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Introduction
Silver compounds have been used for centuries because of their antibacterial activity [1].
However, studies have reported that silver compounds can cause a blue-grey discoloration, in which
this mostly happens at the skin and eyes [2]. Therefore, the use of silver nanoparticles (AgNPs) has
been vastly increasing due to the claim of lower toxicity when compared with silver compounds [3].
Moreover, many researches have reported a broad-range antibacterial activity of AgNPs [4, 5]. Likewise,
they have been widely employed in consumer products, such as cloths, toys and cleaning agents etc
[6]. As well, AgNPs has been used for medical application, such as the use of AgNP-coat heart valves to
reduce a bacterial colonisation on the devices, or the use of AgNP-coated external ventricular drain
catheters to reduce bacterial infection during neurosurgery [7].
Furthermore, many studies have prepared AgNP-polymer composites, and then their
characteristics were determined. For examples, spherical AgNPs/alginate microbeads and
AgNPs/alginate/PVA microbeads were successfully prepared with the size of 720±24 μm and 935±56
μm in diameter, respectively, after evaluated by optical microscope [8]. Also, AgNP-alginate beads,
which were used to embed in gelatin scaffolds for wound dressing application, were prepared as
follows: silver nitrate (a source of silver ions) at different concentrations (0, 4 and 8 %w/v) was
dissolved in alginate solution, and silver ions were reduced to AgNPs using a UV irradiation technique
[9]. After that, the beads were formed by dropping this alginate/AgNPs solution into calcium chloride
solution, and these beads were dried by a lyophilisation method for 20 h. The diameters of the wet
(measured by optical microscope) and dry (measured by SEM) beads was as follows: 485.38±16.35 and
149.02±12.93 μm for the blank beads, 439.52±23.33 and 143.31±12.30 μm for 4%AgNPs-loaded
calcium alginate beads, and 411.21±14.89 and 139.96±11.11 μm for 8%AgNPs-loaded calcium alginate
beads. As well, chitosan/AgNPs nanocomposite hydrogel beads were prepared by a chemical reduction
method as follows: silver nitrate (a source of silver ions) was mixed with chitosan in distilled water, and
then the silver ions were reduced by sodium borohydride which is soluble in sodium tripolyphosphate
solution [10]. Finally, the beads were dried by 4 freezing and thawing cycles. These beads had a
spherical shape with the diameter of ~3-4 mm in the wet state and of ~1 mm in the dry state.
Moreover, the swelling behavior of these beads was studied at pH 2.1 and 7.4, in which a time-
dependent swelling was observed for both pH and the swelling ratio of the beads was greater at pH
2.1 than that at pH 7.4. This might be because the amine groups of chitosan will be protonated at pH
2.1, and this will result in a higher diffusion of proton, counter-ions as well as water to get into the
beads when compared at pH 7.4 [10].
However, the procedure used to prepare calcium alginate beads containing AgNPs, the size of
AgNPs as well as the polymer employed in this study were different to previous studies. Therefore, the
aim of this present study was to determine the size, water loss and swelling ratio of the prepared
