High-strength and self-recoverable silk fibroin cryogels with anisotropic swelling and mechanical properties

Yetiskin, Berkant; Okay, Oğuz

doi:10.1016/j.ijbiomac.2018.09.087

Cited by 51 publications

(42 citation statements)

References 43 publications

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“…In particular, the poor extensibility of RSF hydrogels remains an issue to hinder their wide use as structural materials. A number of mechanisms for toughening RSF hydrogels have been proposed, including enhancing hydrogen bonding, introducing chemical crosslinking, restricting the growth of β‐sheet domains, low temperature crosslinking/cryogelation, and double‐network formation . For instance, Shao et al presented a facile way to construct strong RSF hydrogels simply by adding sodium dodecyl sulfate (SDS) into high molecular weight RSF solutions.…”

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confidence: 99%

Highly Stretchable and Tough Physical Silk Fibroin–Based Double Network Hydrogels

Zhao

Guan

2019

Macromol. Rapid Commun.

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a facile way to construct strong RSF hydrogels simply by adding sodium dodecyl sulfate (SDS) into high molecular weight RSF solutions. The resulting hydrogels demonstrated high tensile strength of ≈0.74 MPa and fair extensibility of 140%. [6] Shao et al. also found that ionic liquid (IL)/water mixtures could generate RSF-based gels, whose tensile strength and breaking elongation reached up to 0.4 MPa and 147%, respectively. [11] Okay et al. reported a novel strategy to design mechanically robust and stretchable silk fibroin/hyaluronic acid hydrogels with chemical cross-links and physical cross-links (β-sheet domains). [7] The hybrid hydrogels exhibited a high extensibility up to around 400% and tensile strength of 65 kPa after equilibrium swelling. Okay also described a directional freezing/cryogelation method to produce high-strength silk fibroin cryogels with a degree of mechanical anisotropy. The compressive modulus of cryogels formed at 16.7 wt% RSF concentration was 45 MPa, but the tensile properties were not shown. [12] Consequently, achieving highly stretchable RSF hydrogels for wide-range applications [13] is still in its infancy.An alternative strategy to prepare strong and tough hydrogels is the double network (DN) hydrogel, which introduces a flexible and stretchable second network. These DN hydrogels demonstrated high fracture strength (0.1-10 MPa) and high water content (60-90%). [14][15][16][17][18][19] A series of DN gels using biomacromolecules (agar, cellulose) had been developed. [20,21] Chen et al. developed RSF-based DN hydrogels via introducing a hydrophobically associated gel of polyacrylamide (HPAAm) as the second network. [10] The DN hydrogels were conveniently synthesized by the one-pot method coupled with photo-polymerization, and the resultant RSF/HPAAm DN gels showed a tensile strength of ≈1.17 MPa, and breaking elongation of ≈1900%, but non-equilibrium RSF/HPAAm DN gels contained excessive residual monomers. It is notable that although the RSF gels could be rapidly achieved via introducing SDS, the gelation that takes only a few minutes is difficult to control. It is quite difficult to achieve uniform mixing between SDS micelles and the hydrophobic monomers via the one-step method, which often resulted in poor homogeneity of the gels. In addition, the swelling of as-prepared hydrogels in water destroys the RSF/SDS network so that equilibrium hydrogels cannot be obtained. In contrast, if the first RSF/SDS network can be stabilized first during the swelling of hydrogels, the Regenerated silk fibroin (RSF) is a promising biomedical material, but the poor mechanical properties of RSF hydrogels may hinder the use as structural components. Herein, an equilibrium RSF hydrogel is prepared and optimized based on the double network (DN) concept. After sufficient soaking in water and removal of small molecules, the equilibrium RSF DN hydrogels prove stable in water, strong, highly extensible, and tough with 0.26-0.44 MPa tensile strength, 500-900% elongation, and 2 MJ m −3 work of extension. The...

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Highly Stretchable and Tough Physical Silk Fibroin–Based Double Network Hydrogels

Zhao

Guan

2019

Macromol. Rapid Commun.

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“…U hys was calculated as,

U_{hys} = \int_{0}^{ε_{\max}} σ_{nom} italicdε - \int_{ε_{\max}}^{0} σ_{nom} italicdε

where the maximum strain ε max equals to 3 in our mechanical tests. Moreover, energy dissipation coefficient μ indicating the ratio of dissipated to the loading energy per tensile cycle was calculated as,

μ = \frac{U_{hys}}{\int_{0}^{ε_{\max}} σ_{nom} italicdε}

…”

