management remains one of the biggest challenges following surgical procedures. Despite widespread recognition of this problem and advances in the mechanistic understanding of pain signaling, post-surgical pain is often undermanaged, with opioid use remaining the clinical standard. As an alternative to current oral, systemic treatments, a degradable bupivacaine-loaded poly(ester urea) (PEU) thin film has been developed to deliver bupivacaine directly to the site of injury over an extended duration. The dose and duration of bupivacaine delivery is controlled using polymer composition and bupivacaine concentration. Systemic bupivacaine concentrations are more than an order of magnitude lower when delivered locally versus intravenous injection. Tissue analysis showed that the majority of bupivacaine is deposited into subcutaneous tissue directly surrounding the implant. Bupivacaine concentration in soft tissue around the implant are 30-fold higher than plasma values, indicating that release from PEU implants remains localized. Bupivacaine-loaded PEU films are assessed into two established mouse models for diabetic neuropathic pain and post-surgical incisional pain. In each model, bupivacaine eluting PEU films effectively block pain for 3-5 days before returning to baseline levels without loss of motor function and without signs of neurotoxicity.

Invited Review for 20th Anniversary Special Issue of PLRev "AI for Mechanomedicine"

Mechanomedicine is an interdisciplinary field that combines different areas including biomechanics, mechanobiology, and clinical applications like mechanodiagnosis and mechanotherapy. The emergence of artificial intelligence (AI) has revolutionized mechanomedicine, providing advanced tools to analyze the complex interactions between mechanics and biology. This review explores how AI impacts mechanomedicine across four key aspects, i.e., biomechanics, mechanobiology, mechanodiagnosis, and mechanotherapy. AI improves the accuracy of biomechanical characterizations and models, deepens the understanding of cellular mechanotransduction pathways, and enables early disease detection through mechanodiagnosis. In addition, AI optimizes mechanotherapy that targets biomechanical features and mechanobiological markers by personalizing treatment strategies based on real-time patient data. Even with these advancements, challenges still exist, particularly in data quality and the ethical integration into AI in clinical practice. The integration of AI with mechanomedicine offers transformative potential, enabling more accurate diagnostics and personalized treatments, and discovering novel mechanobiological pathways.

MRI-compatible abdomen phantom to mimic respiratory-triggered organ movement while performing needle-based interventions

PURPOSE

In vivo studies are often required to prove the functionality and safety of medical devices. Clinical trials are costly and complex, adding to ethical scrutiny of animal testing. Anthropomorphic phantoms with versatile functionalities can overcome these issues with regard to medical education or an effective development of assistance systems during image-guided interventions (e.g., robotics, navigation/registration algorithms). In this work, an MRI-compatible and customizable motion phantom is presented to mimic respiratory-triggered organ movement as well as human anatomy.

METHODS

For this purpose, polyvinyl alcohol cryogel (PVA-C) was the foundation for muscles, liver, kidneys, tumors, and remaining abdominal tissue in different sizes of the abdominal phantom body (APB) with the ability to mimic human tissue in various properties. In addition, a semi-flexible rib cage was 3D-printed. The motion unit (MU) with an electromagnetically shielded stepper motor and mechanical extensions simulated a respiration pattern to move the APB.

RESULTS

Each compartment of the APB complied the relaxation times, dielectricity, and elasticity of human tissue. It showed resistance against mold and provided a resealable behavior after needle punctures. During long-term storage, the APB had a weight loss of 2.3%, followed by changes to relaxation times of 9.3% and elasticity up to 79%. The MU was able to physiologically appropriately mimic the organ displacement without reducing the MRI quality.

CONCLUSION

This work presents a novel modularizable and low-cost PVA-C based APB to mimic fundamental organ motion. Beside a further organ motion analysis, an optimization of APB's chemical composition is needed to ensure a realistic motion simulation and reproducible long-term use. This phantom enhances diverse and varied training environments for prospective physicians as well as effective R&D of medical devices with the possibility to reduce in vivo experiments.

Destruction mechanism of anterior cervical discectomy and fusion in frontal impact

The aim of this study was to quantitatively study the effect of anterior cervical discectomy and fusion (ACDF) on the risk of spinal injury under frontal impact. A head-neck finite element model incorporating active neck muscles and soft tissues was developed and validated. Based on the intact head-neck model, three ACDF models (single-level, two-level and three-level) were used to analyze the frontal impact responses of the head-neck. The results revealed that various surgical approaches led to distinct patterns of vertebral damage under frontal impact. For single-level and three-level ACDFs, vertebral destruction was mainly concentrated at the lower end of the fused segment, while the other vertebrae were not significantly damaged. For two-level ACDF, the lowest vertebra was the first to suffer destruction, followed by severe damage to both the upper and lower vertebrae, while the middle vertebra of the cervical spine exhibited only partial damage around the screws. Fusion surgery for cervical spine injuries predominantly influences the vertebral integrity of the directly fused segments when subjected to frontal impact, while exerting a comparatively lesser impact on the cross-sectional properties of adjacent, non-fused segments.

Effective protection of biological tissues from severe blunt force injury by engineered nanoscale liquid flow

Blunt force trauma (BFT), the injury of the body by forceful impacts such as falls, motor vehicle crashes and collisions, causes damage to bio-organs that can lead to life-threatening situations. To address the unmet need of bioprotection materials for BFT, we developed a novel, liquid nanofoam (LN)-based system. The LN system employs a unique mechanism of energy absorption, i.e. the external force-aided, nanoscale liquid flow. Under mechanical loading, the LN system effectively protected human cells from force-induced deformation and cell death. In addition to effective mitigation of the upregulation of stress and inflammatory genes, LN prevented blunt-force-induced damage of multiple vital organs including liver, kidney, heart, and lungs. To our knowledge, this is the first material of its kind that is biocompatible and capable of effectively protecting biotissues from BFT on molecular, cellular and tissue levels.

Design, implementation and effectiveness of human fascia lata biomechanics for tissue engineering

The fascia lata (FL) is a multi-layered connective tissue with anisotropic mechanical behavior due to its fiber organization. It plays a key role in musculoskeletal functionality, making it important in tissue engineering. Understanding its mechanical response to stimuli like movement or applied pressure is crucial, as the elastic and viscoelastic behavior can vary significantly based on morphological characteristics, harvesting site, and load direction. Thus, the aim of this review is to summarise through a gap analysis the scientific literature on the biomechanical properties of the human FL, identifying all those features (from the experimental set up to its inherent structural variability) that could affect its biomechanical behaviour, and thus unveiling these emerging correlations. Our research reported key mechanical properties of the FL, such as Young's modulus, Ultimate Tensile Strength, failure strain, and anisotropic response, which are crucial for designing and applying obtained allografts and autografts in soft tissue repair. These insights can help surgeons optimize graft applications-selecting the proper harvesting location, technique, graft type, and suture size-and guide clinicians in rehabilitation for personalized medicine.

