Page 231 - IJB-10-4

International Journal of Bioprinting N-PLN hydrogels for human skin modeling

Collagen represents the gold-standard biomaterial for the is a non-sulfated glycosaminoglycan, can also be viewed as
fabrication of skin surrogates since it is the main structural an alternative. It participates in several crucial functions
protein found in connective tissues, including the skin, and in vivo, such as tissue hydrodynamics and regulation in
4
the most abundant protein in the extracellular matrix. wound healing processes, generating networks that are
5,6
Usually, collagen is derived from raw materials such as bovine suitable for cell growth and migration, thereby promoting
and porcine tissues, possessing good flexibility, as well as angiogenesis. 17,18 For in vitro applications, synthetic
7
thermal and enzymatic stability. Different collagen-based polymers are regarded as excellent alternatives due to
models have been developed as in vitro systems, including a their non-degradability, reproducibility, and ability to
model for irritation testing. In vivo clinical skin equivalents endure long-term studies, as in the case of polyethylene
8
built with collagen have also garnered considerable interest. glycol (PEG) and polyvinyl alcohol (PVA). However, some
An example is FortiCell Bioscience, designed by Orcel®, limitations also occur when they are used alone, such as
which integrates human epidermal keratinocytes and insufficient elasticity. Thus, they could also be blended with
dermal fibroblasts cultured on a type I bovine collagen natural polymers to develop new materials with enhanced
19
substrate. This innovative formulation is specifically properties, specifically for applications in wound healing.
tailored to address the complexities of wound healing in Pullulan (PLN), a water-soluble microbial polysaccharide,
limb afflictions, notably skin ulcers and diabetic conditions. is an emerging biopolymer with a set of advantageous
However, it is not exempt from drawbacks. It has been properties: it is non-immunogenic, non-toxic, non-
observed that natural collagen is fraught with a perennial carcinogenic, non-mutagenic, and hemocompatible. 20,21 It
problem of batch-to-batch variability, which is not easy to is also a water-soluble, environmentally friendly polymer.
address. It also may produce pathogenic adverse reactions, PLN can be crosslinked forming hydrogels with excellent
evidenced by the side effects of bovine collagen implants mechanical properties such as tensile strength and
identified in a small percentage of treated patients. In modulus, which are attractive for several biomedical and
9,10
addition, collagen scaffolds tend to collapse under traction engineering applications, including the production of skin
forces, especially when the cells are embedded, thus surrogates. To this end, it has been employed together with
compromising the mechanical stability of the constructs. gelatin to create dermal substitutes both for in vitro and in
11
22
While culturing, fibroblasts may contract collagen-based vivo testings.
hydrogels, causing the loss of close connection between the To produce tissue-engineered constructs, one
epidermal layer and the corresponding cell culture support, popular approach is the use of three-dimensional (3D)
leading to the loss of skin barrier function. Hence, some extrusion bioprinting techniques. However, despite the
12
23
reinforcements are necessary to improve the mechanical uncontested usefulness, obtaining bioinks with shear
properties and to reinforce the gel, as reported in a study by thinning properties and addressing the nozzle clogging
11
Bacakova et al. where a nanofibrous poly-L-lactide (PLLA) issues triggered by bioinks still impose some limitations.
24
membrane was used. As an alternative, light-based systems have recently gained
In this context, artificial, recombinant, and synthetic popularity for the fabrication of tissue constructs, offering
collagens are becoming new options. Also, alternative improved spatial resolution, pattern fidelity, and increased
13
biomaterials are being considered. Owing to their fabrication speed. 25,26 These systems involve a light source,
hydrophilic nature and variable degree of swelling, typically ultraviolet (UV) or visible light, and low-energy
hydrogels has a better capability in mimicking natural dosages that minimize cell toxicity. A pre-gel solution
soft tissue than any other types of polymeric biomaterials, containing a photoinitiator and eventually a cell suspension
proving good biocompatibility, and thus, resulting in is then crosslinked upon illumination. By including a light-
attractive scaffolds for cell encapsulation. Gelatin, patterning feature, modulating the printing parameters,
14
which is a natural polymer obtained after hydrolysis and and selecting the proper photopolymerizable materials,
denaturation of collagen, has been used as wound dressing 3D cell-laden scaffolds with high cell viability can
27
mostly in the form of gelatin methacrylate (GelMA), which be produced.
allows light-based chemical crosslinking of the chains, In this study, a novel photocrosslinkable bioink suitable
adding further mechanical stability than just physical for the engineering of human skin constructs is presented.
15
crosslinking. Methacrylate kappa-carrageenan (kCA) This bioink capitalizes upon the excellent properties of
hydrogels, based on kCA, a natural linear water-soluble PLN, which was further functionalized with norbornene
polysaccharide, have also been employed for this purpose groups to form hydrogels upon thiol-norbornene
since kCA resembles natural glycosaminoglycan structure, photopolymerization. Upon visible light irradiation, in
19
supplying physical and chemical properties similar to the presence of a photoinitiator, PLN hydrogels were then
those in native human skin Hyaluronic acid (HA), which formed through a thiol-ene click reaction. Compared to
16
.
Volume 10 Issue 4 (2024) 223 doi: 10.36922/ijb.3395