Ice as a Green-Structure-Directing Agent in the Synthesis of Macroporous MWCNTs and Chondroitin Sulphate Composites.

Stefania Nardecchia,María C Gutiérrez,Marcelo E H Maia Da Costa,Sara García-Argüelles,María Concepción Serrano,María Luisa Ferrer

doi:10.3390/ma10040355

Abstract

The incorporation of multi-walled carbon nanotubes (MWCNTs) into chondroitin sulphate-based scaffolds and the effect on the structural, mechanical, conductive, and thermal properties of the resulting scaffolds is investigated. Three-dimensional hierarchical materials are prepared upon the application of the ice segregation-induced self-assembly (ISISA) process. The use of ice as structure-directing agents avoids chemicals typically used for this purpose (e.g., surfactants, block copolymers, etc.), hence, emphasising the green features of this soft-templating approach. We determine the critical parameters that control the morphology of the scaffolds formed upon ice-templating (i.e., MWCNTs type, freezing conditions, polymer and MWCNT concentration). MWCNTs are surface functionalized by acidic treatment. MWCNT functionalization is characterized by Raman, Fourier transfer infrared (FTIR) and X-ray Photoelectron (XPS) spectroscopies. Scanning electron microscopy (SEM) analysis and porosity studies reveal that MWCNT content modifies the morphology of the macroporous structure, which decreases by increasing MWCNT concentration. Differences in scaffold morphology should be translated into their conductivity and mechanical properties. As a general trend, the Young’s modulus and the electrical conductivity of the scaffolds increase with the MWCNT content. Preliminary biocompatibility tests with human osteoblast-like cells also reveal the capability of these structures to support cell growth.

Highlights

Since pioneering work by Iijima in 1991 [1], carbon nanotubes (CNTs) have been the subject of numerous studies given their unique properties, including extremely high electrical and thermal conductivities, outstanding mechanical properties, and ability to form interconnected porous networks with high surface areas.Materials 2017, 10, 355; doi:10.3390/ma10040355 www.mdpi.com/journal/materialsA significant amount of research has been performed on the assembly of CNTs into three-dimensional (3D) macrostructures [2,3]
In order to thoroughly control the assembling of CNTs into 3D macrostructures, we systematically investigated the effect of polymer and multi-walled carbon nanotubes (MWCNTs) concentration and freezing conditions on the properties of the resulting structures
The scaffold morphology was modified by the incorporation of two different types of

Summary

Introduction

Since pioneering work by Iijima in 1991 [1], carbon nanotubes (CNTs) have been the subject of numerous studies given their unique properties, including extremely high electrical and thermal conductivities, outstanding mechanical properties, and ability to form interconnected porous networks with high surface areas.Materials 2017, 10, 355; doi:10.3390/ma10040355 www.mdpi.com/journal/materialsA significant amount of research has been performed on the assembly of CNTs into three-dimensional (3D) macrostructures [2,3]. The incorporation of CNTs into polymer-based composites has arisen as an attractive strategy frequently pursued, but the fabrication of 3D architectures, with the use of natural polymers, has been more rarely accomplished [4]. Processes based on unidirectional freezing and subsequent freeze-drying, such as the ice segregation-induced self-assembly (ISISA). Technique [5], are gaining increased interest since they have been proven as excellent techniques for creating scaffolds with sophisticated, hierarchical, and interconnected porous 3D architectures either with or without CNTs [6,7]. Ice-templating involves the use of ice crystals as a template for building up hierarchical 3D structures, with the ice crystals being formed by freezing an aqueous suspension [8]

Methods

Results

Conclusion