Host Response to Human Acellular Dermal Matrix Transplantation in a Primate Model of Abdominal Wall Repair

HLA Awareness in tissue decellularization: A paradigm shift for enhanced biocompatibility, studied on the model of the human fascia lata graft

Last twenties, tissue engineering has rapidly advanced to address the shortage of organ donors. Decellularization techniques have been developed to mitigate immune rejection and alloresponse in transplantation. However, a clear definition of effective decellularization remains elusive. This study compares various decellularization protocols using the human fascia lata model. Morphological, structural and cytotoxicity/viability analyses indicated that all the five tested protocols were equivalent and met Crapo's criteria for successful decellularization. Interestingly, only the in vivo immunization test on rats revealed differences. Only one protocol exhibited Human Leucocyte Antigen (HLA) content below 1% residual threshold, the only criterion preventing rat immunization with an absence of rat anti-human IgG switch after one month (N=4 donors for each of the 7 groups, added by negative and positive controls, n=28). By respecting a refined set of criteria, i.e. lack of visible nuclear material, <50ng DNA/mg dry weight of extracellular matrix, and <1% residual HLA content, the potential for adverse host reactions can be drastically reduced. In conclusion, this study emphasizes the importance of considering not only nuclear components but also major histocompatibility complex in decellularization protocols and proposes new guidelines to promote safer clinical development and use of bioengineered scaffolds.

Performance of Human and Porcine Derived Acellular Dermal Matrices in Prepectoral Breast Reconstruction: A Long-term Clinicaland Histologic Evaluation

BACKGROUND

Human acellular dermal matrices (ADMs) remain the most used matrices in prosthetic breast reconstruction. However, the availability and cost of ADMs limit their use in prepectoral reconstruction-which requires large amounts of ADM-and alternative matrices are therefore being explored.

OBJECTIVES

The aim of this study was to demonstrate the safety and efficacy of human-porcine ADM constructs via clinical outcomes and histologic evidence of graft integration.

METHODS

Consecutive patients undergoing tissue-expander/implant reconstructions with human-porcine ADM constructs were included. Biopsies of both ADMs were obtained at expander/implant exchange and evaluated for cellularization, vascularization, and inflammation. Postoperative complications were retrieved from patient records.

RESULTS

Fifty-nine patients met the inclusion criteria. Mean [standard deviation] follow-up was 6.7 [0.56] years; minimum follow-up was 5 years. Any complication rate was 8.6%, including skin necrosis (6.9%), seroma (1.7%), expander/implant exposure (1.7%), and return to the operating room (2.6%). A total of 138 ADM biopsy specimens were obtained from 38 patients at expander/implant exchange. Histologic analyses revealed lower fibroblast infiltration and vascularization and higher inflammatory response in porcine vs human ADM specimens, consistent with published results in nonhuman primates. Despite these differences, there were no cases of graft rejection, capsular contracture, or expander/implant loss.

CONCLUSIONS

Porcine ADM performs clinically in a similar manner to human ADM, albeit with minor differences in cellular ingrowth and vascularization, suggesting that it may be an alternative to human ADM in prepectoral breast reconstruction.

LEVEL OF EVIDENCE: 3

Therapeutic Effect of Decellularized Extracellular Matrix from Fish Skin for Accelerating Skin Regeneration

A cellular matrix derived from natural tissue functions as a highly biocompatible and versatile material for wound healing application. It provides a complex and highly organized environment with biological molecules and physical stimuli. Recently, various kinds of tissue/organ decellularized extracellular matrixes (dECMs) from bovine and porcine have been used as biomedical applications to support tissue regeneration but inherit religious restrictions and the risk of disease transmission to humans. Marine fish-derived dECMs are seen as attractive alternatives due to their similarity to mammalian physiology, reduced biological risks, and fewer religious restrictions. The aim of this study was to derive a decellularized matrix from the olive flounder (Paralichthys olivaceus) skin and evaluate its suitability as a wound healing application. Olive flounder skin was treated with a series of chemical treatments to remove cellular components. Decellularized fish skin (dFS) was confirmed to be successful in decellularization by evaluating the DNA content (2.84%). The dFS was characterized and evaluated in vivo to assess its biological activities. The mouse wound defect model was used to evaluate the in vivo performance of the dFS compared with that of the decellularized porcine skin (dPS). The resultant dFS was shown to enhance wound healing compared with the no-treatment group and dPS. This study suggests that dFS has potential for skin regeneration application.

Vascularization of Human Acellular Dermal Matrices: A Comparative Study in a Nonhuman Primate Model

Four human acellular dermal matrices (hADMs) were characterized in a nonhuman primate abdominal wall repair model by evaluating host immune response, vascularization, and incorporation into host tissues. AlloDerm™ (electron beam-sterilized hADM [e-hADM]), AlloMax™ (gamma beam-sterilized hADM, freeze-dried [g-hADM-FD]), DermaMatrix™ (hADM, freeze-dried [hADM-FD]), and FlexHD™ (ethanol-treated hADM [EtOH-hADM]) were each implanted in an abdominal wall-bridging defect in nonhuman primates (n = 3 animals/time point, n = 36 animals). Immunohistochemical and histological assessments were conducted on biopsies from each hADM at 1-, 3-, and 6-months postimplantation to assess vascularization (hematoxylin and eosin [H&E], CD31, alpha smooth muscle actin [αSMA], collagen IV), inflammatory/immune response (H&E, CD3, CD20, CD68), and collagen turnover (H&E, matrix metalloproteinase-9 [MMP-9]). MMP-9 immunolabeling was similar among different hADMs at 1 month; however, hADM-FD and EtOH-hADM showed higher total mean MMP-9-immunopositive areas at approximately 16% compared with <1% for e-hADM and g-hADM at 6 months postimplantation. Cells that stained positively for CD68, CD3, and CD20 were generally higher for hADM-FD and EtOH-hADM compared with other hADMs. The mean CD31-immunopositive area, CD31 vessel density, CD31 vessel diameter, and collagen IV-immunopositive area increased over time. Among all the hADM types, e-hADM had the highest mean (±standard deviation [SD]) CD31-immunopositive area at 1.54% ± 1.01%, vessel density at 7.86 × 10-5 ± 3.96 × 10-5 vessels/µm2, and collagen IV-immunopositive area at 2.55% ± 0.73% 1-month postimplantation. The pattern of αSMA immunolabeling varied among the hADMs. Histology showed that overall inflammation was mild at 1 month. Overall fibroblast repopulation and collagen remodeling increased over time from 1 to 6 months postimplantation. Fibroblast infiltration was minimal to mild at 1 month, with e-hADM showing the highest mean (±SD) score at 2.00 ± 0.00 compared with other hADMs. Only hADM-FD was not completely replaced by neotissue formation at 6 months postimplantation. All hADMs promoted vascularization, cell infiltration, and incorporation into host tissue, which were associated with acute inflammation and immune responses, within a 6-month period. A trend toward relatively enhanced early vascularization in e-hADM compared with other hADMs was observed. Immunogenic responses among the hADMs in the present study showed a slight distinction toward more quiescent terminally sterilized hADMs (e-hADM, g-hADM-FD) versus aseptically processed hADMs (EtOH-hADM, hADM-FD).

