About Natural Materials
This page aims to provide the reader with insights into the breadth of natural materials, their use and their properties. Contributions will be made by Board Members of the Natural Materials Association, and by invitation to experts within the natural materials sectors. The page will be updated over the course of the coming months. Until then, we hope you enjoy reading the articles we put up.
Dr Parvez Alam, School of Engineering, The University of Edinburgh, UK
The original article can be found in "Materials World", the official magazine of the IOM3, HERE.
Biological adhesions between bacterial cellulose nanofibrils can improve the performance of biomedical skins and grafts.
Bacterial cellulose (BC) discovered by A J Brown in 1886 is somewhat similar to plant cellulose. It has the same molecular formula, but is chemically more pure as it is free from other plant polysaccharides such as hemicellulose and lignin. It has a higher tensile strength, can be grown into almost any shape, has a superior water retention capacity, and a considerably finer architecture.
Properties such as these have made bacterial cellulose an ideal ingredient in foods such as nata de coco, a sweet jelly with increased fibrousness, chewiness and texture through the addition of bacterial cellulose. It has also been used as a thickener and stabiliser to help retain the viscosity of softer foods.
More recently, the properties of BC have gained the attention of materials scientists in the biomedical sectors where it is used as a wound dressing material, in the pulp and paper industries where it is used as an ultra-stiff paper base, and in coatings industries, where it can be used to stabilise coating suspensions.
BC is sourced naturally in South East Asia from microorganisms such as Acetobacter xyllinum, to cater for the multifaceted Asian food industries. It is a renewable, sustainable and biodegradable nanofibril, and has a nanoscale filamentous structure with very high crystallinity and outstanding properties of stiffness ranging on average between 78-143GPa. Separating the nanofibrils of BC is far simpler and less process-intensive than it is for plant-derived cellulose nanofibrils, making it an attractive ‘green nanomaterial’ with considerable potential in biomaterials applications.
The bulk matter of BC is effectively networked by β conform hydrogen bonds, which help align cellulose molecules into its tight crystalline structure. The β-conformation, as it is known, is a straight-backed molecular chain. The straightness of the molecules allows them to pack densely together, which can improve molecule to molecule interactions through hydrogen bonding. Therefore, BC surfaces are dense with hydrogen bonding sites, however the stiffness of the individual nanofibrils makes it difficult for interfibrilar alignment. BC nanofibrils can therefore create a weak network continuum when packed together with other BC nanofibrils, however, the true mechanical potential of BC is never reached in this way. This is reflected in the stiffness of BC sheets, which is reported to be between 2-15GPa, and is therefore a factor of 10 lower than the nanofibrillar stiffness. How can we scale up BC in a way that reduces losses from its nanofibrillar stiffness? Natural bio-adhesives may have some of the answers.
For materials scientists, the natural world is a constant source of design inspiration. Topics such as structural hierarchy, adhesion and material morphology are of particular interest, since they elucidate novel design guidelines in the advancement of mechanical materials. Biological adhesion is ubiquitous in the natural world, where it exists in a plethora of different function- specific chemical forms.
The design and utility of bio-adhesives in natural materials technologies also constitute an environmentally responsible engineering practice. Synthetic adhesives that could be used to connect BC nanofibrils are often toxic to the environment and do not easily degrade. This is why, when incredible examples of stickiness are found in the natural world - for example, aggregate and flagelliform silks, extracellular polymeric substances (EPS) from biofouling diatoms and mussels - attempts should be made to mimic at least their function and design strategies by using similar, naturally sourced bio-adhesives, preferably with minimal chemical modification.
When bio-adhesive functions are considered, it is possible to some degree to simplify their mechanisms of adhesion to those dominated by intermolecular secondary forces such as electrostatic and van der Waals, and those dominated by off axis sidechains that obstruct intermolecular shear. A good example of the former can be observed in the nanocrystals of structural biological silks. The stiffness of such nanocrystals is derived primarily from a large concentration of hydrogen bonds that arrange in a quasi-planar manner between β-sheet layers within the nanocrystal. The result is a nanostructure with an exceptionally high stiffness for a polymer.
Sidechains described in the latter case are different, as secondary interactions that arise between side chains and molecules tend to be off-axis, and therefore less likely to have the same cumulative level of quasi-planar resistance described in the first example.
