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1.  Complementary Effects of Two Growth Factors in Multifunctionalized Silk Nanofibers for Nerve Reconstruction 
PLoS ONE  2014;9(10):e109770.
With the aim of forming bioactive guides for peripheral nerve regeneration, silk fibroin was electrospun to obtain aligned nanofibers. These fibers were functionalized by incorporating Nerve Growth Factor (NGF) and Ciliary NeuroTrophic Factor (CNTF) during electrospinning. PC12 cells grown on the fibers confirmed the bioavailability and bioactivity of the NGF, which was not significantly released from the fibers. Primary neurons from rat dorsal root ganglia (DRGs) were grown on the nanofibers and anchored to the fibers and grew in a directional fashion based on the fiber orientation, and as confirmed by growth cone morphology. These biofunctionalized nanofibers led to a 3-fold increase in neurite length at their contact, which was likely due to the NGF. Glial cell growth, alignment and migration were stimulated by the CNTF in the functionalized nanofibers. Organotypic culture of rat fetal DRGs confirmed the complementary effect of both growth factors in multifunctionalized nanofibers, which allowed glial cell migration, alignment and parallel axonal growth in structures resembling the ‘bands of Bungner’ found in situ. Graftable multi-channel conduits based on biofunctionalized aligned silk nanofibers were developed as an organized 3D scaffold. Our bioactive silk tubes thus represent new options for a biological and biocompatible nerve guidance conduit.
PMCID: PMC4196919  PMID: 25313579
2.  Enhanced Cellular Adhesion on Titanium by Silk Functionalized with titanium binding and RGD peptides 
Acta biomaterialia  2012;9(1):4935-4943.
Soft tissue adhesion on titanium represents a challenge for implantable materials. In order to improve adhesion at the cell/material interface we used a new approach based on the molecular recognition of titanium by specific peptides. Silk fibroin protein was chemically grafted with titanium binding peptide (TiBP) to increase adsorption of these chimeric proteins to the metal surface. Quartz Crystal Microbalance was used to quantify the specific adsorption of TiBP-functionalized silk and an increase in protein deposition by more than 35% was demonstrated due to the presence of the binding peptide. A silk protein grafted with TiBP and fibronectin-derived RGD peptide was then prepared. The adherence of fibroblasts on the titanium surface modified with the multifunctional silk coating demonstrated an increase in the number of adhering cells by 60%. The improved adhesion was demonstrated by Scanning Electron Microscopy and immunocytochemical staining of focal contact points. Chick embryo organotypic culture also revealed strong adhesion of endothelial cells expanding on the multifunctional silk-peptide coating. These results demonstrated that silk functionalized with TiBP and RGD represents a promising approach to modify cell-biomaterial interfaces, opening new perspectives for implantable medical devices, especially when reendothelialization is required.
PMCID: PMC3508072  PMID: 22975628
silk protein; titanium-binding peptide; peptide grafting; cell adhesion; surface modification
3.  Multifunctionalized electrospun silk fibers promote axon regeneration in central nervous system 
Advanced functional materials  2011;21(22):4202.
The repair of central nerves remains a major challenge in regenerative neurobiology. Regenerative guides possessing critical features such as cell adhesion, physical guiding and topical stimulation are needed. To generate such a guide, silk protein materials are prepared using electrospinning. The silk is selected for this study due to its biocompatibility and ability to be electrospun for the formation of aligned biofunctional nanofibers. The addition of Brain Derived Neurotrophic Factor (BDNF), Ciliary Neurotrophic Factor (CNTF) or both to the electrospun fibers enable enhanced function without impact to the structure or the surface morphology. Only a small fraction of the loaded growth factors is released over time allowing the fibers to continue to provide these factors to the cells for extended periods of time. The entrapped factors remain active and available to the cells as rat retinal ganglion cells (RGCs) exhibit longer axonal growth when in contact with the biofunctionalized fibers. Compare to non-functionalized fibers, the growth of neurites increased 2 fold on fibers containing BDNF, 2.5 fold with fibers containing CNTF and by almost 3-fold on fibers containing both factors. The results demonstrate the potential of aligned and functionalized electrospun silk fibers to promote nerve growth in the central nervous system, underlying the great potential of complex biomaterials in neuroregenerative strategies following axotomy and nerve crush traumas.
