Normalization of Fecal Calprotectin Within 12 Months of Diagnosis Is Associated With Reduced Risk of Disease Progression in Patients With Crohn's Disease.

BACKGROUND & AIMS: The level of fecal calprotectin (FC) correlates with endoscopic evidence of inflammation in Crohn's disease (CD). A treat-to-target algorithm for patients with CD, that incorporates FC, outperforms a treatment strategy based on symptoms alone in the induction of mucosal healing at 12 months. We investigated whether normalization of FC within 12 months of diagnosis of CD is associated with a reduction in disease progression. METHODS: We performed a retrospective cohort study at a tertiary IBD centre in the United Kingdom. We identified all incident cases of CD diagnosed from 2005 through 2017. Patients with a FC measurement ≥250 µg/g at diagnosis who also had at least 1 follow-up FC measurement within the first 12 months of diagnosis and >12 months of follow up were included. The last FC measurement within 12 months of diagnosis was used to determine normalization (cut-off <250 µg/g). The primary endpoint was time to first disease progression (composite of progression in Montreal disease behavior B1 to B2/3, B2 to B3, or new perianal disease; CD-related surgery; or CD-related hospitalization). Cox proportional hazards regression analysis was used to determine independent factors associated with time to first disease progression. RESULTS: A total of 375 patients out of 1389 incident cases were included, with a median follow up of 5.3 years (interquartile range, 3.1-7.4 years). Normalization of FC within 12 months of diagnosis was confirmed in 43.5% of patients. Patients with normalized levels of FC had a significantly lower risk of composite disease progression (hazard ratio [HR], 0.36; 95% CI, 0.24-0.53; P < .001). They also had a lower risk of reaching any of the separate progression endpoints (progression in Montreal behavior or new perianal disease HR, 0.22; 95% CI, 0.11-0.45; P < .001; hospitalization HR, 0.33; 95% CI, 0.21-0.53; P <.001; surgery HR, 0.39; 95% CI, 0.19-0.78; P = .008) CONCLUSIONS: Normalization of FC within 12 months of diagnosis is associated with a reduced risk of progression of CD.

Analysis of colectomy rates for ulcerative colitis in pre- and postbiological eras in Lothian, Scotland.

AIM: Biological treatment is effective in maintaining remission in ulcerative colitis (UC), although the effect on colectomy rates remains unclear. In the UK the use of antitumour necrosis factor and anti-α4ß7 treatments for maintenance therapy in UC was restricted until 2015. The aim of this study was to describe the impact that this change in the prescribing of biologicals had on colectomy rates for UC. METHOD: All patients (adult and paediatric) with a diagnosis of UC who received maintenance biological treatment and/or underwent a colectomy in Lothian, Scotland between 2005 and 2018 were identified. Linear and segmental regression analyses were used to identify the annual percentage change (APC) and temporal trends (statistical joinpoints) in biological prescription and colectomy rates. RESULTS: Rates of initiation of maintenance biological therapy increased from 0.05 per 100 UC patients in 2005 to 1.26 in 2018 (p < 0.001). Colectomy rates per 100 UC patients fell from 1.47 colectomies in 2005 to 0.44 in 2018 (p < 0.001). The APC for colectomy decreased by 4.1% per year between 2005 and 2014 and by 18.9% between 2014 and 2018. Temporal trend analysis (2005-2018) identified a significant joinpoint in colectomy rates in 2014 (p = 0.019). CONCLUSION: The use of maintenance biological therapy increased sharply following the change in guidance. This has been paralleled by a significant reduction in the rates of colectomy over the same time period.

IBD prevalence in Lothian, Scotland, derived by capture-recapture methodology.

