Sensory perception and neuroanatomical structures in normal and grafted skin of burn survivors

Are symptoms in pathologic scars related to nerve function or density? A scoping review

BACKGROUND

Hypertrophic scars and keloids are forms of pathologic scarring that can give rise to pain and pruritus. The link between nerve function and nerve density and the symptoms in pathologic scars (PS) remains unclear.

OBJECTIVE

We aim to assess current knowledge on nerve function and nerve density in PS, and to explore a possible association between alterations in sensibility/nerve density and pathologic scar symptoms.

METHODS

A scoping review was conducted. After performing a systematic search using PubMed, Embase and Web-of-Science, relevant papers were selected and analyzed by 2 reviewers. Data was charted in tables in combination with a narrative summary of main findings.

RESULTS

Nineteen studies were included. Overall, functional sensibility in PS seems disturbed, with a higher frequency of allodynia and altered thermosensory thresholds, suggesting involvement of small fiber neuropathy. Nerve fiber density varied with the investigated skin layer and the used staining techniques, which implied limitations to compare findings from different studies. However, evidence suggests involvement of neuropeptides in the pathologic scar formation and symptomatology.

CONCLUSIONS

Wide heterogeneity between studies exists. Therefore, no firm conclusions can be formulated. However, evidence suggests involvement of the cutaneous nervous system by neurogenic inflammation in the pathophysiology of pathologic scars and their symptoms.

Towards the development of sensation-enabled skin substitutes

Recent advances in cell and biofabrication technologies have contributed to the development of complex human organs. In particular, several skin substitutes are being generated using tissue engineering and regenerative medicine (TERM) technologies. However, recent studies mainly focus on the restoration of the dermis and epidermis layers rather than the regeneration of a fully functional innervated skin organ. Innervation is a critical step in functional tissue repair which has been overlooked in the current TERM studies. In the current study, we highlight the importance of sensation in the skin as the largest sensory organ in the human body. In large non-healing skin wounds, the skin sensation is severely diminished or completely lost and ultimately lead to chronic pain and wound healing process interruption. Current therapeutics for restoring skin sensation after trauma are limited. Recent regenerative medicine-based studies could successfully induce neural networks in skin substitutes, but the effectiveness of these technologies in enhancing sensory capability needs further investigation.

Direct neurotization of free nipple grafts with cadaveric nerve grafts following mastectomy for gender affirming surgery

BACKGROUND

Free nipple grafting makes sensory recovery challenging. Permanent decreased sensation to touch and temperature in skin-grafted skin is common. Direct neurotization of the nipple-areolar complex (NAC) graft has been described. However, quantitative data regarding degree of nipple reinnervation possible is unknown. This study aims to quantify and qualify sensation recovery following nerve coaptation to reinnervate the NAC.

METHODS

Patients undergoing mastectomy for gender dysphoria from 2020 to 2022 were offered nerve allograft to restore nipple sensation. A lateral intercostal nerve was selected and coapted to allograft which was embedded beneath the nipple graft. Semmes Weinstein testing was used to assess nipple sensation. Assessments were made at visits <1 year and >1 year from surgery. Filaments used represented normal sensation, minor diminished sensation, diminished sensation, loss of protective sensation, and deep pressure sensation only.

RESULTS

A total of 115 patients elected for direct neurotization. Semmes Weinstein testing was limited to 46 patients representing 46 encounters and 92 nipples in the <1 year group and 24 encounters and 48 nipples in the >1 year group. Of the 92 nipples in the <1 year group, 17 (18.5%) noted return of normal sensation and 37 (40.2%) noted minor diminished or diminished sensation, indicating nerve reinnervation. There were 38 (41%) nipples with loss of protective sensation or deep sensation only. There were 48 nipples included in the >1 year group. Of the 48 nipples, 4 (8.3%) noted normal sensation and 30 (62.5%) noted minor diminished or diminished sensation, indicating nerve reinnervation. For the remaining 14 nipples, 14 (29%) noted loss of protective sensation or deep sensation only.

CONCLUSION

Sensory outcomes in NAC grafts used for reconstruction in patients undergoing double incision mastectomy remain poor. Sensation restoration beyond that expected from full thickness skin grafts can be achieved in the majority of patients with nerve allograft via direct neurotization.

Skin neuropathy and immunomodulation in diseases

Skin is a vital barrier tissue of the body. Immune responses in the skin must be precisely controlled, which would otherwise cause severe disease conditions such as psoriasis, atopic dermatitis, or pathogenic infection. Research evidence has increasingly demonstrated the essential roles of neural innervations, i.e., sensory and sympathetic signals, in modulating skin immunity. Notably, neuropathic changes of such neural structures have been observed in skin disease conditions, implicating their direct involvement in various pathological processes. An in-depth understanding of the mechanism underlying skin neuropathy and its immunomodulatory effects could help reveal novel entry points for therapeutic interventions. Here, we summarize the neuroimmune interactions between neuropathic events and skin immunity, highlighting the current knowledge and future perspectives of this emerging research frontier.

Response of bone mineral density and balance performance in post-burn patients with selected Qigong training: A single-blind randomized controlled trial

BACKGROUND

Decreased bone mineral density (BMD) is a common condition after a burn with significant complications that would be a global health problem. Also, balance can further worsen due to burning complications. Therefore, this study aims to analyze the additive effects of selected Qigong training exercises for 2 months to the standard physiotherapy regimen on bone mineral density and balance control post-thermal burn injuries.

METHODS

110 participants (75 males and 35 females), aged 25-50, with deep second and third-degree thermal burns affecting the trunk and lower extremities, and a total body surface area (TBSA) of 30-45%, allocated randomly into two equal groups of 55. Group A has Qigong training along with its standard physiotherapy regimen, and the control group (Group B) has only a standard physiotherapy regimen. For eight weeks, the interventions were used four times a week. The bone mineral density (BMD), T-score of the lumbar spine, the overall stability index (OSI), and the dynamic limits of stability (DLOS) were assessed pre-intervention and after eight weeks of intervention.