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.

Decellularized Human Dermis for Orthoplastic Extremity Reconstruction

The reconstruction of patients who possess multi morbid medical histories remains a challenge. With the ever-increasing number of patients with diabetes, infections, and trauma, there is a consistent need for promotion of soft tissue healing and a reliable substrate to assist with every aspect of soft tissue reconstruction, as well as the loss of fascial domain. Several proprietary products filled some of these needs but have failed to fulfill the needs of the clinician when faced with reconstructing multiple soft tissue systems, such as the integument and the musculoskeletal system. In this paper we discuss the use of decellularized human dermis (DermaPure®, Tissue Regenix, Universal City, TX, USA) through which a unique human tissue processing technique (dCELL® technology, Tissue Regenix, Universal City, TX, USA) and the creation of multiple product forms have proven to exhibit versatility in a wide range of clinical needs for successful soft tissue reconstruction. The background of human tissue processing, basic science, and early clinical studies are detailed, which has translated to the rationale for the success of this unique soft tissue substrate in orthoplastic reconstruction, which is also provided here in detail.

Echo intensity and gray-level co-occurrence matrix analysis of soft tissue grafting biomaterials and dental implants: an in vitro ultrasonographic pilot study

OBJECTIVE

To characterize different allogeneic and xenogeneic soft tissue graft substitutes and to assess their echo intensity and grayscale texture-related outcomes by using high-frequency ultrasonography (HFUS).

METHODS

Ten samples from each of the following biomaterials were scanned using HFUS: bilayered collagen matrix (CM), cross-linked collagen matrix (CCM), multilayered cross-linked collagen matrix (MCCM), human-derived acellular dermal matrix (HADM), porcine-derived acellular dermal matrix (PADM), collagen tape dressing (C) and dental implants (IMPs). The obtained images were then imported in a commercially available software for grayscale analysis. First-order grayscale outcomes included mean echo intensity (EI), standard deviation, skewness, and kurtosis, while second-order grayscale outcomes comprised entropy, contrast, correlation, energy and homogeneity derive from the gray-level co-occurrence matrix analysis. Descriptive statistics were performed for visualization of results, and one-way analysis of variance with Bonferroni post-hoc tests were performed to relative assessments of the biomaterials.

RESULTS

The statistical analysis revealed a statistically significant difference among the groups for EI (p < .001), with the group C showing the lowest EI, and the IMP group presenting with the greatest EI values. All groups showed significantly higher EI when compared with C (p < .001). No significant differences were observed for energy, and correlation, while a statistically significant difference among the groups was found in terms of entropy (p < 0.01), contrast (p < .001) and homogeneity (p < .001). IMP exhibited the highest contrast, that was significantly higher than C, HADM, PADM, CCM and CM.

CONCLUSIONS

HFUS grayscale analysis can be applied to characterize the structure of different biomaterials and holds potential for translation to in-vivo assessment following soft tissue grafting-related procedures.

Comparison of mechanical properties and host tissue response to OviTex™ and Strattice™ surgical meshes

PURPOSE

This study compared the in vitro/benchtop and in vivo mechanical properties and host biologic response to ovine rumen-derived/polymer mesh hybrid OviTex™ with porcine-derived acellular dermal matrix Strattice™ Firm.

METHODS

OviTex 2S Resorbable (OviTex 2S-R) and Strattice morphology were examined in vitro using histology and scanning electron microscopy; mechanical properties were assessed via tensile test; in vivo host biologic response and explant mechanics were evaluated in a rodent subcutaneous model. Separately, OviTex 1S Permanent (OviTex 1S-P) and Strattice were evaluated in a primate abdominal wall repair model.

RESULTS

OviTex 2S-R demonstrated layer separation, whereas Strattice retained its structural integrity and demonstrated higher maximum load than OviTex 2S-R out-of-package (124.8 ± 11.1 N/cm vs 37.9 ± 5.5 N/cm, p < 0.001), 24 h (55.7 ± 7.4 N/cm vs 5.6 ± 3.8 N/cm, p < 0.001), 48 h (45.3 ± 14.8 N/cm vs 2.8 ± 2.6 N/cm, p = 0.003), and 72 h (29.2 ± 10.5 N/cm vs 3.2 ± 3.1 N/cm, p = 0.006) following collagenase digestion. In rodents, inflammatory cell infiltration was observed between OviTex 2S-R layers, while Strattice induced a minimal inflammatory response. Strattice retained higher maximum load at 3 (46.3 ± 27.4 N/cm vs 9.5 ± 3.2 N/cm, p = 0.041) and 6 weeks (28.6 ± 14.1 N/cm vs 7.0 ± 3.0 N/cm, p = 0.029). In primates, OviTex 1S-P exhibited loss of composite mesh integrity whereas Strattice integrated into host tissue with minimal inflammation and retained higher maximum load at 1 month than OviTex 1S-P (66.8 ± 43.4 N/cm vs 9.6 ± 4.4 N/cm; p = 0.151).

CONCLUSIONS

Strattice retained greater mechanical strength as shown by lower susceptibility to collagenase degradation than OviTex 2S-R in vitro, as well as higher maximum load and improved host biologic response than OviTex 2S-R in rodents and OviTex 1S-P in primates.

Use of Decellularized SMILE (Small-Incision Lenticule Extraction) Lenticules for Engineering the Corneal Endothelial Layer: A Proof-of-Concept

PURPOSE

To demonstrate the suitability of using decellularized SMILE (Small-incision Lenticule Extraction) lenticules for culturing and transplanting the corneal endothelium (CE).

METHODS

The SMILE lenticules, obtained during refractive surgery, were decellularized by incubating in CE culture medium and fetal bovine serum. Decellularization was confirmed by hematoxylin and eosin staining, DAPI staining, and gel electrophoresis. The amount of DNA per milligram of dry tissue weight was calculated to quantify the residual nuclear content. The transparency of the decellularized lenticules was determined by calculating the modulation transfer function. Immunostaining for stromal collagens and glycosaminoglycan was performed using specific antibodies. Engineered tissue was constructed by culturing the CE cells on lenticules and staining for ZO-1, Na/K ATPase, and N-cadherin. The functionality of the engineered tissues was assessed by transplanting them onto edematous human donor corneas and perfusing for 10 days ex-vivo.

RESULTS

The residual DNA per milligram of dry tissue weight was found to be significantly reduced (p < 0.0001) in serum (0.255 µg/mg) and Opti-MEM (0.140 µg/mg) when compared to fresh lenticules (3.9 µg/mg). Decellularization did not alter the arrangement of the collagen fibers or the transparency of the lenticules. CE cells attached and matured to express ZO-1, Na/K ATPase, and N-cadherin at two weeks after seeding. The engineered tissue upon transplantation significantly reduced the corneal edema (p < 0.05) and the transplanted cells remained intact on the SMILE lenticule post-transplantation.

CONCLUSION

This study demonstrates the suitability of using SMILE lenticules decellularized using a simple, chemical-free method for engineering the corneal endothelium for transplantation.

