Biomechanical Properties of Abdominal Organs In Vivo and Postmortem Under Compression Loads

Review of non-penetrating ballistic testing techniques for protection assessment: From biological data to numerical and physical surrogates

Human surrogates have long been employed to simulate human behaviour, beginning in the automotive industry and now widely used throughout the safety framework to estimate human injury during and after accidents and impacts. In the specific context of blunt ballistics, various methods have been developed to investigate wound injuries, including tissue simulants such as clays or gelatine ballistic, physical dummies and numerical models. However, all of these surrogate entities must be biofidelic, meaning they must accurately represent the biological properties of the human body. This paper provides an overview of physical and numerical surrogates developed specifically for blunt ballistic impacts, including their properties, use and applications. The focus is on their ability to accurately represent the human body in the context of blunt ballistic impact.

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.

Enhanced grip force estimation in robotic surgery: A sparrow search algorithm-optimized backpropagation neural network approach

The absence of an effective gripping force feedback mechanism in minimally invasive surgical robot systems impedes physicians' ability to accurately perceive the force between surgical instruments and human tissues during surgery, thereby increasing surgical risks. To address the challenge of integrating force sensors on minimally invasive surgical tools in existing systems, a clamping force prediction method based on mechanical clamp blade motion parameters is proposed. The interrelation between clamping force, displacement, compression speed, and the contact area of the clamp blade indenter was analyzed through compression experiments conducted on isolated pig kidney tissue. Subsequently, a prediction model was developed using a backpropagation (BP) neural network optimized by the Sparrow Search Algorithm (SSA). This model enables real-time prediction of clamping force, facilitating more accurate estimation of forces between instruments and tissues during surgery. The results indicate that the SSA-optimized model outperforms traditional BP networks and genetic algorithm-optimized (GA) BP models in terms of both accuracy and convergence speed. This study not only provides technical support for enhancing surgical safety and efficiency, but also offers a novel research direction for the design of force feedback systems in minimally invasive surgical robots in the future.

Mechanical experimentation of the gastrointestinal tract: a systematic review

The gastrointestinal (GI) organs of the human body are responsible for transporting and extracting nutrients from food and drink, as well as excreting solid waste. Biomechanical experimentation of the GI organs provides insight into the mechanisms involved in their normal physiological functions, as well as understanding of how diseases can cause disruption to these. Additionally, experimental findings form the basis of all finite element (FE) modelling of these organs, which have a wide array of applications within medicine and engineering. This systematic review summarises the experimental studies that are currently in the literature (n = 247) and outlines the areas in which experimentation is lacking, highlighting what is still required in order to more fully understand the mechanical behaviour of the GI organs. These include (i) more human data, allowing for more accurate modelling for applications within medicine, (ii) an increase in time-dependent studies, and (iii) more sophisticated in vivo testing methods which allow for both the layer- and direction-dependent characterisation of the GI organs. The findings of this review can also be used to identify experimental data for the readers' own constitutive or FE modelling as the experimental studies have been grouped in terms of organ (oesophagus, stomach, small intestine, large intestine or rectum), test condition (ex vivo or in vivo), number of directions studied (isotropic or anisotropic), species family (human, porcine, feline etc.), tissue condition (intact wall or layer-dependent) and the type of test performed (biaxial tension, inflation-extension, distension (pressure-diameter), etc.). Furthermore, the studies that investigated the time-dependent (viscoelastic) behaviour of the tissues have been presented.

Biomechanical characterization of the passive porcine stomach

The complex mechanics of the gastric wall facilitates the main digestive tasks of the stomach. However, the interplay between the mechanical properties of the stomach, its microstructure, and its vital functions is not yet fully understood. Importantly, the pig animal model is widely used in biomedical research for preliminary or ethically prohibited studies of the human digestion system. Therefore, this study aims to thoroughly characterize the mechanical behavior and microstructure of the porcine stomach. For this purpose, multiple quasi-static mechanical tests were carried out with three different loading modes, i.e., planar biaxial extension, radial compression, and simple shear. Stress-relaxation tests complemented the quasi-static experiments to evaluate the deformation and strain-dependent viscoelastic properties. Each experiment was conducted on specimens of the complete stomach wall and two separate layers, mucosa and muscularis, from each of the three gastric regions, i.e., fundus, body, and antrum. The significant preconditioning effects and the considerable regional and layer-specific differences in the tissue response were analyzed. Furthermore, the mechanical experiments were complemented with histology to examine the influence of the microstructural composition on the macrostructural mechanical response and vice versa. Importantly, the shear tests showed lower stresses in the complete wall compared to the single layers which the loose network of submucosal collagen might explain. Also, the stratum arrangement of the muscularis might explain mechanical anisotropy during tensile tests. This study shows that gastric tissue is characterized by a highly heterogeneous microstructure with regional variations in layer composition reflecting not only functional differences but also diverse mechanical behavior. STATEMENT OF SIGNIFICANCE: Unfortunately, only few experimental data on gastric tissue are available for an adequate material parameter and model estimation. The present study therefore combines layer- and region-specific stomach wall mechanics obtained under multiple loading conditions with histological insights into the heterogeneous microstructure. On the one hand, the extensive data sets of this study expand our understanding of the interplay between gastric mechanics, motility and functionality, which could help to identify and treat associated pathologies. On the other hand, such data sets are of high relevance for the constitutive modeling of stomach tissue, and its application in the field of medical engineering, e.g., in the development of surgical staplers and the improvement of bariatric surgical interventions.

Mechanobiological considerations in colorectal stapling: Implications for technology development

Technological advancements in minimally invasive surgery have led to significant improvements in patient outcomes. One such technology is surgical stapling, which has evolved into a key component of many operating rooms by facilitating ease and efficacy in resection and repair of diseased or otherwise compromised tissue. Despite such advancements, adverse post-operative outcomes such as anastomotic leak remain a persistent problem in surgical stapling and its correlates (i.e., hand-sewing), most notably in low colorectal or coloanal procedures. Many factors may drive anastomotic leaks, including tissue perfusion, microbiome composition, and patient factors such as pre-existing disease. Surgical intervention induces complex acute and chronic changes to the mechanical environment of the tissue; however, roles of mechanical forces in post-operative healing remain poorly characterized. It is well known that cells sense and respond to their local mechanical environment and that dysfunction of this "mechanosensing" phenomenon contributes to a myriad of diseases. Mechanosensing has been investigated in wound healing contexts such as dermal incisional and excisional wounds and development of pressure ulcers; however, reports investigating roles of mechanical forces in adverse post-operative gastrointestinal wound healing are lacking. To understand this relationship well, it is critical to understand: 1) the intraoperative material responses of tissue to surgical intervention, and 2) the post-operative mechanobiological response of the tissue to surgically imposed forces. In this review, we summarize the state of the field in each of these contexts while highlighting areas of opportunity for discovery and innovation which can positively impact patient outcomes in minimally invasive surgery.