In the case of molecules such as chitin, this has been shown to be beneficial to intermolecular adhesion, as the acetyl sidechains laterally stabilise the crystalline form of chitin, resulting in both higher stiffness and fracture toughness than in deacetylated chitin, chitosan, which lacks the side chains. Both of the mechanisms of adhesion described in the examples above can significantly improve the mechanical properties of biopolymers. It would stand to reason, therefore, that it is possible to improve the properties of ‘other’ materials by mimicking similar functional designs.
The materials design team at The University of Edinburgh focuses on biological and biomimetic composites design. They employed both of the bio-adhesive mechanisms previously described to improve the adhesion strength between BC nanofibrils. The specific amino acid monomers alanine and glycine were chosen as they are known to enable hydrogen bonding dominated stickiness in materials such as silk.
In the first instance, the amino acids were used as free-moving secondary bond-forming bio-adhesives between BC nanofibrils. During sheet-forming, the amino acid monomers were able to energetically optimise their locations and orientations between the BC nanofibrils, and in doing so, migrate into the most stable electrostatic attachment. The team also grafted the same amino acids to BC surfaces via esterification reaction on TEMPO-oxidised BC nanofibrils. TEMPO is a free radical reagent used to oxidise primary alcohols aldehydes.
The TEMPO-oxidisation reaction uses 2,2,6,6- tetramethylpiperidine-1-oxyl radicals to oxidise the C6 primary hydroxyl on the cellulose chains to form C6 carboxylate groups. This then allows for the grafting of alanine or glycine as sidechains to the surface of the BC nanofibril. Unlike the free-moving amino acids, when amino acids are grafted to BC surfaces in this way, they are constrained at one end, creating a hairy surface at the molecular-level.
Using experimental tests on manufactured BC sheets using both methods described, coupled with molecular dynamics simulations, the team learned that free-moving amino acids favour adhering BC surfaces together by aligning themselves parallel with the BC. Amino acids covalently attached to the TEMPO-oxidised BC surfaces, on the other hand, are considerably more constrained. The limited mobility in such instances, forces them to electrostatically bond to the nearest available hydrogen-bonding sites.
As such, the mobility of the free amino acid monomers gives them an advantage over pinned sidechains, raising the stiffness of BC sheets to more than 100% that of unglued BC sheets. The sheets made in the laboratory are about the size of a person’s hand – bigger sheets can be made by scaling up the manufacturing technology, which already exists, so sheet size depends solely on the size of the machine.
The researchers also found TEMPO-oxidation and amino acid grafting of BC gives rise to about 50% improvement in stiffness. Clearly, the free movement of bio-adhesives trumps molecular pinned sidechains in this instance, and if BC sheets are to go closer to their theoretical maximum (nanofibrillar) stiffness, bio-adhesives are a good starting point. Considerably more research needs to be done to tighten that hydrogen bonding network between BC nanofibrils to reach their theoretical maximum stiffness. In the future, clever molecular design strategies will need to be applied to bio-adhesive technologies, with the aim of maximising the potential for strong secondary interactions.
Figure caption: Free amino acids, as seen on the left hand side of the figure, are able to position themselves in the most energetically favourable way and are able to attach to cellulose molecules with more hydrogen bonds (red dotted lines) than the amino acids that are grafted to the TEMPO oxidised cellulose molecules, as seen on the right hand side of the figure.
Next, this research will be taken to a more applied environment by engaging industrial support from the paper, board, packaging, and biomedical engineering sectors. The future of TEMPO-oxidised BC needs to be revisited using a variety of different bioglues and bonding methods, given that an end goal is to mechanically enhance BC. The design strategies of molecular materials should be guided by atomistic models, and the most promising of them, chemically replicated and tested.
This research approach is believed to elucidate the larger spectrum of possibilities for the control of the mechanical behavior of BC materials.
Bacterial cellulose is a natural, non-toxic, biodegradable material with exceptional mechanical properties and characteristics. It is, however, a nanomaterial and as such must be conjoined with others of its kind to form larger bodies of engineering material. The properties of the nanofibrils are reduced when they are collected together into larger structures and as such a challenge for materials researchers is to deduce novel methods for combining them without reducing their green-materials character. Bioadhesives are a material choice that potentialises the recovery of nanofibrillar mechanical character by improving stress transfer between the nanofibrils. Free-moving bioglues and bioglues pinned through TEMPO-oxidation show promise in the development of stiffer bacterial cellulose materials, however, research efforts in this area are still sparse and applied research will be needed to control and manipulate their mechanical properties for specific applications.
