Silica-silk fibroin hybrid (bio)aerogels: two-step versus one-step hybridization

Abstract

In this study, silk fibroin as a highly promising naturally occurring biopolymer extracted from silkworm cocoon is applied to mechanically reinforce silica aerogels. To this aim, two different approaches for the incorporation of silk fibroin into the silica network are compared: (1) a one-step acid catalyzed and (2) a two-step acid-base catalyzed sol-gel reaction. The total organosilane concentration, as well as the SF to silane mass fractions, regulated the hybridization process to proceed either through a one-step or two-step sol-gel reaction. In both processes, for an efficient chemical mixing the silk fibroin components with the silane phase, a silane coupling agent, 5-(trimethoxysilyl) pentanoic acid (TMSPA), comprising carboxylic acid groups and a pentyl hydrocarbon chain has been used. For a low organosilane content (3.4 mmol) along with a high SF to silane mass ratio (15-30%), the gelation of the silane and silk fibroin phases took place in a one-pot/one-step process in the presence of an acid catalyst in an entirely aqueous system. In the two-step synthesis approach, which was applied for high initial silane contents (17 mmol), and low SF to silane mass ratios (1-4%), first, the gelation of the silk fibroin phase was triggered by addition of an acid catalyst followed by a more pronounced condensation of the silane catalyzed by the addition of the base. Both synthesis approaches led to materials with promising mechanical propertiesbeing 1) the one-step process resulting in gels with much better compressibility (up to 70% of strain), low density (0.17-0.22 g cm −3 ) and three orders of magnitude improvement in the Young's modulus (13.5 MPa) compared to that of the pristine silica aerogel but with rather high shrinkage (30-40%). The two-step process in principle could result in the hybrid aerogel with interesting bulk density (0.17-0.28 g cm −3 ) with lower shrinkage (10%), but the resultant aerogel was stiff and fragile. Also, both approaches led to a significant reduction in the time required to prepare strong hybrid aerogels compared to conventional hybrid polymer-silica aerogels with the utilization of an entirely aqueous synthesis approach for a wide range of applications. ;,: 1234567890();,:Highlights • Silk fibroin (SF) biopolymer is an interesting biopolymer for mechanical reinforcement of silica aerogel.• Two sustainable sol-gel based approaches are proposed for hybridization of silica with SF. •Hybrids obtained by the one step sol-gel synthesis approach demonstrate better mechanical performance.• Molar ratio of SF to organosilanes is the most determinant factor for resulting final properties.• Both synthesis approaches led to significant reduction in the time required for preparation of strong hybrid aerogels.

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

“…The stress−strain curves in Figure 5i−k display the typical deformation behavior of highly porous 3D scaffolds, i.e., linear elastic behavior at low strain followed by a successive pore collapse-related stress reduction at intermediate strains, and finally, a plastic yielding plateau with subsequent strain hardening at higher strain. We obtained a Young's modulus of ε = 283.5 kPa (for Silica-3-SF-CM-RGD-60) and ε = 31.98 kPa (for Silica-0.6-SF-CM-RGD-60) along the pore (freezing) direction (Figure 5i), which is significantly higher than the values for previously reported pristine silk fibroin (0.09 MPa) 27,28 and silica aerogels (5−20 kPa). 29 3.4.…”

Nacre-Mimetic, Mechanically Flexible, and Electrically Conductive Silk Fibroin-MXene Composite Foams as Piezoresistive Pressure Sensors

“…We used different mass fractions to identify an optimum ratio to achieve a balance of the The lowest bulk density was obtained for the sample X-SF-MXene5-GO (0.006 g cm −3 ), which is considerably lower than that of the previously developed SF-based aerogel composite of ∼0.1 g cm −3 . 14 The SEM images in Figure 2a−c demonstrate the long-range and hierarchically aligned nacre-mimetic brick-and-mortar or lamella-bridge network structures. In such nacre-mimetic structures, GO and MXene 2D nanosheet building blocks were well-dispersed and intertwined together with the crosslinked SF biopolymer and constituted the bridge structures (Figure 2d−f).…”

“…9,10 In this regard, lightweight foams based on sustainable precursors with cellular microarchitecture have demonstrated enormous potential for processing advanced structural and functional materials. 11 Our previous studies have shown the potential of novel silk fibroin (SF)-based aerogels, denoted AeroSF, 12 and their composite counterparts 13,14 for diverse advanced applications, such as thermal insulation, water/oil separation, and as scaffolds for bone repair. 15,16 SF, a biopolymer extracted from Bombyx mori silkworm cocoon, is a biocompatible and biodegradable fibrous protein.…”

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.…”