Enhanced neovascularization of dermis substitutes via low-pressure plasma-mediated surface activation

Improving Vascularization of Biomaterials for Skin and Bone Regeneration by Surface Modification: A Narrative Review on Experimental Research

Artificial tissue substitutes are of great interest for the reconstruction of destroyed and non-functional skin or bone tissue due to its scarcity. Biomaterials used as scaffolds for tissue regeneration are non-vascularized synthetic tissues and often based on polymers, which need ingrowth of new blood vessels to ensure nutrition and metabolism. This review summarizes previous approaches and highlights advances in vascularization strategies after implantation of surface-modified biomaterials for skin and bone tissue regeneration. The efficient integration of biomaterial, bioactive coating with endogenous degradable matrix proteins, physiochemical modifications, or surface geometry changes represents promising approaches. The results show that the induction of angiogenesis in the implant site as well as the vascularization of biomaterials can be influenced by specific surface modifications. The neovascularization of a biomaterial can be supported by the application of pro-angiogenic substances as well as by biomimetic surface coatings and physical or chemical surface activations. Furthermore, it was confirmed that the geometric properties of the three-dimensional biomaterial matrix play a central role, as they guide or even enable the ingrowth of blood vessels into a biomaterial.

Strategies to Induce Blood Vessel Ingrowth into Skin Grafts and Tissue-Engineered Substitutes

Skin is a multilayer organ consisting of several tissues and appendages residing in a complex niche. Adequate and physiologically regulated vascularization is an absolute requirement for skin homeostasis, regeneration, and wound healing. The lack of vascular networks and ischemia results in delayed wound closure. In addition, vascularization is critical for the prolonged function and survival of skin grafts and tissue-engineered skin substitutes. This study highlights the clinical challenges associated with the limited vascularization in the cutaneous wounds. Then, we highlight the novel approaches for the development of vascular networks in the skin autografts, allografts, and artificial substitutes. Also, the future directions to overcome the existing vascularization complications in skin grafting and synthetic skin substitutes are presented. Statement of Significance Delayed closure of large dermal wounds, such as burn injuries, results from the lack of vascular networks and ischemia. The amount of blood supply in the skin graft is the primary factor determining the quality of the transplanted grafts. The current skin grafts and their fabrication methods lack the appropriate features that contribute to the vascularization and integration of the wound bed and graft and adherence to the skin layers. Therefore, the new generation of skin grafts should consider advanced technologies to induce vascularization and overcome current challenges.

Cold helium plasma jet does not stimulate collagen remodeling in a 3D human dermal substitute

Cold Atmospheric Plasma (CAP) is an emerging physical approach displaying encouraging antitumor and wound healing effects both in vitro and in vivo. In this study, we assessed the potential of direct CAP to remodel skin collagens using an original tissue-engineered human dermal substitute model rich in endogenous extracellular matrix (ECM) covered with 600 µl of culture medium and treated with CAP for 30 and 120 s. Our results indicated that Reactive Oxygen and Nitrogen Species (RONS) such as H₂O₂, NO₃^- and NO₂^- were produced in the medium during treatment. It appeared that in the CAP-treated dermal substitutes 1) cell viability was not altered, 2) pro-collagen I secretion was not modified over 48 h of culture after treatment, 3) global activity of matrix metalloproteinases MMPs was not modulated over 48 h after treatment, and 4) no change in hydroxyproline content was observed over 5 days after treatment. In order to confirm the efficiency of our device, we showed that the plasma-activated culture medium induced cell apoptosis and growth delay using a 3D human tumor spheroid model. In conclusion, no effect of direct CAP treatment was monitored on dermal ECM production and degradation, indicating that CAP does not stimulate collagen remodeling at the tissue scale.

