Activation of human mononuclear cells by porcine biologic meshes in vitro

Unraveling and Harnessing the Immune Response at the Cell-Biomaterial Interface for Tissue Engineering Purposes

Biomaterials are defined as "engineered materials" and include a range of natural and synthetic products, designed for their introduction into and interaction with living tissues. Biomaterials are considered prominent tools in regenerative medicine that support the restoration of tissue defects and retain physiologic functionality. Although commonly used in the medical field, these constructs are inherently foreign toward the host and induce an immune response at the material-tissue interface, defined as the foreign body response (FBR). A strong connection between the foreign body response and tissue regeneration is suggested, in which an appropriate amount of immune response and macrophage polarization is necessary to trigger autologous tissue formation. Recent developments in this field have led to the characterization of immunomodulatory traits that optimizes bioactivity, the integration of biomaterials and determines the fate of tissue regeneration. This review addresses a variety of aspects that are involved in steering the inflammatory response, including immune cell interactions, physical characteristics, biochemical cues, and metabolomics. Harnessing the advancing knowledge of the FBR allows for the optimization of biomaterial-based implants, aiming to prevent damage of the implant, improve natural regeneration, and provide the tools for an efficient and successful in vivo implantation.

Recent trends in 3D bioprinting technology for skeletal muscle regeneration

Skeletal muscle is a pro-regenerative tissue, that utilizes a tissue-resident stem cell system to effect repair upon injury. Despite the demonstrated efficiency of this system in restoring muscle mass after many acute injuries, in conditions of severe trauma such as those evident in volumetric muscle loss (VML) (>20 % by mass), this self-repair capability is unable to restore tissue architecture, requiring interventions which currently are largely surgical. As a possible alternative, the generation of artificial muscle using tissue engineering approaches may also be of importance in the treatment of VML and muscle diseases such as dystrophies. Three-dimensional (3D) bioprinting has been identified as a promising technique for regeneration of the complex architecture of skeletal muscle. This review discusses existing treatment strategies following muscle damage, recent progress in bioprinting techniques, the bioinks used for muscle regeneration, the immunogenicity of scaffold materials, and in vitro and in vivo maturation techniques for 3D bio-printed muscle constructs. The pros and cons of these bioink formulations are also highlighted. Finally, we present the current limitations and challenges in the field and critical factors to consider for bioprinting approaches to become more translationa and to produce clinically relevant engineered muscle. STATEMENT OF SIGNIFICANCE: This review discusses the physiopathology of muscle injuries and existing clinical treatment strategies for muscle damage, the types of bioprinting techniques that have been applied to bioprinting of muscle, and the bioinks commonly used for muscle regeneration. The pros and cons of these bioinks are highlighted. We present a discussion of existing gaps in the literature and critical factors to consider for the translation of bioprinting approaches and to produce clinically relevant engineered muscle. Finally, we provide insights into what we believe will be the next steps required before the realization of the application of tissue-engineered muscle in humans. We believe this manuscript is an insightful, timely, and instructive review that will guide future muscle bioprinting research from a fundamental construct creation approach, down a translational pathway to achieve the desired impact in the clinic.

Advanced Immunomodulatory Biomaterials for Therapeutic Applications

The multifaceted biological defense system modulating complex immune responses against pathogens and foreign materials plays a critical role in tissue homeostasis and disease progression. Recently developed biomaterials that can specifically regulate immune responses, nanoparticles, graphene, and functional hydrogels have contributed to the advancement of tissue engineering as well as disease treatment. The interaction between innate and adaptive immunity, collectively determining immune responses, can be regulated by mechanobiological recognition and adaptation of immune cells to the extracellular microenvironment. Therefore, applying immunomodulation to tissue regeneration and cancer therapy involves manipulating the properties of biomaterials by tailoring their composition in the context of the immune system. This review provides a comprehensive overview of how the physicochemical attributes of biomaterials determine immune responses, focusing on the physical properties that influence innate and adaptive immunity. This review also underscores the critical aspect of biomaterial-based immune engineering for the development of novel therapeutics and emphasizes the importance of understanding the biomaterials-mediated immunological mechanisms and their role in modulating the immune system.

Antibacterial and Immunomodulatory Properties of Acellular Wharton’s Jelly Matrix

Of all biologic matrices, decellularized tissues have emerged as a promising tool in the field of regenerative medicine. Few empirical clinical studies have shown that Wharton’s jelly (WJ) of the human umbilical cord promotes wound closure and reduces wound-related infections. In this scope, we herein investigated whether decellularized (DC)-WJ could be used as an engineered biomaterial. In comparison with devitalized (DV)-WJ, our results showed an inherent effect of DC-WJ on Gram positive (S. aureus and S. epidermidis) and Gram negative (E. coli and P. aeruginosa) growth and adhesion. Although DC-WJ activated the neutrophils and monocytes in a comparable magnitude to DV-WJ, macrophages modulated their phenotypes and polarization states from the resting M0 phenotype to the hybrid M1/M2 phenotype in the presence of DC-WJ. M1 phenotype was predominant in the presence of DV-WJ. Finally, the subcutaneous implantation of DC-WJ showed total resorption after three weeks of implantation without any sign of foreign body reaction. These significant data shed light on the potential regenerative application of DC-WJ in providing a suitable biomaterial for tissue regenerative medicine and an ideal strategy to prevent wound-associated infections.

Postoperative Complications in Breast Reconstruction With Porcine Acellular Dermis and Polypropylene Meshes in Subpectoral Implant Placement

AIM

This research compares postoperative complication rates with Strattice™, SERAGYN^® BR, and TiLOOP^® Bra interposition devices for subpectoral implant placement after skin or nipple sparing mastectomy.

PATIENTS AND METHODS

188 breast reconstructions in 157 patients after primary (n=96), secondary (n=71), or prophylactic (n=21) surgery were analyzed regarding major and minor complications.

