Regenerated Silk Fibroin Research Articles

Preparation of Silk Fibroin/Cellulose Blend Films

Regenerated silk fibroin (SF) has excellent biocompatibility and degradability, but its mechanical properties need to be improved. As the most widely distributed and most abundant polysaccharide in nature, the advantage of cellulose material is its good strength and modulus. In this study, SF was dissolved in formic acid and calcium chloride solution. Then glycerol and ultrasonic microcrystalline cellulose were added, and the SF/cellulose blend film was prepared by the delayed flow method. The properties of the blend films were characterized by a series of tests such as electron microscope, FTIR, tensile strength, and so on. The results showed that when the ratio of cellulose to SF reached 30 to 70 and the addition of glycerol was 30% of the total solute, the properties of SF/cellulose blend films were the best. The addition of micro-nano-cellulose fiber improved the mechanical properties of the blend film, and the addition of glycerol greatly improved the flexibility of the blend film, which expanded the application of SF/cellulose blend films in the field of biomaterials.

Silk reservoir implants for sustained drug delivery.

Biomaterial implants for the sustained delivery of therapeutics can be utilized to deliver drugs at near-constant rates over extended time frames to provide an alternative to daily oral medications. The biomaterials used to construct these systems, however, are often not bioresorbable and thus require a secondary surgery for removal from the body, and fabrication of these systems may require the use of harsh chemical solvents. To address these shortcomings, a fabrication process was developed to generate biodegradable drug reservoir systems from regenerated silk fibroin protein solution (23% w/v). The tubular systems, with an inner diameter of 2.0 mm and wall thickness < 250µm, were developed using an all-aqueous solution-gel-solid phase transition curing process. Two different clinically-relevant therapeutics were released at near-constant rates for 30 days (> 100µg/day). The protein secondary structure of the devices consisted of 40% crystalline beta sheet. Mechanically, radial compression (1mm/min) of unloaded systems demonstrated Young's moduli similar to cancellous (spongy) bone (100 to 250 MPa) and the systems showed good recovery under cyclic compression (to 17.5% strain). The devices could be generated in complex shapes (e.g., hollow cylinders) via an additive molding process, offering the potential for drug delivery but also for broader applications in tissue engineering and diagnostics.

Silk-based hybrid microfibrous mats as guided bone regeneration membranes.

The usage of a guided bone regeneration (GBR) membrane that prevents the ingrowth of fibroblast cells and enhances the regeneration rate is an effective strategy for bone regeneration therapy. Herein, LAPONITE® (LAP) nanoplatelets, a bioactive clay with good osteoinductivity, were incorporated within a regenerated silk fibroin (RSF) microfibrous mat via electrospinning. The as-prepared RSF-LAP hybrid microfibrous mats had an interconnected structure with pore size significantly smaller than that of the fibroblast cells, leading to an effective prevention of fibroblast cell ingrowth into the defect sites. As per the water contact angle measurements, the incorporation of LAP significantly improved the hydrophilicity of the RSF microfibrous mats. The in vitro cell experiment results show that the RSF-LAP microfibrous mats exhibited better cell adhesion and proliferation of bone marrow mesenchymal stem cells (BMSCs) than the pristine RSF microfibrous mats. Moreover, the RSF-LAP microfibrous mats promoted osteogenic differentiation by upregulating alkaline phosphatase (ALP) activity and osteo-specific gene expression. Therefore, the results suggest that this easily fabricated LAP-incorporated RSF microfibrous mat has great potential to be a promising biomaterial for GBR applications.

Silk granular hydrogels self-reinforced with regenerated silk fibroin fibers.

