Page 77 - IJB-9-5

International Journal of Bioprinting Biocompatible BSA-GMA and TPP of 3D hydrogels with free radical type I photoinitiator

system and the optimized functional biomaterials are or disulfide bond crosslinking [40] have been reported to
crucial for light-based 3D printing. To better meet the modify BSA. However, hydrogels prepared by thermal
different needs of scale and precision of synthetic 3D gelation have poor mechanical properties and are readily
scaffolds, various microfabrication techniques have soluble in biological fluids. The chemical crosslinking
been developed to construct 3D hydrogels, such as techniques have significant drawbacks in preparing
stereolithography , soft lithography [6,7] , digital light biomaterials with tailored mechanical properties to match
[5]
projection , electrospinning [9,10] , and bioprinting [11,12] . different medical applications. Two-photon polymerized
[8]
However, it is still a challenge to prepare arbitrarily protein hydrogels are widely used for tissue engineering
shaped 3D structures with high resolution and high and drug delivery because of their excellent mechanical
efficiency. Two-photon polymerization (TPP) as a properties and precisely controlled morphology [18,20,45] .
femtosecond laser direct writing technique allows the TPP usually requires the use of photoinitiators to induce
rapid polymerization of transparent polymer solutions the crosslinking of proteins, which are classified as free
into arbitrary, high-resolution 3D microstructures, radical type I and free radical type II initiators [46-49] .
which has been widely used in micro and nano The crosslinking of dye molecules (free radical type II
photonics [13,14] , microfluidics [15] , tissue engineering [16-18] , initiators) with proteins involves two photooxidation
and drug delivery [19,20] . mechanisms. The first one is to excite the dye molecule
Hydrogel, a kind of advanced material that mimics the to extract hydrogen from the protein molecule to induce
extracellular matrix (ECM) in vivo, has been extensively protein crosslinking. This mechanism facilitates the
investigated for biomedical applications due to its crosslinking of proteins containing ketones, phenols,
hydrophilicity and potential biocompatibility [21-25] . In the amines, or hydroquinones amino acid residues. The
study of hydrogel scaffold materials, natural polymeric second is that the singlet oxygen continues to react with
materials (collagen [26,27] , sodium alginate [SA] , oxidizable amino acid residues to produce an electron-
[28]
chitosan , hyaluronic acid , bovine serum albumin deficient protein that may react with an amino acid
[30]
[29]
[50]
[BSA], etc.) have attracted much attention due to their residue of another protein to form a covalent bond .
higher biocompatibility, better flexibility, low toxicity, Protein crosslinking is usually favored for tryptophan,
and greater biodegradability compared to polymeric tyrosine, or histidine residues as well as amino acid
hydrogels [31-33] . Among them, BSA is a monomeric residues containing olefins, diolefins, aromatics, and
protein with 583 amino acids and a molecular weight heterocyclic groups. Therefore, pure BSA can be two-
of about 66 kDa, which is highly abundant in plasma at photon polymerized using a type II photoinitiator like
a concentration of about 30–50 mg mL and is a non- Bengal Red, but it consumes a large amount of amino
-1
[51]
synthetic and easily available biocompatible material. acid groups on BSA .
Furthermore, BSA is a promising scaffold for tissue In this study, a series of BSA molecules modified
engineering, regenerative medicine, and drug delivery by glycidyl methacrylate (GMA) were synthesized by
systems because of its stability, responsiveness to pH and grafting methacrylate groups to the amine-containing
temperature, and ability to gel at low concentrations [34-36] . side groups of BSA, which enables the TPP capability using
Albumin-based biomaterials can control the delivery of free radical type I photoinitiators. Generally, GMA opens
therapeutic drugs and act as functional biological scaffolds the ring via an epoxide mechanism, and the reaction is
in drug delivery applications [36,37] . Albumin is also used stable without acidic by-products. The BSA modified by
to treat blood loss, burns, and shock due to its clinically GMA (BSA-GMA) can interact with free radical type I
established biocompatibility profile for therapeutic initiators other than dyes to crosslink without consuming
applications [38,39] . Numerous studies have demonstrated amino acid groups, and the TPP ability of BSA-GMA
that negatively charged groups such as carboxyl, hydroxyl, hydrogels can also be tailored by changing the degree
and sulfonic acid groups on the surface of BSA can and location of methacrylation. We have evaluated the
induce the chondrogenic differentiation of bone marrow degree of methacrylation on BSA modified by various
mesenchymal stem cells (BMSCs), and promote the amounts of GMA, as well as the TPP performance and
adhesion of chondrocytes on the pore surface and the 3D printing capabilities of BSA-GMA with different
formation of new cartilage [40-42] .
concentrations and degrees of methacrylation.
However, most protein hydrogels are usually not strong Furthermore, we have demonstrated that the as-prepared
enough to be used as scaffolds because the structure of BSA-GMA hydrogels have autofluorescence, pH-
the protein is mainly maintained by primary-level amide responsive characteristics, and good biocompatibility.
bonds and higher-level non-covalent bonds. Therefore, The proposed synthesis strategy and the protocol for
methods including thermal gelation , glutaraldehyde , TPP of 3D bioinspired microstructures would provide
[43]
[44]
Volume 9 Issue 5 (2023) 69 https://doi.org/10.18063/ijb.752