Biomechanics of Scar Tissue and Uninjured Skin

Nanomechanical 3D Depth Profiling of Collagen Fibrils in Native Tendon

Connective tissue displays a large compositional and structural complexity that involves multiple length scales. In particular, on the molecular and the nanometer level, the elementary processes that determine the biomechanics of collagen fibrils in connective tissues are still poorly understood. Here, we use atomic force microscopy (AFM) to determine the three-dimensional (3D) depth profiles of the local nanomechanical properties of collagen fibrils and their embedding interfibrillar matrix in native (unfixed), hydrated Achilles tendon of sheep and chickens. AFM imaging in air with controlled humidity preserves the tissue's water content, allowing the assembly of collagen fibrils to be imaged in high resolution beneath an approximately 5-10 nm thick layer of the fluid components of the interfibrillar matrix. We collect pointwise force-distance (FD) data and amplitude-phase-distance (APD) data, from which we construct 3D depth profiles of the local tip-sample interaction forces. The 3D images reveal the nanomechanical morphology of unfixed, hydrated collagen fibrils in native tendon with a 0.1 nm depth resolution and a 10 nm lateral resolution. We observe a diversity in the nanomechanical properties among individual collagen fibrils in their adhesive and in their repulsive, viscoelastic mechanical response as well as among the contact points between adjacent collagen fibrils. This sheds new light on the role of interfibrillar bonds and the mechanical properties of the interfibrillar matrix in the biomechanics of tendon.

Constitutive description of skin dermis: Through analytical continuum and coarse-grained approaches for multi-scale understanding

Although there are many successful descriptions of the mechanical response of dermis at different levels of complexity and incorporating varying degrees of the physical phenomena involved in deformation, observations indicate that the unraveling of fibers involves a complex three-dimensional process in which they interact in ways that resemble a braided pattern. Here we develop two complementary treatments to gain a better understanding of the mechanical response of dermis: a) an analytical treatment incorporating fibril stiffness, interfibrillar frictional sliding, and the effect of lateral fibers on the extension of a primary fiber; b) a coarse-grained molecular dynamics model comprised of an array of parallel curved fibrils simulating a fiber. Interfibrillar frictional sliding and stiffness are also captured. Both analytical and molecular dynamics models operate at a scale compatible with the wavelength of collagen fibers (~10 µm). The constitutive description presented here incorporates important physical processes taking place during deformation of dermis and thus represents an advance in our understanding of these phenomena. STATEMENT OF SIGNIFICANCE: Microstructural observations of the dermis of skin during tensile deformation indicate that the unraveling of fibers involves a complex three-dimensional process which replicates the effects of braiding. Two complementary constitutive modeling treatments were developed to gain a better understanding of the mechanical response of dermis: an analytical treatment incorporating fibril stiffness, interfibrillar sliding, and the effect of transverse fibers; and a coarse-grained molecular dynamics model describing the fibril bundling effect. An important novel aspect of the current contribution is the recognition that tridimensional collagen fiber arrangements play an important role in the mechanical response. The constitutive description presented here incorporates physical processes taking place during deformation of the dermis and thus represents an advance in our understanding of these phenomena.

The regional-dependent biaxial behavior of young and aged mouse skin: A detailed histomechanical characterization, residual strain analysis, and constitutive model

Skin fulfills several vital functions, many of which are dependent on its mechanical properties. Therefore, as mice have become an invaluable model for skin research, determining murine skin's mechanical properties is important. Specifically, skin's mechanical properties are important for functional tests as well as for prognostic and diagnostic purposes. Additionally, computational simulations of skin behavior are becoming commonplace, rendering accurate models of murine skin's constitutive behavior necessary. To date, our knowledge of mouse skin mechanics shows significant gaps. For example, there are no comprehensive reports correlating skin's mechanical properties with region, age, and direction. Moreover, mouse skin's residual strain behavior has not been reported on. In our current work, we set out to fill these gaps. Based on histology, 2-photon microscopy, and planar biaxial testing, while accurately tracking various reference configurations, we report on differences in gross structure, microstructural organization, and constitutive response of skin, and cast those properties into a versatile Fung-type hyperelastic constitutive law for three reference configurations. Our data is the most comprehensive report contrasting the mechanical properties of young (12 weeks) and aged (52 weeks) mouse skin and will, thus, be valuable to basic science as control data, and provide accurate constitutive laws for mouse skin modeling. STATEMENT OF SIGNIFICANCE: Our findings are significant as they fill several gaps in our understanding of mouse skin mechanics. This is particularly important as mouse skin is becoming a frequent and critical model of human skin for cosmetic and medical science. Specifically, we quantified how mechanical properties of mice skin vary with age, with location, and with direction. Additionally, we cast our findings into constitutive models that can be used by others for predictive computer simulations of skin behavior.