Redox Enzymes of the Thioredoxin Family as Potential and Novel Markers in Pemphigus

Pemphigus vulgaris (PV) is a severe autoimmune blistering disease affecting both skin and mucous membranes. Its pathogenesis is related to IgG autoantibodies primarily targeting the cellular adhesion protein desmoglein (Dsg) 3, one of the major desmosome components. Impaired redox regulation is considered a major player in the pathogenesis of autoimmune diseases such as pemphigus by enhancing inflammation and breakdown of immunological tolerance by structural protein modifications. Despite many recent advances, local and systemic redox profiles that characterize the immune response in pemphigus are virtually unknown but potentially crucial in further advancing our understanding of redox-dependent modifications that eventually lead to clinical manifestation. Here, we have analyzed the individual expression pattern of four major redox enzymes that are members of the thioredoxin (Trx) fold superfamily (peroxiredoxins (Prxs) 1 and 4, glutaredoxin (Grx) 2, and Trx1) in serum and PBMCs as well as their distribution in the skin of pemphigus patients compared to healthy controls. We show that in groups of five pemphigus patients, Prx1 is upregulated in both serum and PBMCs, while its epithelial distribution remains within the spinous epithelial layer. Expression of Grx2 and Prx4 is both reduced in serum and PBMCs, while their distinct and similar expression in the skin changes from an even distribution throughout the basal layer (healthy) to ubiquitous nuclear localization in pemphigus patients. In PV patients, Trx1 is secreted into serum, and cellular distribution appears membrane-bound and cytosolic compared to healthy controls. We furthermore showed that a 3D ex vivo human skin model can indeed be used to reproduce similar changes in the protein levels and distribution of redox enzymes by application of cold atmospheric plasma. Deciphering the relationship between redox enzyme expression and autoimmunity in the context of pemphigus could be critical in elucidating key pathogenic mechanisms and developing novel interventions for clinical management.

The emerging potential of cold atmospheric plasma in skin biology

The maintenance of skin integrity is crucial to ensure the physiological barrier against exogenous compounds, microorganisms and dehydration but also to fulfill social and aesthetic purposes. Besides the development of new actives intended to enter a formulation, innovative technologies based on physical principles have been proposed in the last years. Among them, Cold Atmospheric Plasma (CAP) technology, which already showed interesting results in dermatology, is currently being studied for its potential in skin treatments and cares. CAP bio-medical studies gather several different expertise ranging from physics to biology through chemistry and biochemistry, making this topic hard to pin. In this review we provide a broad survey of the interactions between CAP and skin. In the first section, we tried to give some fundamentals on skin structure and physiology, related to its essential functions, together with the main bases on cold plasma and its physicochemical properties. In the following parts we dissected and analyzed each CAP parameter to highlight the already known and the possible effects they can play on skin. This overview aims to get an idea of the potential of cold atmospheric plasma technology in skin biology for the future developments of dermo-cosmetic treatments, for example in aging prevention.

Vascularization is the next challenge for skin tissue engineering as a solution for burn management

Skin regeneration represents a promising line of management for patients with skin loss, including burn victims. The current approach of spraying single cells over the defective areas results in variable success rates in different centers. The modern approach is to synthesize a multilayer skin construct that is based on autologous stem cells. One of the main complications with different types of transplants is sloughing due to the absence of proper vascularization. Ensuring proper vascularization will be crucial for the integration of skin constructs with the surrounding tissues. Combination of the right cells with scaffolds of proper physico-chemical properties, vascularization can be markedly enhanced. The material effect, pore size and adsorption of certain proteins, as well as the application of appropriate growth factors, such as vascular endothelial growth factors, can have an additive effect. A selection of the most effective protocols is discussed in this review.

Argon plasma surface modification promotes the therapeutic angiogenesis and tissue formation of tissue-engineered scaffolds in vivo by adipose-derived stem cells

Background

Synthetic implants are being used to restore injured or damaged tissues following cancer resection and congenital diseases. However, the survival of large tissue implant replacements depends on their ability to support angiogenesis that if limited, causes extrusion and infection of the implant. This study assessed the beneficial effect of platelet-rich plasma (PRP) and adipose-derived stem cells (ADSCs) on synthetic biomaterials in combination with argon plasma surface modification to enhance vascularisation of tissue-engineered constructs.

Methods

Non-biodegradable polyurethane scaffolds were manufactured and modified with plasma surface modification using argon gas (PM). Donor rats were then used to extract ADSCs and PRP to modify the scaffolds further. Scaffolds with and without PM were modified with and without ADSCs and PRP and subcutaneously implanted in the dorsum of rats for 3 months. After 12 weeks, the scaffolds were excised and the degree of tissue integration using H&E staining and Masson’s trichrome staining, angiogenesis by CD31 and immune response by CD45 and CD68 immunohistochemistry staining was examined.

