Angiogenic and inflammatory host response to surgical meshes of different mesh architecture and polymer composition

Polyglactin 910 Meshes Coated with Sustained-Release Cannabigerol Varnish Inhibit Staphylococcus aureus Biofilm Formation and Macrophage Cytokine Secretion: An In Vitro Study

Synthetic surgical meshes are commonly used in abdominal wall reconstruction surgeries to strengthen a weak abdominal wall. Common mesh-related complications include local infection and inflammatory processes. Because cannabigerol (CBG) has both antibacterial and anti-inflammatory properties, we proposed that coating VICRYL (polyglactin 910) mesh with a sustained-release varnish (SRV) containing CBG would prevent these complications. We used an in vitro infection model with Staphylococcus aureus and an in vitro inflammation model of lipopolysaccharide (LPS)-stimulated macrophages. Meshes coated with either SRV-placebo or SRV-CBG were exposed daily to S. aureus in tryptic soy medium (TSB) or macrophage Dulbecco's modified eagle medium (DMEM). Bacterial growth and biofilm formation in the environment and on the meshes were assessed by changes in optical density, bacterial ATP content, metabolic activity, crystal violet staining, spinning disk confocal microscopy (SDCM), and high-resolution scanning electron microscopy (HR-SEM). The anti-inflammatory effect of the culture medium that was exposed daily to the coated meshes was analyzed by measuring the release of the cytokines IL-6 and IL-10 from LPS-stimulated RAW 264.7 macrophages with appropriate ELISA kits. Additionally, a cytotoxicity assay was performed on Vero epithelial cell lines. We observed that compared with SRV-placebo, the segments coated with SRV-CBG inhibited the bacterial growth of S. aureus in the mesh environment for 9 days by 86 ± 4% and prevented biofilm formation and metabolic activity in the surroundings for 9 days, with respective 70 ± 2% and 95 ± 0.2% reductions. The culture medium that was incubated with the SRV-CBG-coated mesh inhibited LPS-induced secretion of IL-6 and IL-10 from the RAW 264.7 macrophages for up to 6 days without affecting macrophage viability. A partial anti-inflammatory effect was also observed with SRV-placebo. The conditioned culture medium was not toxic to Vero epithelial cells, which had an IC₅₀ of 25 µg/mL for CBG. In conclusion, our data indicate a potential role of coating VICRYL mesh with SRV-CBG in preventing infection and inflammation in the initial period after surgery.

A paradigm shift for diaphragmatic and chest wall reconstruction using a bovine acellular dermal matrix: an analysis versus synthetic meshes

OBJECTIVES

Recently, biologic meshes have gained increasing popularity in soft tissue reconstruction. The aim of this study was to investigate the use of a bovine acellular dermal matrix (SurgiMend, Integra LifeSciences, Princeton, NJ, USA) in diaphragmatic and chest wall reconstruction by comparing it with synthetic meshes.

METHODS

Consecutive patients who underwent diaphragmatic and/or chest wall reconstruction at a single center from 2016 to 2021 were retrospectively reviewed. Outcome measures included surgical site complications, readmission, and reoperation.

RESULTS

Sixty-six patients underwent diaphragmatic and/or chest wall reconstruction for a malignant (74.2%) or benign (25.8%) disease. SurgiMend was used in 26 (39.4%) patients and a synthetic mesh in 40 (60.6%) patients. There were no significant differences in baseline characteristics between the groups. Surgical site complications included prolonged air leak (12.1%), pleural effusion (9.1%), pneumothorax (3%), empyema (1.5%), and wound infection (1.5%). The patients in the synthetic mesh group developed a significantly higher rate of surgical site complications compared to those in the SurgiMend group (37.5% vs. 11.5%; p = 0.025). Similarly, the readmission rate was significantly higher in the synthetic mesh group (17.5% vs. 0%; p = 0.037), with causes including pleural effusion (n = 3), pneumothorax (n = 2), empyema (n = 1), and pneumonia (n = 1). Among the study cohort, only 1 patient with a synthetic mesh underwent reoperation (p > 0.99).

CONCLUSIONS

The use of surgiMend in diaphragmatic and chest wall reconstruction is associated with fewer surgical site complications and readmissions compared to synthetic meshes.

Physician antibiotic hydration preferences for biologic antibacterial envelopes during cardiac implantable device procedures

Background

Cardiac implantable electronic device (CIED) infection is a potentially serious complication of CIED procedures. Infection risk mitigation includes using guideline-recommended pre-operative intravenous antibacterial prophylaxis (IV ABX). The use of antibiotic-eluting CIED envelopes has also been shown to reduce infection risk. The relationship between and potential benefits associated with guideline-recommended IV ABX in combination with antibacterial envelopes have not been characterized.

