Erratum: Publisher's Note: "A suspended layer additive manufacturing approach to the bioprinting of tri-layered skin equivalents" [APL Bioeng. 5, 046103 (2021)].

[This corrects the article DOI: 10.1063/5.0061361.].

Cobalt containing glass fibres and their synergistic effect on the HIF-1 pathway for wound healing applications.

Introduction and Methods: Chronic wounds are a major healthcare problem, but their healing may be improved by developing biomaterials which can stimulate angiogenesis, e.g. by activating the Hypoxia Inducible Factor (HIF) pathway. Here, novel glass fibres were produced by laser spinning. The hypothesis was that silicate glass fibres that deliver cobalt ions will activate the HIF pathway and promote the expression of angiogenic genes. The glass composition was designed to biodegrade and release ions, but not form a hydroxyapatite layer in body fluid. Results and Discussion: Dissolution studies demonstrated that hydroxyapatite did not form. When keratinocyte cells were exposed to conditioned media from the cobalt-containing glass fibres, significantly higher amounts of HIF-1α and Vascular Endothelial Growth Factor (VEGF) were measured compared to when the cells were exposed to media with equivalent amounts of cobalt chloride. This was attributed to a synergistic effect of the combination of cobalt and other therapeutic ions released from the glass. The effect was also much greater than the sum of HIF-1α and VEGF expression when the cells were cultured with cobalt ions and with dissolution products from the Co-free glass, and was proven to not be due to a rise in pH. The ability of the glass fibres to activate the HIF-1 pathway and promote VEGF expression shows the potential for their use in chronic wound dressings.

A suspended layer additive manufacturing approach to the bioprinting of tri-layered skin equivalents.

Skin exhibits a complex structure consisting of three predominant layers (epidermis, dermis, and hypodermis). Extensive trauma may result in the loss of these structures and poor repair, in the longer term, forming scarred tissue and associated reduction in function. Although a number of skin replacements exist, there have been no solutions that recapitulate the chemical, mechanical, and biological roles that exist within native skin. This study reports the use of suspended layer additive manufacturing to produce a continuous tri-layered implant, which closely resembles human skin. Through careful control of the bioink composition, gradients (chemical and cellular) were formed throughout the printed construct. Culture of the model demonstrated that over 21 days, the cellular components played a key role in remodeling the supporting matrix into architectures comparable with those of healthy skin. Indeed, it has been demonstrated that even at seven days post-implantation, the integration of the implant had occurred, with mobilization of the adipose tissue from the surrounding tissue into the construct itself. As such, it is believed that these implants can facilitate healing, commencing from the fascia, up toward the skin surface-a mechanism recently shown to be key within deep wounds.

Trabecular bone organoids: a micron-scale 'humanised' prototype designed to study the effects of microgravity and degeneration.

Bone is a highly responsive organ, which continuously adapts to the environment it is subjected to in order to withstand metabolic demands. These events are difficult to study in this particular tissue in vivo, due to its rigid, mineralised structure and inaccessibility of the cellular component located within. This manuscript presents the development of a micron-scale bone organoid prototype, a concept that can allow the study of bone processes at the cell-tissue interface. The model is constructed with a combination of primary female osteoblastic and osteoclastic cells, seeded onto femoral head micro-trabeculae, where they recapitulate relevant phenotypes and functions. Subsequently, constructs are inserted into a simulated microgravity bioreactor (NASA-Synthecon) to model a pathological state of reduced mechanical stimulation. In these constructs, we detected osteoclastic bone resorption sites, which were different in morphology in the simulated microgravity group compared to static controls. Once encapsulated in human fibrin and exposed to analogue microgravity for 5 days, masses of bone can be observed being lost from the initial structure, allowing to simulate the bone loss process further. Constructs can function as multicellular, organotypic units. Large osteocytic projections and tubular structures develop from the initial construct into the matrix at the millimetre scale. Micron-level fragments from the initial bone structure are detected travelling along these tubules and carried to sites distant from the native structure, where new matrix formation is initiated. We believe this model allows the study of fine-level physiological processes, which can shed light into pathological bone loss and imbalances in bone remodelling.

