Nanoparticle-Integrated Hydrogels as Multifunctional Composite Materials for Biomedical Applications

Abstract

This review focuses on the most recent developments in the field of nanocomposite hydrogels intended for biomedical applications. Nanocomposite hydrogels are hydrated polymeric networks with a physically or covalently crosslinked three-dimensional (3D) structure swollen with water, in the presence of nanoparticles or nanostructures. A wide array of nanomaterials (polymeric, carbon-based, metallic, ceramic) can be incorporated within the hydrogel network to obtain reinforced nanocomposite hydrogels. Nanocomposites represent a new class of materials with properties absent in the individual components. In particular, the incorporation of nanomaterials within a polymeric hydrogel network is an attractive approach to tailor the mechanical properties of the hydrogels and/or to provide the nanocomposite with responsiveness to external stimuli.

Keywords: biomedical applications; hydrogels; nanocomposite hydrogels; nanocomposites; nanoparticles.

Figure 1

Processing parameters influence the structure and the properties of the NCH and, as a consequence, their performance in the medical field. Different polymers, both synthetic and naturally derived, can be used to produce the hydrogel, in which a variety of nanomaterials can be embedded. The resulting NCH can be used for a number of biomedical applications.

Figure 2

Nanocomposite hydrogels (NCHs) from carbon-based nanomaterials such as carbon nanotubes (CNTs) and graphene. CNTs exist in different atomic configurations (namely armchair and zig-zag) and architectures (single- and multi-walled) and can be chemically modified to enhance their hydrophilicity and, therefore, their interaction with the surrounding hydrogel. The addition/conjugation of CNTs and graphene derivatives provides NCHs with improved mechanical properties and electrical conductivity. For these reasons, NCHs embedding carbon-based nanomaterials can be potentially used for numerous applications, such as tissue engineering of electrically conductive tissues along with electrically-stimulated drug delivery.

Figure 3

Nanocomposite hydrogels based on polymeric nanoparticles. Particle inclusion in hydrogels allows an increase of hydrogel mechanical properties, along with the possibility to control drug release rate. Amphiphilic (macro)molecules such as micelles, dendrimers, and hyperbranched polymers can also act as solubility enhancers of sparingly soluble drugs.

Figure 4

Nanocomposite hydrogels from ceramic nanoparticles. The inclusion of these nanomaterials allows a surprising reinforcement of the hydrogel. Furthermore, since most of these inorganic nanoparticles are made of minerals with a crucial role in the normal homeostasis of living tissues, they can provide the NCH with a biological responsiveness.

Figure 5

Nanocomposite hydrogels from metallic nanoparticles. The inclusion of metallic nanoparticles within hydrogels also allows us to obtain NCHs with electrical/magnetic responsiveness. In addition, noble metals such as silver also possess antimicrobial activity, and are therefore interesting for wound dressing.