01520nas a2200205 4500008004100000022001400041245008000055210006900135260007100204300001400275490000700289520077400296100002301070700001901093700002101112700002101133700002401154700003201178856010401210 2009 eng d a0888-588500aSome mechanistic insights into the gelation of regenerated silk fibroin sol0 aSome mechanistic insights into the gelation of regenerated silk  a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcSEP a8014-80230 v483 a

We provide some new insights into the kinetics and mechanism of sol-gel transition as it pertains to regenerated silk fibroin, which is the principle structural protein of silkworm silk fiber. Silk fibroin was dissolved in lithium bromide and dialyzed against deionized water to prepare a regenerated fibroin solution. This solution was found to be unstable at lower pH and transformed into a colloidal gel. The kinetics and mechanism of the sol-gel transition were investigated using rheology and light scattering. We show that gelation proceeds in two steps. In the first step, a weak gel is formed almost immediately upon lowering the pH, while in the second step further gelation proceeds rapidly after a long induction time to form a self-similar structure.

1 aNagarkar, Shailesh1 aPatil, Avinash1 aLele, Ashish, K.1 aBhat, Suresh, K.1 aBellare, Jayesh, R.1 aMashelkar, Raghunath, Anant uhttp://library.ncl.res.in/content/some-mechanistic-insights-gelation-regenerated-silk-fibroin-sol-001760nas a2200181 4500008004100000022001400041245005500055210005500110260011000165300001400275490000700289520110400296100002301400700001801423700002801441700002101469856008801490 2010 eng d a1463-907600aStructure and gelation mechanism of silk hydrogels0 aStructure and gelation mechanism of silk hydrogels aTHOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLANDbROYAL SOC CHEMISTRYcFEB a3834-38440 v123 a

Silk fibroin was regenerated from cocoons produced by the silkworm Bombyx Mori. Light scattering showed that an aqueous solution of the regenerated silk fibroin (RSF) was made of individual proteins with a weight average molar mass of about 4 x 10(5) g mol(-1) and a hydrodynamic radius of about 10 nm. Gel formation of RSF in acidic solutions was investigated as a function of the pH (2-4), concentration (0.5-10 g L(-1)) and temperature (5-70 degrees C). The structure of the gels was studied using light scattering and confocal laser scanning microscopy. The structure was found to be self-similar from length scales of less than 15 nm up to length scales of about 1 mm, and characterized by a correlation length of a few microns. Gel formation was tracked using turbidity, rheology, light scattering and circular dichroism. Gelation involves the formation of self-similar aggregates with a growth rate that increases exponentially. The protein aggregation is correlated to, and perhaps caused by, the formation of beta-sheets, the fraction of which also increases exponentially with time.

1 aNagarkar, Shailesh1 aNicolai, Taco1 aChassenieux, Christophe1 aLele, Ashish, K. uhttp://library.ncl.res.in/content/structure-and-gelation-mechanism-silk-hydrogels-002768nas a2200229 4500008004100000022001400041245013600055210006900191260000800260300001400268490000700282520195800289653002602247653001002273653002602283653001302309100001902322700002302341700002002364700002702384856012702411 2019 eng d a0969-023900aStructure-property relations in regenerated cellulose fibers: comparison of fibers manufactured using viscose and lyocell processes0 aStructureproperty relations in regenerated cellulose fibers comp cAPR a3655-36690 v263 a

Regenerated cellulose fibers are produced using two industrially dominant technologies: the viscose and lyocell processes. Here, we compare commercially available fibers, prepared using the viscose and lyocell processes. Single fibers are subjected to a variety of mechanical deformations to obtain stress-strain, stress relaxation and stress recovery data. These are fitted to a phenomenological model, whose parameters are interpreted in terms of the fiber semicrystalline microstructure. This simple model does not incorporate the complexities of semicrystalline microstructure. Rather, it represents structure in a semicrystalline polymer fiber in terms of an elastic crystalline phase that coexists with a viscoelastic Voigt-like glassy amorphous phase. Lyocell fibers are characterized by higher values of crystalline modulus relative to viscose. Lyocell fibers also have a higher amorphous phase modulus and a wider relaxation spectrum than viscose, suggesting that amorphous and crystalline phases are dispersed in close connectivity in lyocell. Viscose and lyocell fibers exhibit qualitative similarities in their mechanical response. On stretching, there is a transition in the stress-strain curve from a low strain elastic response at a critical value of strain. This critical strain has been incorrectly attributed to yielding of the fiber. We establish that this critical value corresponds to an apparent yield. When subjected to strains higher than this apparent yield point, the fibers develop a memory of the mechanical deformation. This memory decays slowly, logarithmically with time and is lost over about a day as the fiber structure transitions back to the original as spun fiber. Finally, we demonstrate that on wetting the fibers with water, there is an increase in the apparent yield strain for viscose fibers, but not for lyocell. We interpret these results in terms of the semicrystalline microstructure of the fibers.

10amechanical properties10aModel10aRegenerated cellulose10aYielding1 aSharma, Aakash1 aNagarkar, Shailesh1 aThakre, Shirish1 aKumaraswamy, Guruswamy uhttp://library.ncl.res.in/content/structure-property-relations-regenerated-cellulose-fibers-comparison-fibers-manufactured