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Silk's sweet spot: untangling the requirements for artificial silk extrusion using a biomimetic approach

Sanches Pires, Rodrigo LU (2019) KBKM01 20192
Pure and Applied Biochemistry
Abstract
Up to this date, only a few silk hydrogels were reported to be injectable. Of these, none are truly biomimetic, and are instead comprised of blends with limited amounts of silk. Hence, no truly silk-based hydrogels exist as of today. From the reported injectable matrices, only a few have considered the natural progressive acidification to which silk proteins are exposed before spinning. Adding to that, none has considered the physiological limitations of the active silk-spinners, nor even what is the definition of a suitable extrusion.

In this report it is demonstrated that, even though silk spinning is a pultrusion-dominated process, one can achieve a biologically-relevant extrusion of silks that falls within the physiological... (More)
Up to this date, only a few silk hydrogels were reported to be injectable. Of these, none are truly biomimetic, and are instead comprised of blends with limited amounts of silk. Hence, no truly silk-based hydrogels exist as of today. From the reported injectable matrices, only a few have considered the natural progressive acidification to which silk proteins are exposed before spinning. Adding to that, none has considered the physiological limitations of the active silk-spinners, nor even what is the definition of a suitable extrusion.

In this report it is demonstrated that, even though silk spinning is a pultrusion-dominated process, one can achieve a biologically-relevant extrusion of silks that falls within the physiological capacities of the organisms that naturally spin silk. Furthermore, it is reported the existence of a specific concentration of silk where extruded gels reveal characteristics of an ideal injectable matrix. (Less)
Popular Abstract
Silks comprise one of the most fascinating group of natural materials. Spider silk, for instance, is the toughest natural fibre known to man. It is a very fine combination of stretchiness and strength that makes spider silks tougher than Kevlar, steel, and many other man-made polymers. Recently, an interest in using silks as biomedical materials has arisen, mostly due to the fact that they do not trigger an immune response, can degrade easily in the body, and that they provide a friendly environment for cells to grow. Despite all the hype in the biomedical field, only a few examples of Bombyx mori derived fibroin-hydrogels were reported to be injectable. Of these, none are truly biomimetic and are instead comprised of blends with scarce... (More)
Silks comprise one of the most fascinating group of natural materials. Spider silk, for instance, is the toughest natural fibre known to man. It is a very fine combination of stretchiness and strength that makes spider silks tougher than Kevlar, steel, and many other man-made polymers. Recently, an interest in using silks as biomedical materials has arisen, mostly due to the fact that they do not trigger an immune response, can degrade easily in the body, and that they provide a friendly environment for cells to grow. Despite all the hype in the biomedical field, only a few examples of Bombyx mori derived fibroin-hydrogels were reported to be injectable. Of these, none are truly biomimetic and are instead comprised of blends with scarce amounts of silk. Such is of critical level, as it limits the extension of silks to regenerative applications, like 3D-bioprinting, localized drug delivery, and many others. Such technical challenge can be understood as the fact that, in nature, silks are designed to be pultruded and spun, and are the product of 400 million years of evolution and natural selection towards a very cost-efficient spinning system. Although technically challenging, up to this point, only a few have considered the natural progressive acidification to which silk proteins are exposed before spinning. Of those few, none has considered the physiological limitations of the active silk-spinners, nor even what is the definition of a suitable extrusion. When it comes to the design of artificial silk extrusion systems, we considered those to be essential. Throughout this project, the reader will understand that, by using a novel biomimetic acidification to formulate silk hydrogels, and by extruding them at speeds relevant for injection applications, we have been able to successfully achieve an artificial extrusion of purely-made silk hydrogels, which is within the physiological limitations of the active silk-spinners (i.e.: provided silk spinning was an extrusion-dominated process, the animals would not die extruding our gels from their bodies). Adding to that, a silk concentration ideal for extrusion, called here the “silk’s sweet spot”, has also been discovered.

Our findings have important effects in the field of regenerative medicine and biofabrication, as silk hydrogels and injectable systems should then be targeted to be formulated and optimized at this specific sweet spot concentration. With this project, a very critical step in using silks as the ultimate biomedical material has been taken. Hopefully, new injectables and studies using silk-based systems will start targeting this optimal concentration, and significant achievements in the biomedical field should thus be soon seen. (Less)
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author
Sanches Pires, Rodrigo LU
supervisor
organization
course
KBKM01 20192
year
type
H2 - Master's Degree (Two Years)
subject
keywords
silk fibroin, injectability, extrusion, hydrogels, soft matter mechanics, biomimetic progressive acidification, silk self-assembly, thioflavin t, physical chemistry, biofabrication, spectroscopy, silk spinning, applied biochemistry, tillämpad biokemi
language
English
id
8999065
date added to LUP
2020-02-03 13:11:32
date last changed
2020-02-03 13:11:32
@misc{8999065,
  abstract     = {Up to this date, only a few silk hydrogels were reported to be injectable. Of these, none are truly biomimetic, and are instead comprised of blends with limited amounts of silk. Hence, no truly silk-based hydrogels exist as of today. From the reported injectable matrices, only a few have considered the natural progressive acidification to which silk proteins are exposed before spinning. Adding to that, none has considered the physiological limitations of the active silk-spinners, nor even what is the definition of a suitable extrusion. 

In this report it is demonstrated that, even though silk spinning is a pultrusion-dominated process, one can achieve a biologically-relevant extrusion of silks that falls within the physiological capacities of the organisms that naturally spin silk. Furthermore, it is reported the existence of a specific concentration of silk where extruded gels reveal characteristics of an ideal injectable matrix.},
  author       = {Sanches Pires, Rodrigo},
  keyword      = {silk fibroin,injectability,extrusion,hydrogels,soft matter mechanics,biomimetic progressive acidification,silk self-assembly,thioflavin t,physical chemistry,biofabrication,spectroscopy,silk spinning,applied biochemistry,tillämpad biokemi},
  language     = {eng},
  note         = {Student Paper},
  title        = {Silk's sweet spot: untangling the requirements for artificial silk extrusion using a biomimetic approach},
  year         = {2019},
}