OBJECTIVE: IBD prevalence is estimated to be rising, but no detailed, recent UK data are available. The last reported prevalence estimate in the UK was 0.40% in 2003. We aimed to establish the current, and project future, prevalence in Lothian, Scotland. DESIGN: We conducted an all-age multiparameter search strategy using inpatient IBD international classification of disease (ICD-10) coding (K50/51)(1997-2018), IBD pathology coding (1990-2018), primary and secondary care prescribing data (2009-2018) and a paediatric registry, (1997-2018) to identify 'possible' IBD cases up to 31/08/2018. Diagnoses were manually confirmed through electronic health record review as per Lennard-Jones/Porto criteria. Autoregressive integrated moving average (ARIMA) regression was applied to forecast prevalence to 01/08/2028. RESULTS: In total, 24 601 possible IBD cases were identified of which 10 499 were true positives. The point prevalence for IBD in Lothian on 31/08/2018 was 784/100 000 (UC 432/100 000, Crohn's disease 284/100 000 and IBD unclassified (IBDU) 68/100 000). Capture-recapture methods identified an additional 427 'missed' cases (95% CI 383 to 477) resulting in a 'true' prevalence of 832/100 000 (95% CI 827 to 837).Prevalence increased by 4.3% per year between 2008 and 2018 (95% CI +3.7 to +4.9%, p<0.0001). ARIMA modelling projected a point prevalence on 01/08/2028 of 1.02% (95% CI 0.97% to 1.07%) that will affect an estimated 1.53% (95% CI 1.37% to 1.69%) of those >80 years of age. CONCLUSIONS: We report a rigorously validated IBD cohort with all-age point prevalence on 31/08/2018 of 1 in 125, one of the highest worldwide.

Implementation of CT-P13 via a Managed Switch Programme in Crohn's Disease: 12-Month Real-World Outcomes.

BACKGROUND: Switching from Remicade to CT-P13 allows for significant cost savings and has been shown to be non-inferior to continued therapy with Remicade for the treatment of Crohn's disease. AIM: The aim of this work was to prospectively evaluate clinical outcomes in a cohort of patients with Crohn's disease switching from Remicade to CT-P13. METHODS: A prospective service evaluation was performed. The Harvey-Bradshaw index, CRP, faecal calprotectin and serum for infliximab/antibody levels were collected prior to patients' final Remicade infusion and at 6 and 12 months after switching to CT-P13 as part of routine clinical care. All adverse events during follow-up were also recorded. RESULTS: One hundred and ten patients on Remicade switched to CT-P13. No significant difference was observed between the Harvey-Bradshaw Index (p = 0.07), CRP (p = 0.13), faecal calprotectin (p = 0.25) or trough infliximab levels (p = 0.47) comparing before and at 6 and 12 months after the switch to CT-P13. Seven patients developed new infliximab antibodies after switching from Remicade to CT-P13. The majority of patients remained on CT-P13 at 12 months (84.5%) and the rate of adverse events and serious adverse events was 53.8 and 13.5 per 100 patient-years of follow-up, respectively. Switching to CT-P13 resulted in a cost saving of approximately 46.4%. CONCLUSION: The transition to CT-P13 from Remicade for the treatment of Crohn's disease is safe and has no negative effect on clinical outcomes at 12 months.

Long-term outcomes and predictors of vedolizumab persistence in ulcerative colitis.

Background: Long-term vedolizumab (VDZ) outcomes in real-world cohorts have been largely limited to 1-year follow-up, with few bio-naïve patients or objective markers of inflammation assessed. Objectives: We aimed to assess factors affecting VDZ persistence including clinical, biochemical and faecal biomarker remission at 1, 3 and 5 years. Design: We performed a retrospective, observational, cohort study. Methods: All adult inflammatory bowel disease (IBD) patients who had received VDZ induction for ulcerative colitis (UC)/IBD-unclassified (IBDU) were included. Baseline phenotype and follow-up data were collected via a review of electronic medical records. Results: We included 290 patients [UC n = 271 (93.4%), IBDU n = 19 (6.6%)] with a median time on VDZ of 27.6 months (interquartile range: 14.4-43.2). At the end of follow-up, a total of 157/290 (54.1%) patients remained on VDZ. The median time to discontinuation was 14.1 months (7.0-23.3). Previous exposure to ⩾1 advanced therapy, steroid use at baseline and disease extension (E3 and E2 versus E1) were independent predictors for worse VDZ persistence. Clinical remission (partial Mayo < 2) was 75.7% (171/226), 72.4% (157/217) and 70.2% (127/181) at years 1, 3 and 5, respectively. Steroid use during maintenance VDZ therapy occurred in 31.7% (92/290), hospitalization in 15.5% (45/290) and surgery in 3.4% (10/291). The rate of serious adverse events was 1.2 per 100 patient-years of follow-up. Conclusion: VDZ effectiveness appears enduring with favourable long-term safety profile. VDZ persistence was influenced by previous exposure to biologics/small molecules, disease distribution and steroid use at baseline in our study.

