Aldehyde-functionalized Cellulose as Reactive Sorbents for the Capture and Retention of Polyamine Odor Molecules Associated with Chronic Wounds

Abstract

Aldehyde-functionalized cellulose (AFC) was prepared by oxidizing cellulose with sodium metaperiodate. The reaction was characterized by Schiff’s test, FT-IR, and UV-vis study. AFC was evaluated as a reactive sorbent for controlling polyamine-based odor from chronic wounds, and its performance was compared with charcoal, one of the most widely utilized odor-control sorbents through physisorption. Cadaverine was used as the model odor molecule. A liquid chromatography/mass spectrometry (LC/MS) method was established to quantify the compound. AFC was found to rapidly react with cadaverine through the Schiff-base reaction, which was confirmed by FT-IR, visual observation, CHN elemental analysis, and the ninhydrin test. The sorption and desorption behaviors of cadaverine onto AFC were quantified. With clinic-relevant cadaverine concentrations, AFC demonstrated much better sorption performance than charcoal. At even higher cadaverine concentrations charcoal showed higher sorption capacity, probably due to its high surface area. On the other hand, in desorption studies, AFC retained much more of the sorbed cadaverine than charcoal. When AFC and charcoal were combined, the pair demonstrated excellent sorption and desorption behaviors. The XTT (2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide) assay confirmed that AFC has very good in vitro biocompatibility. These results suggest that AFC-based reactive sorption can be a new strategy to control odors associated with chronic wounds for improved healthcare.

Graphical Abstract

1. Introduction

Malignant fungating wounds (MFWs) are caused by cutaneous infiltration of carcinogenic cells, occurring in 5% to 14% of end-of-life cancer patients (Gethin, McIntosh, & Probst, 2016). These chronic wounds hardly heal, and sadly, a person living with MFWs only has a life expectancy of six to twelve months. The goals of care need to be shifted from healing to a palliative approach for symptom management to improve quality of life, a field that has been neglected for a long time. Odor is the most distressing and debilitating symptom associated with MFWs as it can cause vomiting, loss of appetite, and psychological distress (Akhmetova et al., 2016; Fleck, 2006; Lazelle-Ali, 2007; Raffetto, Ligi, Maniscalco, Khalil, & Mannello, 2021; Yazdanpanah, Nasiri, & Adarvishi, 2015). As an integral part of palliative care, odors from chronic wounds like MFWs must be controlled to improve the quality of life of patients and their caregivers.

Odor is caused by aerobic and anaerobic bacteria and contains a cocktail of volatile compounds, including acids (e.g., n-butyric, n-valeric, and n-caproic), polyamines (e.g., putrescine and cadaverine), and sulfur compounds (e.g., dimethyl trisulfide) (Akhmetova et al., 2016; Bowler, Davies, & Jones, 1999; Fleck, 2006). The current methods to manage odor are to reduce the bioburdens that cause odor, mask the odor, and/or sorb the odor. Although numerous dressing materials have been developed for topical applications to control odor, the efficacy of these materials remains low (Akhmetova et al., 2016; Gethin, Grocott, Probst, & Clarke, 2014; Gethin, McIntosh, & Probst, 2016). For example, charcoal-containing sorbents are regarded as the most effective dressings and are the most often used, yet only less than 50% of an international survey precipitants reported that they are effective (Gethin et al., 2014). Silver-containing dressings, as the second-most effective material, had only 23% of the participants confirmed their efficacy (Gethin et al., 2014).

The low sorption efficacy of charcoal is related to the sorption mechanism. Charcoal sorbs odor molecules via physisorption into its heterogeneous pores. The sorption interactions are predominantly van der Waals forces, which are rather weak. A ‘sorption-desorption’ equilibrium quickly establishes for the sorbed molecules (Zhang, Gao, Creamer, Cao, & Li, 2017). Thus, charcoal can serve as a “rechargeable battery” of the odor molecules, allowing a small amount of the sorbed agents to be released continuously into the surrounding environment, causing lingering odor. It is believed that if the sorbents can have stronger forces to not only sorb but also retain odor molecules, the odor-control performance will be significantly improved. Unfortunately, to date, this has not been achieved in general practice.

