Mechanical characterisation of porcine non-intestinal colorectal tissues for innovation in surgical instrument design

Assessment of Urostomy Parastomal Herniation Forces Using Incisional Prevention Strategies with an Abdominal Fascia Model

Background

Approximately 10 000 patients undergo cystectomy/ileal conduit annually in the USA, of whom over 70% subsequently develop a parastomal hernia (PSH). Still, no well-established "best" practice for stoma creation to prevent a PSH exists.

Objective

To measure the relationship between incision size/type/material and axial tension force (ATF) as a surrogate for herniation force, using several models to mimic abdominal fascia.

Design setting and participants

Abdominal fascia models included silicone membrane, ex vivo porcine, and embalmed human cadaveric fascia. A dynamometer pulled a Foley catheter (20 mm/min) with the balloon inflated to 125% incision (linear, cruciate, and circular) diameter using a motorized positioning system. The maximum ATF before herniation was recorded. The study was repeated in unused silicone/tissue for suture reinforcement. We evaluated silicone, ex vivo porcine, and human abdominal fascia.

Intervention

Incision sizes (1-3 cm) in 0.5-cm increments were evaluated in silicone. A 3-cm incision was used in porcine/human tissue.

Outcome measurements and statistical analysis

ATF for herniation was recorded/compared across incision types/sizes using Mann-Whitney U and Kruskal-Wallis tests as appropriate, with α = 0.05.

Results and limitations

Linear incision ATF was significantly greater than cruciate and circular incisions. A cruciate incision had significantly greater ATF than a circular incision. In cadaveric tissue, incisions were significantly greater for linear (34.5 ± 12.8 N) versus cruciate (15.3 ± 2.9 N, p = 0.004) and for cruciate versus circular (p = 0.023) incisions. Results were similar in ex vivo porcine fascia and silicone. Reinforcement with a suture significantly increased ATF in all materials/incision sizes/types. The ex vivo nature is this study's main limitation.

Conclusions

This study suggests that urostomy fascial incision type may influence ATF required for herniation. Linear incisions may be preferable. Urostomy reinforcement may significantly increase ATF required for a PSH. These data may help establish best practices for PSH risk reduction.

Patient summary

The results of this study illustrate that urostomy fascia incision type may influence the force required to create a parastomal hernia. Linear incisions may be preferable.

Estimation of boundary conditions for patient-specific liver simulation during augmented surgery

PURPOSE

Augmented reality can improve the outcome of hepatic surgeries, assuming an accurate liver model is available to estimate the position of internal structures. While researchers have proposed patient-specific liver simulations, very few have addressed the question of boundary conditions. Resulting mainly from ligaments attached to the liver, they are not visible in preoperative images, yet play a key role in the computation of the deformation.

METHOD

We propose to estimate both the location and stiffness of ligaments by using a combination of a statistical atlas, numerical simulation, and Bayesian inference. Ligaments are modeled as polynomial springs connected to a liver finite element model. They are initialized using an anatomical atlas and stiffness properties taken from the literature. These characteristics are then corrected using a reduced-order unscented Kalman filter based on observations taken from the laparoscopic image stream.

RESULTS

Our approach is evaluated using synthetic data and phantom data. By relying on a simplified representation of the ligaments to speed up computation times, it is not estimating the true characteristics of ligaments. However, results show that our estimation of the boundary conditions still improves the accuracy of the simulation by 75% when compared to typical methods involving Dirichlet boundary conditions.

CONCLUSION

By estimating patient-specific boundary conditions, using tracked liver motion from RGB-D data, our approach significantly improves the accuracy of the liver model. The method inherently handles noisy observations, a substantial feature in the context of augmented reality.

Preparation of Gelatin and Gelatin/Hyaluronic Acid Cryogel Scaffolds for the 3D Culture of Mesothelial Cells and Mesothelium Tissue Regeneration

