Bioactive Insulin-Loaded Electrospun Wound Dressings for Localized Drug Delivery and Stimulation of Protein Expression Associated with Wound Healing.

Effective therapy of wounds is difficult, especially for chronic, non-healing wounds, and novel therapeutics are urgently needed. This challenge can be addressed with bioactive wound dressings providing a microenvironment and facilitating cell proliferation and migration, ideally incorporating actives, which initiate and/or progress effective healing upon release. In this context, electrospun scaffolds loaded with growth factors emerged as promising wound dressings due to their biocompatibility, similarity to the extracellular matrix, and potential for controlled drug release. In this study, electrospun core-shell fibers were designed composed of a combination of polycaprolactone and polyethylene oxide. Insulin, a proteohormone with growth factor characteristics, was successfully incorporated into the core and was released in a controlled manner. The fibers exhibited favorable mechanical properties and a surface guiding cell migration for wound closure in combination with a high uptake capacity for wound exudate. Biocompatibility and significant wound healing effects were shown in interaction studies with human skin cells. As a new approach, analysis of the wound proteome in treated ex vivo human skin wounds clearly demonstrated a remarkable increase in wound healing biomarkers. Based on these findings, insulin-loaded electrospun wound dressings bear a high potential as effective wound healing therapeutics overcoming current challenges in the clinics.

Controlling the Release of Proteins from Therapeutic Nanofibers: The Effect of Fabrication Modalities on Biocompatibility and Antimicrobial Activity of Lysozyme.

Therapeutic application of pharmacologically active proteins requires advanced drug delivery systems for stabilizing their activity and preventing denaturation during storage and patient treatment. Depending on their clinical target, controlled drug release is often required to achieve the intended therapeutic effect. In this context, electrospun nanofibers gained considerable attention. However, even though immediate drug release from such fibers can easily be realized, fiber mat fabrication providing long-term controlled protein release still bares challenges.In this study, lysozyme was encapsulated in poly(vinyl alcohol) fibers followed by post-modification with MeOH, glutaraldehyde vapor, or UV light. Subsequently, a systematic investigation of the effect of these post-modification treatments on the physicochemical properties of the fibers and the stability and release kinetics of lysozyme was performed. MeOH treatment did not affect lysozyme release kinetics compared to untreated fibers, whereas glutaraldehyde vapor and UV light treatment prolonged the drug release. Infrared spectroscopy revealed cross-linking of the polymer by glutaraldehyde vapor, which reduced the lysozyme release from the fibers. Further, protein activity was significantly reduced for fibers treated with glutaraldehyde vapor and UV light. In addition, reduced viability was identified for cells in contact with glutaraldehyde vapor-treated fibers and, to a lesser extent, for UV light-treated fibers, whereas MeOH-treated fibers did not affect cell viability. These results elucidated the effects of fiber post-modification on the release kinetics, activity, and biocompatibility of protein drugs and can serve as guidance for rational development of nanomedicines for safe and effective therapeutic delivery of natural proteins.

Delivery of Therapeutic Proteins Using Electrospun Fibers-Recent Developments and Current Challenges.

Proteins play a vital role within the human body by regulating various functions and even serving as structural constituent of many body parts. In this context, protein-based therapeutics have attracted a lot of attention in the last few decades as potential treatment of different diseases. Due to the steadily increasing interest in protein-based therapeutics, different dosage forms were investigated for delivering such complex macromolecules to the human body. Here, electrospun fibers hold a great potential for embedding proteins without structural damage and for controlled release of the protein for therapeutic applications. This review provides a comprehensive overview of the current state of protein-based carrier systems using electrospun fibers, with special emphasis on discussing their potential and key challenges in developing such therapeutic strategies, along with a prospective view of anticipated future directions.

Novel in vitro approaches for the simulation and analysis of human skin wounds.