RESULTS

With acellular dermal matrix (ADM) Strattice™, 27.5% major and 27.5% minor complications occurred. Implant loss rates were 27.3% in primary and 30.8% in secondary reconstructions. With SERAGYN^® BR, 11.1% major and 13,0% minor complications occurred. Implant losses (6.1%) occurred exclusively in primary reconstructions. With TiLOOP^® Bra, 14.9% major and 9.6% minor complications occurred. Implant loss rates were 7.7% in primary and 7.1% in secondary reconstructions.

CONCLUSION

ADM was associated with high complication rates in primary and secondary reconstructions. Low complication rates were seen with mesh interposition devices in primary, secondary, and prophylactic reconstructions.

Decellularized xenografts in regenerative medicine: From processing to clinical application

Decellularized xenografts are an inherent component of regenerative medicine. Their preserved structure, mechanical integrity and biofunctional composition have well established them in reparative medicine for a diverse range of clinical indications. Nonetheless, their performance is highly influenced by their source (ie species, age, tissue) and processing (ie decellularization, crosslinking, sterilization and preservation), which govern their final characteristics and determine their success or failure for a specific clinical target. In this review, we provide an overview of the different sources and processing methods used in decellularized xenografts fabrication and discuss their effect on the clinical performance of commercially available decellularized xenografts.

Human Primary Dermal Fibroblasts Interacting with 3-Dimensional Matrices for Surgical Application Show Specific Growth and Gene Expression Programs

Several types of 3-dimensional (3D) biological matrices are employed for clinical and surgical applications, but few indications are available to guide surgeons in the choice among these materials. Here we compare the in vitro growth of human primary fibroblasts on different biological matrices commonly used for clinical and surgical applications and the activation of specific molecular pathways over 30 days of growth. Morphological analyses by Scanning Electron Microscopy and proliferation curves showed that fibroblasts have different ability to attach and proliferate on the different biological matrices. They activated similar gene expression programs, reducing the expression of collagen genes and myofibroblast differentiation markers compared to fibroblasts grown in 2D. However, differences among 3D matrices were observed in the expression of specific metalloproteinases and interleukin-6. Indeed, cell proliferation and expression of matrix degrading enzymes occur in the initial steps of interaction between fibroblast and the investigated meshes, whereas collagen and interleukin-6 expression appear to start later. The data reported here highlight features of fibroblasts grown on different 3D biological matrices and warrant further studies to understand how these findings may be used to help the clinicians choose the correct material for specific applications.

Regulation of Peritoneal Inflammatory Response to Implant Material Using an Ex Vivo Model System

BACKGROUND

Implants used in abdominal wall reconstruction are associated with intra-abdominal inflammation that can cause complications such as adhesions, fistulae, or failure of the implant. This study analyzed the inflammatory response of human peritoneum explants when exposed to different implant materials including synthetic and biological (cross-linked and non-cross-linked).

MATERIALS AND METHODS

Human peritoneum explants (parietal and visceral) were incubated in culture with implants used for abdominal wall reconstruction. Implants included Permacol (biological implant with chemical cross-linking); Biodesign and Strattice (biological implants without chemical cross-linking); Prolene (synthetic nonabsorbable); and Vicryl (synthetic absorbable). Control peritoneum samples were incubated without implant. Cytokine concentrations and corresponding gene expression were measured by enzyme-linked immunosorbent assay and quantitative polymerase chain reaction, respectively. Further evaluation included assessment of tissue viability and implant-cytokine adsorption.

RESULTS

Incubation of human peritoneal explants with Biodesign or Strattice was associated with a significant reduction in interleukin-6, interleukin-1β, and tumour necrosis factor alpha protein and gene expression compared with control. These could not be explained by reduced cell viability or implant-cytokine adsorption. Incubation of explants in Biodesign-conditioned media displayed a similar effect to incubation of explants with Biodesign itself.

CONCLUSIONS

Human peritoneal explants cultured with different mesh implant materials show an altered inflammatory cytokine response suggesting a tissue-specific response. Downregulation of key inflammatory cytokines by the peritoneum exposed to non-cross-linked biological implants may be mediated by the release of soluble factors from these implants inhibiting cytokine gene expression. This ex vivo human peritoneal system provides a novel preclinical model to investigate peritoneum-implant interactions.

Absorbable Polyglactin vs. Non-Cross-linked Porcine Biological Mesh for the Surgical Treatment of Infected Incisional Hernia

BACKGROUND

The use of absorbable meshes during contaminated or infected incisional hernia (IH) repair is associated with high morbidity and recurrence rates. Biological meshes might be more appropriate but have been described in highly heterogeneous series. This study aimed at comparing the efficacy of absorbable vs. biological meshes for the treatment of contaminated or infected IH in a homogeneous series with a standardized technique.

METHODS

Data of all patients operated on between 2008 and 2015 for contaminated or infected IH, using an absorbable (A) Vicryl® or a biological (B) Strattice® mesh, were reviewed. Patient characteristics, infectious complication rates, and recurrence-free outcome (RFO) were compared between the two groups. A propensity score methodology was applied to a Cox regression model to deal with unbalanced characteristics between groups.

RESULTS

Patient demographics in A (n = 57) and in B (n = 24) were similar except that B patients had larger parietal defects (p < 0.001) and higher Center for Disease Control (CDC) wound class (p = 0.034). Patients in A had statistically significantly more postoperative early (61.4% vs. 33.3%, p = 0.03) and late (31.2% vs. 8.3%, p = 0.046) infectious complications. Six-, 12-, and 36-month RFO rates were 77%, 47%, and 24%, and 96%, 87%, and 82% in A and B, respectively, p < 0.001. Raw multivariable Cox regression analysis found that B (HR = 0.1, 95% CI [0.03-0.34], p < 0.001) was independently associated with prolonged RFO (HR = 0.091, 95% CI [0.045-0.180], p < 0.001).

CONCLUSION

Biological meshes seem to be superior to absorbable meshes in patients with contaminated or infected incisional hernia. These results need to be confirmed by prospective randomized trials.