Mesothelial cells are specific epithelial cells that are lined in the serosal cavity and internal organs. Nonetheless, few studies have explored the possibility to culture mesothelial cells in a three-dimensional (3D) scaffold for tissue engineering applications. Towards this end, we fabricated macroporous scaffolds from gelatin and gelatin/hyaluronic acid (HA) by cryogelation, and elucidated the influence of HA on cryogel properties and the cellular phenotype of mesothelial cells cultured within the 3D scaffolds. The incorporation of HA was found not to significantly change the pore size, porosity, water uptake kinetics, and swelling ratios of the cryogel scaffolds, but led to a faster scaffold degradation in the collagenase solution. Adding 5% HA in the composite cryogels also decreased the ultimate compressive stress (strain) and toughness of the scaffold, but enhanced the elastic modulus. From the in vitro cell culture, rat mesothelial cells showed quantitative cell viability in gelatin (G) and gelatin/HA (GH) cryogels. Nonetheless, mesothelial cells cultured in GH cryogels showed a change in the cell morphology and cytoskeleton arrangement, reduced cell proliferation rate, and downregulation of the mesothelium specific maker gene expression. The production of key mesothelium proteins E-cadherin and calretinin were also reduced in the GH cryogels. Choosing the best G cryogels for in vivo studies, the cell/cryogel construct was used for the transplantation of allograft mesothelial cells for mesothelium reconstruction in rats. A mesothelium layer similar to the native mesothelium tissue could be obtained 21 days post-implantation, based on hematoxylin and eosin (H&E) and immunohistochemical staining.

Adipose-derived stromal cell secreted factors induce the elastogenesis cascade within 3D aortic smooth muscle cell constructs

Objective

Elastogenesis within the medial layer of the aortic wall involves a cascade of events orchestrated primarily by smooth muscle cells, including transcription of elastin and a cadre of elastin chaperone matricellular proteins, deposition and cross-linking of tropoelastin coacervates, and maturation of extracellular matrix fiber structures to form mechanically competent vascular tissue. Elastic fiber disruption is associated with aortic aneurysm; in aneurysmal disease a thin and weakened wall leads to a high risk of rupture if left untreated, and non-surgical treatments for small aortic aneurysms are currently limited. This study analyzed the effect of adipose-derived stromal cell secreted factors on each step of the smooth muscle cell elastogenesis cascade within a three-dimensional fibrin gel culture platform.

Approach and results

We demonstrate that adipose-derived stromal cell secreted factors induce an increase in smooth muscle cell transcription of tropoelastin, fibrillin-1, and chaperone proteins fibulin-5, lysyl oxidase, and lysyl oxidase-like 1, formation of extracellular elastic fibers, insoluble elastin and collagen protein fractions in dynamically-active 30-day constructs, and a mechanically competent matrix after 30 days in culture.

Conclusion

Our results reveal a potential avenue for an elastin-targeted small aortic aneurysm therapeutic, acting as a supplement to the currently employed passive monitoring strategy. Additionally, the elastogenesis analysis workflow explored here could guide future mechanistic studies of elastin formation, which in turn could lead to new non-surgical treatment strategies.

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Stromal cells stimulate smooth muscle cells (SMC) using paracrine signals.

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Stimulated SMC make RNA for both elastin and associated proteins.

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After protein synthesis, new elastic fibers form that contain insoluble elastin.

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Stromal cell products could promote elastin production in vivo.

Development and evaluation of a novel simulation model for transabdominal preperitoneal (TAPP) inguinal hernia repair

BACKGROUND

Transabdominal preperitoneal (TAPP) inguinal hernia repair requires the surgeon to have good manual skills in laparoscopic surgery, as well as an understanding of the laparoscopic features of the groin anatomy. This is why TAPP is considered a more difficult surgical procedure compared to open techniques. Realistic training model for TAPP inguinal hernia repair would enhance surgeons' skills before they enter in the operation room. Our aim was to create a realistic, inexpensive, and easily reproducible model for laparoscopic TAPP inguinal hernia repair and to assess its effectiveness.

METHODS

The applied TAPP inguinal hernia repair training simulator consists of a laparoscopic box and an inguinal region model placed in it. The model of the groin area is made of the porcine stomach and assembling materials. Uniaxial tensile and T-peel tests were performed to compare the mechanical properties of the porcine stomach and the human cadaver peritoneum. Thirty eight surgeons performed TAPP inguinal hernia repair using this model. Their opinions were scored on a five-point Likert scale.

RESULTS

Close elastic modules of the porcine and human tissues (13.5 ± 4.2 kPa vs. 15.8 ± 6.7 kPa, p = 0.531) gave to trainees a realistic tissue feel and instrument usage. All participants strongly agreed that model was highly useful for TAPP inguinal hernia repair training. They also put the following points: the model as a whole 5 (3-5), simulation of anatomy 5 (3-5), simulation of dissection and mobilization 5 (3-5), and simulation of intracorporeal suture 5 (4-5).

CONCLUSIONS

We successfully created a model for TAPP inguinal hernia repair training. The model is made of inexpensive synthetic and biological materials similar to the human tissue. The model is easy to reproduce and can be used in the training programs of surgical residents.