Vedolizumab long-term use in ulcerative colitis What was this study done? • Vedolizumab efficacy and safety in ulcerative colitis have been firmly established by existing evidence. • Long-term data from the GEMINI trial further corroborate the favourable safety profile over an extended duration but there is little data on long-term vedolizumab use over 1 year. What did the researches do? • We performed a retrospective, observational, cohort study. All adult IBD patients who ever received vedolizumab induction from November 2014 to December 2021 for ulcerative colitis/IBDU were included. What did the researchers find? • This real-world study demonstrates that vedolizumab persistence exceeds 80% at 1 year and remains nearly 50% at 5 years with no new safety signals. • Worse vedolizumab persistence is associated with prior exposure to biologics/small molecules, more extensive disease involvement and steroid use at vedolizumab initiation. What do the findings mean? • These findings have important implications for drug positioning and sequencing, as well as for optimizing outcomes when vedolizumab is utilized as first-line therapy. Furthermore, it also emphasizes the long-term safety profile.

Multiple infliximab biosimilar switches appear to be safe and effective in a real-world inflammatory bowel disease cohort.

BACKGROUND: Switching from originator infliximab (IFX) to biosimilar IFX is effective and safe. However, data on multiple switching are scarce. The Edinburgh inflammatory bowel disease (IBD) unit has undertaken three switch programmes: (1) Remicade to CT-P13 (2016), (2) CT-P13 to SB2 (2020), and (3) SB2 to CT-P13 (2021). OBJECTIVE: The primary endpoint of this study was to assess CT-P13 persistence following switch from SB2. Secondary endpoints included persistence stratified by the number of biosimilar switches (single, double and triple), effectiveness and safety. METHODS: We performed a prospective, observational, cohort study. All adult IBD patients on IFX biosimilar SB2 underwent an elective switch to CT-P13. Patients were reviewed in a virtual biologic clinic with protocol driven collection of clinical disease activity, C-reactive protein (CRP), faecal calprotectin (FC), IFX trough/antibody levels, and drug survival. RESULTS: 297 patients (CD n = 196 [66%], ulcerative colitis/inflammatory bowel disease unclassified n = 101, [34%]) were switched (followed-up: 7.5 months [6.8-8.1]). This was the third, second and first IFX switch for 67/297 (22.5%), 138/297 (46.5%) and 92/297 (31%) of the cohort respectively. 90.6% of patients remained on IFX during follow-up. The number of switches was not independently associated with IFX persistence after adjusting for confounders. Clinical (p = 0.77), biochemical (CRP ≤5 mg/ml; p = 0.75) and faecal biomarker (FC<250 µg/g; p = 0.63) remission were comparable at baseline, week 12 and week 24. CONCLUSION: Multiple successive switches from IFX originator to biosimilars are effective and safe in patients with IBD, irrespective of the number of IFX switches.

Rates, predictive factors and effectiveness of ustekinumab intensification to 4- or 6-weekly intervals in Crohn's disease.