Macrophages Are Key Regulators of Stem Cells during Skeletal Muscle Regeneration and Diseases

Muscle regeneration is a closely regulated process that involves a variety of cell types such as satellite cells, myofibers, fibroadipogenic progenitors, endothelial cells, and inflammatory cells. Among these different cell types, macrophages emerged as a central actor coordinating the different cellular interactions and biological processes. Particularly, the transition of macrophages from their proinflammatory to their anti-inflammatory phenotype was shown to regulate inflammation, myogenesis, fibrosis, vascularization, and return to homeostasis. On the other hand, deregulation of macrophage accumulation or polarization in chronic degenerative muscle disorders was shown to impair muscle regeneration. Considering the key roles of macrophages in skeletal muscle, they represent an attractive target for new therapeutic approaches aiming at mitigating various muscle disorders. This review aims at summarizing the novel insights into macrophage heterogeneity, plasticity, and functions in skeletal muscle homeostasis, regeneration, and disease.

Biomaterials: Foreign Bodies or Tuners for the Immune Response?

The perspectives of regenerative medicine are still severely hampered by the host response to biomaterial implantation, despite the robustness of technologies that hold the promise to recover the functionality of damaged organs and tissues. In this scenario, the cellular and molecular events that decide on implant success and tissue regeneration are played at the interface between the foreign body and the host inflammation, determined by innate and adaptive immune responses. To avoid adverse events, rather than the use of inert scaffolds, current state of the art points to the use of immunomodulatory biomaterials and their knowledge-based use to reduce neutrophil activation, and optimize M1 to M2 macrophage polarization, Th1 to Th2 lymphocyte switch, and Treg induction. Despite the fact that the field is still evolving and much remains to be accomplished, recent research breakthroughs have provided a broader insight on the correct choice of biomaterial physicochemical modifications to tune the reaction of the host immune system to implanted biomaterial and to favor integration and healing.

Production and Characterization of Chemically Cross-Linked Collagen Scaffolds

Chemical cross-linking of collagen-based devices is used as a means of increasing the mechanical stability and control the degradation rate upon implantation. Herein, we describe techniques to produce cross-linked with glutaraldehyde (GTA; amine terminal cross-linker), 4-arm polyethylene glycol succinimidyl glutarate (4SP; amine terminal cross-linker), diphenyl phosphoryl azide (DPPA; carboxyl terminal cross-linker), and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC; carboxyl terminal cross-linker) collagen films. In addition, we provide protocols to characterize the biophysical (swelling), biomechanical (tensile), and biological (metabolic activity, proliferation and viability using human dermal fibroblasts and THP-1 macrophages) properties of the cross-linked collagen scaffolds.

Acetic acid and pepsin result in high yield, high purity and low macrophage response collagen for biomedical applications

Collagen based devices are frequently associated with foreign body response. Although several pre- (e.g. species, state of animal, tissue) and post- (e.g. cross-linking, scaffold architecture) extraction method factors have a profound effect on foreign body response, little is known about which and how during the extraction process factors mediate foreign body response. In this study, we assessed the influence of acetic acid and hydrochloric acid and the utilisation or not of pepsin or salt precipitation during collagen extraction on the yield, purity, free amines, denaturation temperature, resistance to collagenase degradation and macrophage response. Acetic acid/pepsin extracted collagen exhibited the highest yield, purity and free amine content and the lowest denaturation temperature. No differences in resistance to collagenase digestion were detected between the groups. Although all treatments exhibited similar macrophage morphology comprised of round cells (M1 phenotype), elongated cells (M2 phenotype) and cell aggregates (foreign body response), significantly more elongated cells were observed on HC films. Although no differences in metabolic activity were observed between the groups, the DNA concentration was significantly lower for the hydrochloric acid treatments. Further, cytokine analysis revealed that hydrochloric acid treatments induced significantly higher IL-1β and TNF-α release with respect to acetic acid treatments. Salt precipitation did not influence the parameters assessed. Collectively, these data suggest that during the collagen extraction process variables should also be monitored as, evidently, they affect the physicochemical and biological properties of collagen preparations.

Modulating Immunological Responses of Electrospun Fibers for Tissue Engineering

The promise of tissue engineering is to improve or restore functions of impaired tissues or organs. However, one of the biggest challenges to its translation to clinical applications is the lack of tissue integration and functionality. The plethora of cellular and molecular events occurring following scaffold implantation is a major bottleneck. Recent studies confirmed that inflammation is a crucial component influencing tissue regeneration. Immuno-modulation or immune-engineering has been proposed as a potential solution to overcome this key challenge in regenerative medicine. In this review, strategies to modify scaffold physicochemical properties through the use of the electrospinning technique to modulate host response and improve scaffold integration will be discussed. Electrospinning, being highly versatile allows the fabrication of ECM-mimicking scaffolds and also offers the possibility to control scaffold properties for instance, tailoring of fiber properties, chemical conjugation or physical adsorption of non-immunogenic materials on the scaffold surface, encapsulating cells or anti-inflammatory molecules within the scaffold. Such electrospun scaffold-based immune-engineering strategies can significantly improve the resulting outcomes of tissue engineering scaffolds.

Promoting tissue regeneration by modulating the immune system

The immune system plays a central role in tissue repair and regeneration. Indeed, the immune response to tissue injury is crucial in determining the speed and the outcome of the healing process, including the extent of scarring and the restoration of organ function. Therefore, controlling immune components via biomaterials and drug delivery systems is becoming an attractive approach in regenerative medicine, since therapies based on stem cells and growth factors have not yet proven to be broadly effective in the clinic. To integrate the immune system into regenerative strategies, one of the first challenges is to understand the precise functions of the different immune components during the tissue healing process. While remarkable progress has been made, the immune mechanisms involved are still elusive, and there is indication for both negative and positive roles depending on the tissue type or organ and life stage. It is well recognized that the innate immune response comprising danger signals, neutrophils and macrophages modulates tissue healing. In addition, it is becoming evident that the adaptive immune response, in particular T cell subset activities, plays a critical role. In this review, we first present an overview of the basic immune mechanisms involved in tissue repair and regeneration. Then, we highlight various approaches based on biomaterials and drug delivery systems that aim at modulating these mechanisms to limit fibrosis and promote regeneration. We propose that the next generation of regenerative therapies may evolve from typical biomaterial-, stem cell-, or growth factor-centric approaches to an immune-centric approach.

