Tissue Rupture Research Articles

Rupture strength of living cell monolayers.

To fulfil their function, epithelial tissues need to sustain mechanical stresses and avoid rupture. Although rupture is usually undesired, it is central to some developmental processes, for example, blastocoel formation. Nonetheless, little is known about tissue rupture because it is a multiscale phenomenon that necessitates comprehension of the interplay between mechanical forces and biological processes at the molecular and cellular scales. Here we characterize rupture in epithelial monolayers using mechanical measurements, live imaging and computational modelling. We show that despite consisting of only a single layer of cells, monolayers can withstand surprisingly large deformations, often accommodating several-fold increases in their length before rupture. At large deformation, epithelia increase their stiffness multiple fold in a process controlled by a supracellular network of keratin filaments. Perturbing the keratin network organization fragilized the monolayers and prevented strain-stiffening. Although the kinetics of adhesive bond rupture ultimately control tissue strength, tissue rheology and the history of deformation set the strain and stress at the onset of fracture.

Preventive impact of probiotic supplements on heart injury and inflammatory indices in a rat model of myocardial infarction: histopathological and gene expression evaluation.

Although there is a bulk of evidence on the favorable effect of probiotics on the cardiac system, their role in the management of myocardial infarction is not clear. Three viable probiotic bacterial strains, namely Lactobacillus reuteri, Bifidobacterium longum, and Bifidobacterium lactis, were gavaged to the rats daily for 28 days prior to the induction of myocardial injury. Myocardial injury was induced by the use of isoproterenol (ISO) in the probiotics, control and sham groups. The heart tissues were catheterized to evaluate the histopathological parameters and measure the expression of genes related to inflammation. Treatment with ISO caused subendocardial necrosis and rupture of cardiac myofibrils. Pretreatment with probiotics reduced the size of myocardial infarction caused by ISO. Also, in the probiotic group, a relative decrease in the amount of tissue fibrosis and rupture of cardiomyocytes fibers was seen. Pretreatment with probiotics partially ameliorated myocardial necrosis, edema and leukocyte infiltration. Also, a remarkable decrease was detected in the expression of tissue proinflammatory genes in the pretreated group with probiotics. Thus, viable probiotic supplementation may ameliorate or prevent cardiac injury. Additional preclinical and clinical studies are required to clarify the impact of probiotics in the prevention and management of cardiovascular disease.

Clinical effect of XEN gel stent implantation or combined with phacoemusification and intraocular lens implantation on glaucoma

Objective: To evaluate the efficacy and safety of internal XEN gel stent implantation or combined with phacoemusification and intraocular lens (IOL) implantation in the treatment of glaucoma. Methods: It was a retrospective case series study. Forty-five patients (28 males and 17 females; 52 eyes) who had different types of glaucoma treated at the Shenzhen Eye Hospital from December 2021 to June 2023 were included. XEN gel stent implantation (the XEN group) or XEN implantation combined with phacoemusification and IOL implantation (the combined group) were performed in these patients. The postoperative follow-up was 18 months. The observational indexes included the best corrected visual acuity (recorded as the logarithm of the minimum angle of resolution), intraocular pressure (IOP), XEN implantation quadrant, number of IOP-lowering medications, corneal endothelial cell count, operation success rate and surgical complications. The one-way repeated measures of variance, LSD-t test, and rank sum test were used for statistical analysis. Results: There were 28 patients (33 eyes) in the XEN group and 17 patients (19 eyes) in the combined group. The postoperative best corrected visual acuity had no significant change in the XEN group, but improved significantly (0.21±0.30 at 6 months; P<0.05) in the combined group, compared with the preoperative value. The IOP of the two groups at 18 months after surgery [(12.2±3.1) and (11.9±3.9) mmHg (1 mmHg=0.133 kPa)] was significantly lower than that before surgery [(22.1±8.5) and (19.4±10.2) mmHg; P<0.05]. The average number of IOP-lowering medications in all patients was 3 (2, 3) before surgery and 0 (0, 0) at 18 months after surgery. The difference was statistically significant (P<0.05). In the XEN group, the corneal endothelial cell count was (2 387.37±478.22) cells/mm² preoperatively and (2 193.89±311.96) cells/mm² at 12 months. The decrease showed no statistical significance. The XEN gel stent was implanted in the supranasal quadrant in 8 eyes (15.4%), in the inferonasal quadrant in 36 eyes (69.2%), and in the infratemporal quadrant in 8 eyes (15.4%). The operation success rate [complete success rate, 86.5% (45/52); conditional success rate, 9.6% (5/52)] was 96.2% (50/52). The filtering bleb scarring occurred in 9.6% (5/52) of eyes. A small amount of hyphema, postoperative shallow anterior chamber, transient hypertension, and intraoperative drain breakage were found in 7.7% (4/52) of eyes, respectively. A small amount of subconjunctival bleeding was observed in 5.8%(3/52) of eyes. Re-implantation of an XEN gel stent was performed in 5.8% (3/52) of eyes. The intraoperative conjunctival tissue rupture, hypotony macular edema, and drain exposure were observed in 1.9% (1/52) of eyes, respectively. Conclusion: The XEN gel stent implantation or combined with phacoemusification and IOL implantation was effective and safe in treating different types of glaucoma, but its long-term clinical efficacy needs further follow-up observations in multi-center, larger-scale research.

