Development of Silk Fibroin Scaffolds by Using Indirect 3D-Bioprinting Technology

Due to the excellent biocompatibility of natural polymers, a variety of natural polymers have been widely used as biomaterials for manufacturing tissue engineered scaffolds. Despite the excellent biological activity of natural polymers, there have been obstacles in using them on their own to prepare 3D scaffolds with sufficient mechanical strength. Although multiple 3D-bioprinting technologies have recently emerged as effective manufacturing tools for scaffold preparation, scaffold preparation using only natural polymers with tunable mechanical properties is still difficult. Herein, we introduce novel scaffold fabrication methods using the natural polymer silk fibroin via indirect 3D-bioprinting technology. The developed silk fibroin scaffolds showed biocompatibility and tunable mechanical strength by changing the concentration of the silk fibroin. Furthermore, controlling the flexibility of the silk fibroin scaffolds was made possible by changing the solvent for the silk fibroin solution used to fabricate the scaffold. Consequently, silk fibroin scaffolds fabricated via our method can be considered for various applications in the bioengineering of either soft or musculoskeletal tissues.

Production of Silk Fibroin Membrane for Heavy Metal Removal in Water

Thermodynamically driven salts and annealing processes developed the pure silk fibroin (SF) membranes from Bombyx mori cocoons. For more generation, the silk fibroin solution 5 wt% mixed the sodium chloride (NaCl) and polyethylene glycol (PEG). The top surface and cross-section of silk fibroin mixed with NaCl (SF/NaCl) showed pore in the surface membrane and hydrophilic property. The β-sheet content in the SF/NaCl membrane is higher than pure silk fibroin (SF) and the silk fibroin mixed with PEG (SF/PEG) membranes. Then cadmium (Cd), lead (Pb), and mercury (Hg) metals in water filtered pass through only SF/NaCl experimented. The pressure, pH, and temperature were effect by the flow rate efficiency of SF/NaCl membranes. The results showed that the highest % removal of Cd, Pb, and Hg were 45.36%, 61.43%, and 86.87%, respectively. The best condition of absorption capacity was 8.50, 6.42, and 41.14 mg/g for Cd, Pb, and Hg. As a natural biopolymer, SF/NaCl possibly apply for Hg removal for water treatment, its nontoxicity, excellent biocompatibility, and mechanical toughness.

A Fast and Reliable Process to Fabricate Regenerated Silk Fibroin Solution from Degummed Silk in 4 Hours

Silk fibroin has a high potential for use in several approaches for technological and biomedical applications. However, industrial production has been difficult to date due to the lengthy manufacturing process. Thus, this work investigates a novel procedure for the isolation of non-degraded regenerated silk fibroin that significantly reduces the processing time from 52 h for the standard methods to only 4 h. The replacement of the standard degumming protocol by repeated short-term microwave treatments enabled the generation of non-degraded degummed silk fibroin. Subsequently, a ZnCl2 solution was used to completely solubilize the degummed fibroin at only 45 °C with an incubation time of only 1 h. Desalting was performed by gel filtration. Based on these modifications, it was possible to generate a cytocompatible aqueous silk fibroin solution from degummed silk within only 4 h, thus shortening the total process time by 48 h without degrading the quality of the isolated silk fibroin solution.

Investigation of the biological activity, mechanical properties and wound healing application of a novel scaffold based on lignin–agarose hydrogel and silk fibroin embedded zinc chromite nanoparticles

Given the important aspects of wound healing approaches, in this work, an innovative biocompatible nanobiocomposite scaffold was designed and prepared based on cross-linked lignin–agarose hydrogel, extracted silk fibroin solution, and zinc chromite (ZnCr2O4) nanoparticles.

