A short lecture on bionanocomposites.pptx

The slide covers an overview of the theory and applications of bio-nanocomposites.

1. Nanocomposites Nanocomposites are a class of materials in which one or more phases with nanoscale dimensions (0-D, 1-D, and 2-D) are embedded in a metal, ceramic, or polymer matrix. The general idea behind the addition of the nanoscale second phase is to create a synergy between the various constituents, such that novel properties capable of meeting or exceeding design expectations can be achieved . The properties of nanocomposites rely on a range of variables, particularly the matrix material, which can exhibit nanoscale dimensions, loading, degree of dispersion, size, shape, and orientation of the nanoscale second phase and interactions between the matrix and the second phase. Among the various nanocomposites types, the polymer-matrix nanocomposites have been the most studied. Much like traditional composite systems, polymer-matrix nanocomposites consist of a matrix made from a polymeric material. However, the second phase (usually a few percent by weight, wt%), which is dispersed within the matrix, has nanoscale dimensions.

2. Nanocomposites can be considered solid structures with nanometer-scale dimensional repeat distances between the different phases that constitute the structure. These materials typically consist of an inorganic (host) solid containing an organic component or vice versa . Or they can consist of two or more inorganic/organic phases in some combinatorial form with the constraint that at least one of the phases or features be in the nanosize . Extreme examples of nanocomposites can be porous media, colloids, gels, and copolymers nanostructured phases present in nanocomposites as zero-dimensional (e.g., embedded clusters), 1D (one-dimensional; e.g., nanotubes), 2D ( nanoscale coatings), and 3D (embedded networks ). In general, nanocomposite materials can demonstrate different mechanical, electrical, optical, electrochemical, catalytic, and structural properties than those of each individual component. The multifunctional behavior for any specific property of the material is often more than the sum of the individual components .

3. Apart from the properties of individual components in a nanocomposite , interfaces play an important role in enhancing or limiting the overall properties of the system . Due to the high surface area of nanostructures, nanocomposites present many interfaces between the constituent intermixed phases. Special properties of nanocomposite materials often arise from interaction of its phases at the interfaces . An excellent example of this phenomenon is the mechanical behavior of nanotube-filled polymer composites. Although adding nanotubes could conceivably improve the strength of polymers (due to the superior mechanical properties of the nanotubes), a noninteracting interface serves only to create weak regions in the composite, resulting in no enhancement of its mechanical properties.

4. The inclusion of 1-D nanomaterials , in particular carbon nanotubes (CNTs) for the reinforcement of nanocomposites . The use of CNTs in composites has received wide attention due to their extraordinary physical and mechanical properties . However, to take full advantage of CNTs for nanocomposite applications, several critical factors need to be addressed: (1) uniform dispersion of carbon nanotubes within the polymer matrix, (2) alignment of CNTs in the nanocomposite , and (3) good interfacial bonding between the CNTs and the polymer matrix. With respect to the dispersion of CNTs, the work has been very challenging , particularly compared with the procedure for dispersing carbon fibers in traditional composite materials. This is because CNTs exhibit smooth surfaces and intrinsic Van der Waals interactions, which tend to promote clustering when dispersed in a polymer matrix If agglomeration occurs, the CNTs are less adhered to the matrix and will slip against each other under an applied stress , with drastic consequences for the mechanical properties

5. Typical agglomeration of carbon nanotubes . Dispersion of CNT in chitosan

6. Natural nanobiocomposites are exactly what the name implies, that is, natural composite materials with structure on the nanoscale . Biomimetic nanocomposites are synthetic nanocomposite materials formed through processes that mimic biology as closely as possible; And biologically inspired nanocomposites are composite materials with nanoscale order created through processes that are inspired by a biological process or a biological material, but without attempting to mimic, or directly copy , the mechanism of formation of the biological material. There are many areas including mixtures of two or more materials in which the materials form a homogeneous mixture (and thus are not composites) or in which the organic molecule is simply dispersed in an organic host, such as organic molecules in a sol–gel matrix. Ajaun cover the widely publicized work on mesoporous silica and related materials, because several very good reviews on this subject already.