Conductive, injectable, and self-healing collagen-hyaluronic acid hydrogels loaded with bacterial cellulose and gold nanoparticles for heart tissue engineering

The increasing demand for advanced biomaterials in nerve tissue engineering presents numerous challenges due to the complexity of nerve tissues and the need for materials that can accurately replicate their intricate structure and function. In response, this study introduces a novel injectable hydrogel that is thermosensitive, self-healing, and conductive, offering promising potential for heart and nerve tissue engineering applications. The hydrogel is based on collagen and hyaluronic acid functionalized with 3-aminopropyl-triethoxysilane (APTES)-grafted oxidized bacterial cellulose and gold nanoparticles (~50 nm). Rheological analysis reveals a substantial enhancement in the elastic modulus of the collagen-hyaluronic acid matrix with the incorporation of bacterial cellulose/gold nanoparticles, improving by an order of magnitude at 1 % strain. This improvement comes with a slight decrease in gelation temperature, from 36 °C to 32 °C. Besides thermo-sensitivity, the nanocomposite hydrogel exhibits a remarkable self-sealing response (about 80 % effectiveness) due to reversible physical crosslinking. Electrical spatial resistance measurements on human embryonic stem cell-derived cardiomyocytes-loaded hydrogels yield a value of ~0.1 S/m, which is suitable for electrical stimulation. In vitro extracellular field potential measurements also affirm the hydrogel's potential as an injectable scaffold for heart tissue engineering, i.e., the electrically stimulated human stem cells exhibit 47 beats per minute with a cell discharge (depletion) of 5.47 μv. A rapid gel formation in the physiological temperature (about 2 min) and high H9C2 cytotoxicity (viability of >90 % after 72 h incubation) is attainable. The developed collagen-based nanocomposite hydrogel offers an injectable, thermosensitive, and self-healing biomaterial platform for nerve or myocardium regeneration.

The influence of cooling on biomechanical time since death estimations using ovine brain tissue

The significance of biomechanical analyses for forensic time since death estimations has recently been demonstrated. Previous biomechanical analyses successfully discriminated post-mortem brain tissue from tissue with a post-mortem interval of at least one day when held at 20 °C. However, the practical utility of such analyses beyond day one at 20 °C was limited. This study investigates the storage, loss, and complex shear modulus of various brain regions in sheep stored at 4 °C in 24-hour intervals over four days post-mortem using rheometry tests. The aim is to identify the critical biomechanical tissue property values to predict post-mortem time and assess the temperature sensitivity of the rheometry method by comparing results to recent findings at 20 °C. Thirty sheep brains were examined, including the frontal lobe, parietal lobe, anterior and posterior deep brain, superior colliculi, pons, medulla, and cerebellum. Rheometry tests were conducted, and receiver operator characteristic analyses were employed to establish cut-off values. At 4 °C storage, all investigated biomechanical properties of the examined brain regions remained stable for at least one day post-mortem. Using cerebellar samples stored at 4 °C, a post-mortem interval of at least two days could be determined with excellent diagnostic ability. Complex shear modulus values below 1435 Pa or storage modulus values below 1313 Pa allowed prediction of two or more days post-mortem. Comparisons between 4 °C and 20 °C revealed brain region-specific results. For instance, the complex shear moduli of the anterior deep brain at 4 °C were significantly higher on all individual testing days when compared to 20 °C. In contrast, the combined medulla and pons samples were similar on each day. Rheometry testing of brain tissue consistently stored at 4 °C since death proved valuable for forensic time since death estimations starting from two days after death.

Phloretin@cyclodextrin/natural silk protein/polycaprolactone nanofiber wound dressing with antioxidant and antibacterial activities promotes diabetic wound healing

In patients with diabetes, chronic hyperglycemia impairs immune function at wound sites, increasing susceptibility to infections, prolonging inflammation, and delaying healing. This study aimed to develop wound dressings that control bacterial infections and accelerate healing. Phloretin (PHL), which has antibacterial and anti-inflammatory properties, was encapsulated with γ-cyclodextrin (γ-CD) to form a PHL@CD complex with enhanced bioavailability. This complex was incorporated into nanofiber wound dressings composed of polycaprolactone and natural silk protein. The resulting dressings exhibited favorable physical and chemical properties, including nutrient transport and gas exchange, which are essential for wound healing. The nanofiber membranes exhibited antibacterial activity against Staphylococcus aureus (90.31 ± 4.41 % inhibition), with high antioxidant capacity (91.48 ± 0.33 % ABTS scavenging) and blood compatibility. The membranes also promoted cell viability. Importantly, the nanofiber dressings accelerated wound healing in a diabetic mouse model by reducing the duration of inflammation. The novel nanofiber wound dressing can significantly improve the treatment of diabetic wounds.

Implantable Fluorogenic DNA Biosensor for Stress Detection

Implantable sensors that can monitor analytes related to cognitive and physiological status have gained significant focus in recent years. We have developed an implantable biosensor to detect dehydroepiandrosterone sulfate (DHEA-S), a biomarker related to stress. The biosensor strategy was based on the principle of forced intercalation (FIT) aptamers designed to detect subtle intramolecular changes during aptamer-target binding events. By incorporating a steroid-specific fluorogenic aptamer into a hydrogel, the sensitivity and biostability of the FIT biosensor fiber were improved, which were essential for designing implantable sensors to monitor biomarker levels in the living body. The polyethylenimine-based hydrogel chosen for this study produced an optically transparent cross-linked network with optimal microstructure, physicochemical, and mechanical properties, making it suitable for optical biosensors. The in vitro studies showed that the biosensor fiber was successfully activated in human serum and skin analogue, providing a linear response to physiological concentrations of the steroid. We believe that this type of implantable platform can be effective in monitoring more complex biomarkers associated with physiological or psychological health.

Characterization of Decellularized Plant Leaf as an Emerging Biomaterial Platform

Decellularized plants have emerged as promising biomaterials for cell culture and tissue engineering applications due to their distinct material characteristics. This study explores the biochemical, mechanical, and structural properties of decellularized leaves that make them useful as biomaterials for cell culture. Five monocot leaf species were decellularized via alkali treatment, resulting in the effective removal of DNA and proteins. The Van Soest method was used to quantitatively evaluate the changes in cellulose, hemicellulose, and lignin content during decellularization. Tensile tests revealed considerable variations in mechanical strength depending on the plant species, the decellularization state, and the direction of applied mechanical force. Decellularized monocot leaves exhibited a notable reduction in mechanical strength and anisotropic properties depending on the leaf orientation. Imaging revealed inherent microgrooves on the epidermis of the monocot leaves. Permeability studies, including water uptake and biomolecule transport through decellularized leaves, confirmed excellent water uptake capability but limited biomolecule transport. Lastly, the plants were enzymatically degradable using typical plant enzymes, which were minimally cytotoxic to mammalian cells. Taken together, the features of decellularized plant leaves characterized in this study suggest ways in which they can be useful in cell culture and tissue engineering applications.

Ultrathin crystalline silicon-based omnidirectional strain gauges for implantable/wearable characterization of soft tissue biomechanics

Monitoring soft-tissue biomechanics is of interest in biomedical research and clinical treatment of diseases. An important focus is biointegrated strain gauges that track time-dependent mechanics of targeted tissues with deforming surfaces over multidirections. Existing methods provide limited gauge factors, tailored for sensing within specific directions under quasi-static conditions. We present development and applicability of implantable/wearable strain gauges that integrate multiple ultrathin monocrystalline silicon-based sensors aligned with different directions, in stretchable formats for dynamically monitoring direction angle-sensitive strain. We experimentally and computationally establish operational principles, with theoretical systems that enable determination of intensities and direction of applied strains at an omnidirectional scale. Wearable evaluations range from cardiac pulse to intraocular pressure monitoring of eyeballs. The device can evaluate cardiac disorders of myocardial infarction and hypoxia of living rats and locate the pathological orientation associated with infarction, in designs with possibilities as biodegradable implants for stable operation. These findings create clinical significance of the devices for monitoring complex dynamic biomechanics.