Section: Resultsmentioning

confidence: 99%

Hydrophobically modified nanocomposite hydrogels with self‐healing ability

Akca

Yetiskin

Okay

2019

J of Applied Polymer Sci

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Several strategies have been developed in the past two decades to increase the mechanical performance of the hydrogels, and to generate self-healing function within the polymer network. Here, we combine two of these strategies to create hydrophobically modified nanocomposite (NC) hydrogels with high mechanical strength and self-healing efficiency. The hydrogels were prepared by in situ copolymerization of N,N-dimethylacrylamide and n-octadecyl acrylate (C18A) in the presence of 2 w/v % Laponite clay nanoparticles in an aqueous solution of worm-like sodium dodecyl sulfate micelles. Incorporation of hydrophobic C18A segments into the gel network significantly increases both the storage and loss moduli of NC hydrogels indicating increasing elasticity and energy dissipation. An improvement in the mechanical performance and self-recoverability of NC hydrogels was also observed after hydrophobic modification. The compressive fracture stress and Young's modulus increase with increasing amount of C18A, and they become 9 AE 1 MPa and 30 AE 2 kPa, respectively, at 4 mol % C18A. Incorporation of hydrophobic segments also provides a larger energy dissipation under large strain as compared to the traditional NC hydrogels providing a self-healing efficiency of 90 AE 10% in mechanically strong NC hydrogels.

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“…According to the measured values, all the scaffolds showed a degree of tendency to interact with water molecules, so that a direct relationship was observed between the time of enhancement and the absorbed PBS. In all the samples, a high water uptake was observed during the first 3 h that was followed by a steady gradient to 24 h. However, PCB constructs showed a higher slope in water uptake compared to the other samples within 24 h. Although both PCL and BGNPs have hydrophobic natures, which is not an appropriate property for cell performance, the tubular porous microstructure of scaffolds and a higher surface area/volume ratio are considered responsible factors for the absorption capability of the scaffolds (Prabha et al, 2018) According to a previous study, directional pore channels can facilitate fluid transfer and also improve the absorption rate compared with the prepared scaffolds by other technologies with randomly-oriented microstructures, which finally affect the regeneration process (Yetiskin and Okay, 2019). Based on the obtained results, although PCB scaffolds showed a larger pore size, the addition of BGNPs to PCL matrixes led to a significant reduction in the absorption capacity in all time intervals, in a way that some statistically considerable differences were observed in PBS uptake after 12 and 24 h. This phenomenon may arise from decreasing the interaction of scaffolds with PBS molecules owing to the formation of a barrier by BGNPs on the surface of PCL strands.…”

Section: Absorption Capacity and Biodegradationmentioning

confidence: 99%

Surface Functionalization of Three Dimensional-Printed Polycaprolactone-Bioactive Glass Scaffolds by Grafting GelMA Under UV Irradiation

et al. 2020

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In this study, bioactive glass nanoparticles (BGNPs) with an average diameter of less than 10 nm were synthesized using a sol-gel method and then characterized by transmission electron microscopy (TEM), differential scanning calorimetric (DSC), Fourier transforms infrared spectroscopy (FTIR), and x-ray spectroscopy (XRD). Afterward, three dimensional (3D)-printed polycaprolactone (PCL) scaffolds along with fused deposition modeling (FDM) were incorporated with BGNPs, and the surface of the composite constructs was then functionalized by coating with the gelatin methacryloyl (GelMA) under UV irradiation. Field emission scanning electron microscopy micrographs demonstrated the interconnected porous microstructure with an average pore diameter of 260 µm and homogeneous distribution of BGNPs. Therefore, no noticeable shrinkage was observed in 3D-printed scaffolds compared with the computer-designed file. Besides, the surface was uniformly covered by GelMA, and no effect of surface modification was observed on the microstructure while surface roughness increased. The addition of the BGNPs the to PCL scaffolds showed a slight change in pore size and porosity; however, it increased surface roughness. According to mechanical analysis, the compression strength of the scaffolds was increased by the BGNPs addition and surface modification. Also, a reduction was observed in the absorption capacity and biodegradation of scaffolds in phosphate-buffered saline media after the incorporation of BGNPs, while the presence of the GelMA layer increased the swelling potential and stability of the composite matrixes. Moreover, the capability of inducing bio-mineralization of hydroxyapatite-like layers, as a function of BGNPs content, was proven by FE-SEM micrographs, EDX spectra, and x-ray diffraction spectra (XRD) after soaking the obtained samples in concentrated simulated body fluid. A higher potential of the modified constructs to interact with the aqueous media led to better precipitation of minerals. According to in-vitro assays, the modified scaffolds can provide a suitable surface for the attachment and spreading of the bone marrow mesenchymal stem cells (BMSCs). Furthermore, the number of the proliferated cells confirms the biocompatibility of the scaffolds, especially after a modification process. Cell differentiation was verified by alkaline phosphatase activity as well as the expression of osteogenic genes such as osteocalcin and osteopontin. Accordingly, the scaffolds showed an initial potential for reconstruction of the injured bone.

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High-strength and self-recoverable silk fibroin cryogels with anisotropic swelling and mechanical properties

Cited by 51 publications

References 43 publications

Highly Stretchable and Tough Physical Silk Fibroin–Based Double Network Hydrogels

Highly Stretchable and Tough Physical Silk Fibroin–Based Double Network Hydrogels

Hydrophobically modified nanocomposite hydrogels with self‐healing ability

Surface Functionalization of Three Dimensional-Printed Polycaprolactone-Bioactive Glass Scaffolds by Grafting GelMA Under UV Irradiation

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