Granular hydrogels with high stability, strength, and toughness are laborious to develop. Post-curing is often employed to bind microgels chemically and enhance mechanical properties. Here a unique strategy was investigated to maintain microgels together with a novel self-reinforced silk granular hydrogel composed of 10 wt% 20 kDa poly(ethylene glycol) dimethacrylate microgels and regenerated silk fibroin fibers. The principle is to use the swelling of microgels to concentrate the surrounding solution and regenerate silk fibroin in situ. Self-reinforcement is subsequently one of the added functions. We showed that silk fibroin in most compositions was homogeneously distributed and had successfully regenerated in situ around microgels, holding them together in a network-like structure. FTIR analysis revealed the presence of amorphous and crystalline silk fibroin, where 50% of the secondary structures could be assigned to strong β-sheets. Swelling ratios, i.e. 10-45 vol%, increased proportionally with the microgel content, suggesting that mainly microgels governed swelling. In contrast, the elastic modulus, i.e. 58-296 kPa, increased almost linearly with silk fibroin content. Moreover, we showed that the precursor could be injected and cast into a given shape. Viscous precursors of various compositions were also placed side by side to create mechanical gradients. Finally, it was demonstrated that silk granular hydrogel could successfully be synthesized with other microgels like gelatin methacryloyl. Silk granular hydrogels represent, therefore, a novel class of self-reinforced hydrogel structures with tunable swelling and elastic properties.

Self-Assembly of Bombyx mori Silk Fibroin.

Silk fibroin from Bombyx mori (silkworm) distinguishes for its unique mechanical performance, controllable degradation rates, and easily large-scale production, making it attractive models for a variety of biomaterial design. These outstanding properties of silk fibroin originate from its unique modular composition of silk proteins. To exploit the structure-function relationship and fabricate silk fibroin-based biomaterials, comprehensive strategies to uncover assembly behaviors of fibrous proteins are necessary. This chapter describes methods to produce regenerated silk fibroin protein from Bombyx mori silk and their self-assembly strategies. This could provide insight into the fabrication of various silk fibroin-based biomaterials, such as hydrogels, tubes, sponges, fibers, microspheres, and diverse thin film patterns, which can be used for textiles, electronics and optics, environmental engineering, and biomedical applications.

A Promising Wound Dressing from Regenerated Silk Fibroin Sponge with Sustain-ed Release of Silver Nanoparticles

A silk fibroin (SF) spongy wound dressing incorporated with silver nanoparticles (Ag-NPs) was developed for biomedical applications. Ag-NPs were efficiently synthesized in situ via ultra violet (UV) with AgNO3 as precursor and silk fibroin as reducing and protecting agent, respectively. After lyophilization, the formed silk fibroin spongy wound dressing (SFWD) exhibited polyporous morphology and inner lamellae structures, with uniform dispersion of Ag-NPs. The porous structure provided SFWD with the ability to absorb tissue exudatealmost 6 times of its own weight, which could guarantee the sustained release of Ag-NPs. By methanol treatment, SFWD showed much improved mechanical properties and more stable to protease XIV. The cyto-compatibility of SFWD was supported by normal adherence and proliferation of NIH3T3 fibroblasts in sponges extracting culture medium. More important, the SFWD showed significant growth inhibition in both plate culture assays and bacterial suspension assays, with Grampositive (Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa and Escherichia coli). In a cutaneous excisional mouse model, the average healing rates of SFWD was significantly higher than control and commercial bandages. The hematoxylin-eosin (HE) staining results of the wound section also showed that SFWD could recruit more cells and promote tissue formation on the wound edges.

Adsorption of Ag (I) from Aqueous Solutions Using Regenerated Silk Fibroin Adsorbent Beads

ABSTRACT In this work, a novel and eco-friendly biosorbent, regenerated silk fibroin bead (rSFB) was successfully produced and used as a low-cost adsorbent to remove silver ion from wastewater. Batch adsorption experiments demonstrated that rSFB could effectively remove silver ion in particular. Factors influencing the adsorption of silver ion, e.g. contact time, solution pH, and adsorbent dosage were systematically investigated. Isotherm equilibrium studies demonstrated that the silver ion adsorption process followed the Langmuir model. The maximum adsorption capacity for silver ion was estimated to be 62.50 mg/g and the removal efficiency could reach up to 98.82%. The kinetics study showed that the adsorption process followed the second-order kinetic model. The adsorbent was stable and active for up to four successive cycles. The batch experimental results suggested that rSFB could be used as an efficient adsorbent to remove silver from wastewater.

Biomimicking Antibacterial Opto-Electro Sensing Sutures Made of Regenerated Silk Proteins.