Methods

Biologic envelopes made from non-crosslinked extracellular matrix (ECM) were implanted into 1,102 patients receiving CIEDs. The implanting physician decided patient selection for using a biologic envelope and envelope hydration solution. Observational data was analyzed on IV ABX utilization rates, antibacterial envelope usage, and infection outcomes.

Results

Overall compliance with IV ABX was 96.6%, and most patients received a biologic envelope hydrated in antibiotics (77.1%). After a mean follow-up of 223 days, infection rates were higher for sites using IV ABX <80% of the time vs. sites using ≥80% (5.6% vs. 0.8%, p = 0.008). Physicians demonstrated preference for hydration solutions containing gentamicin in higher-risk patients, which was found by multivariate analysis to be associated with a threefold reduction in infection risk (OR 3.0, 95% CI, 1.0-10.0).

Conclusion

These findings suggest that use of antibiotics, particularly gentamicin, in biologic envelope hydration solution may reduce infection risk, and use of antibacterial envelopes without adjunct IV ABX may not be sufficient to reduce CIED infections.

Clinical trial registration

[https://clinicaltrials.gov/], identifier [NCT02530970].

Risk Profiles and Outcomes of Patients Receiving Cardiovascular Implantable Electronic Devices With and Without Antibacterial Envelopes

Background

The increasing use of cardiac implantable electronic devices (CIEDs) in a growing patient population has led to an even greater increase in CIED infection rates. Antibacterial CIED envelopes are often used as part of an infection risk-reduction strategy. However, best practices for when to use an envelope and which envelope to choose remain to be elucidated.

Methods

In this retrospective study, the records of 455 patients undergoing CIED implantation by a single surgeon were reviewed to identify trends in envelope use and outcomes after implantation through 12 months of follow-up. Of these patients, 165 were managed with a biologic antibacterial CIED envelope (CanGaroo®, Aziyo Biologics, Inc., Silver Spring, MD), 219 with a non-biologic envelope (Tyrx®, Medtronic Inc., Monmouth Junction, NJ), and 71 with no envelope.

Results

Most patients had two or more infection risk factors (77.9% with any envelope vs. 52.1% with no envelope; P < 0.001). Factors significantly associated with the use of an envelope included the history of heart failure, systemic anticoagulant use, the use of high-power or more complex devices, and reoperations. The overall rate of adverse events was 9.2% (n = 42). Rates of infection and hematoma were 1.8% and 2.6%, respectively. A decision tree is proposed that may aid clinical decision-making when considering CIED envelope usage.

Conclusions

There were no significant differences between groups in overall or individual adverse event rates. These data provide insight into real-world clinical decisions regarding the use of CIED envelopes and support the use of antibiotic-eluting CIED envelopes to limit infection risk in high-risk patients.

Risk profiles and outcomes of patients receiving antibacterial cardiovascular implantable electronic device envelopes: A retrospective analysis

BACKGROUND

Cardiovascular implantable electronic devices (CIEDs) are implanted in an increasing number of patients each year, which has led to an increase in the risk of CIED infection. Antibacterial CIED envelopes locally deliver antibiotics to the implant site over a short-term period and have been shown to reduce the risk of implant site infection. These envelopes are derived from either biologic or non-biologic materials. There is a paucity of data examining patient risk profiles and outcomes from using these envelope materials in the clinical setting and comparing these results to patients receiving no envelope with their CIED implantation.

AIM

To evaluate risk profiles and outcomes of patients who underwent CIED procedures with an antibacterial envelope or no envelope.

METHODS

After obtaining Internal Review Board approval, the records of consecutive patients who underwent a CIED implantation procedure by a single physician between March 2017 and December 2019 were retrospectively collected from our hospital. A total of 248 patients within this period were identified and reviewed through 12 mo of follow up. The CIED procedures used either no envelope (n = 57), a biologic envelope (CanGaroo^®, Aziyo Biologics) that was pre-hydrated by the physician with vancomycin and gentamicin (n = 89), or a non-biologic envelope (Tyrx™, Medtronic) that was coated with a resorbable polymer containing the drug substances rifampin and minocycline by the manufacturer (n = 102). Patient selection for receiving either no envelope or an envelope (and which envelope to use) was determined by the treating physician. Statistical analyses were performed between the 3 groups (CanGaroo, Tyrx, and no envelope), and also between the No Envelope and Any Envelope groups by an independent, experienced biostatistician.

