Wound-healing gene family expression differences between fetal and foreskin cells used for bioengineered skin substitutes

Fetal Skin Wound Healing: Key Extracellular Matrix Components and Regulators in Scarless Healing

Fetal skin at early gestational stage is able to regenerate and heal rapidly after wounding. The exact mechanisms and molecular pathways involved in this process are however still largely unknown. The numerous differences in the skin of the early fetus versus skin in later developmental stages might provide clues for the mechanisms of scarless healing. This review summarizes the differences between mammalian fetal skin and the skin at later developmental phases in healthy and wounded conditions, focusing on extracellular matrix components, which are crucial factors in the microenvironment that direct cells and tissue functions and hence the wound healing process.

Establishing a Xenograft Model with CD-1 Nude Mice to Study Human Skin Wound Repair

BACKGROUND

A significant gap exists in the translatability of small-animal models to human subjects. One important factor is poor laboratory models involving human tissue. Thus, the authors have created a viable postnatal human skin xenograft model using athymic mice.

METHODS

Discarded human foreskins were collected following circumcision. All subcutaneous tissue was removed from these samples sterilely. Host CD-1 nude mice were then anesthetized, and dorsal skin was sterilized. A 1.2-cm-diameter, full-thickness section of dorsal skin was excised. The foreskin sample was then placed into the full-thickness defect in the host mice and sutured into place. Xenografts underwent dermal wounding using a 4-mm punch biopsy after engraftment. Xenografts were monitored for 14 days after wounding and then harvested.

RESULTS

At 14 days postoperatively, all mice survived the procedure. Grossly, the xenograft wounds showed formation of a human scar at postoperative day 14. Hematoxylin and eosin and Masson trichome staining confirmed scar formation in the wounded human skin. Using a novel artificial intelligence algorithm using picrosirius red staining, scar formation was confirmed in human wounded skin compared with the unwounded skin. Histologically, CD31 + immunostaining confirmed vascularization of the xenograft. The xenograft exclusively showed human collagen type I, CD26 + , and human nuclear antigen in the human scar without any staining of these human markers in the murine skin.

CONCLUSION

The proposed model demonstrates wound healing to be a local response from tissue resident human fibroblasts and allows for reproducible evaluation of human skin wound repair in a preclinical model.

CLINICAL RELEVANCE STATEMENT

Radiation-induced fibrosis is a widely prevalent clinical phenomenon without a well-defined treatment at this time. This study will help establish a small-animal model to better understand and develop novel therapeutics to treat irradiated human skin.

Cutaneous Cell Therapy Manufacturing Timeframe Rationalization: Allogeneic Off-the-Freezer Fibroblasts for Dermo-Epidermal Combined Preparations (DE-FE002-SK2) in Burn Care

Autologous cell therapy manufacturing timeframes constitute bottlenecks in clinical management pathways of severe burn patients. While effective temporary wound coverings exist for high-TBSA burns, any means to shorten the time-to-treatment with cytotherapeutic skin grafts could provide substantial therapeutic benefits. This study aimed to establish proofs-of-concept for a novel combinational cytotherapeutic construct (autologous/allogeneic DE-FE002-SK2 full dermo-epidermal graft) designed for significant cutaneous cell therapy manufacturing timeframe rationalization. Process development was based on several decades (four for autologous protocols, three for allogeneic protocols) of in-house clinical experience in cutaneous cytotherapies. Clinical grade dermal progenitor fibroblasts (standardized FE002-SK2 cell source) were used as off-the-freezer substrates in novel autologous/allogeneic dermo-epidermal bilayer sheets. Under vitamin C stimulation, FE002-SK2 primary progenitor fibroblasts rapidly produced robust allogeneic dermal templates, allowing patient keratinocyte attachment in co-culture. Notably, FE002-SK2 primary progenitor fibroblasts significantly outperformed patient fibroblasts for collagen deposition. An ex vivo de-epidermalized dermis model was used to demonstrate the efficient DE-FE002-SK2 construct bio-adhesion properties. Importantly, the presented DE-FE002-SK2 manufacturing process decreased clinical lot production timeframes from 6-8 weeks (standard autologous combined cytotherapies) to 2-3 weeks. Overall, these findings bear the potential to significantly optimize burn patient clinical pathways (for rapid wound closure and enhanced tissue healing quality) by combining extensively clinically proven cutaneous cell-based technologies.