Surgical sutures play an important role across a wide range of medical treatments and a wide variety exist, differing in strength, size, composition, and performance. Recently, increasing interest has been paid to bioactive and electronic sutures made of synthetic polymers, owing to their ability to reduce inflammation as well as medically and/or electronically facilitate wound healing. However, integrating sensing capabilities into bioactive sutures without adversely affecting their mechanical strength, biocompatibility, and/or bioactivity remains challenging. In this work, a set of biomimicking, antibacterial, and sensing sutures based on the regenerated silk fibroin is designed and fabricated. These sensing sutures, inspired by the "core-shell" multilayered structure of natural spider-silk fibers, are hierarchically structured and heterogeneously functionalized to allow for the integration of multiple, clinically favorable functions into one suture device. These functions included: reducing inflammation and bacterial infection in wound sites, measuring tension of both the tissue and suture, and aiding tissue healing via multi-modal controlled drug and growth factor release. Critically, these functions are coupled with real-time optical and electronic monitoring capabilities. This approach provides greater insight into multifunctional sutures with inherent sensing capabilities and offers enormous potential in both therapeutic and diagnostic applications.

Application of Bombyx mori Silk Fibroin Films for Liquid-Crystal Devices.

Biocompatible and biodegradable silk fibroin films show promise as an eco-friendly biomaterial with excellent mechanical, thermal, and optical transparency properties. In contrast, polyimide (PI) films adopted in the liquid-crystal display (LCD) industry for aligning LC molecules are synthesized using toxic chemicals, which are nonrecyclable and nonbiodegradable. In this work, Bombyx mori silk fibroin films are fabricated from the aqueous solution and applied as alignment films for LCDs. The thermal properties of the prepared regenerated silk fibroin materials under different heat treatment temperatures are investigated using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The crystallinity of different heat-treated silk fibroin materials is determined by infrared spectroscopy. The silk fibroin film treated at a higher temperature exhibits better thermal stability due to the higher crystallinity of the β-form structure. The LCDs using silk fibroin alignment films show a low pretilt angle of 0.5° and an anchoring energy of ∼10-3 J/m2 similar to those of the conventional polyimide films.

Silk fibroin/reduced graphene oxide composite mats with enhanced mechanical properties and conductivity for tissue engineering

In this work, we described a green and simple approach for fabricating regenerated silk fibroin (RSF)/reduced graphene oxide (RGO) fibrous mats by reducing GO in the RSF/GO mats through hydrothermal treatment. As a comparison, RSF mat incorporated with graphene (Gr) was fabricated by solution mixing method. Results showed that the reduction of GO in the mats did take place during hydrothermal treatment. An increase in the crystallinity of the mats was induced by hydrothermal treatment. The maximum Young’s modulus of RSF/RGO mats reached (122.7 ± 3.1) MPa, which was at least 9-fold higher than RSF mats. As the mass ratio of RGO/RSF was 1.5/100, the average sheet resistance of RSF/RGO mats reached (1.2 ± 0.1)×108 Ω/sq, which was better and more stable than that of RSF/Gr mats. Furthermore, cellular tests and antibacterial tests demonstrated that RSF/RGO mats possessed better biocompatibility and antibacterial property in comparison with RSF mats incorporated with GO or Gr. Thus, the RSF/RGO mats could be a good candidate for tissue engineering applications.

Biopolymer Composite Nanofibers Electrospun from Regenerated Silk Fibroin and PHBV: Fabrication Method, Morphology and Thermal Stability

Silk fibroin (SF) and polyhydroxyalkanoate (PHA) have received increasing attention in recent years because of their unique biodegradability and biocompatibility. Studies on SF or PHA-based materials that are intended for use as biomaterials have attracted great attention, but few studies have been conducted on SF/PHA composite materials. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) copolymers with varying ratios of the 3-hydroxyvalerate (HV) component are the most widely used member of PHAs. In this study, SF/PHBV composite nanofibers were prepared by electrospinning. The stability of the mixed solution of SF/PHBV was explored first. Fourier transform infrared (FTIR) spectroscopy was used to study the composition of the precipitates caused by mixing the SF solution with the PHBV solution. The morphology of the electrospun SF/PHBV composite nanofibers was observed by scanning electron microscopy (SEM). The average diameters of the pure PHBV, pure SF, SF/PHBV (the content ratio of solute SF/PHBV (w/w) was 10/1), and SF/PHBV (the content ratio of solute SF/PHBV (w/w) was 4/1) nanofibers were 495.12 ± 82.27, 67.88 ± 14.52, 171.10 ± 40.38, and 149.70 ± 28.57 nm, respectively. To discuss the influence of the electrospinning parameters on the spinning stability and morphology of the electrospun SF/PHBV (10/1) composite nanofibers, a univariate analysis experiment was designed. When the applied voltage was 15 kV, the feeding rate was 0.3 mL/h, and the tip-to-collector distance was 13 cm, the spinning stability, uniformity and formability of the SF/PHBV (10/1) composite nanofibers were excellent. In addition to FTIR analysis, X-ray diffraction (XRD) was also used to explore the structure of the electrospun SF/PHBV composite nanofibers. As the content of PHBV increased, the crystallinity of the SF/PHBV composite nanofibers could be improved. The thermogravimetric analysis (TGA) results indicated that the thermal stability of SF was better than that of PHBV. As the content of PHBV increased, the thermal stability of the SF/PHBV composite nanofibers would decrease.