BAMBOO HYBRIDS CAN BOLSTER UK TIMBER SUPPLIES
Hector Archila, University of the West of England, and Founder, Amphibia BASE Ltd.
The original article can be found in "Materials World", the official magazine of the IOM3, HERE.
A relatively common material is not being embraced fully for building supplies.
Interest in bamboo is growing, through research and media campaigning about the material’s environmental benefits, properties and its ability to replace wood, steel and carbon-fibre. But bamboo is not commonly used in high-performance applications or permanent structures, and its potential in construction remains untapped.
Academic and industrial research carried out in the UK aimed to address the challenges associated with using bamboo in durable, safe and cost-efficient structures. Further combining the grass with UK-grown wood could maximise use of this material and make economic sense for the domestic forest sector.
Figure caption: A 2,000m² warehouse using Guadua in Bogotá DC, Colombia. All images credited to: Hector Archila.
High bamboo scaffoldings used when working on Hong Kong’s skyscrapers, and earthquake and typhoon-proof structures in Ecuador, Colombia and in the Philippines are a testament to the material’s mechanical properties. While regarding bamboo as a green steel and drawing a like-by-like replacement for steel is fundamentally wrong, as I said in the previous work Bamboo reinforced concrete: a critical review on the website Open Access, July 2018, the axial stiffness-to-weight ratio of bamboo is remarkably high and almost the same as that achieved for steel (25 x 106m2s2).
However, this only applies to the mechanical properties of bamboo in the direction of its fibres i.e. it is longitudinal only. In any other direction, radially or tangentially, bamboo is very weak and tends to split and crush, unlike steel, which is isotropic. This is not to say bamboo should be scrapped, but more carefully considered.
Bamboo has a higher CO2 absorption than other materials. Compared with a native British tree like Scots Pine, Guadua – a giant species
of a tropical ‘woody’ bamboo endemic to South America – is able to absorb about five times more CO2 in a given period.
The mean yield class for Scots Pine in the UK, as given by the Forestry Commission, is an increment of 10m3 per hectare per year, while for Guadua it is 45m3 per hectare per year. Scots Pine would reach maturity at around 40 years old, while Guadua would be ready to harvest aged between three-five years.
Bamboo could provide large quantities of feedstock material for construction products that retain the fixed CO2 for long periods of time, for example in buildings where an effective lifespan ranges between 50-100 years. A way to unlock bamboo’s potential is by combining it with complementary materials like wood, which can address its radial weakness and thin-walled section, while exploiting its high axial stiffness and maintaining its high carbon and environmental credentials.
Based on research carried out at the University of Bath, UK, Amphibia BASE is working to commercialise bamboo and demonstrate the business case for structural engineered bamboo products in the UK and worldwide. The key to making this a reality has been the use of thermo-hydro-mechanical (THM) technologies, which rapidly and efficiently transform bamboo into flat planks with higher density and improved mechanical properties.
THM technologies involve temperature, moisture content and mechanical pressure controls to modify the material’s properties, for example its density and hardness, or to shape it into the desired form. Processing can be finished in 15 minutes, compared with three hours by conventional means. The company’s THM process reduces the void spaces within bamboo conductive tissues, bringing the naturally scattered bamboo fibres closer together without causing cell damage – effectively densifying bamboo and producing a more homogeneous cross-section. This is evident from microscopy analysis of the material before and after THM densification. These are desirable features in structural engineering when designing and predicting the behaviour of materials in high-performance applications.
As a result of the THM process, the density and Young’s modulus of bamboo are both increased almost two-fold from 540–890kg/cm3 and 16.88-30.72GPa – the force applied in kilonewton per square millimetre – respectively. This straightforward densification process, reduces waste by 50%, as well as the high energy and labour intensity of conventional manufacturing processes of engineered bamboo products (EBPs) for non-structural applications. When laminating the THM densified bamboo, glue use is reduced from 30–3% per overall weight of the final product in some commercially available EBPs. These features were demonstrated in cross-laminated bamboo products G-XLam, manufactured by Amphibia BASE in the UK, at lab-scale.