Biomechanical properties of the stomach: A comprehensive comparative analysis of human and porcine gastric tissue

BACKGROUND

Stomach-related disorders impose medical challenges and are associated with significant social and economic costs. The field of biomechanics is promising for understanding tissue behavior and for development of medical treatments and surgical interventions. In gastroenterology, animal models are often used when studies on humans are not possible. Often large animal models with similar anatomical characteristics (size and shape) are preferred. However, it is uncertain if stomachs from humans and large animals have similar mechanical properties. The aim of the present study is to characterize and compare hyper- and viscoelastic properties of porcine and human gastric tissue using tension and radial compression tests.

METHODS

Hyperelastic and viscoelastic properties were quantified from quasi-static ramp tests and stress relaxation tests. Tension in two directions and radial compression experiments were done on intact stomach wall samples as well as on separated mucosa and muscularis layer samples from porcine and human fundus, corpus and antrum.

RESULTS AND CONCLUSIONS

Similar hyper- and viscoelastic constitutive models can be used to describe porcine and human gastric tissue. In total, 19 constitutive parameters were compared and results showed significant variations between species. For example, for intact circumferential samples from antrum, the stiffness (a) and relaxation (τ₁) were greater for human samples than for porcine samples (p < 0.0001). The constitutive parameters were condition-, region- and layer-dependent and no distinct pattern hereof between species was found. This indicates that different parameters must be used to describe the specific situation. The present work provides insight into porcine and human gastric radial compressive and tensile hyper- and viscoelastic properties, strengthening the inter-species relation of the biomechanical properties. Constitutive relations were established that may aid development and translation of diagnostic or therapeutic devices with computational models.

Variability of tissue mechanical response in Sus Domesticus porcine models from in vivo to ex vivo conditions

BACKGROUND

Healthcare simulators have been demonstrated to be a valuable resource for training several technical and nontechnical skills. A gap in the fidelity of tissues has been acknowledged as a barrier to application for current simulators; especially for interventional procedures. Inaccurate or unrealistic mechanical response of a simulated tissue to a given surgical tool motion may result in negative training transfer and/or prevents the "suspension of disbelief" necessary for a trainee to engage in the activity. Thus, where it is relevant to training outcomes, there should be an effort to create healthcare simulators with simulated tissue mechanical responses that match or represent those of biological tissues. Historically, this data is most often gathered from preserved (post mortem) tissue; however, there is a concern that the mechanical properties of preserved tissue, that lacks blood flow, may lack adequate accuracy to provide the necessary training efficacy of simulators.

METHODS AND FINDINGS

This work explores the effect of the "state" of the tissue testing status on liver and peritoneal tissue by using a customized handheld grasper to measure the mechanical responses of representative porcine (Sus domesticus) tissues in n = 5 animals across five test conditions: in vivo, post mortem (in-situ), ex vivo (immediately removed from fresh porcine cadaver), post-refrigeration, and post-freeze-thaw cycle spanning up to 72 hours after death. No statistically significant difference was observed in the mechanical responses due to grasping between in vivo and post-freeze conditions for porcine liver and peritoneum tissue samples (p = 0.05 for derived stiffness at grasping force values F = 5N and 6.5N). Furthermore, variance between in vivo and post-freeze conditions within each animal, was comparable to the variance of the in vivo condition between animals.

CONCLUSIONS

Results of this study further validate the use of preserved tissue in the design of medical simulators via observing tissue mechanical responses of post-freeze tissue comparable to in vivo tissue. Therefore, the use of thawed preserved tissue for the further study and emulation of mechanical perturbation of the liver and peritoneum can be considered. Further work in this area should investigate these trends further, particularly in regard to other tissues and the potential effects varying preservation methods may yield.

Total collagen content and distribution is increased in human colon during advancing age

Background

The effect of ageing on total collagen content of human colon has been poorly investigated. The aim of this study was to determine if ageing altered total collagen content and distribution in the human colon.

Methods

Macroscopically normal ascending colon was obtained at surgery from cancer patients (n = 31) without diagnosis of diverticular disease or inflammatory bowel disease. Masson’s trichrome and Picrosirius red stains were employed to identify the total collagen content and distribution within the sublayers of the colonic wall for adult (22–60 years; 6 males, 6 females) and elderly (70 – 91years; 6 males, 4 female) patients. A hydroxyproline assay evaluated the total collagen concentration for adult (30–64 years; 9 male, 6 female) and elderly (66–91 years; 8 male, 8 female) patients.

Key results

Histological studies showed that the percentage mean intensity of total collagen staining in the mucosa, submucosa and muscularis externa was, respectively, 14(1.9) %, 74(3.2) % and 12(1.5) % in the adult ascending colon. Compared with the adults, the total collagen fibres content was increased in the submucosa (mean intensity; 163.1 ± 11.1 vs. 124.5 ± 7.8; P < 0.05) and muscularis externa (42.5 ± 8.0 vs. 20.6 ± 2.8; P < 0.01) of the elderly patients. There was no change in collagen content of the mucosa. The total collagen concentration was increased in the elderly by 16%. Sex-related differences were not found, and data were combined for analysis.

Conclusions

Greater total collagen content was found in the submucosa and muscularis externa of the elderly human male and female colon. These changes may contribute to a possible loss of function with ageing.

Compression automation of circular stapler for preventing compression injury on gastrointestinal anastomosis

Background

Conventional manual compression relies on the surgeon's subjective sensations, so excessive compression can cause tissue injury to the stapling line of the intestinal anastomosis.

Methods

Automatic compression monitoring and compression control system was developed for circular stapler. The tissue injury related compression variables were evaluated and accommodated by compression control device. The compression injury‐reducing performance was verified on collagen sheets of in vitro experiments.

Results

Excessive pressure and tissue deformation were associated with compression‐induced tissue damages. The safe pressure range was very narrow in weaker tissue than normal collagen. The automatic system performed proper compression within a safe pressure range without tissue injury.

Conclusions

Manual compression of circular stapler could cause tissue injuries by excessive pressure and tissue deformation. Our automatic compression system is designed to control peak pressure to prevent the compressive tissue injury.

CoreView: fresh tissue biopsy assessment at the bedside using a millifluidic imaging chip

Minimally invasive core needle biopsies for medical diagnoses have become increasingly common for many diseases. Although tissue cores can yield more diagnostic information than fine needle biopsies and cytologic evaluations, there is no rapid assessment at the point-of-care for intact tissue cores that is low-cost and non-destructive to the biopsy. We have developed a proof-of-concept 3D printed millifluidic histopathology lab-on-a-chip device to automatically handle, process, and image fresh core needle biopsies. This device, named CoreView, includes modules for biopsy removal from the acquisition tool, transport, staining and rinsing, imaging, segmentation, and multiplexed storage. Reliable removal from side-cutting needles and bidirectional fluid transport of core needle biopsies of five tissue types has been demonstrated with 0.5 mm positioning accuracy. Automation is aided by a MATLAB-based biopsy tracking algorithm that can detect the location of tissue and air bubbles in the channels of the millifluidic chip. With current and emerging optical imaging technologies, CoreView can be used for a rapid adequacy test at the point-of-care for tissue identification as well as glomeruli counting in renal core needle biopsies.

