Hydrated vs. freeze-dried human acellular dermal matrix for hernia repair: a comparison in a rabbit model

Regenerative Engineering: Current Applications and Future Perspectives

Many pathologies, congenital defects, and traumatic injuries are untreatable by conventional pharmacologic or surgical interventions. Regenerative engineering represents an ever-growing interdisciplinary field aimed at creating biological replacements for injured tissues and dysfunctional organs. The need for bioengineered replacement parts is ubiquitous among all surgical disciplines. However, to date, clinical translation has been limited to thin, small, and/or acellular structures. Development of thicker tissues continues to be limited by vascularization and other impediments. Nevertheless, currently available materials, methods, and technologies serve as robust platforms for more complex tissue fabrication in the future. This review article highlights the current methodologies, clinical achievements, tenacious barriers, and future perspectives of regenerative engineering.

A comparative study between sterile freeze-dried and sterile pre-hydrated acellular dermal matrix in tissue expander/implant breast reconstruction

BACKGROUND

In implant-based breast reconstruction, acellular dermal matrix (ADM) is essential for supporting the inferolateral pole. Recent studies have compared non-sterilized freeze-dried ADM and sterilized pre-hydrated ADM, but have not assessed whether differences were attributable to factors related to sterile processing or packaging. This study was conducted to compare the clinical outcomes of breast reconstruction using two types of sterile-processed ADMs.

METHODS

Through a retrospective chart review, we analyzed 77 consecutive patients (85 breasts) who underwent tissue expander/implant breast reconstruction with either freezedried ADM (35 breasts) or pre-hydrated ADM (50 breasts) from March 2016 to February 2018. Demographic variables, postoperative outcomes, and operative parameters were compared between freeze-dried and pre-hydrated ADM. Biopsy specimens were obtained for histologic analysis.

RESULTS

We obtained results after adjusting for variables found to be significant in univariate analyses. The total complication rate for freeze-dried and pre-hydrated ADMs was 25.7% and 22.0%, respectively. Skin necrosis was significantly more frequent in the freeze-dried group than in the pre-hydrated group (8.6% vs. 4.0%, P=0.038). All other complications and operative parameters showed no significant differences. In the histologic analysis, collagen density, inflammation, and vascularity were higher in the pre-hydrated ADM group (P=0.042, P=0.006, P=0.005, respectively).

CONCLUSIONS

There are limited data comparing the outcomes of tissue expander/implant breast reconstruction using two types of sterile-processed ADMs. In this study, we found that using pre-hydrated ADM resulted in less skin necrosis and better integration into host tissue. Pre-hydrated ADM may therefore be preferable to freeze-dried ADM in terms of convenience and safety.

Acellular dermal matrix contributes to epithelialization in patients with chronic sinusitis

BACKGROUND

Nasal endoscopic surgery is widely used for nasal diseases, including sinusitis and tumors. However, scar hyperplasia, nasal irritation, scab, and nasal obstruction delay nasal mucosal recovery, with prolonged cleaning exacerbating the patient's financial burden. Here, we presented a novel approach for the treatment of nasal mucosal defects, termed acellular dermal matrix.

METHODS

A total of 31 patients with bilateral chronic sinusitis (maxillary sinusitis and ethmoid sinusitis) underwent nasal surgery and nasal mucosal repair in September-October 2016. We divided the nasal cavities of each patient into control and acellular dermal matrix groups, randomly selected one side for nasal mucosal repair by surgery. A suitable acellular dermal matrix size was selected according to the defect in each patient. After pruning, the acellular dermal matrix was placed on the wound surface and filled with gelatin sponge. All patients were followed up for 14 weeks to compare nasal mucosal epithelialization between the control and acellular dermal matrix groups. Results：No obvious complications and adverse reactions were observed after nasal surgery. Lund-Kennedy scores in the acellular dermal matrix group were significantly decreased compared with the control group at 8 (0 (0, 1) vs. 2 (2, 4); P<0.05) weeks. Epithelialization time of eight weeks in the acellular dermal matrix groups was significantly decreased than the control group of 14 weeks.

CONCLUSION

Acellular dermal matrix provides a growth framework for the healthy mucosa on the wounded surface and reduces postoperative epithelialization time.