3D printed hydrogels with oxidized cellulose nanofibers and silk fibroin for the proliferation of lung epithelial stem cells.

A novel biomaterial ink consisting of regenerated silk fibroin (SF) and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized bacterial cellulose (OBC) nanofibrils was developed for 3D printing lung tissue scaffold. Silk fibroin backbones were cross-linked using horseradish peroxide/H2O2 to form printed hydrogel scaffolds. OBC with a concentration of 7wt% increased the viscosity of inks during the printing process and further improved the shape fidelity of the scaffolds. Rheological measurements and image analyses were performed to evaluate inks printability and print shape fidelity. Three-dimensional construct with ten layers could be printed with ink of 1SF-2OBC (SF/OBC = 1/2, w/w). The composite hydrogel of 1SF-1OBC (SF/OBC = 1/1, w/w) printed at 25 °C exhibited a significantly improved compressive strength of 267 ± 13 kPa and a compressive stiffness of 325 ± 14 kPa at 30% strain, respectively. The optimized printing parameters for 1SF-1OBC were 0.3 bar of printing pressure, 45 mm/s of printing speed and 410 μm of nozzle diameter. Furthermore, OBC nanofibrils could be induced to align along the print lines over 60% degree of orientation, which were analyzed by SEM and X-ray diffraction. The orientation of OBC nanofibrils along print lines provided physical cues for guiding the orientation of lung epithelial stem cells, which maintained the ability to proliferate and kept epithelial phenotype after 7 days’ culture. The 3D printed SF-OBC scaffolds are promising for applications in lung tissue engineering.Electronic supplementary materialThe online version of this article (10.1007/s10570-020-03526-7) contains supplementary material, which is available to authorized users.

Direct Femtosecond Laser Printing of Silk Fibroin Microstructures.

Fabrication of functional silk fibroin microstructures has extensive applications in biotechnology and photonics. Considerable progress has been made based on lithographic methods and self-assembly approaches. However, most methods require chemical modification of silk fibroin, which restricts the functionalities of the designed materials. At the same time, femtosecond laser-induced forward transfer (fs-LIFT) has been explored as a simple and attractive processing tool for microprinting of high-resolution structures. In this paper, we propose the use of LIFT with fs-pulses for creating high-resolution structures of regenerated silk fibroin (SF). Furthermore, upon adding Eu3+/Tb3+ complexes to SF, we have been able to demonstrate the printing by LIFT of luminescent SF structures with a resolution on the order of 2 μm and without material degradation. This approach provides a facile method for printing well-defined two-dimensional (2D) micropatterns of pure and functionalized SF, which can be used in a wide range of optical and biomedical applications.

Forward Wound Closure with Regenerated Silk Fibroin and Polylysine-Modified Chitosan Composite Bioadhesives as Dressings.

