**4. Drug delivery and textile applications of dual-responsive (pH and temperature) hydrogels**

The hydrogel system combined both pH-responsive polymer and thermoresponsive polymer-enhanced efficiency of stimuli-responsive hydrogels for drug delivery applications [134]. The swelling behavior of dual-responsive (pH and temperature) hydrogel has been schematically represented in **Figure 3**.

Natural polymer like chitosan was used as pH-responsive polymer to combine with thermoresponsive synthetic polymer pNIPAAm in order to create dual-responsive (pH and temperature) hydrogel-based drug delivery systems [135–137]. Dual-responsive hydrogels based on glycidyl methacrylated chitosan and pNIPAAm via photopolymerization were used as drug delivery systems for

**Figure 3.** *The schematic representation of swelling/shrinking of dual-responsive (pH and temperature) hydrogels.*

**17**

*Stimuli-Responsive Hydrogels: An Interdisciplinary Overview*

for modifying surface property of textile materials [147].

hydrophobicity to the cotton fabric [151].

temperature) hydrogels are briefly summarized in **Table 3**.

acid orange 8 (AO8) and 5-fluorouracil (5-Fu), and the hydrogels showed response to both temperature and pH as external stimuli [135]. Chitosan and pNIPAAm formed dual (pH/temperature)-responsive hydrogel network with semi-interpenetrating polymeric network via radical-induced polymerization of NIPAAm in the presence of chitosan using tetraethyleneglycoldiacrylate as a cross-linker, and this dual-responsive hydrogel was used as drug delivery system for pilocarpine hydrochloride [136]. Dual-responsive hydrogels based on pH-responsive chitosan and temperature responsive pNIPAAm were applied on textile fabrics (cotton fabrics) to modify their surface properties, and these functionalized textiles showed advanced functionalities and environmental responsiveness [83, 138, 139]. Surface modification of cotton fabric with pH and temperature dual-responsive hydrogels of chitosan and pNIPAAm improved air and moisture management activities of

Dual-responsive hydrogels made of pNIPAAm as thermoresponsive polymer and PAA as pH-responsive polymer found drug delivery applications [77, 140]. The hydrogel system made from copolymer of NIPAAm and itaconic acid [NIPAAm*co*-itaconic acid] showed dual responsiveness to external stimuli temperature and pH and was proposed as effective drug delivery system [141]. Dual hydrogel system made of pNIPAAm and PDMAEMA by the combination of atom transfer radical polymerization, reversible addition-fragmentation chain transfer polymerization, and click chemistry showed dual responsiveness for temperature and pH, and this dual-responsive hydrogel was used as drug delivery system for ceftriaxone sodium [142, 143]. Dual-responsive biodegradable hydrogel made from thermoresponsive copolymer p(NIPAAm-*co*-hydroxyethyl methacrylate) and pH-responsive poly(L-glutamic acid) was applied as drug delivery system for hydrophilic drugs [144]. Dual-responsive (pH and temperature) hydrogel system was developed using thermoresponsive polymer pNIPAAm and cellulose nanofibril isolated by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation and applied as carrier for drug [145]. Dual-responsive (pH and temperate) hydrogels made from synthetic polymers pNIPAAm and vinyl-capped polyurethane were graft copolymerized onto nonwoven cellulose/PET fabric by ammonium persulfate initiation to modify surface properties of textile material [146]. Dual-responsive hydrogels made of pNIPAAm and polyurethane were grafted onto nonwoven fabric

Chitosan-coated alginate hydrogel beads with pNIPAAm showed pH and temperature dual responsiveness and were applied as drug delivery system with improved encapsulation efficiency and sustained drug release property [148]. The hydrogel consisting of sugarcane bagasse cellulose, carboxymethyl cellulose, and pNIPAAm was applied as a dual-responsive (pH and temperature) drug carrier for BSA, and the drug carrier system showed sustained release of drug [149]. Cellulose-based dual-responsive (pH and temperature) hydrogel was prepared from carboxymethyl cellulose and hydroxyethyl cellulose in an aqueous medium using citric acid (CA) as a cross-linking agent and applied on knitted cotton fabric to modify its surface properties [150]. Chitosan with other biopolymers including β-cyclodextrin (β-CD), arabic gum, guar gum, and pullulan formed four different types of dual-responsive (pH and temperature) hydrogels using glycidoxypropyltrimethoxysilan as a cross-linker, and depending on the nature of biopolymers used in hydrogels, the texture of the hydrogels varied [151]. All the varieties of hydrogels were applied on textile fabrics to modify surface properties like antibacterial, water uptake, and moisture retention, and the hydrogels imparted

The chemical nature and biomedical applications of dual-responsive (pH and

*DOI: http://dx.doi.org/10.5772/intechopen.80536*

functionalized textiles [83].