In vitro modelling of disease-induced changes in the diabetic wound fibroblast.

OBJECTIVE: Fibroblasts have been shown to play an increasingly important role within diabetic wounds. While several in vitro models of diabetic wound fibroblasts have been reported, none replicate the natural progression of the disease over time, recapitulating the acquisition of the diseased phenotype. Therefore, this study aimed to establish an in vitro model of the diabetic wound fibroblast through sustained exposure of healthy dermal fibroblasts to hyperglycaemia. METHOD: Primary human fibroblasts were isolated from discarded healthy skin tissue and were either exposed to normoglycaemic (control 5.5mM glucose) media or hyperglycaemic (25mM glucose) media for four weeks. Quantitative polymerase chain reaction was performed to measure the expression of inflammatory cytokines and chemokines. RESULTS: In the hyperglycaemia model, stromal cell-derived factor (SDF)-1 expression remained consistently downregulated across all four weeks (p<0.01), while monocyte chemoattractant protein (MCP)-1 (p<0.001), interleukin (IL)-8 (p=0.847) and chemokine (C-X-C motif) ligand 1 (CXCL1) (p=0.872) were initially downregulated at one week followed by subsequent upregulation between 2-4 weeks. CONCLUSION: This hyperglycaemia model may serve as a useful tool to characterise pathological changes in the diabetic wound fibroblast and help identify candidate therapeutic targets, such as SDF-1, that may reverse the pathology.

Bioactive glasses and electrospun composites that release cobalt to stimulate the HIF pathway for wound healing applications.

BACKGROUND: Bioactive glasses are traditionally associated with bonding to bone through a hydroxycarbonate apatite (HCA) surface layer but the release of active ions is more important for bone regeneration. They are now being used to deliver ions for soft tissue applications, particularly wound healing. Cobalt is known to simulate hypoxia and provoke angiogenesis. The aim here was to develop new bioactive glass compositions designed to be scaffold materials to locally deliver pro-angiogenic cobalt ions, at a controlled rate, without forming an HCA layer, for wound healing applications. METHODS: New melt-derived bioactive glass compositions were designed that had the same network connectivity (mean number of bridging covalent bonds between silica tetrahedra), and therefore similar biodegradation rate, as the original 45S5 Bioglass. The amount of magnesium and cobalt in the glass was varied, with the aim of reducing or removing calcium and phosphate from the compositions. Electrospun poly(ε-caprolactone)/bioactive glass composites were also produced. Glasses were tested for ion release in dissolution studies and their influence on Hypoxia-Inducible Factor 1-alpha (HIF-1α) and expression of Vascular Endothelial Growth Factor (VEGF) from fibroblast cells was investigated. RESULTS: Dissolution tests showed the silica rich layer differed depending on the amount of MgO in the glass, which influenced the delivery of cobalt. The electrospun composites delivered a more sustained ion release relative to glass particles alone. Exposing fibroblasts to conditioned media from these composites did not cause a detrimental effect on metabolic activity but glasses containing cobalt did stabilise HIF-1α and provoked a significantly higher expression of VEGF (not seen in Co-free controls). CONCLUSIONS: The composite fibres containing new bioactive glass compositions delivered cobalt ions at a sustained rate, which could be mediated by the magnesium content of the glass. The dissolution products stabilised HIF-1α and provoked a significantly higher expression of VEGF, suggesting the composites activated the HIF pathway to stimulate angiogenesis.

Ex vivo culture of keratinocytes on papillary and reticular dermal layers remodels skin explants differently: towards improved wound care.