PMCID: PMC3404853  PMID: 22844266
Silk; Nerve regeneration; BDNF; CNTF; biofunctionalization
4.  Three-Dimensional Human Tissue Models of Wounded Skin 
Human skin equivalents (HSEs) are in vitro tissues in which a fully differentiated, stratified squamous epithelium is grown at an air–liquid interface on a Type I collagen gel harboring human dermal fibroblasts. HSEs now provide experimental human tissue models to study factors that direct re-epithelialization and epithelial–mesenchymal cross-talk following wounding. This chapter describes the fabrication of HSEs from human keratinocytes and fibroblasts and how HSEs can be modified to characterize the response of the human epithelium during wound repair. The protocols outlined first describe techniques for the generation of human tissues that closely approximate the architectural features, differentiation, and growth of human skin. This will be followed by a description of a protocol that enables HSEs to be adapted to monitor their response following wounding. These engineered human tissues provide powerful tools to study biological process in tissues that mimic the healing of human skin and of the epithelial tissue.
PMCID: PMC3076317  PMID: 19908015
Organotypic culture; Three-Dimensional model; Human skin; Wound repair; Fibroblasts
5.  Fibroblasts derived from human embryonic stem cells direct development and repair of 3D human skin equivalents 
Pluripotent, human stem cells hold tremendous promise as a source of progenitor and terminally differentiated cells for application in future regenerative therapies. However, such therapies will be dependent upon the development of novel approaches that can best assess tissue outcomes of pluripotent stem cell-derived cells and will be essential to better predict their safety and stability following in vivo transplantation.
In this study we used engineered, human skin equivalents (HSEs) as a platform to characterize fibroblasts that have been derived from human embryonic stem (hES) cell. We characterized the phenotype and the secretion profile of two distinct hES-derived cell lines with properties of mesenchymal cells (EDK and H9-MSC) and compared their biological potential upon induction of differentiation to bone and fat and following their incorporation into the stromal compartment of engineered, HSEs.
While both EDK and H9-MSC cell lines exhibited similar morphology and mesenchymal cell marker expression, they demonstrated distinct functional properties when incorporated into the stromal compartment of HSEs. EDK cells displayed characteristics of dermal fibroblasts that could support epithelial tissue development and enable re-epithelialization of wounds generated using a 3D tissue model of cutaneous wound healing, which was linked to elevated production of hepatocyte growth factor (HGF). Lentiviral shRNA-mediated knockdown of HGF resulted in a dramatic decrease of HGF secretion from EDK cells that led to a marked reduction in their ability to promote keratinocyte proliferation and re-epithelialization of cutaneous wounds. In contrast, H9-MSCs demonstrated features of mesenchymal stem cells (MSC) but not those of dermal fibroblasts, as they underwent multilineage differentiation in monolayer culture, but were unable to support epithelial tissue development and repair and produced significantly lower levels of HGF.
Our findings demonstrate that hES-derived cells could be directed to specified and alternative mesenchymal cell fates whose function could be distinguished in engineered HSEs. Characterization of hES-derived mesenchymal cells in 3D, engineered HSEs demonstrates the utility of this tissue platform to predict the functional properties of hES-derived fibroblasts before their therapeutic transplantation.
PMCID: PMC3092150  PMID: 21338517
6.  Integrin-Blocking Antibodies Delay Keratinocyte Re-Epithelialization in a Human Three-Dimensional Wound Healing Model 
PLoS ONE  2010;5(5):e10528.