BACKGROUND: The UNITI trial reports efficacy of ustekinumab (UST) dose intensification in Crohn's disease (CD) from 12- to 8-weekly, but not 4-weekly. We aimed 1) to assess the cumulative incidence of UST dose intensification to 4- or 6-weekly, 2) to identify factors associated with dose intensification, and 3) to assess the effectiveness of this strategy. METHODS: We performed a retrospective, observational cohort study in NHS Lothian including all UST treated CD patients (2015-2020). RESULTS: 163 CD patients were treated with UST (median follow-up: 20.3 months [13.4-38.4]), of whom 55 (33.7%) underwent dose intensification to 4-weekly (n = 50, 30.7%) or 6-weekly (n = 5, 3.1%). After 1 year 29.9% were dose intensified. Prior exposure to both anti-TNF and vedolizumab (HR 9.5; 1.3-70.9), and concomitant steroid use at UST start (HR 1.8; 1.0-3.1) were associated with dose intensification. Following dose intensification, 62.6% patients (29/55) remained on UST beyond 1 year. Corticosteroid-free clinical remission was achieved in 27% at week 16 and 29.6% at last follow-up. CONCLUSION: One third of CD patients treated with UST underwent dose intensification to a 4- or 6-weekly interval within the first year. Patients who failed both anti-TNF and vedolizumab, or required steroids at initiation were more likely to dose intensify.

Patterns of emergency admission for IBD patients over the last 10 years in Lothian, Scotland: a retrospective prevalent cohort analysis.

OBJECTIVE: It is unclear how the compounding prevalence of inflammatory bowel disease (IBD) has translated into the causes and rates of hospitalisation, particularly in an era of increased biologic prescribing. We aimed to analyse these trends in a population-based IBD cohort over the last 10 years. DESIGN: The Lothian IBD registry is a complete, validated, prevalent database of IBD patients in NHS Lothian, Scotland. ICD-10 coding of hospital discharge letters from all IBD patient admissions to secondary care between 1 January 2010 and 31 December 2019 was interrogated for admission cause, with linkage to local/national data sets on death and prescribed drugs. RESULTS: Fifty-seven per cent (4673/8211) of all IBD patients were admitted to secondary care for >24 h between 1 January 2010 and 31 December 2019. In patients <40 years, IBD was the commonest reason for admission (38% of admissions), whereas infection was the most common cause in those >60 years (19% of admissions). Three per cent (243/8211) of IBD patients accounted for 50% of the total IBD bed-days over the study period. Age-standardised IBD admission rates fell from 39.4 to 25.5 admissions per 100,000 population between 2010 and 2019, an average annual percentage reduction of 3% (95% CI -4.5% to -2.1%, p < 0.0001). Non-IBD admission rates were unchanged overall (145-137 per 100,000 population) and specifically for serious (hospitalisation) and severe (ITU admission or death) infection over the same period. CONCLUSION: Despite compounding prevalence and increased biologic use, IBD admission rates are falling. The cause of admission varies with age, with infection the predominant cause in older patients.

Remote diagnosis of surgical-site infection using a mobile digital intervention: a randomised controlled trial in emergency surgery patients.

Surgical site infections (SSI) cause substantial morbidity and pose a burden to acute healthcare services after surgery. We aimed to investigate whether a smartphone-delivered wound assessment tool can expedite diagnosis and treatment of SSI after emergency abdominal surgery. This single-blinded randomised control trial (NCT02704897) enroled adult emergency abdominal surgery patients in two tertiary care hospitals. Patients were randomised (1:1) to routine postoperative care or additional access to a smartphone-delivered wound assessment tool for 30-days postoperatively. Patient-reported SSI symptoms and wound photographs were requested on postoperative days 3, 7, and 15. The primary outcome was time-to-diagnosis of SSI (Centers for Disease Control definition). 492 patients were randomised (smartphone intervention: 223; routine care: 269). There was no significant difference in the 30-day SSI rate between trial arms: 21 (9.4%) in smartphone vs 20 (7.4%, p = 0.513) in routine care. Among the smartphone group, 32.3% (n = 72) did not utilise the tool. There was no significant difference in time-to-diagnosis of SSI for patients receiving the intervention (-2.5 days, 95% CI: -6.6-1.6, p = 0.225). However, patients in the smartphone group had 3.7-times higher odds of diagnosis within 7 postoperative days (95% CI: 1.02-13.51, p = 0.043). The smartphone group had significantly reduced community care attendance (OR: 0.57, 95% CI: 0.34-0.94, p = 0.030), similar hospital attendance (OR: 0.76, 95% CI: 0.28-1.96, p = 0.577), and significantly better experiences in accessing care (OR: 2.02, 95% CI: 1.17-3.53, p = 0.013). Smartphone-delivered wound follow-up is feasible following emergency abdominal surgery. This can facilitate triage to the appropriate level of assessment required, allowing earlier postoperative diagnosis of SSI.