Small AAAs: Recommendations for Rodent Model Research for the Identification of Novel Therapeutics.

Most abdominal aortic aneurysms (AAAs) are small with low rupture risk (<1%/y) when diagnosed but slowly expand to ≥55 mm and undergo surgical repair. Patients and clinicians require medications to limit AAA growth and rupture, but drugs effective in animal models have not translated to patients. Use models that simulate human AAA tissue pathology, growth patterns, and rupture; focus on the clinically relevant outcomes of growth and rupture; design studies with the rigor required of human clinical trials; monitor AAA growth using reproducible ultrasound; and perform studies in both males and females. The aortic adventitial elastase oral β-aminopropionitrile model has many strengths including simulating human AAA pathology and modeling prolonged aneurysm growth. The Ang II (angiotensin II) model performed less well as it better simulates acute aortic syndrome than AAA. The elastase plus TGFβ (transforming growth factor-β) blocking antibody model displays a high rupture rate, making prolonged monitoring of AAA growth not feasible. The elastase perfusion and calcium chloride models both display limited AAA growth.

ELUCIDATING THE EFFECTS OF FORMALIN AS FOOD PRESERVATIVE ON GROSS AND HISTOARCHITECTURE OF VITAL ORGANS OF SWISS ALBINO MICE

Formalin usage as food preservative in Bangladesh has dramatically increased recently, especially in fish, fruits, and many other food products, putting the vast majority of people in serious health risk. With this background, the study was aimed to detect the alterations of gross structure and histoarchitecture of vital organs in Swiss albino mice due to the consumption of formalin. Mice were divided into five groups at the age of four weeks. Normal drinking water was supplied to the control group of mice. Mice of group 1, 2, 3 and 4 were supplied normal drinking water mixed with formalin at 1%, 5%, 10% and 20% concentrations, respectively up to week 24. Mice treated with varying concentrations of formalin for 24 weeks was assessed for the weight change of their liver, heart, kidney and lung weights. Investigations were also conducted on histological alterations in the liver, heart, kidney and lung. After 24 weeks of treatment of mice with different concentrations of formalin, the weight of all four major organs (liver, heart, kidney and lung) was decreased in all formalin-treated mice in comparison to control mice. Petechial hemorrhages, congestion, necrosis, and parenchymatous cell degeneration have been found in liver. Kidney sections have shown decreased Bowman’s space, hypertrophied glomerulus and tubular dilatation. Leucocyte infiltration, necrosis, and rupture of connective tissue have been seen in the heart sections. Lung sections have shown pulmonary alterations, including hemorrhages, thicker alveolar walls, and inflammatory cells. It was, concluded that formalin has adverse effects on vital organs of Swiss Albino mice.