7. Nanobiocomposite form a fasinating interdisciplinary area that brings together biology, materials science and nanotechnology Bionanocomposite a new dimension to enhance the properties in that they are biocomposite and or biodegradable materials These nanocomposites are of immunse interest to biomedical technologies such as tissue engineering, bone repalcemnetr / repair, dental applications and controlled drug delivery. Natural organic/inorganic Nanocomposites Biological nanocomposite materials Natural nanobiocomposite materials Types of nanocomposites

8. Biological nanocomposite materials Can be divide into three: Entirely inorganic Entirely organic Mixture of inorganic and organic materials What is unique about synthetic process? “even final material may be entirely one class of material, multiple classes of materials may be involved in the synthetic process, which may or may not remain in the final structure ”.

9. Example of biological nanocomposites The organic material does not remain in the final product : Enamel of the mature human tooth 95wt% consist of hydroxyapatite During tooth formation; Enamel consist of proteins (primarily amelogenin and enamelin ) and hydroxyapatite. But the proteins removed as the tooth develop. Presence of protein and self-assembled structures they form with other biological macromolecules – help generate the mineral cross-ply structure of the enamel (plays a major part in its toughness)

10. Example of biological nanocomposites Inorganic/organic structural composite for both phases remain in the final product Aragonitic nacreous layer of the abalone shell It is exceptionally strong because of its organic/inorganic layered nanocomposite structure Crystalline ceramic layers are separated by highly elastic organic layers Synthetic efforts have been made for more than 10 years- their properties have been inferior.

11. Natural nanobiocomposite materials Natural composite materials with structure on the nanoscale All the functionality provided by these materials- direct consequence of the nanoscale dimensions of the structure. Example of nanoscale materials in biology: Lipid cellular membranes Ion channels Proteins DNA Actin Spider silk and etc.

12. NATURAL NANOCOMPOSITE MATERIALS Natural composite materials with structure on the nanoscale 2. BIOMIMETIC NANOCOMPOSITES Synthetic nanocomposite materials formed through processes that mimic biology as closely as possible 3. BIOLOGICALLY INSPIRED NANOCOMPOSITES Composite materials with nanoscale order created through processes that are inspired by a biological process or a biological material. Without attempting to mimic or directly copy the mechanism of formation of the biological materials

13. Natural organic/inorganic Nanocomposites 3 types according to level of complexity: Simplest example- those in which mineral phase is simply deposited onto or within an organic structure (1 st route) . Eg : Grasses – many species precipitate SiO 2 within their cellular structures Bacteria- magnetic bacteria has internal chain of magnetite (Fe 3 O 4 ) nanocrystals running down their long axis. Medium level- in which the structure of mineral phase is clearly determined by the organic matrix (1 st route) . Bacteria S-layer- serves as protein template for the formation of thin film of mesostructured gypsum Highest level- in which the structure of mineral is intimately associated with the organic phase to create a structure with properties superior to those of either the mineral or organic phases (2 nd route) Sea urchin spine- single crystal essentially composed of calcite, containing only about 0.02% glycoproteins trapped within the crystal lattice of the spine Nacreous (mother-of-pearl) layer of the abalone shell- alternating layers of 500 nm thick aragonite platelets and ~30 nm thick sheets of an organic matrix Bone - Complex structure and function

14. Completely organic nanocomposites (Spider silk) Dragline spider silk which makes up the spokes of a spider web Criteria: Strong core that composed of primarily of two protein components that self assemble into crystalline and amorphous regions Crystalline regions- alternating alanine-rich crystalline forming block; impart hardness Amorphous regions- glycine-rich amorphous blocks; provide elasticity Properties: Five times tougher than steel by weight Can stretch 30-40% without breaking Elastic modulus is significantly less than of steel For application in which flexibility and toughness are the primary need ( bullet proof vest )  synthetic route to create material with properties equivalent to spider silk

15. Spiders cannot be kept in close quarters and harvested, because they eat one another; thus the only route to creating quantities of spider silk sufficient for application will be synthetic. Knowledge of the molecular structure of spider silk is not sufficient for creating a synthetic material with its properties. Inside the spider, the silk precursor exists as a lyotropic liquid crystal that is approximately 50% silk . As the silk is excreted, the protein molecules that make up silk fold and are aligned as they approach and then pass through the spinneret , forming a complex insoluble nanostructured fiber. In fact, not only is the spider silk made up of crystalline and amorphous regions, but the crystalline regions are in turn composed of both highly oriented crystals and less oriented, but still crystalline, regions.