However, when densified bamboo is laminated on its own, the resulting product is very stiff, heavy, over-engineered and costly. The bending modulus of G-XLam 3 – three layers – obtained through testing was 23.68GPa, twice the value for the same property in cross-laminated timber (CLT) panels with the same three layers 11.6GPa. CLT is becoming increasingly popular for use in buildings reaching heights once thought unviable with timber. For instance, an 85.4m-high, all-timber tower designed by Voll Arkitekter was recently finished in Brumunddal, Norway, and is currently the highest tall timber building in the world. Overall, G-XLam panels have one-fifth of the thickness of CLT panels and double the density. By contrast, when a lower density timber is used, the number of laminations and product density can be reduced to an acceptable and cost-efficient level while retaining the stiffness and stability of the laminated product. Therefore, THM-densified bamboo can be used to strengthen low-density and low-strength wood, adding value to the final product and reducing the overall section of the structural timber product. This can also be applied to other low-density cores forming the hybrid composite.
In the case of wood, statistics from 2018 by the Forestry Commission show about 70% of the sawn wood and 100% of the plywood and structural timber products used in construction in the UK were imported mainly from Europe. This is partly due to the low density, poor finishing and unsuitability of UK-grown wood, it being used mostly in low value-added applications, for example fencing. Timber experts may argue that in the UK, we need to loosen strength-grading standards for homegrown timber and establish a robust capacity to dry the wood for high value-added products such as CLT.
Around 50% of the forested areas of the UK is Sitka spruce. Due to the UK climate, Sitka grows very quickly, which does not allow for tissue consolidation and renders a low strength (C16) and lightweight timber that is commonly considered low-quality and value. However, when combining UK timber of lower strength class with THM-densified bamboo of higher stiffness, the resulting hybrid product can achieve properties equal to those achieved using timber from mainland Europe, for example in CLT panels. Although UK forests have recovered since the industrial revolution, there is limited land, thus the available timber.
Wood-bamboo hybrids could significantly reduce the amount of wood required for engineered products and tackle quality and strength issues in UK-grown supplies. Further benefits include the support of the local UK forest industry and rural economy, the reduction of the UK’s reliance on imported European timber and CLT elements, and the development of new markets locally and internationally. Also, exploitation of under-utilised and readily available bamboo resources in tropical countries using state-of-the-art technologies developed in the UK can offer a cost-effective and highly sustainable alternative to carbon and energy-intense conventional materials used in construction, such as steel and cement.
Technological challenges regarding adhesion and drying of home-grown wood to acceptable levels, which are key to the success of this commercial venture, are being addressed. Additionally, the use of the vast knowledge and expertise on timber for building applications helps tackle the current lack of internationally recognised standards for standalone structural bamboo products. Currently, funding and investment is being sought to develop a pilot facility that rolls out the technology and showcases the viability of producing wood-bamboo hybrids in the UK.
SPIDERS 'GO WITH THE FLOW'
Dr Chris Holland, Department of Materials Science and Engineering, University of Sheffield, UK
Figure caption: The golden orb-weaving spider Nephila edulis
When asked by my Dphil supervisor if I would like to look into silk rheology I didn’t know what rheology was and how it would shape my research career. Five years on when asked what I do for a living I now reply with enthusiasm “I study how spiders and silkworms spin silk”.
Rheology concerns the study of the flow and deformation of matter. Here I will discuss how we have found use for this technology to study features of the natural world, specifically in understanding how Nature produces one of her finest materials, silk. More usual for this technique are questions about engineering materials such as the visco-elastic properties of paints, polymers and food.
Silk is a biological material, a protein fibre produced through a process called spinning. It is unique to the arthropods, where it is wide spread. The most famous silk producers are the spider and many moths, foremost among them the silkworm. However it may surprise you that silk is spun by some bee’s and ants too! The evolutionary success of silk can be attributed to its versatility, being used for protection from predators to capturing of prey with reproduction and dispersal of young in-between. Spiders are exceptional in producing more than one type of silk. Indeed they are able to make up to seven different types of silk, with each fibre possessing mechanical properties specifically tuned to their biological function.
Whilst silk is clearly an attractive material in nature man has also been captured by its qualities. The silk of the Chinese silkworm (Bombyx mori) is the world’s oldest commercial fibre, dating back over 5000 years. Being one of only two truly domesticated insects (bees being the other) today Bombyx are reared in the millions and current worldwide production of silk is in excess of 100,000 metric tonnes with a value of over $1bn (before the added value of high-end textiles). However the reasons for the commercial success of silk go way beyond simple aesthetics. Spider silk in particular is weight for weight stronger than steel and it is much tougher than Kevlar. It could be considered the pinnacle of any fibre production process and quite unlike its industrial counterparts silk is ‘green’, being produced sustainably at room temperatures, using only water as a solvent and being completely biodegradable.