Considering the increasing incidence of chronic wounds and severe wound infections, effective drug delivery to wounded skin is of high importance. The rational development of novel therapeutic systems requires appropriate in vitro testing methodologies. In this context, suitable and reliable in vitro models simulating human wounds and advanced analytical techniques for precise wound characterization are urgently needed. In this study, we introduce a novel in vitro model based on excised human skin. In contrast to the established wound models, our novel approach has a coffin-shaped, linear, rectangular geometry with defined wound edges exhibiting consistent appearance along the entire wound bed. In addition, we introduce optical profilometry as a novel technique for nondestructive wound analysis. We successfully demonstrate the applicability of this optical imaging method based on white light reflection for three-dimensional visualization of different wound models. Furthermore, we create virtual noninvasive cross sections of these wounds to assess wound geometry in direct comparison to conventional histological analysis. Imaging analysis of our novel coffin-shaped model resulted in reproducible virtual sections along the entire wound bed. Our findings indicate the potential of our novel in vitro model for improved simulation of human wounds. Further, we successfully overcome the limitations of conventional histological analysis by the employment of optical profilometry for nondestructive three-dimensional wound characterization.

Combining confocal Raman microscopy and freeze-drying for quantification of substance penetration into human skin.

In the area of dermatological research, the knowledge of rate and extent of substance penetration into the human skin is essential not only for evaluation of therapeutics, but also for risk assessment of chemicals and cosmetic ingredients. Recently, confocal Raman microscopy emerged as a novel analytical technique for analysis of substance skin penetration. In contrast to destructive drug extraction and quantification, the technique is non-destructive and provides high spatial resolution in three dimensions. However, the generation of time-resolved concentration depth profiles is restrained by ongoing diffusion of the penetrating substance during analysis. To prevent that, substance diffusion in excised human skin can instantly be stopped at defined time points by freeze-drying the sample. Thus, combining sample preparation by freeze-drying with drug quantification by confocal Raman microscopy yields a novel analytical platform for non-invasive and quantitative in vitro analysis of substance skin penetration. This work presents the first proof-of-concept study for non-invasive quantitative substance depth profiling in freeze-dried excised human stratum corneum by confocal Raman microscopy.

The interplay of Pseudomonas aeruginosa and Staphylococcus aureus in dual-species biofilms impacts development, antibiotic resistance and virulence of biofilms in in vitro wound infection models.

Due to high tolerance to antibiotics and pronounced virulence, bacterial biofilms are considered a key factor and major clinical challenge in persistent wound infections. They are typically composed of multiple species, whose interactions determine the biofilm's structural development, functional properties and thus the progression of wound infections. However, most attempts to study bacterial biofilms in vitro solely rely on mono-species populations, since cultivating multi-species biofilms, especially for prolonged periods of time, poses significant challenges. To address this, the present study examined the influence of bacterial composition on structural biofilm development, morphology and spatial organization, as well as antibiotic tolerance and virulence on human skin cells in the context of persistent wound infections. By creating a wound-mimetic microenvironment, the successful cultivation of dual-species biofilms of two of the most prevalent wound pathogens, Pseudomonas aeruginosa and Staphylococcus aureus, was realized over a period of 72 h. Combining quantitative analysis with electron microscopy and label-free imaging enabled a comprehensive evaluation of the dynamics of biofilm formation and matrix secretion, revealing a twofold increased maturation of dual-species biofilms. Antibiotic tolerance was comparable for both mono-species cultures, however, dual-species communities showed a 50% increase in tolerance, mediated by a significantly reduced penetration of the applied antibiotic into the biofilm matrix. Further synergistic effects were observed, where dual-species biofilms exacerbated wound healing beyond the effects observed from either Pseudomonas or Staphylococcus. Consequently, predicting biofilm development, antimicrobial tolerance and virulence for multi-species biofilms based solely on the results from mono-species biofilms is unreliable. This study underscores the substantial impact of a multi-species composition on biofilm functional properties and emphasizes the need to tailor future studies reflecting the bacterial composition of the respective in vivo situation, leading to a more comprehensive understanding of microbial communities in the context of basic microbiology and the development of effective treatments.

Unravelling host-pathogen interactions by biofilm infected human wound models.

