Elsevier

Journal of Molecular Liquids

Volume 265, 1 September 2018, Pages 327-336
Journal of Molecular Liquids

Thermal, microstructural, and spectroscopic analysis of Ca2+ alginate/clay nanocomposite hydrogel beads,☆☆

https://doi.org/10.1016/j.molliq.2018.06.005Get rights and content

Highlights

  • Several clay and zeolite-starch nanocomposites have been studied.

  • Fourier-transform infrared analysis detected the presence of functional groups of each component.

  • The elemental composition of the hydrogels was investigated by energy dispersive X-ray spectrometry (EDX).

  • Thermal stability of the hydrogels was increased by crosslinking with calcium or by the incorporation of nanoclays.

Abstract

Polymeric hydrogels are important biomaterials with potential for various applications including the controlled release of drugs. Clay and zeolite nanostructures can enhance the absorption and release properties of hydrogels. In our previous work, a procedure was optimized for making hydrogel beads. The objectives of this study were to use the optimized bead forming procedure to prepare clay and zeolite nanocomposite hydrogel beads and characterize their microstructure, thermal and chemical properties. The hydrogels were prepared by dripping solutions of either sodium alginate or sodium alginate/nanostructure (clay and/or zeolite) into beakers containing different concentrations of CaCl2 at 25 °C. Fourier transform infrared spectroscopy (FTIR) analysis detected the presence of functional groups associated with alginate, clay and zeolite. The microstructure of the alginate beads was somewhat rough with small protrusions. Flakes were visible in micrographs of beads containing nanoclay. The elemental composition of the hydrogels was investigated by energy dispersive X-ray spectrometry (EDX). EDX spectra revealed magnesium, sodium, aluminum, silicon and increased the levels of oxygen in the nanoclay compositions. The incorporation of nanoclays decreased the percentage of organic matter lost as detected by thermogravimetric analysis (TG). TG was also able to detect the incorporation of nanoclay in hydrogels. The nanoclays proved to be more effective than zeolites in producing alginate hydrogels with satisfactory swelling characteristics.

Introduction

Various polymers used in biomedical applications have important functional properties including biocompatibility and biodegradability [1]. Some polymers can be classified as biomaterials precisely for such properties. Moreover, in human trials their performance is very satisfactory. Polymers can even be used in prosthetic devices where they prove to be highly functional and can displace high-cost equipment [2].

Among the materials designated as polymers, alginate is a polysaccharide of particular interest. In addition to the benefits already highlighted above, alginate is hydrophilic in nature, has low toxicity, and is relatively inexpensive [3, 4]. The alginate polymer is composed of linear chains of α-l-guluronic acid (G) and β-d-manuronic acid (M) blocks identified as rigid and flexible blocks, respectively. Alginate is extracted from brown algae (Phaeophyceae) [5].

Alginate is particularly useful in the production of firm hydrogels through the use of multi-valent cations [6]. When exposed to multi-valent cations, the alginate chains begin to interact with the ions that form crosslinks with other nearby chains. This characteristic crosslinking behavior with multi-valent cations is a key to the formation of alginate hydrogels. Several studies also describe the preparation of hydrogels formed by crosslinking alginate with other polymers [[7], [8], [9]]. For instance, Facchi et al. [7] prepared hydrogel beads by using a steady drip of alginate solution into a slowly stirred chitosan solution.

Hydrogels are polymeric materials known particularly for the ability to absorb high amounts of water in their three-dimensional structure. In contrast to hydrogels that are chemically crosslinked to form covalent bonds and do not dissolve after the chemical reaction is complete, hydrogels that are crosslinked with ionic bonds can dissolve depending on the external factors to which it is exposed, such as changes in pH, temperature, saline solutions, among others [10]. The softness and flexibility of hydrogels contribute to their wide use in biomedicine, they are mainly used to deliver medications that reduce inflammation and discomfort in patients. Other uses of hydrogels within the medical field include their use in contact lenses and for tissue engineering (bone regeneration), healing ointments, drug coating, and controlled delivery systems [[11], [12], [13]]. There are many studies that report the effective use of hydrogels containing nanostructures. Nanostructures such as nanoparticles have been shown to improve the absorption and release of active agents. Among the nanoparticles studied, clays and zeolites are the most common. Clays and zeolites are materials classified as minerals that are naturally formed by geological events and hydrothermal variations of volcanic lavas, respectively. Clays and zeolites are generally considered to be non-toxic when ingested [14]. Several applications for alginate-clay and alginate-zeolite nanocomposites have been reported [[15], [16], [17]].

Clay minerals have a sheet-like structure and are mainly composed of tetrahedrally arranged silicate and octahedrally arranged aluminate groups. The sheet-like structures form platelets that remain bound together by means of the van der Waals forces and relatively weak polar forces. Among these platelets are cationic metals that are compacted due to internal electrostatic forces [14, 18]. Today, hydrogels are valued in applications that exploit their absorption capacity, chemical inertness, low toxicity, and their ability to control the release of various pharmaceuticals [19, 20]. Zeolites are minerals that are porous, comprised mostly aluminosilicate and are used as adsorbents and catalysts as well as in medical applications [21]. Various studies have shown zeolites to be highly effective for topical wound dressings, kidney dialysis, and diarrheal drugs, and have shown antitumor, antimicrobial, and antiviral activity and are of interest in controlled drug release systems [22].