RESULTS

A two-way mixed MANOVA showed that there was a significant increase in BMD, T-score, and DLOS and a significant decrease in OSI in a favor of the Qigong training group after eight weeks of treatment compared with that of the control group. Both groups showed a significant improvement in BMD, T- score, DLOS, and OSI post-treatment compared with that at the baseline. There were statistical significances in the favor of the Qigong training group after eight weeks of treatment (P < 0.001).

CONCLUSION

In patients with repaired second and third-degree thermal burns of the trunk and lower legs, Qigong training activities combined with a standard physiotherapy regimen for 2 months were more helpful in increasing bone mineral density and improving balance control than the standard physiotherapy regimen alone.

Effect of anti-gravity treadmill (Alter G) training on gait characteristics and postural stability in adult with healed burns: A single blinded randomized controlled trial

BACKGROUND

Burns constitute one of the foremost contributors to premature mortality and morbidity, and the recovery process from burn injuries is characterized by its intricate and protracted nature.

OBJECTIVE

The principal aim of this study was to assess the influence of an anti-gravity treadmill (Alter G) training program on both gait characteristics and postural stability indices (PSI) in adult individuals who have recovered from burns.

DESIGN

This study followed a single-blind, randomized, controlled design.

METHODS

A total of 45 adults, aged 18-35 years, with healed lower extremity burns that were circumferential and encompassed 35-50% of their total body surface area (TBSA) were randomly allocated to either the anti-gravity treadmill (Alter G) Training group (n = 22) or the traditional physical therapy program (TPTP) group (n=23). The TPTP group received conventional physical therapy, while the anti-gravity treadmill (Alter G) training group engaged in anti-gravity treadmill exercises alongside the traditional physical therapy program. The primary outcome measures, evaluated at both baseline and the conclusion of the 12-week intervention, included gait characteristics assessed using the GAITRite system and PSI measured by the Biodex Balance System (BBS).

RESULTS

The anti-gravity treadmill (Alter G) training group exhibited significantly greater enhancements than the TPTP group in terms of mean values and percentage changes in gait characteristics and PSI. Specifically, the percentage changes for the Alter G group were as follows: stride length (20.57%), step time (22.58%), step length (20.47%), velocity (15.67%), cadence (23.28%), and double support time (29.03%). In contrast, the TPTP group's percentage changes were: 6.73%, 8.19%, 7.65%, 7.75%, 8.89%, and 9.37%, respectively. Concerning PSI, the Alter G group exhibited percentage changes of 55.17% for the medio-lateral stability index (MLI), 48.21% for antero-posterior stability index (API), and 48.48% for the overall stability index (OSI). The TPTP group's corresponding percentage changes were 20%, 14.03%, and 16.41%.

CONCLUSIONS

The amalgamation of anti-gravity treadmill training with the traditional physical therapy program yields greater efficacy than TPTP in isolation. Consequently, the findings underscore the efficiency of anti-gravity treadmill (Alter G) Training as a valuable tool for rehabilitating patients with burn injuries.

Functional Brain Changes Following Burn Injury: A Narrative Review

BACKGROUND

Burn injuries cause significant motor and sensory dysfunctions that can negatively impact burn survivors' quality of life. The underlying mechanisms of these burn-induced dysfunctions have primarily been associated with damage to the peripheral neural architecture, however, evidence points to a systemic influence of burn injury. Central nervous system (CNS) reorganizations due to inflammation, afferent dysfunction, and pain could contribute to persistent motor and sensory dysfunction in burn survivors. Recent evidence shows that the capacity for neuroplasticity is associated with self-reported functional recovery in burn survivors.

OBJECTIVE

This review first outlines motor and sensory dysfunctions following burn injury and critically examines recent literature investigating the mechanisms mediating CNS reorganization following burn injury. The review then provides recommendations for future research and interventions targeting the CNS such as non-invasive brain stimulation to improve functional recovery.

CONCLUSIONS

Directing focus to the CNS following burn injury, alongside the development of non-invasive methods to induce functionally beneficial neuroplasticity in the CNS, could advance treatments and transform clinical practice to improve quality of life in burn survivors.

Balance Impairment in the Burn Population: A Burn Model System National Database Study

Balance is an important component of daily function and impairments can lead to injury and quality-of-life limitations. Balance is not well studied in the burn population. This study examines the frequency of long-term balance impairments and associated factors after a burn injury. The Burn Model System National Database was analyzed. Trouble with balance was self-reported at discharge, 6, 12, 24, and 60 months after injury. Regression analyses examined the associations between demographic and clinical characteristics and balance impairments at 12 months. Of 572 participants, balance impairments were most reported at discharge (40.3%), continuing over 60 months (26.8-36.0%). Those reporting balance impairments (n = 153) were more likely to be older, unemployed, have Medicaid or Medicare, receive inpatient rehabilitation, receive outpatient physical or occupational therapy, have vision problems, have leg or feet burns and swelling, and have foot numbness compared to those without (p ≤ 0.001). Regression analysis demonstrated a 4% increased odds of balance impairment for every increase in year of age (p < 0.001), 71% lower odds if employed at time of injury (p < 0.001), and 140% higher odds if receiving outpatient physical or occupational therapy at 12 months (p = 0.008). Common reports of balance impairments highlight the need for routine screenings to identify burn survivors that may benefit from targeted interventions.

Preoperative expectations, postoperative satisfaction and patient directed priorities for clinical burn research

INTRODUCTION

Burn patients receiving split thickness skin grafting are left with scarring and chronically dysfunctional grafted skin. Given evidence that patients' preoperative expectations mediate postoperative outcomes and satisfaction, we described burn patients' experience, expectations, and satisfaction with their skin graft, their views towards a cell based clinical trial to improve their graft and identified graft outcome measures for use in future studies.