Borate bioactive glass enhances 3D bioprinting precision and biocompatibility on a sodium alginate platform via Ca2+ controlled self-solidification

Sodium alginate (SA) has gained widespread acclaim as a carrier medium for three-dimensional (3D) bioprinting of cells and a diverse array of bioactive substances, attributed to its remarkable biocompatibility and affordability. The conventional approach for fabricating alginate-based tissue engineering constructs entails a post-treatment phase employing a calcium ion solution. However, this method proves ineffectual in addressing the predicament of low precision during the 3D printing procedure and is unable to prevent issues such as non-uniform alginate gelation and substantial distortions. In this study, we introduced borate bioactive glass (BBG) into the SA matrix, capitalizing on the calcium ions released from the degradation of BBG to incite the cross-linking reaction within SA, resulting in the formation of BBG-SA hydrogels. Building upon this fundamental concept, it unveiled that BBG-SA hydrogels greatly enhance the precision of SA in extrusion-based 3D printing and significantly reduce volumetric contraction shrinkage post-printing, while also displaying certain adhesive properties and electrical conductivity. Furthermore, in vitro cellular experiments have unequivocally established the excellent biocompatibility of BBG-SA hydrogel and its capacity to actively stimulate osteogenic differentiation. Consequently, BBG-SA hydrogel emerges as a promising platform for 3D bioprinting, laying the foundation for the development of flexible, biocompatible electronic devices.

Being thin-skinned can still reduce damage from dynamic puncture

The integumentary system in animals serves as an important line of defence against physiological and mechanical external forces. Over time, integuments have evolved layered structures (scales, cuticle and skin) with high toughness and strength to resist damage and prevent wound expansion. While previous studies have examined their defensive performance under low-rate conditions, the failure response and damage resistance of these thin layers under dynamic biological puncture remain underexplored. Here, we utilize a novel experimental framework to investigate the mechanics of dynamic puncture in both bilayer structures of synthetic tissue-mimicking composite materials and natural skin tissues. Our findings reveal the remarkable efficiency of a thin outer skin layer in reducing the overall extent of dynamic puncture damage. This enhanced damage resistance is governed by interlayer properties through puncture energetics and diminishes in strength at higher puncture rates due to rate-dependent effects in silicone tissue simulants. In addition, natural skin tissues exhibit unique material properties and failure behaviours, leading to superior damage reduction capability compared with synthetic counterparts. These findings contribute to a deeper understanding of the inherent biomechanical complexity of biological puncture systems with layered composite material structures. They lay the groundwork for future comparative studies and bio-inspired applications.

3D Printing of Tough Hydrogel Scaffolds with Functional Surface Structures for Tissue Regeneration

Hydrogel scaffolds have numerous potential applications in the tissue engineering field. However, tough hydrogel scaffolds implanted in vivo are seldom reported because it is difficult to balance biocompatibility and high mechanical properties. Inspired by Chinese ramen, we propose a universal fabricating method (printing-P, training-T, cross-linking-C, PTC & PCT) for tough hydrogel scaffolds to fill this gap. First, 3D printing fabricates a hydrogel scaffold with desired structures (P). Then, the scaffold could have extraordinarily high mechanical properties and functional surface structure by cycle mechanical training with salting-out assistance (T). Finally, the training results are fixed by photo-cross-linking processing (C). The tough gelatin hydrogel scaffolds exhibit excellent tensile strength of 6.66 MPa (622-fold untreated) and have excellent biocompatibility. Furthermore, this scaffold possesses functional surface structures from nanometer to micron to millimeter, which can efficiently induce directional cell growth. Interestingly, this strategy can produce bionic human tissue with mechanical properties of 10 kPa-10 MPa by changing the type of salt, and many hydrogels, such as gelatin and silk, could be improved with PTC or PCT strategies. Animal experiments show that this scaffold can effectively promote the new generation of muscle fibers, blood vessels, and nerves within 4 weeks, prompting the rapid regeneration of large-volume muscle loss injuries.

Human Skeletal Muscle Myoblast Culture in Aligned Bacterial Nanocellulose and Commercial Matrices

Bacterial nanocellulose (BNC) is a durable, flexible, and dynamic biomaterial capable of serving a wide variety of fields, sectors, and applications within biotechnology, healthcare, electronics, agriculture, fashion, and others. BNC is produced spontaneously in carbohydrate-rich bacterial culture media, forming a cellulosic pellicle via a nanonetwork of fibrils extruded from certain genera. Herein, we demonstrate engineering BNC-based scaffolds with tunable physical and mechanical properties through postprocessing. Human skeletal muscle myoblasts (HSMMs) were cultured on these scaffolds, and in vitro electrical stimulation was applied to promote cellular function for tissue engineering applications. We compared physiologic maturation markers of human skeletal muscle myoblast development using a 2.5-dimensional culture paradigm in fabricated BNC scaffolds, compared to two-dimensional (2D) controls. We demonstrate that the culture of human skeletal muscle myoblasts on BNC scaffolds developed under electrical stimulation produced highly aligned, physiologic morphology of human skeletal muscle myofibers compared to unstimulated BNC and standard 2D culture. Furthermore, we compared an array of metrics to assess the BNC scaffold in a rigorous head-to-head study with commercially available, clinically approved matrices, Kerecis Omega3 Wound Matrix (Marigen) and Phoenix as well as a gelatin methacryloyl (GelMA) hydrogel. The BNC scaffold outcompeted industry standard matrices as well as a 20% GelMA hydrogel in durability and sustained the support of human skeletal muscle myoblasts in vitro. This work offers a robust demonstration of BNC scaffold cytocompatibility with human skeletal muscle cells and sets the basis for future work in healthcare, bioengineering, and medical implant technological development.

Orthogonally woven 3D nanofiber scaffolds promote rapid soft tissue regeneration by enhancing bidirectional cell migration

Repairing large-area soft tissue defects caused by traumas is a major surgical challenge. Developing multifunctional scaffolds with suitable scalability and favorable cellular response is crucial for soft tissue regeneration. In this study, we developed an orthogonally woven three-dimensional (3D) nanofiber scaffold combining electrospinning, weaving, and modified gas-foaming technology. The developed orthogonally woven 3D nanofiber scaffold had a modular design and controlled fiber alignment. In vitro, the orthogonally woven 3D nanofiber scaffold exhibited adjustable mechanical properties, good cell compatibility, and easy drug loading. In vivo, for one thing, the implantation of an orthogonally woven 3D nanofiber scaffold in a full abdominal wall defect model demonstrated that extensive granulation tissue formation with enough mechanical strength could promote recovery of abdominal wall defects while reducing intestinal adhesion. Another result of diabetic wound repair experiments suggested that orthogonally woven 3D nanofiber scaffolds had a higher wound healing ratio, granulation tissue formation, collagen deposition, and re-epithelialization. Taken together, this novel orthogonally woven 3D nanofiber scaffold may provide a promising and effective approach for optimal soft tissue regeneration.

Biomechanical properties of the human superficial fascia: Site-specific variability and anisotropy of abdominal and thoracic regions

Superficial fascia is a fibrofatty tissue found throughout the body. Initially described in relation to hernias, it has only recently received attention from the scientific community due to new evidence on its role in force transmission and structural integrity of the body. Considering initial difficulties in its anatomical identification, to date, a characterization of the superficial fascia through mechanical tests is still lacking. The mechanical properties of human superficial fasciae of abdominal and thoracic districts (back) of different subjects (n = 4) were then investigated, focusing on anisotropy and viscoelasticity. Experimental tests were performed on samples taken in two perpendicular directions according to body planes (cranio-caudal and latero-medial axes). Data collected from two different uniaxial tensile protocols, failure (i.e., ultimate tensile strength and strain at break, Young's modulus and toughness) and stress-relaxation (i.e., residual stress), were processed and then grouped for statistical analysis. Failure tests confirmed tissue anisotropy, revealing the stiffer nature of the latero-medial direction compared to the cranio-caudal one, for both the districts (with a ratio of the respective Young's moduli close to 2). Furthermore, the thoracic region exhibited significantly greater strength and resultant Young's modulus compared to the abdomen (with greater results along the latero-medial direction, such as 6.13 ± 3.11 MPa versus 0.85 ± 0.39 MPa and 24.87 ± 15.23 MPa versus 3.19 ± 1.62 MPa, respectively). On the contrary, both regions displayed similar strain at break (varying between 38 and 47%), with no clear dependence from the loading directions. Stress-relaxation tests highlighted the viscous behavior of the superficial fascia, with no significant differences in the stress decay between directions and districts (35-38% of residual stress after 300 s). All these collected results represent the starting point for a more in-depth knowledge of the mechanical characterization of the superficial fascia, which can have direct implications in the design, implementation, and effectiveness of site-specific treatments.