RESULTS

On average, patients who received any envelope (biologic or non-biologic) were younger (70.7 ± 14.0 vs 74.9 ± 10.6, P = 0.017), had a greater number of infection risk factors (81.2% vs 49.1%, P < 0.001), received more high-powered devices (37.2% vs 5.8%, P = 0.004), and were undergoing more reoperative procedures (47.1% vs 0.0%, P < 0.001) than patients who received no envelope. Between the two envelopes, biologic envelopes tended to be used more often in higher risk patients (84.3% vs 78.4%) and reoperative procedures (62.9% vs 33.3%) than non-biologic envelopes. The rate of CIED implant site pocket infection was low (any envelope 0.5% vs no envelope 0.0%) and was statistically equivalent between the two envelope groups. Other reported adverse events (lead dislodgement, lead or pocket revision, device migration or erosion, twiddler’s syndrome, and erythema/fever) were low and statistically equivalent between groups (biologic 2.2%, non-biologic 3.9%, no envelope 1.8%).

CONCLUSION

CIED infection rates for biologic and non-biologic antibacterial envelopes are similar. Antibacterial envelopes may benefit patients who are higher risk for infection, however additional studies are warranted to confirm this.

Evaluation of a Novel Absorbable Mesh in a Porcine Model of Abdominal Wall Repair

Bioabsorbable meshes have seen increasing clinical use to reinforce soft tissue, and exist on a spectrum of strength loss versus absorption: several retain their strength for months, but remain in situ for years. Others lose strength fully by 6 weeks. An intermediate profile, with some strength for 3 -4 months, but consistent absorption in less than a year, may be an optimal balance of near-term support and long-term safety. In this large animal study, we evaluate such a mesh (DuraSorb, SIA), assessing its utility in a porcine model of abdominal wall repair.

METHODS

Two full-thickness defects were created in the abdominal walls of nine Yucatan swine via midline approach and repaired preperitoneally with either DuraSorb or long-lasting control mesh (TIGR, Novus Scientific). At 30 days, 3 months, and 1 year, the implantations were assessed by clinical pathology, post-necropsy histopathology, and burst strength testing.

RESULTS

No device-associated complications were found in vivo, at necropsy, or histologically. DuraSorb was well-integrated and vascularized by 30 days. DuraSorb demonstrated minimal/mild inflammation and fibroplasia, and lower inflammatory scores when compared with TIGR at all time points (P < 0.05). Burst strength of the repair sites was higher than adjacent abdominal wall at all time points (P < 0.05).

CONCLUSIONS

DuraSorb provided durable long-term support, minimal inflammation, and consistent absorption in this porcine model of abdominal wall repair, as compared to a long-term control. Clinical data is needed, but these results suggest that this mesh provides adequate structural support while potentially reducing long-term device reactions.

Functionalized Strategies and Mechanisms of the Emerging Mesh for Abdominal Wall Repair and Regeneration

Meshes have been the overwhelmingly popular choice for the repair of abdominal wall defects to retrieve the bodily integrity of musculofascial layer. Broadly, they are classified into synthetic, biological and composite mesh based on their mechanical and biocompatible features. With the development of anatomical repair techniques and the increasing requirements of constructive remodeling, however, none of these options satisfactorily manages the conditional repair. In both preclinical and clinical studies, materials/agents equipped with distinct functions have been characterized and applied to improve mesh-aided repair, with the importance of mesh functionalization being highlighted. However, limited information exists on systemic comparisons of the underlying mechanisms with respect to functionalized strategies, which are fundamental throughout repair and regeneration. Herein, we address this topic and summarize the current literature by subdividing common functions of the mesh into biomechanics-matched, macrophage-mediated, integration-enhanced, anti-infective and antiadhesive characteristics for a comprehensive overview. In particular, we elaborate their effects separately with respect to host response and integration and discuss their respective advances, challenges and future directions toward a clinical alternative. From the vastly different approaches, we provide insight into the mechanisms involved and offer suggestions for personalized modifications of these emerging meshes.

In Vitro and in Vivo Analysis of Adhesive, Anti-Inflammatory, and Proangiogenic Properties of Novel 3D Printed Hyaluronic Acid Glycidyl Methacrylate Hydrogel Scaffolds for Tissue Engineering

In this study, we prepared hydrogel scaffolds for tissue engineering by computer-assisted extrusion three-dimensional (3D) printing with photocured (λ = 445 nm) hyaluronic acid glycidyl methacrylate (HAGM). The developed product was compared with the polylactic-co-glycolic acid (PLGA) scaffolds generated by means of the original antisolvent 3D printing methodology. The cytotoxicity and cytocompatibility of the scaffolds were analyzed in vitro by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide tests, flow cytometry, and scanning electron microscopy. Anti-inflammatory and proangiogenic properties of the scaffolds were evaluated in the dorsal skinfold chamber mouse model by means of intravital fluorescence microscopy, histology, and immunohistochemistry throughout an observation period of 14 days. In vitro, none of the scaffolds revealed cytotoxicity on days 1, 2, and 5 after seeding with umbilical cord-derived multipotent stromal cells, and the primary cell adhesion to the surface of HAGM scaffolds was low. In vivo, implanted HAGM scaffolds showed enhanced vascularization and host tissue ingrowth, and the inflammatory response to them was less pronounced compared with PLGA scaffolds. The results indicate excellent biocompatibility and vascularization capacity of the developed 3D printed HAGM scaffolds and position them as strong candidates for advanced tissue engineering applications.