Retrospectives on Three Decades of Safe Clinical Experience with Allogeneic Dermal Progenitor Fibroblasts: High Versatility in Topical Cytotherapeutic Care

Allogeneic dermal progenitor fibroblasts constitute cytotherapeutic contenders for modern cutaneous regenerative medicine. Based on advancements in the relevant scientific, technical, and regulatory fields, translational developments have slowly yet steadily led to the clinical application of such biologicals and derivatives. To set the appropriate general context, the first aim of this study was to provide a current global overview of approved cell and gene therapy products, with an emphasis on cytotherapies for cutaneous application. Notable advances were shown for North America, Europe, Iran, Japan, and Korea. Then, the second and main aim of this study was to perform a retrospective analysis on the various applications of dermal progenitor fibroblasts and derivatives, as clinically used under the Swiss progenitor cell transplantation program for the past three decades. Therein, the focus was set on the extent and versatility of use of the therapies under consideration, their safety parameters, as well as formulation options for topical application. Quantitative and illustrative data were summarized and reported for over 300 patients treated with various cell-based or cell-derived preparations (e.g., progenitor biological bandages or semi-solid emulsions) in Lausanne since 1992. Overall, this study shows the strong current interest in biological-based approaches to cutaneous regenerative medicine from a global developmental perspective, as well as the consolidated local clinical experience gathered with a specific and safe allogeneic cytotherapeutic approach. Taken together, these current and historical elements may serve as tangible working bases for the further optimization of local and modern translational pathways for the provision of topical cytotherapeutic care.

Evolution of Diploid Progenitor Lung Cell Applications: From Optimized Biotechnological Substrates to Potential Active Pharmaceutical Ingredients in Respiratory Tract Regenerative Medicine

The objective of this review is to describe the evolution of lung tissue-derived diploid progenitor cell applications, ranging from historical biotechnological substrate functions for vaccine production and testing to current investigations around potential therapeutic use in respiratory tract regenerative medicine. Such cell types (e.g., MRC-5 or WI-38 sources) were extensively studied since the 1960s and have been continuously used over five decades as safe and sustainable industrial vaccine substrates. Recent research and development efforts around diploid progenitor lung cells (e.g., FE002-Lu or Walvax-2 sources) consist in qualification for potential use as optimal and renewed vaccine production substrates and, alternatively, for potential therapeutic applications in respiratory tract regenerative medicine. Potentially effective, safe, and sustainable cell therapy approaches for the management of inflammatory lung diseases or affections and related symptoms (e.g., COVID-19 patients and burn patient severe inhalation syndrome) using local homologous allogeneic cell-based or cell-derived product administrations are considered. Overall, lung tissue-derived progenitor cells isolated and produced under good manufacturing practices (GMP) may be used with high versatility. They can either act as key industrial platforms optimally conforming to specific pharmacopoeial requirements or as active pharmaceutical ingredients (API) for potentially effective promotion of lung tissue repair or regeneration.

Antimicrobial Peptide Dendrimers and Quorum-Sensing Inhibitors in Formulating Next-Generation Anti-Infection Cell Therapy Dressings for Burns

Multidrug resistance infections are the main cause of failure in the pro-regenerative cell-mediated therapy of burn wounds. The collagen-based matrices for delivery of cells could be potential substrates to support bacterial growth and subsequent lysis of the collagen leading to a cell therapy loss. In this article, we report the development of a new generation of cell therapy formulations with the capacity to resist infections through the bactericidal effect of antimicrobial peptide dendrimers and the anti-virulence effect of anti-quorum sensing MvfR (PqsR) system compounds, which are incorporated into their formulation. Anti-quorum sensing compounds limit the pathogenicity and antibiotic tolerance of pathogenic bacteria involved in the burn wound infections, by inhibiting their virulence pathways. For the first time, we report a biological cell therapy dressing incorporating live progenitor cells, antimicrobial peptide dendrimers, and anti-MvfR compounds, which exhibit bactericidal and anti-virulence properties without compromising the viability of the progenitor cells.