Results

H&E and Masson’s trichrome staining showed PM+PRP+ADSC and PM+ADSC scaffolds had the greatest tissue integration, but there was no significant difference between the two scaffolds (p < 0.05). The greatest vessel formation after 3 months was shown with PM+PRP+ADSC and PM+ADSC scaffolds using CD31 staining compared to all other scaffolds (p < 0.05). The CD45 and CD68 staining was similar between all scaffolds after 3 months showing the ADSCs or PRP had no effect on the immune response of the scaffolds.

Conclusions

Argon plasma surface modification enhanced the effect of adipose-derived stem cells effect on angiogenesis and tissue integration of polyurethane scaffolds. The combination of ADSCs and argon plasma modification may improve the survival of large tissue implants for regenerative applications.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1195-z) contains supplementary material, which is available to authorized users.

Argon plasma improves the tissue integration and angiogenesis of subcutaneous implants by modifying surface chemistry and topography

BACKGROUND

Tissue integration and vessel formation are important criteria for the successful implantation of synthetic biomaterials for subcutaneous implantation.

OBJECTIVE

We report the optimization of plasma surface modification (PSM) using argon (Ar), oxygen (O2) and nitrogen (N2) gases of a polyurethane polymer to enhance tissue integration and angiogenesis.

METHODS

The scaffold's bulk and surface characteristics were compared before and after PSM with either Ar, O2 and N2. The viability and adhesion of human dermal fibroblasts (HDFs) on the modified scaffolds were compared. The formation of extracellular matrix by the HDFs on the modified scaffolds was evaluated. Scaffolds were subcutaneously implanted in a mouse model for 3 months to analyze tissue integration, angiogenesis and capsule formation.

RESULTS

Surface analysis demonstrated that interfacial modification (chemistry, topography and wettability) achieved by PSM is unique and varies according to the gas used. O2 plasma led to extensive changes in interfacial properties, whereas Ar treatment caused moderate changes. N2 plasma caused the least effect on surface chemistry of the polymer. PSM-treated scaffolds significantly (P<0.05) enhanced HDF activity and growth over 21 days. Among all three gases, Ar modification showed the highest protein adsorption. Ar-modified scaffolds also showed a significant upregulation of adhesion-related proteins (vinculin, focal adhesion kinase, talin and paxillin; P<0.05) and extracellular matrix marker genes (collagen type I, fibronectin, laminin and elastin) and deposition of associated proteins by the HDFs. Subcutaneous implantation after 3 months demonstrated the highest tissue integration and angiogenesis and the lowest capsule formation on Ar-modified scaffolds compared with O2- and N2-modified scaffolds.

CONCLUSION

PSM using Ar is a cost-effective and efficient method to improve the tissue integration and angiogenesis of subcutaneous implants.

In-vivo monitoring of infection via implantable microsensors: a pilot study

The most common complication after implantation of foreign material is infection, leading to implant failure and severe patient discomfort. Smoldering-infections proceed inapparently and might not get verified by radiological diagnostics. Early identification of this type of infection might significantly reduce the rate of complications. Therefore, we manufactured a microsensor strip in a hybrid of thin-film and laminate technology in a wafer-level process. It comprises electrochemical, amperometric microsensors for glucose, oxygen and lactate as well as an integrated reference electrode. Microsensors have been implanted in the mouse dorsal skin fold chamber, which got inoculated with a human-pathogen bacterial strain. A selective signal could be measured for all parameters and time points. The infection led to measurable changes of the wound environment as given by a decrease of the oxygen- as well as the glucose-concentration while the lactate concentration increased markedly over time. The given results in this study are the first hints on a promising new tool and should therefore be interpreted as a proof of the principle to show the functionality of the microsensors in an in vivo setting. These microsensors could be used to monitor smoldering infections of implantable foreign materials reducing foreign implant associated complications.

