Hierarchically structured adhesives

Arnold M, Schwieder M, Blummel J et al (2009) Cell interactions with hierarchically structured nano-pattemed adhesive surfaces. Soft Matter 5(l) 72-77... 

Techniques to produce multiscale biomaterial scaffolds with designer geometries are the need of the hour to provide improved biomimetic properties for functional tissue replacements. While micrometer fibers generate an open pore stnicture, nanofibers support cell adhesion and facilitate cell-cell interactions. This was further proven by cell penetration studies, which showed superior ingrowth of cells into hierarchical structures. Mixed bimodal scaffolds of two different polymers are another promising approach, because they exhibit hierarchical pore/ surface systems and combine the beneficial properties of both polymers at two different scales. Vaiious 3D micro- and nanoscale multiscale scaffolds have been fabricated through various techniques and were found to have the potential to essentially recreate natural bone, cardiac, neural, and vascular tissues. 

Aligned multiwall CNT arrays were synthesized as a basis for a microstructured catalyst, which was then tested in the Fischer-Tropsch reaction in a microchannel reactor [269]. Fabrication of such a structured catalyst first involved MOCVD of a thin but dense A1203 film on a FeCrAlY foam to enhance the adhesion between the catalyst and the metal substrate. Then, multiwall CNTs were deposited uniformly on the substrate by controlled catalytic decomposition of ethene. Coating the outer surfaces of the nanotube bundles with an active catalyst layer results in a unique hierarchical structure with small interstitial spaces between the carbon bundles. The microstructured catalyst was characterized by the excellent thermal conductivity inherent to CNTs, and heat could be efficiently removed from the catalytically active sites during the exothermic Fischer-Tropsch synthesis. 

Broz A, Baresova V, Kromka A, Rezek B, Kalbacova M. Strong influence of hierarchically structured diamond nanotopography on adhesion of human osteoblasts and mesenchymal ceUs. Phys Statns SoUdi A-Appl Mater Sci 2009 206 2038-41. 

The previous three sections involved the treatment of natural fibres by removing substances from the natural fibres. This section, however, describes a new modification that does not involve the removal but the addition of new material onto the surface of natural fibres. This type of modification involves the deposition of nanosized cellulosic materials onto the surface of natural fibres to enhance the interfacial adhesion between the fibres and the matrix [9,10,14,104]. By doing so, a hierarchical structure can be created. These works were inspired by nature. Nature maximises the efficiency of structural materials by creating hierarchical stmctures the arrangement of the constituents at every level, from the molecular level to the macroscopic level. By applying this concept, composites that possess a hierarchical structure with improved mechanical properties can be manufactured. 

High performance composite materials can be obtained with a good level of dispersion, mainly when the hierarchical structure of cellulose and use of a water soluble polymer to form the matrix are considered. For most materials applications, the main biopolymers of interest are cellixlose and starch. The ease of adhesion that occurs in cellulose has contributed to its use in paper and other fiber-based composite materials. 

Arnold, M., Schwieder, M., Blummel, J., Cavalcanti-Adam, E.A., Lopez-Garcia, M., Kessler, H. et al. (2009) Cell interactions with hierarchically structured nano-patterned adhesive surfaces. Sofi Matter, 5, 22-11. 

Yao H, Gao H (2006) Mechanics of robust and releasable adhesion in biology Bottom—up designed hierarchical structures of gecko. J Medi Phys Solids 54 1120-1146... 

Another possibility, which is widely used for the production of bio-nanocomposites, also with resin directty obtained from biomass, is extracting cellulose nanociystals (CNC) from other biomass source or from aspecilic cellulose. This led also to original solutions, such as the fabrication of materials including a kind of hierarchical structure, hence introducing both a macrosized reinforcement and a nanosized one. In particular, in a jute and soy flour composite, with glutaraldehyde providing suitable interface adhesion, cellulose nanowhiskers have been introduced in addition or not to nanoclay (Fig. 13.5), a procedure which provided improved thermal, mechanical and dimensional stability (Iman et al., 2013). 

Koch, K., Bhushan, B.,Jung,Y.C., Barthlott, W., 2009. Fabrication of artificial lotus leaves and significance of hierarchical structure for superhydrophobicity and low adhesion. Soft Matter 5,1386. 

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