Virulence and Pathological Characteristics of a New Metarhizium anisopliae Strain against Asian Long-Horn Beetle Anoplophora glabripennis Larvae

The Asian long-horn beetle (ALB) is a serious wood-boring insect. Continuous isolation of different fungal strains is vital for using fungi for the control of ALB. The virulence and pathological characteristics of a new Metarhizium anisopliae strain DES3 isolated from the desert afforestation stands against the larvae of ALB were assessed in this study. The corrected mortality reached 100% at the conidial concentration of 109 and 108 conidia/mL, and 91.11 ± 4.44% at 107 conidia/mL. Similarly, the LC/LT showed high virulence as well. Meanwhile, the virulence of a commercial M. anisopliae strain against the ALB larvae was evaluated. The corrected mortality was only 33.33% at 109 conidia/mL, and less than 10% at 108 conidia/mL. The pathological characteristics after infection by the M. anisopliae strain DES3 were evident, mainly embodied in the rupture of the adipose tissue, muscle tissue, and midgut. But there was no obvious change after infection by the commercial M. anisopliae strain. In conclusion, these results establish that the M. anisopliae strain DES3 has high virulence in a dosage-dependent manner against ALB larvae, indicating the potential of fungal strain DES3 to be developed as biopesticide for biocontrol of A. glabripennis.

Kinematics, kinetics, and new insights from a contemporary analysis of the first experiments to produce cervical facet dislocations in the laboratory.

The first experimental study to produce cervical facet dislocation (CFD) in cadaver specimens captured the vertebral motions and axial forces that are important for understanding the injury mechanics. However, these data were not reported in the original manuscript, nor been presented in the limited subsequent studies of experimental CFD. Therefore, the aim of this study was to re-examine the analog data from the first experimental study to determine the local and global spinal motions, and applied axial force, at and preceding CFD. In the original study, quasistatic axial loading was applied to 14 cervical spines by compressing them between two metal plates. Specimens were fixed caudally via a steel spindle positioned within the spinal canal and a bone pin through the inferior-most vertebral body. Global rotation of the occiput was restricted but its anterior translation was unconstrained. The instant of CFD was identified on sagittal cineradiograph films (N = 10), from which global and intervertebral kinematics were also calculated. Corresponding axial force data (N = 6) were extracted, and peak force and force at the instant of injury were determined. CFD occurred in eight specimens, with an intervertebral flexion angle of 34.8 ± 5.6 degrees, and a 3.1 ± 1.9 mm increase in anterior translation, at the injured level. For seven specimens, CFD was produced at the level of transition from upper neck lordosis to lower neck kyphosis. Five specimens with force data underwent CFD at 545 ± 147 N, preceded by a peak axial force (755 ± 233 N) that appeared to coincide with either fracture or soft tissue failure. Re-examining this rich dataset has provided quantitative evidence that small axial compression forces, combined with anterior eccentricity and upper neck extension, can cause flexion and shear in the lower neck, leading to soft tissue rupture and CFD.

Mechanical characterization of regenerating Hydra tissue spheres

Hydra vulgaris, long known for its remarkable regenerative capabilities, is also a long-standing source of inspiration for models of spontaneous patterning. Recently it became clear that early patterning during Hydra regeneration is an integrated mechanochemical process whereby morphogen dynamics is influenced by tissue mechanics. One roadblock to understanding Hydra self-organization is our lack of knowledge about the mechanical properties of these organisms. In this study, we combined microfluidic developments to perform parallelized microaspiration rheological experiments and numerical simulations to characterize these mechanical properties. We found three different behaviors depending on the applied stresses: an elastic response, a viscoelastic response, and tissue rupture. Using models of deformable shells, we quantify their Young’s modulus, shear viscosity, and the critical stresses required to switch between behaviors. Based on these experimental results, we propose a description of the tissue mechanics during normal regeneration. Our results provide a first step toward the development of original mechanochemical models of patterning grounded in quantitative experimental data.

Characterization of ovarian progenitor cells for their potential to generate steroidogenic theca cells in vitro.