Regeneration and expansion of autologous full-thickness skin through a self-propagating autologous skin graft technology

New autologous skin regeneration technology yielded full-thickness skin as evidenced by clinical observation and skin biopsy 5 months after surgery, providing relief for debilitating split-thickness skin graft contracture in a pediatric burn case.

Fabrication of Convex PDMS-Parylene Microstructures for Conformal Contact of Planar Micro-Electrode Array

Polymer-based micro-electrode arrays (MEAs) are gaining attention as an essential technology to understand brain connectivity and function in the field of neuroscience. However, polymer based MEAs may have several challenges such as difficulty in performing the etching process, difficulty of micro-pattern generation through the photolithography process, weak metal adhesion due to low surface energy, and air pocket entrapment over the electrode site. In order to compensate for the challenges, this paper proposes a novel MEA fabrication process that is performed sequentially with (1) silicon mold preparation; (2) PDMS replica molding, and (3) metal patterning and parylene insulation. The MEA fabricated through this process possesses four arms with electrode sites on the convex microstructures protruding about 20 μm from the outermost layer surface. The validity of the convex microstructure implementation is demonstrated through theoretical background. The electrochemical impedance magnitude is 204.4 ± 68.1 kΩ at 1 kHz. The feasibility of the MEA with convex microstructures was confirmed by identifying the oscillation in the beta frequency band (13–30 Hz) in the electrocorticography signal of a rat olfactory bulb during respiration. These results suggest that the MEA with convex microstructures is promising for applying to various neural recording and stimulation studies.

Current and upcoming therapies to modulate skin scarring and fibrosis

Skin is the largest organ of the human body. Being the interface between the body and the outer environment, makes it susceptible to physical injury. To maintain life, nature has endowed skin with a fast healing response that invariably ends in the formation of scar at the wounded dermal area. In many cases, skin remodelling may be impaired, leading to local hypertrophic scars or keloids. One should also consider that the scarring process is part of the wound healing response, which always starts with inflammation. Thus, scarring can also be induced in the dermis, in the absence of an actual wound, during chronic inflammatory processes. Considering the significant portion of the population that is subject to abnormal scarring, this review critically discusses the state-of-the-art and upcoming therapies in skin scarring and fibrosis.

Collagen Fibrils Mechanically Contribute to Tissue Contraction in an In Vitro Wound Healing Scenario

Wound contraction is an ancient survival mechanism of vertebrates that results from tensile forces supporting wound closure. So far, tissue tension was attributed to cellular forces produced by tissue-resident (myo-)fibroblasts alone. However, difficulties in explaining pathological deviations from a successful healing path motivate the exploration of additional modulatory factors. Here, it is shown in a biomaterial-based in vitro wound healing model that the storage of tensile forces in the extracellular matrix has a significant, so-far neglected contribution to macroscopic tissue tension. In situ monitoring of tissue forces together with second harmonic imaging reveal that the appearance of collagen fibrils correlates with tissue contraction, indicating a mechanical contribution of tensioned collagen fibrils in the contraction process. As the re-establishment of tissue tension is key to successful wound healing, the findings are expected to advance the understanding of tissue healing but also underlying principles of misregulation and impaired functionality in scars and tissue contractures.

Using Artificial Skin Devices as Skin Replacements: Insights into Superficial Treatment

Artificial skin devices are able to mimic the flexibility and sensory perception abilities of the skin. They have thus garnered attention in the biomedical field as potential skin replacements. This Review delves into issues pertaining to these skin-deep devices. It first elaborates on the roles that these devices have to fulfill as skin replacements, and identify strategies that are used to achieve such functionality. Following which, a comparison is done between the current state of these skin-deep devices and that of natural skin. Finally, an outlook on artificial skin devices is presented, which discusses how complementary technologies can create skin enhancements, and what challenges face such devices.

Enhanced in vitro efficacy for inhibiting hypertrophic scar by bleomycin-loaded dissolving hyaluronic acid microneedles

Hypertrophic scarring is a widespread skin disorder that affects a patient's confidence and quality of life.