Effectiveness and Safety of Adalimumab Biosimilar SB5 in Inflammatory Bowel Disease: Outcomes in Originator to SB5 Switch, Double Biosimilar Switch and Bio-Naïve SB5 Observational Cohorts.

BACKGROUND AND AIMS: Multiple adalimumab [ADA] biosimilars are now approved for use in inflammatory bowel disease [IBD]; however, effectiveness and safety data remain scarce. We aimed to investigate long-term outcomes of the ADA biosimilar SB5 in IBD patients following a switch from the ADA originator [SB5-switch cohort] or after start of SB5 [SB5-start cohort]. METHODS: We performed an observational cohort study in a tertiary IBD referral centre. All IBD patients treated with Humira underwent an elective switch to SB5. We identified all these patients in a biological prescription database that prospectively registered all ADA start and stop dates including brand names. Data on IBD phenotype, C-reactive protein [CRP], drug persistence, ADA drug and antibody levels, and faecal calprotectin were collected. RESULTS: In total, 481 patients were treated with SB5, 256 in the SB5-switch cohort (median follow-up: 13.7 months [IQR 8.6-15.2]) and 225 in the SB5-start cohort [median follow-up: 8.3 months [4.2-12.8]). Of the SB5-switch cohort, 70.8% remained on SB5 beyond 1 year; 90/256 discontinued SB5, mainly due to adverse events [46/90] or secondary loss of response [37/90]. In the SB5-start cohort, 81/225 discontinued SB5, resulting in SB5-drug persistence of 60.3% beyond 1 year. No differences in clinical remission [p = 0.53], CRP [p = 0.80], faecal calprotectin [p = 0.40] and ADA trough levels [p = 0.55] were found between baseline, week 26 and week 52 following switch. Injection site pain was the most frequently reported adverse event. CONCLUSION: Switching from ADA originator to SB5 appeared effective and safe in this study with over 12 months of follow-up.

Association of trough vedolizumab levels with clinical, biological and endoscopic outcomes during maintenance therapy in inflammatory bowel disease.

OBJECTIVE: To establish the relationship between trough vedolizumab levels and outcomes during maintenance therapy. DESIGN: Cross-sectional service evaluation was performed on patients with inflammatory bowel disease (IBD) receiving maintenance vedolizumab therapy (minimum of 12 weeks following induction). Prior to infusion, data on clinical activity (Harvey-Bradshaw Index or partial Mayo score), trough C-reactive protein (CRP)/vedolizumab levels and faecal calprotectin were collected. Endoscopic data (±8 weeks from vedolizumab level testing) were obtained by review of medical records. Vedolizumab levels were processed using the Immundiagnostik monitor ELISA. SETTING: The Edinburgh IBD Unit, Western General Hospital (tertiary IBD referral centre). PATIENTS: Seventy-three patients (30 ulcerative colitis and 43 Crohn's disease) were identified who fulfilled inclusion criteria and had vedolizumab levels matched with clinical activity scores, CRP and faecal calprotectin. Of these, 40 patients also had matched endoscopic data. MAIN OUTCOME MEASURES: The association of trough vedolizumab levels with clinical remission (Harvey-Bradshaw Index <5 or partial Mayo <2), biologic remission (faecal calprotectin <250 µg/g+CRP <5 mg/L) and endoscopic remission (Mayo score 0/no inflammation and ulceration on colonoscopy). RESULTS: The median trough vedolizumab levels were similar between patients in and not in clinical remission (10.6 vs 9.9 µg/mL, p=0.54); biologic remission (10.6 vs 9.8 µg/mL, p=0.35) and endoscopic remission (8.1 vs 10.2 µg/mL, p=0.21). Quartile analysis revealed no significant increase in the proportion of patients in clinical remission, biologic remission or endoscopic remission with increasing trough vedolizumab levels (p<0.05). CONCLUSIONS: In this cohort, trough vedolizumab levels were not associated with clinical, biological or endoscopic outcomes during maintenance therapy.