Figure caption: The Chinese silkworm Bombyx mori
Yet despite our fascination with this supermaterial for five millennia we know surprisingly little about its evolutionary origins and synthesis. However because silk has been selected primarily for its physical properties and to perform outside the body, it is possible to translate the testing methodologies we use to characterise our man-made materials to try to understand why silk is so interesting and important.
One such technique applied to silk has been straightforward tensile testing. By stretching silk fibres we are able to determine many of their physical properties, from how stiff they are to how much energy they can absorb (toughness). The most informative animal to use in this approach is the multi-talented spider. By carefully ‘silking’ the spider onto a reel we are able to control the production rate (reeling speed) of a silk and in conjunction with varying the temperature and humidity it is possible to produce silks from the same feedstock with a wide range of mechanical properties. By repeating this for different spiders we begin to see overlaps in these properties, to the extent that even silks with different amino acid compositions can be tuned to have almost identical material properties. This implies that the processing of a silk is as important as the feedstock in defining a silk fibre’s performance.
Figure caption: Spiders can produce up to seven different types of silk each with mechanical properties optimised for their usage
Therefore a pertinent question to ask is how is silk spun? Quite unlike other biological materials which are grown slowly over months and years (like hair bone and feathers), silk is by definition spun, in seconds transforming from gel to fibre. In the spider and silkworm the silk protein feedstock is stored as a gel, potentially for extended periods of time, in specialised organs called silk glands. Upon spinning these proteins travel down an elongated tapering tubular duct (shaped like an industrial hyperbolic dye) during which they undergo a transition into a solid fibre.
Examining these events on molecular scale reveals that in order to spin you need a source of energy. This energy fuels the removal of water from the silk proteins and the subsequent alignment and formation of a network of strong amide-amide intra and intermolecular hydrogen bonds. This network consists of ordered (high H-bonding) and disordered (low H-bonding) regions. Whilst it may be thought that a fully ordered crystalline material may be preferable, it is this careful balance of order and disorder at the nano-meter level that is responsible for silk’s superior mechanical properties. When silk deformed (i.e. stretched) stress is concentrated in the ordered regions (the stiffest parts) and then quickly and efficiently transferred to the disordered regions which are able to dissipate this excess energy as heat. Because silk is excellent at dissipating energy it is very tough, making it the ideal material to absorb impact (from a fly hitting a web to a bird attempting to break a cocoon).
But what is the main source of energy that fuels the transition from gel to fibre? Here we draw inspiration from an unlikely source: fishermen. Prior to the introduction of nylon fishing lines in the second half of last century fishermen took the silk glands of Bombyx and repeatedly drew them through their teeth, much like pulling chewing gum. If sufficiently skilled the fishermen could produce fibres that were very strong and in fact superior to the first plastic alternative lines that came onto the market. We now know that quite like the spider and the silkworm, the fishermen were using the same method of introducing energy into silk, by shearing the silk proteins. Here we can use rheology to further our understanding. By characterising exactly how these materials respond to shear deformation (mechanical energy input), we can begin to determine how silk is spun. Through rheology, the study of flow and deformation of matter, we are able to apply these shearing conditions to silk in vitro, thus providing us with a window into the silk production process.
Figure caption: Viscosity shear rate curves of the spider and silkworm reveal they are very similar and can be compared to polymer models, however they are completely different to the same amount of reconstituted (artificial) silk.
Whilst fortunately my research does not involve me pulling silk trough my teeth, there have been moments where studying this material has felt like pulling teeth.
One such moment arose at the start of this work: We quickly discovered that preparing unspun silk for rheological testing requires incredible care and attention. Unspun silk is maintained at the precipice of the transition from gel to fibre, so much so that the smallest introduction of energy initiates this process. Thus when handling these materials the slightest shearing of the material through pinch of the forceps or accidental bump leads to massive variations in the data (over two orders of magnitude for viscosity). This can essentially mask any intended induced experimental variation. Thus during the first year I had to develop new ways of handling silk feedstocks and loading them onto the rheometer before we were able to even start investigating them.