In this study, we characterised the effect that seeding keratinocytes on the papillary and reticular dermis had on the extracellular matrix and tissue integrity ex vivo. Human skin explants from consented patients (n = 6) undergoing routine surgery were cultured at a liquid-air interface, dermal-side up, and autologous keratinocytes seeded on the exposed papillary or reticular layer. After 7-21 days, histological and immunohistochemical evaluation of the morphology and extracellular matrix was performed. While the dermis remained robust in all explants cultures, keratinocytes seeded on the papillary layer showed less tissue infiltration and remodelling and formed clusters across the tissue. In contrast, keratinocytes seeded on the reticular layer infiltrated the tissue homogenously with an intact single-cell-layer surface coverage and structural changes characterised by increased deposition of ground substance, glycosaminoglycans, and collagen VII in 14 days. In addition, while the papillary section showed more new laminin deposition by 14 days than the reticular section, the latter expressed more connexin 43. These differences in re-epithelialisation and extracellular matrix characteristics suggest that wound depth and graft thickness may play a key role in wound healing and indicate that ECM characteristics should be factored in when designing biomaterials for wound applications and in the selection of recipient sites when using cells for grafting.

Development of a High-Throughput ex-Vivo Burn Wound Model Using Porcine Skin, and Its Application to Evaluate New Approaches to Control Wound Infection.

Biofilm formation in wounds is considered a major barrier to successful treatment, and has been associated with the transition of wounds to a chronic non-healing state. Here, we present a novel laboratory model of wound biofilm formation using ex-vivo porcine skin and a custom burn wound array device. The model supports high-throughput studies of biofilm formation and is compatible with a range of established methods for monitoring bacterial growth, biofilm formation, and gene expression. We demonstrate the use of this model by evaluating the potential for bacteriophage to control biofilm formation by Staphylococcus aureus, and for population density dependant expression of S. aureus virulence factors (regulated by the Accessory Gene Regulator, agr) to signal clinically relevant wound infection. Enumeration of colony forming units and metabolic activity using the XTT assay, confirmed growth of bacteria in wounds and showed a significant reduction in viable cells after phage treatment. Confocal laser scanning microscopy confirmed the growth of biofilms in wounds, and showed phage treatment could significantly reduce the formation of these communities. Evaluation of agr activity by qRT-PCR showed an increase in activity during growth in wound models for most strains. Activation of a prototype infection-responsive dressing designed to provide a visual signal of wound infection, was related to increased agr activity. In all assays, excellent reproducibility was observed between replicates using this model.

Bacteriophage Can Prevent Encrustation and Blockage of Urinary Catheters by Proteus mirabilis.

Proteus mirabilis forms dense crystalline biofilms on catheter surfaces that occlude urine flow, leading to serious clinical complications in long-term catheterized patients, but there are presently no truly effective approaches to control catheter blockage by this organism. This study evaluated the potential for bacteriophage therapy to control P. mirabilis infection and prevent catheter blockage. Representative in vitro models of the catheterized urinary tract, simulating a complete closed drainage system as used in clinical practice, were employed to evaluate the performance of phage therapy in preventing blockage. Models mimicking either an established infection or early colonization of the catheterized urinary tract were treated with a single dose of a 3-phage cocktail, and the impact on time taken for catheters to block, as well as levels of crystalline biofilm formation, was measured. In models of established infection, phage treatment significantly increased time taken for catheters to block (∼ 3-fold) compared to untreated controls. However, in models simulating early-stage infection, phage treatment eradicated P. mirabilis and prevented blockage entirely. Analysis of catheters from models of established infection 10 h after phage application demonstrated that phage significantly reduced crystalline biofilm formation but did not significantly reduce the level of planktonic cells in the residual bladder urine. Taken together, these results show that bacteriophage constitute a promising strategy for the prevention of catheter blockage but that methods to deliver phage in sufficient numbers and within a key therapeutic window (early infection) will also be important to the successful application of phage to this problem.

Reduction of tendon adhesions following administration of Adaprev, a hypertonic solution of mannose-6-phosphate: mechanism of action studies.

