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Nanomaterials 2021, 11, x FOR PEER REVIEW 7 of 20 Nanomaterials 2021, 11, 96 The observed change in the color of PVA films containing silver nitrate is consi7stoef n19t with the reduction of silver ions to silver metal nanoparticles. In essence, PVA has a num- ber of active hydroxyl groups available for binding silver. The heat-induced reaction of silver with PVA to generate silver nanoparticles in situ can be described by the equations of active hydroxyl groups available for binding silver. The heat-induced reaction of silver below. with PVA to generate silver nanoparticles in situ can be described by the equations below. >R−OH + Ag+ → >R−O−Ag + H+ >R−OH + Ag+ → >R−O−Ag + H+ >R−O−Ag → −R=O + Ag0 >R−O−Ag → −R=O + Ag0 >R−OH+Ag+ →−R=O+Ag0+H++ 0 >R−OH+Ag →−R=O+Ag +H + In these equations, −R=O represents a monomer of partially oxidized PVA at the re- In these equations, −R=O represents a monomer of partially oxidized PVA at the action surface while H+ r+epresents the nitric acid by-product. reaction surface while H represents the nitric acid by-product. As noted by Longenberger and Mills [22] and more recently by Porel et al. [23], on As noted by Longenberger and Mills [22] and more recently by Porel et al. [23], heating PVA in the presence of silver nitrate the polymer can act as a reducing agent, a on heating PVA in the presence of silver nitrate the polymer can act as a reducing agent, stabilizer and as a matrix for homogeneous distribution and immobilization of silver. It is a stabilizer and as a matrix for homogeneous distribution and immobilization of silver. possible that a side effect of silver nanoparticle production might be the generation of It is possible that a side effect of silver nanoparticle production might be the generation nitrate ions with unknown effects in wounds. However, since silver nitrate solution is of nitrate ions with unknown effects in wounds. However, since silver nitrate solution is available by prescription to treat burns and wounds it is unlikely that such effects might available by prescription to treat burns and wounds it is unlikely that such effects might cause any local toxicity. cause any local toxicity. The release media from selected PVA-silver films were examined using particle size The release media from selected PVA-silver films were examined using particle size analysis.. Khhaannnaa eett all.. [[24]] reviewed the synthesis and characterization of PVA-silver nanocomposites by chemical reduction methods, speciffiically using hydrazine hydrate or sodium formaldehyde sulfoxylate (SFS), which resulted in silver nanoparticles with size less than 10 nm as determined using transmission electron microscopy (TEM). As also pointed out by these authors, there are reports in the literature of the synthesis of silver nanoparticles protected by PVA [23,24]. Our particle size data shown in Figure 4, when compared with similar data for silver nanoparticle standards, indicated that the release media have two populations; ffiirst, a sub-100 nm set and, second, a group of much larger particles, some of which are a micron or more in dimension. The sizes likely reflflect the nanoparticle size presented to potential bacteria in a wound or burn setting but do not necessarily report the size within the PVA films as the particles have been exposed to water necessarily report the size within the PVA films as the particles have been exposed to for some time. water for some time. 8 6 4 2 0 0.1 1 10 100 1000 10000 Size Distribution by Intensity Size (d.nm) Record 3: Ag nanos PVA 5% 140 90 overnight 1 Record 4: Ag nanos PVA 5% 140 90 overnight 2 Record 5: Ag nanos PVA 5% 140 90 overnight 3 Figure 4. Particle size analysis of the aqueous release medium after immersing PVA/silver film (5% w/w silver nitrate, Figure 4. Particle size analysis of the aqueous release medium after immersing PVA/silver film (5% w/w silver nitrate, heat heat cured at◦140 °C for 90 min) in deionized water overnight. cured at 140 C for 90 min) in deionized water overnight. 4.2. Film Swelling 4.2. Film Swelling After an initial brief swelling period of about 10 min, 100 μm- and 200 μm-thick films thatwAeftreruanciunrietidalobrrcieufreswdealtli8n0g°pCerwioedreofualblyoudtis1s0olmveind,w10i0thμinm2-.a5nhdr2e0g0arμdmle-sthsiocfksfiilvmesr that were uncured or cured at 80 ◦C were fully dissolved within 2.5 h regardless of silver nitrate loading. (Figure 5A,B). A similar swelling profile was observed for films cured at 110 ◦C, except that the films dissolved more slowly than the films cured at 80 ◦C (Figure 5C,D). Intensity (Percent)PDF Image | Hydrogel Forming Dressings Containing Silver Nanoparticles
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