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SCIENCE CHINA Technological Sciences, Volume 62, Issue 6: 903-918(2019) https://doi.org/10.1007/s11431-018-9403-8

Silk materials for medical, electronic and optical applications

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  • ReceivedSep 6, 2018
  • AcceptedDec 3, 2018
  • PublishedApr 16, 2019

Abstract

Silk derived from the silkworm Bombyx mori is among the most important fibrous protein biomaterials due to large-scale production from natural sources, excellent biocompatibility, unique mechanical properties and controllable degradation. Silk fibroin can be processed into a variety of formats to match different applications, such as tissue engineering, drug delivery or as the passive substrate of a bio-device. Advances in fabrication technologies provide new possibilities for the combination of silk fibroin with other nanomaterials to functionalize silk fibroin for specialized purposes, including sensing, cell visualization, resistance to ultraviolet light and provision of antibacterial properties. As the requirement for wearable and intelligent devices has become increasingly important over recent years, silk fibroin has been utilized as the active element in electronic and optical instruments. This review summarizes these recent advances in the innovative applications of silk fibroin.


Funded by

the National Natural Science Foundation of China(Grant,No.,21674018)

the National Key Research and Development Program of China(Grant,Nos.,2018YFC1105802,2016YFA0201702,2018YFC1106002)

the International Joint Laboratory for Advanced fiber and Low-dimension Materials(Grant,No.,18520750400)

the “Shuguang Program” supported by Shanghai Education Development Foundation and Shanghai Municipal Education Commission(Grant,No.,15SG30)

and the Youth Foundation of Donghua University(Grant,No.,106-07-0053028)


Acknowledgment

This work was supported by the National Key Research and Development Program of China (Grant Nos. 2016YFA0201702, 2018YFC1105800, 2018YFC1106002), the National Natural Science Foundation of China (Grant No. 21674018), the International Joint Laboratory for Advanced Fiber and Low-dimension Materials (Grant No. 18520750400), the “Shuguang Program” supported by Shanghai Education Development Foundation and Shanghai Municipal Education Commission (Grant No. 15SG30), the Youth Foundation of Donghua University (Grant No. 106-07-0053028), and the Fundamental Research Funds for the Central Universities.


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  • Figure 1

    (Color online) Schematic diagram of the structure, processing, forms and applications of silk materials.

  • Figure 2

    (Color online) Schematic diagram of the electrospinning process (a) and a prepared multilayered RSF/BAMG composite scaffold with aligned regenerated silk fibroin (RSF) fibers (b); (c) stress-strain curves of the post-treated composite scaffolds in dry and wet states, respectively [45] (adapted with permission), copyright (2015) American Chemical Society.

  • Figure 3

    (Color online) (a) Schematic diagram of the fabrication of self-healing SF-based hydrogels for rat cranial bone regeneration; (b) images demonstrating the self-healing properties of the hydrogel [55] (adapted with permission), copyright (2017) John Wiley and Sons.

  • Figure 4

    (Color online) Formation mechanism of radial lamellae and intercalation structure [56] (adapted with permission), copyright (2017) Royal Society of Chemistry.

  • Figure 5

    (Color online) (a) Schematic diagram of the transfer of silk antennae onto curved substrates; (b) frequency-dependent impedance phase angle of a slice of cheese with and without sensors; (c) frequency response of a silk sensor attached to a plastic container filled with milk during spoilage [70] (adapted with permission), copyright (2016) John Wiley and Sons.

  • Figure 6

    (Color online) (a) and (c) Photograph and enlarged optical image of pristine silk fabric; (b) and (d) corresponding images of carbonized silk fabric. (e)–(g) Photographs of a strain sensor connected to a light-emitting diode; detection of finger bending (h) and a wrist bending (i) [96] (adapted with permission), copyright (2017) John Wiley and Sons.

  • Figure 7

    (Color online) (a) Versatile processability of a stable graphene/silk fibroin suspension; the relative change in resistance of graphene/silk fibroin composites for finger movement (b), finger touching (c), breathing (d), and aqueous ethanol solution with different ethanol and water volume ratios (e) [19] (adapted with permission), copyright (2012) John Wiley and Sons.

  • Figure 8

    (Color online) Schematic of silk fibroin lamellar-like layer formation by introduction of KOH [77] (adapted with permission), copyright (2013) John Wiley and Sons.

  • Figure 9

    (Color online) (a) Schematic diagram of a transient resistive switching memory device with scanning tunneling microscopy (STM); (b) STM images of transient resistive switching memory device under different conditions, showing the formation of conducting filaments during SET condition while those disappear during the RESET condition; (c) physical model of switching mechanism of transient resistive switching memory [81] (adapted with permission), copyright (2012) John Wiley and Sons.

  • Figure 10

    (Color online) Schematic diagram of WK@AuNCs meso-functionalized silk memristor (a) and the assembly of AuNCs into an SF nanofibril network (b); (c) resistive switching mechanism of Ag/WK@AuNCs-SF/ITO devices [85] (adapted with permission), copyright (2017) John Wiley and Sons.