STATEMENT OF SIGNIFICANCE

Most regenerative strategies have not yet proven to be safe or reasonably efficient in the clinic. In addition to stem cells and growth factors, the immune system plays a crucial role in the tissue healing process. Here, we propose that controlling the immune-mediated mechanisms of tissue repair and regeneration may support existing regenerative strategies or could be an alternative to using stem cells and growth factors. The first part of this review we highlight key immune mechanisms involved in the tissue healing process and marks them as potential target for designing regenerative strategies. In the second part, we discuss various approaches using biomaterials and drug delivery systems that aim at modulating the components of the immune system to promote tissue regeneration.

The host response to naturally-derived extracellular matrix biomaterials

Biomaterials based on natural materials including decellularized tissues and tissue-derived hydrogels are becoming more widely used for clinical applications. Because of their native composition and structure, these biomaterials induce a distinct form of the foreign body response that differs from that of non-native biomaterials. Differences include direct interactions with cells via preserved moieties as well as the ability to undergo remodeling. Moreover, these biomaterials could elicit adaptive immune responses due to the presence of modified native molecules. Therefore, these biomaterials present unique challenges in terms of understanding the progression of the foreign body response. This review covers this response to natural materials including natural polymers, decellularized tissues, cell-derived matrix, tissue derived hydrogels, and biohybrid materials. With the expansion of the fields of regenerative medicine and tissue engineering, the current repertoire of biomaterials has also expanded and requires continuous investigation of the responses they elicit.

* Collagen Cross-Linking: Biophysical, Biochemical, and Biological Response Analysis

Extracted forms of collagen are subjected to chemical cross-linking to enhance their stability. However, traditional cross-linking approaches are associated with toxicity and inflammation. This work investigates the stabilization capacity, cytotoxicity and inflammatory response of collagen scaffolds cross-linked with glutaraldehyde (GTA), 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide, 4-arm polyethylene glycol (PEG) succinimidyl glutarate (4SP), genipin (GEN), and oleuropein. Although all cross-linking methods reduced free amine groups, variable data were obtained with respect to denaturation temperature, resistance to collagenase digestion, and mechanical properties. With respect to biological analysis, fibroblast cultures showed no significant difference between the treatments. Although direct cultures with human-derived leukemic monocyte cells (THP-1) clearly demonstrated the cytotoxic effect of GTA, THP-1 cultures supplemented with conditioned medium from the various groups showed no significant difference between the treatments. With respect to cytokine profile, no significant difference in secretion of proinflammatory (e.g., interleukin [IL]-1β, IL-8, tumor necrosis factor-α) and anti-inflammatory (e.g., vascular endothelial growth factor) cytokines was observed between the noncross-linked and the 4SP and GEN cross-linked groups, suggesting the suitability of these agents as collagen cross-linkers.

Human immune-cell response towards diverse xenogeneic and allogeneic decellularized biomaterials

BACKGROUND

Immunological knowledge on processed biological implants and mesh-prostheses is still mainly based on animal models, lacking information on the species-specific human immune response. We hypothesized that in contrast to human tissue even decellularized xenogenic specimens would lead to significant and tissue source dependent human immune reactions.

METHODS

Specimens from processed allogenic and xenogenic pulmonary arteries, pericardium or dermis, were co-cultured with human peripheral blood mononuclear cells (PBMNC). Proliferative responses were measured in tritiated thymidine incorporation assays (n = 10). Stimulation indices (SI), calculated as counts-per-minute of co-cultured PBMNC divided by the cpm of basic cell proliferation, were compared.

RESULTS

Compared to native porcine pulmonary artery tissue decellularization significantly reduced human PBMNC proliferation (mean SI: 48.7 vs. 18.0, p < 0.01), which was still higher compared to the human equivalent (SI: 0.7 vs. 1.7). Also the processed human dermal implant did not elicit immune response (SI: 1.5), whereas the decellularized and cross-linked porcine dermis lead to a significant human cell-proliferation (SI: 8.4, p < 0.01). Interestingly, both the processed human (SI: 15.2) and bovine pericardial patches (SI: 15.1) led to higher immune cell proliferation.

CONCLUSION

Even decellularized or cross-linked xenogenic cardiovascular and reconstructive biomaterials elicit increased human immune responses not seen in the majority of allogenic specimens tested.

Fabrication of silk mesh with enhanced cytocompatibility: preliminary in vitro investigation toward cell-based therapy for hernia repair

Recent studies have demonstrated that combining cells with meshes prior to implantation successfully enhanced hernia repair. The idea is to create a biologic coating surrounding the mesh with autologous cells, before transplantation into the patient. However, due to the lack of a prompt and robust cell adhesion to the meshes, extensive in vitro cultivation is required to obtain a homogenous cell layer covering the mesh. In this context, the objective of this publication is to manufacture meshes made of silk fibres and to enhance the cytoadhesion and cytocompatibility of the biomaterial by surface immobilization of a pro-adhesive wheat germ agglutinin (lectin WGA). We first investigated the affinity between the glycoprotein WGA and cells, in solution and then after covalent immobilization of WGA on silk films. Then, we manufactured meshes made of silk fibres, tailored them with WGA grafting and finally evaluated the cytocompatibility and the inflammatory response of silk and silk-lectin meshes compared to common polypropylene mesh, using fibroblasts and peripheral blood mononuclear cells, respectively. The in vitro experiments revealed that the cytocompatibility of silk can be enhanced by surface immobilization with lectin WGA without exhibiting negative response in terms of pro-inflammatory reaction. Grafting lectin to silk meshes could bring advantages to facilitate cell-coating of meshes prior to implantation, which is an imperative prerequisite for abdominal wall tissue regeneration using cell-based therapy.