METHODS

Data were collected via questionnaires preoperatively, one, and three months postoperatively. Longitudinal analyses assessed change over time.

RESULTS

Expectations of graft function were consistent pre- and postoperatively. Expectations of graft appearance showed significant decrease over time (β1 = -0.290, p = 0.008). Significant improvements in skin function (β1 = 0.579, p = 0.000) and appearance (β1 = 0.247, p = 0.025) at the wound site during recovery were observed. Patients noted great difference between grafted and normal skin. Patient satisfaction with their graft did not change significantly over time. Patients were willing to participate in a cell based clinical trial to improve graft symptomology and prioritized improvements in scarring, redness, sensation, and elasticity.

CONCLUSIONS

Outcome measures in trials advancing skin grafting should reflect chronic, patient prioritized limitations. We recommend preoperative educational interventions for burn patients receiving grafting to improve postoperative satisfaction.

Burn Injury Complications Impacting Rehabilitation

Successful post-burn rehabilitation requires an understanding of a wide range of complications to maximize functional recovery. This article reviews a range of potential challenges including burn scar contracture, amputation, peripheral nerve injury, heterotopic ossification, dysphagia, altered skin physiology, pain, and pruritis. The overall focus is to serve as a guide for post-injury therapy and rehabilitation spanning the phases of care and considering evidence-based approaches, prevention, and treatment with an ultimate goal of aiding in the functional recovery and long-term quality of life for burn survivors.

Use of sensory modulation approaches to improve compression garment adherence in adults after burn: An e-Delphi study

BACKGROUND

Sensory over-responsiveness, identified through self-report and quantitative sensory testing, has been associated with compression garment non-adherence in a burn-injured cohort. This study sought expert consensus on the usefulness of, and recommendations for, sensory modulation strategies to improve compression garment adherence in sensory over-responsive adults after burn.

METHOD

Experts in the field of sensory modulation were invited to participate in a mixed-methods, three-round electronic Delphi study.

RESULTS

Experts (N = 18) agreed that sensory modulation therapy may be a useful clinical tool to improve compression garment adherence. Twenty-two items reached consensus as essential to assessment, treatment, or therapist training.

CONCLUSION

With adequate therapist training and individualized assessment and treatment, sensory modulation strategies may be a useful clinical approach to improving compression garment adherence in those who are sensory over-responsive after burn. Further research is needed to gather perceptions from burns therapists, and to implement and evaluate the effectiveness in clinical practice.

"Out of Touch"-Recovering Sensibility after Burn Injury: A Review of the Literature

BACKGROUND

Full-thickness burn injuries (FTBI) not only lead to a significant burden in multiple ways, including social life and self-esteem, but have also a tremendous impact on environmental interaction by reducing sensibility in manifold ways. On these grounds, possible ways and solutions to recover sensibility in burn wounds are essentials and should not be overlooked.

METHODS

A review of experimental, clinical studies and the related literature was performed with the aim to highlight post-burn nerve regeneration and discover ways for sensory re-integration to complement the therapeutic concept.

RESULTS

In human burn injuries, it has been hypothesized that grafted cells, partly multipotent stem cells, could be additionally responsible for nerve regeneration in burn wound areas. In addition, burn eschar excision, performed within a short post-burn time frame, can reduce or even avoid long-term nerve damage by reducing post-burn toxic mediator release. Various animal studies could demonstrate sensory reinnervation of different qualities in burn wounds. Post-burn scar tissue prevents, or at least decelerates, nerve reinnervation, but could be reduced by targeted mediators.

CONCLUSION

Sensory loss is present in skin grafted areas following full-thickness burn-wound excision, thereby leading to a reduction in quality of life. In addition, various mediators might reduce or avoid nerve damage and should be considered at an early stage as part of a holistic burn-patient therapeutic approach. In addition, supportive multifaceted physical therapy strategies are essential.

Transgenic Epidermal Cultures for Junctional Epidermolysis Bullosa - 5-Year Outcomes

Inherited junctional epidermolysis bullosa is a severe genetic skin disease that leads to epidermal loss caused by structural and mechanical fragility of the integuments. There is no established cure for junctional epidermolysis bullosa. We previously reported that genetically corrected autologous epidermal cultures regenerated almost an entire, fully functional epidermis on a child who had a devastating form of junctional epidermolysis bullosa. We now report long-term clinical outcomes in this patient. (Funded by POR FESR 2014-2020 - Regione Emilia-Romagna and others.).

Sensory processing and detection thresholds of burn-injured patients: A comparison to normative data

OBJECTIVE

Emerging evidence suggests that individual levels of sensory sensitivity may impact treatment outcomes for people recovering from burn injuries. For example, individuals with higher levels of sensory sensitivity were less adherent with compression garment wear, often used for scar management. The purpose of this study was to characterise sensory patterns for a sample of burn-injured patients as a cohort, using normative data as the reference. As different patterns of sensory processing can have implications clinically, understanding this at the cohort level may provide valuable insight for therapy.

METHOD

This was a secondary analysis of data collected during a cross-sectional study. Adults (N = 117) attending the Professor Stuart Pegg Adult Burns Unit outpatient clinic completed the Adolescent/Adult Sensory Profile and the following quantitative sensory tests: two-point discrimination; mechanical detection threshold; and pressure pain threshold.

RESULTS

Compared to matched normative data, burn-injured patients reported higher levels of sensory sensitive and avoiding patterns, and experienced lower detection thresholds for touch and pain.

CONCLUSIONS

Higher reports of sensory sensitivity and sensory avoiding, and lower thresholds for touch and pain, have been correlated with tactile defensiveness. Tactile defensiveness has been associated with social withdrawal and isolation, all of which could contribute to decreased engagement in therapy. The ways in which these sensory characteristics impact on burn-related treatments, such as compression garment adherence, warrant further investigation.