Biological coating with platelet-rich plasma and adipose tissue-derived microvascular fragments improves the vascularization, biocompatibility and tissue incorporation of porous polyethylene

Porous polyethylene (pPE) is a commonly used biomaterial in craniofacial reconstructive surgery. However, implant failure due to insufficient vascularization represents a major issue. To overcome this problem, we herein introduce an effective strategy to improve the vascularization and incorporation of pPE. Adipose tissue-derived microvascular fragments (MVF) from transgenic green fluorescent protein (GFP)⁺ mice were suspended in platelet-rich plasma (PRP) for the coating of pPE. PRP/MVF-coated pPE as well as PRP-coated and uncoated controls were subsequently implanted into the dorsal skinfold chamber and the flanks of GFP^- wild-type mice to analyze their in vivo performance throughout 2, 4 and 8 weeks by means of intravital fluorescence microscopy, histology and immunohistochemistry. The GFP⁺/GFP^- cross-over design allowed the identification of GFP⁺ MVF within the implants. Shortly after implantation, they rapidly reassembled into new blood-perfused microvascular networks, resulting in a significantly accelerated vascularization of PRP/MVF-coated pPE when compared to both controls. The overall numbers of rolling and adherent leukocytes within the microcirculation as well as macrophages, multi-nucleated giant cells and mast cells around the implants did not differ between the three groups. However, in contrast to uncoated controls, PRP/MVF-coated and PRP-coated pPE promoted pro-angiogenic M2 macrophage polarization at the implantation site. These findings demonstrate that PRP/MVF-coating represents a highly effective strategy to enhance the vascularization, biocompatibility and tissue incorporation of pPE. STATEMENT OF SIGNIFICANCE: The clinical in vivo performance of implanted biomaterials is crucially dependent on their adequate incorporation into the body. To achieve this, we herein introduce an effective biological coating strategy. Our results demonstrate that coating with PRP and MVF accelerates and enhances the vascularization, biocompatibility and tissue incorporation of porous polyethylene. Because this type of biological coating is easily applicable on any type of biomaterial, our approach may rapidly be translated into clinical practice to improve the outcome of various regenerative approaches.

Does a bilateral polypropylene mesh alter the duct deferens morphology, testicular size and testosterone levels? Experimental study in rats

Purpose

To evaluate the effect of a PP mesh on duct deferens morphology, testicular size and testosterone levels.

Methods

Forty adult male rats were distributed into groups: 1) no surgery; 2) inguinotomy; 3) mesh placed on the duct deferens; and 4) mesh placed on the spermatic funiculus. After 90 postoperative days, the inguinal region was resected, and blood samples were collected for the measurement of serum testosterone (pg/dl). The ducts deferens were sectioned in three axial sections according to the relationship with the mesh — cranial, medial and caudal. The wall thickness and duct deferens lumen area were measured.

Results

The morphology of the duct deferens was preserved in all groups. The mesh placement did not alter this morphology in any of the analyzed segments. Surgery, with or without mesh placement, did not alter the morphology, wall thickness or lumen area (p>0.05). In all operated groups, serum testosterone levels were similar (p>0.05) but there was a decrease in testicle size (p<0.05).

Conclusion

Surgery, with or without mesh placement, did not alter the morphology of the duct deferens and, although this treatment resulted in testicular size reduction, it did not affect serum testosterone levels.

Clinically available reinforcing materials for soft tissue reconstruction

Navigating the rapidly evolving field of materials for soft tissue reinforcement is challenging given the volume of clinically available options. Additionally, the current generally accepted classifications of these mesh materials confound the understanding of their utility by grouping disparate materials that have attributes overlapping category boundaries and that do not fully consider their clinically functionality. This review article highlights, from a materials science perspective, the most important attributes of these materials to improve the clinical decision-making process in the selection of the most appropriate features and design for the patient, surgery and clinical need. These characteristics include the physical attributes that directly impact the surgical procedure and immediate postoperative mechanical requirements as well as the post-implantation properties such as an adequate reinforcement time, strength of the resulting tissue and infection risk profile.

