3D Printing of Antibacterial, Biocompatible, and Biomimetic Hybrid Aerogel-Based Scaffolds with Hierarchical Porosities via Integrating Antibacterial Peptide-Modified Silk Fibroin with Silica Nanostructure

Abstract

Scaffold-mediated tissue engineering has become a golden solution for the regeneration of damaged bone tissues that lack self-regeneration capability. A successful scaffold in bone tissue engineering comprises a multitude of suitable biological, microarchitectural, and mechanical properties acting as different signaling cues for the cells to mediate the new tissue formation. Therefore, careful design of bioactive scaffold macro-and microstructures in multiple length scales and biophysical properties fulfilling the tissue repair demands are necessary yet challenging to achieve. Herein, we have developed an antibacterial and biocompatible silica-silk fibroin (SF) gel-based ink through novel yet simple chemical approaches of sol−gel and self-assembly followed by processing the obtained gels as three-dimensional (3D) hybrid aerogel-based scaffolds exploiting the advanced materials design approaches of micro-extrusion-based 3D printing, and directional freeze-casting/drying approaches. As the main constituent of the hybrid biocompatible scaffold of this study, we used the SF extracted from Bombyx mori silkworm cocoon. However, to increase the cell responsivity and bactericidal efficiency of the final scaffold, thiol-ended antimicrobial and cell adhesive peptide sequence (SH-CM-RGD) was conjugated to silica-SF hybrid gels via covalent attachment using a spacer molecule through either preprint (prior to sol−gel) or during the post-printing steps on the previously printed silica-SF gel. In the next step, the hybrid Silica-SF-CM-RGD hydrogel ink was 3D-printed into the construct with interconnected porous structure with hierarchically organized porosity and a combination of several promising properties. Namely, due to the covalent linkage of the antibacterial peptide to the SF, the scaffold shows potent bactericidal efficiency toward Gram-positive and Gram-negative bacteria. Moreover, nanostructured silica components in the 3D-printed composites could intertwine with SF-CM-RGD to support the mechanical properties in the final scaffold and the final osteoconductivity of the scaffold. This study supports the promising properties of 3D-printed silica-SF-based hybrid aerogels constructs for repairing bone defect.

Fabrication of Antibacterial, Osteo‐Inductor 3D Printed Aerogel‐Based Scaffolds by Incorporation of Drug Laden Hollow Mesoporous Silica Microparticles into the Self‐Assembled Silk Fibroin Biopolymer

“…However, the formation of later bonds has been thoroughly investigated in our previous works for the composite of silica and SF through in situ sol-gel reaction and self-assembly process. [4,7,[26][27][28] A major part of gel printing is devoted to controlling the gel viscosity and optimizing its rheological performance to obtain the best printability window for the as-synthesized gels. In extrusionbased 3D printing, printability is generally defined as the "suitable" extrudability, struts' formation, and shape fidelity which all indicate the degree of dimensional preciseness of the printed ob-ject in comparison to the computer-aided design model one.…”

“…We estimated the printability index (Pr, %) of printed construct near to 100% for the best printed construct. [ 7 ] The viscosity of the gel necessary for printing was carefully optimized by controlling the gelation time to obtain a continuous gel flow upon extrusion. Thus, as it is evident from Figure 3b, the as‐synthesized SF‐MA‐15, 30‐HMSC‐1, ‐2 gels prepared by a higher concentration of SF‐MA (4%) immediately after the onset of gelation were not printable as the gel viscosity was still not sufficient to result in a construct with good shape fidelity.…”

“…However, in its peptide sequence, SF still lacks the arginine (Arg)-glycine (Gly)-aspartic acid (Asp) (RGD) integrin, a peptide motif responsible for the cell adhesion to the ECM. [7,13] It has been shown that the incorporation of bioactive functional organic and inorganic additives, such as PVA, [14] chitosan, [15] hydroxyapatite, [16] TiO 2 , [17] bioactive glass, [18] or other ceramics [4,7] can compensate for the RGD deficiency in SF, evidenced by the proliferation of osteoblasts, chondrocytes, or bone marrow-derived mesenchymal stem cells (MSCs).…”

“…In our previous work, we chemically modified SF with a short peptide sequence of RGD‐antibacterial peptide (AMP) and synthesized a 3D printable gel by reacting organosilanes with sol‐gel processable silane‐modified SF‐RGD‐AMP precursors by implementing in situ sol‐gel synthesis and self‐assembly strategies, carefully controlling the synthetic parameters. [ 7 ] The final 3D printed scaffolds were equipped with cellular responsivity, mechanical strength, and multi‐scale porosity suitable for cell ingrowth, vascularization, and anti‐infectivity. In the same line, we have developed functional biomimetic printed aerogel‐based scaffolds with antibacterial activity and encourage osteogenic induction using SF biopolymer, chemically bonded to the micron‐sized hollow mesoporous silica capsules (HMSC) during the post‐printing photo‐crosslinking of the as‐printed construct.…”

Scaffolds in the microbial resistant era: Fabrication, materials, properties and tissue engineering applications

“…Electrostatic deposition of cationic oligopeptides in a PCL/CS nanofiber scaffold inhibited S. aureus while promoting osteoblast adhesion, spread, and proliferation [ 132 ]. Another strategy consists of either incorporating antibacterial peptides into the scaffolds or coating the scaffolds with them [ 137 , 140 , 141 ]. A mineralized collagen scaffold containing PLGA microspheres loaded with two antibacterial synthetic peptides was found to promote osteogenic capacity and antibacterial properties [ 137 ].…”