Three-Axis Tension-Measuring Vitreoretinal Forceps Using Strain Sensor for Corneal Surgery

Precise motion control is important in robotic surgery, especially corneal surgery. This paper develops a new tension-measurement system for forceps used in corneal surgery, wherein contact force is applied only to a specific location for precise control, with precise movements detected by attaching a nano-crack sensor to the corresponding part. The nano-crack sensor used here customizes the working range and sensor sensitivity to match the strain rate of the tip of the forceps. Therefore, the tension in the suture can be sufficiently measured even at suture failure. The printed circuit board attached to the bottom of the system is designed to simultaneously collect data from several sensors, visualizing the direction and magnitude of the tension in order to inform the surgeon of how much tension is being applied. This system was verified by performing pig-corneal suturing.

Coupled experimental and computational approach to stomach biomechanics: Towards a validated characterization of gastric tissues mechanical properties

Gastric diseases are one of the most relevant healthcare problems worldwide. Interventions and therapies definition/design mainly derive from biomedical and clinical expertise. Computational biomechanics, with particular regard to the finite element method, provides hard-to-measure quantities during in-vivo tests, such as strain and stress distribution, leading to a more comprehensive and promising approach to improve the effectiveness of many different clinical activities. However, reliable finite element models of biological organs require appropriate constitutive formulations of building tissues, whose parameters identification needs an experimental campaign consisting in different tests on human tissues and organs. The aim of the reported here research activities was the identification of mechanical properties of human gastric tissues. Human gastric specimens were tested at tissue, sub-structural and structural levels, by tensile, membrane indentation and inflation tests, respectively. On the other hand, animal experimentations on tissue layers from literature pointed out the mechanical response at sub-tissue level during tensile loading conditions. In detail, the analysis of experimental results at sub-tissue and tissue levels led to a fibre-reinforced visco-hyperelastic constitutive formulation and to the identification of gastric layers mechanical behaviour. Results from experimentations on human samples were coupled with data derived from animal models. Data from sub-structural and structural experimentations were exploited to upgrade and validate the constitutive formulations and parameters. The developed investigations led to a reliable constitutive framework of human gastric tissues that both describe stomach mechanical functionality and allow computational investigations. Indeed, the comparisons among average computational data and experimental medians provided the following RMSEs (Root Mean Square Errors): 0.89 N, 0.15 N for corpus and fundus during membrane indentation test, respectively, and 0.44 kPa during inflation test. Accounting for the magnitude of experimental and computational data, the RMSEs can be considered low and acceptable because they concerned biological samples. In fact, biological tissues and structures are affected by a high inherent inter-samples' variability, which is detectable in both the geometrical configuration and the mechanical behaviour. The specific values of the here reported RMSEs ensured the reliability of the achieved parameters and the quality of the overall developed procedure. Reliable computational models of the gastric district could become efficient clinical tools to find out the main crucial aspects of bariatric procedures, such as the mechanical stimulation of gastric mechano-receptors. Moreover, the methods of computational biomechanics will permit to run the preliminary tests of new and innovative bariatric procedures, on one hand, predicting the successful rate and the effectiveness, and, on other hand, reducing the use of animal testing.

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

The mechanical properties of soft tissues play a key role in studying human injuries and their mitigation strategies. While such properties are indispensable for computational modelling of biological systems, they serve as important references in loading and failure experiments, and also for the development of tissue simulants. To date, experimental studies have measured the mechanical properties of peripheral tissues (e.g. skin)in-vivoand limited internal tissuesex-vivoin cadavers (e.g. brain and the heart). The lack of knowledge on a majority of human tissues inhibit their study for applications ranging from surgical planning, ballistic testing, implantable medical device development, and the assessment of traumatic injuries. The purpose of this work is to overcome such challenges through an extensive review of the literature reporting the mechanical properties of whole-body soft tissues from head to toe. Specifically, the available linear mechanical properties of all human tissues were compiled. Non-linear biomechanical models were also introduced, and the soft human tissues characterized using such models were summarized. The literature gaps identified from this work will help future biomechanical studies on soft human tissue characterization and the development of accurate medical models for the study and mitigation of injuries.

SuP-Ring: A pneumatic tactile display with substitutional representation of contact force components using normal indentation

BACKGROUND

Shear force is important for tumour detection and can contribute to minimally invasive surgery (MIS). A popular method uses lateral skin stretch to produce shear force but has some limitations.

METHODS

We have developed a ring-type pneumatic tactile display that employs normal indentation substituted for lateral skin stretch to represent normal and shear feedback, called SuP-Ring. Psychophysical experiments were conducted to evaluate how users perceive the provided feedback and the effectiveness of SuP-Ring in tumour localisation.

RESULTS

The experimental results show that the participants could perceive the provided normal and shear feedback well. Shear feedback enables users to enhance their performance in localising the tumour and normal feedback could contribute to ensuring the safety requirements in MIS.

CONCLUSIONS

The proposed tactile display could be useful for intraoperative tumour localisation and has the potential to be used in a wide variety of applications.

A literature review on large intestinal hyperelastic constitutive modeling

Impacts, traumas and strokes are spontaneously life-threatening, but chronic symptoms strangle patient every day. Colorectal tissue mechanics in such chronic situations not only regulates the physio-psychological well-being of the patient, but also confirms the level of comfort and post-operative clinical outcomes. Numerous uniaxial and multiaxial tensile experiments on healthy and affected samples have evidenced significant differences in tissue mechanical behavior and strong colorectal anisotropy across each layer in thickness direction and along the length. Furthermore, this study reviewed various forms of passive constitutive models for the highly fibrous colorectal tissue ranging from the simplest linearly elastic and the conventional isotropic hyperelastic to the most sophisticated second harmonic generation image based anisotropic mathematical formulation. Under large deformation, the isotropic description of tissue mechanics is unequivocally ineffective which demands a microstructural based tissue definition. Therefore, the information collected in this review paper would present the current state-of-the-art in colorectal biomechanics and profoundly serve as updated computational resources to develop a sophisticated characterization of colorectal tissues.

Toward Mechanochromic Soft Material-Based Visual Feedback for Electronics-Free Surgical Effectors

A chromogenically reversible, mechanochromic pressure sensor is integrated into a mininvasive surgical grasper compatible with the da Vinci robotic surgical system. The sensorized effector, also featuring two soft-material jaws, encompasses a mechanochromic polymeric inset doped with functionalized spiropyran (SP) molecule, designed to activate mechanochromism at a chosen pressure and providing a reversible color change. Considering such tools are systematically in the visual field of the operator during surgery, color change of the mechanochromic effector can help avoid tissue damage. No electronics is required to control the devised visual feedback. SP-doping of polydimethylsiloxane (2.5:1 prepolymer/curing agent weight ratio) permits to modulate the mechanochromic activation pressure, with lower values around 1.17 MPa for a 2% wt. SP concentration, leading to a shorter chromogenic recovery time of 150 s at room temperature (25 °C) under green light illumination. Nearly three-times shorter recovery time is observed at body temperature (37 °C). To the best of knowledge, this study provides the first demonstration of mechanochromic materials in surgery, in particular to sensorize unpowered surgical effectors, by avoiding dramatic increases in tool complexity due to additional electronics, thus fostering their application. The proposed sensing strategy can be extended to further tools and scopes.