16. Spider silks have potential in many applications Surgical sutures Scaffolds for tissue engineering Biomedical applications Parachutes High strength ropes/cables Fishing line Technical and industrial applications Ballistics

17. Applications of Spider Silk Humans have been making use of spider silk for thousands of years.  Current research in spider silk involves its potential use as an incredibly strong and versatile material.    The interest in spider silk is mainly due to a combination of its mechanical properties and the non-polluting way in which it is made.  The production of modern man-made super- fibres such as Kevlar involves petrochemical processing which contributes to pollution .   Kevlar is also drawn from concentrated sulphuric acid.  In contrast, the production of spider silk is completely environmentally friendly.  It is made by spiders at ambient temperature and pressure and is drawn from water.    In addition, silk is completely biodegradable . If the production of spider silk ever becomes industrially viable, it could replace Kevlar and be used to make a diverse range of items such as: Bullet-proof clothing Wear-resistant lightweight clothing Ropes, nets, seat belts, parachutes Rust-free panels on motor vehicles or boats Biodegradable bottles Bandages, surgical thread Artificial tendons or ligaments, supports for weak blood vessel

18. Spiders spin 6 different fibers Web reinforcement (Minor ampullate 1 and 2) Dragline (major ampullate 1 and 2) Wrapping and egg case fiber (aciniform) Pyriform silk (?) Acini- form Capture Spiral (Flagelliform) Glue coating (Aggregate silk) (?) Large diameter egg Case fiber (Tubuliform) Aggregate Tubuliform Flagelliform Pyriform Minor ampullate Major ampullate

19. Forced silking to obtain silk fibers Spiders are anesthetized with CO 2 and secured ventral side up Silk is pulled from the spinneret, attached to a reel, and drawn at a specified speed

20. Spiders are highly developed fiber “spinners” Lewis, R. Chem. Rev. 2006 , 106 , 3762-3774. Dicko , C.; Vollrath , F.; Kenney, J.M. Biomacromolecules 2004 , 5 , 704-710. Spidroin secretion Lumen Spinneret Duct Fiber alignment Duct Tail Funnel 1 mm

21. Nanocomposites from silica and spider silk Silica is widely found in biological systems , where it supports and protects single-celled organisms , such as diatoms . It also exists in the skeletons of some higher animals and even in plants. Spider silk, meanwhile, is a highly flexible material that has a high tensile strength. What's more, it can self assemble to produce well-defined sheet-like structures. Researchers combined two different materials from nature, both of which have unique and important properties, into one material system via genetic engineering. By combining the features of silk with biosilica through the design, synthesis, and characterization of a novel family of chimeric proteins an innovative biomimetic nanocomposite was fabricated. Biosilica skeletons found in nature are based on nanoscale composites wherein the organic components, usually proteins, are functional parts of the skeletal structures while also serving as silica-forming components . As a result, materials’ toughness is improved, strength is retained, and fine morphological control is achieved, all hallmark attributes of biological composites. Controlled synthesis of bioinspired silica composites   in vitro  for novel materials design is a big challenge for researchers and materials engineers.

22. The new composite was made by David Kaplan at  Tufts University  in Massachusetts and his colleagues, who used genetic engineering to make a cloned spider silk protein that can form films and fibers. By mixing this material with biosilica – from the proteins of diatoms – in aqueous solution, the researchers were able to create a composite nanomaterial with exceptional mechanical properties. The researchers found that the elliptically shaped silica particles attached themselves to the protein fibers, which as a result became "sticky". According to Kaplan and co-workers, the new material could be used in industrial and biomedical applications, and to make new composites. An example is novel biomaterials for making artificial bone .

23. Schematic representation of the design of fusion proteins and their use in controlled silica nanocomposite formation. (A) Scheme of chimeric design with two functional domains: silk and R5. (B) Model of spider silk protein processing into films and fibers and silicification reactions on the assembled materials. (Source: PNAS, National Academy of Sciences