Progenitor Biological Bandages: An Authentic Swiss Tool for Safe Therapeutic Management of Burns, Ulcers, and Donor Site Grafts

Clinical experience gathered over two decades around therapeutic use of primary human dermal progenitor fibroblasts in burn patient populations has been at the forefront of regenerative medicine in Switzerland. Relative technical simplicity, ease of extensive serial multitiered banking, and high stability are major advantages of such cell types, assorted to ease of safety and traceability demonstration. Stringent optimization of cell source selection and standardization of biobanking protocols enables the safe and efficient harnessing of the considerable allogenic therapeutic potential yielded by primary progenitor cells. Swiss legal and regulatory requirements have led to the procurement of fetal tissues within a devised Fetal Progenitor Cell Transplantation Program in the Lausanne University Hospital. Proprietary nonenzymatic isolation of primary musculoskeletal cell types and subsequent establishment of progeny tiered cell banks under cGMP standards have enabled safe and effective management of acute and chronic cutaneous affections in various patient populations. Direct off-the-freezer seeding of viable dermal progenitor fibroblasts on a CE marked equine collagen scaffold is the current standard for delivery of the therapeutic biological materials to patients suffering from extensive and deep burns. Diversification in the clinical indications and delivery methods for these progenitor cells has produced excellent results for treatment of persistent ulcers, autograft donor site wounds, or chronic cutaneous affections such as eczema. Herein we describe the standard operating procedures for preparation and therapeutic deployment of the progenitor biological bandages within our translational musculoskeletal regenerative medicine program, as they are routinely used as adjuvants in our Burn Center to treat critically ailing patients.

Retrospective Evaluation of Progenitor Biological Bandage Use: A Complementary and Safe Therapeutic Management Option for Prevention of Hypertrophic Scarring in Pediatric Burn Care

Progenitor Biological Bandages (PBB) have been continuously applied clinically in the Lausanne Burn Center for over two decades. Vast translational experience and hindsight have been gathered, specifically for cutaneous healing promotion of donor-site grafts and second-degree pediatric burns. PBBs constitute combined Advanced Therapy Medicinal Products, containing viable cultured allogeneic fetal dermal progenitor fibroblasts. Such constructs may partly favor repair and regeneration of functional cutaneous tissues by releasing cytokines and growth factors, potentially negating the need for subsequent skin grafting, while reducing the formation of hypertrophic scar tissues. This retrospective case-control study (2010-2018) of pediatric second-degree burn patients comprehensively compared two initial wound treatment options (i.e., PBBs versus Aquacel® Ag, applied during ten to twelve days post-trauma). Results confirmed clinical safety of PBBs with regard to morbidity, mortality, and overall complications. No difference was detected between groups for length of hospitalization or initial relative burn surface decreasing rates. Nevertheless, a trend was observed in younger patients treated with PBBs, requiring fewer corrective interventions or subsequent skin grafting. Importantly, significant improvements were observed in the PBB group regarding hypertrophic scarring (i.e., reduced number of scar complications and related corrective interventions). Such results establish evidence of clinical benefits yielded by the Swiss fetal progenitor cell transplantation program and favor further implementation of specific cell therapies in highly specialized regenerative medicine.