We hypothesize that if wound-dressing sorbents can sorb and covalently immobilize odor molecules generated by chronic wounds, odor-control performance in patient care will be significantly improved. To test this hypothesis, aldehyde-functionalized cellulose (AFC) was synthesized as a reactive sorbent. Cadaverine was used as a representative polyamine-based odor molecule in chronic wounds, which is generated from the putrefaction of tissue by bacteria (Akhmetova et al., 2016; Bowler et al., 1999; Fleck, 2006). Cellulose is widely used as wound-dressing materials, and AFC has been extensively utilized in the fabrication of various functional materials for biomedical, environmental, and industrial applications (Errezma, Mabrouk, Magnin, Dufresne, & Boufi, 2018; Hashem, Hasanin, Kamel, & Dacrory, 2022; Plappert et al., 2018; Tang, Sisler, Grishkewich, & Tam, 2017). However, the use of AFC as odor-controlling materials for chronic wounds has never been reported. We find that AFC rapidly reacts with cadaverine to covalently immobilize the volatile compounds onto the sorbents. The cadaverine-AFC conjugates are stable, with much less cadaverine released into the surrounding environment than charcoal. Thus, AFC acts as a novel reactive sorbent that catches and retains odor molecules generated from chronic wounds. Further, AFC showed very good in vitro biocompatibility, making it even more attractive for wound odor management.

2. Experimental

2.1. Materials

Cadaverine was purchased from Tokyo Chemical Industry (TCI, Portland, OR). Optima^® LC/MS grade acetonitrile (ACN), acetic acid, XTT (2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide), ninhydrin, and ammonium acetate (NH₄OAc) were obtained from Fisher Scientific (Waltham, MA). Sodium metaperiodate (NaIO₄) was provided by VWR (Radnor, PA). The Schiff′s reagent for aldehydes was purchased from Sigma Aldrich (Milwaukee, WI). Bleached cotton fabrics (style 400) were from Testfabrics, Inc (West Pittston, PA). Medical-grade charcoal knitted fabrics (surface area 1000-2000 m²/g) were obtained from Charcoalhouse^™ (Crawford, NE). L929 mouse fibroblasts (ATCC CCL-1) were purchased from the American Type Culture Collection (ATCC, Manassas, VA).

2.2. Preparation and characterization of AFC

AFC was prepared through periodate oxidation of cotton cellulose. Briefly, cotton fabrics (5cm x 5cm; bath ratio: 1/50) were immersed into an aqueous solution of NaIO₄ in the dark. The molar ratio of NaIO₄ to the anhydroglucose units (AGU) of the cellulose was kept at 0.3:1. The mixture was shaken at 48 °C for 3 hours. Periodate concentration of the solution was determined before and immediately after oxidation with an Evolution 60S UV/vis spectrometer (Thermo Fisher Scientific, USA) at 290 nm to calculate the aldehyde contents on the fabrics (see Figure S1 in Supporting Information), following published protocols (Kim & Kuga, 2001; Plappert et al., 2018). Afterward, the fabrics were thoroughly washed with deionized water. KI/starch test strips were used to ensure that the washing water contained no residual for the complete removal of the oxidants (Simon et al., 2023). The resulting fabrics were air-dried. Fourier transform infrared (FT-IR) study of the fabric samples was carried out on a Thermo Nicolet iS10 FT-IR spectrometer. Schiff′s test was performed to confirm the presence of aldehyde groups on the oxidized fabrics (Robins, Abrams, & Pincock, 1980). Scanning electron microscope (SEM) study of the fabric samples was performed on a JEOL JSM 7401 FE-SEM.

