Mechanical behavior of surgical meshes for abdominal wall repair: In vivo versus biaxial characterization.

Despite the widespread use of synthetic meshes in the surgical treatment of the hernia pathology, the election criteria of a suitable mesh for specific patient continues to be uncertain. Thus, in this work, we propose a methodology to determine in advance potential disadvantages on the use of certain meshes based on the patient-specific abdominal geometry and the mechanical features of the certain meshes. To that purpose, we have first characterized the mechanical behavior of four synthetic meshes through biaxial tests. Secondly, two of these meshes were implanted in several New Zealand rabbits with a total defect previously created on the center of the abdominal wall. After the surgical procedure, specimen were subjected to in vivo pneumoperitoneum tests to determine the immediate post-surgical response of those meshes after implanted in a healthy specimen. Experimental performance was recorded by a stereo rig with the aim of obtaining quantitative information about the pressure-displacement relation of the abdominal wall. Finally, following the procedure presented in prior works (Simón-Allué et al., 2015, 2017), a finite element model was reconstructed from the experimental measurements and tests were computationally reproduced for the healthy and herniated cases. Simulations were compared and validated with the in vivo behavior and results were given along the abdominal wall in terms of displacements, stresses and strain. Mechanical characterization of the meshes revealed SurgiproTM as the most rigid implant and Neomesh SuperSoft® as the softer, while other two meshes (Neomesh Soft®, Neopore®) remained in between. These two meshes were employed in the experimental study and resulted in similar effect in the abdominal wall cavity and both were close to the healthy case. Simulations confirmed this result while showed potential objections in the case of the other two meshes, due to high values in stresses or elongation that may led to discomfort in real tissue. The use of this methodology on human surgery may provide the surgeons with reliable and useful information to avoid certain meshes on specific-patient treatment.

Biomechanical and histologic evaluation of two application forms of surgical glue for mesh fixation to the abdominal wall.

The use of an adhesive for mesh fixation in hernia repair reduces chronic pain and minimizes tissue damage in the patient. This study was designed to assess the adhesive properties of a medium-chain (n-butyl) cyanoacrylate glue applied as drops or as a spray in a biomechanical and histologic study. Both forms of glue application were compared to the use of simple-loose or continuous-running polypropylene sutures for mesh fixation. Eighteen adult New Zealand White rabbits were used. For mechanical tests in an ex vivo and in vivo study, patches of polypropylene mesh were fixed to an excised fragment of healthy abdominal tissue or used to repair a partial abdominal wall defect in the rabbit respectively. Depending on the fixation method used, four groups of 12 implants each or 10 implants each respectively for the ex vivo and in vivo studies were established: Glue-Drops, Glue-Spray, Suture-Simple and Suture-Continuous. Biomechanical resistance in the ex vivo implants was tested five minutes after mesh fixation. In vivo implants for biomechanical and histologic assessment were collected at 14 days postimplant. In the ex vivo study, the continuous suture implants showed the highest failure sample tension, while the implants fixed with glue showed lower failure sample tension values. However, the simple and continuous suture implants returned the highest stretch values. In the in vivo implants, failure sample tension values were similar among groups while the implants fixed with a continuous running suture had the higher stretch values, and the glue-fixed implants the lower stretch values. All meshes showed good tissue integration within the host tissue regardless of the fixation method used. Our histologic study revealed the generation of a denser, more mature repair tissue when the cyanoacrylate glue was applied as a spray rather than as drops.

In-vitro development of an effective treatment for Acanthamoeba keratitis.

