Natural biological systems make use of capillary-type hierarchical structures in order to enhance surface functionality within limited size. This paper discusses fabrication of similar synthetic structures by grafting carbon nanotubes (CNTs) on microcellular substrates such as graphitic foam. A major hurdle so far had been deposition of dense CNT layers inside uneven pores. This has been overcome in this study by pre-coating the porous surface with plasma-derived silica molecules. It is seen that the pre-coating not only increases the density of nanocatalyst attachment on the surface but also makes each nanocatalyst more effective in nucleation and growth of nanotubes. The CNT layers formed are strongly attached to the substrate, which makes them particularly suitable for use in robust hierarchical devices in the future.

Due to limited regenerative potential of skeletal muscle, strategies stimulating regeneration of functional muscles are important. These strategies are aimed at promoting differentiation of progenitor cells (myoblasts) into multinucleated myotubes, a key initial step in functional muscle regeneration. Recent tissue engineering approaches utilize various scaffolds ranging from decellularized matrices to aligned biomaterial scaffolds. Although, majority of them have focused on nano- or microscale organization, a systematic approach to build the multiscale hierarchy into these scaffolds is lacking. Here, we engineered multiscale hierarchy into carbon-based materials and demonstrated that the nanoscale features govern the differentiation of individual myoblasts into myocytes whereas microscale alignment cues orchestrate fusion of multiple myocytes into multinucleated myotubes underlining the importance of multiscale hierarchy in enhancing coordinated tissue regeneration.

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Carpet-like arrays of carbon nanotubes (CNTs) on graphitic carbon materials have been investigated in order to understand all-carbon hierarchical structures for multifunctional surface-active devices. Pure CNT carpets are seen to be super-hydrophobic as long as they are well aligned. For future applications involving aqueous environments, the ability to tailor the surface wettability and switch it on demand can be very useful, and enable unprecedented devices related to microfluidics, catalysis and sensing/ detection systems. In this study, microwave plasma treatments were used to functionalize CNT carpets for a progressive increase in wettability so that they could eventually become super-hydrophilic. This change could be reversed by heating. Alternating between microwave plasma treatment and heating enabled repeated cycling of the CNT carpets between super-hydrophobic and super-hydrophilic states. This paper focuses on the influence of these two treatments on surface chemical states and multiscale morphology of CNT carpets, and their relation to wettability. It was shown by X-ray Photoelectron Spectroscopy (XPS) that oxygen-containing groups attached to surface carbon atoms are created during plasma treatment. These species desorb at temperatures of about 110 C. The strength of C 1s and O 1s XPS signals from these radicals were seen to have direct correlation with water contact angles. In addition to surface chemistry, carpet morphology plays an important role in contact angle variations. Extreme surface roughness caused by high aspect-ratio of nanotubes would strongly accentuate both hydrophobic and hydrophilic behavior compared to flat surfaces. Classical geometric models of liquid droplets on uneven solids have been considered. Topological image analysis combined with intrinsic contact angle on flat graphene is used to predict the contact angle of these carpets, which matches well with experimental results. This analysis further explains why observed contact angles change if the vertical alignment of CNT is disturbed.