In Vivo Comparison of Synthetic Macroporous Filamentous and Sponge-like Skin Substitute Matrices Reveals Morphometric Features of the Foreign Body Reaction According to 3D Biomaterial Designs.

Synthetic macroporous biomaterials are widely used in the field of skin tissue engineering to mimic membrane functions of the native dermis. Biomaterial designs can be subclassified with respect to their shape in fibrous designs, namely fibers, meshes or fleeces, respectively, and porous designs, such as sponges and foams. However, synthetic matrices often have limitations regarding unfavorable foreign body responses (FBRs). Severe FBRs can result in unfavorable disintegration and rejection of an implant, whereas mild FBRs can lead to an acceptable integration of a biomaterial. In this context, comparative in vivo studies of different three-dimensional (3D) matrix designs are rare. Especially, the differences regarding FBRs between synthetically derived filamentous fleeces and sponge-like constructs are unknown. In the present study, the FBRs on two 3D matrix designs were explored after 25 days of subcutaneous implantation in a porcine model. Cellular reactions were quantified histopathologically to investigate in which way the FBR is influenced by the biomaterial architecture. Our results show that FBR metrics (polymorph-nucleated cells and fibrotic reactions) were significantly affected according to the matrix designs. Our findings contribute to a better understanding of the 3D matrix tissue interactions and can be useful for future developments of synthetically derived skin substitute biomaterials.

Semiautomated quantification of the fibrous tissue response to complex three-dimensional filamentous scaffolds using digital image analysis.

Fibrosis represents a relevant response to the implantation of biomaterials, which occurs not only at the tissue-material interface (fibrotic encapsulation) but also within the void fraction of complex three-dimensional (3D) biomaterial constructions (fibrotic ingrowth). Usual evaluation of the biocompatibility mostly depicts fibrosis at the interface of the biomaterial using semiquantitative scores. Here, the relations between encapsulation and infiltrating fibrotic growth are poorly represented. Virtual pathology and digital image analysis provide new strategies to assess fibrosis in a more differentiated way. In this study, we adopted a method previously used to quantify fibrosis in visceral organs to the quantification of fibrosis to 3D biomaterials. In a proof-of-concept study, we transferred the "Collagen Proportionate Area" (CPA) analysis from hepatology to the field of biomaterials. As one task of an experimental animal study, we used CPA analysis to quantify the fibrotic ingrowth into a filamentous scaffold after subcutaneous implantation. We were able to demonstrate that the application of the CPA analysis is well suited as an additional fibrosis evaluation strategy for new biomaterial constructions. The CPA method can contribute to a better understanding of the fibrotic interactions between 3D scaffolds and the host tissue responses.

Tissue response to five commercially available peritoneal adhesion barriers-A systematic histological evaluation.

Separating wounded serosa by physical barriers is the only clinically approved adjunct for postoperative adhesion prevention. Since the optimal adhesion barrier has not been found, it is essential to improve our pathogenic understanding of adhesion formation and to compare the effects of different barrier materials on tissue and cells. Wistar rats underwent standardized peritoneal damage and were treated either with Seprafilm, Adept, Intercoat, Spraygel, SupraSeal or remained untreated as a control. 14 days postoperatively, the lesions were explanted and histomorphologically analyzed using the European ISO score to evaluate material implants. Striking differences between the material groups were present regarding the inflammation, fibrosis, and foreign body reaction. According to the ISO score, Intercoat and Spraygel were considered as nonirritating to tissue. Adept, Seprafilm, and SupraSeal were assessed as mild-irritating materials. Interestingly, the most effective material in adhesion prevention revealed moderate inflammation accompanied by minor fibrosis. The degree of inflammation to barrier materials does not predict the efficacy in the prevention of adhesions. Histopathological investigations are crucial to improve our understanding of the cellular mechanisms during adhesion formation and elucidate the tissue response to material approaches used in adhesion prevention. This will lead to improved antiadhesive strategies and the development of functional barrier biomaterials. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 598-609, 2018.

Expression of CD68 positive macrophages in the use of different barrier materials to prevent peritoneal adhesions-an animal study.

