Sandra Sotomayor

Behaviour of a new composite mesh for the repair of full-thickness abdominal wall defects in a rabbit model.

Introduction Composite biomaterials designed for the repair of abdominal wall defects are composed of a mesh component and a laminar barrier in contact with the visceral peritoneum. This study assesses the behaviour of a new composite mesh by comparing it with two latest-generation composites currently used in clinical practice. Methods Defects (7x5cm) created in the anterior abdominal wall of New Zealand White rabbits were repaired using a polypropylene mesh and the composites: PhysiomeshTM; VentralightTM and a new composite mesh with a three-dimensional macroporous polyester structure and an oxidized collagen/chitosan barrier. Animals were sacrificed on days 14 and 90 postimplant. Specimens were processed to determine host tissue incorporation, gene/protein expression of neo-collagens (RT-PCR/immunofluorescence), macrophage response (RAM-11-immunolabelling) and biomechanical resistance. On postoperative days 7/14, each animal was examined laparoscopically to quantify adhesions between the visceral peritoneum and implant. Results The new composite mesh showed the lowest incidence of seroma in the short term. At each time point, the mesh surface covered with adhesions was greater in controls than composites. By day 14, the implants were fully infiltrated by a loose connective tissue that became denser over time. At 90 days, the peritoneal mesh surface was lined with a stable mesothelium. The new composite mesh induced more rapid tissue maturation than PhysiomeshTM, giving rise to a neoformed tissue containing more type I collagen. In VentralightTM the macrophage reaction was intense and significantly greater than the other composites at both follow-up times. Tensile strengths were similar for each biomaterial. Conclusions All composites showed optimal peritoneal behaviour, inducing good peritoneal regeneration and scarce postoperative adhesion formation. A greater foreign body reaction was observed for VentralightTM. All composites induced good collagen deposition accompanied by optimal tensile strength. The three-dimensional macroporous structure of the new composite mesh may promote rapid tissue regeneration within the mesh.

Cytotoxicity of Cyanoacrylate-Based Tissue Adhesives and Short-Term Preclinical In Vivo Biocompatibility in Abdominal Hernia Repair

Background Cyanoacrylate(CA)-based tissue adhesives, although not widely used, are a feasible option to fix a mesh during abdominal hernia repair, due to its fast action and great bond strength. Their main disadvantage, toxicity, can be mitigated by increasing the length of their alkyl chain. The objective was to assess the in vitro cytotoxicity and in vivo biocompatibility in hernia repair of CAs currently used in clinical practice (Glubran(n-butyl) and Ifabond(n-hexyl)) and a longer-chain CA (OCA(n-octyl)), that has never been used in the medical field. Methods Formaldehyde release and cytotoxicity of unpolymerized(UCAs) and polymerized CAs(PCAs) were evaluated by macroscopic visual assessment, flow cytometry and Alamar Blue assays. In the preclinical evaluation, partial defects were created in the rabbit abdominal wall and repaired by fixing polypropylene prostheses using the CAs. At 14 days post-surgery, animals were euthanized for morphology, macrophage response and cell damage analyses. Results Formaldehyde release was lower as the molecular weight of the monomer increased. The longest side-chain CA(OCA) showed the highest cytotoxicity in the UCA condition. However, after polymerization, was the one that showed better behavior on most occasions. In vivo, all CAs promoted optimal mesh fixation without displacements or detachments. Seroma was evident with the use of Glubran, (four of six animals: 4/6) and Ifabond (2/6), but it was reduced with the use of OCA (1/6). Significantly greater macrophage responses were observed in groups where Glubran and Ifabond were used vs. sutures and OCA. TUNEL-positive cells were significantly higher in the Glubran and OCA groups vs. the suture group. Conclusions Although mild formaldehyde release occurred, OCA was the most cytotoxic during polymerization but the least once cured. The CAs promoted proper mesh fixation and have potential to replace traditional suturing techniques in hernia repair; the CAs exhibited good tissue integration and effective short-term biocompatibility, with the slightest seroma and macrophage response induced by OCA.

Repair of Abdominal Wall Defects with Biodegradable Laminar Prostheses: Polymeric or Biological?