Integration of Biomechanical and Biological Characterization in the Development of Porous Poly(caprolactone)-Based Membranes for Abdominal Wall Hernia Treatment

Aims. Synthetic meshes are the long-standing choice for the clinical treatment of abdominal wall hernias: the associated long-term complications have stimulated the development of a new generation of bioresorbable prostheses. In this work, polycaprolactone (PCL) porous membranes prepared by solvent casting/porogen leaching of PCL/poly(ethylene glycol) (PEG) blends with different compositions (different PCL/PEG weight ratios and PEG molecular weights) were investigated to be applied in the field. An optimal porous membrane structure was selected based on the evaluation of physicochemical, biomechanical, and in vitro biological properties, compared to a reference commercially available hernia mesh (CMC). Findings. Selected PCL7-2i membranes, derived from PCL/PEG 70/30 (PCL: Mw 70,000-90,000 Da; PEG: 35,000 Da), showed suitable pore size for the application, intermediate surface hydrophilicity, and biomimetic mechanical properties. In vitro cell tests performed on PCL7-2i membranes showed their cytocompatibility, high cell growth during 21 days, a reduced production of proinflammatory IL-6 with respect to CMC, and a significant secretion of collagen type I. Conclusions. PCL7-2i membranes showed biomimetic biomechanical properties and in vitro biological properties similar to or even better than - in the case of anti-inflammatory behavior and collagen production - CMC, a commercially available product, suggesting potentially improved integration in the host tissue.

An experimental research in mice on the "soft tissue reaction to 3 different mesh implants: Titanium silk, Parietene Progrip and Prolene"

Purpose

To analyze the soft tissue reaction of 'Titanium Silk' mesh implant in comparison with 'Parietene Progrip' and 'Prolene' mesh implants for the reinforcement and augmentation of soft tissues to improve the results of static correction in Facial Paralysis and other defects of Maxillofacial region.

Materials and methods

Under standard laboratory conditions, 89 mice were divided into 4 groups: a control group of 5 mice; first group of 28 mice with Titanium mesh implant, second group of 28 mice with semi-resorbable 'Parietene Progrip' implant and third group of 28 mice with 'Prolene' implant. Under inhalational anesthesia with ethyl ether at days 7, 14, 30 and 60, seven mice from each experimental group underwent Gross and histological analysis of the mesh structures for the following characteristics: Macrophage Infiltration, Multinucleated Macrophages, Meshwork around the implant fibers, Connective tissue proliferation, Angiogenesis and Fibroblasts.

Results

Histological analysis revealed a significantly less pronounced inflammatory response to Titanium mesh implant resulting in the formation of a more delicate connective tissue network around the mesh elements.

Conclusion

The experiment clearly demonstrated the cellular and tissue responses to different implantable mesh materials at various times of its integration. It revealed that the titanium mesh is the most bio-inert alloplastic material suitable for reinforcement of soft tissue augmentation and to prioritize it's use in static correction of facial paralysis and other defects of the maxillofacial region. A postoperative timeframe of 30 days is considered appropriate for the adequate formation of connective tissue around the mesh elements.

In vivo response to decellularized mesothelium scaffolds

Biological surgical scaffolds are used in plastic and reconstructive surgery to support structural reinforcement and regeneration of soft tissue defects. Macrophage and fibroblast cell populations heavily regulate scaffold integration into host tissue following implantation. In the present study, the biological host response to a commercially available surgical scaffold (Meso BioMatrix Surgical Mesh (MBM)) was investigated for up to 9 weeks after subcutaneous implantation; this scaffold promoted superior cell migration and infiltration previously in in vitro studies relative to other commercially available scaffolds. Infiltrating macrophages and fibroblasts phenotypes were assessed for evidence of inflammation and remodeling. At week 1, macrophages were the dominant cell population, but fibroblasts were most abundant at subsequent time points. At week 4, the scaffold supported inflammation modulation as indicated by M1 to M2 macrophage polarization; the foreign body giant cell response resolved by week 9. Unexpectedly, a fibroblast subpopulation expressed macrophage phenotypic markers, following a similar trend in transitioning from a proinflammatory to anti-inflammatory phenotype. Also, α-smooth muscle actin-expressing myofibroblasts were abundant at weeks 4 and 9, mirroring collagen expression and remodeling activity. MBM supported physiologic responses observed during normal wound healing, including cellular infiltration, host tissue ingrowth, remodeling of matrix proteins, and immune modulation. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 716-725, 2018.