Comparison of AlloDerm and AlloMax tissue incorporation in rats

BACKGROUND

Human acellular dermal matrices (HADMs) are used in a variety of settings. AlloMax is a new HADM currently being used for breast reconstruction and hernia repair. We compared the in vivo tissue integration of AlloMax to AlloDerm, a well-studied HADM, in rats.

METHODS

We implanted AlloDerm and AlloMax patches into subcutaneous pockets on the backs of 32 male Sprague-Dawley rats. The animals were killed after either 4 or 8 weeks, and the patches were recovered and stained for histopathologic analyses. Microscopic end points included patch thickness, vascularization, tissue in-growth, fibroblast proliferation, and inflammation.

RESULTS

All animals completed the study without complications or infection. There were no significant differences in graft thicknesses at 4 and 8 weeks. Microscopically, at 4 weeks, AlloDerm sections had significantly more microvessels than AlloMax (P = 0.02). This disparity increased by 8 weeks (P < 0.01). Similarly, we found greater tissue in-growth and fibroblast proliferation in AlloDerm than AlloMax sections at 4 (P < 0.01) and at 8 (P < 0.01) weeks. Inflammatory infiltrates consisted of lymphocytes, histiocytes, eosinophils, and plasma cells. Deep graft infiltration by predominately lymphocytic inflammatory cells was significantly higher in AlloDerm than AlloMax grafts at 4 (P = 0.01) and 8 (P = 0.02) weeks. Graft necrosis was uncommon, but marginal fibrosis was similar in both.

CONCLUSIONS

AlloDerm grafts had greater neovascularization, tissue infiltration, fibroblast proliferation, and inflammatory reaction than AlloMax grafts when placed subcutaneously in rats. AlloDerm may be better incorporated than AlloMax when placed in vivo.

Reducing postoperative infections and red breast syndrome in patients with acellular dermal matrix-based breast reconstruction: the relative roles of product sterility and lower body mass index

PURPOSE

The use of human acellular dermal matrices (ADM) has become routinely used in implant-based breast surgery. Notwithstanding the many benefits for tissue support, the morbidity associated with its use includes seroma and infection, among other potential complications. Some patients experience a specific complication called red breast syndrome (RBS), which has been linked to ADM use, but its exact etiology remains elusive. In our institution, AlloDerm aseptic regenerative tissue matrix was recently replaced with a ready-to-use sterile version that undergoes terminal sterilization, eliminating the need for rehydration. We want to determine if this change in processing affected complications, including RBS.

METHODS

We conducted a retrospective chart review analyzing patients from January 1, 2011, to June 1, 2013, who underwent breast surgery with human ADM. Patients with aseptic AlloDerm were compared to patients with sterile AlloDerm. Data were analyzed using the Fisher exact test.

RESULTS

A total of 167 reconstructed breasts from 105 patients met inclusion criteria: 56% (n=93) with aseptic ADM, 44% (n=74) with sterile ADM. When comparing the two, patients had a decrease in overall necrosis, infection, seroma, and RBS with sterile ADM. However, the rates did not reach statistical significance. For example, the incidence of RBS decreased from 7.5% to 2.7% (P=0.301) and seroma decreased from 8.6% to 2.7% (P=0.188). The infection rate proved to be equivocal at 11.8% with aseptic ADM to 10.8% with sterile ADM (P=1.000). The only statistically significant change was a decrease in the total complication rate from 41.9% to 27.0% (P=0.046). The absolute risk reduction for total complications was 14.9% with a number-needed-to-treat of 7.

CONCLUSION

According to our study, sterile AlloDerm has a clinically decreased incidence of complications compared to aseptic AlloDerm. Whereas RBS decreased, it was interesting to see that it was not eliminated altogether. This suggests that the etiology may be unrelated to ADM processing and warrants further investigation. Overall, the most notable difference was the statistically significant decrease in the total complication rate. Therefore, the change to sterile AlloDerm seems to be beneficial. Further benefit arises from ease of preparation in the operating room.

Use of Acellular Dermal Matrix in Postmastectomy Breast Reconstruction: Are All Acellular Dermal Matrices Created Equal?

BACKGROUND

AlloDerm and FlexHD are two types of acellular dermal matrices commonly used in implant-based reconstruction. Although the use of acellular dermal matrix has revolutionized immediate breast reconstruction in the setting of breast cancer, it remains unclear which type of acellular dermal matrix is best. The purpose of this retrospective cohort study was to compare postoperative complication rates between these two types of acellular dermal matrix.