Repaired tendons may be complicated by progressive fibrosis, causing adhesion formation or tendon softening leading to tendon rupture and subsequent reduced range of motion. There are few therapies available which improve the gliding of damaged tendons in the hand. We investigate the role of Mannose 6-phosphate (M6P) in a 600 mM hypertonic solution (Adaprev) on tendon adhesion formation in vivo using a mouse model of severed tendon in conjunction with analysis of collagen synthesis, cellular proliferation and receptors involved in TGF beta signalling. Cytotoxicity was assessed by measuring tissue residency, mechanical strength and cell viability of tendons after treatment with Adaprev. To elicit potential modes of action, in vitro and ex vivo studies were performed investigating phosphorylation of p38, cell migration and proliferation. Adaprev treatment significantly (p<0.05) reduced the development of adhesions and improved collagen organisation without reducing overall collagen synthesis following tendon injury in vivo. The bioavailability of Adaprev saw a 40% reduction at the site of administration over 45 minutes and tendon fibroblasts tolerated up to 120 minutes of exposure without significant loss of cell viability or tensile strength. These favourable effects were independent of CI-MPR and TGF-ß signalling and possibly highlight a novel mechanism of action related to cellular stress demonstrated by phosphorylation of p38. The effect of treatment reduced tendon fibroblast migration and transiently halted tendon fibroblast proliferation in vitro and ex vivo. Our studies demonstrate that the primary mode of action for Adaprev is potentially via a physical, non-chemical, hyperosmotic effect.

The effect of isolation and culture methods on epithelial stem cell populations and their progeny-toward an improved cell expansion protocol for clinical application.

BACKGROUND AIMS: The use of cultured epithelial keratinocytes in the treatment of burns and skin graft donor sites is well established in clinical practice. The most widely used culture method for clinical use was originally developed by Rheinwald and Green 40 years ago. This system uses irradiated mouse dermal fibroblasts as a feeder cell layer to promote keratinocyte growth, a process that is costly and labor-intensive for health care providers. The medium formulation contains several components of animal origin, which pose further safety risks for patients. Improvements and simplification in the culturing process would lead to clear advantages: improved safety through reduction of xenobiotic components and reduction in cost for health care providers by dispensing with feeder cells. METHODS: We compared the Rheinwald and Green method to culture in three commercially available, feeder-free media systems with defined/absent components of animal origin. RESULTS: During the isolation process, short incubation times in high-strength trypsin resulted in increased numbers of liberated keratinocyte stem cells compared with longer incubation times. All three commercially available media tested in this study could support the expansion of keratinocytes, with phenotypes comparable to cells expanded using the established Rheinwald and Green method. Growth rates varied, with two of the media displaying comparable growth rates, whereas the third was significantly slower. DISCUSSION: Our study demonstrates the suitability of such feeder-free media systems in clinical use. It further outlines a range of techniques to evaluate keratinocyte phenotype when assessing the suitability of cells for clinical application.

Effects of interleukin-10 on cutaneous wounds and scars in humans of African continental ancestral origin.