Angiogenesis and Re-endothelialization in decellularized scaffolds: Recent advances and current challenges in tissue engineering

Decellularization of tissues and organs has recently become a promising approach in tissue engineering and regenerative medicine to circumvent the challenges of organ donation and complications of transplantations. However, one main obstacle to reaching this goal is acellular vasculature angiogenesis and endothelialization. Achieving an intact and functional vascular structure as a vital pathway for supplying oxygen and nutrients remains the decisive challenge in the decellularization/re-endothelialization procedure. In order to better understand and overcome this issue, complete and appropriate knowledge of endothelialization and its determining variables is required. Decellularization methods and their effectiveness, biological and mechanical characteristics of acellular scaffolds, artificial and biological bioreactors, and their possible applications, extracellular matrix surface modification, and different types of utilized cells are factors affecting endothelialization consequences. This review focuses on the characteristics of endothelialization and how to optimize them, as well as discussing recent developments in the process of re-endothelialization.

In-Vivo Evaluation of a Reinforced Ovine Biologic for Plastic and Reconstructive Procedures in a Non-human Primate Model of Soft Tissue Repair

BACKGROUND

Biologic matrices are used in plastic and reconstructive surgical procedures to aid in the kinetics of soft tissue repair and promote functional tissue formation. The human acellular dermal matrix AlloDerm is widely used; however, it is offered at a relatively high cost, and its dermal composition may not provide an ideal remodeling scaffold. OviTex Plastic and Reconstructive Surgery (PRS) Resorbable and Permanent are reinforced biologic matrices engineered with layers of ovine forestomach matrix embroidered with small amounts of polymer to optimize biophysical performance. This study compared the healing outcomes of these matrices in a non-human primate model of soft tissue repair.

METHODS

Animals were implanted with test articles in surgically created full-thickness midline abdominal wall defects and evaluated macroscopically and histologically at 2, 4, 12, and 24 weeks.

RESULTS

Both OviTex PRS Permanent and Resorbable matrices exhibited earlier host cell infiltration, neovascularization, and collagen deposition and also fully remodeled into the host tissue by 12 weeks post implantation. AlloDerm had less host cell infiltration and neovascularization at early time points and never fully integrated into the surrounding host tissue. There was no statistical difference in overall inflammation between AlloDerm and either OviTex PRS product at any time point, despite small amounts of polymer reinforcement in OviTex products.

CONCLUSIONS

In a primate soft tissue repair model, OviTex PRS Permanent and Resorbable matrices performed comparably with the leading human acellular dermal matrix. OviTex PRS Permanent and Resorbable are less expensive than alternatives like AlloDerm and may promote faster host cell proliferation and functional remodeling in some soft tissue repair applications.

Acellular Dermal Matrix Favorably Modulates the Healing Response after Surgery

SUMMARY

When first described for breast reconstruction, the presence of acellular dermal matrices (ADM) was associated with increased seroma formation and infection. However, clinical safety data has gradually improved with surgeon experience to an acceptable outcomes profile of ADM-assisted reconstruction when compared to submuscular implant coverage. In fact, ADM use potentially decreases capsular contracture rates and facilitates expansion for staged pre-pectoral breast reconstruction. Due to new regulatory requirements, the collection of unbiased, well-powered pre-market approval data summarizing long-term clinical outcomes will be essential over the coming years to understand the clinical performance of ADM usage in breast reconstruction.Currently, we can highlight the physiologic benefits of ADM use in breast reconstruction by evaluating the components of surgical wound healing that are favorably augmented by the implanted collagen substrate. ADM takes advantage of the wound healing cascade to incorporate into the patient's tissues - a process that requires a coordinated inflammatory infiltrate and angiogenesis. The presence of ADM augments and modulates the wound healing process to its advantage by simultaneously increasing the invasion of appropriate cellular constituents to facilitate expeditious healing and accelerate angiogenesis. Herein, we summarize the wound healing literature to demonstrate the mechanisms ADM use to biointegrate and the literature in which cellular constituents and soluble growth factors are upregulated in the presence of ADM. Lastly, we use our experimental observations of ADM incorporation to corroborate the literature.

Use of Xenogenic Collagen Matrices in Peri-Implant Soft Tissue Volume Augmentation: A Critical Review on the Current Evidence and New Technique Presentation

Plastic peri-implant surgical procedures aiming to increase soft tissue volume around dental implants have long been well-described. These are represented by: pedicle soft tissue grafts (rotational flap procedures and advanced flap procedures) and free soft tissue grafts (epithelialized, also called free gingival graft (FGG), and non-epithelialized, also called, connective tissue graft (CTG) or a combination of both. To bypass the drawback connected with autologous grafts harvesting, xenogenic collagen matrices (XCM)s and collagen-based matrices derived from porcine dermis (PDXCM)s have been introduced, as an alternative, in plastic peri-implant procedures. Aim: This review is aimed to evaluate and to critically analyze the available evidence on the effectiveness of XCMs and PDXCMs in soft tissue volume augmentation around dental implants. Moreover, a clinical case with a new soft tissue grafting procedure technique (Guided Soft Tissue Regeneration, GSTR) is presented. Material and Methods: An electronic search was performed on the MEDLINE database, SCOPUS, Cochrane Library and Web of Science. The electronic search provided a total of 133 articles. One hundred and twenty-eight not meeting the inclusion criteria were excluded. Seven articles of human randomized clinical trials were selected. A total number of 108 patients were treated with CTG, and 110 patients with XCM. Results: in peri-implant soft tissue augmentation procedures, XCMs seem an effective alternative to CTGs, associated with lower patient morbidity and lower operative times.

Comparative Effectiveness Analysis of Resorbable Synthetic Onlay and Biologic Intraperitoneal Mesh for Abdominal Wall Reconstruction: A 2-Year Match-Paired Analysis

BACKGROUND

Abdominal wall reconstruction persists as a challenging surgical issue with a multitude of management strategies available. The aim of this study was to examine the efficacy of resorbable synthetic mesh onlay plane against biologic mesh in the intraperitoneal plane.

METHODS

A single-center, two-surgeon, 5-year retrospective review (2014 to 2019) was performed examining subjects who underwent abdominal wall reconstruction in the onlay plane with resorbable synthetic mesh or in the intraperitoneal plane with biologic mesh. A matched paired analysis was conducted. Data examining demographic characteristics, intraoperative variables, postoperative outcomes, and costs were analyzed.

RESULTS

Eighty-eight subjects (44 per group) were identified (median follow-up, 24.5 months). The mean age was 57.7 years, with a mean body mass index of 30.4 kg/m2. The average defect size was 292 ± 237 cm2, with most wounds being clean-contaminated (48.9 percent) and 55 percent having failed prior repair. Resorbable synthetic mesh onlay subjects were significantly less likely (4.5 percent) to experience recurrence compared to biologic intraperitoneal mesh subjects (22.7 percent; p < 0.026). In addition, mesh onlay suffered fewer postoperative surgical-site occurrences (18.2 percent versus 40.9 percent; p < 0.019) and required fewer procedural interventions (11.4 percent versus 36.4 percent; p < 0.011), and was also associated with significantly lower total costs ($16,658 ± $14,930) compared to biologic intraperitoneal mesh ($27,645 ± $16,864; p < 0.001).

CONCLUSIONS

Abdominal wall reconstruction remains an evolving field, with various techniques available for treatment. When faced with hernia repair, resorbable synthetic mesh in the onlay plane may be preferable to biologic mesh placed in the intraperitoneal plane because of lower long-term recurrence rates, surgical-site complications, and costs.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, III.