Higher Adalimumab Drug Levels During Maintenance Therapy for Crohn's Disease Are Associated With Biologic Remission.

BACKGROUND: Adalimumab is an established treatment for Crohn's disease. Limited data are available regarding the relationship between adalimumab drug levels and serum/fecal markers of gut inflammation. We therefore aimed to characterize the relationship between adalimumab levels and biologic remission during maintenance therapy. METHODS: A single-center prospective cross-sectional study was undertaken on Crohn's disease patients who had received adalimumab therapy for a minimum of 12 weeks after induction. Data on clinical activity (Harvey-Bradshaw Index), C-reactive protein (CRP), adalimumab drug and antibody levels, and fecal calprotectin were collected. Biologic remission was defined as a CRP <5 mg/L and fecal calprotectin <250 µg/g. Adalimumab drug and antibody levels were processed using the Immundiagnostik monitor enzyme-linked immunosorbent assay. RESULTS: One hundred fifty-two patients had drug and antibody samples matched with CRP and fecal calprotectin. Patients in biologic remission had significantly higher adalimumab levels compared with others (12.0 µg/mL vs 8.0 µg/mL, P < 0.0001). Receiver operating characteristic curve analysis demonstrated an optimal adalimumab level of >8.5 µg/mL (sensitivity, 82.2%; specificity, 55.7%; likelihood ratio, 1.9) for predicting biologic remission. Multivariable logistic regression revealed that adalimumab levels >8.5 µg/mL were independently associated with biologic remission (odds ratio, 5.27; 95% confidence interval, 2.43-11.44; P < 0.0001). CONCLUSIONS: Higher adalimumab levels are associated with biologic remission. An optimal level of >8.5 µg/mL was identified.

The influence of passenger car front shape on pedestrian injury risk observed from German in-depth accident data.

Quantified relationships between passenger car front shape and pedestrian injury risk derived from accident data are sparse, especially considering the significant recent changes in car front design. The purpose of this paper is therefore to investigate the detailed effects of passenger car front shape on injury risk to a pedestrian's head, thorax, pelvis and leg in the event of a vehicle pedestrian impact. Firstly, an accident sample of 594 pedestrian cases captured during 2000-2015 from the German In-Depth Accident Study (GIDAS) database was employed. Multicollinearity diagnostic statistics were then used to detect multicollinearity between the predictors. Following this, logistic regression was applied to quantify the effects of passenger car front shape on injury risks while controlling for impact speed and pedestrian age. Results indicate that the bumper lower depth (BLD), bumper lower height (BLH), bumper upper height (BUH) and normalised bumper lower/upper height (NBLH/NBUH) are statistically significant for AIS2+ leg injury risk. The normalised bonnet leading edge height (NBLEH) has a statistically significant influence on AIS2+ femur/pelvis injury occurrence. The passenger car front shape did not show statistical significance for AIS3+ thorax and head injuries. The impact speed and pedestrian age are generally significant factors influencing AIS2+ leg and pelvis injuries, and AIS3+ thorax and head injuries. However, when head impacts are fixed on the central windscreen region both pedestrian age and impact speed are not statistically significant for AIS3+ head injury. For quantified effects, when controlling for speed, age and BUH, an average 7% and 6% increase in AIS2+ leg injury odds was observed for every 1cm increase in BLD and BLH respectively; 1cm increase in BUH results in a 7% decrease in AIS2+ leg injury odds when the BLD or BLH are fixed respectively (again controlling for impact speed and pedestrian age); the average AIS2+ femur/pelvis injury odds increase by 74% for a 10% increase in NBLEH. These findings suggest that passenger car bumpers should support the lower leg with a low and flat lower bumper and even contact up to the femur area with a high upper bumper which extends above the knee to protect the pedestrian's leg. A low passenger car bonnet leading edge helps to reduce femur/pelvis injury risk. The passenger car front shape parameters are less influential than impact speed and pedestrian age for pedestrian injury risk.

