Question 1

What is silk fibroin and why is it used in bioengineering?

Accepted Answer

Silk fibroin is a protein polymer extracted from silkworm cocoons, characterized by repetitive beta-sheet structures that provide exceptional strength and toughness. Its tensile strength can be up to four times that of bone, making it ideal for bioengineering applications. Silk has been used commercially for medical sutures for decades and offers biocompatibility and controllable mechanical properties for tissue engineering and regenerative medicine.

Question 2

How is silk fibroin extracted and processed from cocoons?

Accepted Answer

Silk cocoons are cut into pieces and boiled in sodium carbonate solution to remove sericin, a glue-like protein. The fibroin is then washed, dried, and dissolved in lithium bromide solution at 60 degrees. The solution undergoes dialysis to remove lithium bromide, followed by centrifugation to eliminate particulates. The resulting aqueous silk solution is stored at four degrees until use.

Question 3

What happens during the electrospinning process?

Accepted Answer

Electrospinning applies high voltage between a syringe needle (spinneret) and a grounded collection surface. Electrostatic forces overcome surface tension, drawing the silk solution into a Taylor cone and then a fluid jet. The fibers solidify and collect randomly on the collector, forming a nanofiber mat. Distance between spinneret and collector must be optimized to ensure proper fiber formation and uniformity.

Question 4

Why does silk solution lose mechanical properties and how is it recovered?

Accepted Answer

When silk fibroin is solubilized, it loses its secondary beta-sheet structure, diminishing mechanical properties. Treatment with methanol can induce partial recovery of these critical beta-sheet structures, restoring strength and toughness. This recovery is essential before electrospinning to ensure the resulting fiber mats possess desired mechanical characteristics for bioengineering applications.

Question 5

How are electrospun silk mats used in tissue engineering?

Accepted Answer

Electrospun silk mats serve as tissue scaffolds, providing structural support for three-dimensional tissue formation. Cells are seeded directly onto these fiber structures, which mimic natural tissue architecture and function. Scaffold design varies by application; muscle tissue scaffolds require more aligned fibers than skin scaffolds. These structures promote favorable cell interactions while maintaining biocompatibility and biodegradation properties.

Question 6

What other biomaterials can be electrospun besides silk?

Accepted Answer

Spider silk, produced synthetically using biotechnology, offers higher mechanical strength than silkworm silk and is electrospun for applications like filtration devices. Man-made polymers such as polycaprolactone and polylactic acid are also electrospun because they are biodegradable and biocompatible. These synthetic materials allow precise tailoring of properties to create hydrophobic or hydrophilic surfaces for specific bioengineering applications.

Question 7

What factors affect the quality of electrospun fiber mats?

Accepted Answer

The distance between spinneret and collection surface critically affects fiber quality. If too small, fibers lack time to solidify, forming inconsistent ribbons. If too large, fibers become clumped or non-uniform. Syringe pump flow rate and voltage settings also influence fiber formation. Using a rotating collection surface enables production of aligned fiber mats instead of randomly arranged ones, depending on application requirements.

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