Design Optimization of a Novel Multifiring Clip Applicator System for Endoscopic Closure of Large Perforations

Endoscopic closure has become the first choice for closing iatrogenic perforations. Previously, we reported a self-developed endoscopic multifiring clip applicator (EMFCA) system. In this paper, a new EMFCA system for endoscopic closure of large perforations with a redesigned clip, the less traumatic grasper, and a highly efficient driving system was presented, and its efficacy was evaluated. The behaviors of the new clip and grasper were verified through finite element analysis (FEA). The capability of pushing transmission for the EMFCA system was identified by the proposed model and the validation experiment. Ex-vivo studies were conducted on porcine stomachs to compare the outcomes of the closures. The FEA results showed that the deformation of the clip was safe and smoother, with a maximum stress of 640.0 MPa. The less traumatic grasper could increase the grasping force and avoid trauma by exerting uniform stress along the axis. The capability of pushing transmission was enhanced by the double-nested tendon-sheath actuation system with an efficiency of 0.45–0.48. The mechanical strength, the leakage pressure, and the operating time for the closures with the new EMFCA system and the previous EMFCA system were 6.1 N ± 0.8 N, 37.1 mmHg ± 6.8 mmHg, 7.3 min ± 0.4 min and 5.1 N ± 1.0 N, 27.4 mmHg ± 6.4 mmHg, 11.4 min ±0.8 min, respectively. The new EMFCA system can realize a superior, reliable, and high-efficiency endoscopic closure of large perforations.

Effect of Suture Type and Suture Distance on Holding Strength in Nasal Septal Laceration Model

Objective:

Septal mucosal-perichondrial flaps can be lacerated during the elevation of the flaps. Appropriate repair of the lacerations is essential to prevent the development of septal perforation during the healing process. We aimed to determine the superior suture type and suture distance to use in repairing the lacerations of nasal septal mucosal-perichondrial flaps.

Methods:

The study used 128 nasal septal mucosal-perichondrial flaps prepared from sheep heads. Experimentally induced lacerations on the mucosal-perichondrial flaps were sutured with two interrupted sutures using one of four suture materials (4-0/5-0 Polyglactin 910, 4-0/5-0 Polydioxanone) and leaving either 5 mm or 10 mm distance between the sutures. Maximum tissue holding strength (HS_max) was measured for each suture material and suture distance used.

Results:

Mean HS_max values were higher for Polyglactin 910 sutures (p<0.001) and 10 mm suture distance (p=0.008) when the groups were compared in terms of suture material and suture distance, respectively. There was no statistically significant difference between the mean HS_max values of sutures with 4-0 and 5-0 diameters (p=0.057).

Conclusion:

Polyglactin 910 suture material with 10 mm space between two adjacent sutures may be more durable than the other suture materials when repairing nasal septal mucosal lacerations.

Evaluations on laser ablation of ex vivo porcine stomach tissue for development of Ho:YAG-assisted endoscopic submucosal dissection (ESD)

Endoscopic submucosal dissection (ESD) is clinically used to remove early gastric cancer in stomach. The aim of the current study is to examine a therapeutic capacity of pulsed Ho:YAG laser for the development of laser-assisted ESD under various surgical parameters. Ex vivo porcine stomach tissue was ablated with 1-J Ho:YAG pulses at 10 Hz at different number of treatments (NT = 1, 2, and 3) and treatment speeds (TS = 0.5, 1, and 2 mm/s) without and with saline injection. Regardless of saline injection, straight tissue ablation showed that ablation depth increased with increasing NT and decreasing TS. At NT = 3 and TS = 0.5 mm/s, no saline injection yielded the maximum ablation depth (3.4 ± 0.3 mm), partially removing muscularis propria. However, saline injection confined the tissue ablation within a submucosal layer (2.1 ± 0.3 mm). Thermal injury was found to be 0.7~1.1 mm in the adjacent tissue with superficial carbonization. Circular tissue ablation (2 cm in diameter) at NT = 3 and TS = 0.5 mm/s presented that no saline injection yielded a reduction in the lesion area, whereas saline injection maintained the ablated lesion area. Histological analysis revealed that unlike no saline injection, saline injection ablated the entire mucosal layer without perforation in the muscular propria. The pulsed Ho:YAG laser can be a potential surgical tool for clinical ESD to incise a target lesion without adverse perforation. Further investigations will validate the efficacy and safety of the Ho:YAG laser-assisted ESD in in vivo porcine stomach models for clinical translation.

Multimodal Ultrasound Including Virtual Touch Imaging Quantification for Differentiating Cervical Lymph Nodes

Defining the entity of cervical lymph nodes (LNs) is essential for the diagnosis and staging of head and neck malignancies. Virtual Touch imaging quantification (VTIQ) is a relatively new method of elastography that measures tissue stiffness quantitatively. A prospective study was conducted that included 108 patients (57 benign and 51 metastatic lymph nodes [MLNs]). Shear wave velocities (SWVs) were analyzed using VTIQ and were compared with the histopathological results. Both maximum and minimum SWVs within the LNs significantly differed between benign masses and MLNs (p < 0.001). Percentage areas of the node with SWVs >6 m/s and <3.5 m/s differed significantly (p < 0.001). Intralesional areas with SWVs ≤3.5 m/s of 0-29% (odds ratio: 93.7) and 30%-69% (odds ratio: 46.3) were predictive of malignant LNs as well as ill-defined tumor (odds ratio: 5.2). VTIQ can provide more information on the entity of cervical LNs.

Biomechanical properties of abdominal organs under tension with special reference to increasing strain rate

Currently, abdominal finite element models overlook the organs such as gallbladder, bladder, and intestines, which instead are modeled as a simple bag that is not included in the analysis. Further characterization of the material properties is required for researchers to include these organs into models. This study characterized the mechanical properties of human and porcine gallbladder, bladder, and intestines using uniaxial tension loading from the rates of 25%/s to 500%/s. Small differences were observed between human and porcine gallbladder elastic modulus, failure stress, and failure strain. Strain rate was determined to be a significant factor for predicting porcine gallbladder elastic modulus and failure stress which were found to be 9.03 MPa and 1.83 MPa at 500%/s. Human bladder was observed to be slightly stiffer with a slightly lower failure stress than porcine specimens. Both hosts, however, demonstrated a strain rate dependency with the elastic modulus and failure stress increasing as the rate increased with the highest elastic modulus (2.16 MPa) and failure stress (0.65 MPa) occurring at 500%/s. Both human and porcine intestines were observed to be affected by the strain rate. Failure stress was found to be 1.6 MPa and 1.42 MPa at 500%/s for the human and porcine intestines respectively. For all properties found to be strain rate dependent, a numerical model was created to quantify the impact. These results will enable researchers to create more detailed finite element models that include the gallbladder, bladder, and intestines.

