Evaluation of the permeability and in vitro cytotoxicity of functionalized titanate nanotubes on Caco-2 cell line

Abstract

Titanate nanotubes (TNTs) are promising vectors for drug delivery due to their unique physicochemical properties such as biocompatibility, mechanical strength, and chemical resistivity. However, considering their strong hydrophilicity, pristine TNTs exert very limited permeability through the intestinal cell layer. The aim of this study was to turn the surface characteristics and thus enhance the permeability of TNTs by functionalization. TNTs were functionalized with trichloro(octyl)silane (TCOS) and magnesium stearate (MgSt). Carbon content and surface free energy of the functionalized TNTs were detected to evaluate the effectiveness of functionalization, by using CHNS analytical and optical contact angle (OCA) measurements, respectively. Caco-2 cell line was applied to test the permeability and the cytotoxicity of the samples. Cytotoxicity was evaluated by using MTT assay. The results revealed that the surface characteristics of TNTs may be adjusted in a wider range with TCOS-TNT than with St, but the samples show higher toxicity. Silane functionalized TNTs may be safe up to 1 mg/ml, while St functionalized TNTs up to 2 mg/ml concentration. The preparation method of MgSt-TNT was also superior from the aspect of environmental safety. The permeability was suitable for samples with moderate hydrophobicity (aqueous contact angle 60-90°).

Surface Modification of Titanate Nanotubes with a Carboxylic Arm for Further Functionalization Intended to Pharmaceutical Applications

“…In the first attempt, the same method which was previously used for functionalization of TNTs with trichloro-octyl-silane [ 20 ] was adopted to TCA. Nevertheless, the trial was not successful, as shown in Figure 2 , as the characteristic peaks of TCA, mainly the C=O, C-O and C-Cl stretching vibration at 1751, 1262 and 679 cm −1 , respectively, are clearly absent in the spectrum of the corresponding composite, which suggests that it was removed during the washing procedure.…”

“…It is worth mentioning that these safety results were not limited to the bare TNTs, but the safety was also evidenced with different types of functionalization and with different chemical structures. For example, Ranjous et al have reported the safety of silan-functionalized TNTs up to 1 mg/mL and stearate-functionalized TNTs up to 2 mg/mL on Caco-2 cell lines using MTT assay for a short exposure (120 min) [ 20 ]. Papa et al have also modified the surface of TNTs with polyethyleneimine (PEI) and then examined the toxicity with MTT assay on cardiomyocytes for 24 and 96 h. No significant toxicity was observed neither with TNTs nor with their functionalized samples in a concentration up to 10 µg/mL [ 41 ].…”

“…Nevertheless, surface modification could be an unavoidable step for further improvement of the existing properties, for adjustment of the unfavorable ones or even for providing them with new characteristics. The surface modification is considered as a recommended solution to overcome TNTs problems and upgrade their use to new scopes; for example, applying a hydrophobic cap for preventing the leaching of hydrophilic drugs to the surrounding environment and achieving a controllable release profile [ 19 ] or for enhancing the permeability of these hydrophilic nanotubes and facilitating their absorption/biological membrane bypassing [ 20 ]. Surface modification of TNTs was also conducted successfully as an approach to enhance the APIs loading, sustain/control the release rate and reduce toxicity using different molecules such as polyamidoamine dendrimers, P25 nanoparticles and chitosan [ 14 , 15 , 21 , 22 ].…”

An Overview of Hydrothermally Synthesized Titanate Nanotubes: The Factors Affecting Preparation and Their Promising Pharmaceutical Applications

“…It is also an available option to tailor the surface chemistry by functionalizing it with different molecules or replacing Na + /H + ions on it with other ions such as Cu 2+ /Ni 2+ and Mg 2+ . This would help to control/adjust TNTs properties and provide them with secondary characteristics and new behaviors other than the original ones, which could be the key to overcome some of their problems and extend their application to further disciplines [60][61][62][63].…”

“…However, the potential utilization of TNTs in health-related applications is supported by the promising results obtained by numerous studies which investigated their cytotoxicity using different cell lines (intact and cancerous) with different concentrations (range from 1 µg/mL to 5 mg/mL) and different times of exposure (from short treatment of 120 min to long exposure of 7 days) [7,8,10,85]. Even surface-modified TNTs with several molecules (silane, stearate, polyethyleneimine, acrylic acid-polyethylene glycol copolymer) have presented similar results which could promote the shifting of TNTs (bare and surface-modified) to the health domain [9,10,61].…”