CD44-dependent inflammation, fibrogenesis, and collagenolysis regulates extracellular matrix remodeling and tensile strength during cutaneous wound healing

Cutaneous wound healing consists of three main phases: inflammation, re-epithelialization, and tissue remodeling. During normal wound healing, these processes are tightly regulated to allow restoration of skin function and biomechanics. In many instances, healing leads to an excess accumulation of fibrillar collagen (the principal protein found in the extracellular matrix - ECM), and the formation of scar tissue, which has compromised biomechanics, tested using ramp to failure tests, compared to normal skin (Corr and Hart, 2013 [1]). Alterations in collagen accumulation and architecture have been attributed to the reduced tensile strength found in scar tissue (Brenda et al., 1999; Eleswarapu et al., 2011). Defining mechanisms that govern cellular functionality and ECM remodeling are vital to understanding normal versus pathological healing and developing approaches to prevent scarring. CD44 is a cell surface adhesion receptor expressed on nearly all cell types present in dermis. Although CD44 has been implicated in an array of inflammatory and fibrotic processes such as leukocyte recruitment, T-cell extravasation, and hyaluronic acid (the principal glycosaminoglycan found in the ECM) metabolism, the role of CD44 in cutaneous wound healing and scarring remains unknown. We demonstrate that in an excisional biopsy punch wound healing model, CD44-null mice have increased inflammatory and reduced fibrogenic responses during early phases of wound healing. At wound closure, CD44-null mice exhibit reduced collagen degradation leading to increased accumulation of fibrillar collagen, which persists after wound closure leading to reduced tensile strength resulting in a more severe scarring phenotype compared to WT mice. These data indicate that CD44 plays a previously unknown role in fibrillar collagen accumulation and wound healing during the injury response.

Biomechanical Modeling of Wounded Skin

Skin injury is the most common type of injury, which manifests itself in the form of wounds and cuts. A minor wound repairs itself within a short span of time. However, deep wounds require adequate care and sometime clinical interventions such as surgical suturing for their timely closure and healing. In literature, mechanical properties of skin and other tissues are well known. However, the anisotropic behavior of wounded skin has not been studied yet, specifically with respect to localized overstraining and possibilities of rupture. In the current work, the biomechanics of common skin wound geometries were studied with a biofidelic skin phantom, using uniaxial mechanical testing and Digital Image Correlation (DIC). Global and local mechanical properties were investigated, and possibilities of rupture due to localized overstraining were studied across different wound geometries and locations. Based on the experiments, a finite element (FE) model was developed for a common elliptical skin wound geometry. The fidelity of this FE model was evaluated with simulation of uniaxial tension tests. The induced strain distributions and stress-stretch responses of the FE model correlated very well with the experiments (R2 > 0.95). This model would be useful for prediction of the mechanical response of common wound geometries, especially with respect to their chances of rupture due to localized overstraining. This knowledge would be indispensable for pre-surgical planning, and also in robotic surgeries, for selection of appropriate wound closure techniques, which do not overstrain the skin tissue or initiate tearing.

Acute Surgical Injury Alters the Tensile Properties of Thoracolumbar Fascia in a Porcine Model

Recent work utilizing ultrasound imaging demonstrated that individuals with low back pain (LBP) have increased thickness and decreased mobility of the thoracolumbar fascia (TLF), an indication that the TLF may play a role in LBP. This study used a porcine injury model (microsurgically induced local injury)-shown to produce similar results to those observed in humans with LBP-to test the hypothesis that TLF mechanical properties may also be altered in patients with LBP. Perimuscular TLF tissue was harvested from the noninjured side of vertebral level L3-4 in pigs randomized into either control (n = 5) or injured (n = 5) groups. All samples were tested with a displacement-controlled biaxial testing system using the following protocol: cyclic loading/unloading and stress relaxation tests at 25%, 35%, and then 45% of their resting length. Tissue anisotropy was also explored by comparing responses to loading in longitudinal and transverse orientations. Tissues from injured pigs were found to have greater stretch-stretch ratio moduli (measure of tissue stiffness), less energy dissipation, and less stress decay compared to tissues from control pigs. Responses across these variables also depended on loading orientation.

CLINICAL SIGNIFICANCE

these findings suggest that a focal TLF injury can produce impairments in tissue mechanical properties away from the injured area itself. This could contribute to some of the functional abnormalities observed in human LBP.

