**1. Introduction**

Hydrogels are used in many fields of the biomedical industry such as therapeutic delivery [1], intraocular lenses, contact lenses and corneal prosthesis in ophthalmology [2], bone cements for orthopedics [3], wound dressing [4], 3D tissue scaffolds in regenerative medicine [5], etc., due to their excellent properties such as biocompatibility, water sorption and suitable mechanical performance, among others [6]. Many of these hydrogels have been approved by the US Food and Drug Administration (FDA) for diverse applications and are currently

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produced massively. However, many of their potential uses required for many biomedical applications are sometimes hindered by their low mechanical strength, biological interactions, electrical and/or thermal properties, water sorption and diffusion, antimicrobial and/ or antifouling activity, porosity etc. Thus, new advanced hydrogels have been developed and are currently under intensive research to solve all these problems by means of multicomponent polymeric systems or by combination with other materials and/or nanomaterials to form composites or nanocomposites with enhanced required properties.