METHODS

The authors reviewed the records of all patients who underwent implant-based breast reconstruction at their institution between 1998 and 2013. Dependent variables of seroma, hematoma, infection, delayed wound healing, implant exposure, and return to the operating room for management of complications were recorded.

RESULTS

A total of 309 consecutive patients were identified. Of these, AlloDerm was used in 123 patients (39.8 percent) and FlexHD was used in 186 patients (60.2 percent). Most patients in the authors' cohort underwent immediate reconstruction [n = 288 (93.2 percent)], with a mean follow-up of 20.0 months. Patients receiving AlloDerm were half as likely to have major infections compared with patients receiving FlexHD (OR, 0.50; 95 percent CI, 0.16 to 1.00; p < 0.05). The rates of other complications were similar between the two groups.

CONCLUSION

There are significantly increased odds of a major infection in patients who undergo implant-based breast reconstruction using FlexHD compared with AlloDerm.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, III.

Complex ventral hernia repair with a human acellular dermal matrix

Purpose

The ideal approach to complex ventral hernia repair is frequently debated. Differences in processing techniques among biologic materials may impact hernia repair outcomes. This study evaluates the outcomes of hernia repair with a terminally sterilized human acellular dermal matrix (TS-HADM) (AlloMax^® Surgical Graft, by C. R. Bard/Davol, Inc., Warwick, RI, USA) treated with low-dose gamma irradiation.

Methods

A single-arm multi-center retrospective observational study of patients undergoing hernia repair with TS-HADM was performed. Data analyses were exploratory only; no formal hypothesis testing was pre-specified.

Results

Seventy-eight patients (43F, 35M) underwent incisional hernia repair with a TS-HADM. Mean follow-up was 20.5 months. Preoperative characteristics include age of 56.6 ± 11.1 years, BMI 36.7 ± 9.9 kg/m², and mean hernia defect size 187 cm². Sixty-five patients underwent component separation technique (CST) with a reinforcing graft. Overall, 21.8 % developed recurrences. Recurrences occurred in 15 % of patients repaired with CST. Major wound complications occurred in 31 % of patients overall. Based upon CDC surgical wound classification, major wound complications were seen in 26, 40, 56, and 50 % of Class 1, 2, 3, and 4 wounds, respectively. No grafts required removal.

Conclusions

Hernia recurrences are not uncommon following complex abdominal wall reconstruction. Improved outcomes are seen when a TS-HADM is utilized as reinforcement to primary fascial closure.

Comparison of different ADM materials in breast surgery

This is a brief review of the history of the role of acellular dermal matrices in breast reconstruction surgery, with a summary of several currently available products, including a table of comparisons. Key features, including biologic tissue source, surgical preparation, sterility, polarity, contraindications, shelf life, and cost, are examined. A paucity of data exists to directly compare AlloDerm®, DermaMatrix®, Strattice™, Permacol™, DermACELL, FlexHD®, SurgiMend®, and ALLOMAX™ for breast reconstruction; most studies relate to hernia repair. An ideal acellular dermal matrix product is still unavailable but the information provided in this review should facilitate a breast surgeons decision-making process.

Spherical indentation of free-standing acellular extracellular matrix membranes

Numerous scaffold materials have been developed for tissue engineering and regenerative medicine applications to replace or repair damaged tissues and organs. Naturally occurring scaffold materials derived from acellular xenogeneic and autologous extracellular matrix (ECM) are currently in clinical use. These biological scaffold materials possess inherent variations in mechanical properties. Spherical indentation or ball burst testing has commonly been used to evaluate ECM and harvested tissue due to its ease of use and simulation of physiological biaxial loading, but has been limited by complex material deformation profiles. An analytical methodology has been developed and applied to experimental load-deflection data of a model hyperelastic material and lyophilized ECM scaffolds. An optimum rehydration protocol was developed based on water absorption, hydration relaxation and dynamic mechanical analysis. The analytical methodology was compared with finite element simulations of the tests and excellent correlation was seen between the computed biaxial stress resultants and geometry deformations. A minimum rehydration period of 5 min at 37°C was sufficient for the evaluated multilaminated ECM materials. The proposed approach may be implemented for convenient comparative analysis of ECM materials and source tissues, process optimization or during lot release testing.

