Nik Ahmad Nizam Nik Malek

Characterization and antibacterial activity of silver exchanged regenerated NaY zeolite from surfactant-modified NaY zeolite

The antibacterial activity of regenerated NaY zeolite (thermal treatment from cetyltrimethyl ammonium bromide (CTAB)-modified NaY zeolite and pretreatment with Na ions) loaded with silver ions were examined using the broth dilution minimum inhibitory concentration (MIC) method against Escherichia coli (E. coli ATCC 11229) and Staphylococcus aureus (S. aureus ATCC 6538). X-ray diffraction (XRD), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) and chemical elemental analyses were used to characterize the regenerated NaY and AgY zeolites. The XRD patterns indicated that the calcination and addition of silver ions on regenerated NaY zeolite did not affect the structure of the regenerated NaY zeolite as the characteristic peaks of the NaY zeolite were retained, and no new peaks were observed. The regenerated AgY zeolite showed good antibacterial activity against both bacteria strains in distilled water, and the antibacterial activity of the samples increased with increasing Ag loaded on the regenerated AgY zeolite; the regenerated AgY zeolite was more effective against E. coli than S. aureus. However, the antibacterial activity of the regenerated AgY was not effective in saline solution for both bacteria. The study showed that CTAB-modified NaY zeolite materials could be regenerated to NaY zeolite using thermal treatment (550°C, 5h) and this material has excellent performance as an antibacterial agent after silver ions loading.

Removal of Ca2+ and Zn2+ from aqueous solutions by zeolites NaP and KP

Zeolites P in sodium (NaP) and potassium (KP) forms were used as adsorbents for the removal of calcium (Ca2+) and zinc (Zn2+) cations from aqueous solutions. Zeolite KP was prepared by ion exchange of K+ with Na+ which neutralizes the negative charge of the zeolite P framework structure. The ion exchange capacity of K+ on zeolite NaP was determined through the Freundlich isotherm equilibrium study. Characterization of zeolite KP was determined using infrared spectroscopy and X‐ray diffraction (XRD) techniques. From the characterization, the structure of zeolite KP was found to remain stable after the ion exchange process. Zeolites KP and NaP were used for the removal of Ca and Zn from solution. The amount of Ca2+ and Zn2+ in aqueous solution before and after the adsorption by zeolites was analysed using the flame atomic absorption spectroscopy method. The removal of Ca2+ and Zn2+ followed the Freundlich isotherm rather than the Langmuir isotherm model. This result also revealed that zeolite KP adsorbs Ca2+ and Zn2+ more than zeolite NaP and proved that modification of zeolite NaP with potassium leads to an increase in the adsorption efficiency of the zeolite. Therefore, the zeolites NaP and KP can be used for water softening (Ca removal) and reducing water pollution/toxicity (Zn removal).

Immobilization of antibacterial chlorhexidine on stainless steel using crosslinking polydopamine film: Towards infection resistant medical devices

Chlorhexidine (CHX) is known for its high antibacterial substantivity and is suitable for use to bio-inert medical devices due to its long-term antibacterial efficacy. However, CHX molecules require a crosslinking film to be stably immobilized on bio-inert metal surfaces. Therefore, polydopamine (PDA) was utilized in this study to immobilize CHX on the surface of 316L type stainless steel (SS316L). The SS316L disks were pre-treated, modified with PDA film and immobilized with different concentrations of CHX (10mM-50mM). The disks were then subjected to various surface characterization analyses (ATR-FTIR, XPS, ToF-SIMS, SEM and contact angle measurement) and tested for their cytocompatibility with human skin fibroblast (HSF) cells and antibacterial activity against Escherichia coli and Staphylococcus aureus. The results demonstrated the formation of a thin PDA film on the SS316L surface, which acted as a crosslinking medium between the metal and CHX. CHX was immobilized via a reduction process that covalently linked the CHX molecules with the functional group of PDA. The immobilization of CHX increased the hydrophobicity of the disk surfaces. Despite this property, a low concentration of CHX optimized the viability of HSF cells without disrupting the morphology of adherent cells. The immobilized disks also demonstrated high antibacterial efficacy against both bacteria, even at a low concentration of CHX. This study demonstrates a strong beneficial effect of the crosslinked PDA film in immobilizing CHX on bio-inert metal, and these materials are applicable in medical devices. Specifically, the coating will restrain bacterial proliferation without suffocating nearby tissues.

Antibacterial Activity of Amine-Functionalized Zeolite NaY against Staphylococcus aureus ATCC6538 and Escherichia coli ATCC11229

The antibacterial activity of functionalized zeolite NaY (CBV100) with different concentrations of 3-aminopropyltriethoxysilane (APTES) (0.01, 0.05, 0.20 and 0.40 M) was studied against Staphylococcus aureus ATCC 6538 (Gram positive) and Escherichia coli ATCC 11229 (Gram negative) through disc diffusion technique (DDT). The characterization of functionalized zeolite NaY with fourier transform infrared (FTIR) spectroscopy indicated the attachment of APTES on zeolite NaY. Through DDT, the inhibition zone of functionalized zeolite NaY increased proportionally to the amount of the amine-functional group attached onto zeolite NaY. Functionalized zeolite NaY showed higher antibacterial activity against Gram-positive compared to Gram-negative bacteria. It can be concluded from this study that amine-functionalized zeolite NaY shows evidence of antibacterial activities.

