Biomedical Engineering Reference
In-Depth Information
Heat
Boiling
Drying
LiBr 9.3 M
Na
2
CO
3
Silk fibers
Cocoons
Silk solution
Silk degumming
Silk
dialysis
Dialysis
HFIP
Lyophilization
HFIP
silk solution
Aqueous
silk solution
Lyophilized silk
Scaffolds
Films
Electrospun mat
Scaffolds
Electrospinning
Microbeads
Hydrogels
FIGURE 7.1
Processing steps of
B. mori
silk cocoons to form regenerated silk solution.
materials, it is typically necessary to regenerate silk by dissolution in a solvent capable of denaturing the
protein (by breaking the strong intermolecular hydrogen bonds—stacks of β-sheets), through the use of
concentrated aqueous solutions of inorganic/organic salts, fluorinated solvents, ionic liquids, or strong
acids (Figure 7.1) [37-39]. Once dissolved, the regenerated silk protein than can be processed into a vari-
ety of different material morphologies (Figure 7.2); for example, silk fibers with micron-scale diameters
can be prepared by hand-drawing or dry-/wet-spinning, and silk fibers with nanometer-scale diameters
can be prepared by electrospinning. Silk films can be fabricated by casting and dip-/spin-coating; silk
hydrogels can be prepared by exposure of aqueous solutions of silk proteins (after dialysis to remove any
denaturant) to various stimuli including salt, shear, and sonication. Similarly, silk foams/scaffolds can
be prepared by freeze-drying frozen silk and or hydrogels, gas foaming, or salt-leaching; silk spheres can
be prepared by electrospraying or precipitation upon addition of solvent to a solution of silk, and silk
capsules can be prepared by adsorption of the protein at the interface of a water-in-oil emulsion. These
silk materials are often treated with alcohols (typically methanol and or ethanol) or aqueous solutions
of salts (such as potassium phosphate) in order to induce β-sheet formation to render them insoluble in
water while also changing the mechanical properties [37-39].
7.4 Engineered Silk Matrices for Cell-Based Engineering
and Drug Delivery
Over the last decade, numerous studies have explored the potential of native and regenerated silk fibroin-
based biomaterials in the context of biomedical applications (Table 7.2). Majority of research activity has
been focused on mulberry silk fibroin from
B. mori
due to the availability of this material as outlined earlier.
Biomaterials need to fulfill certain criteria, including physical, chemical, and biological cues to guide
cells into functional tissues via cell migration, adhesion, and differentiation. Degradation is also impor-
tant, particularly for many biomaterial applications and in regeneration needs in medicine, in general.
Ideally, biomaterials need to degrade at a rate commensurate with new tissue formation to allow cells
