Design of Smart Antimicrobial Materials Based on Silver-Silica Nanocapsules

Abstract

Silver nanoparticles have been commonly used as an antibacterial agent and are often delivered in a burst release manner to the site of infection. However, a drawback of this release mode is the limited lasting duration of the antibacterial properties of the particles. Hence, in order to achieve a more effective and sustained protection against bacteria growth, this project aims to design and create smart antimicrobial materials based on silver-silica nanocapsules that can respond to an acidic environment to release Ag⁺ ions in a targeted, slow and sustained manner. In this project, the as-synthesized silica-silver nanocapsules were found to exhibit excellent colloidal stability, thus allowing for a homogenous distribution within different polymer matrix materials. Explored applications include the incorporation of the silver-silica nanocapsules into F127 hydrogel and poly(vinyl alcohol) (PVA) film so as to develop antibacterial biomaterials that can effectively prevent bacteria growth for a sustained period of time. In subsequent proof-of-concept studies, both the F127 hydrogel and PVA film were able to respond to acidic conditions for a gradual release of Ag⁺ ions. Interestingly, the as-released Ag⁺ ions from the PVA film were effectively entrapped within the polymer matrix, thereby demonstrating their promising potential to sterilize absorbed fluid from wound sites when applied as a wound dressing. On the other hand, the F127 hydrogel exhibited a slow and sustained release of Ag⁺ ions into the surrounding environment, hence affirming their capacity for topical administration in the form of lotions or creams for antibacterial purposes.

Appendices

Appendices

1.1 Appendix 1: Synthesis of Silica Nanocapsules

See Fig. 6.

Fig. 6

Diagram showing the formation of micelle and subsequently the silica nanocapsule [13]

1.2 Appendix 2: Variation of Reaction Conditions to Synthesize AgNCs

See Tables 1, 2, 3 and 4.

Table 1 Variations of glucose concentration for samples g1 to g5 to find the optimal glucose concentration

Table 2 Variations of reagents amount for reactions A1 to A7 to find the optimal glucose amount, based on the optimum glucose concentration of 10 mg/mL, as determined in Table 1

Table 3 Variations of the reagents amount for samples 1 to 9 to find the optimal silica nanocapsule concentration

Table 4 Variations of the silver complex concentration for samples A1 to A4

1.3 Appendix 3: Response of AgNCs to Acidic Conditions

See Fig. 7.

Fig. 7

Shown left to right, image of AgNCs (s) immersed overnight in 1 M HNO₃, 1 M acetic acid and deionized water respectively

1.4 Appendix 4: Incorporation of AgNCs into PVA Film to Form Composite Material

See Fig. 8.

Fig. 8

Results of the composite biomaterials formed from different types of PVA (shown left to right: (i) 80% hydrolyzed, MW 9000–10,000, (ii) 87–89% hydrolyzed, MW 30,000–50,000, (iii) 99+% hydrolyzed, MW 1–30,000, and (iv) 99+% hydrolyzed, MW 85,000–124,000), where only the latter two were formed successfully after 3 freeze-thaw cycles

1.5 Appendix 5: Sol-to-Gel Transition of F127 Hydrogel at Different wt%

See Figs. 9 and 10.

Fig. 9

F127 hydrogels of 18 and 20% F127 at 25 °C, observed to be in gel state

Fig. 10

F127 hydrogel of 16% F127 after heating up to 37 °C in a warm water bath for 1–2 min, observed to be in gel state