*Hydrogels - Smart Materials for Biomedical Applications*

**Charge of pH-responsive hydrogel**

PAA, polyvinyl acetate Anionic Textile application (wound

BSA Anionic Textile application (medical

PDMAEMA Cationic Textile application (medical

Chitosan, PEG Cationic Textile application (medical

Chitosan Cationic Textile application (medical

PAA, poly(l-glutamic acid) Anionic Drug delivery application [114]

Albumin Anionic Drug delivery application [116] BSA, methacrylate Anionic Drug delivery application [117]

Chitosan, poly(ethylene oxide) Cationic Drug delivery application [128] Carboxymethyl chitosan, PEG Cationic Drug delivery application [130]

**Biomedical application of pH-responsive hydrogel**

healing monitoring)

Cationic Drug delivery application [124]

textiles)

textiles)

textiles)

textiles)

**References**

[115]

[118]

[126]

[120]

[131, 132]

**Chemical constituents of pH-responsive hydrogels**

PDMAEMA, poly(vinyl

alcohol)

**Table 2.**

**16**

**Figure 3.**

*The schematic representation of swelling/shrinking of dual-responsive (pH and temperature) hydrogels.*

**4. Drug delivery and textile applications of dual-responsive (pH and** 

Natural polymer like chitosan was used as pH-responsive polymer to combine with thermoresponsive synthetic polymer pNIPAAm in order to create dual-responsive (pH and temperature) hydrogel-based drug delivery systems [135–137]. Dual-responsive hydrogels based on glycidyl methacrylated chitosan and pNIPAAm via photopolymerization were used as drug delivery systems for

The hydrogel system combined both pH-responsive polymer and thermoresponsive polymer-enhanced efficiency of stimuli-responsive hydrogels for drug delivery applications [134]. The swelling behavior of dual-responsive (pH and temperature)

**temperature) hydrogels**

hydrogel has been schematically represented in **Figure 3**.

*The chemical nature and biomedical applications of pH-responsive hydrogels.*

acid orange 8 (AO8) and 5-fluorouracil (5-Fu), and the hydrogels showed response to both temperature and pH as external stimuli [135]. Chitosan and pNIPAAm formed dual (pH/temperature)-responsive hydrogel network with semi-interpenetrating polymeric network via radical-induced polymerization of NIPAAm in the presence of chitosan using tetraethyleneglycoldiacrylate as a cross-linker, and this dual-responsive hydrogel was used as drug delivery system for pilocarpine hydrochloride [136]. Dual-responsive hydrogels based on pH-responsive chitosan and temperature responsive pNIPAAm were applied on textile fabrics (cotton fabrics) to modify their surface properties, and these functionalized textiles showed advanced functionalities and environmental responsiveness [83, 138, 139]. Surface modification of cotton fabric with pH and temperature dual-responsive hydrogels of chitosan and pNIPAAm improved air and moisture management activities of functionalized textiles [83].

Dual-responsive hydrogels made of pNIPAAm as thermoresponsive polymer and PAA as pH-responsive polymer found drug delivery applications [77, 140]. The hydrogel system made from copolymer of NIPAAm and itaconic acid [NIPAAm*co*-itaconic acid] showed dual responsiveness to external stimuli temperature and pH and was proposed as effective drug delivery system [141]. Dual hydrogel system made of pNIPAAm and PDMAEMA by the combination of atom transfer radical polymerization, reversible addition-fragmentation chain transfer polymerization, and click chemistry showed dual responsiveness for temperature and pH, and this dual-responsive hydrogel was used as drug delivery system for ceftriaxone sodium [142, 143]. Dual-responsive biodegradable hydrogel made from thermoresponsive copolymer p(NIPAAm-*co*-hydroxyethyl methacrylate) and pH-responsive poly(L-glutamic acid) was applied as drug delivery system for hydrophilic drugs [144]. Dual-responsive (pH and temperature) hydrogel system was developed using thermoresponsive polymer pNIPAAm and cellulose nanofibril isolated by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation and applied as carrier for drug [145]. Dual-responsive (pH and temperate) hydrogels made from synthetic polymers pNIPAAm and vinyl-capped polyurethane were graft copolymerized onto nonwoven cellulose/PET fabric by ammonium persulfate initiation to modify surface properties of textile material [146]. Dual-responsive hydrogels made of pNIPAAm and polyurethane were grafted onto nonwoven fabric for modifying surface property of textile materials [147].

Chitosan-coated alginate hydrogel beads with pNIPAAm showed pH and temperature dual responsiveness and were applied as drug delivery system with improved encapsulation efficiency and sustained drug release property [148]. The hydrogel consisting of sugarcane bagasse cellulose, carboxymethyl cellulose, and pNIPAAm was applied as a dual-responsive (pH and temperature) drug carrier for BSA, and the drug carrier system showed sustained release of drug [149]. Cellulose-based dual-responsive (pH and temperature) hydrogel was prepared from carboxymethyl cellulose and hydroxyethyl cellulose in an aqueous medium using citric acid (CA) as a cross-linking agent and applied on knitted cotton fabric to modify its surface properties [150]. Chitosan with other biopolymers including β-cyclodextrin (β-CD), arabic gum, guar gum, and pullulan formed four different types of dual-responsive (pH and temperature) hydrogels using glycidoxypropyltrimethoxysilan as a cross-linker, and depending on the nature of biopolymers used in hydrogels, the texture of the hydrogels varied [151]. All the varieties of hydrogels were applied on textile fabrics to modify surface properties like antibacterial, water uptake, and moisture retention, and the hydrogels imparted hydrophobicity to the cotton fabric [151].

The chemical nature and biomedical applications of dual-responsive (pH and temperature) hydrogels are briefly summarized in **Table 3**.


**Table 3.**

*The chemical nature and biomedical applications of dual-responsive (pH and temperature) hydrogels.*