The Effect of Biomaterials Used for Tissue Regeneration Purposes on Polarization of Macrophages

Activation of macrophages is critical in the acute phase of wound healing after implantation of surgical biomaterials. To understand the response of macrophages, they are often cultured in vitro on biomaterials. Since a wide range of biomaterials is currently used in the clinics, we undertook a systematic review of the macrophage polarization in response to these different surgical biomaterials in vitro. Beside the chemistry, material characteristics such as dimension, pore size, and surface topography are of great influence on the response of macrophages. The macrophage response also appears to depend on the differences in sterilization techniques that induce lasting biochemical changes or residues of chemicals and their byproducts used for sterilization. Regarding tissue-based biomaterials, macrophages on human or porcine dermis, strongly cross-linked by chemicals elicit in general a proinflammatory response with higher amounts of proinflammatory cytokines. Synthetic biomaterials such as polyethylene, polyethylene terephthalate (PET) + polyacrylamide (PAAm), PET + sodium salt of poly(acrylic acid) (PAANa), perfluoropolyether (PFPE) with large posts, PEG-g-PA, and polydioxanone (PDO) always appear to elicit an anti-inflammatory response in macrophages, irrespective of origin of the macrophages, for example, buffy coats or full blood. In conclusion, in general in vitro models contribute to evaluate the foreign body reaction on surgical biomaterials. Although it is difficult to simulate complexity of host response elicited by biomaterials, after their surgical implantation, an in vitro model gives indications of the initial foreign body response and allows the comparison of this response between biomaterials.

Remodeling of Noncrosslinked Acellular Dermal Matrices in a Rabbit Model of Ventral Hernia Repair

Background: Bioprostheses represent a significant advance in the abdominal wall reconstruction since they become degraded until their complete elimination in the recipient organism. This study examines remodeling in the host of three noncrosslinked porcine dermal collagen biomeshes: Strattice™ (St; LifeCell Corp.), XCM Biologic® Tissue Matrix (XCM; Synthes CMF) and Protexa® (Pr; Deco Med S.R.L.). Methods: Partial ventral hernia defects created in New Zealand White rabbits were repaired using the biomeshes that were placed in an inlay, preperitoneal position. At 14 and 90 days after implantation, explants were assessed in terms of their host tissue incorporation by morphological studies, collagen gene/protein expression (quantitative real-time PCR/immunofluorescence), macrophage response (immunohistochemistry) and biomechanical strength. Results: There were no cases of mortality or infection. Among our macroscopic findings, the mesh detachment detected in one third of the Pr implants at 90 days was of note. The host tissue response to all the biomeshes was similar at both time points, with a tendency observed for their encapsulation. There were no appreciable signs of mesh degradation. The extent of host tissue infiltration and collagenization was greater for St and Pr than for XCM. Macrophages were observed in zones of inflammation and tissue infiltration inside the mesh. XCM showed a greater macrophage response at 90 days (p < 0.05). Improved tensile strength was observed for St (p < 0.05) over Pr and unrepaired defects. Conclusions:St showed the best behavior, featuring good collagenization and tensile strength while also inducing a minimal foreign body reaction.

Emerging Trends in Abdominal Wall Reinforcement: Bringing Bio-Functionality to Meshes

Abdominal wall hernia is a recurrent issue world-wide and requires the implantation of over 1 million meshes per year. Because permanent meshes such as polypropylene and polyester are not free of complications after implantation, many mesh modifications and new functionalities have been investigated over the last decade. Indeed, mesh optimization is the focus of intense development and the biomaterials utilized are now envisioned as being bioactive substrates that trigger various physiological processes in order to prevent complications and to promote tissue integration. In this context, it is of paramount interest to review the most relevant bio-functionalities being brought to new meshes and to open new avenues for the innovative development of the next generation of meshes with enhanced properties for functional abdominal wall hernia repair.

The open abdomen, indications, management and definitive closure

The indications for Open Abdomen (OA) are generally all those situations in which is ongoing the development an intra-abdominal hypertension condition (IAH), in order to prevent the development of abdominal compartmental syndrome (ACS). In fact all those involved in care of a critically ill patient should in the first instance think how to prevent IAH and ACS. In case of ACS goal directed therapy to achieve early opening and early closure is the key: paradigm of closure shifts to combination of therapies including negative pressure wound therapy and dynamic closure, in order to reduce complications and avoid incisional hernia. There have been huge studies and progress in survival of critically ill trauma and septic surgical patients: this in part has been through the great work of pioneers, scientific societies and their guidelines; however future studies and continued innovation are needed to better understand optimal treatment strategies and to define more clearly the indications, because OA by itself is still a morbid procedure.

To cross-link or not to cross-link? Cross-linking associated foreign body response of collagen-based devices

Collagen-based devices, in various physical conformations, are extensively used for tissue engineering and regenerative medicine applications. Given that the natural cross-linking pathway of collagen does not occur in vitro, chemical, physical, and biological cross-linking methods have been assessed over the years to control mechanical stability, degradation rate, and immunogenicity of the device upon implantation. Although in vitro data demonstrate that mechanical properties and degradation rate can be accurately controlled as a function of the cross-linking method utilized, preclinical and clinical data indicate that cross-linking methods employed may have adverse effects on host response, especially when potent cross-linking methods are employed. Experimental data suggest that more suitable cross-linking methods should be developed to achieve a balance between stability and functional remodeling.

Effectiveness of porcine dermal collagen in giant hernia closure in patients with deleterious fascia constitution after orthotopic liver transplantation

Incisional hernias (IHs) occur universally after orthotopic liver transplantation (OLT). This study aimed to investigate the effectiveness of porcine dermal collagen (PDC) as a closing aid in giant hernias after OLT in a prospective trial. If direct closure (DC) was not feasible due to the hernia size and abdominal wall constitution, a PDC mesh was implanted. All patients from the PDC and DC groups were followed prospectively for 24 months. IH recurrence rates served as the primary endpoint, and the development of infections and wound healing disorders served as the secondary endpoints. Recurrence rate was 21% (4/19) in DC patients and 12% (2/16) in PDC patients (P = 0.045). Implant site infections occurred in five of PDC and one of DC patients (P < 0.05). All of them were managed with antibiotics; two of the PDC patients required surgical drainage. Histological analysis of PDC mesh biopsies indicated good angiogenesis and integration of the PDC into the abdominal wall. PDC was effective in our study for incisional hernia repair, and our results compared favourably with those of patients in whom direct hernia closure was feasible.