  • Figure 11

    (Color online) (a) Schematic of optofluidic device setup; (b) absorbance spectra of the CO2H azo-silk optofluidic device as a function of wavelength and pH; (c) transient response of the optofluidic device probed at 550 nm [89] (adapted with permission), copyright (2010) John Wiley and Sons.

  • Figure 12

    (Color online) (a) A perspective view of a silk-MCM integrated into a micro fluidic cell; (b) ultrasensitive detection of water impurity in IPA based on the optical chirality of the silk-MCMs [92] (adapted with permission), copyright (2018) American Chemical Society.

  • Figure 13

    (Color online) (a) Process for fabrication of silk fibroin inverse opals; (b) optical microscopy of silk fibroin inverse opals in different humidities; (c) creation of structural color on silk fabrics [94] (adapted with permission), copyright (2013) John Wiley and Sons.

  • Figure 14

    (a) Schematic diagram of silk nanofibril fabrication by liquid exfoliation, and representative optical microscopy and SEM images; (b) photograph illustrating the transparency of SNF membranes; (c) UV-vis transmittance of SNF and silk fibroin membranes with a thickness of approximately 200 µm [99] (adapted with permission), copyright (2016) John Wiley and Sons.

  • Table 1   Overview of the structure and mechanical properties of typical post-treated silk fibroin fibers

    Sample

    Post-treatmentmethod

    β-sheetcontent (%)

    Xc (%)

    Molecular orientation

    (birefringence index)

    Breaking stress (MPa)

    Breakingstrain (%)

    Dry-spun fibers [32]

    PDICa)

    +b)

    +

    +

    298

    16

    Dry-spun fibers [3]

    PDIC

    40

    n.s.c)

    0.038

    301.5

    35.8

    Microfluidic dry-spun fibers [33]

    PDIC

    38.9

    36.5

    0.0482

    541.3

    19.3

    Wet-spun fibers [34]

    Immersion in coagulant and further drawing

    n.s.

    n.s.

    +

    470.4

    38.6

    Wet-spun fibers [35]

    Post-drawing and steam annealing

    n.s.

    n.s.

    n.s.

    ~200

    ~18

    Wet-spun fibers [36]

    Post-drawing under stream

    n.s.

    +

    +

    450

    27.7

    Degummed silk [37]

    43.8

    48.6

    0.0377

    350

    16

    PDIC: Post-drawing and immersion in coagulant; b) +: Values of post-treated silk fibroin fibers increase compared to as-spun fibers, but no quantitative values were published; c) n.s.: not specified.

  • Table 2   Medical applications of silk fibroin-based materials

    Applications

    Material formats

    Advantages

    Preparation methods

    Refs.

    Wound dressing

    Mats

    Mimicking the extracellular matrix

    Electrospinning

    [43]

    Blood vessel

    Aligned fibers, tubular scaffolds

    Enhanced tensile properties and suture retention

    Electrospinning

    [45,46]

    Skeletal muscle tissue

    Nanoyarns

    Larger pore size, looser packed structure

    Electrospinning

    [47,48]

    Bone regeneration

    Hydrogel,

    composite bulks

    Larger size, porous structure, controllable thickness,

    ability to encapsulate cell

    Photolithography, heating, bioprinting

    [4951]

    Drug delivery

    Hydrogel, microsphere, nanofilm and sponge

    Controllable release rate,biodegradability

    Sonication,

    self-assembly, lyophilization, casting,

    phase separation, desolvation

    [6269]

    Storage of vaccines and antibiotics

    Hydrogel

    Longer storage life, higher storage temperature (60°C)

    Casting, lyophilization

    [66]

  • Table 3   Novel electronic and optical applications of silk fibroin-based materials

    Devices

    Working mechanism

    Potential applications

    Refs.

    Biosensing devices

    For passive substrate: flexibility, water-solubility, biocompatibility;

    for active elements: different folding-unfoldingstates of silk fibroin at molecular levelunder external stimulus

    Monitoring the quality of food, monitoring full-range human motions for health

    [19,7075]

    Electrode

    Formation of hierarchical porous nitrogen-doped carbon nanosheets after effectiveactivation-graphitization

    Energy storage

    [7578]

    Resistive switchingmemory devices

    Formation and rupture of conducting filamentsunder different applied electrical field

    Green information storage, write-once read-many-times memory devices

    [17,7987]

    Diffractive optical elements

    Diffraction efficiency is easily affected by the attached chemical or biological molecules

    Biological concealment,

    air monitors

    [20,8789]

    Optical sensor

    Refractive index is affected by constituent, arrangement, fabrication condition and environmental factors

    Humidity indicator,

    solvent purity detecting

    [9092]

    Photonic crystals

    Nanoscale periodic optical structure causes structural coloration once interacting with light

    Display,

    sensing technologies, eco-dye and multi-functionalization of fabric

    [9395]

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