Introduction Biological and synthetic laminar absorbable prostheses are available for the repair of hernia defects in the abdominal wall. They share the important feature of being gradually degraded in the host, resulting in place the formation of a neotissue. This study was designed to assess the host tissue’s incorporation of collagen bioprostheses and a synthetic absorbable prosthesis. Methods Partial defects were created in the abdominal walls of 72 New Zealand rabbits and repaired using collagen bioprostheses Tutomesh® and Strattice® or a synthetic prosthesis Bio-A®. Specimens were collected for light microscopy, collagens gene and protein expression, macrophage response and biomechanical resistance at 14, 30, 90 and 180 days post-implantation. Results Tutomesh® and Bio-A® were gradually infiltrated by the host tissue and almost completely degraded by 180 days post-implantation. In contrast, Strattice® exhibited material encapsulation, no prosthetic degradation and low cell infiltration at earlier timepoints, whereas at later study time, collagen deposition could be observed within the mesh. In the short term, Bio-A® exhibited higher level of collagen 1 and 3 mRNA expression compared with the two other biological prostheses, which exhibited two peaks of higher expression at 14 and 90 days. The expression of collagen III was homogeneous throughout the study and collagen I deposition was more evident in Strattice®. Macrophage response decreased over time in biomeshes. However, in the synthetic mesh remained high and homogeneous until 90 days. The biomechanical analysis demonstrated the progressively increasing tensile strength of all biomaterials. Conclusions The tissue infiltration of laminar absorbable prostheses is affected by the structure and composition of the mesh. The synthetic prosthesis exhibited a distinct pattern of tissue incorporation and a greater macrophage response than did the biological prostheses. Of all of the laminar, absorbable biomaterials that were tested in this study, Strattice® demonstrated the optimal levels of integration and degradation.

Chemical Adhesion Barriers: Do They Affect the Intraperitoneal Behavior of a Composite Mesh?

ABSTRACT Introduction: The intraperitoneal behavior of a prosthetic material used to repair a hernia is key to the success of the postimplant repair process. This study was designed to laparoscopically examine the real-time behavior of three composite meshes incorporating a chemical adhesion barrier when placed in contact with the visceral peritoneum. Material and Methods: The defects of 7 × 5 cm were created in the ventral abdominal wall of 18 New Zealand White rabbits and repaired using Parietex Composite® (n = 6), Sepramesh® (n = 6), or Proceed® (n = 6). At 24 hr, 3, 7, and 14 days postimplant, adhesion formation was quantified by subjecting photographs obtained during laparoscopy to image analysis. At 14 days, specimens of the implants and surrounding host tissue were obtained for histologic, morphometric, and immunohistochemical analyses. Results: There were no cases of infection and/or rejection of the implant. Adhesion formation followed by laparoscopy 3, 7, and 14 days after implant was significantly lower for Parietex® than the other biomaterials. Degradation of the chemical barrier occurred earliest in Sepramesh®, this barrier being most stable at 14 days for the Parietex® implants. Macrophage counts were significantly greater for Sepramesh®. The thickness of the neoformed peritoneum formed on the three implants varied significantly (p < .05): 276.89 ± 38.87 μm, 84.49 ± 19.05 μm, and 161.97 ± 47.05 μm, respectively for Paritex®, Sepramesh®, and Proceed®. Conclusions: (a) The most stable barrier against biodegradation was that of Parietex®; (b) the first postimplant week was the most critical period for adhesion formation; and (c) all three biomaterials showed good intraperitoneal behavior.

Long term behavior of biological prostheses used as abdominal wall substitutes

BACKGROUND Despite their degradation in the host organism, the benefits of collagen bioprostheses remain unclear. This study addresses the absorption and long-term host tissue incorporation of several collagen biomeshes. MATERIAL AND METHODS Partial ventral hernial defects created in the abdominal wall of rabbits were repaired using the crosslinked meshes Permacol® or CollaMend®, or the non-crosslinked Surgisis®, Tutomesh® or Strattice®. After 90 and 180 days of implant, morphological studies and morphometric analysis of the thickness of the meshes were performed. Immunofluorescence confocal microscopy combined with differential interference contrast (DIC) imaging was used to distinguish newly formed collagen from that comprising the mesh. The macrophage response was examined by immunohistochemistry. RESULTS At 90 days, the thinner non-crosslinked biomeshes Tutomesh and Surgisis were more fully degraded with much of their collagen replaced with loose connective tissue. By 180 days, both implants had been practically fully absorbed. In contrast, in Strattice only the outermost third was infiltrated by neoformed tissue. On both surfaces of the crosslinked meshes, a fibrous capsule with host cells lining its perimeter was observed at both time points, though at 180 days these cells had penetrated the mesh interior. At both implant times, Strattice showed the higher expression of collagen type I while collagen III expression was similar for all the meshes. The non-crosslinked materials elicited lower macrophage counts at both time points, significantly so for Strattice. The macrophage response decreased over time for all the meshes but Surgisis. CONCLUSIONS Strattice, the thicker, more compacted non-crosslinked mesh showed the best balance between tissue incorporation and absorption while eliciting a minimal foreign-body reaction in the long-term.