Controlled Delivery of a Focal Adhesion Kinase Inhibitor Results in Accelerated Wound Closure with Decreased Scar Formation

Formation of scars after wounding or trauma represents a significant health care burden costing the economy billions of dollars every year. Activation of focal adhesion kinase (FAK) has been shown to play a pivotal role in transducing mechanical signals to elicit fibrotic responses and scar formation during wound repair. We have previously shown that inhibition of FAK using local injections of a small molecule FAK inhibitor (FAKI) can attenuate scar development in a hypertrophic scar model. Clinical translation of FAKI therapy has been challenging, however, because of the lack of an effective drug delivery system for extensive burn injuries, blast injuries, and large excisional injuries. To address this issue, we have developed a pullulan collagen-based hydrogel to deliver FAKI to excisional and burn wounds in mice. Specifically, two distinct drug-laden hydrogels were developed for rapid or sustained release of FAKI for treatment of burn wounds and excisional wounds, respectively. Controlled delivery of FAKI via pullulan collagen hydrogels accelerated wound healing and reduced collagen deposition and activation of scar-forming myofibroblasts in both wound healing models. Our study highlights a biomaterial-based drug delivery approach for wound and scar management that has significant translational implications.

Once episiotomy, always episiotomy?

OBJECTIVE

To investigate the association between episiotomy and perineal damage in the subsequent delivery.

STUDY DESIGN

A retrospective cohort study was conducted, comparing outcome of subsequent singleton deliveries of women with and without episiotomy in their first (index) delivery. Deliveries occurred between the years 1991-2015 in a tertiary medical center. Traumatic vaginal tears, multiple pregnancies, and cesarean deliveries (CD) in the index pregnancy were excluded from the analysis. Multiple logistic regression models were used to control for confounders.

RESULTS

During the study period, 43,066 women met the inclusion criteria; of them, 50.4% (n = 21,711) had subsequent delivery after episiotomy and 49.6% (n = 21,355) had subsequent delivery without episiotomy in the index pregnancy. Patients with episiotomy in the index birth higher rates of subsequent episiotomy (17.5 vs. 3.1%; P < 0.001; OR 1.9; 95% CI). In addition, the rates of the first and second degree perineal tears as well as the third and fourth degree perineal tears were significantly higher in patients following episiotomy (33.6 vs. 17.8%; P < 0.001, and 0.2 vs. 0.1%; P = 0.002, respectively). Nevertheless, there was no significant difference at the rates of CD and instrumental deliveries, between the groups. While adjusting for maternal age, ethnicity, birth weight, and vacuum delivery-the previous episiotomy was noted as an independent risk factor for recurrent episiotomy in the subsequent delivery (adjusted OR 6.7; 95% CI 6.2-7.3, P < 0.001). The results remained significant for term (adjusted OR 6.8; 95% CI 6.2-7.4, P < 0.001) as well as preterm deliveries (adjusted OR 4.5; 95% CI 3.3-6.3, P < 0.001) in two different models.

CONCLUSION

Episiotomy is an independent risk factor for recurrent episiotomy in the subsequent delivery.

Designing the stem cell microenvironment for guided connective tissue regeneration

Adult mesenchymal stem cells (MSCs) are an attractive cell source for regenerative medicine because of their ability to self-renew and their capacity for multilineage differentiation and tissue regeneration. For connective tissues, such as ligaments or tendons, MSCs are vital to the modulation of the inflammatory response following acute injury while also interacting with resident fibroblasts to promote cell proliferation and matrix synthesis. To date, MSC injection for connective tissue repair has yielded mixed results in vivo, likely due to a lack of appropriate environmental cues to effectively control MSC response and promote tissue healing instead of scar formation. In healthy tissues, stem cells reside within a complex microenvironment comprising cellular, structural, and signaling cues that collectively maintain stemness and modulate tissue homeostasis. Changes to the microenvironment following injury regulate stem cell differentiation, trophic signaling, and tissue healing. Here, we focus on models of the stem cell microenvironment that are used to elucidate the mechanisms of stem cell regulation and inspire functional approaches to tissue regeneration. Recent studies in this frontier area are highlighted, focusing on how microenvironmental cues modulate MSC response following connective tissue injury and, more importantly, how this unique cell environment can be programmed for stem cell-guided tissue regeneration.

A treatment algorithm for the management of intraoral burns: A narrative review

Oral mucosa follows a distinctly different trajectory of wound healing than skin. Although there are contemporary guidelines regarding treatment of burns to the skin, there is no standard of care specific to intraoral burns. This narrative review proposes an evidence-based treatment algorithm for the management of intraoral burns. Data was collated through a comprehensive review of the literature and only included studies that have reported particular success with favorable short- and long-term prognoses. In order to critically appraise the strength of the treatment recommendations, the GRADE criteria was applied to each arm of the algorithm. The algorithm was initially subdivided into the four primary etiologies of intraoral burns - thermogenic, cryogenic, chemical, electrical. Our findings emphasize the importance of conservative modalities of intra-oral burn treatment.