Application of Surfactant-Modified Clinoptilolite in Peat Substrate on the Growth of Orthosiphon stamineus

ABSTRACT This study covers the application of surfactant-modified clinoptilolite (SMC) in peat substrate on the growth of Orthosiphon stamineus. SMC added in peat substrate may increase nutrient availability to O. stamineus by controlling anionic nutrients (phosphate and nitrate) leach to the environment. The modification of clinoptilolite (Cli) by using hexadecyltrimethyl ammonium surfactant alters the surface charge of Cli from negative to positive which is likely to attract anions when applied in the substrates. In leachate study, there was a higher amount of phosphate− and nitrate released (19.67 and 139.00 mg/L, respectively) by the commercial propagating substrate (PS) in the first day of the experiment. However, the application of Cli and SMC in peat substrate significantly reduced the concentrations of both nutrients, especially when 20% of the SMC was added in the peat substrates. There were significant differences in the growth parameters of O. stamineus, particularly those grown in 10% Cli-amended peat substrate. Results of leachate and plant growth studies indicate that Peat + 20% SMC could be a potential substrate to replace the commercial PS as it reduces the release of phosphate and nitrate, at the same time allows maximum uptake of nitrogen and phosphorus, which promotes the growth and development of O. stamineus.

Influence of Coating Time on Immobilization of Chlorhexidine on Polydopamine Grafted Stainless Steel 316L: Characterization, Adsorption and Cytotoxicity Analyses

Chlorhexidine (CHX) has a broad antimicrobial range. The immobilization of CHX on a polydopamine (PDA) layer may acts as an antibacterial coating on medical grade stainless steel (SS316L). In this study, the immobilization of CHX on PDA grafted SS316L was performed at different immersion times (3, 6, 9, 12, 24 and 48 hours). The samples were subjected to ATR-FTIR and AFM analyses, adsorption test and cytotoxicity test. The immobilization of CHX at 24 hours produced a stable CHX coating on the PDA layer as evidenced by prominent indicator of CHX long hydrocarbon chain in the FTIR spectra. The CHX coating has higher surface roughness due to CHX aggregation and several protrusions on the grafted PDA layer. Longer immersion time in the CHX salt solution led to high diffusivity rate of solubilized CHX which cause higher absorptivity of CHX on the PDA grafted SS316L. While, the viability study indicated no significant cytotoxicity on osteoblast cells for all time points. The immobilization of CHX on the PDA layer at 24 hours contributed to a stable coating with acceptable cytotoxicity range which could be utilized in the development of an antibacterial coating on metallic implants.

Effect of mass concentration on bioactivity and cell viability of calcined silica aerogel synthesized from rice husk ash as silica source

The biocompatibility of calcined silica aerogel (900 °C) synthesized from rice husk ash via sol–gel ambient-pressure drying technique was studied. The silica aerogel was characterized by Fourier transform infrared spectroscopy, X-ray diffraction and field emission-scanning electron microscopy. The structure of silica aerogel remains intact but is deficient in silanol groups after calcination. The bioactivity of the silica aerogel was tested by immersion in simulated body fluid for 7 days with various mass concentrations (0.08–0.8 wt%). The results from Fourier transform infrared, X-ray diffraction, field emission-scanning electron microscopy and phosphorous analyses confirm that the silica aerogel could facilitate the nucleation of apatite. The silica aerogel was simultaneously resorbed and the broken Si–O–Si bonds were replaced with new apatite bonds. The optimal mass concentration was 0.16 wt%. At a higher mass concentration (0.8 wt%), silica aerogel tends to form polymeric interactions with tris-hydroxymethyl-aminomethane, a chemical compound in simulated body fluid. In the in vitro cell viability assay of the calcined silica aerogel against human dermal fibroblast cells, the cell viability increased with the increase of silica aerogel mass concentration. This early evidence shows that the calcined silica aerogel synthesized from rice husk ash via the sol–gel ambient-pressure drying technique can be considered as a potential alternative material for tissue engineering applications.Graphical Abstract

FTIR Study on the Preliminary Development of Synthesis Methods for Hydroxyapatite Modified Silica Aerogel

Hydroxyapatite (HA) modified silica aerogel (SA) was synthesized based on 2 different techniques namely encapsulation and in-situ via aqueous colloidal sol-gel process. The structure of the synthesized HA modified SA have been studied using Fourier transform infrared (FTIR) spectroscopy. FTIR spectra of HA modified SA, derived from in-situ technique appear to be different from those of encapsulation technique and free HA, with the main difference lying in the phosphate bending absorbance. Results showed that the encapsulation technique preserved the native confirmation of HA in SA frameworks compared to in-situ technique. It confirms that the use of an aqueous sol-gel encapsulation route provides a promising approach for the stabilization of HA in SA networks.