Mechanisms of Colloidal Stabilization of Oxidized Nanocarbons in the Presence of Polymers: Obtaining Highly Stable Colloids in Physiological Media

Abstract

There are successful protocols for dispersing carbon nanotubes and graphene oxide in physiological media by using biocompatible polymers, which enable their use in nanomedicine. However, there is not a clear understanding regarding the mechanisms of the colloidal stabilization manifested (i.e., electric, steric or electrosteric or through depletion forces). Here we show that the manifestation of a particular mechanism of stabilization for oxidized carbon nanotubes (CNTs) and graphene oxide (GO) in the presence of Pluronic F-127 (PF127) and short-and long-chain polyethylene glycol (PEG 1,500 or 35,000 respectively) depends on a proper matching between the nanocarbon morphology and the polymer chain length, chemical structure and concentration. The high aspect ratio one dimensional morphology of CNTs enables an initial steric and electrosteric stabilization through the nanotube wrapping (i.e., adsorption) by PF127 present in low concentrations (<0.1%). Depletion stabilization for CNTs manifests when PF127 is present in high concentrations (≥1.0%), thus enabling the formation of highly stable CNT colloids even in a 0.9% NaCl saline solution. This depletion stabilization depends little on the CNT structure (i.e., single-or multi-wall), surface charge (i.e., zeta potential), oxidation and carboxylation degree or the nanotube length. On the other hand, large-sized sheets of GO could be colloidally stabilized in NaCl 0.9% only in the presence of PEG 35,000 through repulsive depletion forces, whose manifestation occurs with a polymer concentration threshold of 5.0 wt%. Comparatively, in a physiological saline solution, PF127 is able to colloidally stabilize CNTs to a much large extent than PEG 35,000 stabilizes the large GO sheets.

Nanoecotoxicity assessment of graphene oxide and its relationship with humic acid

“…Table 2 shows the respective quantities found for each group. Similar results have been reported in the literature for other samples of graphene oxide (Faria et al 2012;Padovani et al 2015).…”

Hybrid biomaterial based on porous silica nanoparticles and Pluronic F-127 for sustained release of sildenafil: in vivo study on prostate cancer

“…The manifestation of attractive or repulsive depletion forces depends mostly on the polymer concentration. [38][39][40] When mixed with MSNs in the NaCl 0.9% solution, it was observed that at 3 wt% PF127 leads to a destabilization of the MSNs sols (i.e., colloidal suspension), whereas at 5 wt% (or above) the same polymer is able to stabilize MSN ( Fig. SM-3; ESI †).…”

“…The manifestation of both kinds of interactions (short-and long-range; i.e., adsorption and depletion forces) was previously observed for PF127 (ref. 40) and also for polyethylene glycol. 39 Therefore, as in the hybrid systems the PF127 concentration is 18 wt% (to form hydrogels), much higher than the observed threshold for repulsive depletions forces to occur, this polymer will act as an initial stabilizing agent for MSNs from the time of injection up to a possible formation of the protein capping (i.e., corona effect), resulted from the adsorption of proteins on the MSNs surface, [41][42][43] which are also able to provide colloidal stabilization for MSNs.…”

Silver Nanocoatings at Large Length Scales: Influence of the AgNPs Morphology and Capping Agents on the Coating Chemical Stability and Antimicrobial Effect

“…In the particular case of biogenic AgNPs (Ag-Glutinis and Ag-Mucilaginosa), the colloidal stabilization by steric/electrosteric mechanisms must also be accounted due to the presence of macromolecules in the protein corona. 8,48 Assessment of the AgNPs coatings at multiple scales with LF X-ray imaging…”