On a coupled electro-chemomechanical model of gastric smooth muscle contraction

The stomach is a central organ in the gastrointestinal tract that performs a variety of functions, in which the spatio-temporal organisation of active smooth muscle contraction in the stomach wall (SW) is highly regulated. In the present study, a three-dimensional model of the gastric smooth muscle contraction is presented, including the mechanical contribution of the mucosal and muscular layer of the SW. Layer-specific and direction-dependent model parameters for the active and passive stress-stretch characteristics of the SW were determined experimentally using porcine smooth muscle strips. The electrical activation of the smooth muscle cells (SMC) due to the pacemaker activity of the interstitial cells of Cajal (ICC) is modelled by using FitzHugh-Nagumo-type equations, which simulate the typical ICC and SMC slow wave behaviour. The calcium dynamic in the SMC depends on the SMC membrane potential via a gaussian function, while the chemo-mechanical coupling in the SMC is modelled via an extended Hai-Murphy model. This cascade is coupled with an additional mechano-electrical feedback-mechanism, taking into account the mechanical response of the ICC and SMC due to stretch of the SW. In this way the relaxation responses of the fundus to accommodate incoming food, as well as the typical peristaltic contraction waves in the antrum for mixing and transport of the chyme, have been well replicated in simulations performed at the whole organ level. STATEMENT OF SIGNIFICANCE: In this article, a novel three-dimensional electro-chemomechanical model of the gastric smooth muscle contraction is presented. The propagating waves of electrical membrane potential in the network ofinterstitial cells of Cajal (ICC) and smooth muscle cells (SMC) lead to a global pattern of change in the calciumdynamics inside the SMC. Taking additionally into account the mechanical response of the ICC and SMC due to stretch of the stomach wall, also referred to as mechanical feedback-mechanism, the result is a complex spatio-temporal regulation of the active contraction and relaxation of the gastric smooth muscle tissue. Being a firstapproach, in future view such a three-dimensional model can give an insight into the complexload transferring system of the stomach wall, as well as into the electro-chemomechanicalcoupling process underlying smooth muscle contraction in health and disease.

The differences in measured prostate material properties between probing and unconfined compression testing methods

Characterization of the mechanical properties of organs is important for determining their behavior under load and understanding and predicting their response. In order to appropriately understand behavior, including developing predictive models, the method used to measure the properties should match the application as different testing techniques can yield different results. One of the organs where little mechanical testing has been performed is the prostate. Therefore, the goal of this paper is to expand the knowledge of prostate gland mechanical behavior by using two different compressive testing methods under various loading rates. No differences were found between the elastic modulus measured using the compression and probing protocols for both human and porcine specimens. The elastic modulus ranged from 0.08 MPa at 1%/s to 0.24 MPa at 25%/s for human specimens and from 0.2 MPa at 1%/s to 0.4 MPa at 25%/s for porcine specimens. A strain rate dependency of the elastic modulus was observed for both testing methods. The dependency on strain rate started to saturate at higher rates and a material model was created to quantify this dependence as well as the stress-strain behavior. No strain rate dependency was observed for failure stress or failure strain. Overall, similar values of elastic modulus were found for both probing and compression protocols and the relationship developed between elastic modulus and strain rate could be implemented in models of the prostate gland to aid in understanding the response to dynamic loads.

Nonlinear viscoelastic constitutive model for bovine liver tissue

Soft tissue mechanical characterisation is important in many areas of medical research. Examples span from surgery training, device design and testing, sudden injury and disease diagnosis. The liver is of particular interest, as it is the most commonly injured organ in frontal and side motor vehicle crashes, and also assessed for inflammation and fibrosis in chronic liver diseases. Hence, an extensive rheological characterisation of liver tissue would contribute to advancements in these areas, which are dependent upon underlying biomechanical models. The aim of this paper is to define a liver constitutive equation that is able to characterise the nonlinear viscoelastic behaviour of liver tissue under a range of deformations and frequencies. The tissue response to large amplitude oscillatory shear (1–50%) under varying preloads (1–20%) and frequencies (0.5–2 Hz) is modelled using viscoelastic-adapted forms of the Mooney–Rivlin, Ogden and exponential models. These models are fit to the data using classical or modified objective norms. The results show that all three models are suitable for capturing the initial nonlinear regime, with the latter two being capable of capturing, simultaneously, the whole deformation range tested. The work presented here provides a comprehensive analysis across several material models and norms, leading to an identifiable constitutive equation that describes the nonlinear viscoelastic behaviour of the liver.

Reliability of shear wave elastography ultrasound to assess the supraspinatus tendon: An intra and inter-rater in vivo study

INTRODUCTION

Shear wave elastography ultrasound is a relatively new technique that evaluates the tissue elasticity by applying an acoustic radiation force impulse. It is undetermined how reliable this modality is in assessing rotator cuff tendons. The aim of this study, therefore, was to evaluate the reliability of shear wave elastography ultrasound to assess the stiffness of normal and tendinopathic supraspinatus tendons.

METHODS

An inter- and intra-rater reliability trial was carried out using shear wave elastography to assess the supraspinatus tendon at its distal insertion, by measuring shear wave velocity and elasticity. Twenty participants with a mean age of 37 (21-69) years old were evaluated. Ten subjects with normal supraspinatus tendon and 10 subjects with tendinopathic tendon were selected. The Virtual Touch Imaging Quantification program was used to generate the acoustic radiation force impulse and to obtain the elastography data. Three raters with different experience in conventional ultrasound were used for the inter-rater trial in normal tendons and the most experienced rater examined all subjects for the intra-rater reliability evaluation. Each rater obtained three readings in three different examinations per subject over a one-week period.

RESULTS

The mean (±SEM) shear wave velocity for the normal supraspinatus tendon was 9.96 ± 0.02 m/s (=297 kPa), while in the tendinopathic supraspinatus tendon was 8.3 ± 0.2 m/s (=207 kPa) (p < 0.001). The intra-rater trial agreement was excellent, with an intraclass correlation coefficient = 0.96. In the inter-rater testing, the mean shear wave velocity in normal tendons was 9.90 ± 0.07 m/s (=294 kPa), with intraclass correlation coefficient = 0.45.

CONCLUSION

Shear wave elastography ultrasound was able to show that tendinopathic tendons were less stiff than normal tendons. It was a reliable imaging technique to assess the supraspinatus tendon, especially when used by a single experienced musculoskeletal sonographer.

Biomechanical and microstructural characterisation of the porcine stomach wall: Location- and layer-dependent investigations

The mechanical properties of the stomach wall help to explain its function of storing, mixing, and emptying in health and disease. However, much remains unknown about its mechanical properties, especially regarding regional heterogeneities and wall microstructure. Consequently, the present study aimed to assess regional differences in the mechanical properties and microstructure of the stomach wall. In general, the stomach wall and the different tissue layers exhibited a nonlinear stress-stretch relationship. Regional differences were found in the mechanical response and the microstructure. The highest stresses of the entire stomach wall in longitudinal direction were found in the corpus (201.5 kPa), where food is ground followed by the antrum (73.1 kPa) and the fundus (26.6 kPa). In contrast, the maximum stresses in circumferential direction were 39.7 kPa, 26.2 kPa, and 15.7 kPa for the antrum, fundus, and corpus, respectively. Independent of the fibre orientation and with respect to the biaxial loading direction, partially clear anisotropic responses were detected in the intact wall and the muscular layer. In contrast, the innermost mucosal layer featured isotropic mechanical characteristics. Pronounced layers of circumferential and longitudinal muscle fibres were found in the fundus only, whereas corpus and antrum contained almost exclusively circumferential orientated muscle fibres. This specific stomach structure mirrors functional differences in the fundus as well as corpus and antrum. Within this study, the load transfer mechanisms, connected with these wavy layers but also in total with the stomach wall's microstructure, are discussed. STATEMENT OF SIGNIFICANCE: This article examines for the first time the layer-specific mechanical and histological properties of the stomach wall attending to the location of the sample. Moreover, both mechanical behaviour and microstructure were explicitly match identifying the heterogeneous characteristics of the stomach. On the one hand, the results of this study contribute to the understanding of stomach mechanics and thus to their functional understanding of stomach motility. On the other hand, they are relevant to the fields of constitutive formulation of stomach tissue, whole stomach mechanics, and stomach-derived scaffolds i.e., tissue-engineering grafts.