Holistic Approach of Swiss Fetal Progenitor Cell Banking: Optimizing Safe and Sustainable Substrates for Regenerative Medicine and Biotechnology

Safety, quality, and regulatory-driven iterative optimization of therapeutic cell source selection has constituted the core developmental bedrock for primary fetal progenitor cell (FPC) therapy in Switzerland throughout three decades. Customized Fetal Transplantation Programs were pragmatically devised as straightforward workflows for tissue procurement, traceability maximization, safety, consistency, and robustness of cultured progeny cellular materials. Whole-cell bioprocessing standardization has provided plethoric insights into the adequate conjugation of modern biotechnological advances with current restraining legislative, ethical, and regulatory frameworks. Pioneer translational advances in cutaneous and musculoskeletal regenerative medicine continuously demonstrate the therapeutic potential of FPCs. Extensive technical and clinical hindsight was gathered by managing pediatric burns and geriatric ulcers in Switzerland. Concomitant industrial transposition of dermal FPC banking, following good manufacturing practices, demonstrated the extensive potential of their therapeutic value. Furthermore, in extenso, exponential revalorization of Swiss FPC technology may be achieved via the renewal of integrative model frameworks. Consideration of both longitudinal and transversal aspects of simultaneous fetal tissue differential processing allows for a better understanding of the quasi-infinite expansion potential within multi-tiered primary FPC banking. Multiple fetal tissues (e.g., skin, cartilage, tendon, muscle, bone, lung) may be simultaneously harvested and processed for adherent cell cultures, establishing a unique model for sustainable therapeutic cellular material supply chains. Here, we integrated fundamental, preclinical, clinical, and industrial developments embodying the scientific advances supported by Swiss FPC banking and we focused on advances made to date for FPCs that may be derived from a single organ donation. A renewed model of single organ donation bioprocessing is proposed, achieving sustained standards and potential production of billions of affordable and efficient therapeutic doses. Thereby, the aim is to validate the core therapeutic value proposition, to increase awareness and use of standardized protocols for translational regenerative medicine, potentially impacting millions of patients suffering from cutaneous and musculoskeletal diseases. Alternative applications of FPC banking include biopharmaceutical therapeutic product manufacturing, thereby indirectly and synergistically enhancing the power of modern therapeutic armamentariums. It is hypothesized that a single qualifying fetal organ donation is sufficient to sustain decades of scientific, medical, and industrial developments, as technological optimization and standardization enable high efficiency.

Anti-Microbial Dendrimers against Multidrug-Resistant P. aeruginosa Enhance the Angiogenic Effect of Biological Burn-wound Bandages

Multi-drug resistant Pseudomonas aeruginosa has increased progressively and impedes further regression in mortality in burn patients. Such wound infections serve as bacterial reservoir for nosocomial infections and are associated with significant morbidity and costs. Anti-microbial polycationic dendrimers G3KL and G3RL, able to kill multi-drug resistant P. aeruginosa, have been previously developed. The combination of these dendrimers with a class of biological bandages made of progenitor skin cells, which secrete growth factors, could positively impact wound-healing processes. However, polycations are known to be used as anti-angiogenic agents for tumor suppression. Since, neovascularization is pivotal in the healing of deep burn-wounds, the use of anti-microbial dendrimers may thus hinder the healing processes. Surprisingly, we have seen in this study that G3KL and G3RL dendrimers can have angiogenic effects. Moreover, we have shown that a dendrimer concentration ranging between 50 and 100 μg/mL in combination with the biological bandages can suppress bacterial growth without altering cell viability up to 5 days. These results show that antimicrobial dendrimers can be used in combination with biological bandages and could potentially improve the healing process with an enhanced angiogenesis.

Characterization and Differentiation of Stem Cells Isolated from Human Newborn Foreskin Tissue