Scars in humans of African continental ancestry heal with an exaggerated inflammatory response and a generally wider scar. Interleukin-10 is an anti-inflammatory and antifibrotic cytokine. A randomized controlled trial in Caucasians found that exogenous interleukin-10 resulted in improved macroscopic scar appearance and reduced scar redness. We investigated the effects of interleukin-10 on cutaneous scarring in volunteers of African ancestral origin in an exploratory, single-center, within-subject, double-blind randomized controlled trial. Fifty-six subjects received two of four potential prerandomized concentrations of interleukin-10 (5, 25, 100, and 250 ng/100 µL) in two full-thickness incisions on the upper inner arms. Anatomically matching incisions on the contralateral arm were treated with placebo. Scars were excised at 1 month for histological analysis and were redosed with the same regimen. Resultant excision scars were followed up for 12 months for scar width measurement and scoring. Scoring was performed by trial doctors, subjects, and a panel. Incisions treated with 100 ng/100 µL interleukin-10 had significantly reduced microscopic scar widths. Incisions treated with 5 and 25 ng/100 µL interleukin-10 were also narrower, but not significantly. There were no differences observed in pro-inflammatory or pro-fibrotic markers between interleukin-10 and placebo treatment. There was no long-term evidence that 100 ng/100 µL interleukin-10 had a therapeutic effect on macroscopic scar width or appearance, as excisions treated with this concentration were significantly wider than placebo between 8 and 12 months of maturation. Doctors showed a trend toward favoring the macroscopic appearance of placebo-treated excisions compared with those treated with 250 ng/100 µL interleukin-10. Panelists scored placebo-treated excisions as significantly better-appearing than those treated with 250 ng/100 µL interleukin-10. Doctors' scores showed a trend toward favoring treatment with 5 ng/100 µL interleukin-10 at 10 and 11 months post-excision. Subjects showed a trend toward favoring treatment with 5 ng/100 µL interleukin-10 between 5 and 9 months postexcision. Analysis of images of markedly improved scars revealed a potential subset of responders among those treated with 5 ng/100 µL interleukin-10. No concentration of interleukin-10 produced a statistically significant improvement in scarring compared with placebo.

Interleukin-10 reduces scar formation in both animal and human cutaneous wounds: results of two preclinical and phase II randomized control studies.

Cutaneous scarring affects up to 100 million people per annum. There is no effective scar reducing/preventing therapeutic developed to date. Interleukin (IL)-10 is an anti-inflammatory and antifibrotic cytokine. In the embryo it is important for scarless wound repair. We investigated the effect on wound healing and scarring of a double deletion of the IL-10 and IL-4 genes in a knockout (KO) mouse model, and also the effect of exogenous addition of recombinant human (rh) IL-10 into rat and human cutaneous incisions. Mouse study: Two incisions were made on the dorsal skin of 20 double IL-4/IL-10 KO mice and 20 wild-type (WT) controls. Rat study: Three concentrations of rhIL-10 were investigated. Four incisions were made on the dorsal skin of 30 rats. Each rat received two concentrations. Each incision receiving a concentration of rhIL-10 was matched with a control incision, which received either placebo or standard care. Human study: Eight concentrations of rhIL-10 were investigated. Four incisions were made on each arm of 175 healthy volunteers. Four incisions received four different concentrations, which were matched with four control incisions that received either standard care or placebo. KO mice healed with poor scar histology and increased inflammation. rhIL-10-treated rat incisions healed with decreased inflammation, better scar histology, and better macroscopic scar appearance. rhIL-10-treated human incisions at low concentrations healed with better macroscopic scar appearance and less red scars. IL-10 is an important cytokine in wound healing and its suppression of inflammation and scarring is demonstrated in mice and rats with a translational effect in humans.

Denervation affects regenerative responses in MRL/MpJ and repair in C57BL/6 ear wounds.

The MRL/MpJ mouse displays the rare ability amongst mammals to heal injured ear tissue without scarring. Numerous studies have shown that the formation of a blastema-like structure leads to subsequent tissue regeneration in this model, indicating many parallels with amphibian limb regeneration and mammalian embryogenesis. We have recently shown that the MRL/MpJ mouse also possesses an enhanced capacity for peripheral nerve regeneration within the ear wound. Indeed, nerves are vital for the initial phase of blastema formation in the amphibian limb. In this study we investigated the capacity for wound regeneration in a denervated ear. The left ears of MRL/MpJ mice and C57BL/6 (a control strain known to have a poorer regenerative capacity) were surgically denervated at the base via an incision and nerve transection, immediately followed by a 2-mm ear punch wound. Immunohistochemical analysis showed a lack of neurofilament expression in the denervated ear wound. Histology revealed that denervation prevented blastema formation and chrondrogenesis, and also severely hindered normal healing, with disrupted re-epithelialisation, increasing wound size and progressive necrosis towards the ear tip. Denervation of the ear obliterated the regenerative capacity of the MRL/MpJ mouse, and also had a severe negative effect on the ear wound repair mechanisms of the C57BL/6 strain. These data suggest that innervation may be important not only for regeneration but also for normal wound repair processes.

