Pekel et al. (2004) investigated electron beam crosslinking of HPMC hydrogels with various degrees of substitution (DS 1.9 and 1.4) and viscosity (4270 mPa.s and 4370 mPa.s) for biomedical applications. It was exhibited that the swelling percentage did not change significantly till pH = 7 and significant changes were observed from pH = 8.0. The swelling percentage of thermal-sensitive hydrogels was found to be 2000% in cold water and 500% at 60°C. It was observed that tensile strength of the hydrogels increased with irradiation dosages. It was found that HPMC hydrogels with low DS showed 95% weight loss up to 24 h based on enzymatic degradation study.
Liu et al. (2009) synthesized superporous HPMC gel beads using divinylsulphone (DVS) as a crosslinker and nano-CaCO3 as a porogen through inversing phase suspension crosslinking. It was found that porogen affected the morphology of hydrogel beads and interpenetrate pores formed at 70% of porogen. The equilibrium swelling ratio increased with porogen dosages whereas equilibrium swelling time decreased with porogen dosages. The higher swelling ratio of the superporous gel beads was due to larger surface area and loose structure, which was created by higher dosages of porogen.
The prepared superporous gel beads can be useful in drug delivery applications.
Barros et al. (2014) probed physical crosslinking of chitosan (CH) and HPMC by casting-solvent evaporation (SC) method or by freeze–thaw (FT) technique for textile applications. In this study, a series of different weight ratios of CH and HPMC was used to prepare the hydrogel films. The miscibility of the polymers was studied by FTIR, SEM and AFM analysis. It was found that the films containing high CH showed swelling capability of 1,172% and 7,323% for SC and FT preparations, respectively.
Lower swelling percentage was found for equivalent concentration of both polymers.
The low critical solution temperature (LCST) was found to be between 85.2°C and 87.5°C for thermoreversible hydrogel films.
Barros et al. (2015) synthesized CH/HPMC hydrogel films via solvent casting (SC) and freeze–thaw (FT) techniques for textile applications. The thermal, mechanical and structural properties were evaluated by DSC and TGA, DMA and XRD, respectively.
It was concluded from characterization studies that the films had good miscibility between both polymers. Decomposition temperature, glass transition temperature and tensile strength of 50:50 (CH/CMC) compositions were found to be >270°C, > 194°C and 7.07 MPa, respectively. The prepared hydrogel films are suitable candidates to release active species (fragrances and antiperspirants) when body temperature increases.
Das et al. (2015) fabricated ethylene glycol dimethacrylate (EGDMA) crosslinked PAAm/HPMC/Au nanocomposite hydrogels for colon targeted drug delivery. The nanocomposite hydrogels were comprehensively characterized by XRD, FTIR, TGA,
13C NMR, FESEM/EDAX/elemental mapping and HR-TEM. It was found that inorganic fillers (Au) enhanced higher gel strength in the nanocomposite hydrogels than pure PAAm/HPMC crosslinked hydrogels. The swelling ratio was higher at pH 7.4 at 37°C. The hydrogels did not elicit any cytotoxicity towards human mesenchymal stem cells (hMSCs). The release of colonic drugs such as ornidazole and 5-ASA were found to be sustainable for nanocomposite hydrogels.
Ghorpade et al. (2016) prepared β-cyclodextrin (βCD) grafted HPMC hydrogel films using citric acid as a crosslinker for controlled release of hydrophobic drug (ketoconazole). In this study, FTIR and 13C NMR were investigated to prove the ester crosslinking between βCD and HPMC. It was found that swelling ratio, drug loading
and drug release were mainly dependent on βCD content. The maximum drug release was found to be 64.99% at the end of 24 h and its release mechanism was non-Fickian.
The hydrogel films showed good biocompatibility according to hemolytic assay.
Iohara et al. (2017) synthesized thermoresponsive hydrogels composed of cyclodextrins (CDs) and hydrophobically modified HPMC (HM-HPMC) for ocular drug delivery.
The thermoresponsive behavior of the gel was due to addition of CDs which interacted with HM-HPMC. The potential use of the prepared hydrogels was tested on the eyes of a rabbit. The solution (HM-HPMC/α-CD) containing diclofenac sodium drug was absorbed by formation of a gel on the ocular surface.