Comparison of amateur boxing before and after the 2013 rules change and the impact on boxers' safety

OBJECTIVES

The effect of the rules change in 2013 on amateur boxing strategy, technique and safety in comparison with pre-2013 is unknown.

METHODS

Pre-2013 and post-2013 3×3 min elite level amateur boxing was compared from video footage of 29 Olympic (pre-2013) and 50 World Championship bouts (post-2013) totalling 99 male boxers (mean±SD) age: 24.3±3.2 years, height: 177.3±11.3 cm and body mass: 70.7±16.4 kg.

RESULT

Many techniques that were dominant pre-2013 were used less post-2013, including: total punches thrown, rear hand punches, hook rear hand, punches landed, uppercut punches, total punches to the body (all <0.05), while movement around the ring and defensive movements were higher post-2013 (both p<0.004). Post-2013 boxers have increased their foot movement by 20% to move in and then away from their opponent, combined with long-range punches and deliberate defensive movements. The percentage of rounds where standing counts were issued changed from 9% to 3% pre-2013 to post-2013. However, pre-2013, 1.7% of bouts did not last the full duration due to referee stoppage, while post-2013, this increased to 4.2% as a result of two knockouts and eight technical knockouts.

DISCUSSION AND CONCLUSION

Boxers should be aware of the large changes in technical demands of boxing. An increased risk of concussive or traumatic brain injury post-2013 is equivocal. However, an increase in skin splits and technical knockouts is apparent. It is likely that boxers believe head guard removal has made them more prone to knockouts.

Reproducibility analysis on shear wave elastography (SWE)-based quantitative assessment for skin elasticity

Shear Wave Elastography (SWE) is an objective and non-invasive method widely used to quantify the tissue solidity. However, there are concerns about the accuracy of the skin SWE results due to the low signal-to-noise ratio (SNR) caused by subcutaneous fat, muscle and bone. This article analyzed the reproducibility of the result for skin SWE and therefore evaluated the availability of SME for skin elasticity involved diseases. Thirty volunteers (mean age: 37 ± 12 years) were selected. SWE were taken on the skin of abdomen and the middle tibia in order to assess the impact of fat, muscle and bone on SWE results. Skin in the area of anterior and lateral tibia marked with seven parallel lines, and each line indicated an identical thickness of the subcutaneous fat from 1-7 mm. Intra-class correlation coefficients (ICC) were used to evaluate the intra-observer and inter-observer reproducibility. The solidity of abdominal skin showed soft and small individual differences (12.4 ± 2.7 kPa), whereas high shear moduli (25-48 kPa) were observed in the skin above tibia and tibialis anterior muscle. When the subcutaneous fat was thicker than 3 mm (≥3), we obtained excellent intra-observer reproducibility (ICC range 0.78-0.98) and inter-observer reproducibility (ICC range 0.75-0.98). The thickness of subcutaneous fat could affect the reproducibility of skin SWE. The further study on skin SWE standardization should be taken.

Liposome-Adenoviral hTERT-siRNA Knockdown in Fibroblasts from Keloids Reduce Telomere Length and Fibroblast Growth

Keloids, which possess invasive tumor-like behavior, have been clinically challenging to clinicians especially surgeons. Excessive extracellular matrix secreted from fibroblasts is the main histo-pathological feature of keloids. In this study, we transfected hTERT-siRNA into scar fibroblasts by liposome-adenoviral transduction in order to disrupt telomere length homeostasis and influence the cell cycle of fibroblasts. Our results showed that liposome hTERT-siRNA was able to knock down hTERT gene expression in scar fibroblasts. Moreover, the telomerase activity in hTERT-siRNA group was significantly reduced compared with the control groups. And the telomeric length of hTERT-siRNA group was significantly shortened as well. Further, flow cytometry studies and MTT assay demonstrated that apoptosis rate of fibroblasts in liposome hTERT-siRNA group significantly increased. These results indicated that the liposome-mediated hTERT gene transduction could inhibit the growth of fibroblasts in scar tissues suggesting a promising strategy of keloids treatment in the future.

Biomechanics in dermatology: Recent advances and future directions

Biomechanics is increasingly being recognized as an important research area in dermatology. To highlight only a few examples, biomechanics has contributed to the development of novel topical therapies for aesthetic and medical purposes, enhanced our understanding of the pathogenesis of plantar melanoma, and provided insight into the epidemiology of psoriatic disease. This article summarizes the findings from recent studies to demonstrate the important role that biomechanics may have in dermatologic disease and therapy and places these biomechanical findings in a clinical context for the practicing physician. In addition, areas for future biomechanics research and development in dermatology are discussed.