Synthesis and Solvent Free DLP 3D Printing of Degradable Poly(Allyl Glycidyl Ether Succinate)

Digital light processing (DLP) printing forms solid constructs from fluidic resins by photochemically crosslinking polymeric resins with reactive functional groups. DLP is used widely due to its efficient, high-resolution printing, but its use and translational potential has been limited in some applications as state-of-the-art resins experience unpredictable and anisotropic part shrinkage due to the use of solvent needed to reduce resin viscosity and layer dependent crosslinking. Herein, poly(allyl glycidyl ether succinate) (PAGES), a low viscosity, degradable polyester, was synthesized by ring opening copolymerization and used in combination with degradable thiol crosslinkers to afford a solvent free resin that can be utilized in DLP printing. Varying resin formulations of PAGES polymer are shown to decrease part shrinkage from 14 % to 0.3 %. Photochemically printed parts fabricated from PAGES possess tensile moduli between 0.43 and 6.18 MPa and degradation profiles are shown to vary between 12 and 40 days under accelerated conditions based on degree of polymerization and crosslink ratio.

Mussel Foot Protein-Inspired Adhesive Tapes with Tunable Underwater Adhesion

Instant and strong adhesion to underwater adherends is a big challenge due to the continuous interference of water. Mussel foot protein-bioinspired catechol-based adhesives have garnered great interest in addressing this issue. Herein, a novel self-made catecholic compound with a long aliphatic chain was utilized to prepare thin (∼0.07 mm) and optically transparent (>80%) wet/underwater adhesive tapes by UV-initiated polymerization. Its adhesion activity was water-triggered, fast (<1 min), and strong (adhesion strength to porcine skin: ∼1.99 MPa; interfacial toughness: ∼610 J/m2, burst pressure: ∼1950 mmHg). The effect of the catechol/phenol group and positively charged moiety on the wet/underwater adhesion to abiotic/biotic substrates was investigated. On the wet/underwater adherends, the tape with catechol groups presented much higher interfacial toughness, adhesion strength, and burst pressure than the analogous tape with phenol groups. The tape with both the catechol group and cationic polyelectrolyte chitosan had a more impressive improvement in its adhesion to wet/underwater biological tissues than to abiotic substrates. Therefore, catechol and a positive moiety in the tape would synergistically enhance its wet/underwater adhesion to various substrates, especially to biological tissues. The instant, strong, and noncytotoxic tape may provide applications in underwater adhesion for sealing and wound closure.

The Synergic Effect of Tubal Endometriosis and Women's Aging on Fallopian Tube Function: Insights from a 3D Mechanical Model

The fallopian tubes are essential for human fertility, facilitating the movement of sperm and oocytes to the fertilization site and transporting fertilized oocytes to the uterus. Infertility can result from changes in the fallopian tubes due to tubal endometriosis and women's aging. In this study, we modeled human fallopian tubes with and without endometriosis for different women's age groups to evaluate the chances of normal sperm cells reaching the fertilization site and oocytes arriving at the uterine cavity. For this purpose, we employed a distinctive combination of simulation tools to develop a dynamic three-dimensional (3D) model of normal human sperm cells and oocytes swimming inside normal and endometriosis-affected human fallopian tubes for different women's group ages. We observed that in tubal endometriosis cases, fewer sperm cells reach the fertilization site and more oocytes become trapped in the tube walls compared to normal tubes. Additionally, aging decreases the number of sperm cells and oocytes reaching the fertilization site in normal and endometriosis-affected tubes. Our model evaluates the mechanisms of sperm and oocyte behaviors due to women's aging and fallopian tube issues caused by endometriosis, presenting new avenues for developing diagnostic and treatment tools for tubal endometriosis and age-related infertility issues.

Biodegradable Tyramine Functional Gelatin/6 Arms-PLA Inks Compatible with 3D Two Photon-Polymerization Printing and Meniscus Tissue Regeneration

The meniscus regeneration can present major challenges such as mimicking tissue microstructuration or triggering cell regeneration. In the case of lesions that require a personalized approach, photoprinting offers the possibility of designing resolutive biomaterial structures. The photo-cross-linkable ink composition determines the process ease and the final network properties. In this study, we designed a range of hybrid inks composed of gelatin(G) and 6-PLA arms(P) that were photo-cross-linked using tyramine groups. The photo-cross-linking efficiency, mechanical properties, degradation, and biological interactions of inks with different G/P mass ratios were studied. The G50P50 network properties were suitable for meniscus regeneration, with Young's modulus of 6.5 MPa, degradation in 2 months, and good cell proliferation. We then confirmed the potential of these inks to produce high-resolution microstructures by printing well-defined microstructures using two-photon polymerization. These hybrid inks offer new perspectives for biocompatible, degradable, and microstructured tissue engineering scaffold creation.

Enhanced boxing punch impact with silicone cushioning

Introduction

Elastic cushioning materials protect human tissue from injury by absorbing impact energy and delaying its transfer. However, the potential compromise in force delivery to the hitting target remains unknown.

Methods

To examine if silicone cushioning compromises punch force delivery to a hitting target, a double-blind crossover trial with 12 elite boxers was conducted following material tests. Each boxer delivered five maximal punches under two conditions: silicone-hand wrapping and gauze-hand wrapping, in counterbalanced order, with a 3-day interval between sessions. Force distribution along the Z-axis indicated the punch's intended direction, while forces along the X and Y axes represented force dissipation toward unwanted direction.

Results

The material tests (based on ASTM International, West Conshohocken, PA, USA) demonstrated substantially higher compression to disruption for silicone than gauze of similar thickness. During the punching trials, the silicon-based hand wrapping exhibited slightly higher total force production (436 ± 33 N vs. 372 ± 12 N, p < 0.001) than the gauze-based hand wrapping. Moreover, force wastage, calculated as the sum of forces along the X and Y axes vs. the total force produced in percentage, was notably lower for silicone material (2.0% wastage) compared to gauze (3.8% wastage) (p < 0.001). The use of silicone materials lengthened the contact time between the punching fist and the hitting target from 35 ms to 50 ms (p < 0.001).

Conclusion

The elastic cushion does not compromise the force delivery of the boxing glove to the hitting target. Instead, it appears to allow for additional maneuvering time for alignment during the fist-target contact with higher impact.

Simulation-based Flexible Needle Control with Single-core FBG Feedback for Spinal Injections

Objective

We present a general framework of simultaneous needle shape reconstruction and control input generation for robot-assisted spinal injection procedures, without continuous imaging feedback.

Methods

System input-output mapping is generated with a real-time needle-tissue interaction simulation, and single-core FBG sensor readings are used as local needle shape feedback within the same simulation framework. FBG wavelength shifts due to temperature variation is removed by exploiting redundancy in fiber arrangement.

Results

Targeting experiments performed on both plastisol lumbar phantoms as well as an ex vivo porcine lumbar section achieved in-plane tip errors of 0.6 ± 0.3 mm and 1.6 ± 0.9 mm , and total tip errors of 0.9 ± 0.7 mm and 2.1 ± 0.8 mm for the two testing environments.