In preventing postoperative adhesion formation the optimal barrier material has still not been found. It is therefore imperative to assess the biocompatibility of potential barrier devices. Macrophages play a decisive role in the regulation of wound healing, tissue regeneration and foreign body reaction. Since the number of CD68-positive macrophages represents an important parameter within biomaterial testing, in the present study it was analysed whether a correlation exists between the total number of CD68-positive macrophages and the extent of fibrosis or inflammation in peritoneal adhesion prevention using biomaterials. After standardized peritoneal wounding, Wistar rats were treated with five adhesion barriers or remained untreated as a control. After 14 days, animals were sacrificed and the treated areas were evaluated histomorphologically and immunohistologically. A heterogeneous pattern of macrophage count in relation to fibrosis or inflammation was found. While some groups described a moderate macrophage infiltration without fibrosis, others showed similar numbers of macrophages, but accompanied by moderate fibrosis. Moreover, a minimal number of macrophages was associated with minimal fibrosis. Mild inflammation was seen both with minimal and moderate macrophage infiltration. Altogether, no correlation could be established between the tissue response and the count of CD68-positive macrophages. With a view to macrophage heterogeneity further studies are required to determine the different macrophage subpopulations and clarify the role of these in the tissue responses to barrier materials.

Mesothelial morphology and organisation after peritoneal treatment with solid and liquid adhesion barriers--a scanning electron microscopical study.

Separation of traumatized tissue represents the only promising strategy in postoperative adhesion prevention, a relevant clinical problem after surgical intervention. In the present study scanning electron microscopy (SEM) and subsequent morphometry were used to analyse the tissue response to five commercial adhesion barriers. Standardised peritoneal lesions in Wistar rats were covered with solid and viscous barrier materials and semiquantitatively analysed 14 days postoperatively. Striking morphological differences in lesion surface organisation between the barrier groups became apparent with colonisation of the barrier by mesothelial cells to different degrees. Furthermore, the mesothelial cells showed either a normal or activated phenotype depending on the underlying biomaterial. These experiments demonstrate that the examination by SEM gives useful insights into the performance of barrier materials and the cellular processes of adhesion prevention, since mesothelial cells play an active role in the pathogenesis of adhesion formation.

Current strategies and future perspectives for intraperitoneal adhesion prevention.

INTRODUCTION: The formation of peritoneal adhesions still is a relevant clinical problem after abdominal surgery. Until today, the most important clinical strategies for adhesion prevention are accurate surgical technique and the physical separation of traumatized serosal areas. Despite a variety of barriers which are available in clinical use, the optimal material has not yet been found. DISCUSSION: Mesothelial cells play a crucial physiological role in friction less gliding of the serosa and the maintenance of anantiadhesive surface. The formation of postoperative adhesions results from a cascade of events and is regulated by various cellular and humoral factors. Therefore, optimization or functionalization of barrier materials by developments interacting with this cascade on a structural or pharmacological level could give an innovative input for future strategies in peritoneal adhesion prevention. For this purpose, the proper understanding of the formal pathogenesis of adhesion formation is essential. Based on the physiology of the serosa and the pathophysiology of adhesion formation, the available barriers in current clinical practice as well as new innovations are discussed in the present review.

Intraperitoneal adhesions--an ongoing challenge between biomedical engineering and the life sciences.

Peritoneal adhesions remain a relevant clinical problem despite the currently available prophylactic barrier materials. So far, the physical separation of traumatized serosa areas using barriers represents the most important clinical strategy for adhesion prevention. However, the optimal material has not yet been found. Further optimization or pharmacological functionalization of these barriers could give an innovative input for peritoneal adhesion prevention. Therefore, a more complete understanding of pathogenesis is required. On the basis of the pathophysiology of adhesion formation the main barriers currently in clinical practice as well as new innovations are discussed in the present review. Physiologically, mesothelial cells play a decisive role in providing a frictionless gliding surface on the serosa. Adhesion formation results from a cascade of events and is regulated by a variety of cellular and humoral factors. The main clinically applied strategy for adhesion prevention is based on the use of liquid or solid adhesion barriers to separate physically any denuded tissue. Both animal and human trials have not yet been able to identify the optimal barrier to prevent adhesion formation in a sustainable way. Therefore, further developments are required for effective prevention of postoperative adhesion formation. To reach this goal the combination of structural modification and pharmacological functionalization of barrier materials should be addressed. Achieving this aim requires the interaction between basic research, materials science and clinical expertise.

A new technique for ureteral defect lesion reconstruction using an autologous vein graft and a biodegradable endoluminal stent.