Current and emerging vascularization strategies in skin tissue engineering

Vascularization is a key process in skin tissue engineering, determining the biological function of artificial skin implants. Hence, efficient vascularization strategies are a major prerequisite for the safe application of these implants in clinical practice. Current approaches include (i) modification of structural and physicochemical properties of dermal scaffolds, (ii) biological scaffold activation with growth factor-releasing systems or gene vectors, and (iii) generation of prevascularized skin substitutes by seeding scaffolds with vessel-forming cells. These conventional approaches may be further supplemented by emerging strategies, such as transplantation of adipose tissue-derived microvascular fragments, 3D bioprinting and microfluidics, miRNA modulation, cell sheet engineering, and fabrication of photosynthetic scaffolds. The successful translation of these vascularization strategies from bench to bedside may pave the way for a broad clinical implementation of skin tissue engineering.

Preliminary results in single-step wound closure procedure of full-thickness facial burns in children by using the collagen-elastin matrix and review of pediatric facial burns

BACKGROUND

Management of full-thickness facial burns remains one of the greatest challenges. Controversy exists among surgeons regarding the use of early excision for facial burns. Unfortunately, delayed excision of deeper burns often results in more scarring and subsequent reconstruction becomes more difficult. A collagen-elastin matrix is used to improve the quality of the reconstructed skin, to reduce scarring and to prevent wound contraction. It serves as a foundation for split thickness skin graft and enhances short and long-term results.

AIM

We report the usage of a collagen-elastin matrix during single-step wound closure technique of severe full-thickness facial burns in 15 children with large burned body surface area, and also we review the literature about pediatric facial burns.

RESULTS

There were 15 pediatric patients with severe facial burns, 8 girls and 7 boys ranging in age from 10 months to 12 years, mean age 7 years and 6 months old. The facial burn surface area (FBSA) among the patients includes seven patients with 100%, five with 75%, and three with 50%. The average total body surface area (TBSA) for the patients was 72%, ranging between 50 and 90%. 5 of the patients' admissions were late, more than four days after burns while the rest of the patients were admitted within the first four days (acute admission time). The burns were caused by flame in eight of the patients, bomb blast in four, and scalding in three. All patients were treated by the simultaneous application of the collagen-elastin matrix and an unmeshed split thickness skin graft at Turgut Özal Medical Center, Pediatric Burn Center, Malatya, Turkey. After the treatment only two patients needed a second operation for revision of the grafts. All grafts transplanted to the face survived. The average Vancouver scar scales (VSS) were 2.55±1.42, ranging between one and six, in the first 10 of 15 patients at the end of 6 months postoperatively. VSS measurements of the last 5 patients were not taken since the 6 months postoperative period was not over.

CONCLUSION

In regard to early results, graft quality was close to normal skin in terms of vascularity, elasticity, pliability, texture and color. Esthetic and functional results have been encouraging. This study shows us that the collagen-elastin matrix as a dermal substitute is a useful adjunct, which may result in quick healing with satisfying esthetic and functional results. It also may enhance short and long-term results in after burn facial wound closure in children.

The mouse dorsal skin fold chamber as a means for the analysis of tissue engineered skin

The therapy of extensive and deep burn wounds is still a challenging task for reconstructive plastic surgery. The outcome is generally not satisfactory, neither from the functional nor from the aesthetic aspect. Several available skin substitutes are used but there is need for optimization of new skin substitutes which have to be tested in vitro as well as in vivo. Here, we show that the dorsal skin fold chamber preparation of mice is well suited for the testing of skin substitutes in vivo. Dermal skin constructs consisting of matriderm(®) covered with a collagen type I gel were inserted into full thickness skin wounds in the skin fold chambers. The skin substitutes integrated well into the adjacent skin and got epithelialized from the wound edges within 11 days. The epithelialization by keratinocytes is the prerequisite that also cell-free dermal substitutes might be used in the case of the lack of sufficient areas to gain split thickness skin grafts. Further advantage of the chambers is the lack of wound contraction, which is common but undesired in rodent wound healing. Furthermore, this model allows a sophisticated histological as well as immunohistochemical analysis. As such, we conclude that this model is well suited for the analysis of tissue engineered skin constructs. Besides epithelialization the mode and extend of neovascularization and contraction of artificial grafts may be studied under standardized conditions.