Modular Bioreactor Design for Directed Tendon/Ligament Tissue Engineering

Functional tissue-engineered tendons and ligaments remain to be prepared in a reproducible and scalable manner. This study evaluates an acellular 3D extracellular matrix (ECM) scaffold for tendon/ligament tissue engineering and their ability to support strain-induced gene regulation associated with the tenogenesis of cultured mesenchymal stromal cells. Preliminary data demonstrate unique gene regulation patterns compared to other scaffold forms, in particular in Wnt signaling. However, the need for a robust bioreactor system that minimizes process variation was also evident. A design control process was used to design and verify the functionality of a novel bioreactor. The system accommodates 3D scaffolds with clinically-relevant sizes, is capable of long-term culture with customizable mechanical strain regimens, incorporates in-line load measurement for continuous monitoring and feedback control, and allows a variety of scaffold configurations through a unique modular grip system. All critical functional specifications were met, including verification of physiological strain levels from 1–10%, frequency levels from 0.2–0.5 Hz, and accurate load measurement up to 50 N, which can be expanded on the basis of load cell capability. The design process serves as a model for establishing statistical functionality and reliability of investigative systems. This work sets the stage for detailed analyses of ECM scaffolds to identify critical differentiation signaling responses and essential matrix composition and cell–matrix interactions.

Application of Allogeneic Human Acellular Dermal Matrix Reduces the Incidence of Fistula in Hypospadias Repair

BACKGROUND

Urethrocutaneous fistula is one of the most common complications arising from hypospadias surgery. The purpose of our study was to investigate the effectiveness and safety of allogeneic human acellular dermal matrix (HADM) application as a means of preventing the occurrence of urethrocutaneous fistula following hypospadias surgery.

METHODS

This is a non-randomized study of 219 cases (out of 270 patients with hypospadias) which satisfied inclusion and exclusion criteria. These patients were divided into two groups: 101 HADM patients, and 118 control patients (who did not receive HADM). In the control group, 77 boys were treated by single-stage urethroplasty (TIP) and 41 underwent staged urethroplasty (Thiersch-Duplay). In the HADM group, 59 boys underwent the TIP and 42 underwent the Thiersch-Duplay. In the postoperative period, we recorded the incidence of infection, urethrocutaneous fistula, and urethral stricture complications in these two groups of patients. The effectiveness and safety of HADM in preventing urethrocutaneous fistula following hypospadias surgery were evaluated according to these indicators.

RESULTS

In the control group, following the operation there were 16 cases of infection, 38 cases of urethrocutaneous fistula after extubating, and 5 cases of urethral stricture. In the HADM group, there were 19 cases of postoperative infection, 12 cases of urethrocutaneous fistula after extubating, and 5 children with urethral stricture. In comparing the two groups, it was found that the postoperative infection rate (13.6 vs. 18.8%) and the incidence of urethral stricture (4.2 vs. 5.0%) were not statistically significant (P > 0.05), while the postoperative urethrocutaneous fistula rate (32.2 vs. 11.9%) was statistically significant (P < 0.001).

CONCLUSION

It is found that HADM application can significantly reduce the incidence of urethrocutaneous fistula complications, without increasing the risk of infection and urethral stricture.

Characterization of Mono- and Bi-Transgenic Pig-Derived Epidermal Keratinocytes Expressing Human FUT2 and GLA Genes-In Vitro Studies

Pig-to-human xenotransplantation seems to be the response to the contemporary shortage of tissue/organ donors. Unfortunately, the phylogenetic distance between pig and human implies hyperacute xenograft rejection. In this study, we tested the hypothesis that combining expression of human α1,2-fucosyltransferase (hFUT2) and α-galactosidase A (hGLA) genes would allow for removal of this obstacle in porcine transgenic epidermal keratinocytes (PEKs). We sought to determine not only the expression profiles of recombinant human α1,2-fucosyltransferase (rhα1,2-FT) and α-galactosidase A (rhα-Gal A) proteins, but also the relative abundance (RA) of Galα1→3Gal epitopes in the PEKs stemming from not only hFUT2 or hGLA single-transgenic and hFUT2×hGLA double-transgenic pigs. Our confocal microscopy and Western blotting analyses revealed that both rhα1,2-FT and rhα-Gal A enzymes were overabundantly expressed in respective transgenic PEK lines. Moreover, the semiquantitative levels of Galα1→3Gal epitope that were assessed by lectin fluorescence and lectin blotting were found to be significantly diminished in each variant of genetically modified PEK line as compared to those observed in the control nontransgenic PEKs. Notably, the bi-transgenic PEKs were characterized by significantly lessened (but still detectable) RAs of Galα1→3Gal epitopes as compared to those identified for both types of mono-transgenic PEK lines. Additionally, our current investigation showed that the coexpression of two protective transgenes gave rise to enhanced abrogation of Galα→3Gal epitopes in hFUT2×hGLA double-transgenic PEKs. To summarize, detailed estimation of semiquantitative profiles for human α-1,2-FT and α-Gal A proteins followed by identification of the extent of abrogating the abundance of Galα1→3Gal epitopes in the ex vivo expanded PEKs stemming from mono- and bi-transgenic pigs were found to be a sine qua non condition for efficiently ex situ protecting stable lines of skin-derived somatic cells inevitable in further studies. The latter is due to be focused on determining epigenomic reprogrammability of single- or double-transgenic cell nuclei inherited from adult cutaneous keratinocytes in porcine nuclear-transferred oocytes and corresponding cloned embryos. To our knowledge, this concept was shown to represent a completely new approach designed to generate and multiply genetically transformed pigs by somatic cell cloning for the needs of reconstructive medicine and dermoplasty-mediated tissue engineering of human integumentary system.

Decellularized dermis extracellular matrix alloderm mechanically strengthens biological engineered tunica adventitia-based blood vessels

The ideal engineered vascular graft would utilize human-derived materials to minimize foreign body response and tissue rejection. Current biological engineered blood vessels (BEBVs) inherently lack the structure required for implantation. We hypothesized that an ECM material would provide the structure needed. Skin dermis ECM is commonly used in reconstructive surgeries, is commercially available and FDA-approved. We evaluated the commercially-available decellularized skin dermis ECM Alloderm for efficacy in providing structure to BEBVs. Alloderm was incorporated into our lab’s unique protocol for generating BEBVs, using fibroblasts to establish the adventitia. To assess structure, tissue mechanics were analyzed. Standard BEBVs without Alloderm exhibited a tensile strength of 67.9 ± 9.78 kPa, whereas Alloderm integrated BEBVs showed a significant increase in strength to 1500 ± 334 kPa. In comparison, native vessel strength is 1430 ± 604 kPa. Burst pressure reached 51.3 ± 2.19 mmHg. Total collagen and fiber maturity were significantly increased due to the presence of the Alloderm material. Vessels cultured for 4 weeks maintained mechanical and structural integrity. Low probability of thrombogenicity was confirmed with a negative platelet adhesion test. Vessels were able to be endothelialized. These results demonstrate the success of Alloderm to provide structure to BEBVs in an effective way.