Wound dressing has been used for decades to be effective for accelerating skin wound healing. However, practical applications are still limited due to their lower cell affinity, tissue adhesiveness, and biocompatibility. Natural polymers are the important biomaterials because of their excellent biodegradability, biocompatibility, and low immunogenicity. In this work, the composite bioadhesives (PLS-CS/RSF) were prepared from regenerated silk fibroin (RSF) and polylysine-modified chitosan (PLS-CS) that were cross-linked by Ca2+ ions. The adhesion property tests showed that the PLS-CS/RSF exhibited excellent bonding potentials for various substrates, and the adhesive strength was up to 70 kPa for isolated porcine skin by the extension test. The as-prepared PLS-CS/RSF was nontoxic, displayed obvious antibacterial effects against Staphylococcus aureus and Escherichia coli in vitro, and their bacteriostasis rates were 100% after 120 min treatment. In addition, the PLS-CS/RSF exhibited favorable cytocompatibility by cell counting kit-8 assay. The animal model of wound closure results showed that PLS-CS/RSF can promote wound closure and the integrity of wound healing, inhibiting the secretion of inflammatory factor and tumor necrosis factor and stimulating vascular factor and α-smooth muscle actin to the release of vascular growth factor and promote angiogenesis during the process of wound healing by immunohistochemical assay.

Improving the Activity of DNA-Encoded Sensing Elements through Confinement in Silk Microcapsules.

Assembling synthetic bioparts into simplified artificial cells holds tremendous promise for advancing studies into the synthesis, biosensing, and delivery of biomolecules. Currently, the most successful techniques for encapsulation of the transcription-translation machinery exploit compartmentalization in liposomal vesicles. However, improvements to these methods may increase permeability to polar molecules, functionalization of the membrane with biologically active elements, and encapsulation efficiency. Microcapsules prepared via templated layer-by-layer (LbL) assembly using natural polymers have the potential to resolve some of the hurdles associated with liposomes. Here, we introduce a design for immobilizing DNA templates encoding translationally activated riboswitches and RNA aptamers into microcapsules prepared from regenerated silk fibroin protein. Adjusting several key parameters such as the presence of a polymer primer, concentration of silk protein, and DNA loadings during LbL assembly resulted in biocompatible, semipermeable, DNA-laden microcapsules. To preserve bioactivity, DNA was immobilized inside of the capsule membrane, which not only promoted stability during long-term storage at ambient conditions but also improved output response from spatially confined DNA-encoded sensing elements (SEs). Multiple copies of mRNA and GFPa1 protein were synthesized upon activation with specific analytes during in vitro transcription/translation reactions, demonstrating that selective permeability of silk microcapsules was essential for the diffusion of components of the cell-free system inside of the capsules. Further functionalization of capsule shells with gold nanoparticles (AuNPs) and antibodies (IgG) demonstrated the applicability of microcompartmentalized colloidal objects carrying SEs for remote sensing and/or targeted delivery. In the future, multifunctional, biocompatible silk-based microcapsules loaded with different RNA sensors can help advance the design of multiplexed biosensors tracking multiple biomarkers in complex media.

Preparation of silk fibroin-based microspheres under high-gravity field

The possibility of preparing regenerated silk fibroin (RSF)-based microspheres by a high-gravity anti-solvent precipitation method was explored. The high-gravity environment was generated by a rotating packed bed (RPB) reactor. Aqueous RSF solutions and ethanol were used as solvent and anti-solvent, respectively. The effects of liquid flow rates and anti-solvent/solvent ratios, as well as centrifugation and freezing time, on the formation, size distribution and morphology of RSF microspheres were investigated. The results showed that RSF microspheres, with diameters of 0.1–1.6 μm, can be prepared under high-gravity field via self-assembly of RSF molecular chains induced by ethanol and quenched by freezing and lyophilization. The mechanism of RSF microsphere formation was also discussed. In addition, rhodamine B was used as a model drug for evaluation of drug delivery capability of the RSF microspheres. The merits of this study lie in a simple low-cost apparatus with ease for scale-up and thereby potential high volume continuous production capacity, which is of practical advantages and industrial significance in preparation of protein microspheres for commercial mass production.

Adhesive tape-assisted etching of silk fibroin film with LiBr aqueous solution for microfluidic devices

The regenerated silk fibroin (RSF)-based microfluidic device has attracted tremendous interests in recent years due to its excellent biocompatibility, mild processing conditions, and all aqueous casting production. However, the need of a micro-fabricated mold in the manufacture process greatly hinder its practical applications. Herein, we introduce an adhesive tape-assisted etching method with LiBr solution as the etchant to prepare RSF microfluidic devices. An engraved adhesive tape is used as the mask to cover on the surface of a RSF film. Then, LiBr solution is dropped on the mask to etch RSF in concentration- and duration-dependent manners. During this process, the LiBr-treated RSF transits from insoluble β-sheet crystallites to soluble conformations. The as-prepared RSF microfluidic devices possess good chemical resistance and excellent tolerance to mechanical deformation. RSF microfluidic systems with different patterns were fabricated to demonstrate the universality of the approach. A concentration gradient generator and a blood vessel-like channel were manufactured for the preparation of solutions with gradient pHs and the growth of living cells, respectively. The proposed strategy has great potentials in the facile fabrication of low-cost RSF microfluidic devices for tissue engineering and biomedical analysis.

