Patent Application
20120276154
Not applicable.
The present invention relates to a tissue-engineered skin graft, and more particularly to a tissue-engineered skin graft with hair follicles.
Current tissue-engineered skin grafts have been recognized as a promising treatment for chronic ulcers and acute burns, leading to a rapid closure of wounds to prevent further dehydration and potential infection. However, known grafts fail to regenerate many essential skin structures such as hair, nerves, vessels and glands. The lack of hair in healed wounds not only fails to provide the necessary physiologic protection to skin, but also psychosocially impacts an individual's self-esteem and interpersonal relationships within a society. Extensive efforts have been made to reconstitute hair follicles, but mainly focus on in vivo regeneration.
Hair follicles are complex miniorgans with numerous functions including production of hair shafts, acting as a sensory instrument and serving as a psychosocial communication tool symbolically representing youth, health, and fertility. Hair undergoes cyclical growth patterns through the stages of anagen (rapid growth), telogen (quiescence), and catagen (regression). This growth cycle provides a mechanism for cleaning skin debris, parasites, and harmful chemicals by encapsulating them within trichocytes. It also protects rapidly dividing keratinocytes from malignant degeneration and oxidative damage. In addition to production of keratins and melanin for the hair shaft, hair follicles produce a wide array of hormones, neurotransmitters, neuropeptides, and growth factors. Many of these growth factors, such as the molecules FGF, EGF, IGF, HGF, TGF-beta, VEGF, and NGF, are known for their crucial roles in wound healing and skin homeostasis. Apart from its clinical importance, the hair follicle offers an easily manipulated, widely available test system for many areas of general biology including differentiation, proliferation, apoptosis, stem cell biology, extracellular matrix remodeling, immune defense, and immune privilege.
In one aspect, the present invention provides a tissue-engineered skin graft capable of developing hair follicles. In some embodiments of the present invention, the skin graft includes multiple alternating mats of biocompatible nanofibers and layers of skin cells. In some such embodiments, the skin cells include cultured fibroblasts. In some such embodiments, the skin cells include aggregates of dermal papilla cells (dermal papilla aggregates) capable of differentiating into hair follicles. In some such embodiments, the dermal papilla aggregates are embedded within the skin graft in a predetermined arrangement. In some such embodiments, the dermal papilla aggregates are embedded within the skin graft to provide the skin graft with predictable hair follicle and hair formation capabilities. In some embodiments, the outer layers of the skin graft include layers of epidermal keratinocytes. In some such embodiments, the skin graft has distinguishable dermal and epidermal sections. In some embodiments, the skin graft provides a biomimetic environment for interactions between the dermis, epidermis, hair follicles and proto hairs. In some such embodiments, the nanofiber mats include biodegradable or bioresorbable materials. In some such embodiments, the biodegradable or bioresorbable materials include synthetic polymers, natural polymers, or blends thereof. In some such embodiments, the biodegradable or bioresorbable materials include polycaprolactone, collagen, or blends thereof. In some such embodiments, different layers of nanofibers have different chemical compositions. In some embodiments, the nanofiber layers include substances such as drugs or growth factors to be released in situ after transplantation of the skin graft into a patient.
In another aspect, the present invention provides a method for making a tissue-engineered skin graft capable of developing hair follicles. In some embodiments, the method includes, but is not limited to, the steps of: (1) isolating skin and hair-follicle forming cells (e.g., dermal papilla cells) from intact skin and culturing the isolated cells for assembly into tissue-engineered skin grafts; (2) formation of dermal papilla aggregrates by culturing the isolated dermal papilla cells; and (3) layer-by-layer assembly of cultured skin cells and dermal papilla aggregates with alternating layers of biocompatible nanofiber mats so as to form three-dimensional constructs. In some such embodiments, the three-dimensional constructs are further cultured to differentiate the dermal papilla aggregrates into hair follicles and produce proto hairs. In some such embodiments, the dermal papilla aggregates are cultured by a hanging drop method. In some such embodiments, the method includes building up alternating layers of nanofibers and fibroblasts, adding a layer of a dermal papilla aggregates, adding further alternating layers of nanofibers and fibroblasts, and adding layers of keratinocytes as an epidermal layer. In some such embodiments, dermal papilla aggregates are selectively deposited where hair growth is desired. In some such embodiments, the skin structure is formed so as to have distinct dermal and epidermal layers.