TP63 basal cells are indispensable during endoderm differentiation into proximal airway cells on acellular lung scaffolds

The use of decellularized whole-organ scaffolds for bioengineering of organs is a promising avenue to circumvent the shortage of donor organs for transplantation. However, recellularization of acellular scaffolds from multicellular organs like the lung with a variety of different cell types remains a challenge. Multipotent cells could be an ideal cell source for recellularization. Here we investigated the hierarchical differentiation process of multipotent ES-derived endoderm cells into proximal airway epithelial cells on acellular lung scaffolds. The first cells to emerge on the scaffolds were TP63⁺ cells, followed by TP63⁺/KRT5⁺ basal cells, and finally multi-ciliated and secretory airway epithelial cells. TP63⁺/KRT5⁺ basal cells on the scaffolds simultaneously expressed KRT14, like basal cells involved in airway repair after injury. Removal of TP63 by CRISPR/Cas9 in the ES cells halted basal and airway cell differentiation on the scaffolds. These findings suggest that differentiation of ES-derived endoderm cells into airway cells on decellularized lung scaffolds proceeds via TP63⁺ basal cell progenitors and tracks a regenerative repair pathway. Understanding the process of differentiation is key for choosing the cell source for repopulation of a decellularized organ scaffold. Our data support the use of airway basal cells for repopulating the airway side of an acellular lung scaffold.

Transcriptome-targeted analysis of human peripheral blood-derived macrophages when cultured on biomaterial meshes

Surgical meshes are commonly used to repair defects and support soft tissues. Macrophages (Mφs) are critical cells in the wound healing process and are involved in the host response upon foreign biomaterials. There are various commercially available permanent and absorbable meshes used by surgeons for surgical interventions. Polypropylene (PP) meshes represent a permanent biomaterial that can elicit both inflammatory and anti-inflammatory responses. In contrast, poly-4-hydroxybutyrate (P4HB) based meshes are absorbable and linked to positive clinical outcomes but have a poorly characterized immune response. This study evaluated the in vitro targeted transcriptomic response of human Mφs seeded for 48 h on PP and P4HB surgical meshes. The in vitro measured response from human Mφs cultured on P4HB exhibited inflammatory and anti-inflammatory gene expression profiles typically associated with wound healing, which aligns with in vivo animal studies from literature. The work herein provides in vitro evidence for the early transcriptomic targeted signature of human Mφs upon two commonly used surgical meshes. The findings suggest a transition from an inflammatory to a non-inflammatory phenotype by P4HB as well as an upregulation of genes annotated under the pathogen response pathway.

Characterization of Inflammatory and Fibrotic Aspects of Tissue Remodeling of Acellular Dermal Matrix in a Nonhuman Primate Model

Human acellular dermal matrices (hADMs) are applied in various soft tissue reconstructive surgeries as scaffolds to support tissue remodeling and regeneration. To evaluate the clinical efficacy of hADM implants, it is integral that the hADM does not induce a host chronic inflammatory response leading to fibrotic encapsulation of the implant. In this study, we characterized the inflammatory and fibrosis-related tissue remodeling response of 2 commercial hADM products (SimpliDerm and AlloDerm RTU) in a nonhuman primate model using histology and gene expression profiling.

METHODS

Eighteen African green monkeys with abdominal wall defects were applied to evaluate the performance of SimpliDerm and AlloDerm RTU implants (N = 3) at 2, 4, and 12-weeks post-implantation. Using histology and gene expression profiling, tissue responses such as implant integration, degradation, cell infiltration, immune response, neovascularization, and pro-fibrotic responses over time were evaluated.

RESULTS

SimpliDerm showed a lower initial inflammatory response and slower implant degradation rate than AlloDerm RTU evidenced by histomorphological analysis. These factors led to a more anti-inflammatory and pro-remodeling microenvironment within SimpliDerm, demonstrated by lower TNFα levels and lower expression levels of pro-fibrotic markers, and promoted tissue repair and regeneration by 3-months post-implantation.

CONCLUSIONS

Overall, histology and gene expression profiling analyses shown in this study demonstrated an effective model for analyzing hADM performance in terms of host inflammatory and fibrotic response. Further studies are warranted to fully evaluate the utility of this novel hADM in the clinical setting and verify the prognosis of our pre-clinical analysis model.

Long-term preservation effects on biological properties of acellular placental sponge patches

Decellularization, preservation protocol and storage time influence the biomechanical and biological properties of allografts and xenografts. Here, we examined the consequences of storage time on the antibacterial, angiogenic and biocompatibility properties of the decellularized placental sponge (DPS) in vitro and in vivo. The DPS samples were preserved for one, three and six months at -20 °C. The decellularized scaffolds showed uniform morphology with interconnected pores compared with not decellularized sponges. Storage time did not interfere with collagen and vascular endothelial growth factor contents, and cytobiocompatibility for Hu02 fibroblast cells. Chorioallantoic membrane assay and subcutaneous implantation indicated a decreased new vessel formation and neovascularization in six months DPS sample compared with other experimental groups. The number of CD4⁺ and CD68⁺ cells infiltrated into the six months DPS on the implanted site showed a significant increase compared with one and three months sponges. The antibacterial activities and angiogenic properties of the DPS decreased over storage time. Three months preservation at -20 °C is suggested as the optimal storage period to retain its antibacterial activity and high stimulation of new vessel formation. This storage protocol could be considered for preservation of similar decellularized placenta-derived products with the aim of retaining their biological properties.

In-vivo evaluation of a reinforced ovine biologic: a comparative study to available hernia mesh repair materials

PURPOSE

Two innovative reinforced biologic materials were studied in a non-human primate hernia repair model. The test articles, which combine layers of ovine decellularized extracellular matrix with minimal amounts of synthetic polymer, were evaluated for their biologic performance as measured by inflammatory response, healing kinetics, integration, and remodeling into functional host tissue. For comparison, seven clinically used biologic and synthetic meshes were also studied.

METHODS

Animals were implanted with test articles in surgically created full-thickness midline abdominal wall defects, and evaluated macroscopically and histologically at 4, 12, and 24 weeks.

RESULTS

Macroscopically, biologics resorbed and remodeled into naturally appearing tissue; the reinforced biologics appeared similar, but remodeled earlier and were less prone to stretch. Synthetics developed a layer of reactive tissue above and separate from the contracted mesh structure. At early time points, the collagen networks of biologics and reinforced biologics were infiltrated by host cells primarily as a peripheral layer on the biologics. As early as 12 weeks, the collagen networks associated with the reinforced biologics remodeled into organized host collagen. By 24 weeks, both reinforced biologics and biologics had low levels of inflammation. In contrast, a foreign body response persisted at 24 weeks with the synthetics, which had developed less organized collagen, separate in space from the actual mesh.

CONCLUSIONS

The current study shows a favorable response to reinforced biologics, which were associated with an initial inflammatory response, resolving by later time points, followed by active remodeling, and the formation of new morphologically functional collagen.