The α6β4 integrin plays a significant role in tumor growth, angiogenesis and metastasis through modulation of growth factor signaling, and is a potentially important therapeutic target. However, α6β4-mediated cell-matrix adhesion is critical in normal keratinocyte attachment, signaling and anchorage to the basement membrane through its interaction with laminin-5, raising potential risks for targeted therapy. Bioengineered Human Skin Equivalent (HSE), which have been shown to mimic their normal and wounded counterparts, have been used here to investigate the consequences of targeting β4 to establish toxic effects on normal tissue homeostasis and epithelial wound repair. We tested two antibodies directed to different β4 epitopes, one adhesion-blocking (ASC-8) and one non-adhesion blocking (ASC-3), and determined that these antibodies were appropriately localized to the basal surface of keratinocytes at the basement membrane interface where β4 is expressed. While normal tissue architecture was not altered, ASC-8 induced a sub-basal split at the basement membrane in non-wounded tissue. In addition, wound closure was significantly inhibited by ASC-8, but not by ASC-3, as the epithelial tongue only covered 40 percent of the wound area at 120 hours post-wounding. These results demonstrate β4 adhesion-blocking antibodies may have adverse effects on normal tissue, whereas antibodies directed to other epitopes may provide safer alternatives for therapy. Taken together, we conclude that these three-dimensional tissue models provide a biologically relevant platform to identify toxic effects induced by candidate therapeutics, which will allow generation of findings that are more predictive of in vivo responses early in the drug development process.
PMCID: PMC2873945  PMID: 20502640
7.  Three-Dimensional Tissue Models of Normal and Diseased Skin 
Over the last decade, the development of in vitro, human, three-dimensional (3D) tissue models, known as human skin equivalents (HSEs), has furthered understanding of epidermal cell biology and provided novel experimental systems. Signaling pathways that mediate the linkage between growth and differentiation function optimally when cells are spatially organized to display the architectural features seen in vivo, but are uncoupled and lost in two-dimensional culture systems. HSEs consist of a stratified squamous epithelium grown at an air-liquid interface on a collagen matrix populated with dermal fibroblasts. These 3D tissues demonstrate in vivo–like epithelial differentiation and morphology, and rates of cell division, similar to those found in human skin. This unit describes fabrication of HSEs, allowing the generation of human tissues that mimic the morphology, differentiation, and growth of human skin, as well as disease processes of cancer and wound re-epithelialization, providing powerful new tools for the study of diseases in humans.
PMCID: PMC2811850  PMID: 19085986
organotypic culture; three-dimensional model; human skin; wound repair; intraepithelial neoplasia
8.  Denatured Collagen Modulates the Phenotype of Normal and Wounded Human Skin Equivalents 
Epithelial–mesenchymal interactions are known to play an important role in modulating homeostasis and repair. However, it remains unclear how the composition of the extracellular matrix may regulate the ability of dermal fibroblasts to engage in such cross talk. To address this, we studied how fibroblast phenotype was linked to the behavior of normal and wounded human skin equivalents (HSE) by comparing human dermal fibroblasts (HDF) incorporated into the three-dimensional tissues to those extensively cultivated in two-dimensional (2D) monolayer culture on denatured collagen (DC) matrix, native collagen, or tissue culture plastic before incorporation into HSEs. We first established that prolonged passage and growth of HDF on DC increased their migratory potential in a 2D monolayer culture. When HDF variants were grown in HSEs, we found that extended passage on DC and incorporation of DC directly into the collagen gel enhanced proliferation of both HDF and basal keratinocytes in HSEs. By adapting HSEs to study wound reepithelialization, we found that the extended passage of HDF on DC accelerated the rate of wound healing by 38%. Thus, extensive ex vivo expansion on DC was able to modify the phenotype of skin fibroblasts by augmenting their reparative properties in skin-like HSEs.