2.3. Sorption and desorption of cadaverine

Cadaverine was used as the representative polyamine odor molecule, and its concentration was varied between 0.46 mM and 4.7 mM to simulate different chronic wound situations. In the sorption tests, an AFC fabric swatch, a charcoal fabric swatch, or an AFC + charcoal pair containing an AFC swatch and a charcoal swatch was immersed individually into 100 mL of a cadaverine aqueous solution. The swatch size was 5cm x 5cm. The sorption test was performed at room temperature with gentle shaking for 0-24 hours. The cadaverine concentration at different time points was measured by liquid chromatography/mass spectrometry (LC/MS) as described below. All experiments were performed in triplicate.

After the sorption tests, the resulting fabric swatches were taken out and washed with deionized water three times (3 x 100 mL) to remove the loosely sorbed cadaverine. Some of the swatches were used in the ninhydrin test to detect the presence of primary amines (Friedman, 2004; Soto-Cantu, Cueto, Koch, & Russo, 2012). Briefly, a 2% (w/v) ninhydrin ethanol solution was prepared, and 1.0 mL of the ninhydrin solution was added to 10 mL of deionized water containing the fabric swatch immediately after cadaverine sorption. The vial was kept in a water bath at 65 °C for 30 min. The swatch sample was washed thoroughly with deionized water, and its image was taken with a digital camera.

The rest of the swatches were immersed individually into 40 mL of deionized water for the desorption test, which was performed at room temperature with gentle shaking for 8 hours. The cadaverine concentration in the desorption solution was quantified with LC/MS. Elemental analysis of selected fabric samples was performed by Galbraith Laboratories (Knoxville, TN) on a PerkinElmer 2400 Series II CHNS/O Analyzer to determine the carbon, hydrogen, and nitrogen contents.

2.4. LC/MS quantification of cadaverine

In the sorption and desorption experiments, 0.5 mL of the test solution was aliquoted at each predetermined time point for LC/MS quantification (Gianotti et al., 2008; Zhang et al., 2021). The aliquot was further diluted 10-50 folds with ACN before injection. The LC/MS measurement employed a Waters ACQUITY ultra-performance liquid chromatography H-Class system interfaced with a Sciex TripleTOF^® 6600 mass spectrometer system. The diluted sample solutions were loaded and separated on a Waters Acquity UPLC^® BEH HILIC column (1.7 μm, 2.1 × 150 mm) coupled with a Waters VanGuard^™ BEH HILIC pre-column (1.7 μm, 2.1 × 5 mm) heated at 40°C with a column oven. The mobile phases were 20 mM NH₄OAc aqueous solution (pH 4.5, A) and ACN (B). The samples were eluted at a flow rate of 0.3 mL/min within a total of 8-min gradient. The LC gradient started with 60 % of B and held for 3 min. The fraction of B was decreased to 20% at 4 min and held for 1 min. At 5.1 min, the fraction of B was brought back to 60% and maintained for the remaining gradient.

An electrospray ionization source (ESI) was used to couple the LC with the MS. The LC elute was monitored in positive mode with a spray voltage of 5000 V. The source gas settings for the nebulizer (GS1), drying (GS2), and curtain were: 20 psi, 15 psi, and 25 psi, respectively. The declustering potential (DP) was 80 V. Three parallel scans were performed during the LC gradient, including 1 TOF-MS scan and 2 high-resolution product ion scans. All scan ranges were between 50 Da and 500 Da. The accumulated time for the TOF-MS scan was 0.25 s and that of the product ion scan was 0.1 s. The two product ion scans targeted the molecular ions at m/z 103 and m/z 86, with the corresponding collision energy settings of 10 V and 30 V, respectively.