Outcome of Abdominal Wall Hernia Repair with Biologic Mesh: Permacol™ versus Strattice™

The use of biologic mesh in abdominal wall operations has gained popularity despite a paucity of outcome data. Numerous biologic products are available with virtually no clinical comparison studies. A retrospective study was conducted to compare patients who underwent abdominal wall hernia repair with Permacol™ (crosslinked porcine dermis) and Strattice™ (noncrosslinked porcine dermis). Of 270 reviewed patients, 195 were implanted with Permacol™ and 75 with Strattice™. Ventral hernia repairs comprised the majority (85% for Permacol, 97% for Strattice™). Postoperative infection rate was lower in the Strattice™ group (5 vs 21%, P < 0.01). In the Permacol™ group only, the overall complication rates were significantly higher in patients with infected versus clean wounds (55 vs 35%, P < 0.05) and in obese patients (body mass index 40 kg/m2 or greater [57 vs 34%], P < 0.01). Short-term complication and recurrence rates were higher when mesh was used as a fascial bridge: 51 versus 28 per cent for Permacol™, 58 versus 20 per cent for Strattice™. The hernia recurrence was similar in both groups. In this review of patients undergoing abdominal hernia repair with biologic mesh, Strattice™ mesh was associated with a lower short-term complication rate compared with Permacol™, but the hernia recurrence rate was similar.

Predicting in vivo responses to biomaterials via combined in vitro and in silico analysis

The host response to both synthetic and biologically derived biomaterials is a temporally regulated, complex process that involves multiple interacting cell types. This complexity has classically limited the efficacy of in vitro assays for predicting the in vivo outcome, necessitating the use of costly animal models for biomaterial development. The present study addressed these challenges by developing an in vitro assay that characterized the dynamic inflammatory response of human monocyte-derived-macrophages to biomaterials, coupled with quasi-mechanistic analysis in silico analysis: principal component analysis (PCA) and dynamic network analysis (DyNA). Synthetic and extracellular matrix (ECM)-derived materials were evaluated using this method, and were then associated with the in vivo remodeling and macrophage polarization response in a rodent skeletal muscle injury model. PCA and DyNA revealed a distinct in vitro macrophage response to ECM materials that corresponded to constructive remodeling and an increased M2 macrophage presence in vivo. In contrast, PCA and DyNA suggested a response to crosslinked ECM and synthetic materials characteristic of a foreign body reaction and dominant M1 macrophage response. These results suggest that in silico analysis of an in vitro macrophage assay may be useful as a predictor for determining the in vivo host response to implanted biomaterials.

Long-term outcome of biologic graft: a case report

INTRODUCTION

Biologic grafts have been shown to support tissue regeneration in various animal models. Very few reports in the literature exist to show tissue remodeling in patients after placement of a biologic graft.

CASE PRESENTATION

We report the case of a 69-year-old Caucasian man with a history of small bowel carcinoid resection and concurrent recurrent ventral hernia repair with component separation and underlay biologic graft placement who underwent re-operation for metastatic carcinoid tumor to his liver. Complete incorporation of the biologic graft was observed. Tissue analysis of the incised midline fascia revealed tissue remodeling at the site of the previous abdominal wall defect.

CONCLUSION

Placement of a biologic graft in ventral hernia repair supports tissue regeneration similar to that previously reported in animal models.

Delayed primary closure of contaminated abdominal wall defects with non-crosslinked porcine acellular dermal matrix compared with conventional staged repair: a retrospective study

INTRODUCTION

Synthetic mesh has been used traditionally to repair abdominal wall defects, but its use is limited in the case of bacterial contamination. New biological materials are now being used successfully for delayed primary closure of contaminated abdominal wall defects. The costs of biological materials may prevent surgeons from using them. We compared the conventional staged repair of contaminated abdominal wall defects with a single-stage procedure using a non-crosslinked porcine acellular dermal matrix.

METHODS

A total of 14 cases with Grade 3 contaminated abdominal wall defects underwent delayed primary closure of the abdomen using a non-crosslinked porcine acellular dermal matrix (Strattice™ Reconstructive Tissue Matrix, LifeCell Corp., Branchburg, NJ, USA). The results were compared with a group of 14 patients who had received conventional treatment for the repair of contaminated abdominal wall defects comprising a staged repair during two separate hospital admissions employing synthetic mesh. Treatment modalities, outcomes, and costs were compared.

RESULTS

In all cases treated with delayed primary closure employing non-crosslinked porcine acellular dermal matrix, there were no complications related to its use. Two patients died due to unrelated events. Although treatment costs were estimated to be similar in the two groups, the patients treated with porcine acellular dermal matrix spent less time as an inpatient than those receiving conventional two-stage repair.

CONCLUSIONS

Delayed primary closure of contaminated abdominal wall defects using a non-crosslinked porcine acellular dermal matrix may be a suitable alternative to conventional staged repair. In our patients, it resulted in early restoration of abdominal wall function and shorter hospitalization. The costs for treating contaminated abdominal wall defects using porcine acellular dermal matrix during a single hospital admission were not higher than costs for conventional two-stage repair. Further randomized studies are needed to expand upon these findings.

Effects of mesenchymal stem cell and fibroblast coating on immunogenic potential of prosthetic meshes in vitro

BACKGROUND

The aim of this study was to reveal the effect of fibroblast or mesenchymal stem cell (MSC) coating on the mesh-induced production of IL-1β, IL-6, and VEGF by macrophages.

