Soy Protein-Based Hydrogel under Microwave-Induced Grafting of Acrylic Acid and 4-(4-Hydroxyphenyl)butanoic Acid: A Potential Vehicle for Controlled Drug Delivery in Oral Cavity Bacterial Infections

Abstract

The objective of this work was to evaluate grafted soy protein isolate (SPI) for pharmaceutical applications. The present work reports the microwave-assisted preparation of soy protein isolate\grafted[acrylic acid-co-4-(4-hydroxyphenyl)butanoic acid] [SPI-g-(AA-co-HPBA)] hydrogel via graft copolymerization using N,N-methylene-bis-acrylamide and potassium persulphate as the cross-linker and initiator, respectively. The chemical and physical properties of the synthesized polymeric hydrogels were analyzed by Fourier transform infrared spectroscopy, liquid chromatography-mass spectrometry (LCMS), nuclear magnetic resonance ¹H-NMR, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The SEM, TEM, and XRD analyses have confirmed the formation of hydrogel SPI-g-(AA-co-HPBA) with the network structure having a layered and crystalline surface. The SPI-g-(AA-co-HPBA) hydrogel was investigated for the sustained and controlled drug delivery system for the release of model drug ciprofloxacin at basic pH for its utilization against bacterial infection in oral cavity. The drug release profile for SPI-g-(AA-co-HPBA) hydrogels was studied using LCMS at the ppb level at pH = 7.4. The synthesized hydrogel was found to be noncytotoxic, polycrystalline in nature with a network structure having good porosity, increased thermal stability, and pH-responsive behavior. The hydrogel has potential to be used as the vehicle for controlled drug delivery in oral cavity bacterial infections.

Scheme 1. Mechanism of Grafting Using Microwave Conditions

Figure 1

(a) Effect of heating temperature in MW on grafting, (b) effect of preheating time in MW on grafting, (c) effect of concentration of initiator on grafting, and (d) effect of monomer concentration on grafting.

Figure 2

Graph showing% of swelling behavior of (a) (1) SPI-g-(AA-co-HPBA), (2) neat SPI, and (3) SPI-g-AA at pH 7.4 and (b) (1) neat SPI, (2) SPI-g-AA, and (3) SPI-g-(AA-co-HPBA) at pH 1.2.

Figure 3

(a) Calibration curve for linearity of ciprofloxacin. (b) Absorption study of ciprofloxacin on the hydrogel by LC–MS/MS.

Figure 4

(a) Ciprofloxacin release study from the grafted hydrogel at pH 7.4, and (b) percentage release of ciprofloxacin from the grafted hydrogel at pH 7.4 over 14 h, using Agilent 6470 LC–MS/MS.

Figure 5

XRD data for neat SPI and SPI-g-(AA-co-HPBA).

Figure 6

FTIR spectra of neat SPI and SPI-g-(AA-co-HPBA).

Figure 7

TGA/DTG of neat SPI and SPI-g-(AA-co-HPBA).

Figure 8

(a) SEM of neat SPI (×3.0 K) at 10 μm, (b) SPI-g-AA (×20.32 K) at 1 μm, (c) SPI-g-AA (×30.8 K) at 1 μm, (d) SPI-g-AA (×8.4 K) at 2 μm, (e) SPI-g-(AA-co-HPBA) (×2.07 K) at 2 μm, (f) SPI-g-(AA-co-HPBA) (×30.84 K) at 1 μm, (g) SPI-g-(AA-co-HPBA) (×20.0 K) at 2 μm, and (h) SPI-g-(AA-co-HPBA) (×8.15 K) at 1 μm.

Figure 9

TEM images: (a) neat SPI at 50 nm, (b) neat SPI at 100 nm, (c) neat SPI at 51 nm, (d) neat SPI electron image at 5 μm, (e) SPI-g-(AA-co-HPBA) at 50 nm, (f) SPI-g-(AA-co-HPBA) at 1 μm, (g) SPI-g-(AA-co-HPBA) at 51 nm, and (h) SPI-g-(AA-co-HPBA) electron image at 1 μm.

Figure 10

¹H NMR in D₂O comparison of neat SPI and SPI-g-(AA-co-HPBA).

Figure 11

Antibacterial activity (ZI size) of neat ciprofloxacin, SPI-g-(AA-co-HPBA) hydrogel, and ciprofloxacin-loaded SPI-g-(AA-co-HPBA) hydrogel against E. coli bacterial strain. The untreated group did not receive any treatment in the well formed on E. coli-plated agar plates.

Figure 12

Effect of different treatments on the viability of HepG-2 cells as evaluated by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay. The control group was not subjected to any treatment and was considered to have 100% cell viability. The effect of different treatments on cell viability has been presented as per cent of control group (100%). Each value depicts an average of three sets of experiments and was expressed as mean ± SE. Significance at *P < 0.05, compared with the control (Student’s t-test).