Histomorphometric changes in repaired mouse sciatic nerves are unaffected by the application of a scar-reducing agent.

Microsurgical repair of transected peripheral nerves is compromised by the formation of scar tissue and the development of a neuroma, thereby limiting the success of regeneration. The aim of this study was to quantify histomorphometrically the structural changes in neural tissue that result from repair, and determine the effect of mannose-6-phosphate (M6P), a scar-reducing agent previously shown to enhance regeneration. In anaesthetised C57-black-6 mice, the left sciatic nerve was sectioned and repaired using four epineurial sutures. Either 100 µL of 600 mm M6P (five animals) or 100 µL of phosphate-buffered saline (placebo controls, five animals) was injected into and around the nerve repair site. A further group acted as sham-operated controls. After recovery for 6 weeks, the nerve was harvested for analysis using light and electron microscopy. Analysis revealed that when compared with sham controls, myelinated axons had smaller diameters both proximal and distal to the repair. Myelinated axon counts, axonal density and size all decreased across the repair site. There were normal numbers and densities of non-myelinated axons both proximal and distal to the repair. However, there were more Remak bundles distal to the repair site, and fewer non-myelinated axons per Remak bundle. Application of M6P did not affect any of these parameters.

Avotermin for scar improvement following scar revision surgery: a randomized, double-blind, within-patient, placebo-controlled, phase II clinical trial.

BACKGROUND: Skin scarring is associated with psychosocial distress and has a negative effect on quality of life. The transforming growth factor (TGF)-ß family of cytokines plays a key role in scarring. TGF-ß3 improves scar appearance in a range of mammalian species. This study was performed to assess the efficacy of intradermal avotermin (TGF-ß3) for the improvement of scar appearance following scar revision surgery. METHODS: Sixty patients (35 men and 25 women; age, 19 to 78 years; 53 Caucasians; scar length, 5 to 21 cm) received intradermal avotermin (200 ng/100 µl/linear cm wound margin) and placebo to outer wound segments immediately after, and again 24 hours after, complete (group 1) or staged (group 2) scar revision surgery. A within-patient design was chosen to control for interindividual factors that affect scarring. The primary efficacy variable was a total scar score derived from a visual analogue scale, scored by a lay panel from standardized photographs from months 1 through 7 following treatment. RESULTS: : Primary endpoint data from the combined surgical groups showed that avotermin significantly improved scar appearance compared with placebo (total scar score difference, 21.93 mm; p = 0.04). Profilometry showed a greater reduction in scar surface area from baseline with avotermin treatment compared with placebo, significant in group 2 at months 7 and 12 (difference, 41.99 mm and 25.85 mm, respectively; p = 0.03 for both comparisons). Histologic analysis from group 2 showed that, compared with placebo treatment, collagen organization in avotermin-treated scars more closely resembled normal skin in 14 of 19 cases. Avotermin was well tolerated. CONCLUSION: Avotermin administration following scar revision surgery is well tolerated and significantly improves scar appearance compared with placebo. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, I.(Figure is included in full-text article.).

The effect of Mannose-6-Phosphate on recovery after sciatic nerve repair.