Circumcision is described as a cultural, medical, and religious process which states surgical removal of the foreskin either partly or fully. Cells isolated from the circumcised tissues are referred as foreskin cells. They have been thought as feeder cell lines for embryonic stem cells. Their fibroblastic properties were also utilized for several experiments. The waste tissues that remain after the circumcision thought to have stem cell properties. Therefore, there have been very few attempts to expose their stem cell properties without turning them into induced pluripotent stem cells. Although stem cell isolation from prepuce and their mesenchymal multilineage differentiation potential have been presented many times in the literature, the current study explored hematopoietical phenotype of newborn foreskin stem cells for the first time. According to the results, human newborn foreskin stem cells (hnFSSCs) were identified by their capability to turn into all three germ layer cell types under in vitro conditions. In addition, these cells have exhibited a stable phenotype and have remained as a monolayer in vitro. hnFSSCs suggested to carry different treatment potentials for bone damages, cartilage problems, nerve damages, lesion formations, and other diseases that are derive from mesodermal, endodermal, and ectodermal origins. Owing to the location of the tissue in the body and differentiation capabilities of hnFSSCs, these cells can be considered as easily obtainable and utilizable even better than the other stem cell sources. In addition, hnFSSCs offers a great potential for tissue engineering approaches due to exhibiting embryonic stem cell-like characteristics, not having any ethical issues, and teratoma induction as in embryonic stem cell applications.

Galvanic microparticles increase migration of human dermal fibroblasts in a wound-healing model via reactive oxygen species pathway

Electrical signals have been implied in many biological mechanisms, including wound healing, which has been associated with transient electrical currents not present in intact skin. One method to generate electrical signals similar to those naturally occurring in wounds is by supplementation of galvanic particles dispersed in a cream or gel. We constructed a three-layered model of skin consisting of human dermal fibroblasts in hydrogel (mimic of dermis), a hydrogel barrier layer (mimic of epidermis) and galvanic microparticles in hydrogel (mimic of a cream containing galvanic particles applied to skin). Using this model, we investigated the effects of the properties and amounts of Cu/Zn galvanic particles on adult human dermal fibroblasts in terms of the speed of wound closing and gene expression. The collected data suggest that the effects on wound closing are due to the ROS-mediated enhancement of fibroblast migration, which is in turn mediated by the BMP/SMAD signaling pathway. These results imply that topical low-grade electric currents via microparticles could enhance wound healing.

Molecular and cellular mechanisms of bone morphogenetic proteins and activins in the skin: potential benefits for wound healing

Bone morphogenetic proteins (BMPs) and activins are phylogenetically conserved proteins, belonging to the transforming growth factor-β superfamily, that signal through the phosphorylation of receptor-regulated Smad proteins, activating different cell responses. They are involved in various steps of skin morphogenesis and wound repair, as can be evidenced by the fact that their expression is increased in skin injuries. BMPs play not only a role in bone regeneration but are also involved in cartilage, tendon-like tissue and epithelial regeneration, maintain vascular integrity, capillary sprouting, proliferation/migration of endothelial cells and angiogenesis, promote neuron and dendrite formation, alter neuropeptide levels and are involved in immune response modulation, at least in animal models. On the other hand, activins are involved in wound repair through the regulation of skin and immune cell migration and differentiation, re-epithelialization and granulation tissue formation, and also promote the expression of collagens by fibroblasts and modulate scar formation. This review aims at enunciating the effects of BMPs and activins in the skin, namely in skin development, as well as in crucial phases of skin wound healing, such as inflammation, angiogenesis and repair, and will focus on the effects of these proteins on skin cells and their signaling pathways, exploring the potential therapeutic approach of the application of BMP-2, BMP-6 and activin A in chronic wounds, particularly diabetic foot ulcerations.

Novel differences in the expression of inflammation-associated genes between mid- and late-gestational dermal fibroblasts

While cutaneous wounds of late-gestational fetuses and on through adulthood result in scar formation, wounds incurred early in gestation have been shown to heal scarlessly. Unique properties of fetal fibroblasts are believed to mediate this scarless healing process. In this study, microarray analysis was used to identify differences in the gene expression profiles of cultured fibroblasts from embryonic day 15 (E15; midgestation) and embryonic day 18 (E18; late-gestation) skin. Sixty-two genes were differentially expressed and 12 of those genes are associated with inflammation, a process that correlates with scar formation in fetal wounds. One of the differentially expressed inflammatory genes was cyclooxygenase-1 (COX-1). COX-1 was more highly expressed in E18 fibroblasts than in E15 fibroblasts, and these differences were confirmed at the gene and protein level. Differences in COX-1 protein expression were also observed in fetal skin by immunohistochemical and immunofluorescence staining. The baseline differences in gene expression found in mid- and late-gestational fetal fibroblasts suggest that developmental alterations in fibroblasts could be involved in the transition from scarless to fibrotic fetal wound healing. Furthermore, baseline differences in the expression of inflammatory genes by fibroblasts in E15 and E18 skin may contribute to inflammation and scar formation late in gestation.