2.5. In vitro biocompatibility

L929 mouse fibroblast (ATCC CCL-1) was used to test the in vitro cytotoxicity of the sorbents in the direct contact mode following the ISO 10993-5 standard (Wen, Khan, Sartorelli, Goodyear, & Sun, 2022; Wen, Yeh, & Sun, 2018). The fibroblasts were cultured in DMEM (Dulbecco's Modified Eagle Medium) with 10% FBS (Fetal bovine serum) at 37°C in 95% air and 5% CO₂. At confluence, the cells were trypsinized. The cells were centrifuged, collected, and resuspended in the culture medium to a level of 1.0 × 10⁵ cells/mL. One milliliter of the fibroblast suspension was inoculated in a well of a 24-well plate and pre-cultured for 24 h for subconfluency. Each sorbent fabric swatch (4mm x 5mm) was placed individually into each well to cover one-tenth of the cell layer surface. The plates were further incubated for 24 hours. The swatches were then removed carefully from the cell surface. The culture medium was replaced using 1 mL of fresh culture medium containing 500 μL of XTT reagents in each well. The plates were incubated in the dark for another 4 h at 37°C. Metabolic activities of the fibroblasts in each well were determined on a microplate reader (Infinity M200 Pro, Tecan). The absorbance of the solution was recorded at 475 nm, using 660 nm as the reference. Culture plates with cells only were used to serve as the negative controls. The positive controls were cells incubated in a culture medium containing 1% of triton X-100.

2.6. Statistical analysis

Data presented were representative results from at least three independent tests and were expressed as means ± standard deviations. Statistical analysis was carried out using the Student’s t-test. The confidence level was set at 95%.

3. Results and Discussion

3.1. Preparation and characterization of AFC

Cellulose is a widely used wound-dressing material, but it does not have any odor-control effect. In the present study, NaIO₄ was used to modify cellulose, making the resulting AFC capable of chemically immobilizing cadaverine, a representative polyamine-based odor molecule. It has been well established that periodate oxidation selectively converts the C2 and C3 hydroxyl groups on the AGU of cellulose into aldehyde moieties, accompanied by the cleavage of the corresponding C─C bond (Figure 1D) (Kim & Kuga, 2001; Plappert et al., 2018). This reaction was confirmed by FT-IR studies, as shown in Figure 1. Pure cellulose (Figure 1A) displayed a weak band at 1630 cm⁻¹, which was due to the water of hydration. After oxidization, a new band at 1732 cm⁻¹ appeared in the spectrum of AFC (Figure 1B), which could be attributable to the C═O stretching vibrations of the newly formed aldehyde groups. The presence of aldehyde groups on the AFC fabrics was further confirmed by Schiff’s test (Figure 1E) (Robins et al., 1980). While the original cotton did not show any color change in this test, the AFC fabric swatch developed a magenta color instantly upon the addition of Schiff’s reagent. Further, the surrounding solution remained clear, suggesting that the aldehyde groups were covalently bonded to the AFC fabrics and no release/diffusion occurred. The aldehyde content on the AFC fabrics prepared in our study was calculated to be 3.2 mmol/g based on the UV-Vis results (see Figure S1 in Supporting Information).

Figure 1.

FT-IR spectra of (A) pure cotton cellulose, (B) AFC, (C) after AFC reacts with cadaverine; (D) reaction pathways in the synthesis of AFC from cotton cellulose through periodate oxidation and reactive sorption of cadaverine on AFC; and (E) images of AFC and cotton fabrics in Schiff’s test

3.2. Quantification of cadaverine with LC/MS

Cadaverine concentration was quantified with LC/MS (Gianotti et al., 2008; Zhang et al., 2021). Under our experimental conditions, cadaverine was eluted at 2.8 min, as shown in Figure 2A. At this time point, two major peaks were observed in the TOF-MS spectrum. One was the molecular ion ([M+H]⁺) of protonated cadaverine at m/z 103. The other was observed at m/z 86, which was also the base peak of the collected mass spectrum (Figure 2B).

Figure 2.

Representative extract ion chromatogram (XIC) and mass spectrum of cadaverine (0.04 mM)

The collected LC/MS mass spectrum at 2.8 min was the same as the mass spectrum obtained by directly injecting cadaverine solution with a syringe, in which peaks at m/z 103 and m/z 86 were also observed (spectrum not shown). The peak at m/z 86 could be interpreted as the NH₃ neutral loss peak of the molecular ion ([M+H-NH₃]⁺). This was supported by the MS² experiment of [M+H]⁺ at m/z 103, in which the fragment peak of m/z 86 was observed as the dominant peak with extremely small collision energy. This finding suggested that the [M+H]⁺ peak at m/z 103 was not stable in the gas phase, which inclined to lose a neutral NH₃ group and generated a more stable fragment with m/z 86. In addition, the extracted ion chromatogram (XIC) of both peaks at m/z 103 and m/z 86 eluted at the same time of 2.8 min (Figure 2A), further supporting that these two ions came from the same molecule of cadaverine. Therefore, both m/z 103 and m/z 86 peak areas in XICs were used to quantify the concentration of cadaverine.

