Hydrogels with Essential Oils: Recent Advances in Designs and Applications

Abstract

The innovative fusion of essential oils with hydrogel engineering offers an optimistic perspective for the design and development of next-generation materials incorporating natural bioactive compounds. This review provides a comprehensive overview of the latest advances in the use of hydrogels containing essential oils for biomedical, dental, cosmetic, food, food packaging, and restoration of cultural heritage applications. Polymeric sources, methods of obtaining, cross-linking techniques, and functional properties of hydrogels are discussed. The unique characteristics of polymer hydrogels containing bioactive agents are highlighted. These include biocompatibility, nontoxicity, effective antibacterial activity, control of the sustained and prolonged release of active substances, optimal porosity, and outstanding cytocompatibility. Additionally, the specific characteristics and distinctive properties of essential oils are explored, along with their extraction and encapsulation methods. The advantages and disadvantages of these methods are also discussed. We have considered limitations due to volatility, solubility, environmental factors, and stability. The importance of loading essential oils in hydrogels, their stability, and biological activity is analyzed. This review highlights through an in-depth analysis, the recent innovations, challenges, and future prospects of hydrogels encapsulated with essential oils and their potential for multiple applications including biomedicine, dentistry, cosmetics, food, food packaging, and cultural heritage conservation.

Keywords: active food packaging; biomedical applications; cosmetics; dentistry; encapsulation; essential oils; hydrogels; restoration of cultural heritage.

Figure 1

Classifications of hydrogels.

Figure 2

SEM images of the hydrogel samples [43].

Figure 3

Photo of hydrogel films based on polyvinyl alcohol–cornstarch–patchouli oil and Ag nanoparticles [45].

Figure 4

SEM images of hydrogel films based on polyvinyl alcohol/corn starch/patchouli oil (A) with Ag nanoparticles (samples F0–F4); (B) Dry samples; (C) Dry samples soaked in water; (D) Dry samples soaked with phosphate buffer [45].

Figure 5

Wound healing activity: (A) for in vitro scratch assay in HaCaT cell lines. Images were taken before (Control t0) and 24 h after incubation: untreated samples (control and 24 h) and treated samples, respectively thyme oil (THO) and functionalized hydrogels and their corresponding empty NPs. (B) Skin surface showed a reduction in methylene blue following ex vivo antioxidant activity of the samples [47].

Figure 6

SEM micrographs at 1000× magnifications showing the microstructure in cross-sectional of composite sponges [49].

Figure 7

Photos of the stable chitosan emulsion with clove EO content (after 0–4 days) kept in the dark and ambient conditions [52].

Figure 8

Cross-sectional SEM images of chitosan and oxidized pullulan-based hydrogels loaded with clove EO: overview (a), wall detail (b), and pore size distribution with corresponding diagrams (c) [52].

Figure 9

Antibacterial effect of clove oil-loaded hydrogels evaluated by the time-kill method, after 3–72 h of incubation with S. aureus (a), E. coli (b), and C. albicans (c) [52].

Figure 10

SEM micrographs of polymeric hydrogel (control), oregano essential oil, and micelle-based hydrogel sample containing oregano EO [57].

Figure 11

Optical microscopy images of polymer capsules of different shapes loaded with pine, thyme, and mint EO [63].

Figure 12

Photo and SEM images of different hydrogel formulations, with and without EO, nanoliposomes, and nanoliposome/maltodextrin complexes. (A): control hydrogel; (B): hydrogel with EO; (C): hydrogel with lecithin and EO (14.23%); (D): hydrogel with lecithin, maltodextrin and EO (20%); (E): hydrogel with lecithin, maltodextrin and EO (25%); (F): hydrogel with lecithin, maltodextrin, and EO (33%) [79].

Figure 13

Photo of the composite films based on sodium alginate and acacia gum with different concentrations of cinnamon EO: (AC1—without EO) (AC2—15 μL EO) (AC3—20 μL EO) (AC4—30 μL EO) [129].