Progenitor cells with ovulation-related tissue repair activity were identified with defined markers (LGR5, EPCR, LY6A, and PDGFRA), but their potentials to form steroidogenic cells were not known. This study shows that the cells can generate progenies with different steroidogenic activities. Adult mammalian ovaries contain stem/progenitor cells necessary for folliculogenesis and ovulation-related tissue rupture repair. Theca cells are recruited and developed from progenitors during the folliculogenesis. Theca cell progenitors were not well defined. The aim of current study is to compare the potentials of four ovarian progenitors with defined markers (LY6A, EPCR, LGR5, and PDGFRA) to form steroidogenic theca cells in vitro. The location of the progenitors with defined makers was determined by immunohistochemistry and immunofluorescence staining of ovarian sections of adult mice. Different progenitor populations were purified by magnetic-activated cell sorting (MACS) and/or fluorescence-activated cell sorting (FACS) techniques from ovarian cell preparation and were tested for their abilities to generate steroidogenic theca cells in vitro. The cells were differentiated with a medium containing LH, ITS, and DHH agonist for 12 days. The results showed that EPCR+ and LGR5+ cells primarily distributed along the ovarian surface epithelium (OSE), while LY6A+ cells distributed in both the OSE and parenchyma. However, PDGFRA+ cells were exclusively located in interstitial compartment. When the progenitors were purified by these markers and differentiated in vitro, LY6A+ and PDGFRA+ cells formed steroidogenic cells expressing both CYP11A1 and CYP17A1 and primarily producing androgens, showing characteristics of theca-like cells, while LGR5+ cells generated steroidogenic cells devoid of CYP17A1 expression and androgen production, showing a characteristic of progesterone-producing cells (granulosa- or lutea-like cells). In conclusion, progenitors from both OSE and parenchyma of adult mice are capable of generating steroidogenic cells with different steroidogenic capacities, showing a possible lineage preference.

Maximum resistance pressure at the time of lung tissue rupture after porcine lung transection using automatic linear staplers with different reinforcement methods.

Polyglycolic acid (PGA) sheets, fibrin glue, and staple line reinforcement are frequently used to prevent air leakage during lung resection. However, the optimal staple-line reinforcement method remains unclear. Cranial lung lobes of pigs were used to evaluate different staple line reinforcement methods (n = 6). Ventilator-assisted manometry was used to measure the maximum resistance pressure at the time of rupture of the lung tissue after stapling. The mean maximum resistance pressures at the time of lung tissue rupture after using the stapler alone, stapler with PGA sheet and fibrin glue, and stapler with reinforcement were 38.0 cmH2O, 51.3 cmH2O, and 62.7 cmH2O, respectively. A significant increase in the maximum resistance pressure was observed with stapler reinforcement (P < 0.001), while the differences between the other groups were not statistically significant (P = 0.055, P = 0.111). A histological assessment revealed disruption of alveolar structures near the needle-stitching site in the stapler alone, and in the stapler with PGA sheet and fibrin glue groups. Pleural rupture near the staple line was observed in the stapler with reinforcement group. The maximum resistance pressure before air leakage was significantly higher when using a stapler with reinforcement than when using a stapler alone.

Computational Investigation of Vessel Injury Due to Catheter Tracking During Transcatheter Aortic Valve Replacement.

Catheter reaction forces during transcatheter valve replacement (TAVR) may result in injury to the vessel or plaque rupture, triggering distal embolization or thrombosis. In vitro test methods represent the arterial wall using synthetic proxies to determine catheter reaction forces during tracking, but whether they can account for reaction forces within the compliant aortic wall tissue in vivo is unknown. Moreover, the role of plaque inclusions is not well understood. Computational approaches have predicted the impact of TAVR positioning, migration, and leaflet distortion, but have not yet been applied to investigate aortic wall reaction forces and stresses during catheter tracking. In this study, we investigate the role that catheter design and aorta and plaque mechanical properties have on the risk of plaque rupture during TAVR catheter delivery. We report that, for trackability testing, a rigid test model provides a reasonable estimation of the peak reaction forces experienced during catheter tracking within compliant vessels. We investigated the risk of rupture of both the aortic tissue and calcified plaques. We report that there was no risk of diseased aortic tissue rupture based on an accepted aortic tissue stress threshold (4.2MPa). However, we report that both the aortic and plaque tissue exceed a rupture stress threshold (300kPa) with and without the presence of stiff and soft plaque inclusions. We also highlight the potential risks associated with shorter catheter tips during catheter tracking and demonstrate that increasing the contact surface will reduce peak contact pressures experienced in the tissue.

A New Strain of Metarhizium robertsii Isolated from Loess Plateau and Its Virulence and Pathological Characteristics against Monochamus alternatus.