Use of Adipose-Derived Stem Cells to Support Topical Skin Adhesive for Wound Closure: A Preliminary Report from Animal In Vivo Study

The aim of this study was to determine the local and systemic effects of adipose-derived stem cells (ADSCs) as a component of topical skin adhesive in an animal artificial wound closure model. In presented study the cosmetic effects, histological analysis, mechanical properties, and cell migration have been assessed to evaluate the usefulness of ADSCs as supporting factor for octyl blend cyanoacrylate adhesive. The total of 40 rats were used and divided into six groups. In the Study Group, ADSCs were administered by multipoint injection of the six surrounding intrawound areas with additional freely leaving procedure of the cells between the skin flaps just before applying adhesive to close the wound. Five control groups without using ADSCs, utilizing different types of standard wound closure, were created in order to check efficiency of experimental stem cell therapy. In our study, we proved that ADSCs could be used effectively also as a supportive tool in topical skin adhesive for wound closure. However we did not achieve any spectacular differences related to such aspects as better mechanical properties or special biological breakthroughs in wound healing properties. The use of stem cells, especially ADSCs for wound closure can provide an inspiring development in plastic and dermatologic surgery.

Reconstitution of full-thickness skin by microcolumn grafting

In addition to providing a physical barrier, skin also serves a diverse range of physiological functions through different specialized resident cell types/structures, including melanocytes (pigmentation and protection against ultraviolet radiation), Langerhans cells (adaptive immunity), fibroblasts (maintaining extracellular matrix, paracrine regulation of keratinocytes), sweat glands (thermoregulation) and hair follicles (hair growth, sensation and a stem cell reservoir). Restoration of these functional elements has been a long-standing challenge in efforts to engineer skin tissue, while autologous skin grafting is limited by the scarcity of donor site skin and morbidity caused by skin harvesting. We demonstrate an alternative approach of harvesting and then implanting μm-scale, full-thickness columns of human skin tissue, which can be removed from a donor site with minimal morbidity and no scarring. Fresh human skin microcolumns were used to reconstitute skin in wounds on immunodeficient mice. The restored skin recapitulated many key features of normal human skin tissue, including epidermal architecture, diverse skin cell populations, adnexal structures and sweat production in response to cholinergic stimulation. These promising preclinical results suggest that harvesting and grafting of microcolumns may be useful for reconstituting fully functional skin in human wounds, without donor site morbidity. © 2016 The Authors Journal of Tissue Engineering and Regenerative Medicine Published by John Wiley & Sons Ltd.

Physical, morphological, and wound healing properties of a polyurethane foam-film dressing

Background

We investigated the physicochemical properties of Medifoam® N and its wound healing performance compared to other commercially available polyurethane (PU) foam dressing in vitro and in vivo to gain insight in their clinical performance.

Methods

Wound contact layer and cross-section of eleven polyurethane foam dressings were assessed with field-emission scanning electron microscope. Thickness, density, tensile strength, elongation, moisture-vapor transmission rate (MVTR), retention and absorptivity were measured to compare physical properties. Phosphate-buffered saline (PBS) solution absorption patterns were compared. An animal model for wound-healing was applied to validate in vitro findings.

Results

Among eleven tested foam dressings, Medifoam® N has the smallest pore and cell sizes with excellent uniformity, i.e. it has 25 ~ 75 μm on the wound contact layer and 100 ~ 350 μm in the cross-section while other dressings have a larger pose size with larger variability. Compared to other PU foams, Medifoam® N also has moderate thickness, density, tensile strength, elongation and MVTR. Furthermore, it has excellent fluid absorption and retention capacity. These intrinsic properties of Medifoam® N contributed to improve fluid absorption patterns, i.e. other dressing material flawed out PBS solution on the dressings while Medifoam® N retained all the tested solutions. In animal wound-healing study, Medifoam® N treated animals showed excellent angiogenesis and collagen deposition even though epithelial recovery rate was not significantly different to other dressings.

Conclusions

Medifoam® N has optimized physical properties and thus improved fluid absorption/retention capacity. Compared to other dressings, Medifoam® N showed excellent fluid absorption patterns and these characteristics contributed to improved wound healing and excellent angiogenic potential. We found that Medifoam® N showed the best results among the employed dressing samples.

Electronic supplementary material

The online version of this article (doi:10.1186/s40824-016-0063-5) contains supplementary material, which is available to authorized users.