The Role of Autologous PRP on Deep Partial-Thickness Burn Wound Healing in Bama Pigs

In this study, we aimed to evaluate the therapeutic effects of autologous platelet-rich plasma (PRP) on deep partial-thickness burns in Bama pigs. Deep partial-thickness burn wounds were created on the back of Bama pigs. The reepithelialization time was compared between the PRP and control groups. The mean score of Ki67 (+) cells and α-SMA (+) vessels, the mean thickness of epidermis and dermis of the healing wounds were determined via H&E staining and immunohistochemical assay. The levels of the growth factors epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), and vascular endothelial growth factor (VEGF) were examined by ELISA. Our data showed that the time to wound reepithelialization was shorter in the PRP group compared with the control group. The thickness of the epidermis was larger in the PRP group compared with the control group. On the 7th and 14th days after the treatment, the mean score of Ki67 (+) cells and α-SMA (+) vessels were higher in the PRP group compared with the control group. The PRP group showed higher levels of growth factors (EGF, bFGF, and VEGF) compared with the control group by ELISA. The results indicated that PRP could improve wound healing process of deep partial-thickness burns in Bama pigs. The PRP increased the thickness of epidermis of the healed wounds, cell proliferation, and angiogenesis. We demonstrated that applying PRP had a greater potential for the treatment of deep partial-thickness burns.

Recent innovations in artificial skin

The skin is a "smart", multifunctional organ that is protective, self-healing and capable of sensing and many forms of artificial skins have been developed with properties and functionalities approximating those of natural skin. Starting from specific commercial products for the treatment of burns, progress in two fields of research has since allowed these remarkable materials to be viable skin replacements for a wide range of dermatological conditions. This review maps out the development of bioengineered skin replacements and synthetic skin substitutes, including electronic skins. The specific behaviors of these skins are highlighted, and the performances of both types of artificial skins are evaluated against this. Moving beyond mere replication, highly advanced artificial skin materials are also identified as potential augmented skins that can be used as flexible electronics for health-care monitoring and other applications.

Identification of Merkel cells associated with neurons in engineered skin substitutes after grafting to full thickness wounds

Engineered skin substitutes (ESS), prepared using primary human fibroblasts and keratinocytes with a biopolymer scaffold, were shown to provide stable closure of excised burns, but relatively little is known about innervation of ESS after grafting. This study investigated innervation of ESS and, specifically, whether Merkel cells are present in healed grafts. Merkel cells are specialized neuroendocrine cells required for fine touch sensation in skin. We discovered cells positive for keratin 20 (KRT20), a general marker for Merkel cells, in the basal epidermis of ESS after transplantation to mice, suggesting the presence of Merkel cells. Cells expressing KRT20 were not observed in ESS in vitro. However, widely separated KRT20-positive cells were observed in basal epidermis of ESS by 2 weeks after grafting. By 4 weeks, these cells increased in number and expressed keratins 18 and 19, additional Merkel cells markers. Putative Merkel cell numbers increased further between weeks 6 and 14; their densities varied widely and no specific pattern of organization was observed, similar to Merkel cell localization in human skin. KRT20-positive cells co-expressed epidermal markers E-cadherin and keratin 15, suggesting derivation from the epidermal lineage, and neuroendocrine markers synaptophysin and chromogranin A, consistent with their identification as Merkel cells. By 4 weeks after grafting, some Merkel cells in engineered skin were associated with immature afferents expressing neurofilament-medium. By 8 weeks, Merkel cells were complexed with more mature neurons expressing neurofilament-heavy. Positive staining for human leukocyte antigen demonstrated that the Merkel cells in ESS were derived from grafted human cells. The results identify, for the first time, Merkel cell-neurite complexes in engineered skin in vivo. This suggests that fine touch sensation may be restored in ESS after grafting, although this must be confirmed with future functional studies.

Genetic influence on scar height and pliability after burn injury in individuals of European ancestry: A prospective cohort study

After similar extent of injury there is considerable variability in scarring between individuals, in part due to genetic factors. This study aimed to identify genetic variants associated with scar height and pliability after burn injury. An exome-wide array association study and gene pathway analysis were performed on a prospective cohort of 665 patients treated for burn injury. Outcomes were scar height (SH) and scar pliability (SP) sub-scores of the modified Vancouver Scar Scale (mVSS). DNA was genotyped using the Infinium^® HumanCoreExome-24 BeadChip. Associations between genetic variants (single nucleotide polymorphisms) and SH and SP were estimated using an additive genetic model adjusting for age, sex, number of surgical procedures and % total body surface area of burn in subjects of European ancestry. No individual genetic variants achieved the cut-off threshold of significance. Gene regions were analysed for spatially correlated single nucleotide polymorphisms and significant regions identified using comb-p software. This gene list was subject to gene pathway analysis to find which biological process terms were over-represented. Using this approach biological processes related to the nervous system and cell adhesion were the predominant gene pathways associated with both SH and SP. This study suggests genes associated with innervation may be important in scar fibrosis. Further studies using similar and larger datasets will be essential to validate these findings.

Evaluation of Not-Activated and Activated PRP in Hair Loss Treatment: Role of Growth Factor and Cytokine Concentrations Obtained by Different Collection Systems

Platelet rich plasma (PRP) was tested as a potential therapy for androgenetic alopecia (AGA) through two different clinical protocols in which one population (18 participants) received half-head treatment with autologous non-activated PRP (A-PRP) produced by CPunT Preparation System (Biomed Device, Modena, Italy) and the other half-head with placebo, and a second separated population in which all participants (n = 6, 3 participants per group) received treatment with calcium-activated PRP (AA-PRP) produced from one of two different PRP collection devices (Regen Blood Cell Therapy or Arthrex Angel System). For the A-PRP study, three treatments were administered over 30-day intervals. Trichoscan analysis of patients, three months post-treatment, showed a clinical improvement in the number of hairs in the target area (36 ± 3 hairs) and in total hair density (65±  5 hair cm2), whereas negligible improvements in hair count (1.1±  1.4 hairs) and density (1.9 ± 10.2 hair cm2) were seen in the region of the scalp that received placebo. Microscopic evaluation conducted two weeks after treatment showed also an increase in epidermal thickness, Ki67+ keratinocytes, and in the number of follicles. The AA-PRP treatment groups received a singular set of injections, and six months after the treatments were administered, notable differences in clinical outcomes were obtained from the two PRP collection devices (+90 ± 6 hair cm2 versus -73 ± 30 hair cm2 hair densities, Regen versus Arthrex). Growth factor concentrations in AA-PRP prepared from the two collection devices did not differ significantly upon calcium activation.