Monochamus alternatus is a serious trunk-boring pest. The isolation and utilization of entomopathogenic fungi to manage M. alternatus is important. Here, a new strain GQH6 of Metarhizium robertsii, isolated from the Loess Plateau, was identified morphologically and molecularly. The virulence of the strain GQH6 against the third-instar larvae of M. alternatus was studied. Then, the pathological process, including symptom observation and histopathological observation, was also researched. The corrected mortality was 100% at 109 and 108 conidia/mL, and 88.89 ± 5.88% at 107 conidia/mL. The LC50 was 1.93 × 106 conidia/mL and the LC90 was 1.35 × 107 conidia/mL. And the LT50 of the strain GQH6 was 3.96 days at 109 conidia/mL, and 4.99 days at 108 conidia/mL. These virulence indices showed high virulence against M. alternatus larvae. In addition, the symptoms of the infected M. alternatus larvae were obvious. After one day, dark spots appeared and increased in number. By four days, white mycelia appeared. Finally, the larvae body became green. Similarly, the histopathological changes after infection were obvious, mainly manifested in muscle tissue rupture, adipose tissue fracture and midgut disintegration. These results demonstrated that the M. robertsii strain GQH6 isolated from the Loess Plateau was highly virulent against M. alternatus larvae of the third instar.

Investigating the influence of collagen cross-linking on mechanical properties of thoracic aortic tissue.

Vascular diseases, such as abdominal aortic aneurysms, are associated with tissue degeneration of the aortic wall, resulting in variations in mechanical properties, such as tissue ultimate stress and a high slope. Variations in the mechanical properties of tissues may be associated with an increase in the number of collagen cross-links. Understanding the effect of collagen cross-linking on tissue mechanical properties can significantly aid in predicting diseased aortic tissue rupture and improve the clarity of decisions regarding surgical procedures. Therefore, this study focused on increasing the density of the aortic tissue through cross-linking and investigating the mechanical properties of the thoracic aortic tissue in relation to density. Uniaxial tensile tests were conducted on the porcine thoracic aorta in four test regions (anterior, posterior, distal, and proximal), two loading directions (circumferential and longitudinal), and density increase rates (0%-12%). As a result, the PPC (Posterior/Proximal/Circumferential) group experienced a higher ultimate stress than the PDC (Posterior/Distal/Circumferential) group. However, this relationship reversed when the specimen density exceeded 3%. In addition, the ultimate stress of the ADC (Anterior/Distal/Circumferential) and PPC group was greater than that of the APC (Anterior/Proximal/Circumferential) group, while these findings were reversed when the specimen density exceeded 6% and 9%, respectively. Finally, the high slope of the PDL (Posterior/Distal/Longitudinal) group was lower than that of the ADL (Anterior/Distal/Longitudinal) group, but the high slope of the PDL group appeared larger due to the stabilization treatment. This highlights the potential impact of density variations on the mechanical properties of specific specimen groups.

Vibrio splendidus AJ01 Promotes Pathogenicity via L-Glutamic Acid.

Vibrio splendidus is a pathogen that infects a wide range of hosts, especially the sea cucumber species Apostichopus japonicus. Previous studies showed that the level of L-glutamic acid (L-Glu) significantly increased under heat stress, and it was found to be one of the best carbon sources used by V. splendidus AJ01. In this study, the effects of exogenous L-Glu on the coelomocyte viability, tissue status, and individual mortality of sea cucumbers were analyzed. The results showed that 10 mM of L-Glu decreased coelomocyte viability and increased individual mortality, with tissue rupture and pyknosis, while 0.1 mM of L-Glu slightly affected the survival of sea cucumbers without obvious damage at the cellular and tissue levels. Transcriptomic analysis showed that exogenous L-Glu upregulated 343 and downregulated 206 genes. Gene Ontology (GO) analysis showed that differentially expressed genes (DEGs) were mainly enriched in signaling and membrane formation, while a Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that DEGs were significantly enriched in the upregulated endocytosis and downregulated lysosomal pathways. The coelomocyte viability further decreased by 20% in the simultaneous presence of exogenous L-Glu and V. splendidus AJ01 compared with that in the presence of V. splendidus AJ01 infection alone. Consequently, a higher sea cucumber mortality was also observed in the presence of exogenous L-Glu challenged by V. splendidus AJ01. Real-time reverse transcriptase PCR showed that L-Glu specifically upregulated the expression of the fliC gene coding the subunit protein of the flagellar filament, promoting the swimming motility activity of V. splendidus. Our results indicate that L-Glu should be kept in a state of equilibrium, and excess L-Glu at the host-pathogen interface prompts the virulence of V. splendidus via the increase of bacterial motility.