We have determined the effect of applying Mannose-6-Phosphate (M6P), a scar reducing agent, to a site of sciatic nerve repair. In anaesthetised C57-Black-6 mice, the left sciatic nerve was sectioned and repaired using 4 epineurial sutures. Either 100 µl of 600 mM Mannose-6-Phosphate (29 animals), or 100 µl of phosphate buffered saline as a placebo control (29 animals), was injected into and around the nerve repair site. A further group acted as sham-operated controls. After 6 or 12 weeks of recovery the extent of regeneration was assessed electrophysiologically and the percentage area of collagen staining at the repair site was analysed using picrosirius red and image analysis. Gait analysis was undertaken pre-operatively and at 1, 3, 6, 9 and 12 weeks postoperatively, to assess functional recovery. At 6 weeks the compound action potentials recorded from the regenerated nerves in the M6P group were significantly larger than in the placebo controls (P=0.015), and the conduction velocities were significantly faster (P=0.005), but there were no significant differences between these groups at 12 weeks. Gait analysis suggested better early functional recovery in the M6P group. In both repair groups there was a significant reduction in collagen staining between 6 and 12 weeks, suggestive of scar remodelling. We conclude that the normal scar remodelling process aids long term recovery in repaired nerves. Administration of 600 mM M6P to the nerve repair site enhances nerve regeneration and functional recovery in the early stages, and may lead to improved outcomes.

Peripheral nerve regeneration in the MRL/MpJ ear wound model.

The MRL/MpJ mouse displays an accelerated ability to heal ear punch wounds without scar formation (whereas wounds on the dorsal surface of the trunk heal with scar formation), offering a rare opportunity for studying tissue regeneration in adult mammals. A blastema-like structure develops and subsequently the structure of the wounded ear is restored, including cartilage, skin, hair follicles and adipose tissue. We sought to assess if the MRL/MpJ strain also possessed an enhanced capacity for peripheral nerve regeneration. Female MRL/MpJ and C57BL/6 mice were wounded with a 2-mm excisional biopsy punch to the centre of each ear and two 4-mm excisional biopsy punches to the dorsal skin. Immunohistochemical dual staining of pan-neurofilament and CD31 markers was used to investigate reinnervation and vascularisation of both the dorsal surface of the trunk and ear wounds. The MRL/MpJ mouse ear exhibited a significantly (P > 0.01) higher density of regenerated nerves than C57BL/6 between 10 and 21 days post-wounding when the blastema-like structure was forming. Unlike dorsal skin wounds, nerve regeneration in the ear wound preceded vascularisation, recapitulating early mammalian development. Immunohistochemical data suggest that factors within the blastemal mesenchyme, such as aggrecan, may direct nerve regrowth in the regenerating ear tissue.

Therapeutic improvement of scarring: mechanisms of scarless and scar-forming healing and approaches to the discovery of new treatments.

Scarring in the skin after trauma, surgery, burn or sports injury is a major medical problem, often resulting in loss of function, restriction of tissue movement and adverse psychological effects. Whilst various studies have utilised a range of model systems that have increased our understanding of the pathways and processes underlying scar formation, they have typically not translated to the development of effective therapeutic approaches for scar management. Existing treatments are unreliable and unpredictable and there are no prescription drugs for the prevention or treatment of dermal scarring. As a consequence, scar improvement still remains an area of clear medical need. Here we describe the basic science of scar-free and scar-forming healing, the utility of pre-clinical model systems, their translation to humans, and our pioneering approach to the discovery and development of therapeutic approaches for the prophylactic improvement of scarring in man.

Bioengineering skin using mechanisms of regeneration and repair.

The development and use of artificial skin in treating acute and chronic wounds has, over the last 30 years, advanced from a scientific concept to a series of commercially viable products. Many important clinical milestones have been reached and the number of artificial skin substitutes licensed for clinical use is growing, but they have yet to replace the current "gold standard" of an autologous skin graft. Currently available skin substitutes often suffer from a range of problems that include poor integration (which in many cases is a direct result of inadequate vascularisation), scarring at the graft margins and a complete lack of differentiated structures. The ultimate goal for skin tissue engineers is to regenerate skin such that the complete structural and functional properties of the wounded area are restored to the levels before injury. New synthetic biomaterials are constantly being developed that may enable control over wound repair and regeneration mechanisms by manipulating cell adhesion, growth and differentiation and biomechanics for optimal tissue development. In this review, the clinical developments in skin bioengineering are discussed, from conception through to the development of clinically viable products. Central to the discussion is the development of the next generation of skin replacement therapy, the success of which is likely to be underpinned with our knowledge of wound repair and regeneration.