Table 2.

A summary of bioengineered constructs used for skin appendage regeneration. Abbreviations: 6‐bromoindirubin‐3′‐oxime (BIO); basic fibroblast growth factor (bFGF); bone morphogenetic proteins (BMP); dermal papilla (DP); epidermal growth factor (EGF); extracellular matrix (ECM); fibroblasts (Fbs); green fluorescent protein (GFP); hair follicles (HFs); human pluripotent stem cells (hPSCs); human umbilical vein endothelial cells (HUVECs); keratinocytes (Kcs); mesenchymal stem cells (MSCs); not reported (NR); poly(ethylene glycol) (PEG); poly(lactic‐co‐glycolic acid) (PLGA); Rho‐associated coiled‐coil kinase (ROCK); severe combined immunodeficient (SCID); skin‐derived precursors (SKPs); sweat glands (SGs); 3D; transforming growth factor (TGF); vascular endothelial growth factor (VEGF)

Type and source of cells/tissues	Culturing units	Matrix used for in vitro/ vivo models	Morphogens/ biochemical factors	Study model	Regenerative outcome	Refs.
Human hair DP cells	3D culture	PLGA‐PEG‐PLGA hydrogels	Icariin	In vitro; culture of the DP cells with the hydrogels In vivo; direct injection of the hydrogels onto the surface of skin full‐thickness wounds in the back of male C57BL/6 mice	HFs	[78]
DP cells from human scalps Kcs from human middle follicle outer root sheath	Cell aggregates from a coculture system	Follicular skin composites from ICR mice, including the dermis and epidermis, with cell aggregates being between them	DP activation culture medium containing recombinant BMP2, bFGF, and BIO	In vivo; subcutaneous engraftment of footpad skin composites into BALB/cnu/nu nude mice	Hair	[60]
Human DP cells and Kcs	Cell aggregates	Interfacial polyelectrolyte complexation fiber hydrogel	NR	In vivo; implantation of the cell‐laden scaffolds into SCID mice	HFs	[79]
DP cells from human scalps Neonatal dermal Kcs from human foreskin	Cell spheroids with and without cellular reprogramming of Lef‐1 and Fli‐1	Human skin constructs including dermal compartment (fb‐populated collagen type I matrix) and DP cells and Kcs on its top	NR	In vivo; engraftment of human skin constructs onto nude mice In vivo; engraftment of human skin constructs encapsulating GFP‐tagged HUVECs in the dermal compartment to nude mice	HFs Vascular network	[59]
DP cells from human scalps Hair germinal matrix cells	3D spheroids	Matrigel	NR	In vitro; seeding germinal matrix cells and DP spheroids onto Matrigel‐coated plates	HFs	[63]
Epidermal cells (epidermal SCs) from adult human foreskin Dermal cells (SKPs) from adult human foreskin	SKP spheroids	Matrigel	BMP4 for SKPs treatment	In vivo; implantation of Matrigel containing epidermal and culture‐expanded dermal cells into BALB/c nu/nu mice	HFs	[52]
DP cells from human adult scalps	Neopapillae spheroids from expanded and self‐aggregating DP cells	Reconstructed human skin including the epidermis grown on a dermal fb‐populated hydrogel	NR	In vitro; culturing reconstructed human skin with neopapillae spheroids at the air‐liquid interface	HFs	[80]
hPSC line	3D organoids	Matrigel	BMP4, TGF‐β inhibitor; bFGF, and BMP inhibitor	In vivo; grafting pigmented or albino hair‐bearing skin organoids after maturation onto immunodeficient nude mice	HFs Sebaceous glands Stratified epidermis Fat‐rich dermis	[76d]
Mesenchymal and epithelial cells from mouse embryos	HF‐germ‐like aggregates from 3D coculture	HF‐germ‐like grafts containing printed collagen microgel beads	NR	In vivo; injection of the grafts into a pocket on the dorsal skin of ICR‐nude mice Transplantation of the grafts into a shallow stan wound on the skin surface of ICR‐nude mice	HFs	[81]
DP cells from vibrissa pads of C57BL/6 mice	3D spheroid culture	Keratin hydrogel	Exosomes or secretome (high level of miR‐218‐5p) from DP spheroids	In vivo; subcutaneous injection of cells‐hydrogel into C57BL/6 mice	HFs	[82]
SKPs from neonatal dorsal skin from C57BL/6 or C57BL/GFP mice & mouse epidermal cells	3D coculture	Self‐assembling peptide hydrogel (RADA‐PRG) or Matrigel	NR	In vivo; implantation of cells‐hydrogel into BALB/c nu/nu mice	HFs	[76f]
DP cells from Wistar rat vibrissa & newborn C57BL/6 epidermal cells	Spheroidal microtissues	Poly(ethylene‐co‐vinyl alcohol) membranes	NR	In vivo; injection of microtissues‐epidermal cells into nude mice	HFs Sebaceous glands	[83]
DP and epidermal cells from neonatal mice	3D spheres (spheroids) and single cells	Hydrogel (Extracel) containing crosslinked gelatin and hyaluronic acid	NR	In vivo; transplantation of epidermal cells, freshly isolated DP cells, and cells released from hydrogels in nude mice	HFs	[84]