Evaluation of porcine hydrated dermis augmented repair in a fascial defect model

Surgical mesh composed of extracellular matrix promotes healing of difficult soft tissue and orthopedic repairs in preclinical and clinical trials. In this study, a novel extracellular matrix prepared from porcine hydrated dermis was evaluated in an in vivo fascial defect model in sheep. Fascial defects were created, and then acutely repaired with surgical mesh. Healed surgical sites were evaluated grossly, histologically, and biomechanically at 6 and 12 weeks. Porcine hydrated dermis extracellular matrix performed favorably compared to negative control empty defects and native fascia, with minimal gross adhesion, low histologic inflammatory scores, and significantly greater tensile strength of the healing surgical site when compared with native fascia.

Evaluation of human acellular dermis versus porcine acellular dermis in an in vivo model for incisional hernia repair

Incisional hernias commonly occur following abdominal wall surgery. Human acellular dermal matrices (HADM) are widely used in abdominal wall defect repair. Xenograft acellular dermal matrices, particularly those made from porcine tissues (PADM), have recently experienced increased usage. The purpose of this study was to compare the effectiveness of HADM and PADM in the repair of incisional abdominal wall hernias in a rabbit model. A review from earlier work of differences between human allograft acellular dermal matrices (HADM) and porcine xenograft acellular dermal matrices (PADM) demonstrated significant differences (P < 0.05) in mechanical properties: Tensile strength 15.7 MPa vs. 7.7 MPa for HADM and PADM, respectively. Cellular (fibroblast) infiltration was significantly greater for HADM vs. PADM (Armour). The HADM exhibited a more natural, less degraded collagen by electrophoresis as compared to PADM. The rabbit model surgically established an incisional hernia, which was repaired with one of the two acellular dermal matrices 3 weeks after the creation of the abdominal hernia. The animals were euthanized at 4 and 20 weeks and the wounds evaluated. Tissue ingrowth into the implant was significantly faster for the HADM as compared to PADM, 54 vs. 16% at 4 weeks, and 58 vs. 20% for HADM and PADM, respectively at 20 weeks. The original, induced hernia defect (6 cm²) was healed to a greater extent for HADM vs. PADM: 2.7 cm² unremodeled area for PADM vs. 1.0 cm² for HADM at 20 weeks. The inherent uniformity of tissue ingrowth and remodeling over time was very different for the HADM relative to the PADM. No differences were observed at the 4-week end point. However, the 20-week data exhibited a statistically different level of variability in the remodeling rate with the mean standard deviation of 0.96 for HADM as contrasted to a mean standard deviation of 2.69 for PADM. This was significant with P < 0.05 using a one tail F test for the inherent variability of the standard deviation. No significant differences between the PADM and HADM for adhesion, inflammation, fibrous tissue or neovascularization were noted.

In vivo evaluation of acellular human dermis for abdominal wall repair

Limitations of synthetic biomaterials for abdominal wall repair have led investigators to seek naturally derived matrices, such as human acellular dermis, because of their excellent biocompatibility and their ability to naturally interface with host tissues with minimal tissue response. In this study, we investigated two different biomaterials derived from human dermis (FlexHD acellular dermis and FlexHD acellular dermis-thick) in a rabbit abdominal hernia repair model. One quarter of the abdominal wall was replaced with each biomaterial, and the animals were followed for up to 24 weeks. Rabbit hernias repaired with AlloDerm, a commercially available acellular dermal matrix, and sham operated animals served as controls. Retrieved samples of these implants were assessed grossly and histologically. Collagen production measurements and tension studies were performed. FlexHD acellular dermis, FlexHD acellular dermis-thick, and AlloDerm maintained their strength in the rabbit hernia repair model with no incidence of hernia formation or bowel adhesion. The exact size measurements at 24 weeks were 217.0 +/- 20.9% for FlexHD acellular dermis, 200.8 +/- 23.5% for FlexHD acellular dermis-thick, and 209.7 +/- 32.9% for AlloDerm. Macroscopic and microscopic evaluation showed excellent integration and tissue formation. All biomaterials studied harbored cells that produced new collagen fibers, and a six-fold increase in these fibers was observed at 24 weeks. This study shows that acellular biomaterials derived from human dermis are suitable for abdominal hernia repair.