Nanocellulose composite wound dressings for real-time pH wound monitoring

Abstract

The skin is the largest organ of the human body. Wounds disrupt the functions of the skin and can have catastrophic consequences for an individual resulting in significant morbidity and mortality. Wound infections are common and can substantially delay healing and can result in non-healing wounds and sepsis. Early diagnosis and treatment of infection reduce risk of complications and support wound healing. Methods for monitoring of wound pH can facilitate early detection of infection. Here we show a novel strategy for integrating pH sensing capabilities in state-of-the-art hydrogel-based wound dressings fabricated from bacterial nanocellulose (BC). A high surface area material was developed by self-assembly of mesoporous silica nanoparticles (MSNs) in BC. By encapsulating a pH-responsive dye in the MSNs, wound dressings for continuous pH sensing with spatiotemporal resolution were developed. The pH responsive BC-based nanocomposites demonstrated excellent wound dressing properties, with respect to conformability, mechanical properties, and water vapor transmission rate. In addition to facilitating rapid colorimetric assessment of wound pH, this strategy for generating functional BC-MSN nanocomposites can be further be adapted for encapsulation and release of bioactive compounds for treatment of hard-to-heal wounds, enabling development of novel wound care materials.

Keywords: Bacterial nanocellulose; Infection; Mesoporous silica nanoparticles; Wound dressing; pH sensor.

Graphical abstract

Fig. 1

pH-responsive nanocomposite wound dressings were obtained by impregnating bacterial nanocellulose with mesoporous silica nanoparticles loaded with a pH-responsive dye.

Fig. 2

a) SEM micrograph of BC, scale bar: 2 ​μm ​b) ​TEM micrograph of MSN (SBA-15), scale bar: 50 ​nm. c) Schematic representation of MSN self-assembly process in BC. d) UV–vis spectra of BC and BC-MSN (5 ​mg/mL and 5 days incubation time), n ​> ​3. Shaded areas show standard deviations. e) Photographs of circular (ø 20 ​mm) BC (i) and BC-MSN (ii) dressings, scale bar: 1 ​cm. f) SEM micrograph of BC-MSN (5 ​mg/mL and 5 days incubation time), scale bar: 1 ​μm. g) Dry weight % of MSN in the BC dressings after incubation for 1 day at different MSN concentrations. h) Dry weight % of MSN in the BC dressings after incubation with BC for different times. i) Nitrogen physisorption isotherms of MSN, BC-MSN (5 ​mg/mL and 5 days incubation time) and BC.

Fig. 3

BTB-loading and pH-response of the nanocomposite wound dressings. a) Photograph of MSNs loaded with BTB and functionalized with PEI. b) pH@BC synthesis by i) BC-MSN incubated in BTB with subsequent functionalization of PEI, and ii) BTB and PEI pre-functionalized MSN loaded onto BC, n ​= ​6, shaded areas show standard deviation. c) Effect of varying BTB concentration on sensor color intensity. d) Photographs of pH@BC at different pH values ranging from pH 5.5 to 8.5. e) Spatial pH sensing with a pH-responsive dressing subject to: left pH ​< ​6 and right pH ​> ​8, scale bar: 2 ​mm. f) Extinction spectra of pH@BC at different pH measured between 400 and 800 ​nm. g) Ratio between the two BTB peaks (∼430 and ∼613 ​nm) as a function of pH between pH 5.5 and 8.5, n = 3. h) BTB peak ratio for a sensor repeatedly exposed to buffers with pH 4 and 7, n ​= ​2. Error bars show standard deviations. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 4

Physical and mechanical properties of BC-MSN composite wound dressings. a) Conformability of 6 ​mm dressings of (i) BC, (ii) BC-MSN and (iii) pH@BC on untreated skin (pH ​∼ ​5.5) and skin subject to a pH 7.4 buffer (scale bar: 2 ​mm). b) Thickness of BC dressings, BC-MSN and pH@BC, n ​≥ ​6. Error bars show standard deviations. c) Water retention ratio (WRR), n ​≥ ​5. Error bars show standard deviation. d) WVTR of BC, BC-MSN and pH@BC dressings, n ​= ​5. Error bars show standard deviation. Significance was tested using one way ANOVA, p ​< ​0.01. e–h) Rheological compression-relaxation characterization of BC, BC-MSN and pH@BC dressings. e) Axial force as a function of time. f) Young's modulus as a function of dry weight %. g) Stress relaxation after 5 ​min from the onset of stress relaxation step as a function of dry weight %. h) Storage and loss moduli (G′, G″) evaluated under oscillatory shear during relaxation as a function of dry weight %. i) Representative stress and strain curves from tensile testing of BC, BC-MSN, and pH@BC dressings.

Fig. 5

Biocompatibility testing of the pH-responsive wound dressings. a, c) Keratinocyte and b, d) fibroblast normalized cell count and migration rate over 72 ​h when cultured in extracts from pH@BC. Results displayed as mean and standard error of the mean, ∗P ​< ​0.1; P ​< ​0.0001 whereas not indicated (n ​= ​8). Photographs of pH-responsive wound dressings applied on (e) non-infected wound and (g) a wound infected with Staphylococcus aureus, scale bar: 2 ​mm. Photographs were recorded 1 ​min after application of the dressings. f, h) show dressings (e) and (g), respectively, after being recovered from the wound and rinsed in water, scale bar: 2 ​mm.