Tag Archives: fibroin

Coat fruit with silk to keep it fresh

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A May 6, 2016 news item on ScienceDaily describes a way to keep fruit fresh without refrigeration,

Half of the world’s fruit and vegetable crops are lost during the food supply chain, due mostly to premature deterioration of these perishable foods, according to the Food and Agriculture Organization (FAO) of the United Nations.

Tufts University biomedical engineers have demonstrated that fruits can stay fresh for more than a week without refrigeration if they are coated in an odorless, biocompatible silk solution so thin as to be virtually invisible. The approach is a promising alternative for preservation of delicate foods using a naturally derived material and a water-based manufacturing process.

A May 6, 2016 Tufts University news release (also on EurekAlert), which originated the news item, describes the work,

Silk’s unique crystalline structure makes it one of nature’s toughest materials. Fibroin, an insoluble protein found in silk, has a remarkable ability to stabilize and protect other materials while being fully biocompatible and biodegradable.

For the study, researchers dipped freshly picked strawberries in a solution of 1 percent silk fibroin protein; the coating process was repeated up to four times.  The silk fibroin-coated fruits were then treated for varying amounts of time with water vapor under vacuum (water annealed) to create varying percentages of crystalline beta-sheets in the coating. The longer the exposure, the higher the percentage of beta-sheets and the more robust the fibroin coating. The coating was 27 to 35 microns thick.

The strawberries were then stored at room temperature. Uncoated berries were compared over time with berries dipped in varying numbers of coats of silk that had been annealed for different periods of time. At seven days, the berries coated with the higher beta-sheet silk were still juicy and firm while the uncoated berries were dehydrated and discolored.

Tests showed that the silk coating prolonged the freshness of the fruits by slowing fruit respiration, extending fruit firmness and preventing decay.

“The beta-sheet content of the edible silk fibroin coatings made the strawberries less permeable to carbon dioxide and oxygen. We saw a statistically significant delay in the decay of the fruit,” said senior and corresponding study author Fiorenzo G. Omenetto, Ph.D. Omenetto is the Frank C. Doble Professor in the Department of Biomedical Engineering and also has appointments in the Department of Electrical Engineering and in the Department of Physics in the School of Arts and Sciences.

Similar experiments were performed on bananas, which, unlike strawberries, are able to ripen after they are harvested. The silk coating decreased the bananas’ ripening rate compared with uncoated controls and added firmness to the fruit by preventing softening of the peel.

The thin, odorless silk coating did not affect fruit texture.  Taste was not studied.

“Various therapeutic agents could be easily added to the water-based silk solution used for the coatings, so we could potentially both preserve and add therapeutic function to consumable goods without the need for complex chemistries,” said the study’s first author, Benedetto Marelli, Ph.D., formerly a post-doctoral associate in the Omenetto laboratory and now at MIT.

Here’s a link to and a citation for the paper,

Silk Fibroin as Edible Coating for Perishable Food Preservation by B. Marelli, M. A. Brenckle, D. L. Kaplan & F. G. Omenetto. Scientific Reports 6, Article number: 25263 (2016) doi:10.1038/srep25263 Published online: 06 May 2016

This is an open access paper.

Silky smooth tissue engineering

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Virginia Commonwealth University (VCU) researchers have announced a new technique for tissue engineering that utilizes silk proteins. From a May 13, 2014 news item on Nanowerk,

When most people think of silk, the idea of a shimmering, silk scarf, or luxurious gown comes to mind.

But few realize, in its raw form, this seemingly delicate fiber is actually one of the strongest natural materials around – often compared to steel.

Silk, made up of the proteins fibroin and sericin, comes from the silkworm, and has been used in textiles and medical applications for thousands of years. The [US] Food and Drug Administration has classified silk as an approved biomaterial because it is nontoxic, biodegradable and biocompatible.

Those very properties make it an attractive candidate for use in widespread applications in tissue engineering. One day, silk could be an exciting route to create environmentally sound devices called “green devices,” instead of using plastics. However, forming complex architectures at the microscale or smaller, using silk proteins and other biomaterials has been a challenge for materials experts.

Now, a team of researchers from the Virginia Commonwealth University School of Engineering has found a way to fabricate precise, biocompatible architectures of silk proteins at the microscale.

A May 12, 2014 VCU news release by Sathya Achia Abraham, which originated the news item, describes the research underlying two recently published papers by the research team

    Kurland [Nicholas Kurland, Ph.D.] and Yadavalli [Vamsi Yadavalli, Ph.D., associate professor of chemical and life science engineering] successfully combined silk proteins with the technique of photolithography in a process they term “silk protein lithography” (SPL). Photolithography, or “writing using light,” is the method used to form circuits used in computers and smartphones, Yadavalli said.

According to Yadavalli, SPL begins by extracting the two main proteins from silk cocoons. These proteins are chemically modified to render them photoactive, and coated on glass or silicon surfaces as a thin film. As ultraviolet light passes through a stencil-like patterned mask, it crosslinks light-exposed proteins, turning them from liquid to solid.

The protein in unexposed areas is washed away, leaving behind patterns controllable to 1 micrometer. In comparison, a single human hair is 80-100 micrometers in diameter.

“These protein structures are high strength and excellent at guiding cell adhesion, providing precise spatial control of cells,” Yadavalli said.

“One day, we can envision implantable bioelectronic devices or tissue scaffolds that can safely disappear once they perform their intended function,” he said.

The team’s current research focuses on combining the photoreactive material with techniques such as rapid prototyping, and developing flexible bioelectronic scaffolds.

Study collaborators included S.C. Kundu, Ph.D., professor of biotechnology at the Indian Institute of Technology Kharagpur in India, and Tuli Dey, Ph.D., postdoctoral associate, at the Indian Institute of Technology Kharagpur in India, who provided the silk cocoons used in the study and assisted with cell culture experiments. VCU has recently filed a patent on this work.

Here’s a link to and a citation for both papers,

Silk Protein Lithography as a Route to Fabricate Sericin Microarchitectures by Nicholas E. Kurland, Tuli Dey, Congzhou Wang, Subhas C. Kundu and Vamsi K. Yadavalli. Article first published online: 16 APR 2014 DOI: 10.1002/adma.201400777

© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Precise Patterning of Silk Microstructures Using Photolithography by Nicholas E. Kurland, Tuli Dey, Subhas C. Kundu, and Vamsi K. Yadavalli. Advanced Materials Volume 25, Issue 43, pages 6207–6212, November 20, 2013 Article first published online: 20 AUG 2013 DOI: 10.1002/adma.201302823

© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Both papers are behind a paywall.

I have written about silk proteins in a Nov. 28, 2012 post (Producing stronger silk musically) that briefly mentioned tissue engineering with regard to a new technique for biosynthesising  materials.