Page 468 - IJB-9-5

International Journal of Bioprinting 3D printed hydrogel for infected wound healing via PDT

1. Introduction today. It has the advantage of simplicity of operation, but
cell viability is reduced . For this experiment, extrusion-
[18]
Skin is the largest organ of the human body and is based bioprinting was chosen because the hydrogel
vulnerable to various types of traumas, such as wounds. dressings are cell-free, and the structure does not require
Wound healing has been an ongoing topic of research and high-resolution printing. Hydrogels can be deposited
[1]
an area of concern in the medical field . When skin trauma layer by layer to fabricate artificial skin tissue with porous
occurs, the skin’s protective barrier is damaged, leaving structures customized through computer-aided design [19,20] .
the wound site vulnerable to invasion by microorganisms Moreover, various photo-crosslinked polymers have been
[2]
in the environment, which can lead to severe infection . widely incorporated as a material for 3D-bioprinted tissue-
Moreover, bacteria-associated wound infection prevents engineered scaffolds due to their mild reaction conditions,
wound healing and may be life-threatening [3,4] . Therefore, highly tunable mechanical and structural properties,
wound management in the early stages is essential for printability, biodegradability, and biocompatibility [19,21] .
preventing wound infection and promoting wound Natural polymers, which can be used as biological inks,
healing. Currently, wound dressings that contain such as alginate, gelatin, and SF, have recently attracted
antiseptics or antibiotics are commonly used to prevent wide attention [22-26] .
and treat wound infections. However, these dressings have
significant limitations, including long-term treatment, Silk fibroin (SF) extracted from Bombyx mori, which
inefficacy, and high cost [5-7] . Long-term use of antibiotics has good biocompatibility, adjustable biodegradability,
can lead to bacterial resistance, which is a major clinical and mechanical properties, has been used in various
problem [8,9] . Therefore, it is necessary to develop a new type biomedical applications and was approved by the U.S. Food
of non-antibiotic multifunctional wound dressing with and Drug Administration (FDA) for use in drug delivery
antibacterial properties that can reduce the risk of wound and surgical suture applications [27,28] . SF can be prepared
infection caused by bacteria and promote wound healing. into scaffolds, films, hydrogels, etc., to meet different
clinical needs. It was reported that ultrasound or chemical
Hydrogels have been widely used in skin, fat, and vessel crosslinkers could induce the formation of SF hydrogels .
[29]
tissue engineering due to their advantages including good However, the addition of ultrasound or toxic chemical
hydrophilicity and biocompatibility . Hydrogels have a crosslinkers is not conducive to the clinical promotion of
[10]
similar 3D porous structure to the extracellular matrix, SF hydrogels. Photo-crosslinking technology can be used
making them one of the most competitive candidates for to prepare SF hydrogels in a controllable manner without
wound dressings [11-13] . Meanwhile, hydrogels can maintain chemical grafting or the introduction of toxic chemical
the high moisture level of the wound bed; therefore, crosslinking agents . Previous studies have shown that
[30]
hydrogels can provide an optimal 3D environment for by using riboflavin (RPS) and sodium persulfate (SPS) as
cells to promote soft tissue regeneration . Furthermore, a photoinitiator under blue light irradiation, the tyrosine
[14]
hydrogels can be a platform for loading cells, antimicrobial (Tyr) on the molecular chain of SF can be combined to
agents, growth factors, and unique complementary and form a stable tyrosine–tyrosine (Tyr–Tyr) bond .
[30]
biological macromolecules .
[15]
Moreover, the SF hydrogel may have difficulty meeting
3D bioprinting is a promising technology in the the needs of tissue regeneration due to its relatively dense
manufacture of hydrogels, offering a high degree of internal pores and slow degradation . The β-sheet
[29]
flexibility and reproducibility. The three most commonly formation in SF hydrogels could cause changes to the
used bioprinting techniques according to the American internal structure, compressing the internal pores and
Society for Testing and Materials are jetting-based, water content. Therefore, it is necessary to introduce other
extrusion-based, and vat photopolymerization-based components to control the conformational changes of SF.
bioprinting processes. The inkjet technique offers the The introduction of other polymers can reduce the contact
advantages of low cost and fast printing speed but has the between SF molecules, thereby preventing the formation of
limitations of low accuracy and need for low-viscosity the β-sheet as well as regulating the mechanical properties
bioinks . The vat photopolymerization technique offers for soft tissue engineering . Gelatin, a natural polymer
[31]
[16]
higher resolution and accuracy than other bioprinting with high biocompatibility and a cell attachment sequence
techniques. The high-resolution printing facilitates that is similar to the extracellular matrix, has excellent
the fabrication of bionic mircoorganisms. However, its performance in cell fixation and proliferation . It contains
[32]
complex design, limited choice of biocompatible materials, about 1% of Tyr residues in the amino acid sequence of
and cumbersome operation hinder its wide application in the gelatin strands, which can be crosslinked with the SF
the field of tissue engineering . Extrusion bioprinting molecular chain through Tyr–Tyr bonding without chemical
[17]
is the most common bioprinting technology available modifications. Adding gelatin as a spacer molecule to the

Volume 9 Issue 5 (2023) 460 https://doi.org/10.18063/ijb.773