Significance

Our clinically inspired control strategy and workflow is self-contained and not dependent on the modality of imaging guidance. The generalizability of the proposed approach can be applied to other needle-based interventions where medical imaging cannot be reliably utilized as part of a closed-loop control system for needle guidance.

Immediate but Temporal Response: The Role of Distal Epithelial Cells in Wound Healing

Efficient oral mucosal wound healing requires coordinated responses from epithelial progenitor cells, yet their spatiotemporal recruitment and activation remain unclear. Using a mouse model of palatal mucosal wound healing, we investigated the dynamics of epithelial cells during this process. Proliferation analysis revealed that, in addition to the expected proliferation center near the wound edge, distal cell populations rapidly activated post-injury by elevating their mitotic activity. These distal cells displayed predominant lateral expansion in the basal layer, suggesting roles beyond just tissue renewal. However, while proximal proliferation center cells sustained heightened proliferation until re-epithelialization was completed, distal cells restored basal turnover rates before wound closure, indicating temporally confined contributions. Lineage tracing of Wnt-responsive epithelial cells showed remarkable clone expansion in basal layers both proximally and distally after wounding, contrasting with gradual clone expansion in homeostasis. Although prioritizing tissue repair, epithelial progenitor cells maintained differentiation programs and barrier functions, with the exception of the leading edge. At the leading edge, we found accelerated cell turnover, but the differentiation program was suspended. In summary, our findings uncovered that oral wound re-epithelialization involves two phases: an initial widespread response with proliferation of proximal and distal cells, followed by proliferation confined to the wound proximal region. Uncovering these stage-specific healing mechanisms provides insights for developing targeted therapeutic strategies to improve wound care.

Conductive Peptide-Based MXene Hydrogel as a Piezoresistive Sensor

Wearable pressure sensors have become increasingly popular for personal healthcare and motion detection applications due to recent advances in materials science and functional nanomaterials. In this study, a novel composite hydrogel is presented as a sensitive piezoresistive sensor that can be utilized for various biomedical applications, such as wearable skin patches and integrated artificial skin that can measure pulse and blood pressure, as well as monitor sound as a self-powered microphone. The hydrogel is composed of self-assembled short peptides containing aromatic, positively- or negatively charged amino acids combined with 2D Ti3C2Tz MXene nanosheets. This material is low-cost, facile, reliable, and scalable for large areas while maintaining high sensitivity, a wide detection range, durability, oxidation stability, and biocompatibility. The bioinspired nanostructure, strong mechanical stability, and ease of functionalization make the assembled peptide-based composite MXene-hydrogel a promising and widely applicable material for use in bio-related wearable electronics.

A Data-Driven Design Framework for Structural Optimization to Enhance Wearing Adaptability of Prosthetic Hands

Prosthetic hands have significant potential to restore the manipulative capabilities and self-confidence of amputees and enhance their quality of life. However, incompatibility between prosthetic devices and residual limbs can lead to secondary injuries such as skin pressure ulcers and restricted joint motion, contributing to a high prosthesis abandonment rate. To address these challenges, this study introduces a data-driven design framework (D3Frame) utilizing a multi-index optimization method. By incorporating motion/ pressure data, as well as clinical criteria such as pain threshold/ tolerance, from various anatomical sites on the residual limbs of amputees, this framework aims to optimize the structural design of the prosthetic socket, including the Antecubital Channel (AC), Lateral Epicondylar Region Contour (LC), Medial Epicondylar Region Contour (MC), Olecranon Region Contour (OC), Lateral Flexor/ Extensor Region (LR), and Medial Flexor/ Extensor Region (MR). Experiments on five forearm amputees verified the improved adaptability of the optimized socket compared to traditional sockets under three load conditions. The experimental results revealed a modest score enhancement on standard clinical scales and reduced muscle fatigue levels. Specifically, the percent effort of muscles and slope value of mean/ median frequency decreased by 19%, 70%, and 99% on average, respectively, and the average values of mean/ median frequency in the motion cycle both increased by approximately 5%. The proposed D3Frame in this study was applied to optimize the structural aspects of designated regions of the prosthetic socket, offering the potential to aid prosthetists in prosthesis design and, consequently, augmenting the adaptability of prosthetic devices.

3D printable and biocompatible PEDOT:PSS-ionic liquid colloids with high conductivity for rapid on-demand fabrication of 3D bioelectronics

3D printing has been widely used for on-demand prototyping of complex three-dimensional structures. In biomedical applications, PEDOT:PSS has emerged as a promising material in versatile bioelectronics due to its tissue-like mechanical properties and suitable electrical properties. However, previously developed PEDOT:PSS inks have not been able to fully utilize the advantages of commercial 3D printing due to its long post treatment times, difficulty in high aspect ratio printing, and low conductivity. We propose a one-shot strategy for the fabrication of PEDOT:PSS ink that is able to simultaneously achieve on-demand biocompatibility (no post treatment), structural integrity during 3D printing for tall three-dimensional structures, and high conductivity for rapid-prototyping. By using ionic liquid-facilitated PEDOT:PSS colloidal stacking induced by a centrifugal protocol, a viscoplastic PEDOT:PSS-ionic liquid colloidal (PILC) ink was developed. PILC inks exhibit high-aspect ratio vertical stacking, omnidirectional printability for generating suspended architectures, high conductivity (~286 S/cm), and high-resolution printing (~50 µm). We demonstrate the on-demand and versatile applicability of PILC inks through the fabrication of 3D circuit boards, on-skin physiological signal monitoring e-tattoos, and implantable bioelectronics (opto-electrocorticography recording, low voltage sciatic nerve stimulation and recording from deeper brain layers via 3D vertical spike arrays).

Development of novel iron(III) crosslinked bioinks comprising carboxymethyl cellulose, xanthan gum, and hyaluronic acid for soft tissue engineering applications

The advent of three-dimensional (3D) bioprinting offers a feasible approach to construct complex structures for soft tissue regeneration. Carboxymethyl cellulose (CMC) has been emerging as a very promising biomaterial for 3D bioprinting. However, due to the inability to maintain the post-printed stability, CMC needs to be physically blended and/or chemically crosslinked with other polymers. In this context, this study presents the combination of CMC with xanthan gum (XG) and hyaluronic acid (HA) to formulate a multicomponent bioink, leveraging the printability of CMC and XG, as well as the cellular support properties of HA. The ionic crosslinking of printed constructs with iron(III) via the metal-ion coordination between ferric cations and carboxylate groups of the three polymers was introduced to induce improved mechanical strength and long-term stability. Moreover, immortalized human epidermal keratinocytes (HaCaT) and human foreskin fibroblasts (HFF) encapsulated within iron-crosslinked printed hydrogels exhibited excellent cell viability (more than 95%) and preserved morphology. Overall, the presented study highlights that the combination of these three biopolymers and the ionic crosslinking with ferric ions is a valuable strategy to be considered for the development of new and advanced hydrogel-based bioinks for soft tissue engineering applications.

Digital light processing printed hydrogel scaffolds with adjustable modulus

Hydrogels are extensively explored as biomaterials for tissue scaffolds, and their controlled fabrication has been the subject of wide investigation. However, the tedious mechanical property adjusting process through formula control hindered their application for diverse tissue scaffolds. To overcome this limitation, we proposed a two-step process to realize simple adjustment of mechanical modulus over a broad range, by combining digital light processing (DLP) and post-processing steps. UV-curable hydrogels (polyacrylamide-alginate) are 3D printed via DLP, with the ability to create complex 3D patterns. Subsequent post-processing with Fe3+ ions bath induces secondary crosslinking of hydrogel scaffolds, tuning the modulus as required through soaking in solutions with different Fe3+ concentrations. This innovative two-step process offers high-precision (10 μm) and broad modulus adjusting capability (15.8-345 kPa), covering a broad range of tissues in the human body. As a practical demonstration, hydrogel scaffolds with tissue-mimicking patterns were printed for cultivating cardiac tissue and vascular scaffolds, which can effectively support tissue growth and induce tissue morphologies.