Cyclic loading induces anabolic gene expression in ACLs in a load-dependent and sex-specific manner.

Anterior cruciate ligament (ACL) injuries are historically thought to be a result of a single acute overload or traumatic event. However, recent studies suggest that ACL failure may be a consequence of fatigue damage. Additionally, the remodeling response of ACLs to fatigue loading is unknown. Therefore, the objective of this study was to investigate the remodeling response of ACLs to cyclic loading. Furthermore, given that women have an increased rate of ACL rupture, we investigated whether this remodeling response is sex specific. ACLs were harvested from male and female New Zealand white rabbits and cyclically loaded in a tensile bioreactor mimicking the full range of physiological loading (2, 4, and 8 MPa). Expression of markers for anabolic and catabolic tissue remodeling, as well as inflammatory cytokines, was quantified using quantitative reverse transcriptionpolymerase chain reaction. We found that the expression of markers for tissue remodeling of the ACL is dependent on the magnitude of loading and is sex specific. Male ACLs activated an anabolic response to cyclic loading at 4 MPa but turned off remodeling at 8 MPa. These data support the hypothesis that noncontact ACL injury may be a consequence of failed tissue remodeling and inadequate repair of microtrauma resulting from elevated loading. Compared to males, female ACLs failed to increase anabolic gene expression with loading and exhibited higher expression of catabolic genes at all loading levels, which may explain the increased rate of ACL tears in women. Together, these data provide insight into load-induced ACL remodeling and potential causes of tissue rupture.

Linking myosin heavy chain isoform shift to mechanical properties and fracture modes in skeletal muscle tissue.

Muscle fibers play a crucial role in the mechanical action of skeletal muscle tissue. However, it is unclear how the histological variations affect the mechanical properties of tissues. In this study, the shift of myosin heavy chain (MHC) isoforms is used for the first time to establish a linkage between tissue histological variation and passive mechanical properties. The shift of MHC isoform is found not only to induce significant differences in skeletal muscle passive mechanical properties, but also to lead to differences in strain rate responses. Non-negligible rate dependence is observed even in the conventionally defined quasi-static regime. Fidelity in the estimated constitutive parameters, which can be impacted due to variation in MHC isoforms and hence in rate sensitivity, is enhanced using a Bayesian inference framework. Subsequently, scanning electron microscopy and fluorescence microscopy are used to characterize the fracture morphology of muscle tissues and fibers. The fracture mode of both MHC I and II muscle fibers exhibited shearing of endomysium. Results show that the increase in strain rate only leads to stronger rebounding of the muscle fibers during tissue rupture without changing fracture modes.

Fracture of porcine aorta—Part 1: symconCT fracture testing and DIC

Tissue failure and damage are inherent parts of vascular diseases and tightly linked to clinical events. Additionally, experimental set-ups designed to study classical engineering materials are suboptimal in the exploration of vessel wall fracture properties. The classical Compact Tension (CT) test was augmented to enable stable fracture propagation, resulting in the symmetry-constraint Compact Tension (symconCT) test, a suitable set-up for fracture testing of vascular tissue. The test was combined with Digital Image Correlation (DIC) to study tissue fracture in 45 porcine aorta specimens. Test specimens were loaded in axial and circumferential directions in a physiological solution at 37 °C. Loading the aortic vessel wall in the axial direction resulted in mode I tissue failure and a fracture path aligned with the circumferential vessel direction. Circumferential loading resulted in mode I-dominated failure with multiple deflections of the fracture path. The aorta ruptured at a principal Green-Lagrange strain of approximately 0.7, and strain rate peaks that develop ahead of the crack tip reached nearly 400 times the strain rate on average over the test specimen. It required approximately 70% more external work to fracture the aorta by circumferential than axial load; normalised with the fracture surface, similar energy levels are, however, observed. The symconCT test resulted in a stable fracture propagation, which, combined with DIC, provided a set-up for the in-depth analysis of vascular tissue failure. The high strain rates ahead of the crack tip indicate the significance of rate effects in the constitutive description of vascular tissue fracture. Statement of significanceThis paper represents a significant step forward in understanding the fracture properties of porcine aorta. Inspired by the Compact Tension test, we developed an ad hoc experimental protocol to investigate stable crack propagation in soft materials, providing new insights into the mechanical processes that lead to the rupture of vascular tissue. The set-up enables the assessment of strains and strain rates ahead of the crack tip, and our findings could improve the clinical risk assessment of vascular pathologies as well as optimise medical device design.