A standard curve was built using the pure cadaverine solution. The curve in the range of 0.004 mM to 0.1 mM showed an excellent linear correlation with an R² value equal to 0.99 (see Figure S2 in Supporting Information). Cadaverine solutions collected from different sorption and desorption experiments were then diluted to the linear range and quantified according to the standard curve. The original cadaverine concentrations in the testing solutions at different time points were thus calculated.

3.3. Sorption of cadaverine

Our screening tests found that pure cellulose had negligible sorption of cadaverine (data not shown). The sorbents (AFC, charcoal, and AFC + charcoal pair) performed differently at various cadaverine initial concentrations. Figure 3A showed the sorption curve when the starting cadaverine concentration was 0.46 mM. This concentration was used because previous studies found that the mean levels of cadaverine presented in the wound exudate of breast cancer patients with MFWs are 10⁻⁷ to 10⁻⁶ mol/g, corresponding to the range of 0.1 mM to 1.0 mM (Tamai et al., 2016). All the sorbents showed fast cadaverine sorption (reduction of cadaverine concentration in the solution) within the first hour, and the sorption rate gradually decreased until 4 hours. After that, a further increase in sorption time did not increase the cadaverine sorption level (data not shown), suggesting that the sorption reactions are reversible reactions, and the sorption dynamic equilibrium was reached within 4 hours. AFC (circle in Figure 3A) performed better than charcoal (square in Figure 3A), showing both a faster sorption rate and higher sorption capacity. It is interesting to note that combining AFC and charcoal into a sorbent pair (triangle in Figure 3A) led to even better performance, i.e., sorption rate and sorption capacity both increased.

Figure 3.

Sorption curves of cadaverine with different sorbents when the starting cadaverine concentration was (A) 0.46 mM, (B) 0.76 mM, (C) 1.45 mM, and (D) 4.7 mM. Reduction of cadaverine concentration in the solution suggests sorption of the compound onto the sorbents. Since the clinical cadaverine concentration range is between 0.1 mM and 1.0 mM (Tamai et al., 2016), Figure 3A and 3B represented clinic-relevant situations, and Figures 3C and 3D represented the worst-case scenarios.

A similar trend was observed when the initial cadaverine concentration was increased to 0.76 mM (Figure 3B). These findings suggest that at the clinic-relevant cadaverine content (0.1 mM to 1.0 mM) (Tamai et al., 2016), the AFC-based sorbent approach is more effective than charcoal, which could be related to the sorption mechanisms. While charcoal sorbs cadaverine through physisorption into the heterogeneous pores (Zhang et al., 2017), AFC was believed to react with cadaverine through the Schiff-base reaction to covalently immobilize it onto the fabrics (Figure 1D) (Goszczyńska, Kwiecień, & Fijałkowski, 2015).

One piece of evidence of this hypothesis is from FT-IR studies. As shown in Figure 1, after the sorption of cadaverine (Figure 1C), the intensity of the C═O stretching vibration band of the aldehyde groups at 1732 cm⁻¹ significantly decreased, accompanied by the appearance of a shoulder band at 1674 cm⁻¹, which could be attributed to the C═N stretching of the imine groups formed by the reaction of aldehydes on AFC with the amine groups of cadaverine (Figure 1D) (Horton, Herne, & Myles, 1997). After the first amine group reacted with AFC to form imines, the second amine group on cadaverine could either react with another aldehyde group to form imines or be left unreacted (Figure 1D). Thus, the fabric could contain both imine and amine groups. To test this, the ninhydrin reaction, a colorimetric method to detect primary amines (Friedman, 2004; Soto-Cantu et al., 2012) was performed. As shown in Figure 4, the AFC fabric swatch was white (Figure 4A). After the reaction with cadaverine, the swatch became yellow due to the presence of imine groups (Figure 4B). After reacting with the ninhydrin agent, the swatch showed a dark yellow/brown color (Figure 4C). The Schiff-base adduct formed between amino groups and ninhydrin should have a purple color (Friedman, 2004; Soto-Cantu et al., 2012), and this could add to the yellow color of the fabric, leading to the formation of a brown color.