Defining the Relationship Between Compressive Stress and Tissue Trauma During Laparoscopic Surgery Using Human Large Intestine

Excessive magnitudes of compressive stress exerted on gastrointestinal tissues can lead to pathological scar tissue or adhesion formation, bleeding, inflammation or even death from bowel perforation and sepsis. It is currently unknown however, at exactly what magnitude of compressive stress that these pathologies occur. A novel simple compressive device was engineered to provide an objective means of producing discrete compressive stresses on human tissues. Samples of human large intestine (colon) were removed from consenting patients as a part of their standard surgical procedure. These samples were compressed with a range of loads normally produced by standard laparoscopic graspers in representative abdominal surgeries. After compression, specimens were processed for histological analysis and assessed. The two independent pathologists who were blinded to stress magnitudes were both able to quantify increasing tissue damage that corresponded to increasing amounts of compressive force. A threshold between 350–450 kPa was discovered that corresponded to both significant serosal thickness change and a positive histological trauma score rating. Whether the tissue injury quantified is pathologic is subject for future in-vivo longitudinal investigation but certainly based on literature, can be the basis of pathological adhesion formation or an area for hemorrhage and scar formation.

Constitutive law of healthy gallbladder walls in passive state with damage effect

Biomechanical properties of human gallbladder (GB) wall in passive state can be valuable to diagnosis of GB diseases. In the article, an approach for identifying damage effect in GB walls during uniaxial tensile test was proposed and a strain energy function with the damage effect was devised as a constitutive law phenomenologically. Scalar damage variables were introduced respectively into the matrix and two families of fibres to assess the damage degree in GB walls. The parameters in the constitutive law with the damage effect were determined with a custom MATLAB code based on two sets of existing uniaxial tensile test data on human and porcine GB walls in passive state. It turned out that the uniaxial tensile test data for GB walls could not be fitted properly by using the existing strain energy function without the damage effect, but could be done by means of the proposed strain energy function with the damage effect involved. The stresses and Young moduli developed in two families of fibres were more than thousands higher than the stresses and Young's moduli in the matrix. According to the damage variables estimated, the damage effect occurred in two families of fibres only. Once the damage occurs, the value of the strain energy function will decrease. The proposed constitutive laws are meaningful for finite element analysis on human GB walls.

Mechanical effects of load speed on the human colon

The aim of this study was to examine the mechanical behavior of the colon using tensile tests under different loading speeds. Specimens were taken from different locations of the colonic frame from refrigerated cadavers. The specimens were submitted to uniaxial tensile tests after preconditioning using a dynamic load (1 m/s), intermediate load (10 cm/s), and quasi-static load (1 cm/s). A total of 336 specimens taken from 28 colons were tested. The stress-strain analysis for longitudinal specimens indicated a Young's modulus of 3.17 ± 2.05 MPa under dynamic loading (1 m/s), 1.74 ± 1.15 MPa under intermediate loading (10 cm/s), and 1.76 ± 1.21 MPa under quasi-static loading (1 cm/s) with p < 0.001. For the circumferential specimen, the stress-strain curves indicated a Young's modulus of 3.15 ± 1.73 MPa under dynamic loading (1 m/s), 2.14 ± 1.3 MPa under intermediate loading (10 cm/s), and 0.63 ± 1.25 MPa under quasi-static loading (1 cm/s) with p < 0.001. The curves reveal two types of behaviors of the colon: fast break behavior at high speed traction (1 m/s) and a lower break behavior for lower speeds (10 cm/s and 1 cm/s). The circumferential orientation required greater levels of stress and strain to obtain lesions than the longitudinal orientation. The presence of taeniae coli changed the mechanical response during low-speed loading. Colonic mechanical behavior varies with loading speeds with two different types of mechanical behavior: more fragile behavior under dynamic load and more elastic behavior for quasi-static load.

T-Cell Mechanobiology: Force Sensation, Potentiation, and Translation

A T cell is a sensitive self-referential mechanical sensor. Mechanical forces influence the recognition, activation, differentiation, and function throughout the lifetime of a T cell. T cells constantly perceive and respond to physical stimuli through their surface receptors, cytoskeleton, and subcellular structures. Surface receptors receive physical cues in the form of forces generated through receptor-ligand binding events, which are dynamically regulated by contact tension, shear stress, and substrate rigidity. The resulting mechanotransduction not only influences T-cell recognition and signaling but also possibly modulates cell metabolism and gene expression. Moreover, forces also dynamically regulate the deformation, organization, and translocation of cytoskeleton and subcellular structures, leading to changes in T-cell mobility, migration, and infiltration. However, the roles and mechanisms of how mechanical forces modulate T-cell recognition, signaling, metabolism, and gene expression, are largely unknown and underappreciated. Here, we review recent technological and scientific advances in T-cell mechanobiology, discuss possible roles and mechanisms of T-cell mechanotransduction, and propose new research directions of this emerging field in health and disease.

Mechanical behaviors of tension and relaxation of tongue and soft palate: Experimental and analytical modeling

This study is to characterize mechanical properties of uniaxial tension and stress relaxation responses of muscle tissues of tongue and soft palate. Uniaxial tension test and stress relaxation test on 39 fresh tissue samples from four five-month-old boars (65 ± 15 kg) are conducted. Firstly, the rationality of the samples' dimension design and experimenal data measurement is validated by one-way ANOVA F-type test. Mechanical properties, including stress-strain relationship and stress relaxation characteristic, are then investigated in details to show the nonlinear behaviors of the tissue samples clearly. Finally, a constitutive model of representing the mechanical properties is formulated within the nonlinear integral representation framework proposed by Pinkin and Rogers, and corresponding material parameters are fitted to the experimental data based on the Levenberg-Marquardt minimization algorithm. The results of the fitting comparison prove that the formulated constitutive model can capture the observed nonlinear behaviors of the muscle tissue samples in both the axial tension and stress relaxation experiments.

Evaluation of the Safety and Efficacy of Soft Tissue Augmentation With a Compressive-Resistant Collagen Matrix in a Nonhuman Primate Model

PURPOSE

The purpose of the present study was to evaluate the safety and efficacy of the compression-resistant collagen-based cross-linked matrix for augmentation of maxillary and mandibular soft tissue defects in an animal model.