Approximately 80 % of persistent wound infections are affected by the presence of bacterial biofilms, resulting in a severe clinical challenge associated with prolonged healing periods, increased morbidity, and high healthcare costs. Unfortunately, in vitro models for wound infection research almost exclusively focus on early infection stages with planktonic bacteria. In this study, we present a new approach to emulate biofilm-infected human wounds by three-dimensional human in vitro systems. For this purpose, a matured biofilm consisting of the clinical key wound pathogen Pseudomonas aeruginosa was pre-cultivated on electrospun scaffolds allowing for non-destructive transfer of the matured biofilm to human in vitro wound models. We infected tissue-engineered human in vitro skin models as well as ex vivo human skin explants with the biofilm and analyzed structural tissue characteristics, biofilm growth behavior, and biofilm-tissue interactions. The structural development of biofilms in close proximity to the tissue, resulting in high bacterial burden and in vivo-like morphology, confirmed a manifest wound infection on all tested wound models, validating their applicability for general investigations of biofilm growth and structure. The extent of bacterial colonization of the wound bed, as well as the subsequent changes in molecular composition of skin tissue, were inherently linked to the characteristics of the underlying wound models including their viability and origin. Notably, the immune response observed in viable ex vivo and in vitro models was consistent with previous in vivo reports. While ex vivo models offered greater complexity and closer similarity to the in vivo conditions, in vitro models consistently demonstrated higher reproducibility. As a consequence, when focusing on direct biofilm-skin interactions, the viability of the wound models as well as their advantages and limitations should be aligned to the particular research question of future studies. Altogether, the novel model allows for a systematic investigation of host-pathogen interactions of bacterial biofilms and human wound tissue, also paving the way for development and predictive testing of novel therapeutics to combat biofilm-infected wounds.

First Structure-Activity Relationship Study of Potent BLT2 Agonists as Potential Wound-Healing Promoters.

The first potent leukotriene B4 (LTB4) receptor type 2 (BLT2) agonists, endogenous 12(S)-hydroxyheptadeca-5Z,8E,10E-trienoic acid (12-HHT), and synthetic CAY10583 (CAY) have been recently described to accelerate wound healing by enhanced keratinocyte migration and indirect stimulation of fibroblast activity in diabetic rats. CAY represents a very valuable starting point for the development of novel wound-healing promoters. In this work, the first structure-activity relationship study for CAY scaffold-based BLT2 agonists is presented. The newly prepared derivatives showed promising in vitro wound-healing activity.

A Selective Modulator of Peroxisome Proliferator-Activated Receptor γ with an Unprecedented Binding Mode.

The nuclear peroxisome proliferator-activated receptor γ has well-validated therapeutic potential in metabolic, inflammatory, and neurodegenerative pathologies, but its activation is also associated with marked adverse effects and novel modes of PPARγ modulation are required. Here, we report the discovery and profiling of a new PPARγ modulator chemotype endowed with remarkable potency and a distinct binding mode in the orthosteric PPARγ ligand-binding site. Its R-enantiomer evolved as a eutomer regarding PPARγ activation with a high eudysmic ratio. The new PPARγ modulator revealed outstanding selectivity over the PPARα and PPARδ subtypes and did not promote adipogenesis in primary human fibroblasts, discriminating it from established agonists.

Establishment of a cell-based wound healing assay for bio-relevant testing of wound therapeutics.

INTRODUCTION: Predictive in vitro testing of novel wound therapeutics requires adequate cell-based bio-assays. Such assays represent an integral part during preclinical development as pre-step before entering in vivo studies. Simple "scratch tests" based on defected skin cell monolayers exist, however these can solely be used for testing liquids, as cell monolayer destruction and excessive hydration limit their applicability for (semi-)solid systems like wound dressings. In this context, a cell-based wound healing assay is introduced for rapid and predictive testing of wound therapeutics independent of their physical state in a bio-relevant environment. METHODS: A novel wound healing assay was established for bio-relevant and predictive testing of (semi-) solid wound therapeutics. RESULTS: The assay allows for physiologically relevant hydration of the tested wound therapeutics at the air-liquid interface and their removal without cell monolayer disruption. In a proof-of-concept study, the applicability and discriminative power could be demonstrated by examining unloaded and drug-loaded wound dressings with two different established wound healing actives (dexpanthenol and metyrapone) and their effect on skin cell behavior. The influence of the released drug on the cells´ healing behavior could successfully be monitored over time. Wound size assessment after 96h resulted in an eight fold smaller wound area for drug treated models compared to the ones treated with unloaded fibers and non-treated wounds. DISCUSSION: This assay provides valuable first insights towards the establishment of a valid screening and evaluation tool for preclinical wound therapeutic development from liquid to (semi-)solid systems to improve predictability in a simple, yet standardized way.

Multifunctional electrospun nanofibers for wound application - Novel insights into the control of drug release and antimicrobial activity.