PURPOSE: Ureteral defect lesions are severe complications caused by iatrogenic lesions or trauma. For ureteral defect lesions elaborate surgical intervention is needed, such as autotransplantation or ureteral replacement with small bowel. Thus, we developed a new technique for ureteral defect reconstruction in a pig model using an autologous vein graft splinted by an endoluminal biodegradable poly-L-lactic acid stent (Institute of Textile Technology and Process Engineering, Denkendorf, Germany). MATERIALS AND METHODS: In 42 pigs we removed the external jugular vein and used it as an autologous vein graft. After median laparotomy a 3 cm segment was resected from the proximal ureter and replaced by the vein with or without an endoluminal biodegradable poly-L-lactic acid stent. As controls, we used 14 pigs. We observed survival, kidney function, and neoureteral and kidney morphological changes for 7 days and for 6 months. RESULTS: After 6 months the stent material was completely broken down and the vein graft was relined with urothelium. It resembled native ureter with cytokeratin-7 positive columnar epithelium and newly formed capillaries in the ureteral wall. All animals had normal kidney function without renal pelvis congestion. CONCLUSIONS: This new technique for ureteral defect reconstruction using an autologous vein graft and a biodegradable endoluminal stent is feasible. It is an interesting alternative in the clinic due to the preservation of physiological urine passage and the antireflux mechanism.

A pilot study of laparoscopic adhesion prophylaxis after myomectomy with a copolymer designed for endoscopic application.

STUDY OBJECTIVE: To assess the laparoscopic handling and safety of D,L-polylactide-epsilon-caprolactone-trimethylene carbonate (PCT) copolymer after myomectomy and compare it with icodextrin. In contrast to previously developed solid barriers, the material has rationally designed properties that are advantageous for convenient laparoscopic application. DESIGN: A randomized, single-blinded clinical study (Canadian Task Force Classification I). SETTING: Single-center study in a German University Hospital. PATIENTS: Thirty patients who underwent laparoscopic myomectomy were enrolled. INTERVENTIONS: After laparoscopic myomectomy and subsequent reconstruction of the uterus with interrupted sutures, adhesion prophylaxis with either site-specific PCT copolymer or icodextrin occurred as per randomization. MEASUREMENTS AND MAIN RESULTS: Except in 1 case, complete coverage of the uterine wound was achieved with PCT copolymer, and the mean time taken for application was 6.7 minutes. Mean application time for icodextrin was 1.1 minute. After introduction into the abdomen, PCT copolymer changed into a flexible state that adapted very well to the operative anatomy. The patients were followed up according to the study protocol for 3 months. There were no unforeseen adverse events, possible adhesion-related complications, or nonspecific complications in either study arm. There was no significant difference in pelvic pain scores between PCT copolymer and icodextrin groups 3 months after surgery. CONCLUSION: In this pilot study, there were no adverse events, and the rationally designed material properties are favorable for laparoscopic application. No differences in postoperative pelvic pain were ascertained between PCT copolymer and icodextrin. Therefore a human phase II trial including second-look laparoscopy should be conducted to further evaluate this new solid adhesion barrier PCT copolymer.

Adhesion prophylaxis using a copolymer with rationally designed material properties.

BACKGROUND: Physical barriers are the only licensed adjuncts for adhesion prophylaxis in the United States and Europe. Here, we investigate D,L-polylactide-epsilon-caprolactonetrimethylenecarbonate (PCT copolymer), which is a rationally designed biomaterial, as an adhesion barrier. METHODS: PCT copolymer membranes were produced by polymerization of the monomers, dissolution in organic solvents, and subsequently processing them by means of modified phase inversion and freeze drying. In vitro cytotoxicity was assayed by fibroblast culture. In vivo adhesion prophylaxis was studied in a rat model that involved standardized traumatization by electrocautery and suturing. The quantity and quality of the resulting adhesions were scored 14 days postoperatively. Complete autopsy was performed in each animal, and the implantation sites were examined histologically. The suitability for human laparoscopic application was investigated in a patient admitted for routine myomectomy. RESULTS: The PCT copolymer had no effect on the proliferation of cultured cells in vitro. The in vivo model showed that the quantity of adhesions that cover the traumatized areas was significantly less in animals treated with PCT copolymer membrane (32%) than in untreated animals (78%) (P < .01). Adhesions of both dense and filmy quality were affected. In the animals, autopsy and histologic examination of the relevant tissues revealed no indication of adverse reactions to the PCT copolymer. Human laparoscopic application was successful. CONCLUSION: The PCT copolymer membrane is biocompatible with the abdominal cavity and decreased adhesions in the animal model. It is also suitable for human laparoscopic application. Therefore, the PCT copolymer represents a candidate for additional clinical evaluation.

Suprathel, a new skin substitute, in the management of partial-thickness burn wounds: results of a clinical study.