Effects of collagen prosthesis cross-linking on long-term tissue regeneration following the repair of an abdominal wall defect

Collagen prostheses used to repair abdominal wall defects, depending on their pretreatment (noncross‐linked vs. cross‐linked), besides repair may also achieve tissue regeneration. We assessed the host tissue incorporation of different bioprostheses using a new tool that combines immunofluorescence confocal microscopy with differential interference contrast images, making it possible to distinguish newly formed collagen. Partial hernial defects in the abdominal wall of rabbits were repaired using cross‐linked/noncross‐linked bioprostheses. Expanded polytetrafluoroethylene (ePTFE) was used as control. After 14/30/90/180 days of implant, specimens were taken for microscopy, immunohistochemistry, and quantitative‐reverse transcription‐polymerase chain reaction to determine host tissue ingrowth and collagen I/III protein and 1a1/3a1 gene expression. Shrinkage and stress resistance were also examined. At 14 days, cross‐linked prostheses had suffered significantly less shrinkage than ePTFE or noncross‐linked prostheses. Significantly higher shrinkage was recorded for ePTFE in the longer term. Microscopy revealed encapsulation of ePTFE by neoformed tissue, while the bioprostheses became gradually infiltrated by host tissue. Noncross‐linked prosthesis showed better tissue ingrowth, more intense inflammatory reaction and more rapid degradation than the cross‐linked prostheses. At 14 days, cross‐linked prostheses induced up‐regulated collagen 1a1 and 3a1 gene expression, while noncross‐linked only showed increased collagen III protein expression at 90 days postimplant. At 6 months, the tensile strengths of cross‐linked prostheses were significantly greater compared with ePTFE. Our findings demonstrate that despite the cross‐linked collagen prostheses promoting less tissue ingrowth than the noncross‐linked meshes, they became gradually replaced by good quality host tissue and were less rapidly degraded, leading to improved stress resistance in the long term.

Regulation of HER expression and transactivation in human prostate cancer cells by a targeted cytotoxic bombesin analog (AN-215) and a bombesin antagonist (RC-3095)

Bombesin (BN) and gastrin‐releasing peptide (GRP) have been shown to stimulate the growth of human prostate cancer in vivo and in vitro by mechanisms initiated by binding of the peptide to BN/GRP receptor (GRPR). GRPR is overexpressed in a variety of human cancers, including human prostatic carcinoma. This led us to evaluate the effectiveness of blocking GRPR and of chemotherapy targeted to GRPR in androgen‐dependent (LNCaP) and androgen‐independent (PC‐3) prostate cancer cells, which exhibit different features of disease progression. Thus, we used a cytotoxic BN/GRP analog, AN‐215, consisting of 2‐pyrrolinodoxorubicin (AN‐201) linked to BN‐like carrier peptide, and a BN/GRP receptor antagonist, RC‐3095. Semiquantitative RT‐PCR and Western blotting revealed that mRNA and protein levels for GRPR increased in prostate cancer cells as compared with nonneoplastic RWPE‐1 cells. Immunofluorocytochemistry and Western blot assays revealed that AN‐215 was the most effective analog decreasing both the expression of epidermal growth factor receptor family members and the activation of epidermal growth factor receptor and HER‐2, which are associated to a poor prognosis. Furthermore, analogs targeted to BN/GRP receptors, AN‐215 and RC‐3095, blocked the effect of BN on cell growth in RWPE‐1, LNCaP and PC‐3 cells. These findings shed light on the mechanisms of action of these analogs and support the view that the use of AN‐215 and RC‐3095 for blocking BN/GRP receptors for targeted therapy may be of benefit for treatment of advanced prostate cancer.

Short- and long-term biomechanical and morphological study of new suture types in abdominal wall closure.