METHODS

Four commonly used surgical meshes were tested in this study, including Parietex, SoftMesh, TIGR, and Strattice. One-square-centimeter pieces of each mesh were placed on top of a monolayer of human fibroblasts or rat MSCs. The coating status was monitored with a light microscope. The human promonocytic cell line U937 was induced to differentiate into macrophages (MΦ). Three weeks later, meshes were transferred to new 24-well plates and cocultured with the MΦs for 72 h. Culture medium was collected and analyzed for IL-1β, IL-6, and VEGF production using standard ELISA essays. Parallel mesh samples were fixed with paraformaldehyde or glutaraldehyde for histology or transmission electronic microscopy (TEM) analyses, respectively.

RESULTS

Uncoated meshes induced increased production of all three cytokines compared with macrophages cultured alone. HF coating further increased the production of both IL-6 and VEGF but reduced IL-1β production. Except for the SoftMesh group, MSC coating significantly blunted release of all cytokines to levels even lower than with MΦs cultured alone. MΦs tended to deteriorate in the presence of MSCs. Both histology and TEM revealed intimate interactions between cell-coated meshes and MΦs.

CONCLUSIONS

Cytokine response to fibroblast coating varied, while MSC coating blunted the immunogenic effect of both synthetic and biologic meshes in vitro. Cell coating appears to affect mesh biocompatibility and may become a key process in mesh evolution.

Bioprosthetic tissue matrices in complex abdominal wall reconstruction

Background:

Complex abdominal defects are difficult problems encountered by surgeons in multiple specialties. Although current evidence supports the primary repair of these defects with mesh reinforcement, it is unclear which mesh is superior for any given clinical scenario. The purpose of this review was to explore the characteristics of and clinical relevance behind bioprosthetic tissue matrices in an effort to better clarify their role in abdominal wall reconstruction.

Methods:

We reviewed the peer-reviewed literature on the use of bioprosthetic mesh in human subjects. Basic science articles and large retrospective and prospective reviews were included in author’s analysis. The clinical performance and characteristics of 13 bioprosthetic tissue matrices were evaluated.

Results:

The majority of the products evaluated perform well in contaminated fields, where the risk of wound-healing difficulties is high. Clinical outcomes, which included infection, reherniation, and bulge formation, were variable, and the majority of the studies had a mean follow-up of less than 24 months.

Conclusions:

Although bioprosthetic matrix has a multitude of indications within the growing field of abdominal wall reconstruction, the functionality, regenerative capacity, and long-term fate of these products have yet to be fully established. Furthermore, the clinical performance, indications, and contraindications for each type of matrix need to be fully evaluated in long-term outcome studies.

Complete horizontal skin cell resurfacing and delayed vertical cell infiltration into porcine reconstructive tissue matrix compared to bovine collagen matrix and human dermis

BACKGROUND

Xenogenous dermal matrices are used for hernia repair and breast reconstruction. Full-thickness skin replacement is needed after burn or degloving injuries with exposure of tendons or bones. The authors used a human skin organ culture model to study whether porcine reconstructive tissue matrix (Strattice) is effective as a dermal tissue replacement.

METHODS

Skin cells or split-thickness skin grafts were seeded onto human deepidermized dermis, Strattice, and Matriderm. Cellular resurfacing and matrix infiltration were monitored by live fluorescence imaging, histology, and electron microscopy. Proliferation, apoptosis, cell differentiation, and adhesion were analyzed by immunohistochemistry.

RESULTS

Epithelial resurfacing and vertical proliferation were reduced and delayed with both bioartificial matrices compared with deepidermized dermis; however, no differences in apoptosis, cell differentiation, or basement membrane formation were found. Vertical penetration was greatest on Matriderm, whereas no matrix infiltration was found on Strattice in the first 12 days. Uncompromised horizontal resurfacing was greatest with Strattice but was absent with Matriderm. Strattice showed no stimulatory effect on cellular inflammation.

CONCLUSIONS

Matrix texture and surface properties governed cellular performance on tissues. Although dense dermal compaction delayed vertical cellular ingrowth for Strattice, it allowed uncompromised horizontal resurfacing. Dense dermal compaction may slow matrix decomposition and result in prolonged biomechanical stability of the graft. Reconstructive surgeons should choose the adequate matrix substitute depending on biomechanical requirements at the recipient site. Strattice may be suitable as a dermal replacement at recipient sites with high mechanical load requirements.

Decellularized dermis-polymer complex provides a platform for soft-to-hard tissue interfaces

To develop a soft-to-hard tissue interface, we made a decellularized dermis/poly(methyl methacrylate) (PMMA) complex by soaking the decellularized dermis in methyl methacrylate (MMA) and an initiator, and then polymerizing the MMA. The decellularized tissue was chosen because of its good biocompatibility and the easiness of suturing it, and MMA because of its hard tissue compatibility and wide use in the biomedical field. The MMA filled the cavities in the dermis and polymerized within 10 min. No leaking or polymer aggregation was observed, implying that a homogenous tissue-polymer complex had formed. The cell infiltration and the integration between the tissue and the dermis occurred in vivo, whereas the cells could not infiltrate the tissue-polymer complex. This implies that the interface tissue should possess both complex and noncomplex parts, where the cells infiltrate the noncomplex part and stop when they encounter the complex part, integrating the soft and hard tissue or hard polymer.

Biology of biological meshes used in hernia repair

Successful repair of most hernias requires the use of a prosthetic implant for reinforcement of the defect. Because of the need for prosthetic implants to resist infections as well to support repairs in contaminated or potentially contaminated fields, biological meshes have been developed to take the place of nondegradable synthetic meshes in cases where mesh infection is of high concern. The ideal is a biological matrix that resists infection while providing durable reinforcement of a hernia repair. This article reviews the validity of assumptions that support the purported notion of the biological behavior of biological meshes.