PMCID: PMC2810554  PMID: 18200055
Epithelial-mesenchymal interactions promote the morphogenesis and homeostasis of human skin. However, the role of the basement membrane (BM) during this process is not well-understood. To directly study how BM proteins influence epidermal differentiation, survival and growth, we developed novel 3D human skin equivalents (HSEs). These tissues were generated by growing keratinocytes at an air-liquid interface on polycarbonate membranes coated with individual matrix proteins (Type I Collagen, Type IV Collagen or fibronectin) that were placed on contracted Type I Collagen gels populated with dermal fibroblasts. We found that only keratinocytes grown on membranes coated with the BM protein Type IV Collagen showed optimal tissue architecture that was similar to control tissues grown on de-epidermalized dermis (AlloDerm) that contained intact BM. In contrast, tissues grown on proteins not found in BM, such as fibronectin and Type I Collagen, demonstrated aberrant tissue architecture that was linked to a significant elevation in apoptosis and lower levels of proliferation of basal keratinocytes. While all tissues demonstrated a normalized, linear pattern of deposition of laminin 5, tissues grown on Type IV Collagen showed elevated expression of α6 integrin, Type IV Collagen and Type VII Collagen, suggesting induction of BM organization. Keratinocyte differentiation (Keratin 1 and filaggrin) was not dependent on the presence of BM proteins. Thus, Type IV Collagen acts as a critical microenvironmental factor in the BM that is needed to sustain keratinocyte growth and survival and to optimize epithelial architecture.
PMCID: PMC2810484  PMID: 18029161
basement membrane; human skin equivalent; Type IV Collagen; microenvironment; keratinocytes
10.  Soft Tissue Augmentation Using Silk Gels: An In Vitro and In Vivo Study 
Journal of periodontology  2009;80(11):1852-1858.
Restoration of a three-dimensional shape with soft tissue augmentation is a challenge for surgical reconstruction and esthetic improvement of intraoral mucosa and perioral skin tissues. A connective tissue graft or free gingival graft, classically used for such indications, requires a donor site, which may lead to various clinical complications.
In this article, a new three-dimensional scaffold made of silk fibroin that could be of great interest for these indications was studied. Mechanical tests were conducted to characterize the physical properties of the materials. The biocompatibility of such scaffolds was positively assessed in vitro using a combination of immunostaining, 5-bromo-2′-deoxyuridine proliferation assays, and histologic staining. Finally, the shaped material was grafted subcutaneously in nude mice for a long-time implantation study.
Human fibroblasts embedded in this material had a survival rate up to 68.4% and were able to proliferate and synthesize proteins. One month after subcutaneous implantation, the three-dimensional soft tissue augmentation was stable, and histologic analysis revealed revascularization of the area through the biomaterial. A mild inflammatory reaction disappeared after 12 weeks.
The results indicate that silk-gel material was able to create a lasting three-dimensional soft tissue augmentation and is a promising biomaterial for periodontal and maxillofacial therapies, either as a scaffold for cells or alone as a biomaterial.
PMCID: PMC2810482  PMID: 19905955
Biocompatible materials; fibroblasts; grafts; regeneration; silk
11.  Self-Assembling Peptide Nanofiber Scaffolds Accelerate Wound Healing 
PLoS ONE  2008;3(1):e1410.
Cutaneous wound repair regenerates skin integrity, but a chronic failure to heal results in compromised tissue function and increased morbidity. To address this, we have used an integrated approach, using nanobiotechnology to augment the rate of wound reepithelialization by combining self-assembling peptide (SAP) nanofiber scaffold and Epidermal Growth Factor (EGF). This SAP bioscaffold was tested in a bioengineered Human Skin Equivalent (HSE) tissue model that enabled wound reepithelialization to be monitored in a tissue that recapitulates molecular and cellular mechanisms of repair known to occur in human skin. We found that SAP underwent molecular self-assembly to form unique 3D structures that stably covered the surface of the wound, suggesting that this scaffold may serve as a viable wound dressing. We measured the rates of release of EGF from the SAP scaffold and determined that EGF was only released when the scaffold was in direct contact with the HSE. By measuring the length of the epithelial tongue during wound reepithelialization, we found that SAP scaffolds containing EGF accelerated the rate of wound coverage by 5 fold when compared to controls without scaffolds and by 3.5 fold when compared to the scaffold without EGF. In conclusion, our experiments demonstrated that biomaterials composed of a biofunctionalized peptidic scaffold have many properties that are well-suited for the treatment of cutaneous wounds including wound coverage, functionalization with bioactive molecules, localized growth factor release and activation of wound repair.
PMCID: PMC2157486  PMID: 18183291

Results 1-11 (11)