MATERIALS AND METHODS

Six rhesus macaque monkeys were subjected to soft tissue grafting in 4 sites intraorally; the anterior maxilla was subjected to hard and soft tissue grafting with implant placement. Each site was randomly assigned 1 of 3 treatments: a compressive-resistant collagen matrix membrane (CM), a subepithelial connective tissue autograft (SCTG), or sham treatment, in which a partial-thickness flap was elevated and then sutured closed with no further treatment (control). The following methods were used for data collection: in vivo evaluation by periodontal probing, ultrasound, shear modulus elasticity, polyether impressions for volumetric analysis, and in vitro analysis by histologic biopsy examinations. In vitro analysis provided by histologic measurements and evaluations was performed on nondecalcified sections. The follow-up period was 6 months.

RESULTS

The SCTG and CM showed favorable tissue integration. No adverse reaction to or deviation from the normal healing processes was detected. The CM integrated well in all sites, with a variable range of soft tissue volume increases. Volumetric discrepancies were appreciated in the histologic analyses and differences were found when the CM and SCTG were applied in the anterior maxilla in combination with hard tissue grafting and implant placement. Histologic evaluation showed favorable integration, no immunogenic response to the CM, and stable volumetric retention in autograft and CM sites during the experimental period.

CONCLUSION

The compressive-resistant CM could be a safe and efficacious alternative for soft tissue augmentation by obviating a donor site and the consequent morbidity. Although a similar performance between the CM and SCTG was observed, further studies will be necessary to estimate the clinical potentiality and describe the limits of the technique.

Effects of precompression time and strength on the physical characteristics of quasi-stapled porcine small intestinal tissue

Precompression is vital when performing gastrointestinal anastomosis with staplers. However, research on the internal changes in intestinal tissue under stapling is lacking, and the effects of precompression have not been clarified. In this study, a stapler was modified, and the multifrequency bioimpedance of porcine small intestinal tissue was measured from before clamping the tissue with the stapler until the release of the tissue after precompression without firing. The Cole _Y model was fitted to the bioimpedance, and the changes in the tissue were analyzed using the model parameters: G₀, extracellular fluid conductance, and Δ G, intracellular fluid conductance. The results show that the changes of G₀ and Δ G could be divided into four stages: rapid decrease, slow decrease, intense resilience, and slow recovery. During slow decrease stage, there was a greater decrease of G₀ and Δ G (1.02E-05 ± 1.12E-05 S and 1.73E-05 ± 2.12E-05 S in precompression time's increase, 1.68E-05 ± 8.74E-06 S and 1.20E-05 ± 1.09E-05 S in precompression strength's increase). On the contrary, during intense resilience stage, there was a less increase of G₀ and Δ G (0.88E-05 ± 4.86E-05 S and 9.15E-05 ± 9.37E-05 S in precompression time's increase, 2.72E-05 ± 3.53E-05 S and 1.02E-04 ± 8.54E-05 S in precompression strength's increase). In conclusion, the effects of precompression factors on tissue have been preliminary revealed: the tissue under precompression becomes thinner and less resilient. To improve the precompression effects and reduce any excessive pressure exerted on the staples by tissue resilience, the precompression time and strength should be increased appropriately.

Proof of Concept Study: Investigating Force Metrics of an Intracorporeal Suturing Knot Task

BACKGROUND

Mastering proper force manipulation in minimally invasive surgery can take many hours of practice and training. Improper force control can lead to necrosis, infection, and scarring. A force-sensing skin (FSS) has been developed, which measures forces at the distal end of minimal access surgeries' (MAS) instruments without altering the instrument's structural integrity or the surgical workflow, and acts as a minimally disruptive add-on to any MAS instrument.

METHODS

A proof of concept study was conducted using a FSS-equipped 5 mm straight-tip needle holder. Participants (n = 19: 3 novices, 11 fellows, and 5 staff surgeons) performed one intracorporeal suturing knot task (ISKT). Using participant task video footage, each participant's two puncture forces (each wall of the Penrose drain) and three knot tightening forces were measured. Force metrics from the three expertise groups were compared using analysis of variance (ANOVA) and Tukey's honest significance test with statistical significance assessed at P < .05.

RESULTS

Preliminary ISKT force metric data showed differences between novices and more experienced fellows and surgeons. Of the five stages of the ISKT evaluated, the first puncture force of the Penrose drain seemed to best reflect the difference in skill among participants. The study demonstrated ISKT knot tightening and puncture force ranges across three expertise levels (novices, surgical fellows, and staff surgeons) of 0.586 to 6.089 newtons (N) and 0.852 to 2.915 N, respectively.

CONCLUSION

The investigation of force metrics is important for the implementation of future force feedback systems as it can provide real-time information to surgeons in training and the operating theater.

Holding Strength of Suture: An Experimental Study Using Porcine Kidney

Background and Objectives:

The search for the perfect suture is going on and has resulted in the introduction of many different suture types into the market. The purpose of this study is to investigate the holding strength (HS) of different sutures in the renal parenchyma in an experimental study on pig kidneys.

Methods:

The HS that caused sliding of the suture was investigated in 5 adult porcine kidneys with 7 suture variants. HS-caused tearing of the kidney was investigated with 3 suture types on 5 kidneys. The third investigation, performed on 5 porcine kidneys, was a comparison between 2-0 Vicryl sutures with a Hem-o-lok clip and 2-0 V-Loc sutures with 1 knot. The Friedman test was used to compare the groups. Post hoc analysis was performed with the Wilcoxon signed ranks test (Bonferroni corrected).

Results:

For HS causing sliding of the suture, the mean HSs of the tested sutures were as follows: 2-0 Vicryl with 1 Hem-o-lok clip, 3.26 ± 0.55 N; 2-0 Vicryl with 2 Hem-o-lok clips, 4.1 ± 0.46 N; 2-0 V-Loc, 2.52 ± 0.63 N; 4-0 V-Loc, 1.62 ± 0.17 N; 0 Quill, 0.48 ± 0.16 N; 2-0 Vicryl with 1 Hem-o-lok clip (halfway), 3.62 ± 0.66 N; and 2-0 V-Loc (halfway), 1.02 ± 0.40 N. For HS causing tearing of the kidney, the mean value of 2-way 2-0 Vicryl (Hem-o-lok in the middle) was 13.28 ± 1.38 N, 2-0 2-way Vicryl (Hem-o-lok at the end) was 5.86 ± 0.75 N, and 2-way 2-0 V-Loc was 3.98 ± 1.60 N. For the third group, the difference between the 2 suture variants was not statistically significant.

Conclusion:

Our study revealed that 2-0 Vicryl (polyglactin 910) sutures with 2 Hem-o-lok clips had the maximum HS in renal parenchyma when compared with other sutures.

In Vivo Measurement of Surface Pressures and Retraction Distances Applied on Abdominal Organs During Surgery

This study undertook the in vivo measurement of surface pressures applied by the fingers of the surgeon during typical representative retraction movements of key human abdominal organs during both open and hand-assisted laparoscopic surgery. Surface pressures were measured using a flexible thin-film pressure sensor for 35 typical liver retractions to access the gall bladder, 36 bowel retractions, 9 kidney retractions, 8 stomach retractions, and 5 spleen retractions across 12 patients undergoing open and laparoscopic abdominal surgery. The maximum and root mean square surface pressures were calculated for each organ retraction. The maximum surface pressures applied to these key abdominal organs are in the range 1 to 41 kPa, and the average maximum surface pressure for all organs and procedures was 14 ± 3 kPa. Surface pressure relaxation during the retraction hold period was observed. Generally, the surface pressures are higher, and the rate of surface pressure relaxation is lower, in the more confined hand-assisted laparoscopic procedures than in open surgery. Combined video footage and pressure sensor data for retraction of the liver in open surgery enabled correlation of organ retraction distance with surface pressure application. The data provide a platform to design strategies for the prevention of retraction injuries. They also form a basis for the design of next-generation organ retraction and space creation surgical devices with embedded sensors that can further quantify intraoperative retraction forces to reduce injury or trauma to organs and surrounding tissues.