For a more complete understanding of the present invention, reference is made to the following detailed description of exemplary embodiments thereof, considered in conjunction with the accompanying drawings, in which:
The present invention provides tissue-engineered skin grafts having hair follicles capable of providing new hair and methods of making such skin grafts. These skin grafts are prepared in vitro using a biomimetic approach to generating hair follicle-like structures directly in tissue-engineered skin grafts. In embodiments of the present invention, the biomimetic approach involves three major types of cells, including hair-forming cells (i.e., dermal papilla) and cells from the inner and outermost layers of skin (i.e., dermal fibroblasts and keratinocytes), which may be autologous or allogenic with regard to the subject receiving the skin graft. In some embodiments of the present invention, the dermal papilla (“DP”) cell aggregates may be made by a hanging droplet method, and assembled with the skin cells into three-dimensional (“3D”) skin substitutes with the assistance of biocompatible nanofibers, such as polycaprolactone (PCL)/collagen-blended electrospun nanofibers, following a layer-by-layer assembly approach. The 3D skin substitutes develop hair follicle-like structures in vitro (“proto hair”), and consequently form new hairs in vivo after transplantation to full-thickness skin wounds. Compared to conventional in vivo injection of hair cells, the inventive process provides better control of the number of hair follicles formed within a specific area of skin, and at specified locations in the skin, by embedding various amount of DP aggregates at specified locations within the skin grafts. In addition, hair follicle size can be controlled by controlling the size of the DP aggregates. For those deep wounds like third degree skin burns, which lose epidermis and dermis portions, injection of hair cells cannot make any new hair shafts because of the lack of dermal-epidermal interaction. As a result of the presence of hair structures in tissue-engineered skin grafts, the wound-healing process can be accelerated by transplanting such grafts to the wounded area. Further, the tissue-engineered skin grafts provide the potential for new hair shafts to form.
Referring to an exemplary tissue-engineered skin graft 10 of
An exemplary method of forming a tissue-engineered skin graft, such as skin graft 10 of
Step 1: Isolation of skin and hair follicle-forming cells. Three major types of cells (dermal papillae, dermal fibroblast and epidermal keratinocyte) are isolated by enzymatic methods and cultured in vitro to obtain cells needed to construct the skin graft 10. DP cells are isolated from intact hair follicles and keratinocyte and fibroblasts are isolated from intact skin.
Step 2: Formation of dermal papilla aggregates. DP aggregates are formed from the DP cells obtained in step 1 using an adaptation of a hanging droplet method.
Step 3: Layer-by-layer assembly of skin cells and DP aggregates into 3D constructs with formation of hair follicle-like structures. PCL/collagen nanofibers are used to assist the assembly of skin cells (dermal fibroblast and keratinocyte) together with DP aggregates into 3D skin substitutes, and the formed constructs are further cultured in 5% CO2 and 37° C. for 14 days to form the proto hair-like structures.
Representative methods useful for step 1 may be found in the following references, each of which is incorporated by reference herein in its entirety: (Ref. 1) Chiu, H. C., et al. An efficient method for isolation of hair papilla and follicle epithelium from human scalp specimens. Br J Dermatol. (1993) 129:350-351; (Ref. 2) Wu, J. J., et al. Enzyme digestion to isolate and culture human scalp dermal papilla cells: a more efficient method. Arch Dermatol Res. (2005) 297:60-67; (Ref. 3) Li, Y., et al. One-step collagenase I treatment: an efficient way for isolation and cultivation of human scalp dermal papilla cells. J Dermatol Sci. 2005; 37: 58-60; (Ref. 4) Vaughan, F. L., et al. Isolation, Purification, and Cultivation of Murine and Human Keratinocytes. Methods in Molecular Biology. (2005) 290:187-206; and (Ref. 5) Wang, H., et al. Improved enzymatic isolation of fibroblasts for the creation of autologous skin substitutes. In Vitro Cellular & Developmental Biology—Animal (2004) 40 (8 & 9): 268-277. Representative methods useful for step 2 may be found in the following reference, which is incorporated by reference herein in its entirety: (Ref. 6) Qiao, J., et al. Hair morphogenesis in vitro: Formation of structures suitable for implantation. Regen. Med. (2008) 3 (5), 683-692. Representative methods useful for step 3 may be found in the following reference, which is incorporated by reference herein in its entirety: (Ref. 7) Yang, X, et al. Nanofiber enabled layer-by-layer approach toward three-dimensional tissue formation. Tissue Engineering Part A. (2009) 15: 945. Certain applications of the aforesaid methods are discussed more fully hereinbelow.
To demonstrate the feasibility of an embodiment of the present invention, the prototype study described hereinbelow was performed using rat skin cells and rat hair follicle cells. Rat cells were selected as models for the embodiment because of similarities between the growth cycles of rat hair and those of human hair. The prototype study is discussed in the following Example 1. The following example is presented to illustrate certain embodiments of the present invention, and is not intended to limit the scope of the invention in any way.
The present Example 1 employs steps 1-3 of the exemplary method discussed above with respect to an embodiment of the present embodiment to construct an exemplary skin graft, such as skin graft 10 of
Enzymatic dissociation methods employing collagenase I and dispase II were optimized and established for obtaining keratinocytes from skin epidermis and DP cells from vibrissa hair follicles of the same female pregnant Sprague Dawley rat. To circumvent the relatively low yield and limited proliferation capacity of fibroblasts isolated from rat skin, fibroblasts were isolated from a fetus of the same female rat.
