The Effect of Strain Rate on the Stress Relaxation of the Pig Dermis: A Hyper-Viscoelastic Approach

The understanding of strain rate-dependent mechanical properties of the skin is important for accurate prediction of its biomechanics under different loading conditions. This study investigated the effect of strain rate, i.e., 0.025/s (low), 0.5/s (medium), and 1.25/s (high), ranging in the physiological loading rate of connective tissue, on the stress-relaxation response of the porcine dermis. Results show that in the initial phase of the relaxation, the value of stress relaxation (extent of relaxation) was found higher for high strain rate. However, the equilibrium stress was found strain rate independent. A Mooney–Rivlin-based five-term quasi-linear viscoelastic (QLV) model was proposed to determine the effect of strain rate on the stress-relaxation behavior of the porcine dermis. The value of relaxation modulus G1 and G2 were found higher for the high strain rate, whereas the reverse trend was observed for G3, G4, and G5. Moreover, the value of time constants τ1,τ2,τ3τ4, and τ5 were found higher for low strain rate. Statistical analysis shows no significant difference in the values of G5, τ4, and τ5 among the three strain rates. The proposed model was found capable to fit the stress-relaxation response of skin with great accuracy, e.g., root-mean-squared-error (RMSE) value equal to 0.015 ± 0.00012 MPa. Moreover, this hyper-viscoelastic model can be utilized: to quantify the effects of age and diseases on the skin; to simulate the stresses on sutures during large wound closure and impact loading.

Mussel Adhesive Protein as a Promising Alternative to Fibrin for Scaffold Fixation during Cartilage Repair Surgery

Objective Fibrin has been used as a standard material for scaffold fixation during cartilage repair surgery. Most of the commercially available fibrin preparations need an additional method for scaffold fixation, most often with sutures, thus damaging the surrounding healthy cartilage. There is therefore a need to find alternatives to this method. In our study, we have investigated the potential possibility to use mussel adhesive protein as such an alternative. Methods In this study, hydrophobic plastic was coated with the mussel adhesive protein Mefp-1 as well as with other cell adhesives (poly-lysine, fibronectin, and collagen). Human keratinocytes and chondrocytes were seeded on these substrates at 37°C in culture medium, followed by analysis of attachment and proliferation by crystal violet staining and metabolic labelling. Performance of Mefp-1 and fibrin as tissue glues were estimated by tensional force resistance measurement of moist porcine dermis (as a correlate to scaffold) glued to dermis, cartilage, or bone at 37°C. Results Mefp-1 supported maximal cell attachment at a coating density of approximately 1 µg/cm2. This was at least as good as the other adhesives tested. In addition, it supported cell proliferation at least as good as regular tissue culture plastic over a 7-day period. Measurement of tensional force resistance showed that Mefp-1 performed equally well as fibrin when porcine dermis was glued to cartilage and bone at the same concentration. Separation of the moist tissues after 15-minute incubation required a force of approximately 1 N/cm2 for both compounds. Conclusions Mefp-1 show properties that qualify it as a compound that potentially could replace fibrin as a tissue glue for scaffold fixation. Given the possibilities to modify this protein by bioengineering, it is likely that the properties can be further improved.

Performance of biological mesh materials in abdominal wall reconstruction: study protocol for a randomised controlled trial

IntroductionAbdominal wall hernias are a common source of morbidity and mortality. The use of biological mesh has become an important adjunct in successful abdominal wall reconstruction. There are a variety of biological mesh products available; however, there is limited evidence supporting the use of one type over another. This study aims to compare the performance (eg, the rate of hernia recurrence) of either a crosslinked biological mesh product or a non-crosslinked product in patients undergoing abdominal wall reconstruction.Methods and analysisThis is a single-centre, dual arm randomised controlled trial. Patients requiring abdominal wall reconstruction will be assessed for eligibility. Eligible patients will then undergo an informed consent process following by randomisation to either (1) crosslinked porcine dermis mesh (Permacol); or (2) non-crosslinked porcine dermis mesh (Strattice). These groups will be compared for the rate of hernia recurrence at 1 and 2 years as well as the rate of postoperative complications (eg, surgical site infections).Ethics and disseminationThis study has been approved by the institution’s research ethics board and registered with clinicaltrials.gov. All eligible participants will provide informed consent prior to randomization. The results of this study may help guide the choice of biologic mesh for this population. The results of this study will be published in peer-reviewed journals as well as national and international conferences.Trial registration numberNCT02703662.