In our previous work, a procedure was optimized for making hydrogel beads. The effect of nanoparticle concentration on bead formation and the hydrophilic and structural properties of the beads were investigated [23]. In other related works, there are several reports about alginate-Ca hydrogels and some about alginate-Ca-clay hydrogels that mainly relate to their application [[24], [25], [26], [27]]. For instance, the work described by Iliescu et al. [27] studied the preparation and characterization of clay and sodium alginate nanocomposite beads used for the controlled release of irinotecan. The main objective was the incorporation of the irinotecan, and the potential application of this nanocomposite in chemotherapy. A detailed investigation into how the crosslinker, clay and zeolite affect the nanocomposite properties is needed. The objective of this work was to prepare different formulations of sodium alginate hydrogels containing clay and zeolite nanoparticles, and to characterize in detail the possible interactions by Fourier Transform Infrared Spectroscopy (FTIR) and thermogravimetric (TG) techniques.

Section snippets

Material and methods

Sodium alginate (SA) was obtained from Cromoline® Química Fina Brazil. Pure anhydrous calcium chloride (CaCl2) was acquired from Sigma-Aldrich. The nanostructures used were the zeolite, Clinoptilolite ZK406 H (St. Cloud Zeolite) and the nanoclay, Cloisite-Na+ (Southern Clay Products®). The reagents were used as received without any purification.

Preparation of sodium alginate solutions

A solution of the polysaccharide sodium alginate was made at a concentration of 2% (w/v). The alginate solution was stirred continuously for about 4 h.

Fourier Transform Infrared Spectroscopy (FTIR)

The effect of different concentrations of Ca2+ crosslinker on alginate hydrogels is shown in Fig. 1.

Analyzing the FTIR spectra for sodium alginate revealed a wide band between 3200 and 3600 cm−1 corresponding to the stretching of the –OH groups present in the alginate polymer chain. The intense bands observed in 1414 cm−1 and 1621 cm−1 correlated respectively to the asymmetric and symmetric axial deformations of the –COO groups indicating the presence of the carboxylic acid group in the

Conclusion

Nanocomposite hydrogels can be readily made with nanoclays and zeolites. The nanomaterials used in the hydrogels confer different physicochemical properties. Physical differences such as in surface roughness in hydrogel beads were apparent in SEM micrographs. Chemical differences in the nanocomposite hydrogels were apparent in FTIR analyses of the samples. Thermal stability of the hydrogels was improved by crosslinking with calcium or by the incorporation of nanoclays. The results of this study

Acknowledgments

The authors are grateful to Universidade Estadual Paulista, and Brazilian research financing institutions Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) (2013/03643-0), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (405680/2016-3) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for their financial support.

References (47)

  • B. de Gennaro et al.

    Surface modified natural zeolite as a carrier for sustained diclofenac release: a preliminary feasibility study

    Colloids Surf. B: Biointerfaces

    (2015)
  • A. Olad et al.

    Semi-IPN superabsorbent nanocomposite based on sodium alginate and montmorillonite: reaction parameters and swelling characteristics

    Carbohydr. Polym.

    (2018)
  • R. Fabryanty et al.

    Removal of crystal violet dye by adsorption using bentonite-alginate composite

    J. Environ. Chem. Eng.

    (2017)
  • A.A. Edathil et al.

    Alginate clay hybrid composite adsorbents for the reclamation of industrial lean methyldiethanolamine solutions

    Appl. Clay Sci.

    (2018)
  • R.I. Iliescu et al.

    Montmorillonite-alginate nanocomposite as a drug delivery system – incorporation and in vitro release of irinotecan

    Int. J. Pharm.

    (2014)
  • S. Barreca et al.

    The effect of montmorillonite clay in alginate gel beads for polychlorinated biphenyl adsorption: isothermal and kinetic studies

    Appl. Clay Sci.

    (2014)
  • S. Hua et al.

    pH – sensitive sodium alginate/poly(vinyl alcohol) hydrogel beads prepared by combined Ca2+ crosslinking and freeze-thawing cycles for controlled release of diclofenac sodium

    Int. J. Biol. Macromol.

    (2010)
  • S. Mallakpour et al.

    Preparation and characterization of new organoclays using natural amino acids and Cloisite-Na+

    Appl. Clay Sci.

    (2011)
  • B.Y. Swamy et al.

    In vitro release of metformin from iron (III) cross-linked alginate-carboxymethyl cellulose hydrogel beads

    Int. J. Biol. Macromol.

    (2015)
  • H. Bera et al.

    Alginate-sterculia gum gel-coated oil-entrapped alginate beads for gastroretentive risperidone delivery

    Carbohydr. Polym.

    (2015)
  • G. Pasparakis et al.

    Swelling studies and in vitro release of verapamil from calcium alginate and calcium alginate-chitosan beads

    Int. J. Pharm.

    (2006)
  • H. Kaygusuz et al.

    Alginate/BSA/montmorillonite composites with enhanced protein entrapment and controlled release efficiency

    React. Funct. Polym.

    (2013)
  • Q. Wang et al.

    Preparation and characterization of a novel pH-sensitive chitosan-g-poly(acrylic acid)/attapulgite/sodium alginate composite hydrogel bead for controlled release of diclofenac sodium

    Carbohydr. Polym.

    (2009)
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