Locally applied macrophage-activating lipopeptide-2 (MALP-2) promotes early vascularization of implanted porous polyethylene (Medpor®)

Porous polyethylene (Medpor®) is frequently used in craniofacial reconstructive surgery. Rapid vascularization of the biomaterial crucially contributes to its adequate incorporation without complications. Macrophage-activating lipopeptide-2 (MALP-2) is a toll-like receptor (TLR)-2/6 agonist with pro-angiogenic properties. Herein we analyzed whether local single-shot application of MALP-2 improves the angiogenic host tissue response to Medpor®. Medpor® (3 mm×3 mm×0.25 mm) was implanted into dorsal skinfold chambers of BALB/c mice topically exposed to different MALP-2 doses (0.1 and 0.5 μg) or vehicle (control). The vascularization of the implants and the inflammatory foreign body reaction was analyzed using intravital fluorescence microscopy, histology and immunohistochemistry over 14 days. MALP-2 treatment dose-dependently improved the vascularization of Medpor®, as indicated by a significantly higher functional microvessel density at the border and center of the implants when compared to controls. This was associated with a temporary increase of adherent leukocytes in host tissue venules during the first 3 days after implantation. At day 14, implants in MALP-2-treated chambers were surrounded by granulation tissue, which exhibited a significantly higher density of CD31-positive microvessels and number of F4/80-positive macrophages when compared to controls. Additional biomaterial-free chambers did not show any signs of angiogenesis when treated with MALP-2. This indicates that locally applied MALP-2 effectively stimulates the early vascularization of Medpor® without inducing any local or systemic side effects. Accordingly, this easy approach may further improve the rapid incorporation of this biomaterial at the implantation site.

Early and late postoperative inflammatory and collagen deposition responses in three different meshes: an experimental study in rats

PURPOSE

Although meshes reduce abdominal hernia recurrence, they increase the risk of inflammatory complications. This study aimed to compare the early and late postoperative inflammation and collagen deposition responses induced by three meshes.

METHODS

Rats were allocated into three groups. In group I, a polypropylene (PP) mesh was implanted in the abdominal wall. In groups II and III, PP + polyglactin (PP + PG) and PP + titanium (PP + TI) meshes were employed, respectively. On the seventh (7th) postoperative day, collagen deposition and inflammation were evaluated, and immunohistochemistry was performed on abdominal wall biopsies. These data were compared with those obtained on the fortieth (40th) postoperative day in a previous study.

RESULTS

The early inflammatory responses were the same in all groups. With time, it decreased in group I (p = 0.047) and increased in group II (p = 0.003). Group I exhibited early elevated VEGF (p < 0.001), COX2 (p < 0.001), and collagen (p = 0.023) levels, and group II exhibited the most severe inflammatory tissue response. On the 40th postoperative day, the VEGF (p < 0.001) and collagen (p < 0.005) were reduced as compared with the 7th postoperative day in all groups.

CONCLUSIONS

Belatedly, the inflammatory reaction decreased in PP mesh group and increased in PP + PG mesh group. The PP mesh induced early great elevations in VEGF, COX2 and collagen levels, whereas the PP + PG mesh caused severe tissue inflammation with small elevation in these levels. PP + TI mesh induced inflammatory response levels between the others. In conclusion, the inflammatory response depends on the mesh density and also the mesh material with clinical implications.

Characterization of the Mechanical Strength, Resorption Properties, and Histologic Characteristics of a Fully Absorbable Material (Poly-4-hydroxybutyrate-PHASIX Mesh) in a Porcine Model of Hernia Repair

Purpose. Poly-4-hydroxybutyrate (P4HB) is a naturally derived, absorbable polymer. P4HB has been manufactured into PHASIX Mesh and P4HB Plug designs for soft tissue repair. The objective of this study was to evaluate mechanical strength, resorption properties, and histologic characteristics in a porcine model. Methods. Bilateral defects were created in the abdominal wall of n = 20 Yucatan minipigs and repaired in a bridged fashion with PHASIX Mesh or P4HB Plug fixated with SorbaFix or permanent suture, respectively. Mechanical strength, resorption properties, and histologic characteristics were evaluated at 6, 12, 26, and 52 weeks (n = 5 each). Results. PHASIX Mesh and P4HB Plug repairs exhibited similar burst strength, stiffness, and molecular weight at all time points, with no significant differences detected between the two devices (P > 0.05). PHASIX Mesh and P4HB Plug repairs also demonstrated significantly greater burst strength and stiffness than native abdominal wall at all time points (P < 0.05), and material resorption increased significantly over time (P < 0.001). Inflammatory infiltrates were mononuclear, and both devices exhibited mild to moderate granulation tissue/vascularization. Conclusions. PHASIX Mesh and P4HB Plug demonstrated significant mechanical strength compared to native abdominal wall, despite significant material resorption over time. Histological assessment revealed a comparable mild inflammatory response and mild to moderate granulation tissue/vascularization.