Comparison of the histological morphology between normal skin and scar tissue

Skin wound healing is a complex event, and interrupted wound healing process could lead to scar formation. The aim of this study was to examine the morphological changes of scar tissue. Pathological staining (HE staining, Masson's trichrome staining, methenamine silver staining) was used to evaluate the morphological changes of regenerating epidermis in normal skin and scar tissue, and immunofluorescence staining to detect the expression of collagen IV, a component of basement membrane (BM), and the expression of integrinβ4, a receptor for BM laminins. Additionally, the expression of CK14, CK5, and CK10 was measured to evaluate the proliferation and differentiation of keratinocytes in normal skin and scar tissue. The results showed that the structure of the skin was histologically changed in scar tissue. Collagen IV, expressed under the epidermis of normal skin, was reduced distinctly in scar tissue. Integrinβ4, expressed in the basal layer of normal skin, was found absent in the basal layer of scar tissue. Additionally, it was found that keratinocytes in scarring epidermis were more proliferative than in normal skin. These results indicate that during the skin wound healing, altered formation of BM may affect the proliferation of keratinocytes, reepithelial and tissue remodeling, and then result in scar formation. Thus, remodeling BM structure during wound repair may be beneficial for improving healing in cutaneous wounds during clinical practice.

Biostable electrospun microfibrous scaffolds mitigate hypertrophic scar contraction in an immune-competent murine model

Burn injuries in the United States account for over one million hospital admissions per year, with treatment estimated at four billion dollars. Of severe burn patients, 30-90% will develop hypertrophic scars (HSc). In this study, we evaluate the impact of an elastomeric, randomly-oriented biostable polyurethane (PU) scaffold on HSc-related outcomes. In vitro, fibroblast-seeded PU scaffolds contracted significantly less and demonstrated fewer αSMA(+) myofibroblasts compared to fibroblast-seeded collagen lattices. In a murine HSc model, collagen coated PU (ccPU) scaffolds significantly reduced HSc contraction as compared to untreated control wounds and wounds treated with the clinical standard of care. Our data suggest that electrospun ccPU scaffolds meet the requirements to reduce HSc contraction including reduction of in vitro HSc related outcomes, diminished scar stiffness, and reduced scar contraction. While clinical dogma suggests treating severe burn patients with rapidly biodegrading skin equivalents, our data suggest that a more long-term scaffold may possess merit in reducing HSc.

STATEMENT OF SIGNIFICANCE

In severe burns treated with skin grafting, between 30% and 90% of patients develop hypertrophic scars (HSc). There are no therapies to prevent HSc, and treatments are marginally effective. This work is the first example we are aware of which studies the impact of a permanent electrospun elastomer on HSc contraction in a murine model that mimics the human condition. Collagen coated polyurethane scaffolds decrease αSMA+ myofibroblast formation in vitro, prevent stiffening of scar tissue, and mitigate HSc contraction. Unlike current standards of care, electrospun, polyurethane scaffolds do not lose architecture over time. We propose that the future bioengineering strategy of mitigating HSc contraction should consider a long-term elastomeric matrix which persists within the wound bed throughout the remodeling phase of repair.

Finite Element Model Analysis of Cephalic Trim on Nasal Tip Stability

IMPORTANCE

Alar rim retraction is the most common unintended consequence of tissue remodeling that results from overresection of the cephalic lateral crural cartilage; however, the complex tissue remodeling process that produces this shape change is not well understood.

OBJECTIVES

To simulate how resection of cephalic trim alters the stress distribution within the human nose in response to tip depression (palpation) and to simulate the internal forces generated after cephalic trim that may lead to alar rim retraction cephalically and upward rotation of the nasal tip.

DESIGN, SETTING, AND PARTICIPANTS

A multicomponent finite element model was derived from maxillofacial computed tomography with 1-mm axial resolution. The 3-dimensional editing function in the medical imaging software was used to trim the cephalic portion of the lower lateral cartilage to emulate that performed in typical rhinoplasty. Three models were created: a control, a conservative trim, and an aggressive trim. Each simulated model was imported to a software program that performs mechanical simulations, and material properties were assigned. First, nasal tip depression (palpation) was simulated, and the resulting stress distribution was calculated for each model. Second, long-term tissue migration was simulated on conservative and aggressive trim models by placing normal and shear force vectors along the caudal and cephalic borders of the tissue defect.