Therapeutic management of skin wounds is still faced with major challenges associated with chronicity and bacterial infection. Consequently, there is a high clinical need for effective therapeutic approaches addressing these aspects. In this context, electrospun fibers emerged as beneficial carrier systems for local and controlled delivery of wound healing agents, additionally providing a protective barrier against bacterial invasion. However, depending on the material, such fibers were also shown to provide a potential substrate for bacterial colonization and growth. Thus, profound understanding of fiber characteristics and the respective interactions of fibers with biological systems, cells as well as bacteria, is of major importance. To address these issues, we designed drug-loaded hybrid fibers consisting of polycaprolactone (PCL) and chitosan. Pure PCL fibers provided suitable drug release kinetics for wound healing, but were colonized by Pseudomonas bacteria which were used as model pathogens. The addition of chitosan to the fiber matrix reduced the number of adherent bacteria by tenfold compared to pure PCL fibers and did not show any adverse effects to human skin cells. Further, chitosan incorporation significantly improved fiber hydrophilicity, identified as one of the key regulators of optimized cell-fiber interactions. We successfully encapsulated dexpanthenol as an established wound healing active into these hybrid fibers and solvent polarity was found to be a key factor for controlling drug release kinetics from the fibers. For the final formulation, controlled drug release over seven days with a burst release of 11.54% within 3 h could be achieved and the wound healing effect of the fiber mats could successfully be demonstrated in a cell-based wound healing assay as a proof-of-concept. Such multifunctional fibers simultaneously deliver actives and prevent bacterial growth, and consequently show a high potential for future wound therapy.

In vitro models for evaluating safety and efficacy of novel technologies for skin drug delivery.

For preclinical testing of novel therapeutics, predictive in vitro models of the human skin are required to assess efficacy, absorption and safety. Simple as well as more sophisticated three-dimensional organotypic models of the human skin emerged as versatile and powerful tools simulating healthy as well as diseased skin states. Besides addressing the demands of research and industry, such models serve as valid alternative to animal testing. Recently, the acceptance of several models by regulatory authorities corroborates their role as important building block for preclinical development. However, valid assessment of readout parameters derived from these models requires suitable analytical techniques. Standard analytical methods are mostly destructive and limited regarding in-depth investigation on molecular level. The combination of adequate in vitro models with modern non-invasive analytical modalities bears a great potential to address important skin drug delivery related questions. Topics of interest are for instance the assessment of repeated dosing effects and xenobiotic biotransformation, which cannot be analyzed by destructive techniques. This review provides a comprehensive overview of current in vitro skin models differing in functional complexity and mimicking healthy as well as diseased skin states. Further, benefits and limitations regarding analytical evaluation of efficacy, absorption and safety of novel drug carrier systems applied to such models are discussed along with a prospective view of anticipated future directions. In addition, emerging non-invasive imaging modalities are introduced and their significance and potential to advance current knowledge in the field of skin drug delivery is explored.

Three-dimensional hierarchical cultivation of human skin cells on bio-adaptive hybrid fibers.

The human skin comprises a complex multi-scale layered structure with hierarchical organization of different cells within the extracellular matrix (ECM). This supportive fiber-reinforced structure provides a dynamically changing microenvironment with specific topographical, mechanical and biochemical cell recognition sites to facilitate cell attachment and proliferation. Current advances in developing artificial matrices for cultivation of human cells concentrate on surface functionalizing of biocompatible materials with different biomolecules like growth factors to enhance cell attachment. However, an often neglected aspect for efficient modulation of cell-matrix interactions is posed by the mechanical characteristics of such artificial matrices. To address this issue, we fabricated biocompatible hybrid fibers simulating the complex biomechanical characteristics of native ECM in human skin. Subsequently, we analyzed interactions of such fibers with human skin cells focusing on the identification of key fiber characteristics for optimized cell-matrix interactions. We successfully identified the mediating effect of bio-adaptive elasto-plastic stiffness paired with hydrophilic surface properties as key factors for cell attachment and proliferation, thus elucidating the synergistic role of these parameters to induce cellular responses. Co-cultivation of fibroblasts and keratinocytes on such fiber mats representing the specific cells in dermis and epidermis resulted in a hierarchical organization of dermal and epidermal tissue layers. In addition, terminal differentiation of keratinocytes at the air interface was observed. These findings provide valuable new insights into cell behaviour in three-dimensional structures and cell-material interactions which can be used for rational development of bio-inspired functional materials for advanced biomedical applications.