Approach for contact medical device development via integrated testing, skeletal muscle modeling, and finite element analysis

Development of novel medical devices for the treatment of musculoskeletal pain associated with neuro-muscular trigger points requires a model for relating the mechanical responses of in vivo biological tissues to applied palliative physical pressures and a method to design treatments for optimal effects. It is reasonable to hypothesize that the efficacy of therapeutic treatment is proportional to the maximum tensile strain at trigger point locations. This work presents modeling of the mechanical behavior of biological tissue structures and treatment simulations, supported by indentation experiments and finite element (FE) modeling. The steady-state indentation responses of the tissue structure of the posterior neck were measured with a testing device, and an FE model was constructed using a first-order Ogden hyperelastic material model and calibrated with the experimental data. The error between experimental and FE-generated displacement-load curves was minimized via a two-stage optimization process comprised of an Optimal Latin Hypercube design-of-experiments analysis and a Bayesian optimization loop. The optimized Ogden model had an initial shear modulus (μ) of 5.16 kPa and a deviatoric exponent (α) of 11.90. Another FE model was developed to simulate the deformation of the tissue structures in the posterior neck adjacent to the C3 vertebrae in response to indentation loading, in order to determine the optimal location and angle to apply an indentation force for maximum therapeutic benefit. The optimal location of indentation was determined to be 28° lateral from the sagittal plane along the surface of the skin, measured from the centerline of the spine, at an angle of 8° counterclockwise from the surface normal vector. The optimized spatial orientation of the indentation corresponded to the average of the maximum principal strain across the deep muscle region of the model.

Mechanical properties of hydrated electrospun polycaprolactone (PCL) nanofibers

Polycaprolactone (PCL) nanofibers are a promising material for biomedical applications due to their biocompatibility, slow degradation rate, and thermal stability. We electrospun PCL fibers onto a striated substrate with 12 μm wide ridges and grooves and determined their mechanical properties in an aqueous solution with a combined atomic force/inverted optical microscopy technique. Fiber diameters, D, ranged from 27 to 280 nm. The hydrated PCL fibers had an extensibility (breaking strain), εmax, of 137%. The Young's modulus, E, and tensile strength, σT, showed a strong dependence on fiber diameter, D; decreasing steeply with increasing diameter, following empirical equations E(D)=(4.3∙103∙e-D51nm+1.1∙102) MPa and σT(D)=(2.6∙103∙e-D55nm+0.6∙102) MPa. Incremental stress-strain measurements were employed to investigate the viscoelastic behavior of these fibers. The fibers exhibited stress relaxation with a fast and slow relaxation time of 3.7 ± 1.2 s and 23 ± 8 s and these experiments also allowed the determination of the elastic and viscous moduli. Cyclic stress-strain curves were used to determine that the elastic limit of the fibers, εelastic, is between 19% and 36%. These curves were also used to determine that these fibers showed small energy losses (<20%) at small strains (ε < 10%), and over 50% energy loss at large strains (ε > 50%), asymptotically approaching 61%, as Eloss=61%·(1-e-0.04*ε). Our work is the first mechanical characterization of hydrated electrospun PCL nanofibers; all previous experiments were performed on dry PCL fibers, to which we will compare our data.

Additive Manufacturing of Head Surrogates for Evaluation of Protection in Sports

Head impacts are a major concern in contact sports and sports with high-speed mobility due to the prevalence of head trauma events and their dire consequences. Surrogates of human heads are required in laboratory testing to safely explore the efficacy of impact-mitigating mechanisms. This work proposes using polymer additive manufacturing technologies to obtain a substitute for the human skull to be filled with a silicone-based brain surrogate. This assembly was instrumentalized with an Inertial Measurement Unit. Its performance was compared to a standard Hybrid III head form in validation tests using commercial headgear. The tests involved impact velocities in a range centered around 5 m/s. The results show a reasonable homology between the head substitutes, with a disparity in the impact response within 20% between the proposed surrogate and the standard head form. The head surrogate herein developed can be easily adapted to other morphologies and will significantly decrease the cost of the laboratory testing of head protection equipment, all while ensuring the safety of the testing process.

Development of bilayer tissue-engineered scaffolds: combination of 3D printing and electrospinning methodologies

Although different fabrication methods and biomaterials are used in scaffold development, hydrogels and electrospun materials that provide the closest environment to the extracellular matrix have recently attracted considerable interest in tissue engineering applications. However, some of the limitations encountered in the application of these methods alone in scaffold fabrication have increased the tendency to use these methods together. In this study, a bilayer scaffold was developed using 3D-printed gelatin methacryloyl (GelMA) hydrogel containing ciprofloxacin (CIP) and electrospun polycaprolactone (PCL)-collagen (COL) patches. The bilayer scaffolds were characterized in terms of chemical, morphological, mechanical, swelling, and degradation properties; drug release, antibacterial properties, and cytocompatibility of the scaffolds were also studied. In conclusion, bilayer GelMA-CIP/PCL-COL scaffolds, which exhibit sufficient porosity, mechanical strength, and antibacterial properties and also support cell growth, are promising potential substitutes in tissue engineering applications.

Self-Assembly Enabled Printable Asymmetric Self-Insulated Stretchable Conductor for Human Interface

Soft and stretchable conductors with high electrical conductivity and tissue-like mechanical properties are crucial for both on-skin and implantable electronic devices. Liquid metal-based conductors hold great promise due to their metallic conductivity and minimal stiffness. However, the surface oxidation of liquid metal particles in polymeric matrices poses a challenge in forming a continuous pathway for highly conductive elastic composites. Here, it is reported a printable composite material based on liquid metal and conducting polymer that undergoes a self-assembly process, achieving high conductivity (2089 S cm-1) in the bottom surface while maintaining an insulated top surface, high stretchability (>800%), and a modulus akin to human skin tissue. This material is further applied to fabricate skin-interfaced strain sensors and electromyogram sensors through 3D printing.

Bevel-Tip Needle Deflection Modeling, Simulation, and Validation in Multi-Layer Tissues

Percutaneous needle insertions are commonly performed for diagnostic and therapeutic purposes as an effective alternative to more invasive surgical procedures. However, the outcome of needle-based approaches relies heavily on the accuracy of needle placement, which remains a challenge even with robot assistance and medical imaging guidance due to needle deflection caused by contact with soft tissues. In this paper, we present a novel mechanics-based 2D bevel-tip needle model that can account for the effect of nonlinear strain-dependent behavior of biological soft tissues under compression. Real-time finite element simulation allows multiple control inputs along the length of the needle with full three-degree-of-freedom (DOF) planar needle motions. Cross-validation studies using custom-designed multi-layer tissue phantoms as well as heterogeneous chicken breast tissues result in less than 1mm in-plane errors for insertions reaching depths of up to 61 mm, demonstrating the validity and generalizability of the proposed method.

A Review of Recent Advancements in Sensor-Integrated Medical Tools

A medical tool is a general instrument intended for use in the prevention, diagnosis, and treatment of diseases in humans or other animals. Nowadays, sensors are widely employed in medical tools to analyze or quantify disease-related parameters for the diagnosis and monitoring of patients' diseases. Recent explosive advancements in sensor technologies have extended the integration and application of sensors in medical tools by providing more versatile in vivo sensing capabilities. These unique sensing capabilities, especially for medical tools for surgery or medical treatment, are getting more attention owing to the rapid growth of minimally invasive surgery. In this review, recent advancements in sensor-integrated medical tools are presented, and their necessity, use, and examples are comprehensively introduced. Specifically, medical tools often utilized for medical surgery or treatment, for example, medical needles, catheters, robotic surgery, sutures, endoscopes, and tubes, are covered, and in-depth discussions about the working mechanism used for each sensor-integrated medical tool are provided.