RESULTS

The von Mises stress distribution created by a 5-mm tip depression revealed consistent findings among all 3 simulations, with regions of high stress being concentrated to the medial portion of the intermediate crus and the caudal septum. Nasal tip reaction force marginally decreased as more lower lateral cartilage tissue was resected. Conservative and aggressive cephalic trim models produced some degree of alar rim retraction and tip rotation, which increased with the magnitude of the force applied to the region of the tissue defect.

CONCLUSIONS AND RELEVANCE

Cephalic trim was performed on a computerized composite model of the human nose to simulate conservative and aggressive trims. Internal forces were applied to each model to emulate the tissue migration that results from decades of wound healing. Our simulations reveal that the degree of tip rotation and alar rim retraction is dependent on the amount of cartilage that was resected owing to cephalic trim. Tip reaction force is marginally reduced with increasing tissue volume resection.

LEVEL OF EVIDENCE

NA.

Solid Microneedles for Transdermal Delivery of Amantadine Hydrochloride and Pramipexole Dihydrochloride

The aim of this project was to study the influence of microneedles on transdermal delivery of amantadine hydrochloride and pramipexole dihydrochloride across porcine ear skin in vitro. Microchannel visualization studies were carried out and characterization of the microchannel depth was performed using confocal laser scanning microscopy (CLSM) to demonstrate microchannel formation following microneedle roller application. We also report, for the first time, the use of TA.XT Plus Texture Analyzer to characterize burst force in pig skin for transdermal drug delivery experiments. This is the force required to rupture pig skin. The mean passive flux of amantadine hydrochloride, determined using a developed LC–MS/MS technique, was 22.38 ± 4.73 µg/cm²/h, while the mean flux following the use of a stainless steel microneedle roller was 49.04 ± 19.77 µg/cm²/h. The mean passive flux of pramipexole dihydrochloride was 134.83 ± 13.66 µg/cm²/h, while the flux following the use of a stainless steel microneedle roller was 134.04 ± 0.98 µg/cm²/h. For both drugs, the difference in flux values following the use of solid stainless steel microneedle roller was not statistically significantly (p > 0.05). Statistical analysis was carried out using the Mann–Whitney Rank sum test.

Correlating the effects of bone morphogenic protein to secreted soluble factors from fibroblasts and mesenchymal stem cells in regulating regenerative processes in vitro

The capacity to regenerate complex tissue structures after amputation in humans is limited to the digit tip. In a comparable mouse digit model, which includes both distal regeneration-competent and proximal regeneration-incompetent regions, successful regeneration involves precise orchestration of complex microenvironmental cues, including paracrine signaling via heterogeneous cell-cell interactions. Initial cellular processes, such as proliferation and migration, are critical in the formation of an initial stable cell mass and the ultimate regenerative outcome. Hence, the objective of these in vitro studies was to investigate the effect of soluble factors secreted by fibroblasts and mesenchymal stem cells (MSCs) on the proliferation and migration of cells from the regeneration-competent (P3) and -incompetent (P2) regions of the mouse digit tip. We found that P2 and P3 cells were more responsive to fibroblasts than MSCs and that the effects were mediated by bi-directional communication. To initiate understanding of the specific soluble factors that may be involved in the fibroblast-mediated changes in migration of P2 and P3 cells, bone morphogenic protein 2 (BMP2) was exogenously added to the medium. We found that changes in migration of P3 cells were similar when exposed to BMP2 or co-cultured with fibroblasts, indicating that BMP signaling may be responsible for the migratory response of P3 cells to the presence of fibroblasts. Furthermore, BMP2 expression in fibroblasts was shown to be responsive to tensile strain, as is present during wound closure. Therefore, these in vitro studies indicate that regenerative processes may be regulated by fibroblast-secreted soluble factors, which, in turn, are modulated by both cross-talk between heterogeneous phenotypes and the physical microenvironment of the healing site.

The pathophysiologic basis of abdominal aortic aneurysm progression: a critical appraisal

An aneurysm of the abdominal aorta is a common pathology and a major cause of sudden death in the elderly. Currently, abdominal aortic aneurysms (AAAs) can only be treated by surgery and an effective medical therapy is urgently missing. The pathophysiology of AAAs is complex and is believed to be best described as a comprehensive inflammatory response with an accompanying proteolytic imbalance; the latter being held responsible for the progressive weakening of the aortic wall. Remarkably, while interference in inflammatory and/or proteolytic cascades proves highly effective in preclinical studies, emerging clinical studies consistently fail to show a benefit. In fact, some anti-inflammatory interventions appear to adversely influence the disease process. Altogether, recent clinical observations not only challenge the prevailing concepts of AAA progression, but also raise doubt on the translatability of findings from rodent models for growing AAA.