OBJECTIVE: A prospective, randomized, bicentric, nonblinded, clinical study was conducted to evaluate the impact on wound healing of Suprathel in partial-thickness burn injuries. Suprathel represents an absorbable, synthetic wound dressing with properties of natural epithelium. METHODS: Thirty patients suffering from second-degree burn injuries were included in the study, with a mean of age 40.4 years old. Burn injuries were randomly selected, partly treated with Omiderm and partly treated with Suprathel. The first gauze change was applied the fifth day postoperatively, followed by regular wound inspection until complete reepithelization. The study focused on patient pain score, healing time, analysis of wound bed, ease of care, and treatment costs. RESULTS: There was no significant difference between the 2 materials tested regarding healing time and reepithelization. There was a significant lower pain score for patients treated with Suprathel (P = 0.0072). Suprathel becomes transparent when applied, thus allowing close monitoring of wound healing. In contrast to Omiderm, Suprathel shows better attachment and adherence to wounds. During the course of healing, it detaches smoothly, without damaging the reepithelized wound surface. Moreover, it reduces the frequency of dressing changes required. Ease of care of Suprathel has been rated outstanding by patients and healthcare professionals. When interviewed, patients reported Suprathel as their treatment preference. As dressing material, Omiderm is more cost-effective than Suprathel. CONCLUSION: Suprathel represents a reliable epidermal skin substitute, with a good impact on wound healing and pain reduction in partial-thickness burn injuries. Although it is less cost-effective than Omiderm, the significant increase of patient comfort makes this material represent a reliable and solid treatment alternative when dealing with partial-thickness burn injuries. Further studies with this synthetic dressing on other types of wounds are warranted.

Stimulation of steroid-suppressed cutaneous healing by repeated topical application of IGF-I: different mechanisms of action based upon the mode of IGF-I delivery.

BACKGROUND: Insulin-like growth factor-I (IGF-I) is accepted as a potent stimulus of wound healing when applied in combination with its binding proteins. However, there is only one study published that has investigated the effect of repeated topical application of unbound IGF-I on ischemic wound healing. The aim of this study was to show the effect of daily topical IGF-I therapy on cutaneous ulcer healing in a steroid-suppressed wound model. MATERIALS AND METHODS: Full-thickness wounds were created on the back of 40 male Sprague-Dawley rats. Before surgery, animals received depot-steroids subcutaneously. Wounds were treated daily with either a standard hydrogel dressing (control), topical IGF-I dissolved in 0.2% methylcellulose gel (IGF-I gel), or a hydrogel dressing containing IGF-I (IGF-I dressing). After 7 days of treatment, wounds were excised and measured by photoplanimetry. SMA- and PCNA-expression as well as the formation of granulation tissue were assessed in tissue sections. Results are given as median(min-max). Differences between groups were calculated by the Mann-Whitney U test. RESULTS: Subcutaneous injection of depot-steroids induced a significant delay in healing, as shown by an enlarged wound size [44(33-65) versus 25(20-35)] mm(2); P = 0.001). In steroid-treated rats, both IGF-I gel and IGF-I dressing enhanced excisional healing, as shown by a significant reduction in wound size (P = 0.0001), with IGF-I released from the dressing being even more effective than IGF-I gel (P = 0.03). However, in these animals only IGF-I released from the hydrogel dressing stimulated SMA- (P = 0.03) as well as PCNA-expression (P = 0.001) and increased granulation tissue formation (P = 0.018). CONCLUSIONS: Our data indicate that a repeated application of topical IGF-I enhances cutaneous ulcer healing. In addition, only the controlled release of IGF-I from the hydrogel dressing is capable of reversing the steroid-induced delay of healing, suggesting different mechanisms of action with respect to the mode of IGF-I delivery.

Development of a gel-simulation model and generation of standard tables for the complete extirpation of benign breast lesions with vacuum assisted biopsy under ultrasound guidance.

In combination with high-resolution ultrasound (US), vacuum-assisted biopsy (VB) techniques can be used for accurate diagnosis confirmation and therapeutic minimally invasive removal of benign breast lesions. We developed a gel-simulation model to imitate the removal of benign breast lesions (e.g., fibroadenoma) with VB from a turkey breast-phantom. Bilobular US-sensitive models in the form of a fibroadenoma were manufactured from flexible, cuttable synthetic material (longitudinal diameters of 4-20 mm). They were implanted in turkey meat and vacuum biopsied under 2-D and 3-D imaging with 11G and 8 G needles. The minimum number of cylinders removed per tumour volume, the maximum complete excision tumour size and the optimum needle gauge were determined. Lesions with a longitudinal diameter of up to 10 to 12 mm could be removed with the 11G needle, those up to 20 mm with the 8G needle. The values for the correct needle size, number of cylinders per tumour size to be removed produced with the gel turkey phantoms provide a reference for clinicians performing VB with total excision intent. VB is suitable for the removal of benign lesions with a diameter of up to 20 mm.