An in vivo evaluation of induced chondrogenesis by decellularized extracellular matrix particles

Bioengineered scaffolds composed of synthetic materials and extracellular matrix (ECM) components can offer a tissue-specific microenvironment capable of regulating cells to regenerate the structure and function of the native cartilage. Here, given the potential preservation of biomechanical and biochemical cues found in the native cartilage, particulate decellularized ECM (DC-ECM) was utilized for immobilization on the surface of nanofibrous scaffolds. Afterward, the chondro-inductive potential and ectopic cartilage formation after subcutaneous implantation of bioengineered DC-ECM scaffolds were investigated in mice model. Eight weeks post-implantation, no growth of considerable inflammatory response and neovascularization was observed in histological images of bioengineered DC-ECM scaffolds. Pre-seeded bioengineered scaffolds with human adipose-derived stem cells exhibited high levels of chondro-induction capability, indicated with immunohistochemical and gene expression results. In both interval times, we also observed chondrogenesis and tissue formation after implanting unseeded bioengineered scaffolds, which denote that the presence of DC-ECM particles can even enhance attachment and migration of the host cells and induce chondrogenesis to them. To sum up, the incorporation of DC-ECM materials to tissue engineered constructs is a promising avenue to mimic the native tissue environment for regulation of cartilage regeneration in both in vivo and in vitro settings.

Outcome after pediatric liver transplantation for staged abdominal wall closure with use of biological mesh-Study with long-term follow-up

Abdominal wall closure after pediatric liver transplantation (pLT) in infants may be hampered by graft-to-recipient size discrepancy. Herein, we describe the use of a porcine dermal collagen acellular graft (PDCG) as a biological mesh (BM) for abdominal wall closure in pLT recipients. Patients <2 years of age, who underwent pLT from 2011 to 2014, were analyzed, divided into definite abdominal wall closure with and without implantation of a BM. Primary end-point was the occurrence of postoperative abdominal wall infection. Secondary end-points included 1- and 5-year patient and graft survival and the development of abdominal wall hernia. In five out of 21 pLT recipients (23.8%), direct abdominal wall closure was achieved, whereas 16 recipients (76.2%) received a BM. BM removal was necessary in one patient (6.3%) due to abdominal wall infection, whereas no abdominal wall infection occurred in the no-BM group. No significant differences between the two groups were observed for 1- and 5-year patient and graft survival. Two late abdominal wall hernias were observed in the BM group vs none in the no-BM group. Definite abdominal wall closure with a BM after pLT is feasible and safe when direct closure cannot be achieved with comparable postoperative patient and graft survival rates.

Limitations of recellularized biological scaffolds for human transplantation

A shortage of donor organs for transplantation and the dependence of the recipients on immunosuppressive therapy have motivated researchers to consider alternative regenerative approaches. The answer may reside in acellular scaffolds generated from cadaveric human and animal tissues. Acellular scaffolds are expected to preserve the architectural and mechanical properties of the original organ, permitting cell attachment, growth, and differentiation. Although theoretically, the use of acellular scaffolds for transplantation should pose no threat to the recipient's immune system, experimental data have revealed significant immune responses to allogeneic and xenogeneic transplanted scaffolds. Herein, we review the various factors of the scaffold that could trigger an inflammatory and/or immune response, thereby compromising its use for human transplant therapy. In addition, we provide an overview of the major cell types that have been considered for recellularization of the scaffold and their potential contribution to triggering an immune response.

Surgical outcomes of tympanoplasty using a sterile acellular dermal allograft: a prospective randomised controlled study

Acellular human dermal allografts have been shown to be effective for soft-tissue implantation. We compared treatment outcomes of tympanoplasty using tragal perichondrium and acellular human dermal allograft (MegaDerm^®). In a prospective randomised controlled study, 60 patients scheduled to undergo tympanoplasty were randomly assigned to the autologous tragal perichondrium group (n = 33) or acellular human dermal allograft group (n = 27). Postoperative hearing gain, graft success rate at 1 and 6 months and operation times were compared between groups. Graft success rate, defined as the complete closure of tympanic membrane perforation, did not show any significant intergroup difference (75.8% vs 85.2%, p = 0.519). Air conduction thresholds and air-bone gaps showed significant improvements in both groups; from 38.7 ± 15.9 dB to 30.2 ± 15.6 dB (p < 0.001) and from 17.8 ± 7.3 dB to 11.5 ± 7.0 (p = 0.001) in the autologous tragal perichondrium group, and from 30.4 ± 12.2 dB to 24.5 ± 13.0 dB (p = 0.006) and from 14.3 ± 5.1 dB to 7.6 ± 4.6 dB (p < 0.001) in the acellular human dermal allograft group. The amount of hearing gain (p = 0.31) and closure of air-bone gap (p = 0.863) were not meaningfully different between groups. The mean operation time was significantly lower in the acellular human dermal allograft group (35.2 min vs 27.4 min, p = 0.039). In this prospective randomised controlled study, acellular human dermal allograft was shown to be an effective alternative to tragal perichondrium, with similar graft success rates and postoperative hearing results, but with reduced operation times.

Erratum: Addendum: Abdominal Wall Reconstruction: An Integrated Approach

[This corrects the article DOI: 10.1055/s-0038-1667062.].

Biodegradable hyaluronan hydrogel coatings on acellular dermis grafts-A potential strategy to improve biologic graft durability in hernia repair application

Biologic grafts used in hernia repair undergo rapid cellular infiltration and remodeling, but their premature degradation often results in hernia recurrence. We hypothesize that a temporary barrier that prevents infiltration of acute inflammatory cells into the graft during the initial 4 weeks of implantation could mitigate graft degradation. The purpose of this study is to design tyramine-substituted hyaluronan (THA) hydrogel coatings with tunable degradation properties, as a means to develop a resorbable barrier for human acellular dermis grafts (HADM). THA plugs prepared at different cross-linking densities, by varying cross-linking agent concentration (0.0001-0.0075% H₂ O₂ ), demonstrated varying rates of in vitro degradation (25 U/mL hyaluronidase, 48 h). Based on these results, HADM grafts were coated with THA at three cross-linking densities (0.0001%, 0.00075%, and 0.003% H₂ O₂ ) and THA coating degradation was evaluated in vitro (25 U/mL hyaluronidase, 48 h) and in vivo (rat intraperitoneal implantation, 1-4 weeks). THA coatings degraded in vitro and in vivo with the lowest cross-linking density (0.0001% H₂ O₂ ), generally showing greater degradation as evidenced by significant decrease in coating cross-sectional area. However, all three coatings remained partially degraded after 4 weeks of in vivo implantation. Alternate strategies to accelerate in vivo degradation of THA coatings are required to allow investigation of the study hypothesis. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B:2664-2672, 2019.

Duraplasty Type as a Predictor of Meningitis and Shunting After Chiari I Decompression

BACKGROUND

Expansile duraplasty is frequently performed during Chiari I decompression. Aseptic and bacterial meningitis are possible complications of this procedure. We sought to compare the rates of meningitis and subsequent need for cerebrospinal fluid (CSF) diversion with duraplasty using bovine pericardial (BPC) xenograft and allograft.

METHODS

We conducted a retrospective review of 112 patients who underwent Chiari I decompression. All patients underwent duraplasty with either allograft or BPC. Occurrence of postoperative lumbar punctures and associated data were recorded to determine rates of meningitis. Rates of subsequent shunting were also recorded.