Mechanical characterisation of porcine rectus sheath under uniaxial and biaxial tension.

Incisional hernia development is a significant complication after laparoscopic abdominal surgery. Intra-abdominal pressure (IAP) is known to initiate the extrusion of intestines through the abdominal wall, but there is limited data on the mechanics of IAP generation and the structural properties of rectus sheath. This paper presents an explanation of the mechanics of IAP development, a study of the uniaxial and biaxial tensile properties of porcine rectus sheath, and a simple computational investigation of the tissue. Analysis using Laplace׳s law showed a circumferential stress in the abdominal wall of approx. 1.1MPa due to an IAP of 11kPa, commonly seen during coughing. Uniaxial and biaxial tensile tests were conducted on samples of porcine rectus sheath to characterise the stress-stretch responses of the tissue. Under uniaxial tension, fibre direction samples failed on average at a stress of 4.5MPa at a stretch of 1.07 while cross-fibre samples failed at a stress of 1.6MPa under a stretch of 1.29. Under equi-biaxial tension, failure occurred at 1.6MPa with the fibre direction stretching to only 1.02 while the cross-fibre direction stretched to 1.13. Uniaxial and biaxial stress-stretch plots are presented allowing detailed modelling of the tissue either in silico or in a surrogate material. An FeBio computational model of the tissue is presented using a combination of an Ogden and an exponential power law model to represent the matrix and fibres respectively. The structural properties of porcine rectus sheath have been characterised and add to the small set of human data in the literature with which it may be possible to develop methods to reduce the incidence of incisional hernia development.

Extrusion properties of porcine intestines and surrogate materials for ventral hernia modelling.

A physical model of the abdomen can be a clean and cheap surrogate environment to assess new and existing closure solutions for post-laparoscopic wound closure, but a particular challenge is finding a surrogate material to replicate intestines which may protrude through a hernia. The literature shows no focus on this topic, and this paper therefore presents an investigation of the extrusion properties of fresh porcine intestines compared to a number of potential surrogate materials: silicone, edible gelatine, dough and reconstituted powdered potatoes (RPP). An extrusion rig was developed to simulate the mechanical environment of a post-operative hernia formation. Displacement controlled extrusion tests were performed, and the force-extrusion relationships at different extrusion velocities were compared for the intestines and the surrogate materials. The intestines showed a peak extrusion force ranging from 9 N to 14.8 N when pushed through a 13 mm hole, and similar extrusion properties between cleaned and uncleaned fresh porcine intestines were observed. The tests on surrogate materials showed that the surface tension properties of silicone gel resulted in high friction, that edible gelatine extruded like a liquid and that dough is very stiff, rendering all three materials unsuitable for use as surrogates. However, the RPP mix showed very similar force-extrusion properties compared to both the cleaned and uncleaned intestines. Viscoelastic testing (7.5 mm/min, 15 mm/min and 30 mm/min) showed little rate dependency in the extrusion properties for either the porcine intestines or the RPP. Despite the complexity of intestinal tissue and the obvious physical differences between intestine and RPP, it was found that there is no statistical difference between the yield strength of intestines and RPP (P values ranged between 0.14 and 0.3) at the rates tested.