Mut et al. (2018) developed topical hydrogels contained chitosan and HPMC as polymers and sucrose palmitate and sucrose laurate as penetration enhancers for fluconazole delivery. The prepared hydrogels were evaluated for their drug content, viscosity, pH, in vitro drug release and ex vivo drug permeation. It was observed that all developed hydrogels fulfilled the requirements of drug content, viscosity and pH. In vitro release study showed that high flux and drug release rate were observed for all fluconazole incorporated chitosan-HPMC based hydrogels. According to ex vivo drug permeation study, sucrose laurate was an effective penetration enhancer for fluconazole.
Zhang et al. (2019) investigated potential use of HPMC, which were seeded with human adipose-derived stromal cells (ADSCs) for constructing lymphoid nodes in vivo. The grown hADSCs combined with 13% (w/v) HPMC were injected into mice subcutaneously. It was found that lymphoid nodes were developed at the injected sites after eight weeks. This technique could be an alternative method for adjunctive therapy for malignancies or engineering immune organs or immunodeficiency diseases.
The advantages and disadvantages of various hydrogels containing nanomaterials were listed in Table 2.1.
Table 2.1: Advantages and disadvantages of various hydrogels containing nanomaterials.
S.No. Hydrogel compositions
Advantages Disadvantages Reference
1. NaCMC,
diallyldimethylamm onium chloride and MBA
Form: Hydrogel coated cotton fabric NPs: CuO and Ag
Hydrogels exhibited excellent antibacterial activity and swelling ratio.
It can be used for drug delivery and wound healing applications.
Graft polymerization was tedious process and
involved toxic
crosslinkers and initiators.
Mechanical properties were not reported.
Biocompatibility of hydrogels was not reported.
Hebeish and Sharaf (2015)
2. NaCMC, PVA and ethylene glycol diglycidyl ether (EGDE).
Form: Hydrogel NPs: Ag
Hydrogel showed excellent antibacterial activity. It can be used for
wound healing
applications.
Chemical crosslinking of EGDE by microwave radiation cannot be suitable for industry.
EGDE was a toxic chemical crosslinker.
Biocompatibility of hydrogels was not reported. It needed secondary wound dressing materials.
Alshehri et al. (2016)
3. NaCMC and citric acid.
Form: Hydrogel films.
NPs: ZnO in MCM- 41
The process was less cumbersome to fabricate films. It exhibited higher swelling ratio, higher drug loading and prolonged and controlled release of tetracycline. Films showed higher water vapor permeability and
higher oxygen
permeability. Films exhibited antibacterial activity. Films were biocompatible.
Elongation at break of films was 4% (not flexible films). Films did not possess antioxidant activity. In vitro wound closure study was not reported.
Rakhshaei and Namazi (2017)
4. NaCMC and citric acid.
Form: Hydrogel films.
NPs: Ag
The process was less cumbersome to fabricate films. It showed excellent swelling ratio of approximately 420–
1500%. Films showed antibacterial activity.
Films were biocompatible.
Mechanical properties were not reported. It was less transparent. Films did not show antioxidant activity. In vitro wound closure study was not reported.
Capanema
et al.
(2018b)
5. NaCMC and
epichlorohydrin Form: Hydrogel films.
NPs: Graphene
Swelling ratio was found to be 150% at pH 7.4.
Films showed higher water vapor permeability.
Tensile strength was found to be 50 – 55 MPa.
Films were biocompatible.
Films were brittle. The crosslinker was a pungent liquid and moderately soluble in water. The films did not show any antibacterial activity or antioxidant activity.
Javanbakht and Namazi (2018)
6. NaCMC and PVA.
Form: Porous
Films showed excellent swelling ratio and higher
Freeze-thaw cycles were energy and time
Joorabloo et al. (2019)
NPs: ZnO rate. Films were highly flexible. Films showed antibacterial activity and biocompatibility. Films showed good performance in wound healing by scratch assay
Tensile strength was poor (approx. 0.5 MPa) due to physical crosslinking. The films did not show any antioxidant activity. In vitro wound closure study was not reported.
7. NaCMC and silk fibroin
Form: Hydrogels.
NPs: ZnO
The hydrogel exhibited a high swelling ratio of 2000% – 3000%.
Hydrogels showed antimicrobial activity.
Hydrogels were
biocompatible.
In this study, the process of hydrogel fabrication needed a high temperature (122°C) for curing with minimum of 5 h.
Requirement of many chemicals to fabricate
hydrogels and
complicated steps were involved. Hydrogels did not show antioxidant activity. In vitro wound closure study was not reported. It needed secondary wound dressing materials.
Raho et al.
(2020)