Cavitation-induced pressure saturation: a mechanism governing bubble nucleation density in histotripsy

Objective.Histotripsy is a noninvasive focused ultrasound therapy that mechanically disintegrates tissue by acoustic cavitation clouds. In this study, we investigate a mechanism limiting the density of bubbles that can nucleate during a histotripsy pulse. In this mechanism, the pressure generated by the initial bubble expansion effectively negates the incident pressure in the vicinity of the bubble. From this effect, the immediately adjacent tissue is prevented from experiencing the transient tension to nucleate bubbles. Approach.A Keller-Miksis-type single-bubble model was employed to evaluate the dependency of this effect on ultrasound pressure amplitude and frequency, viscoelastic medium properties, bubble nucleus size, and transducer geometric focusing. This model was further combined with a spatial propagation model to predict the peak negative pressure field as a function of position from a cavitating bubble.Main results. The single-bubble model showed the peak negative pressure near the bubble surface is limited to the inertial cavitation threshold. The predicted bubble density increased with increasing frequency, tissue viscosity, and transducer focusing angle. The simulated results were consistent with the trends observed experimentally in prior studies, including changes in density with ultrasound frequency and transducerF-number.Significance.The efficacy of the therapy is dependent on several factors, including the density of bubbles nucleated within the cavitation cloud formed at the focus. These results provide insight into controlling the density of nucleated bubbles during histotripsy and the therapeutic efficacy.

Evaluation of women's aging influence on sperm passage inside the fallopian tube using 3D dynamic mechanical modeling

The fallopian tubes play an important role in human fertility by facilitating the spermatozoa passage to the oocyte as well as later actively facilitating the fertilized oocyte transportation to the uterus cavity. The fallopian tubes undergo changes involving biological, physical, and morphological processes due to women aging, which may impair fertility. Here, we have modelled fallopian tubes of women at different ages and evaluated the chances of normal and pathological sperm cells reaching the fertilization site, the ampulla. By utilizing a unique combination of simulative tools, we implemented dynamic three-dimensional (3D) detailed geometrical models of many normal and pathological sperm cells swimming together in 3D geometrical models of three fallopian tubes associated with different women's age groups. By tracking the sperm cell swim, we found that for all age groups, the number of normal sperm cells in the ampulla is the largest, compared with the pathological sperm cells. On the other hand, the number of normal sperm cells in the fertilization site decreases due to the morphological and mechanical changes that occur in the fallopian tube with age. Moreover, in older ages, the normal sperm cells swim with lower velocities and for shorter distances inside the ampulla toward the ovary. Thus, the changes that the human fallopian tube undergoes due to women's aging have a significant influence on the human sperm cell motility. Our model of sperm cell motility through the fallopian tube in relation to the woman's age morphological changes provides a new scope for the investigation and treatment of diseases and infertility cases associated with aging, as well as a potential personalized medicine tool for evaluating the chances of a natural fertilization per specific features of a man's sperm and a woman's reproductive system.

Fibroblasts and polymer composition are essential for bioengineering of airway epithelium on nonwoven scaffolds

To make tissue engineering a truly effective tool, it is necessary to understand how the patterns of specific tissue development are modulated by and depend on the artificial environment. Even the most advanced approaches still do not fully meet the requirements of practical engineering of tracheobronchial epithelium. This study aimed to test the ability of the synthetic and natural nonwoven scaffolds to support the formation of morphological sound airway epithelium including the basement membrane (BM). We also sought to identify the potential role of fibroblasts in this process. Our results showed that nonwoven scaffolds are generally suitable for producing well-differentiated tracheobronchial epithelium (with cilia and goblet cells), while the structure and functionality of the equivalents appeared to be highly dependent on the composition of the scaffolds. Unlike natural scaffolds, synthetic ones supported the formation of the epithelium only when epithelial cells were cocultured with fibroblasts. Fibroblasts also appeared to be obligatory for basal lamina formation, regardless of the type of the nonwoven material used. However, even in the presence of fibroblasts, the synthetic scaffolds were unable to support the formation of the epithelium and of the BM (in particular, basal lamina) as effectively as the natural scaffolds did.

An Integrated Experimental-Computational Study of Vocal Fold Vibration in Type I Thyroplasty

Subject-specific computational modeling of vocal fold (VF) vibration was integrated with an ex vivo animal experiment of type 1 thyroplasty to study the effect of the implant on the vocal fold vibration. In the experiment, a rabbit larynx was used to simulate type 1 thyroplasty, where one side of the vocal fold was medialized with a trans-muscular suture while the other side was medialized with a silastic implant. Vocal fold vibration was then achieved by flowing air through the larynx and was filmed with a high-speed camera. The three-dimensional computational model was built upon the pre-operative scan of the laryngeal anatomy. This subject-specific model was used to simulate the vocal fold medialization and then the fluid-structure interaction (FSI) of the vocal fold. Model validation was done by comparing the vocal fold displacement with postoperative scan (for medialization), and by comparing the vibratory characteristics with the high-speed images (for vibration). These comparisons showed the computational model successfully captured the effect of the implant and thus has the potential for presurgical planning.

Functionalized Gelatin/Polysaccharide Hydrogels for Encapsulation of Hepatocytes

Liver diseases represent a considerable burden to patients and healthcare systems. Hydrogels play an important role in the engineering of soft tissues and may be useful for embedding hepatocytes for different therapeutic interventions or the development of in vitro models to study the pathogenesis of liver diseases or testing of drugs. Here, we developed two types of hydrogels by crosslinking hydrazide-functionalized gelatin with either oxidized dialdehyde hyaluronan or alginate through the formation of hydrazone bonds. Gel formulations were studied through texture analysis and rheometry, showing mechanical properties comparable to those of liver tissue while also demonstrating long-term stability. The biocompatibility of hydrogels and their ability to host hepatocytes was studied in vitro in comparison to pure gelatin hydrogels crosslinked by transglutaminase using the hepatocellular line HepG2. It was found that HepG2 cells could be successfully embedded in the hydrogels, showing no signs of gel toxicity and proliferating in a 3D environment comparable to pure transglutaminase cross-linked gelatin hydrogels used as control. Altogether, hydrazide gelatin in combination with oxidized polysaccharides makes stable in situ gelling systems for the incorporation of hepatocytes, which may pave the way for use in liver tissue engineering and drug testing.

Shape or size matters? Towards standard reporting of tensile testing parameters for human soft tissues: systematic review and finite element analysis

Material properties of soft-tissue samples are often derived through uniaxial tensile testing. For engineering materials, testing parameters (e.g., sample geometries and clamping conditions) are described by international standards; for biological tissues, such standards do not exist. To investigate what testing parameters have been reported for tensile testing of human soft-tissue samples, a systematic review of the literature was performed using PRISMA guidelines. Soft tissues are described as anisotropic and/or hyperelastic. Thus, we explored how the retrieved parameters compared against standards for engineering materials of similar characteristics. All research articles published in English, with an Abstract, and before 1 January 2023 were retrieved from databases of PubMed, Web of Science, and BASE. After screening of articles based on search terms and exclusion criteria, a total 1,096 articles were assessed for eligibility, from which 361 studies were retrieved and included in this review. We found that a non-tapered shape is most common (209 of 361), followed by a tapered sample shape (92 of 361). However, clamping conditions varied and were underreported (156 of 361). As a preliminary attempt to explore how the retrieved parameters might influence the stress distribution under tensile loading, a pilot study was performed using finite element analysis (FEA) and constitutive modeling for a clamped sample of little or no fiber dispersion. The preliminary FE simulation results might suggest the hypothesis that different sample geometries could have a profound influence on the stress-distribution under tensile loading. However, no conclusions can be drawn from these simulations, and future studies should involve exploring different sample geometries under different computational models and sample parameters (such as fiber dispersion and clamping effects). Taken together, reporting and choice of testing parameters remain as challenges, and as such, recommendations towards standard reporting of uniaxial tensile testing parameters for human soft tissues are proposed.

