Spider silk for artificial corneas and brain implants

New Scientist – Spider silk has a big future in technologies from artificial corneas to brain implants.

Weight for weight, a typical spider silk is 20 times as strong as steel and four times as tough as Kevlar. It is also extremely flexible, stretching up to 50 per cent of its length without breaking. And it’s not just the silk’s physical properties that are impressive. It elicits no immune reaction in our bodies, it is biodegradable, and it is produced at low temperatures and pressures relative to other polymers.

The most enticing aspects of silk are its optical and biological properties.

Researchers have laser-cut a film of artificial silk to create synthetic corneas.

They have developed ways to pattern silk films and has made holograms, lenses, sensors and diffraction gratings from the stuff.

Nature Photonics – A new route for silk

Silk is now finding a new application as a useful biocompatible material in photonic devices. Thin films, diffraction gratings and organic photonic crystals are just a few of the exciting possibilities.

The growing demand for optical interfaces and sensors for biomedical applications is motivating research towards realizing biocompatible photonic components that offer a seamless interface between the optical and biological worlds. Silk — a natural protein fibre — has recently emerged as a highly promising candidate owing to its excellent mechanical and optical properties, biocompatibility, biodegradability and implant ability.

Stem cells are happy to grow around spider silk, so a silk sponge could in theory be used as a scaffold to help mend broken bones or torn muscles.

Enzymes and proteins continue to function when embedded in silk, and that the material can be engineered to release its payload after a delay lasting anything from a few seconds to a year, just by tweaking how fast it will dissolve.

Biomaterials – Silk matrix for tissue engineered anterior cruciate ligaments

A silk-fiber matrix was studied as a suitable material for tissue engineering anterior cruciate ligaments (ACL). The matrix was successfully designed to match the complex and demanding mechanical requirements of a native human ACL, including adequate fatigue performance. This protein matrix supported the attachment, expansion and differentiation of adult human progenitor bone marrow stromal cells based on scanning electron microscopy, DNA quantitation and the expression of collagen types I and III and tenascin-C markers. The results support the conclusion that properly prepared silkworm fiber matrices, aside from providing unique benefits in terms of mechanical properties as well as biocompatibility and slow degradability, can provide suitable biomaterial matrices for the support of adult stem cell differentiation toward ligament lineages. These results point toward this matrix as a new option for ACL repair to overcome current limitations with synthetic and other degradable materials.

Researchers are also developing “meltable electronics” designed to become part of the fabric of living tissue. Last year, they demonstrated that silk could be used to deliver ultra-thin electronics directly onto the surface of the brain, a capability which could one day be used to diagnose epilepsy or improve brain-computer interfaces. Silk films offer a much more useful surface on which to embed electronics than traditional silicon wafers as they can conform to the contours of the brain without damaging tissue. The idea is that once in place, the silk is dissolved with salt water and broken down by the surrounding tissue. Capillary forces between the silk and brain tissue help the electronics to wrap around the brain

Nature Materials – Dissolvable films of silk fibroin for ultrathin conformal bio-integrated electronics

Electronics that are capable of intimate, non-invasive integration with the soft, curvilinear surfaces of biological tissues offer important opportunities for diagnosing and treating disease and for improving brain/machine interfaces. This article describes a material strategy for a type of bio-interfaced system that relies on ultrathin electronics supported by bioresorbable substrates of silk fibroin. Mounting such devices on tissue and then allowing the silk to dissolve and resorb initiates a spontaneous, conformal wrapping process driven by capillary forces at the biotic/abiotic interface. Specialized mesh designs and ultrathin forms for the electronics ensure minimal stresses on the tissue and highly conformal coverage, even for complex curvilinear surfaces, as confirmed by experimental and theoretical studies. In vivo, neural mapping experiments on feline animal models illustrate one mode of use for this class of technology. These concepts provide new capabilities for implantable and surgical devices.

19 pages of supplemental material

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