Mast cells contribute to scar formation during fetal wound healing

Scar formation is a potentially detrimental process of tissue restoration in adults, affecting organ form and function. During fetal development, cutaneous wounds heal without inflammation or scarring at early stages of development, but begin to heal with significant inflammation and scarring as the skin becomes more mature. One possible cell type that could regulate the change from scarless to fibrotic healing is the mast cell. We show here that dermal mast cells in scarless wounds generated at embryonic day 15 (E15) are fewer in number, less mature and do not degranulate in response to wounding as effectively as mast cells of fibrotic wounds made at embryonic day 18 (E18). Differences were also observed between cultured mast cells from E15 and E18 skin with regard to degranulation and preformed cytokine levels. Injection of mast cell lysates into E15 wounds disrupted scarless healing, suggesting that mast cells interfere with scarless repair. Finally, wounds produced at E18, which normally heal with a scar, healed with significantly smaller scars in mast cell-deficient Kit^W/W-v mice compared to Kit^+/+ littermates. Together, these data suggest that mast cells enhance scar formation, and that these cells may mediate the transition from scarless to fibrotic healing during fetal development.

Influence of a single loading episode on gene expression in healing rat Achilles tendons

Mechanical loading stimulates tendon healing via mechanisms that are largely unknown. Genes will be differently regulated in loaded healing tendons, compared with unloaded, just because of the fact that healing processes have been changed. To avoid such secondary effects and study the effect of loading per se, we therefore studied the gene expression response shortly after a single loading episode in otherwise unloaded healing tendons. The Achilles tendon was transected in 30 tail-suspended rats. The animals were let down from the suspension to load their tendons on a treadmill for 30 min once, 5 days after tendon transection. Gene expression was studied by Affymetrix microarray before and 3, 12, 24, and 48 h after loading. The strongest response in gene expression was seen 3 h after loading, when 150 genes were up- or downregulated (fold change ≥2, P ≤ 0.05). Twelve hours after loading, only three genes were upregulated, whereas 38 were downregulated. Fewer than seven genes were regulated after 24 and 48 h. Genes involved in the inflammatory response were strongly regulated at 3 and 12 h after loading; this included upregulation of iNOS, PGE synthase, and IL-1β. Also genes involved in wound healing/coagulation, angiogenesis, and production of reactive oxygen species were strongly regulated by loading. Microarray results were confirmed for 16 selected genes in a repeat experiment (N = 30 rats) using real-time PCR. It was also confirmed that a single loading episode on day 5 increased the strength of the healing tendon on day 12. In conclusion, the fact that there were hardly any regulated genes 24 h after loading suggests that optimal stimulation of healing requires a mechanical loading stimulus every day.

Biologicals and fetal cell therapy for wound and scar management

Few biopharmaceutical preparations developed from biologicals are available for tissue regeneration and scar management. When developing biological treatments with cellular therapy, selection of cell types and establishment of consistent cell banks are crucial steps in whole-cell bioprocessing. Various cell types have been used in treatment of wounds to reduce scar to date including autolog and allogenic skin cells, platelets, placenta, and amniotic extracts. Experience with fetal cells show that they may provide an interesting cell choice due to facility of outscaling and known properties for wound healing without scar. Differential gene profiling has helped to point to potential indicators of repair which include cell adhesion, extracellular matrix, cytokines, growth factors, and development. Safety has been evidenced in Phase I and II clinical fetal cell use for burn and wound treatments with different cell delivery systems. We present herein that fetal cells present technical and therapeutic advantages compared to other cell types for effective cell-based therapy for wound and scar management.

