**3. Electrical properties**

The electrical properties are very important in some biomedical fields because various types of electrical stimulation can regulate cell physiological activities such as division [55], migration [56], differentiation and cell death [57]. The electrical stimulation also has been employed in promoting healing for spinal cord repair and cancer therapy due to its non-invasiveness of these polymers [58–60]. For these reasons, much emphasis was given in developing these new acrylic-based materials in biomedical application where the conductivity of the biomaterials is essential. Recently, nanocarbon materials such as graphene had been considered to be very effective electrode material with very high conductivity. The graphene has high transmittance and excellent conductivity [40] as was mentioned earlier. But, its production is still very expensive, and more studies are expected to carry out with its derivative, graphene oxide. However, in order to develop electrically conductive acrylic-based resins, GO, which has a very low conductivity due to their oxygen-containing functional groups, must be modified to obtain reduced graphene oxide (rGO). Thus, for example, following a single-step procedure starting from a homogeneous water dispersion of GO, it is possible to undergo reduction induced by the UV radiation during the photopolymerization of an acrylic resin [61]. The transparent conductive films were also produced by grafting poly(acryl amide)/poly(acrylic acid) on the GO surface followed by a reduction to rGO nanosheets by a two-step chemical reduction with increased conductivity [62]. The inorganic-organic double network (DN) flexible and conductive hydrogel of rGO and poly(acrylic acid) has also been prepared by a two-step synthesis with a reduction-induced *in situ* self-assembly [63]. Even more recently, a nacre-inspired acrylic-based nanocomposite of rGO and PAA has been prepared *via* a vacuum-assisted filtration self-assembly process (**Figure 2**). The abundant hydrogen bonding between GO and PAA results in both high strength and toughness of the bioinspired nanocomposites, which are 2 and 3.3 times higher than that of pure reduced GO film, respectively. Moreover, this nanocomposite also displays high electrical conductivity of 108.9 S⋅cm−1, which renders it very promising material in many biomedical applications such as flexible electrodes, artificial muscles, etc.

methacrylate) by melt blending. Thus, for example, using an amount of carbon nanofibers of 5 wt.%, the nanocomposites improved over 50% of their axial tensile modulus as compared to the control PMMA. The PMMA/CNFs nanocomposite fibers also show enhanced thermal stability, significantly reduced shrinkage and enhanced modulus retention with temperature, as well as improved compressive strength [50]. The electrical properties and electromechanical responses of acrylic materials such as acrylic elastomers and styrene copolymers can be improved toward electroactive applications such as artificial muscle and/or micro-electro-

The other novel nanocomposite hydrogels such as those prepared with polyacrylamide (PAM) as a matrix material reinforced with natural chitosan nanofibers via *in situ* free-radical polymerization showed that these nanofibers acted as a multifunctional crosslinker and a reinforcing agent in the hydrogel system producing a compression strength and a storage

Reinforcement can be also performed with plant fiber-based nanofibers by a successful fibrillation of wood pulp fibers into nanofiber bundles, which are thin enough to work, as well as

The other nanoparticles such as clay have been employed to reinforce acrylic polymers. These polymer-clay nanocomposites such as PMMA/clay constitute a class of materials in which the polymer matrix is reinforced by uniformly dispersed inorganic particles (usually 10 wt.% or less) having at least one dimension in the nanometre scale and exhibiting enhanced mechanical and thermal properties when compared to pure polymer or conven-

The electrical properties are very important in some biomedical fields because various types of electrical stimulation can regulate cell physiological activities such as division [55], migration [56], differentiation and cell death [57]. The electrical stimulation also has been employed in promoting healing for spinal cord repair and cancer therapy due to its non-invasiveness of these polymers [58–60]. For these reasons, much emphasis was given in developing these new acrylic-based materials in biomedical application where the conductivity of the biomaterials is essential. Recently, nanocarbon materials such as graphene had been considered to be very effective electrode material with very high conductivity. The graphene has high transmittance and excellent conductivity [40] as was mentioned earlier. But, its production is still very expensive, and more studies are expected to carry out with its derivative, graphene oxide. However, in order to develop electrically conductive acrylic-based resins, GO, which has a very low conductivity due to their oxygen-containing functional groups, must be modified to obtain reduced graphene oxide (rGO). Thus, for example, following a single-step procedure starting from a homogeneous water dispersion of GO, it is possible to undergo reduction induced by the UV radiation during the photopolymerization of an acrylic resin [61]. The transparent conductive films were also produced by grafting poly(acryl amide)/poly(acrylic acid) on the

mechanical systems (MEMS) devices [51].

80 Acrylic Polymers in Healthcare

tional composites [54].

**3. Electrical properties**

modulus significantly higher than those of pure PAM [52].

bacterial cellulose in maintaining the transparency of resin [53].

Carbon nanotubes (CNTs), discovered by Iijima [65], have also been attracting intensive attention because of their excellent electrical properties with a superb conductivity, remarkable mechanical strength and modulus with many potential technological applications [66]. CNTs offer the possibility of developing ultrasensitive electrochemical biosensors due to unique electrical properties. Thus, nanofibrous membranes filled with multi-walled carbon nanotubes (MWCNT) were electrospun from the mixture of poly(acrylonitrile-co-acrylic acid) (PANCAA) and MWCNT to develop a glucose biosensor for diabetics [67].

The other nanocomposites of poly(methyl methacrylate) containing various multi-walled carbon nanotube (MWCNT) contents have been prepared using melt mixing to achieve high conductivity levels in the nanocomposites [68].

**Figure 2.** Fabrication process of rGO–PAA nanocomposites: (a) The GO nanosheets/PAA homogeneous solution was filtered by vacuum-assisted filtration into GO–PAA nanocomposites. Then after HI reduction, the rGO–PAA nanocomposites were obtained. (b) A digital photograph of rGO–PAA nanocomposites. (c) and (d) The cross-section surface morphology with different magnifications of rGO–PAA nanocomposites. Reprinted with permission from Ref. [64].