Follicular cells (i.e., DP cells), keratinocytes and fibroblasts were isolated using the established protocols of the References 1-5 that are identified above. DP cells were isolated from rat vibrissae using methods from References 1-3. References 4 and 5 were used as guidance to isolate keratinocytes from the skin epidermal layer and fibroblasts from fetal skin.
In brief, a pregnant, female Sprague-Dawley rat with 15-19 day old fetuses was sacrificed. Under a dissecting microscope, the hair bulbs were isolated from the hair follicles of the adult rat. The hair bulbs thus obtained were then digested in a collagenase I solution [1 mg/mL] at 37° C. to release the DP cells. The collected DP cells were then cultured in Dulbecco's Modified Eagle Medium (DMEM), containing b-FGF at 10 ng/mL, 14% fetal bovine serum (“FBS”), and 1% penicillin/streptomycin, yielding cultured DP cells such as DP cells 28 of
Keratinocytes were isolated from adult rat dorsal skin as described herein, using methods described in References 4 and 5 with modifications to the enzymatic digestion steps. The adult rat was shaved, and then a 3×3 cm area of bare skin was harvested, and incubated in a dispase II solution (0.25% w/v) for 30-60 min to separate the epidermis from dermis. The detached epidermis was then incubated in 0.05% trypsin/EDTA to release keratinocytes. The keratinocytes were then cultured in keratinocyte serum-free medium (KSFM, Invitrogen™, Life Technologies Corporation, Grand Island, N.Y.), yielding cultured keratinocytes such as the keratinocytes 24 of
Fibroblasts were obtained following the same procedure as in Reference 5. Fetal skin was harvested and the dermis was minced and then digested in 0.25% dispase II and 0.75% collagenase I for 1.5-2 hours. After centrifuging, the fibroblasts thus obtained were cultured in DMEM with 10% FBS, and 1% penicillin/streptomycin. Culture medium was refreshed every 2-3 days, yielding cultured fibroblasts, such as fibroblasts 26 of
DP aggregates were generated using a modification of the hanging droplet method of Reference 6, identified above. Briefly, the isolated DP cells obtained in step 1 were suspended in DMEM with high glucose, 14% FBS, and 0.24% methyl cellulose. The cell suspension was titered on the bottom of a 100-mm Petri dish as 20 μL droplets (each droplet containing about 3×104 cells). The Petri dish was then inverted, so that the droplets were suspended from the Petri dish. The suspended droplets were incubated at 37° C. in a 5% CO2 atmosphere. DP aggregates formed within 18-20 h. Upon formation, the DP aggregates were individually transferred to round-bottom 96-well plates with low-ultra retention to prevent DP aggregates from adhering to the plate. The culture medium was changed every 2-3 days.
Step 3: Layer-by-Layer Assembly of Skin Cells and DP Aggregates into 3D Constructs with Formation of Hair Follicle-Like Structures.
To rapidly form skin grafts with spatially-controlled cell distribution (e.g., the distribution of DP aggregates), the layering method of Reference 7 was modified to enable layer-by-layer assembly of an exemplary skin graft having proto-hair follicles. The use of cell layering in combination with the in situ electrospinning of biocompatible nanofibers, enables the maintenance of hydrated cells and nanofibers, better control of cell types and cell seeding density and distribution, and, perhaps most importantly, incorporation of the cells in a 3D biomimetic environment for better expression of their phenotypes.
Referring to
Using this modified approach, constructs with both fibroblasts and keratinocytes (bilayer skin constructs) were created. Referring first to
A simplified schematic of such a construct 56 is shown as
Rat Skin Grafts with Hair Follicle Structures.
The layer-by-layer cell assembly approach discussed above was used to create a bi-layer skin substitute with DP aggregates entrapped in the interface between fibroblasts and keratinocytes. A simplified schematic of a prototype of such a skin substitute was presented in
It was also found that proto hair was formed in the skin substitute after being cultured for 14 days. After being cultured for two weeks, thin cross-sections of cultured skin substitute were stained with hematoxylin and eosin (H&E). Referring to
The exemplary embodiments of the present invention allow the use the inventive skin graft for hair regeneration and wound healing in one transplantation. Wound healing is accelerated by the presence of the hair follicles. The presence of dermal-epidermal interaction can accelerate the hair regeneration. The density, size and location of the hair follicles can be controlled in the skin grafts.
The skin graft and method of its making are also cost-effective, in that the average cost for hair transplantation under current practices (April 2012) can be in the range of from $2,500 to $9,000 for a 5×5 cm skin graft and individual hair implantation costs of $3 to $8. In contrast, the expected cost of transplanting a 5×5 cm skin graft of the present invention, which includes hair follicles grown in the graft, would be less than about $1,000.
It will be understood that the embodiment described herein is merely exemplary and that a person skilled in the art may make many variations and modifications thereto without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention described in the claims appended hereto.
The present application claims the benefit of U.S. Provisional Patent Application No. 61/478,983, filed on Apr. 26, 2011, which is incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61478983 | Apr 2011 | US |
