Electrophoretically prepared hybrid materials for biopolymer hydrogel and layered ceramic nanoparticles
© Gwak et al. 2016
Received: 9 September 2015
Accepted: 4 January 2016
Published: 10 February 2016
In order to obtain biomaterials with controllable physicochemical properties, hybrid biomaterials composed of biocompatible biopolymers and ceramic nanoparticles have attracted interests. In this study, we prepared biopolymer/ceramic hybrids consisting of various natural biopolymers and layered double hydroxide (LDH) ceramic nanoparticles via an electrophoretic method. We studied the structures and controlled-release properties of these materials.
Results and discussion
X-ray diffraction (XRD) patterns and X-ray absorption spectra (XAS) showed that LDH nanoparticles were formed in a biopolymer hydrogel through electrophoretic reaction. Scanning electron microscopic (SEM) images showed that the ceramic nanoparticles were homogeneously distributed throughout the hydrogel matrix. An antioxidant agent (i.e., ferulic acid) was loaded onto agarose/LDH and gelatin/LDH hybrids, and the time-dependent release of ferulic acid was investigated via high-performance liquid chromatography (HPLC) for kinetic model fitting.
Biopolymer/LDH hybrid materials that were prepared by electrophoretic method created a homogeneous composite of two components and possessed controllable drug release properties according to the type of biopolymer.
Biomaterials, in a broad sense of the definition, are materials that can be applied to biological systems. They include materials used in medical devices, artificial tissues/organs, bone cement, dental implants, biosensors, catheters, drug delivery systems, hygiene items, etc. [1–3]. In terms of their material properties, biomaterials can be classified as polymers, metals, ceramics, and hybrid materials. Among them, polymers (e.g., poly(lactic acid) (PLA), poly(glycolic acid) (PGA), and poly(lactic-co-glycolic acid) (PLGA)) have been widely studied for soft tissue applications to recover the structure and function of organs. Polymers are desirable because they possess mechanical flexibility, biodegradability, cellular interaction, easy modification, etc. [4, 5]. Natural polymers, like collagen, have been investigated for use as tissue engineering scaffolds . Ceramics are often utilized in hard tissue applications because they have high mechanical strength and chemical stability. For instance, calcium phosphate and hydroxyapatites have been extensively studied for use in mesenchymal stem cell differentiation, bone engineering, and dental implants [7–9]. Metallic biomaterials, such as stainless steel, Ti alloys, and Co-Cr alloys, can be applied in surgical implants or bone tissue engineering applications due to their easy sterilization, high mechanical strength, fracture resistance, and widely available fabrication techniques [10, 11].
Recently, hybrid biomaterials consisting of two or more components have been developed in order to achieve synergic effects. For instance, polymer/polymer hybrids of gelatin, alginate, hyaluronate, and chitosan were reported as wound dressings; these materials have controlled porosity and water uptake properties . An agarose/chitosan hybrid that was suggested by Z. Cao et al. achieved reasonable mechanical strength and effective neuronal growth in 3D space . C. Du et al. reported a hydroxyapatite-incorporated collagen-ceramic/polymer hybrid that was both bioactive and biodegradable . Y. Ito et al. developed hybrids that were composed of biocompatible and biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) nanofibers and hydroxyapatite in order to achieve high specific surface area, surface hydrophilicity, and enzyme invasion .
Herein, we demonstrate possible biopolymer/LDH hybrids made via an electrophoretic method. The obtained hybrids were analyzed in terms of their structure and nanoparticle distribution utilizing X-ray diffraction, X-ray absorption spectroscopy, and electron microscopy. We also investigated the potential of these prepared hybrids in sustained drug release system utilizing an antioxidant agent, ferulic acid, as the model drug.
Agarose (MW: 120 kDa) was purchased from Bio Basic Inc., Canada. Gelatin (from porcine skin), zinc nitrate hexahydrate (Zn(NO3)2 · 6H2O), aluminum nitrate nonahydrate (Al(NO3)3 · 9H2O), sodium bicarbonate (NaHCO3), tris(hydroxymethyl)aminomethane (Tris: NH2C(CH2OH)3), and the antioxidant agent (ferulic acid (C10H10O4)) were purchased from Sigma-Aldrich Co. LLC, USA. Ammonia water (NH4OH), sodium hydroxide (NaOH), and hydrochloric acid (HCl) were purchased from Daejung Chemicals & Metals Co. LTD., Korea.
In order to prepare biopolymer/LDH hybrid materials electrophoretically, a home-made electrophoretic kit was utilized. First, the biopolymer powder (1 wt/v% for agarose and 2 wt/v% for gelatin and the other biopolymers) was dissolved in tris-HCl buffer (pH 7.4) at 120 oC. Then, the solution was poured into the center of the electrophoretic kit walled by plastic plates and cooled down to room temperature for 4 h to obtain a cuboidal hydrogel. The cationic metal solution (0.16 M Zn2+ and 0.08 M Al3+) and the anionic solution (0.08 M NaHCO3 and 1 mL NH4OH), which were precursors for LDH, were located at each side of the cuboidal hydrogel. Then, electrophoresis was operated with 25 V for 30 min. After reaction, the hydrogel was washed with deionized water and thoroughly dehydrated.
As a reference sample for LDH, ZnAl-CO3-LDH (Zn2Al(OH)6(CO3)0.5) was prepared by conventional coprecipitation method, as reported elsewhere . Typically, the cationic metal solution (0.063 M Zn2+ and 0.0315 M Al3+) was titrated with basic solution (NaOH and NaHCO3) to pH ~8.5 with vigorous stirring. After 24 h, white precipitates formed. These were centrifuged, washed by deionized water, and then dried.
Prepared hybrids were characterized by X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and field emission scanning electron microscope (FE-SEM). In order to identify the crystal structure of the ceramic particles in the hybrid, XRD patterns and XAS spectra were obtained by Bruker D2 phaser with Ni-filtered Cu-Kα radiation (λ = 1.5406 Å) and at the 7D XAFS beam line at the Pohang Accelerator Laboratory (Pohang, Korea), respectively. FE-SEM images, obtained with Hitachi SU-70 at the Korea Basic Science Institute (Gangneung Center, Korea), showed the shape and size of LDH nanoparticles in the hybrids.
Sustained release test
(Qt: release amount at time t, t: time, α and β: Elovich constants representing the initial release rate and the overall release rate, respectively.)
Results and discussion
Hydrogel candidates for the electrophoretic preparation method
Cuboidal hydrogel formation
Electrophoretic hybrid formation
○ (with divalent cations)
○ (with divalent cations)
We prepared polymer/ceramic hybrid biomaterials via an electrophoretic preparation method. These materials are suitable for the homogeneous formation of ceramic nanoparticles in a hydrogel. We chose agarose and gelatin as the polymer component and LDH nanoparticles as the ceramic component. All of these materials have adequate biocompatibility and are widely applied in biomedical fields. We identified the crystal structure of LDH nanoparticles by XRD and XAS, which showed that the ceramic nanoparticles inside of the hybrid had the desired LDH structure. By analyzing SEM images, LDH nanoparticles were determined to be homogeneously formed in the hydrogel as we expected. Ferulic acid (the drug model molecule used in our study) was well-loaded onto the biopolymer/LDH hybrid and was released in a sustained manner.
This work was supported by a grant from the Postharvest Research Project (PJ010502) of RDA, Republic of Korea.
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