To perform an abdominal-wall closure, a continuous suture is the preferred method. The suture materials that are most commonly employed in abdominal surgery are polypropylene and polydioxanone. However, in recent times, new products have been marketed, such as non-absorbable polyurethane with elastic properties (Assuplus(®), Assut Europe, Italy) and absorbable barbed polydioxanone (Filbloc(®), Assut Europe, Italy). The purpose of this study was to compare the ability of those against the standard polypropylene (Surgipro(TM), Covidien, USA) and polydioxanone (Assufil(®), Assut Europe, Italy) to mimic the biomechanical behavior of the abdominal wall closure. Comparison of the sutures was made first with the materials alone and later in a laparotomy closure of a rabbit abdomen, used as an animal model. The biomechanical analysis consisted of uniaxial tensile tests of threads and sutured samples of the animal abdomen. In the latter case, results were analyzed at short- (21days) and long- (180days) term intervals after the surgery. The morphology studies and collagen expression of the samples were also investigated. The results determined that polydioxanone and polypropylene sutures showed a linear elastic behavior, with barbed polydioxanone as the most compliant suture and polyurethane as the stiffest. The sutured samples showed a statistically significant loss of resistance, measured as the load needed to perform a certain stretch, when compared with the corresponding control tissue. Analysis of the stress-stretch curves showed that elastic polyurethane was the only suture able to reproduce the mechanical behavior of healthy tissue in the short term, while the rest of the sutures remained less stiff. This coincides with the expression of type I collagen observed in this group at this point in the study. In the long term, there was no difference among the sutures, and none was able to mimic control behavior.

New suture materials for midline laparotomy closure: an experimental study

BackgroundMidline laparotomy closure carries a significant risk of incisional hernia. This study examines the behavior of two new suture materials, an elastic material, polyurethane (PUe), and a barbed polydioxanone (PDXb) suture thread in a rabbit model of midline incision closure.MethodsThree 2-cm midline incisions were made in 68 New Zealand White rabbits. The incisions were closed by running suture using four 3/0 threads: polypropylene (PP) (Surgipro®, Covidien), PUe (Assuplus®, Assut Europe), PDX (Assufil®, Assut Europe) or PDXb (Filbloc®, Assut Europe). Animals in each suture group were euthanized 3 weeks and 6 months after surgery. Histological sections of the tissue-embedded sutures were subjected to morphological, collagen expression, macrophage response and uniaxial tensiometry studies.ResultsNo signs of wound dehiscence or complications were observed. At 3 weeks, all sutures were surrounded by connective tissue composed mainly of collagen III. PUe showed greater collagen I expression than the other sutures. All sutures elicited a macrophage response that diminished from 3 weeks to 6 months (p < 0.001). This response was similar for the non-reabsorbable sutures (PP and PUe) yet PDXb showed a significantly greater response than the other reabsorbable suture (PDX) at 3 weeks (p < 0.01). At this early time point, the tensile strength of PUe was similar to that of control intact tissue (p > 0.05).ConclusionThree weeks after surgery, PUe revealed more collagen I deposition than the remaining materials and this translated to a similar biomechanical behavior to linea alba, that could avoid the appearance of short term dehiscences and thus reduce the incidence of incisional hernia. PDXb provides no additional advantages in their behavior regarding PDX suture.

Effects of a novel NADPH oxidase inhibitor (S42909) on wound healing in an experimental ischemic excisional skin model.

Chronic wounds are a serious healthcare problem. As non‐healing wounds involve continuous pathologic inflammatory stage, research is focused on anti‐inflammatory treatments. Our objective was to analyze the effect of S42909, a potent NADPH oxidase inhibitor activity, with vascular anti‐inflammatory properties. An ischemic rabbit ear ulcer model (24 New Zealand white rabbits) was used to evaluate the reepithelialization/contraction areas, anti‐/pro‐inflammatory cytokines mRNA (TGF‐β1/IL‐10/IFN‐γ/VEGF) by qRT‐PCR, collagen I/III deposition, and neovascularization (TGF‐β1/VEGF) by morphological and immunohistochemical analyses. Three different doses were administered by gavage for 2 weeks: 10 and 30 mg/kg/d in self‐microemulsion drug delivery system (SMEDDS) and 100 mg/kg/d in arabic gum. Each vehicle was used as control. No signs of infection or necrosis were found. Reepithelialization was almost complete whatever the groups reaching 95% at the dose of 100 mg/kg. Wound contraction was significantly reduced in all S42909‐treated groups. A significant increase in anti‐inflammatory cytokines TGF‐β1 mRNA and IL‐10 mRNA was observed at the dose of 100 and 30 mg/kg/d, respectively. No changes were observed in pro‐inflammatory factors INF‐γ and VEGF mRNA. Ischemic skin wound areas had scarce expression of collagen I/III and showed rich glycosaminoglycans content. Treatment increased the collagen deposition and TGF‐β1 protein expression and decreased glycosaminoglycan content dose dependently; however, no effect in VEGF was appreciated. Therefore, our results indicate that S42909 improved healing process by dampening excessive inflammation and facilitating collagen deposition without wound contraction phenomena. S42909 might be a promising therapy to treat chronic wounds as venous leg ulcers.