Retrieval study at 623 human mesh explants made of polypropylene - impact of mesh class and indication for mesh removal on tissue reaction

Textile meshes frequently are implanted in the abdominal wall to reinforce a hernia repair. However, revisions for mesh associated complications confirm that these devices are not completely free of risk. Explanted devices offer an opportunity to define the impact of mesh structure on tissue response. This retrieval study analyses the tissue reaction to 623 polypropylene mesh samples (170 class 1 with large pores, and 453 class 2 with small pores) explanted for pain, infection, or recurrence. Histopathological assessment included morphometry of inflammatory infiltrate (IF) and connective tissue (CT), and of collagen 1/3 ratio. Half of the meshes were removed after more than 23 month. Despite large inter-individual differences removal for infection showed more IF than for pain or recurrence with significant correlation of IF with CT. Class 1 meshes with large pores showed less IF, CT, fistula formation, calcification, and bridging than class 2 meshes with small pores. Meshes removed for recurrence showed a lowered collagen 1/3 ratio in 70%. Large pore class 1 meshes showed an improved tissue response and may be considered as favorable to prevent inflammatory side effects. The presence of lowered collagen 1/3 ratio in most of the samples with recurrences stresses the relevance of an intact healing process. Late manifestation of complications demands long-lasting follow-up. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2013.

Silver acetate coating promotes early vascularization of Dacron vascular grafts without inducing host tissue inflammation

BACKGROUND

Silver acetate is frequently used as an antimicrobial coating of prosthetic vascular grafts. However, the effects of this coating on the early inflammatory and angiogenic host tissue response still remain elusive. Therefore, the aim of the present in vivo study was to analyze the biocompatibility and vascularization of silver acetate-coated and uncoated vascular grafts during the initial phase after implantation.

METHODS

Two different prosthetic vascular grafts (ie, uncoated Dacron and silver acetate-coated Dacron Silver) were implanted into the dorsal skinfold chamber of C57BL/6 mice (n = 8 per group) to study angiogenesis and leukocytic inflammation at the implantation site by means of repetitive intravital fluorescence microscopy over a 14-day period. At the end of the in vivo experiments, collagen formation, apoptosis, and cell proliferation were analyzed in the newly developed granulation tissue surrounding the implants by histology and immunohistochemistry.

RESULTS

During the initial 14 days after implantation, Dacron Silver exhibited an improved vascularization, as indicated by a significantly increased functional capillary density compared with Dacron. This was not associated with a stronger leukocytic inflammatory host tissue response to the implants. Moreover, silver acetate coating did not affect collagen formation, apoptosis, and cell proliferation at the implantation site.

CONCLUSIONS

Silver acetate coating of prosthetic vascular grafts improves their early vascularization without inducing severe inflammatory side effects. Accordingly, this material modification crucially contributes to an improved incorporation of the implants into the host tissue, which may decrease the risk of vascular graft infection.

Development of novel electrospun absorbable polycaprolactone (PCL) scaffolds for hernia repair applications

INTRODUCTION

Permanent/nonresorbable hernia repair materials rely on profibrotic wound healing, and repair sites are commonly composed of disorganized tissue with inferior mechanical strength and risk of reherniation. Resorbable electrospun scaffolds represent a novel class of biomaterials, which may provide a unique platform for the design of advanced soft tissue repair materials. These materials are simple, inexpensive, nonwoven materials composed of polymer fibers that readily mimic the natural extracellular matrix. The primary goal of the present study was to evaluate the physiomechanical properties of novel electrospun scaffolds to determine their suitability for hernia repair. Based on previous experimentation, scaffolds possessing ≥ 20 N suture retention strength, ≥ 20 N tear resistance, and ≥ 50 N/cm tensile strength are appropriate for hernia repair.

METHODS

Six novel electrospun scaffolds were fabricated by varying combinations of polymer concentration (10-12 %) and flow rate (3.5-10 mL/h). Briefly, poly(ε-caprolactone) (PCL) was dissolved in a solvent mixture and electrospun onto a planar metal collector, yielding sheets with randomly oriented fibers. Physiomechanical properties were evaluated through scanning electron microscopy, laser micrometry, and mechanical testing.