Myelinated and unmyelinated nerve fibers reinnervate tissue-engineered dermo-epidermal human skin analogs in an in vivo model

PURPOSE

The clinical application of autologous tissue-engineered skin analogs is an important strategy to cover large skin defects. Investigating biological dynamics, such as reinnervation after transplantation, is essential to improve the quality of such skin analogs. Previously, we have examined that our skin substitutes are reinnervated by host peripheral nerve fibers as early as 8 weeks after transplantation. Here, we wanted to investigate the presence and possible differences regarding myelinated and unmyelinated host nerve fibers 15 weeks after the transplantation of light and dark human tissue-engineered skin analogs.

METHODS

Human epidermal keratinocytes, melanocytes, and dermal fibroblasts were isolated from human light and dark skin biopsies. Keratinocytes and melanocytes were seeded on fibroblast-containing collagen type I hydrogels after expansion in culture. After additional culturing, the tissue-engineered dermo-epidermal skin analogs were transplanted onto full-thickness skin wounds created on the back of immuno-incompetent rats. Skin substitutes were excised and analyzed 15 weeks after transplantation. Histological sections were examined with regard to the ingrowth pattern of myelinated and unmyelinated nerve fibers into the skin analogs using markers, such as Substance P, NF200, and S100-Beta.

RESULTS

We found myelinated and unmyelinated peripheral host nerve fibers 15 weeks after transplantation in the dermal part of our human skin substitutes. In particular, we identified large-diameter-myelinated Aβ- and Aδ-fibers, and small-diameter C-fibers. Furthermore, we observed myelinated nerves in close proximity to CD31-positive blood capillaries. In the long run, both types of ingrown host fibers showed an identical pattern in both light and dark skin analogs.

CONCLUSION

Our data suggest that myelinated and unmyelinated peripheral nerves reinnervate human skin substitutes in a long-term in vivo transplantation assay. Our tissue-engineered skin analogs attract A- and C-fibers to supply both light and dark skin analogs. Potentially, this process restores skin sensitivity and has, therefore, a significant relevance with regard to future application of autologous pigmented dermo-epidermal skin substitutes onto patients.

Effects of small-fiber neuropathy induced by resiniferatoxin on skin healing and axonal regrowth after burn

BACKGROUND

Damage to the peripheral nervous system influences wound healing and, after a deep burn, imperfect cutaneous nerve regeneration occurs. A third-degree burn model was developed in rats combined with the use of resiniferatoxin (RTX), known to promote sensory neuropathy.

METHODS

Rats were injected intraperitoneally either with RTX or vehicle. A mechanical sensory assay and the hot plate thermal sensory test were performed. The structural integrity of the sciatic nerve was assessed using transmission electron microcopy. After RTX injection, third-degree thermal burns were performed. Wound closure was monitored and samples were collected for histological analysis, immunohistochemistry and immunoblotting for neuronal markers.

RESULTS

RTX promoted both mechanical and thermal hypoalgesia. This transient RTX-mediated sensory deficit occurred without damaging the integrity of nerve fibers and induced a significant depletion of neuropeptides in both neuronal bodies and intraepidermal nerve fibers. Although wound closure rates were similar in both groups, the kinetic of granulation tissue remodeling was delayed in the RTX group compared with control group. A significant reduction of the peripherin expression in the RTX group was observed indicating impaired axonal regrowth of small fibers within the wound.

CONCLUSION

Our study confirms the important roles of innervation during skin healing and the defect of nerve regeneration after burn.

Firefighter willingness to participate in a stem cell clinical trial for burns: A mixed methods study

Adult stem cells represent a potentially renewable and autologous source of cells to regenerate skin and improve wound healing. Firefighters are at risk of sustaining a burn and potentially benefiting from a split thickness skin graft (STSG). This mixed methods study examined firefighter willingness to participate in a future stem cell clinical trial, outcome priorities and factors associated with this decision.

METHODS

A sequential explanatory mixed methods design was used. The quantitative phase (online questionnaire) was followed by the qualitative phase (semi-structured interviews). A sample of 149 firefighters completed the online survey, and a purposeful sample of 15 firefighters was interviewed.

RESULTS

A majority (74%) reported they would participate in a future stem cell clinical trial if they experienced burn benefiting from STSG. Hypothetical concerns related to receiving a STSG were pain, itch, scarring/redness and skin durability. Participants indicated willingness to undergo stem cell therapy if the risk of no improvement was 43% or less. Risk tolerance was predicted by perceived social support and having children. Interviews revealed four main themes: a desire to help others, improving clinical outcomes, trusting relationships, and a belief in scientific investigation. Many participants admitted lacking sufficient knowledge to make an informed decision regarding stem cell therapies.

CONCLUSIONS

Firefighters indicated they were largely willing to participate in a stem cell clinical trial but also indicated a lack of knowledge upon which to make a decision. Public education of the role of stem cells in STSG will be increasingly important as clinical trials are developed.