The aim of this study was to develop an in-vitro topical treatment for Acanthamoeba keratitis (AK) effective against cysts and trophozoites. Qualitative assays were performed with voriconazole, chlorhexidine, propamidine, cellulase, tobramycin, ciprofloxacin and paromomycin as monotherapy and various combinations. Riboflavin with ultraviolet-A (R + UV-A) as monotherapy or combined with voriconazole and moxifloxacin was also tested. Quantitative assays to assess cyst viability after treatment were performed for the chemicals that showed the highest activity in the qualitative assays. Paromomycin and propamidine did not show antiamoebic activity. Regardless of the total dose, no amoebicidal effect was observed for R + UV-A. Tobramycin, ciprofloxacin, voriconazole, chlorhexidine and cellulase were selected for quantitative assays because they appeared to cause greater damage to the structure of amoebae. Chlorhexidine and ciprofloxacin were the most active against Acanthamoeba spp. as monotherapy. Among the combinations evaluated, ciprofloxacin-voriconazole-chlorhexidine showed the greatest amoebicidal activity, with severe damage of the cellular membrane and an important decrease in cell concentration. In summary, ciprofloxacin as monotherapy and in combination with voriconazole and chlorhexidine has been classified as promising treatment. Additional in-vivo studies in animal models and clinical trials in patients with AK should be considered to confirm the efficacy of ciprofloxacin.

A numerical-experimental protocol to characterize corneal tissue with an application to predict astigmatic keratotomy surgery.

Tonometers are intended to determine the intraocular pressure (IOP) and the quality of corneal tissue. In contrast to the physiological state of stress of the cornea, tonometers induce non-physiological bending stress. Recently, the use of a single experiment to calibrate a set of corneal mechanical properties was suggested to be an ill-posed problem. Thus, we propose a numerical-experimental protocol that uses inflation and indentation experiments simultaneously, restricting the optimization space to circumvent the ambiguity of the fitting. For the first time, both corneal behaviors, i.e., biaxial tension (physiological) and bending (non-physiological), are taken into account. The experimental protocol was performed using an animal model (New Zealand rabbit's cornea). The patient-specific geometry and IOP were registered using a MODI topographer (CSO, Italy) and an applanation tonometer, respectively. The mechanical response was evaluated using inflation and indentation experiments. Subsequently, the optimal set of material properties is identified via an inverse finite element method. To validate the methodology, an in vivo incisional refractive surgery (astigmatic keratotomy, AK) is performed on four animals. The optical outcomes showed a good agreement between the real and simulated surgeries, indicating that the protocol can provide a reliable set of mechanical properties that enables further applications and simulations. After a reliable ex vivo database of inflation experiments is built, our protocol could be extended to humans.

The Miller׳s knot as an alternative to the surgical knotting? Characterization of the mechanical behavior.

Several types of materials and surgical suture patterns are used in conventional surgery. Their combination with an appropriate knot is the basis for correct tissue apposition and healing. Knot security is essential to prevent loosening or slipping before the suture line is completely closed. Nevertheless, the knot itself is the weakest link in any surgical handling. The aim of this study is to determine and compare the mechanical behavior of four surgical knot types (square knot, surgeon׳s knot, square slipknot and Miller׳s knot) performed with three different suture materials (absorbable monofilament glyconate, non-absorbable monofilament polyamide and absorbable braided polyglycolic acid) in a non-biological experimental in vitro model (a tube of synthetic material with non-linear mechanical behavior). The mechanical properties of each suture material are also compared. Ten samples were mechanically tested for each suture and knot using a uniaxial tensile test until complete sample rupture. The failure Cauchy stress and stretch were calculated. The Cauchy stress at 5%, 10% and 15% strain and standard deviation were compared for each suture and knot type. The results demonstrated that all the suture materials had statistically significant differences in their non-linear mechanical behavior. Absorbable monofilament glyconate was the most compliant suture with the greatest tensile strength, while absorbable braided polyglycolic acid was the stiffest. Regardless of the suture type used, the Miller׳s knot had the greatest failure Cauchy stress and stretch, while the square, surgeon׳s and square slipknot had the lowest. In all cases, the Miller׳s knot was more compliant and had greater tensile strength than the other knots. The square knot, surgeon׳s knot, and square slipknot had statistically significant similarities in their mechanical behavior. Therefore, the Miller׳s knot could be classified as the gold standard and an alternative to the surgical knotting.