Comparison of the Biomechanical Properties between Healthy and Whole Human and Porcine Stomachs

Gastric cancer poses a societal and economic burden, prompting an exploration into the development of materials suitable for gastric reconstruction. However, there is a dearth of studies on the mechanical properties of porcine and human stomachs. Therefore, this study was conducted to elucidate their mechanical properties, focusing on interspecies correlations. Stress relaxation and tensile tests assessed the hyperelastic and viscoelastic characteristics of porcine and human stomachs. The thickness, stress-strain curve, elastic modulus, and stress relaxation were assessed. Porcine stomachs were significantly thicker than human stomachs. The stiffness contrast between porcine and human stomachs was evident. Porcine stomachs demonstrated varying elastic modulus values, with the highest in the longitudinal mucosa layer of the corpus and the lowest in the longitudinal intact layer of the fundus. In human stomachs, the elastic modulus of the longitudinal muscular layer of the antrum was the highest, whereas that of the circumferential muscularis layer of the corpus was the lowest. The degree of stress relaxation was higher in human stomachs than in porcine stomachs. This study comprehensively elucidated the differences between porcine and human stomachs attributable to variations across different regions and tissue layers, providing essential biomechanical support for subsequent studies in this field.

Electrospun Polycaprolactone Membranes Expanded with Chitosan Granules for Cell Infiltration

The small pore size of electrospun membranes prevents their use as three-dimensional scaffolds. In this work, we produced polycaprolactone (PCL) electrospun fibrous membranes with expanded pores by incorporating chitosan (CS) granules into the PCL solution. Scanning electron microscopy images confirmed the presence of the CS granules embedded in the PCL fibers, creating an open structure. Tensile testing results showed that the addition of CS decreased both Young's modulus and the yield stress, but co-electrospun membranes (PCL fibers blended with CS-containing PCL fibers) exhibited higher values compared to single electrospun membranes (CS-containing PCL fibers). Human fibroblasts adhered to and proliferated on all scaffolds. Nuclear staining revealed that cells populated the entire scaffold when CS granules were present, while in PCL membranes, cells were mostly limited to the surface due to the small pore size. Overall, our findings demonstrate that electrospun membranes containing CS granules have sufficiently large pores to facilitate fibroblast infiltration without compromising the mechanical stability of the structure.

Enhanced solute transport and steady mechanical stimulation in a novel dynamic perifusion bioreactor increase the efficiency of the in vitro culture of ovarian cortical tissue strips

Introduction: We report the development and preliminary evaluation of a novel dynamic bioreactor to culture ovarian cortical tissue strips that leverages tissue response to enhanced oxygen transport and adequate mechanical stimulation. In vitro multistep ovarian tissue static culture followed by mature oocyte generation, fertilization, and embryo transfer promises to use the reserve of dormant follicles. Unfortunately, static in vitro culture of ovarian tissue does not promote development of primordial to secondary follicles or sustain follicle viability and thereby limits the number of obtainable mature oocytes. Enhancing oxygen transport to and exerting mechanical stimulation on ovarian tissue in a dynamic bioreactor may more closely mimic the physiological microenvironment and thus promote follicle activation, development, and viability. Materials and Methods: The most transport-effective dynamic bioreactor design was modified using 3D models of medium and oxygen transport to maximize strip perifusion and apply tissue fluid dynamic shear stresses and direct compressive strains to elicit tissue response. Prototypes of the final bioreactor design were manufactured with materials of varying cytocompatibility and assessed by testing the effect of leachables on sperm motility. Effectiveness of the bioreactor culture was characterized against static controls by culturing fresh bovine ovarian tissue strips for 7 days at 4.8 × 10-5 m/s medium filtration flux in air at -15% maximal total compressive strain and by assessing follicle development, health, and viability. Results and Conclusions: Culture in dynamic bioreactors promoted effective oxygen transport to tissues and stimulated tissues with strains and fluid dynamic shear stresses that, although non-uniform, significantly influenced tissue metabolism. Tissue strip culture in bioreactors made of cytocompatible polypropylene preserved follicle viability and promoted follicle development better than static culture, less so in bioreactors made of cytotoxic ABS-like resin.

Tough and Water-Resistant Bioelastomers with Active-Controllable Degradation Rates

Biodegradable electronic devices have gained significant traction in modern medical applications. These devices are generally desired to have a long enough working lifetime for stable operation and allow for active control over their degradation rates after usage. However, current biodegradable materials used as encapsulations or substrates for these devices are challenging to meet the two requirements due to the constraints of inadequate water resistance, poor mechanical properties, and passive degradation characteristics. Herein, we develop a novel biodegradable elastomer named POC-SS-Res by introducing disulfide linkage and resveratrol (Res) into poly(1,8-octanediol-co-citrate) (POC). Compared to POC, POC-SS-Res exhibits good water resistance and excellent mechanical properties in PBS, providing effective protection for devices. At the same time, POC-SS-Res offers the unique advantage of an active-controllable degradation rate, and its degradation products express low biotoxicity. Good biocompatibility of POC-SS-Res is also demonstrated. Bioelectronic components encapsulated with POC-SS-Res have an obvious prolongation of working lifetime in PBS compared to that encapsulated with POC, and its degradation rate can be actively controlled by the addition of glutathione (GSH).

Ultra-high-speed dynamics of acoustic droplet vaporization in soft biomaterials: Effects of viscoelasticity, frequency, and bulk boiling point

Phase-shift droplets are a highly adaptable platform for biomedical applications of ultrasound. The spatiotemporal response of phase-shift droplets to focused ultrasound above a certain pressure threshold, termed acoustic droplet vaporization (ADV), is influenced by intrinsic features (e.g., bulk boiling point) and extrinsic factors (e.g., driving frequency and surrounding media). A deep understanding of ADV dynamics is critical to ensure the robustness and repeatability of an ADV-assisted application. Here, we integrated ultra-high-speed imaging, at 10 million frames per second, and confocal microscopy for a full-scale (i.e., from nanoseconds to seconds) characterization of ADV. Experiments were conducted in fibrin-based hydrogels to mimic soft tissue environments. Effects of fibrin concentration (0.2 to 8 % (w/v)), excitation frequency (1, 2.5, and 9.4 MHz), and perfluorocarbon core (perfluoropentane, perfluorohexane, and perfluorooctane) on ADV dynamics were studied. Several fundamental parameters related to ADV dynamics, such as expansion ratio, expansion velocity, collapse radius, collapse time, radius of secondary rebound, resting radius, and equilibrium radius of the generated bubbles were extracted from the radius vs time curves. Diffusion-driven ADV-bubble growth was fit to a modified Epstein-Plesset equation, adding a material stress term, to estimate the growth rate. Our results indicated that ADV dynamics were significantly impacted by fibrin concentration, frequency, and perfluorocarbon liquid core. This is the first study to combine ultra-high-speed and confocal microscopy techniques to provide insights into ADV bubble dynamics in tissue-mimicking hydrogels.