Clinical outcomes from a foam wedge splinting program for axillary contracture prevention in the intensive care unit

Preventing scar contracture after burn injury is a critical goal during recovery. Although the need for intervention is well-understood, data on specific techniques are limited. The study's objective is to provide data for the use of a foam abduction wedge in terms of safety, effectiveness, and patient and caregiver satisfaction through a prospective, single-arm trial. All patients presenting with a burn injury that required grafting in the axillary region and placed them at risk for shoulder joint contracture were offered inclusion. Patient outcomes were recorded for the duration of their burn intensive care unit admission. Ten subjects completed the protocol with a mean duration of wedge use of 41.5 ± 32.5 days. At discharge, the mean shoulder abduction was 132° ± 38° on the left and 118° ± 22° on the right. The mean shoulder flexion was 132° ± 31° on the left and 123° ± 29° on the right. As much as 90% of the subjects had greater than 90° of shoulder abduction and flexion at discharge. There were no observations of worsening burn injury wounds, graft failure, or new pressure-related wounds. One patient was found to have an upper-extremity peripheral nerve injury that was not clearly associated with the splint. Patient and nursing surveys indicated areas of satisfaction as well as areas for potential improvement. This study illustrates the anticipated clinical outcomes and care issues associated with the use of a specific contracture prevention method used in the burn intensive care unit setting as well as identifying areas for future research.

The effects of electroacupuncture on analgesia and peripheral sensory thresholds in patients with burn scar pain

The aim of this study is to observe if the effects of electro-acupuncture (EA) on analgesia and peripheral sensory thresholds are transposable from the model of heat pain in volunteers to the clinical setting of burn scar pain. After severe burns, pathological burn scars (PPBS) may occur with excruciating pain that respond poorly to treatment and prevent patients from wearing their pressure garments, thereby leading to unesthetic and function-limiting scars. EA might be of greater benefit in terms of analgesia and functional recovery, should it interrupt this vicious circle by counteracting the peripheral hyperalgesia characterizing PPBS. Therefore we enrolled 32 patients (22 males/10 females) aged of 46±11 years with clinical signs of PPBS and of neuropathic pain despite treatment. The study protocol consisted in 3 weekly 30-min sessions of standardized EA with extra individual needles in accordance to Traditional Chinese Medicine, in addition of previous treatments. We assessed VAS for pain and quantitative sensory testing (QST) twice: one week before and one after protocol. QST measured electrical thresholds for non-nociceptive A-beta fibers, nociceptive A-delta and C fibers in 2 dermatomes, respectively from the PPBS and from the contralateral pain-free areas. Based on heat pain studies, EA consisted in sessions at the extremity points of the main meridian flowing through PPBS (0.300s, 5Hz, sub noxious intensity, 15min) and at the bilateral paravertebral points corresponding to the same metameric level, 15min. VAS reduction of 3 points or below 3 on a 10 points scale was considered clinically relevant. Paired t-test compared thresholds (mean [SD]) and Wilcoxon test compared VAS (median [IQR]) pre and after treatment, significant p<0.05. The reduction of VAS for pain reached statistical but not clinical relevance (6.8 [3] vs. 4.5 [3.6]). This was due to a large subgroup of 14 non-responders whose VAS did not change after treatment (6.6 [2.7] vs. 7.2 [3.8]). That subgroup exhibited significant differences in sensory thresholds when compared to the 18 responders (VAS from 7 [3] to 3 [1]). First, responders' thresholds for A-delta and C fibers in the PPBS area were significantly lower than those in the pain-free area before treatment but corrected after acupuncture (from respectively 60 [30] and 63 [10]% to 91 [11] and 106 [36]%). That might account for a nociceptive hypersensitivity in the PPBS that corrected after treatment. On the contrary, in non-responders nociceptive thresholds were similar in both the PPBS and the pain-free areas before treatment and did not change after EA. However, absolute values for thresholds in the pain-free areas where significantly lower for non-responders than for responders. The fact that non-responders had significant pain scores while presenting with lowered nociceptive thresholds even in the pain-free areas might evoke the possibility of a generalized supra-spinal hyperalgesia. The fact that acupuncture did not correct the pain nor the nociceptive thresholds in this subgroup requires further investigation. We also observed a statistically and clinically relevant reduction in VAS for pruritus for all patients - even those from the subgroup of non-responders to pain - that is worth to be mentioned and requires further studies to be confirmed. This observational study is the first that confirms the effects of acupuncture on analgesia and nociceptive thresholds in the clinical setting of burn pain only for patients presenting with a burn-localized but not a generalized hyperalgesia.

Interrater and intrarater reliability of the Semmes Weinstein aesthesiometer to assess touch pressure threshold in burn scars

Burn scars are frequently accompanied with sensory deficits often remaining present months or even years after injury. Clinimetric properties of assessment tools remain understudied within burn literature. Tactile sense of touch can be examined with the touch pressure threshold (TPT) method using the Semmes Weinstein monofilament test (SWMT). There is in recent research no consensus on the exact measurement procedure when using the SWMT. The aim of this paper was to determine the interrater and intrarater reliability of TPT within burn scars and healthy controls using the 'ascending descending' measurement procedure. We used the newly developed guidelines for reporting reliability and agreement studies (GRRAS) as a basis to report this reliability study. In total 36 individuals were tested; a healthy control group and a scar group. The interrater reliability was excellent in the scar group (ICC=0.908/SEM=0.21) and fair to good in the control group (ICC=0.731/SEM=0.12). In the scar group intrarater ICC value was excellent (ICC=0.822/SEM=0.33). Within the control group also an excellent intrarater reliability (ICC=0.807/SEM=0.27) was found. In conclusion this study shows that the SWMT with the 'ascending descending' measurement procedure is a feasible and reliable objective measure to evaluate TPT in (older) upper extremities burn scars as well as in healthy skin.

Geographical ancestry is a key determinant of epidermal morphology and dermal composition

BACKGROUND

Geographical ancestry plays a key role in determining the susceptibility of human skin to external insults and dermatological disease. Despite this, studies of skin from individuals of diverse geographical ancestry focus primarily on epidermal pigmentation. Few reports characterize the gross morphology and composition of the dermis and dermal-epidermal junction (DEJ).

OBJECTIVES

To characterize epidermal morphology and dermal composition in skin from individuals of diverse geographical ancestry.

