Highlights

Functionalizing Nanotubes for Biomedical Applications

Donghui Zhang, LSU Chemistry Department

Carbon nanotubes (CNT) are one dimensional nano-structures with novel materials properties (e.g., high mechanical strength, thermal and electrical conductivity). Strategies that enable orientational or spatial control of CNT will facilitate their integration with existing technologies where their novel properties can be optimally utilized. In this project, Dr. Donhui Zhang, LSU Department of Chemistry, and her team of researchers investigate the orientational control of CNT through their self-assembly with lyotropic liquid crystals of a biocompatible polypeptide (i.e., PBLG). This study will not only lead to fundamental understanding of solution phase behavior of dimensionally mismatched rods, but also provide access to a new class of anisotropic nano-composite materials that can be potentially utilized in biomedical area (e.g., tissue regeneration scaffolds for nerves or bones) or micro-electronics (e.g., opto-mechanical actuator).

Surface modifications of nanotubes can result in tailored functionality such as new means for biomedical areas such as bio-opto-actuator, tissue regeneration scaffolds for nerves and bones – study biocompatible polypeptides

single-walled carbon nanotubes (SWNTs)	SWNTs functionalized with polypeptide PBLG

How are the polypeptides ordered on the nanotube?

Same physics, different info WAXS gives spatial correlations of interatomic and intramolecular species SAXS gives spacings of intermolecular species and macromolecular order

Models for polypeptide order can be sorted out with SAXS, WAXS

PBLG/SWCNT in the solid state:

Figure 1. SAXS (A) and WAXS (B) profiles of SWCNT-NH2, PBLG-SWCNT, PBLG and PBLG-SWCNT/PBLG mixture; (C) Proposed model for the self-assembly of the PBLG-SWCNT/PBLG in the solid state.

The structure of PBLG-SWCNT was studied by SAXS and WAXS, as shown in Figure 1A and 1B. Samples were annealed at 150 oC under nitrogen for 48 hrs prior to the S/WAXS characterization. WAXS revealed a principle reflection (q=4.8 nm-1) of PBLG151 corresponding to a fundamental domain spacing of 1.31 nm and the higher order reflections at 31/2q and 41/2q are indicative of hexagonally packed cylinders (Figure 1C). The diffraction peak at q=12.4 nm-1 corresponds to a domain spacing of 0.51 nm consistent with the pitch dimension of α-helix. In comparison, PBLG-SWCNT/PBLG151 exhibits a principle reflection at q = 4.6 nm-1 (d=1.37 nm). The d spacing is larger than that observed in the pristine PBLG151, which is consistent with SWCNT evenly dispersed in the PBLG matrices. WAXS also revealed a broad peak at q = 14.6 nm-1 suggesting the presence of amorphous domain. No diffraction peaks are detected in SAXS, implying no long-range ordered structure present in the sample. This is consistent with previous reports that long-range ordered structures (i.e., smetic phase) can only form for mono-disperse PBLG. Missing q value at 18.5 nm-1, which corresponds to scattering from the graphene layers of SWCNT bundles, indicates good dispersion of SWCNT in the PBLG films. The q value of SWCNT rod should merged in the peak of PBLG rod at 4.6 nm-1.

PBLG/SWCNT in the dry gel:

Figure 2. SAXS (A) and WAXS (B) profiles of PBLG-SWCNT/PBLG mixture; (C) Proposed model for the self-assembly of the PBLG-SWCNT/PBLG in the solid state.

As shown in Figure 2A, no obvious slope changes was observed, which indicating no long range ordered structure exist in the dry gel. The WAXS result of the dry gel was shown in Figure 2B. The arrows indicate the higher order reflections with relative positions 1:2 from a lamellar arrangement of α-helices (see Figure 2C) with a pitch size of 0.50 nm (q=12.6 nm-1).