Silk fibroin nanofibers loaded with hydroxytyrosol from hydrolysis of oleuropein in olive leaf extract

The purpose of this study was to prepare antimicrobial silk fibroin nanofibers from the aqueous formic acid solutions of silk fibroin and hydroxytyrosol with the in situ hydrolysis of oleouropein present in olive leaf extract using electrospinning method. With the use of aqueous formic acid solution of olive leaf extract and silk fibroin resulted in more uniform and beadless nanofibers. Morphological properties of electrospun nanofibers were investigated using Scanning Electron Microscope (SEM). The diameter of electrospun nanofibers ranged between 70 nm to 150 nm. The nanofiber diameter did not changed much with increasing concentration of olive leaf extract added into silk fibroin solution to be used in electrospinning process. The increase in olive leaf extract concentration resulted in beadless and uniform nanofiber structures. The average diameter of the nanofibers prepared with fibroin solution having 10 % olive leaf extract was determined as 85 ± 10 nm. Results revealing the formation of smoother and uniform nanofibers was attributed to the crosslinking effect of oleuropein and polyphenols present in olive leaf extract with certain functional groups in silk fibroin structure. Antibacterial properties of hydroxytyrosol loaded nanofibers against Staphylococcus epidermidis (Gram +) and Escherichia coli (Gram -) were confirmed with the clear inhibition zones observed in disc diffusion tests. Silk Fibroin nanofibers loaded with hydroxytyrosol may offer a new alternative biomaterial to be used in wound dressing or medical textile applications.

DESIGN OF EXPERIMENTS MODEL FOR THE OPTIMIZATION OF SILK FIBROIN BASED NANOPARTICLES

Objective: Silk fibroin based nanoparticles have been utilized extensively in biomedical fields. Amongst many preparation methods, desolvation is a favorable one. However, this method yields nanoparticles with unpredictable parameters. Thus, this investigation aimed to systematically study the effects of three independent variables including fibroin concentration (% w/v, X1), volume ratio between fibroin solution and ethanol (X2), formulation time (h, X3) on three main responses, particle size (nm, Y1), polydispersity index (Y2), zeta potential (mV, Y3).Methods: Fibroin was extracted from degummed Bombyx mori silk. The fibroin calibration curve was constructed by UV-spectrophotometer at 276 nm. The nanoparticles were prepared using the desolvation method of aqueous fibroin solution in ethanol. Design Expert® software was used to design the model. The mean particle size, polydispersity index and zeta potential were determined using ZetaPALS®analyzer.Results: By using D-optimal design with the quadratic model, the results showed that all X1, X2, and X3 variables had significant impacts on the fibroin nanoparticles characteristics Y1, Y2, and Y3. The generated model was also validated and demonstrated to be solid and reliable. The obtained optimal nanoparticles possessed Y1 of 238.1 nm, Y2 of 0.12, and Y3of-21.78 mV, which were in agreement with the predicted values, 224.8 nm, 0.13 and-19.31 mV, respectively. The optimal actual and theoretical particle characteristics were correlated with a desirable value of R2 = 0.8770. Conclusion: The D-optimal design proved its effectiveness in the prediction and optimization of fibroin nanoparticle properties.

Investigation of Optimal Silk Film Thickness in Silk Microneedle Fabrication

Injection is one of the most commonly used methods for delivering drugs or vaccines into human bodies. It is rapid, low-cost and compatible with almost any drugs. However, the major drawbacks of the injection by hypodermic needles are the pain associated with the injection and the disposal of used needles. Microneedles have then received wide attention since they can overcome such drawbacks, especially dissolving microneedles. Recently, silk fibroin has been used to fabricate dissolving silk microneedles for transdermal drug delivery at low temperature. In the fabrication process, the quality of the silk microneedles relies on the solidification of silk fibroin solution. This research aims to study the role of silk fibroin concentration (silk film thickness) in the formation of silk microneedles. In the experiment, silk microneedles were fabricated using various concentrations of silk fibroin solution from 3 to 7% while the volume of the silk fibroin solution was fixed. According to the experimental resuls, it was found that the concentrations of 4-5% were suitable for producing silk microneedles (silk film thickness of 470 μm) while the concentrations of 6-7% caused wrinkles on microneedle patch due to mismatch of upper and lower layers of microneedles. Furthermore, the concentration of 3% had a problem with the demolding step of microneedles since it caused mold damage due to strong adhesion force between microneedles and mold.