Modeling fatigue failure in soft tissue using a visco-hyperelastic model with discontinuous damage

Soft tissue is susceptible to injury from single high-magnitude static loads and from repetitive low-magnitude fatigue loads. While many constitutive formulations have been developed and validated to model static failure in soft tissue, a modeling framework is not well-established for fatigue failure. Here we determined the feasibility of using a visco-hyperelastic damage model with discontinuous damage (strain energy-based damage criterion) to simulate low- and high-cycle fatigue failure in soft fibrous tissue. Cyclic creep data from six uniaxial tensile fatigue experiments of human medial meniscus were used to calibrate the specimen-specific material parameters. The model was able to successfully simulate all three characteristic stages of cyclic creep, and predict the number of cycles until tissue rupture. Mathematically, damage propagated under constant cyclic stress due to time-dependent viscoelastic increases in tensile stretch that in turn increased strain energy. Our results implicate solid viscoelasticity as a fundamental regulator of fatigue failure in soft tissue, where tissue with slow stress relaxation times will be more resistant to fatigue injury. In a validation study, the visco-hyperelastic damage model was able to simulate characteristic stress-strain curves of pull to failure experiments (static failure) when using material parameters curve fit to the fatigue experiments. For the first time, we've shown that a visco-hyperelastic discontinuous damage framework can model cyclic creep and predict material rupture in soft tissue, and may enable the reliable simulation of both fatigue and static failure behavior from a single constitutive formulation.

The relative motion concept in acute and chronic boutonniere deformity: Invited commentary

Study designRetrospective. IntroductionBoutonniere deformity (BD) is a troublesome injury occurring from rupture of tissue connecting the extrinsic to intrinsic tendon systems. This causes loss of interphalangeal joint balance, and immobilization often results in adherence and difficulty restoring balance. PurposesReview of relative motion flexion (RMF) orthotic use for safe healing during functional activity in 23 patients, and explanation of the rationale. MethodsAnatomic rationale and clinical experience is reviewed in 8 acute BD patients utilizing RMF orthoses for 6 weeks, and for chronic BD patients, 3 months after serial casting. ResultsAll patients met the Strickland and Steichen criteria for “excellent” results following treatment, with an average of 35° increase in ROM. DiscussionThe anatomic rationale for relative motion recognizes that altering relative positioning between adjacent metacarpophalangeal (MCP) joints produces a protective favorable impact on interphalangeal forces during hand function using 15°-20° greater MCP joint flexion. This provides dorsal and volar protective benefits because the extensor digitorum communis (EDC), a single-muscle-four-tendon system, attaches to the intrinsic lateral band (LB) tendons. With greater MCP flexion, dorsal EDC force is increased, pulling lateral bands medially, while on the volar surface the downward pull of the lumbrical on LB is relaxed due to origin from the flexor digitorum profundus tendon of the injured digit, also a single-muscle-four-tendon system. The RMF orthosis permits protected active motion during functional activity with acute BD. In patients with chronic BD and adequate passive extension, an RMF orthosis for 3 months also produced encouraging results. ConclusionManagement of acute BD with RMF orthoses provided earlier recovery of motion and hand function. Similar results occurred for chronic BD using serial casting for adequate extension followed by 3 months of RMF orthotic use and should be attempted prior to surgical intervention, with surgery remaining an alternative.

Design of patterns in tubular robots using DNN-metaheuristics optimization

Concentric-tube robots for minimally invasive surgery pose a potential risk of tissue rupture because of the structural instabilities caused by high value of bending-to-torsional-stiffness ratio (EI/GJ). In this study, a novel optimization method based on metaheuristic optimization accelerated by a deep neural network (DNN)-based surrogate model to obtain optimized pattern parameters is presented. The method minimizes EI/GJ while conforming to the minimum compliance constraints and geometric restrictions. The proposed optimization process utilizes a DNN trained using 855 datasets generated by finite element analysis that cover the pattern design parameter space. The pattern design parameters were derived from topology optimization. The results demonstrate that the proposed optimization method yielded pattern designs that outperformed previous designs within a reasonable time frame (less than 900 s) without requiring manual parametric study or sensitivity analysis.