RESULTS

Overall, 112 patients were included in the study: 30 underwent duraplasty with allograft (27%) and 82 received BPC (73%). A total of 26 patients developed postoperative meningitis (23 cases of chemical meningitis and 3 of bacterial meningitis). Rates of meningitis were higher in patients who received BPC than patients who received allograft (28% vs. 10%, respectively; P = 0.047). The rate of shunting was greater in patients with meningitis compared with patients without meningitis (56.5% vs. 5.75%, respectively; P < 0.0001). Moreover, 13 of the 15 patients (87%) in the BPC cohort who were shunted were found to have meningitis compared with 0 of the 3 shunted patients (0%) in the allograft cohort (P = 0.044).

CONCLUSIONS

We found that rates of total meningitis were greater in patients who underwent Chiari I decompression and duraplasty with BPC compared with an allograft. The rate of shunting was significantly higher for patients who developed meningitis after decompression compared with patients without meningitis.

In vivo immunogenicity of bovine bone removed by a novel decellularization protocol based on supercritical carbon dioxide

Trauma or infections associated critical bone defects lead to a huge economic burden in the healthcare system worldwide. Recent advances in tissue engineering have led to potential new strategies for the repair, replacement, and regeneration of bone defects, especially in biomaterials and decellularization protocols from xenogenic tissues. However, the complexity in bone structure and mechanical environment limits the synthesis of artificial bone with biomaterials. Thus, the purpose of our study is to develop a natural bone scaffold with great immunocompatibility. We combined decellularization techniques base on SC-CO₂ to decellularize bovine bone. In order to study the immune response of mice to materials, the histology, spleen index, immune cells contents and in vitro proliferative performance, cytokine and immunoglobulin light chain expression of mice were characterized. Compared with the fresh bone group, the immune responses of decellularized group were significantly reduced. In conclusion, decellularization via this method can achieve a decellularized scaffold with great immunocompatibility. Our findings suggest the potential of using decellularized BB as a scaffold for bone bioengineering.

Nitro-Oleic Acid (NO2-OA) Release Enhances Regional Angiogenesis in a Rat Abdominal Wall Defect Model

Ventral hernia is often addressed surgically by the placement of prosthetic materials, either synthetic or from allogeneic and xenogeneic biologic sources. Despite advances in surgical approaches and device design, a number of postsurgical limitations remain, including hernia recurrence, mesh encapsulation, and reduced vascularity of the implanted volume. The in situ controlled release of angiogenic factors from a scaffold facilitating abdominal wall repair might address some of these issues associated with suboptimal tissue reconstruction. Furthermore, a biocomposite material that combines the favorable mechanical properties achievable with synthetic materials and the bioactivity associated with xenogeneic tissue sources would be desirable. In this report, an abdominal wall repair scaffold has been designed based on a microfibrous, elastomeric poly(ester carbonate)urethane urea matrix integrated with a hydrogel derived from decellularized porcine dermis (extracellular matrix [ECM] gel) and poly(lactic-co-glycolic acid) (PLGA) microspheres loaded with nitro-oleic acid (NO₂-OA). NO₂-OA is an electrophilic fatty acid nitro-alkene derivative that, under hypoxic conditions, induces angiogenesis. This scaffold was utilized to repair a rat abdominal wall partial thickness defect, hypothesizing that the nitro-fatty acid release would facilitate increased angiogenesis at the 8-week endpoint. The quantification of neovascularization was conducted by novel methodologies to assess vessel morphology and spatial distribution. The repaired abdominal wall defects were evaluated by histopathologic methods, including quantification of the foreign body response and cellular ingrowth. The results showed that NO₂-OA release was associated with significantly improved regional angiogenesis. The combined biohybrid scaffold and NO₂-OA-controlled release strategy also reduced scaffold encapsulation, increased wall thickness, and enhanced cellular infiltration. More broadly, the three components of the composite scaffold design (ECM gel, polymeric fibers, and PLGA microparticles) enable the tuning of performance characteristics, including scaffold bioactivity, degradation, mechanics, and drug release profile, all decisive factors to better address current limitations in abdominal wall repair or other soft tissue augmentation procedures.

Biomaterial strategies for generating therapeutic immune responses

Biomaterials employed to raise therapeutic immune responses have become a complex and active field. Historically, vaccines have been developed primarily to fight infectious diseases, but recent years have seen the development of immunologically active biomaterials towards an expanding list of non-infectious diseases and conditions including inflammation, autoimmunity, wounds, cancer, and others. This review structures its discussion of these approaches around a progression from single-target strategies to those that engage increasingly complex and multifactorial immune responses. First, the targeting of specific individual cytokines is discussed, both in terms of delivering the cytokines or blocking agents, and in terms of active immunotherapies that raise neutralizing immune responses against such single cytokine targets. Next, non-biological complex drugs such as randomized polyamino acid copolymers are discussed in terms of their ability to raise multiple different therapeutic immune responses, particularly in the context of autoimmunity. Last, biologically derived matrices and materials are discussed in terms of their ability to raise complex immune responses in the context of tissue repair. Collectively, these examples reflect the tremendous diversity of existing approaches and the breadth of opportunities that remain for generating therapeutic immune responses using biomaterials.

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.

Solid organ fabrication: comparison of decellularization to 3D bioprinting

Solid organ fabrication is an ultimate goal of Regenerative Medicine. Since the introduction of Tissue Engineering in 1993, functional biomaterials, stem cells, tunable microenvironments, and high-resolution imaging technologies have significantly advanced efforts to regenerate in vitro culture or tissue platforms. Relatively simple flat or tubular organs are already in (pre)clinical trials and a few commercial products are in market. The road to more complex, high demand, solid organs including heart, kidney and lung will require substantive technical advancement. Here, we consider two emerging technologies for solid organ fabrication. One is decellularization of cadaveric organs followed by repopulation with terminally differentiated or progenitor cells. The other is 3D bioprinting to deposit cell-laden bio-inks to attain complex tissue architecture. We reviewed the development and evolution of the two technologies and evaluated relative strengths needed to produce solid organs, with special emphasis on the heart and other tissues of the cardiovascular system.

Inadequate Processing of Decellularized Dermal Matrix Reduces Cell Viability In Vitro and Increases Apoptosis and Acute Inflammation In Vivo

Decellularized tissue scaffolds are commonly used in the clinic because they can be used as substitutes for more traditional biomaterials, while imparting additional physiological effects. Nevertheless, reports of complications associated with their use are widespread and poorly understood. This study probes possible causes of these complications by examining cell viability and apoptosis in response to eluents from decellularized dermis. Using multiple sources of decellularized dermis, this study shows that typical decellularized scaffolds (prepared with commonly used laboratory techniques, as well as purchased from commercial sources) contain soluble components that are cytotoxic and that these components can be removed by extensive washes in cell culture media. In addition, this study demonstrates that these observed in vitro phenotypes correlate with increased apoptosis and acute inflammation when implanted subcutaneously in mice.