METHODS

Immunohistochemical techniques were used to assess epidermal morphology and protein composition of the DEJ and dermal extracellular matrix in photoprotected skin from young African, Eurasian and Far East Asian individuals (n = 7 per group; age 18-30 years).

RESULTS

The epidermis of African skin was thicker, with deeper rete ridges and a more convoluted DEJ than Eurasian and Far East Asian skin. Compared with Eurasians, protein composition of the DEJ was collagen VII poor in African and Far East Asian skin (P < 0·001 and P < 0·01, respectively); the dermis of African skin was enriched in fibrillar collagens (P < 0·05), but was relatively elastin poor (P < 0·05). African dermis was abundant in fibrillin-rich microfibrils and fibulin-5 (P < 0·001 and P < 0·001, respectively) compared with Eurasian and Far East Asian skin.

CONCLUSIONS

We demonstrate that fundamental differences exist in skin structure and composition in individuals of diverse geographical ancestry. Disparate environmental pressures encountered by ancestral human populations living at different latitudes may have driven adaptations in skin structure and composition. Further research into the functional significance and clinical consequences of these differences is warranted.

Tissue-engineered dermo-epidermal skin analogs exhibit de novo formation of a near natural neurovascular link 10 weeks after transplantation

PURPOSE

Human autologous tissue-engineered skin grafts are a promising way to cover skin defects. Clearly, it is mandatory to study essential biological dynamics after transplantation, including reinnervation. Previously, we have already shown that human tissue-engineered skin analogs are reinnervated by host nerve fibers as early as 8 weeks after transplantation. In this study, we tested the hypothesis that there is a de novo formation of a "classical" neurovascular link in tissue-engineered and then transplanted skin substitutes.

METHODS

Keratinocytes, melanocytes, and fibroblasts were isolated from human skin biopsies. After expansion in culture, keratinocytes and melanocytes were seeded on dermal fibroblast-containing collagen type I hydrogels. These human tissue-engineered dermo-epidermal skin analogs were transplanted onto full-thickness skin wounds on the back of immuno-incompetent rats. Grafts were analyzed after 3 and 10 weeks. Histological sections were examined with regard to the ingrowth pattern of myelinated and unmyelinated nerve fibers into the skin analogs using markers such as PGP9.5, NF-200, and NF-160. Blood vessels were identified with CD31, lymphatic vessels with Lyve1. In particular, we focused on alignment patterns between nerve fibers and either blood and/or lymphatic vessels with regard to neurovascular link formation.

RESULTS

3 weeks after transplantation, blood vessels, but no nerve fibers or lymphatic vessels could be observed. 10 weeks after transplantation, we could detect an ingrowth of myelinated and unmyelinated nerve fibers into the skin analogs. Nerve fibers were found in close proximity to CD31-positive blood vessels, but not alongside Lyve1-positive lymphatic vessels.

CONCLUSION

These data suggest that host-derived innervation of tissue-engineered dermo-epidermal skin analogs is initiated by and guided alongside blood vessels present early post-transplantation. This observation is consistent with the concept of a cross talk between neurovascular structures, known as the neurovascular link.

Concise review: tissue-engineered skin and nerve regeneration in burn treatment

Burns not only destroy the barrier function of the skin but also alter the perceptions of pain, temperature, and touch. Different strategies have been developed over the years to cover deep and extensive burns with the ultimate goal of regenerating the barrier function of the epidermis while recovering an acceptable aesthetic aspect. However, patients often complain about a loss of skin sensation and even cutaneous chronic pain. Cutaneous nerve regeneration can occur from the nerve endings of the wound bed, but it is often compromised by scar formation or anarchic wound healing. Restoration of pain, temperature, and touch perceptions should now be a major challenge to solve in order to improve patients' quality of life. In addition, the cutaneous nerve network has been recently highlighted to play an important role in epidermal homeostasis and may be essential at least in the early phase of wound healing through the induction of neurogenic inflammation. Although the nerve regeneration process was studied largely in the context of nerve transections, very few studies have been aimed at developing strategies to improve it in the context of cutaneous wound healing. In this concise review, we provide a description of the characteristics of and current treatments for extensive burns, including tissue-engineered skin approaches to improve cutaneous nerve regeneration, and describe prospective uses for autologous skin-derived adult stem cells to enhance recovery of the skin's sense of touch.

Rebuild, restore, reinnervate: do human tissue engineered dermo-epidermal skin analogs attract host nerve fibers for innervation?

PURPOSE

Tissue engineered skin substitutes are a promising tool to cover large skin defects, but little is known about reinnervation of transplants. In this experimental study, we analyzed the ingrowth of host peripheral nerve fibers into human tissue engineered dermo-epidermal skin substitutes in a rat model. Using varying cell types in the epidermal compartment, we wanted to assess the influence of epidermal cell types on reinnervation of the substitute.

METHODS

We isolated keratinocytes, melanocytes, fibroblasts, and eccrine sweat gland cells from human skin biopsies. After expansion, epidermal cells were seeded on human dermal fibroblast-containing collagen type I hydrogels as follows: (1) keratinocytes only, (2) keratinocytes with melanocytes, (3) sweat gland cells. These substitutes were transplanted into full-thickness skin wounds on the back of immuno-incompetent rats and were analyzed after 3 and 8 weeks. Histological sections were examined with regard to myelinated and unmyelinated nerve fiber ingrowth using markers such as PGP9.5, NF-200, and NF-145.

RESULTS

After 3 weeks, the skin substitutes of all three epidermal cell variants showed no neuronal ingrowth from the host into the transplant. After 8 weeks, we could detect an innervation of all three types of skin substitutes. However, the nerve fibers were restricted to the dermal compartment and we could not find any unmyelinated fibers in the epidermis. Furthermore, there was no distinct difference between the constructs resulting from the different cell types used to generate an epidermis.