Innovative barriers for peritoneal adhesion prevention: liquid or solid? A rat uterine horn model.

OBJECTIVE: To compare the effects of solid barriers (PDLA membrane and foil, Interceed), innovative barrier solutions (Adept and Hyalobarrier Gel, phospholipid emulsion), and Ringer's lactate solution in preventing postsurgical peritoneal adhesions in the rat. DESIGN: Prospective, randomized experimental study. SETTING: Rat model in an academic research environment. ANIMAL(S): Female, nonpregnant Wistar rats. INTERVENTION(S): Standardized surgical injuries were applied to the parietal and visceral peritoneum and the uterine horns. The barrier agents were applied and the wound was closed. A second-look laparoscopy was performed 31 days after surgery to assess adhesion formation. MAIN OUTCOME MEASURE(S): Severity and extent of adhesion formation assessed using a multidimensional adhesion scoring system. RESULT(S): Significantly fewer postsurgical adhesions were seen after treatment with Adept, Hyalobarrier Gel, Interceed, PDLA membrane, and phospholipid emulsion than after Ringer's lactate solution. Severe, clinically relevant adhesions were not observed after Hyalobarrier Gel and in only one animal after Adept. CONCLUSION(S): Both solid and liquid barriers can prevent adhesions. Hydroflotation formulas, such as Adept and Hyalobarrier Gel, avoid suture-induced adhesions, are easy to use, and their protective effects are evenly distributed. They are suitable for adhesion prevention after multifocal trauma in rats, and require further testing in the everyday clinical situation.

Experimental ischemic wounds: correlation of cell proliferation and insulin-like growth factor I expression and its modification by different local IGF-I release systems.

We investigated cell proliferation and local insulin-like growth factor-I (IGF-I) expression in ischemic wounds after topical application of IGF-I through different delivery systems. IGF-I dressings were fabricated from an IGF-I containing polyvinyl alcohol film placed on a standard hydrogel dressing. In vitro, the release of IGF-I from this dressing was assessed by enzyme-linked immunosorbent assay. For animal experiments, a standardized ischemic skin flap containing a full-thickness wound was created on the back of male Sprague-Dawley rats. An identical wound outside the flap served as control. We initially investigated intracutaneous pO2 (p(ti)O2), cell proliferation, and local IGF-I expression. In a second setting, wounds were treated either with IGF-I dissolved in methylcellulose gel or with an IGF-I dressing, and ulcer size and cell proliferation were assessed. In vitro, approximately 60% of IGF-I was released from the IGF-I dressing, compared to a 97% release from methylcellulose gel. In vivo, ischemic wounds showed less cell proliferation and decreased IGF-I expression than nonischemic wounds. A lower local p(ti)O2 correlated with larger wound size, less cell proliferation, and decreased IGF-I expression. Ulcer size was reduced after treatment with either IGF-I dressing or methylcellulose gel. However, cell proliferation only increased after treatment with IGF-I dressing, but not after methylcellulose gel treatment. We conclude that IGF-I expression is decreased in ischemic wounds and correlates with low cell proliferation. This can be reversed by local IGF-I application, but the efficacy of treatment depends on the delivery system.

Control of material stiffness during degradation for constructs made of absorbable polymer fibers.

Augmentation devices for cruciate ligament surgery should provide gradually decreasing mechanical properties with a half-time strength of at least 6 months to temporarily protect healing tendon grafts or sutured ligaments against high tensile loads during the postoperative healing period. The absorbable material of choice that shows such slow degradation kinetics is poly(L-lactide). However, previous studies have shown that poly(L-lactide) fulfills the requirement of a long half-time strength, while the corresponding stiffness decreases at a much slower rate. An augmentation stiffness that does not change much versus time cannot provide a gradual increase in graft load, which is important to stimulate the orientation of the collagenous tissue. Therefore a new augmentation device was designed, which should decrease both in strength and stiffness during degradation. The cord was braided out of two fibers made of poly(L-lactide) and poly(L-lactide-co-glycolide), which degrade at different rates. The cord prototype was degraded in vitro and the rupture force and stiffness was tested at eight different time points up to 60 weeks. The initial rupture force and stiffness was 522.7 +/- 2.8 N and 104.1 +/- 3.8 N/%, respectively. Both strength and stiffness decreased continuously with a half-time strength of 18 weeks and a half-time stiffness of 39 weeks. The gradually decreasing stiffness was achieved by the breakdown of the faster-degrading fiber component made of poly(L-lactide-co-glycolide). Thus the new augmentation device can provide a continuous increase of forces in a tendon graft or in a healing ligament.