An injectable extracellular matrix for the reconstruction of epidural fat and the prevention of epidural fibrosis

Extensive epidural fibrosis is a common complication following spinal surgery and can cause pain and limited mobility. In the present study, a novel biomimetic approach was developed to prevent postsurgical adhesion of the dura. We aimed to reconstruct epidural fat, which prevents scar-tissue adhesion, through the development of an injectable decellularized adipose matrix (DAM)-containing hyaluronic acid (HA) hydrogel loaded with adipose stromal cells (ASCs). Injectable DAM was prepared from porcine adipose tissue by four freeze-thaw cycles with subsequent pepsin digestion. Residual analyses confirmed the efficacy of detergent-free decellularization, while most sulfated glycosaminoglycans and collagen were preserved. The Transwell migration assay demonstrated the anti-infiltrative property of the DAM-containing HA hydrogel. After 14 d of 3D culture, the DAM-containing HA hydrogel showed inductive potential in the adipogenic differentiation of ASCs. For an in vivo study, the ASC-loaded DAM-containing HA hydrogel (DAM/ASC-incorporated HA hydrogel) was injected into adult laminectomized male rats, and the results were assessed by microscopic histological examination. The in vivo data indicated that HA hydrogel, DAM, and ASCs were all required for the ability of the engineered fat tissue to block the invasion of the fibrous tissue. Our results suggested that this injectable DAM/ASC-incorporated HA hydrogel has potential applications in minimally invasive surgery for soft-tissue reconstruction and epidural fibrosis prevention.

Biocompatibility evaluation of tissue-engineered decellularized scaffolds for biomedical application

Biomaterials based on seeding of cells on decellularized scaffolds have gained increasing interest in the last few years and suggested to serve as an alternative approach to bioengineer artificial organs and tissues for transplantation. The reaction of the host toward the decellularized scaffold and transplanted cells depends on the biocompatibility of the construct. Before proceeding to the clinical application step of decellularized scaffolds, it is greatly important to apply a number of biocompatibility tests in vitro and in vivo. This review describes the different methodology involved in cytotoxicity, pathogenicity, immunogenicity and biodegradability testing for evaluating the biocompatibility of various decellularized matrices obtained from human or animals.

Outcomes Analysis of Biologic Mesh Use for Abdominal Wall Reconstruction in Clean-Contaminated and Contaminated Ventral Hernia Repair

BACKGROUND

Repair of grade 3 and grade 4 ventral hernias is a distinct challenge, given the potential for infection, and the comorbid nature of the patient population. This study evaluates our institutional outcomes when performing single-stage repair of these hernias, with biologic mesh for abdominal wall reinforcement.

METHODS

A prospectively maintained database was reviewed for all patients undergoing repair of grade 3 (potentially contaminated) or grade 4 (infected) hernias, as classified by the Ventral Hernia Working Group. All those patients undergoing repair with component separation techniques and biologic mesh reinforcement were included. Patient demographics, comorbidities, and postoperative complications were analyzed. Univariate analysis was performed to define factors predictive of hernia recurrence and wound complications.

RESULTS

A total of 41 patients underwent single-stage repair of grade 3 and grade 4 hernias during a 4-year period. The overall postoperative wound infection rate was 15%, and hernia recurrence rate was 12%. Almost all recurrences were seen in grade 4 hernia repairs, and in those patients undergoing bridging repair of the hernia. One patient required removal of the biologic mesh. Those factors predicting hernia recurrence were smoking (P = 0.023), increasing body mass index (P = 0.012), increasing defect size (P = 0.010), and bridging repair (P = 0.042). No mesh was removed due to perioperative infection. Mean follow-up time for this patient population was 25 months.

CONCLUSIONS

Single-stage repair of grade 3 hernias performed with component separation and biologic mesh reinforcement is effective and offers a low recurrence rate. Furthermore, the use of biologic mesh allows for avoidance of mesh explantation in instances of wound breakdown or infection. Bridging repairs are associated with a high recurrence rate, as is single-stage repair of grade 4 hernias.

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.

Decreased hernia recurrence using autologous platelet-rich plasma (PRP) with Strattice™ mesh in a rodent ventral hernia model

BACKGROUND

Recurrence after ventral hernia repair (VHR) remains a multifactorial problem still plaguing surgeons today. Some of the many contributing factors include mechanical strain, poor tissue-mesh integration, and degradation of matrices. The high recurrence rate witnessed with the use of acellular dermal matrices (ADM) for definitive hernia repair has reduced their use largely to bridging repair and breast reconstruction. Modalities that improve classic cellular metrics of successful VHR could theoretically result in improved rates of hernia recurrence; autologous platelet-rich plasma (PRP) may represent one such tool, but has been underinvestigated for this purpose.

METHODS

Lewis rats (32) had chronic ventral hernias created surgically and then repaired with Strattice™ mesh alone (control) or mesh + autologous PRP. Samples were harvested at 3 and 6 months postoperatively and compared for gross, histologic, and molecular outcomes of: neovascularization, tissue incorporation, peritoneal adhesions, hernia recurrence, and residual mesh thickness.

RESULTS

Compared to control at 3 months postoperatively, PRP-treated rats displayed significantly more neovascularization of implanted mesh and considerable upregulation of both angiogenic genes (vEGF 2.73-fold, vWF 2.21-fold) and myofibroblastic genes (αSMA 9.68-fold, FSP-1 3.61-fold, Col1a1 3.32-fold, Col31a1 3.29-fold). Histologically, they also showed enhanced tissue deposition/ingrowth and diminished chronic immune cell infiltration. Peritoneal adhesions were less severe at both 3 (1.88 vs. 2.94) and 6 months (1.63 vs. 2.75) by Modified Hopkins Adhesion Scoring. PRP-treated rats experienced decreased hernia recurrence at 6 months (0/10 vs. 7/10) and had significantly improved ADM preservation as evidenced by quantification of residual mesh thickness.

CONCLUSIONS

PRP is an autologous source of pro-regenerative growth factors and chemokines uniquely suited to soft tissue wound healing. When applied to a model of chronic VHR, it incites enhanced angiogenesis, myofibroblast recruitment and tissue ingrowth, ADM preservation, less severe peritoneal adhesions, and diminished hernia recurrence. We advocate further investigation regarding PRP augmentation of human VHR.

Decellularized biological matrices: an interesting approach for cardiovascular tissue repair and regeneration

The repair and replacement of blood vessels is one of the most challenging topics for biomedical research. Autologous vessels are preferred as graft materials, but they still have many issues to overcome: for instance, they need multiple surgical procedures and often patients may not have healthy and surgically valuable arteries useful as an autograft. A tissue-engineering approach is widely desirable to generate biological vascular prostheses. Recently, decellularization of native tissue has gained significant attention in the biomedical research field. This method is used to obtain biological scaffolds that are expected to maintain the complex three-dimensional structure of the extracellular matrix, preserving the biomechanical properties of the native tissues. The decellularizing methods and the biomechanical characteristics of these products are presented in this review. Decellularization of biological matrices induces the loss of major histocompatibility complex (MHC), which is expected to promote an immunological response by the host. All the studies showed that decellularized biomaterials possess adequate properties for xenografting. Concerning their mechanical properties, several studies have demonstrated that, although chemical decellularization methods do not affect the scaffolds' mechanical properties, these materials can be modified through different treatments in order to provide the desired mechanical characteristics, depending on the specific application. A short overview of legislative issues concerning the use of decellularized substitutes and future perspectives in surgical applications is also presented. Copyright © 2015 John Wiley & Sons, Ltd.