CONCLUSION

Our human tissue engineered dermo-epidermal skin substitutes demonstrate a host-derived innervation of the dermal compartment as early as 8 weeks after transplantation. Thus, our substitutes apparently have the capacity to attract nerve fibers from adjacent host tissues, which also grow into grafts and thereby potentially restore skin sensitivity.

Late outcomes after grafting of the severely burned face: a quality improvement initiative

Many approaches to surgical management of the severely burned face are described, but there are few objective outcome studies. The purpose of this study was to perform a detailed evaluation of the late outcomes in adult patients who have undergone grafting using a standardized surgical and rehabilitation approach for full-thickness (FT) facial burns to identify areas for improvement in the treatment strategy of authors. This was a prospective observational study in which patients who had undergone grafting for FT facial burns by the senior investigator at a regional burn centre between 1999 and 2010 were examined by a single evaluator. The surgical approach included tangential excision based on the facial aesthetic units, temporary cover with allograft then autografting with scalp skin preferentially, split grafts for the upper eyelid, and FT grafts for the lower eyelid. Rehabilitation included compression (uvex and or soft cloth), scar massage, and silicone gel sheeting. Of 35 patients with facial grafts, 14 subjects (age 43 ± 16 years with 22 ± 21% TBSA burns) returned for late follow-up at 40 ± 33 months (range, 5-91 months). A mean of four facial aesthetic units per patient were grafted (range, 1-9 units), with six full facial grafts performed. Scalp was used as donor in 10 of 14 cases. Scalp donor sites were well tolerated with minor alopecia visible in only one case although the donor site visibly extended slightly past the hairline in two cases. Color match with native skin was rated at 8.8 ± 0.8 of 10 when scalp skin was used compared with 7.5 ± 1.6 with other donor sites (P = .06). On the lip and chin, hypertrophic scars were significantly worse compared with the rest of the facial grafts (Vancouver scar scale 8 ± 2 vs 3 ± 1, P < .01). Sensory recovery was poor with overall moving two-point discrimination at 11 ± 3 mm (range, 4-15 mm), and monofilament light touch was 3.8 ± 0.6. Graft borders were significantly more elevated than graft seams. On the forehead, the most notable problem was a gap between the graft and hairlines of the frontal scalp and eyebrows (range, 0-40 mm). Grafted eyelids required one or more subsequent ectropion releases in the majority of cases. The most common problem for the nose was asymmetry of the nostril apertures. The most problematic late outcomes that the authors identified after facial grafting for FT facial burns included relatively poor sensory return, elevation of graft edges, eyelid ectropion, gaps between grafts and hairline, and marked hypertrophic scarring around the mouth and chin. The results indicate that possible areas for quality improvement include greater attention to the limits of scalp harvest, more attention to pressure application to graft borders and the lip and chin during rehabilitation, greater accuracy in excision and graft placement on the forehead to avoid gaps with the hairlines, and counseling of the patient regarding the high probability of diminished facial sensation.

Quantitative assessments of burn degree by high-frequency ultrasonic backscattering and statistical model

An accurate and quantitative modality to assess the burn degree is crucial for determining further treatments to be properly applied to burn injury patients. Ultrasounds with frequencies higher than 20 MHz have been applied to dermatological diagnosis due to its high resolution and noninvasive capability. Yet, it is still lacking a substantial means to sensitively correlate the burn degree and ultrasonic measurements quantitatively. Thus, a 50 MHz ultrasound system was developed and implemented to measure ultrasonic signals backscattered from the burned skin tissues. Various burn degrees were achieved by placing a 100 °C brass plate onto the dorsal skins of anesthetized rats for various durations ranged from 5 to 20 s. The burn degrees were correlated with ultrasonic parameters, including integrated backscatter (IB) and Nakagami parameter (m) calculated from ultrasonic signals acquired from the burned tissues of a 5 × 1.4 mm (width × depth) area. Results demonstrated that both IB and m decreased exponentially with the increase of burn degree. Specifically, an IB of -79.0 ± 2.4 (mean ± standard deviation) dB for normal skin tissues tended to decrease to -94.0 ± 1.3 dB for those burned for 20 s, while the corresponding Nakagami parameters tended to decrease from 0.76 ± 0.08 to 0.45 ± 0.04. The variation of both IB and m was partially associated with the change of properties of collagen fibers from the burned tissues verified by samples of tissue histological sections. Particularly, the m parameter may be more sensitive to differentiate burned skin due to the fact that it has a greater rate of change with respect to different burn durations. These ultrasonic parameters in conjunction with high-frequency B-mode and Nakagami images could have the potential to assess the burn degree quantitatively.

Effects of ultraviolet radiation on human cutaneous nerve fibres

Due to an increasing number of skin diseases as a result of exposure to ultraviolet (UV) radiation, it is necessary to evaluate the effectiveness of new skin care formulations with broad-spectrum sunscreens.

OBJECTIVES

This study aims to assess the status of nerve fibres in healthy human skin, to quantify effects of UV radiation on nerve endings, and to evaluate neuroprotective effects of new skin care formulations against UV exposure damage.

METHODS

Samples were obtained from 34 female patients enrolled for plastic surgery and were immediately treated (10 min) with three emulsions: Cream 1, Cream 2 (placebo) and a sunscreen with sun protection factor 15 (SPF15). Control samples and those treated with the cream emulsions were exposed to UVA and UVB for 60 min. Nerve fibres were identified by immunofluorescence using a monoclonal antibody (anti-human CD56/NCAM). Cell damage was assessed by image analysis.

RESULTS

Several cellular nervous structures were identified in the skin samples, including free nerve endings. UVA and UVB significantly decreased (40-60%) density of nerve endings in the control samples and those treated with placebo (Cream 2) or SPF15 (all P < 0.001). Cream 1 completely blocked effects of UV radiation on nerve endings (P > 0.05 vs. control).

CONCLUSIONS

Quantification of cell damage induced by UV radiation provides useful information for identification of new skin care compounds with neuroprotective properties.