Biologic properties of surgical scaffold materials derived from dermal ECM

Surgical scaffold materials manufactured from donor human or animal tissue are increasingly being used to promote soft tissue repair and regeneration. The clinical product consists of the residual extracellular matrix remaining after a rigorous decellularization process. Optimally, the material provides both structural support during the repair period and cell guidance cues for effective incorporation into the regenerating tissue. Surgical scaffold materials are available from several companies and are unique products manufactured by proprietary methodology. A significant need exists for a more thorough understanding of scaffold properties that impact the early steps of host cell recruitment and infiltration. In this study, a panel of in vitro assays was used to make direct comparisons of several similar, commercially-available materials: Alloderm, Medeor Matrix, Permacol, and Strattice. Differences in the materials were detected for both cell signaling and scaffold architecture-dependent cell invasion. Material-conditioned media studies found Medeor Matrix to have the greatest positive effect upon cell proliferation and induction of migration. Strattice provided the greatest chemotaxis signaling and best suppressed apoptotic induction. Among assays measuring structure-dependent properties, Medeor Matrix was superior for cell attachment, followed by Permacol. Only Alloderm and Medeor Matrix supported chemotaxis-driven cell invasion beyond the most superficial zone. Medeor Matrix was the only material in the chorioallantoic membrane assay to support substantial cell invasion. These results indicate that both biologic and structural properties need to be carefully assessed in the considerable ongoing efforts to develop new uses and products in this important class of biomaterials.

Bioprosthetic mesh in abdominal wall reconstruction

Mesh materials have undergone a considerable evolution over the last several decades. There has been enhancement of biomechanical properties, improvement in manufacturing processes, and development of antiadhesive laminate synthetic meshes. The evolution of bioprosthetic mesh materials has markedly changed our indications and methods for complex abdominal wall reconstruction. The authors review the optimal properties of bioprosthetic mesh materials, their evolution over time, and their indications for use. The techniques to optimize outcomes are described using bioprosthetic mesh for complex abdominal wall reconstruction. Bioprosthetic mesh materials clearly have certain advantages over other implantable mesh materials in select indications. Appropriate patient selection and surgical technique are critical to the successful use of bioprosthetic materials for abdominal wall repair.

Acellular dermal matrices in hand reconstruction

BACKGROUND

The goal of this article is to review the current literature on the use of acellular dermal matrix in forearm, wrist, and hand reconstruction.

METHODS

A comprehensive literature search was performed using the Cochrane Database of Systematic Reviews, MEDLINE, PubMed, and Web of Knowledge. Articles were categorized as acellular dermal matrix used in soft-tissue repair and in ligament reconstruction. Search terms included "acellular dermal matrix," "biologic dressing," "skin replacement," "dermal allograft," "AlloDerm," "FlexHD," "Permacol," and "Strattice." These were all cross-referenced with "forearm," "wrist," and "hand." Data extraction focused on indications, surgical techniques, clinical outcomes, and complications. Exclusion criteria included regeneration templates, neonatal foreskin, and review articles.

RESULTS

More than 100 articles published between 1994 and 2011 were identified. Upon final review, five prospective case-control studies, three retrospective case-control studies, four case reports, one cross-sectional cohort, one prospective consecutive series, and one study type unknown were evaluated. Matrix was most commonly used in burn reconstruction. It has also been used in ligament and joint reconstruction for first carpometacarpal arthritis. One article illustrated the use of porcine matrix in basal joint arthritis, a practice that was abruptly terminated because of a concern over increased infections.

CONCLUSIONS

The clinical indications for acellular dermal matrix have increased throughout the last 15 years. Hand surgeons have been cautious but diligent in developing alternative treatment options in hand reconstruction, with a focused effort to reduce donor-site morbidity. Although acellular dermal matrices continue to find innovative uses to solve upper extremity surgical problems, more comparative prospective trials are needed.

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.

A review of available prosthetic material for abdominal wall repair

Abdominal wall incisional and inguinal hernia repair can call for utilization of implants or prostheses as an alternative to simple suture techniques. The various implants can be synthetic, biologic or mixed: their physicochemical properties condition the mechanical results and the long-term outcome of the repair. The increasing number of available materials allows the surgeon to choose between a wide variety depending on the indication, the site of implantation, the surgical approach and whether the operative field is contaminated or not. With regard to evidence-based medicine, while several synthetic implants have been shown to be superior in efficacy to simple suture, other studies are underway to develop the indications for bioprostheses, in particular in contaminated fields. This review of the literature summarizes the current knowledge on synthetic and biologic implants (physicochemical characteristics, forms, indications).

The innate oxygen dependant immune pathway as a sensitive parameter to predict the performance of biological graft materials

Clinical performance of a biomaterial is decided early after implantation as leukocytes interrogate the graft throughout acute inflammation. High degrees of leukocyte activation lead to poor material/patient compliance, accelerated degeneration and graft rejection. A number reactive oxygen species (ROS) are released by leukocytes throughout their interaction with a material, which can be used as a sensitive measure of leukocyte activation. The aim of this study was to compare leukocyte activation by commercially available biologic surgical materials and define the extent manufacturing variables influence down-stream ROS response. Chemiluminescence assays were performed using modifications to a commercially available kit (Knight Scientific, UK). Whole blood was obtained from 4 healthy human adults at 7 day intervals for 4 weeks, combined with Adjuvant K, Pholasin (a highly sensitive ROS excitable photoprotein) and biomaterial, and incubated for 60 min with continuous chemiluminescent measurements. Leukocyte ROS inducers fMLP and PMA were added as controls. Xeno- and allogeneic dermal and small intestinal submucosal (SIS) derived biomaterials were produced commercially (Surgisis Biodesign™, Alloderm(®), Strattice(®)Firm & Pliable & Permacol™) or fabricated in house to induce variations in decellularisation and cross-linking. Statistics were performed using Waller-Duncan post hoc ranking. Materials demonstrated significant differences in leukocyte activation as a function of decellularisation reagent and tissue origin. The data demonstrated SIS was significantly more pro-inflammatory than dermis. Additionally it was deduced that SDS during decellularisation induced pro-inflammatory changes to dermal materials. Furthermore, it was possible to conclude inter-patient variation in leukocyte response. The in vitro findings were validated in vivo which confirmed the chemiluminescence observations, highlighting the potential for translation of this technique as a routine component of pre-surgical evaluation to maximise foreign body compliance.