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Bioprinting Gelatin-Recombinant Type III Collagen Hydrogel for Wound Healing
being the most common treatment for repairing severe to delineate the role of each collagen isotype. We reason
skin defects, autologous skin transplantation has many that a recombinant, pure form of type III collagen will
disadvantages [4,5] . Skin from the patient’s unburned area, be superior for skin regeneration [20] . This then inspired
including the dermis and epidermis, can be used to repair the use of recombinant technology and genetic tools to
burned skin areas. For severe burns larger than 60% of produce type III collagen ex vivo [21-24] . The recombinant
total body surface area, multiple harvests from the donor human type III collagen (rColIII) has been used to treat
site after healing are required. However, this procedure full-thickness skin defects in pigs [25] . Since rColIII is
may increase the risk of infection and cause scarring highly soluble, to form a hydrogel for wound covering,
and pigmentation changes of the donor site. In addition, we sought to use gelatin, the hydrolysate of collagen,
patients need to endure for a long time to wait for the new to provide a framework of crosslinking. Gelatin has
skin to re-epithelize at the donor site. excellent biocompatibility, low immunogenicity,
At present, researchers are developing new low toxicity, and high biodegradability. Therefore,
biomaterials that can be used to replace skin for the gelatin is widely used in hemostatic wound dressings,
short term or permanently; these skin substitutes are vascular stents, drug carriers, tissue engineering stents,
collectively called “artificial skin.” To promote wound coating materials, etc. [26] . In this study, we synthesized
healing, the skin substitute must: (a) Adhere to the gelatin-rColIII hydrogel (GRH) through enzymatic
substrate, (b) has sufficient elasticity and the ability to crosslinking and reported the therapeutic efficacy of the
withstand deformation, (c) allow water to evaporate at all-protein hydrogel in wound healing in a rat model of
a typical rate similar to the stratum corneum, (d) has a skin damage.
microbial barrier, (e) promotes hemostasis and accelerates On the other hand, three-dimensional (3D)
coagulation, (f) is easy to use, (g) be used immediately bioprinting is a manufacturing technology that can
after injury, and (h) causes a “regeneration-like” reaction construct biomaterial scaffolds in a range of biomedical
in the wound bed without causing inflammation or applications. 3D bioprinting of biomaterials can realize
foreign bodies or non-self-immunologic reaction [6-8] . the precise assembly of the polymeric biomacromolecules,
A successful example is given by Burke et al. who which provides a spatial framework for the growth
pioneered classical experiments of the development of of cell cultures and tissue engineering. Biomaterials
dermal equivalents for biological replacement [6-8] . Briefly, amenable to 3D bioprinting should meet the following
starting from glutaraldehyde-cross-linked collagen, requirements [27-31] : (a) Excellent biocompatibility; (b)
glycosaminoglycan was mixed to stimulate the synthesis suitable biodegradability to allow substitution by the
of normal connective tissue matrix in the dermis without extracellular matrix and natural tissues; (c) suitable pore
inflammation, foreign body reaction, or immunologic size and porosity to facilitate the exchange of oxygen,
reaction. Years of work resulted in a product called nutrients, and metabolites; (d) mechanical properties
Integra , which contains collagen extracted from similar to the natural tissues; (e) low toxicity and
®
cowhide and chondroitin 6-sulfate extracted from shark immunogenicity; (f) strong plasticity; and (g) ease of
cartilage to form a collagen-chondroitin-6-sulfate fiber. processing. 3D bioprinting, in general, is achieved through
This product was approved the United States Food and several strategies including material extrusion [32,33] ,
Drug Administration for treating burn patients. material jetting [34,35] , and vat polymerization [36,37] . Among
Notwithstanding the success Integra achieved the three methods, extrusion-based 3D bioprinting
®
over the years, there is still much room to improve. strategies are now the most widely used for producing 3D
Natural collagen purified from animal sources faces tissue constructs. Here, we demonstrated that enzymatic
several limitations in clinical use [9-12] . For example, the crosslinking solidifies the GRH into the ink of 3D
quality control of collagen products from animal sources extrusion bioprinting . The 3D GRH scaffold supports
[38]
is often a challenge because of the heterogeneity of the the growth of mouse embryonic fibroblasts.
natural collagen and the risk of pathogen contamination.
The main ingredients of adult skin tissue are type I and 2. Materials and methods
type III collagen. In contrast, the proportion of type III 2.1. Materials and instruments
collagen in fetal skin is significantly higher than that
of adults [13,14] . It has been reported that the decrease of rColIII (purity >90%) was kindly provided by Jiangsu
type III collagen is associated with the aging of the skin, Chuangjian Medical Technology Co., Ltd. Dulbecco’s
leading to the lack of elasticity and renewability [15-18] . modified Eagle’s medium (DMEM) penicillin-
Supplementing the loss of type III collagen will reduce streptomycin solution, fetal bovine serum (FBS),
scar hyperplasia and promote skin regeneration [19] . In trypsin-EDTA, and gelatin were obtained from Sigma-
this regard, collagens from a natural animal source are Aldrich (USA). Aminoamidase was purchased from
often a mixture of different isotypes, making it difficult BOMEI Company (China). Cell counting kit-8 (CCK-8)

14 International Journal of Bioprinting (2022)–Volume 8, Issue 2