Patterning the neuronal cells via inkjet printing of self-assembled peptides on silk scaffolds

The patterning of neuronal cells and guiding neurite growth are important for neuron tissue engineering and cell-based biosensors. In this paper, inkjet printing has been employed to pattern self-assembled I3QGK peptide nanofibers on silk substrates for guiding the growth of neuron-like PC12 cells. Atomic force microscopy (AFM) confirmed the dynamic self-assembly of I3QGK into nanofiber structures. The printed self-assembled peptide strongly adheres to regenerated silk fibroin (RSF) substrates through charge-charge interactions. It was observed that in the absence of I3QGK, PC12 cells exhibited poor attachment to RSF films, while for RSF surfaces coated or printed with peptide nanofibers, cellular attachment was significantly improved in terms of both cell density and morphology. AFM results revealed that peptide nanofibers can promote the generation of axons and terminal buttons of PC12 cells, indicating that I3QGK nanofibers not only promote cellular attachment but also facilitate differentiation into neuronal phenotypes. Inkjet printing allows complex patterning of peptide nanofibers onto RSF substrates, which enabled us to engineer cell alignment and provide an opportunity to direct axonal development in vitro. The live/dead assay showed that printed I3QGK patterns exhibit no cytotoxicity to PC12 cells demonstrating potential for future nerve tissue engineering applications.

Effect of molecular weight of regenerated silk fibroin on silk-based spheres for drug delivery

Silk fibroin presents a good advantage as a drug carrier for drug delivery, due to the excellent biocompatibility, biodegradability and tunable drug loading and release properties. In this work, we constructed silk spheres by phase separation of the regenerated silk fibroin (RSF) solutions with different MW and polyvinyl alcohol; and it was revealed that MW of RSF can affect the structure, size, surface potential and drug loading and release efficiency of silk spheres. Silk spheres prepared from high MW of RSF were found to load more macromolecular drug with negative charge compared to middle and low MW of RSF. However, for the positive charge and low MW drug, the silk spheres prepared from low MW of RSF could present a high loading efficiency compared to other carriers. Finally, a positive drug with low MW, streptomycin was encapsulated in silk spheres prepared from low MW of RSF, and displayed a long bactericidal and bacteriostatic effect compared to bared streptomycin solution. The results obtained provide guidelines for the modification and options of drug transport vehicles for more efficient drug delivery and utilization through a simple, rapidly constructed, applicable and low-cost drug carrier.

Tailoring of electrical and optical properties of regenerated silk fibroin films with metal oxides

In this study, silk fibroin was used as a matrix to incorporate the metal oxide nanoparticles i.e. zinc oxide (ZnO) and copper oxide (CuO) to form transparent nanocomposite films by solvent casting method. The effect of metal oxide nanoparticles and their concentrations on the conductivity of silk fibroin film were detected by a four-point probe instrument. As the thickness of the films was reduced, the conductivity increased. Hall Effect experiment was carried out to determine the carrier (electron or holes) concentration and identification of the semiconducting behaviour of nanocomposite films. Pure silk fibroin (SF) film showed p-type semiconducting behaviour. Incorporation of zinc oxide and copper oxide nanoparticles in the silk fibroin matrix makes it n-type and p-type semiconductor, respectively. Uniform dispersion of metal oxide nanoparticles in the silk fibroin matrix was observed through field emission scanning electron microscopy. The UV–Vis spectra of nanocomposite films showed 82–84% transmittance and reduction in refractive index. Addition of metal oxide nanoparticles reduced the β sheet content and percentage crystallinity of silk fibroin as observed by FTIR and XRD, respectively. The structural alterations at the molecular level reveal their relationship with electrical and optical properties.