Epithelial and DP cells from adult mouse vibrissa and embryonic skin pelage	3D organ‐germ culture	Collagen gel	NR	In vivo; transplantation of bioengineered murine HF germ to mice	HFs Sebaceous glands	[77d]
DP cells from Wistar rat vibrissae and human scalp Kcs from newborn C57BL/6 mice	Spheroids	Poly(vinyl alcohol) substratum	NR	In vivo; injection of human and rat DP spheroids and Kcs into nude mice	Hair HFs	[85]
DP cells from the vibrissae of neonatal C57BL/6 mice Epidermal Kcs from C57BL/6 mouse skin	3D preculture system	Collagen‐chitosan scaffold	Supernatant of Wnt1a‐expressing bone marrow MSCs	In vivo; transplantation of the scaffold cells in nude mice	HFs	[77a]
DP cells from C57BL/6J mice vibrissae Epidermal cells from newborn C57BL/6 mice	Spheroids	Gelatin/alginate nanogel	NR	In vivo; implantation of DP spheroids with epidermal cells onto nude mice	HFs	[86]
DP cells from human scalp epidermal cells from newborn C57BL/6	Spheroids	Decellularized human placenta ECM hydrogel	NR	In vivo; subcutaneous injection of DP spheroids mixed with epidermal cells into nude mice	HFs	[87]
DP and epidermal cells from C57BL/6 mouse scalp	Multicellular spheroids	Chitosan/polyvinyl alcohol nanofiber sponge	NR	In vivo; injection of DP microtissues and epidermal cells into nude mice	HFs	[88]
Epidermal (stem/progenitor) cells from C57BL/6J mice Neonatal dermal fbs from C57BL/6J mice	3C cells (3D cell clusters)	Matrigel	ROCK inhibitor, FGF2, and VEGF‐A	In vivo; injecting a mixture of 3C cells in Matrigel with neonatal dermal fbs into a full‐thickness wound onto BALB/c nude mice	HFs	[76a]
Epidermal cells (epidermal stem cells) from neonatal mice Dermal cells (SKPs) from neonatal mice	SKP spheroids	Matrigel	BMP4 for SKPs treatment	In vivo; implantation of Matrigel containing epidermal and culture‐expanded dermal cells onto BALB/c nu/nu mice	Hair HFs	[52]
Epidermal cells (epidermal stem cells) from neonatal mice or adult human foreskin Dermal cells (SKPs) from neonatal mice Neonatal mouse dermal Fbs	SKP spheroids	Matrigel	NR	In vitro; culturing of epidermal cells with a PPARγ agonist and a Wnt signaling inhibitor In vivo; implantation of Matrigel containing epidermal cells with dermal cells (SKPs) or dermal fbs onto BALB/c nu/nu mice	Sebocytes Sebaceous glands with or without HFs	[52]
Single Blimp1+ cells (sebaceous gland progenitor) from B6.Cg‐Tg(Prdm1‐EYFP)1Mnz/J mice	3D organoids	Matrigel	EGF, FGF2, BMP inhibitor, and c‐Myc inhibitor	In vitro; culturing of the sebaceous gland organoids	Sebaceous glands	[76c]
SG cells from human skin MSCs from human bone marrow	Cell suspension (coculture)	NR NR Scaffold: a sheet of decellularized allogeneic dermal matrix	NR	In vitro; Coculture of heat‐shocked SG cells with MSCs In vivo; injection of MSCs transdifferentiated SG cells onto BALB/c nude mice Clinical trial; even spread of transdifferentiated MSCs on the excision wound covered with scaffold and granulated autologous skin grafts	SG cells SGs	[34]
SG cells, Kcs, & Fbs from human dorsal skin	Organotypic coculture model	Engineered skin construct: human Kcs on top of a Fbs‐embedded collagen‐based matrix	EGF‐containing gelatin microspheres	In vitro; delivery of SG cells‐microspheres complex into the engineered skin construct In vivo; transplantation of the engineered skin construct onto athymic mice	SGs	[77b]
SG cells from human skin	3D culture	Matrigel	NR	In vitro; culture of SG cells in Matrigel	SGs	[76, 89]
Epithelial stem/progenitor cells from C57/B16 mouse dorsal skin	3D ECM mimics	Cell‐laden composite hydrogel (bioprinted gelatin/ alginate hydrogel)	EGF, BMP4, and dermal components (dermal homogenates from wild‐type C57/B16 mice plantar skin)	In vivo; transplantation of 3D‐ECM mimics into wild‐type C57/B16 mice	SGs	[90]
MSCs from Sprague‐Dawley rat bone marrow	3D culture	Gene‐activated scaffold based on collagen and chitosan	Plasmid DNA encoding rat EGF	In vitro; seeding MSCs into the gene‐activated scaffold In vivo; transplantation of a bilayer dermal equivalent consisting of the MSCs/gene‐activated scaffold and silicone membranes in rats	SGs	[77c]
SG cells from mouse thenar skin	3D organoids	Matrigel	NR	In vitro; seeding of SG single cells at the ALI culture condition In vivo; transplantation of SG organoids in Matrigel® into C57BL/6 mice	Epidermis SGs Re‐epidermatization	[76b]
Mammary progenitor cells from C57BL/6 mice	3D culture	Bioprinted gelatin‐alginate hydrogels	SG‐ECM proteins	In vitro; culturing a mixture of suspended cells and mouse SG‐ECM proteins into the composite hydrogels	SGs	[91]