Novel force-sensing system for minimally invasive surgical instruments

Mastering proper force manipulation in minimally invasive surgery can take many years. Improper force control can lead to necrosis, infection, and scarring. This paper describes a novel system to measure, log, and display external forces at the distal end of minimally invasive surgical instruments in real-time. The system, comprising of a Force- Sensing Sleeve, Bluetooth electronics module, and an Android mobile application. A sensorized 5 mm minimally invasive surgical needle holder was evaluated for bending force accuracy, linearity, and repeatability in six directions. The results showed that the system responded linearly to forces at the tool-tip independent of direction with an RMS error of 0.088 N. Repeatability was affected by system noise potentially arising from temperature drift and thermal noise. Future work will include characterization of communication performance for force feedback in surgical training and assessment.

Characterization of the mechanical properties of resected porcine organ tissue using optical fiber photoelastic polarimetry

Characterizing the mechanical behavior of living tissue presents an interesting challenge because the elasticity varies by eight orders of magnitude, from 50Pa to 5GPa. In the present work, a non-destructive optical fiber photoelastic polarimetry system is used to analyze the mechanical properties of resected samples from porcine liver, kidney, and pancreas. Using a quasi-linear viscoelastic fit, the elastic modulus values of the different organ systems are determined. They are in agreement with previous work. In addition, a histological assessment of compressed and uncompressed tissues confirms that the tissue is not damaged during testing.

Experimental characterization of the biaxial mechanical properties of porcine gastric tissue

Health problems related to the stomach are among the most important sources of morbidity in industrialized countries. There is evidence that mechanics may play an important role in various such pathologies. However, so far experimental data characterizing the mechanical properties of gastric tissue remain scarce, which significantly limits our understanding of the mechanics of the stomach. To help close this gap, we performed biaxial mechanical tests of porcine gastric tissue patches. Our experiments reveal a considerable anisotropy and different mechanical properties in the three major regions of the stomach (fundus, corpus, antrum). Moreover, they demonstrate that the mechanical properties of the gastric wall and the physiological function of the different regions of the stomach are closely related. This finding suggests that further examination of the mechanics of the gastric wall may indeed be a promising avenue of research towards a better understanding of the organic causes of frequent health problems related to the stomach.

Alterations in biomechanical properties and microstructure of colon wall in early-stage experimental colitis

The aim of the current study was to investigate the effects of early-stage dextran sodium sulfate (DSS)-induced mouse colitis on the biomechanical properties and microstructure of colon walls. In the present study, colitis was induced in 8-week-old mice by the oral administration of DSS, and then 10 control and 10 experimental colitis samples were harvested. Uniaxial tensile tests were performed to measure the ultimate tensile strength and ultimate stretches of colon tissues. In addition, histological investigations were performed to characterize changes in the microstructure of the colon wall following treatment. The results revealed that the ultimate tensile stresses were 232±33 and 183±25 kPa for the control and DSS groups, respectively (P=0.001). Ultimate stretches at rupture for the control and DSS groups were 1.43±0.04 and 1.51±0.06, respectively (P=0.006). However, there was no statistically significant difference in tissue stiffness between the two groups. Histological analysis demonstrated high numbers of inflammatory cells infiltrated into the stroma in the DSS group, leading to significant submucosa edema. Hyperplasia was also identified in the DSS-treated submucosa, causing a disorganized microstructure within the colon wall. Furthermore, a large number of collagen fibers in the DSS-treated muscular layer were disrupted, and fiber bundles were thinner when compared with the control group. In conclusion, early-stage experimental colitis alters the mechanical properties and microstructural characteristics of the colon walls, further contributing to tissue remodeling in the pathological process.

Infant Robotic Cleft Palate Surgery: A Feasibility Assessment Using a Realistic Cleft Palate Simulator

BACKGROUND

A surgical robot offers enhanced precision, visualization, and access and the potential to improve outcomes in cleft palate surgery. The goal of this study was to investigate the feasibility of using the da Vinci robot for cleft palate repair in infants using a cleft palate simulator test bed.

METHODS

A high-fidelity cleft palate simulator was developed that allows performance of a robotic cleft palate repair procedure. A complete cleft palate repair was performed with the da Vinci Si with 5-mm instruments and the da Vinci Xi with 8-mm instruments. The advantages of the robotic approach were assessed in comparison with using standard instruments. For each system, arm repositioning, collisions, instrument and endoscope excursion, wrist orientation, and vision were compared for 12 steps of the repair.

RESULTS

The cleft palate simulator provided a reproducible platform for testing robotic cleft palate surgery. The advantages of the robotic approach were the ability to articulate a miniature wrist intraorally with superior visualization, increased ambidexterity, and improved ergonomics compared with using standard instruments. Cleft palate repair with the Xi was superior to the Si with respect to arm repositioning, instrument collisions and excursion, and wrist orientation. However, Xi performance remained suboptimal because of the larger instruments.

CONCLUSIONS

Robotic cleft palate repair using the da Vinci system offers advantages compared with the traditional approach. Cleft palate repair is more feasible with the Xi and 8-mm instruments. However, performance is limited by the instrumentation, which requires modification to ensure safety and efficacy.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, V.

Grasper having tactile sensing function using acoustic reflection for laparoscopic surgery

PURPOSE

In current minimally invasive surgery techniques, the tactile information available to the surgeon is limited. Improving tactile sensation could enhance the operability of surgical instruments. Considering surgical applications, requirements such as having electrical safety, a simple structure, and sterilization capability should be considered. The current study sought to develop a grasper that can measure grasping force at the tip, based on a previously proposed tactile sensing method using acoustic reflection. This method can satisfy the requirements for surgical applications because it has no electrical element within the part that is inserted into the patient's body.

METHODS

We integrated our acoustic tactile sensing method into a conventional grasping forceps instrument. We designed the instrument so that acoustic cavities within a grasping arm and a fork sleeve were connected by a small cavity in a pivoting joint. In this design, when the angle between the two grasping arms changes during grasping, the total length and local curvature of the acoustic cavity remain unchanged. Thus, the grasping force can be measured regardless of the orientation of the grasping arm.

RESULTS

We developed a prototype sensorized grasper based on our proposed design. Fundamental tests revealed that sensor output increased with increasing contact force applied to the grasping arm, and the angle of the grasping arm did not significantly affect the sensor output. Moreover, the results of a grasping test, in which objects with different softness characteristics were held by the grasper, revealed that the grasping force could be appropriately adjusted to handle different objects on the basis of sensor output.

CONCLUSIONS

Experimental results demonstrated that the prototype grasper can measure grasping force, enabling safe and stable grasping.