Human fetal bone cells in delivery systems for bone engineering

The aim of this study was to culture human fetal bone cells (dedicated cell banks of fetal bone derived from 14 week gestation femurs) within both hyaluronic acid gel and collagen foam, to compare the biocompatibility of both matrices as potential delivery systems for bone engineering and particularly for oral application. Fetal bone cell banks were prepared from one organ donation and cells were cultured for up to 4 weeks within hyaluronic acid (Mesolis®) and collagen foams (TissueFleece®). Cell survival and differentiation were assessed by cell proliferation assays and histology of frozen sections stained with Giemsa, von Kossa and ALP at 1, 2 and 4 weeks of culture. Within both materials, fetal bone cells could proliferate in three-dimensional structure at ∼70% capacity compared to monolayer culture. In addition, these cells were positive for ALP and von Kossa staining, indicating cellular differentiation and matrix production. Collagen foam provides a better structure for fetal bone cell delivery if cavity filling is necessary and hydrogels would permit an injectable technique for difficult to treat areas. In all, there was high biocompatibility, cellular differentiation and matrix deposition seen in both matrices by fetal bone cells, allowing for easy cell delivery for bone stimulation in vivo.

Hyaluronan concentration within a 3D collagen matrix modulates matrix viscoelasticity, but not fibroblast response

The use of 3D extracellular matrix (ECM) microenvironments to deliver growth-inductive signals for tissue repair and regeneration requires an understanding of the mechanisms of cell-ECM signaling. Recently, hyaluronic acid (HA) has been incorporated in collagen matrices in an attempt to recreate tissue specific microenvironments. However, it is not clear how HA alters biophysical properties (e.g. fibril microstructure and mechanical behavior) of collagen matrices or what impact these properties have on cell behavior. The present study determined the effects of varying high molecular weight HA concentration on 1) the assembly kinetics, fibril microstructure, and viscoelastic properties of 3D type I collagen matrices and 2) the response of human dermal fibroblasts, in terms of morphology, F-actin organization, contraction, and proliferation within the matrices. Results showed increasing HA concentration up to 1 mg/ml (HA:collagen ratio of 1:2) did not significantly alter fibril microstructure, but did significantly alter viscoelastic properties, specifically decreasing shear storage modulus and increasing compressive resistance. Interestingly, varied HA concentration did not significantly affect any of the measured fibroblast behaviors. These results show that HA-induced effects on collagen matrix viscoelastic properties result primarily from modulation of the interstitial fluid with no significant change to the fibril microstructure. Furthermore, the resulting biophysical changes to the matrix are not sufficient to modulate the cell-ECM mechanical force balance or proliferation of resident fibroblasts. These results provide new insight into the mechanisms by which cells sense and respond to microenvironmental cues and the use of HA in collagen-based biomaterials for tissue engineering.

Chronic wound healing by fetal cell therapy may be explained by differential gene profiling observed in fetal versus old skin cells

Engineering of fetal tissue has a high potential for the treatment of acute and chronic wounds of the skin in humans as these cells have high expansion capacity under simple culture conditions and one organ donation can produce Master Cell Banks which can fabricate over 900 million biological bandages (9 x 12cm). In a Phase 1 clinical safety study, cases are presented for the treatment of therapy resistant leg ulcers. All eight patients, representing 13 ulcers, tolerated multiple treatments with fetal biological bandages showing no negative secondary effects and repair processes similar to that seen in 3rd degree burns. Differential gene profiling using Affymetrix gene chips (analyzing 12,500 genes) were accomplished on these banked fetal dermal skin cells compared to banked dermal skin cells of an aged donor in order to point to potential indicators of wound healing. Families of genes involved in cell adhesion and extracellular matrix, cell cycle, cellular signaling, development and immune response show significant differences in regulation between banked fetal and those from banked old skin cells: with approximately 47.0% of genes over-expressed in fetal fibroblasts. It is perhaps these differences which contribute to efficient tissue repair seen in the clinic with fetal cell therapy.