In practice rheological testing involves placing the fresh silk feedstock between two metal plates (8mm in diameter) and moving the top relative to the bottom, thus subjecting the sample to different combinations of stress and strain. From this we are able to get information regarding the materials ability to handle energy over different timescales (oscillation tests) or the degree of intermolecular associations (viscosity tests).
Once the methodology was mastered we were keen to examine differences between the flow properties of silk feedstocks. Given tens of thousands of silks to choose form we confined our initial studies to comparing the silks of the golden orb weaving spider (Nephila edulis) and the commercial Chinese silkworm (Bombyx mori). Our work confirmed previous rheological studies on silkworm dope in that it is a weak gel with Non-Newtonian properties, therefore what about the spider?
The results were quite surprising. We found that despite hundreds of millions of years of evolutionary separation, using unrelated proteins and being selected to produce materials for completely different purposes (protection, silkworm, and capture, spider) the rheological properties of these two silks were practically identical. From a biological perspective this is important as it is a perfect example of evolutionary convergence, and something that is as yet invisible to molecular approaches. Hence we concluded that in order for Nature to spin a high performance fibre these feedstocks are under evolutionary constraints to have a particular set of rheological properties.
Most surprising however was not that these two materials behaved the same as one another, but that their rheological properties were akin to classic molten polymers! This has opened the door to using tools and techniques developed for the polymer sciences to be adapted to study silk. On the flip-side, because of a similar approach to processing our materials we can now learn from silk to improve our current polymeric fibre production methods.
Hence biotechnologically, the spinning pathway of the spider and silkworm is a highly advanced fibre production system. Through it the animal is able to control the energetically efficient production of fibres, with a wide variation of mechanical properties, using the same feedstock, by just altering the spinning conditions. These properties, perhaps even above the high performance characteristics, makes silk such a highly desirable material.
Therefore it is not surprising that many attempts have been made to recreate silk. Typically such artificial silk fibres are spun from natural silk that is “reconstituted” (chemically broken down) and then respun using processing conditions ranging from classical alcohol baths to electrospinning. However the tensile mechanical properties of these reconstituted fibres pale in comparison to their natural progenitors. Thus we were faced by a problem; by testing the properties of the end product alone it becomes difficult to determine what requires improvement, the feedstock or the processing.
Here we took the evolutionary constraints from our first study and turned them into design criteria for artificial silks. Our hypothesis was simple, if you could match the rheological properties of the reconstituted silk feedstock to the native feedstock then you should be able to process them like a silk into a silk-like fibre. Thus our rheological characterisation methods would help us to determine whether reconstituted silk dope actually has the potential (or not) to form a fibre with the qualities of its natural predecessor and model.
Consequently in our second study we compared the rheological properties of artificial and natural silk feedstocks over a wide range of concentrations (0.1-30% dry weight). Our findings were astonishing. For the same amount of silk protein present in the feedstocks there was over five orders of magnitude - a 10000 fold - difference between native and reconstituted silks in their ability to absorb energy (as defined by the plateau modulus) and the strength of their intermolecular associations (as defined by the zero shear viscosity). Put in real world terms the viscosity differences are akin to comparing lard to that of olive oil. We concluded that the act of reconstitution severely damages the silk proteins and that it will not be possible to spin biomimetically until the quality of the feedstock can be improved although rheology now holds the key to unlocking both the secrets of the feedstock and as a QA tool to improve our methods of reconstitution.
Where are we headed in the future? I have shown that rheology has created two new pathways for the field of studying silk, understanding the processing and development of a next generation artificial silk feedstock. From a scientific perspective we must start integrating new tools with rheology to characterise the responses of the silk proteins to shear on a molecular scale. One such approach is our work with the ISIS pulsed Neutron source at the Rutherford Appleton Laboratories where we are now beginning to combine state-of-the-art rheometry with small angle neutron scattering to understand how the conformation of the silk proteins change as they are being spun. From an industrial perspective things are already moving quickly in interesting directions demonstrating silk is more than just a fibre. Because silk can be chemically “unspun” back into a feedstock is may be reprocessed in new and exciting ways, creating structures from films to foams. The initial use of these materials is found in biomedical devices and implants that make use of silks excellent mechanical properties, biocompatibility and its ability to be chemically functionalised.
And what is the final lesson: stop during your spring-cleaning and spare a thought for the spider and its amazing technology.
PROTECTING VACCINES WITH A SUSTAINABLE 'SMART FIBRE'
Angela Morris – CEO The Wool Packaging Company