RESULTS

Scanning electron micrographs demonstrated fiber diameters ranging from 1.0 ± 0.1 μm (10 % PCL, 3.5 mL/h) to 1.5 ± 0.2 μm (12 % PCL, 4 mL/h). Laser micrometry demonstrated thicknesses ranging from 0.72 ± 0.07 mm (12 % PCL, 10 mL/h) to 0.91 ± 0.05 mm (10 % PCL, 3.5 mL/h). Mechanical testing identified two scaffolds possessing suture retention strengths ≥ 20 N (12 % PCL, 10 mL/h and 12 % PCL, 6 mL/h), and no scaffolds possessing tear resistance values ≥ 20 N (range, 4.7 ± 0.9 N to 10.6 ± 1.8 N). Tensile strengths ranged from 35.27 ± 2.08 N/cm (10 % PCL, 3.5 mL/h) to 81.76 ± 15.85 N/cm (12 % PCL, 4 mL/h), with three scaffolds possessing strengths ≥ 50 N/cm (12 % PCL, 10 mL/h; 12 % PCL, 6 mL/h; 12 % PCL, 4 mL/h).

CONCLUSIONS

Two electrospun scaffolds (12 % PCL, 10 mL/h and 12 % PCL, 6 mL/h) possessed suture retention and tensile strengths appropriate for hernia repair, justifying evaluation in a large animal model. Additional studies examining advanced methods of fabrication may further improve the unique properties of these scaffolds, propelling them into applications in a variety of clinical settings.

Micropatterned angiogenesis induced by poly(d,l-lactic-co-glycolic acid) mesh-structured scaffolds

Angiogenesis is an important process used to guide the regeneration of functional tissues and organs. The incorporation of inductive cues into scaffolds to control angiogenesis is an attractive strategy for scaffold preparation. Four mesh-type scaffolds, including a vascular endothelial growth factor-embedded poly(d,l-lactic- co-glycolic acid) mesh, a vascular endothelial growth factor-coated poly(d,l-lactic- co-glycolic acid) mesh, a collagen-coated poly(d,l-lactic- co-glycolic acid) mesh, and a poly(d,l-lactic- co-glycolic acid) mesh, were compared for their inductive effects on the formation of a micropatterned capillary network. Following subcutaneous implantation, all of the scaffolds induced the formation of micropatterned capillary networks, as observed at 2 and 6 weeks after implantation. The vascular endothelial growth factor-embedded mesh and the vascular endothelial growth factor-coated mesh promoted a higher degree of blood vessel formation than the collagen-coated mesh and the poly(d,l-lactic- co-glycolic acid) mesh. The capillary density in the vascular endothelial growth factor-embedded mesh and the vascular endothelial growth factor-coated mesh increased with time following implantation. The macrophages that surrounded the scaffolds were similar for all the meshes. The microstructure of the poly(d,l-lactic- co-glycolic acid) mesh determined the micropattern of the capillary network, and vascular endothelial growth factor provided a synergistic effect on the micropatterned angiogenesis process.

Intravital microscopic studies of angiogenesis during bone defect healing in mice calvaria

PURPOSE

Due to the great availability of specific antibodies, gene-targeted animals and knockout strains, mouse models came into the focus of musculoskeletal research. Herein, we introduce a calvarian defect model in mice that allows the repetitive analysis of blood vessel formation during bone repair by intravital microscopy.

METHODS

The right parietal calvaria of 20 adult CD-1 mice were exposed by skin excision. Under continuous irrigation, a circular defect (Ø0.75 mm) was drilled into the calvarium without penetrating the inner cortical shell. A circular glass (Ø12 mm; thickness 0.15 mm) was fixed by two microscrews (M1; length 2mm) to cover the bone defect. Angiogenesis was analysed by intravital microscopy at days 0, 3, 6, 9, 12, 15, 18 and 21. In addition, bone repair was evaluated by histomorphometry at days 3, 6, 9 and 15. Immunohistochemical stainings for the angiogenic growth factor vascular endothelial growth factor (VEGF) and the cell proliferation marker proliferating cell nuclear antigen (PCNA) were performed to assess angiogenic and proliferative activity during healing of the calvarian defect.

RESULTS

Histomorphometry showed a typical pattern of intramembranous bone repair. Osseous bridging of the defect was observed at day 9. This was associated with the formation of a neo-periosteum, which covered the new woven bone and contained a dense network of newly formed blood vessels. At day 9, particularly cells of the neo-periosteum showed intense staining for VEGF, whilst PCNA-positive staining was found mainly in osteoblasts. At day 15, the major fraction of fibrous tissue was replaced by bone undergoing extensive remodelling. Intravital microscopy revealed an increase of vascular density between days 3 and 15. Blood vessel diameters showed an increase between days 3 and 9 and a subsequent decrease between days 9 and 21.

CONCLUSIONS

The present calvarian defect model provides a powerful tool to evaluate the process of angiogenesis during intramembranous bone repair in mice.