Figure 4.

AFC swatches (A) before the sorption of cadaverine, (B) after the sorption of cadaverine, and (C) after the ninhydrin test on (B)

CHN elemental analysis was used to further confirm the covalent attachment of cadaverine onto AFC fabrics. As shown in Table 1, the original cotton and AFC fabrics showed similar C and H contents, with a nitrogen content of less than 0.5% (lower than the detection limit). For the AFC fabric, however, after sorbing in 0.46 mM of cadaverine for 4 h, thoroughly washed, and immersed in distilled water for 8 h to remove un-bonded cadaverine, the fabric contained 1.11% of nitrogen, which is close to the theoretical nitrogen content obtained from the sorption/immersing curves (1.01%).

Table 1.

CHN elemental analysis of cotton, AFC, and AFC-Cadaverine fabrics after sorption/immersion

	Carbon	Hydrogen	Nitrogen
Cotton	42.71	6.48	< 0.5
AFC	42.36	6.46	< 0.5
AFC-Cadaverine	43.90	6.68	1.11

In SEM studies, no structural/morphological differences were observed in cotton, AFC, and AFC-Cadaverine (see Figure S3 in Supporting Information), most likely because of a mild oxidation condition used to prepare the AFC fabrics in the current study.

When the initial cadaverine concentration was increased to 1.45 mM (around 1.5 to 15 times higher than the clinical concentration) (Tamai et al., 2016), however, the trend of charcoal and AFC reversed, in which the charcoal swatch (square) provided higher sorption rate and sorption capacity (Figure 3C). These results could also be explained by their sorption mechanisms. AFC (circle) immobilizes cadaverine through the Schiff-base reaction to covalently bind the amine onto the fiber surface (Figure 1D). This would create a positively charged fiber surface because of the protonation of the imine and amino groups, which could repel other “free”, unbonded cadaverine molecules in the sorption solution and limit the cadaverine access to the aldehyde groups on AFC, particularly at high cadaverine concentration in the sorption solution. On the other hand, charcoal has a large surface area (1000 -2000 m²/g) to sorb cadaverine molecules. When the surface pores are occupied, cadaverine can further diffuse into the inner pores driven by concentration gradients, resulting in higher capacity at this cadaverine concentration. On the other hand, the AFC and charcoal pair (triangle) still outperformed either sorbent alone.

A similar trend was observed at an even higher cadaverine initial concentration of 4.7 mM (around 4.7 times to 47 times higher than the clinical concentration) (Tamai et al., 2016), as shown in Figure 3D. The AFC + charcoal pair showed better performance than using either AFC or charcoal alone, confirming that a combination can be an effective strategy to control odor in a wide range of cadaverine concentrations.

3.4. Desorption of cadaverine

Figure 5 displayed the desorption results to determine how well each sorbent can retain the sorbed cadaverine. After cadaverine sorption (4.7 mM for 4 h), the sorbents were washed and placed individually in 40 mL of distilled water at room temperature for 8 h to desorb cadaverine. As the sorption reactions were reversible, certain amounts of cadaverine were desorbed into the solution, but different sorbents behaved very differently.

Figure 5.

Desorption curves of cadaverine from different sorbents. The sorbents were first immersed in 100 mL of 4.7 mM cadaverine for 4 hours, gently washed, and then placed in 40 mL of distilled water at room temperature for up to 8 hours.

Charcoal (solid square) showed the lowest retention capability and desorbed the highest amount of the sorbed cadaverine (around 2.0 mM). These results partially explained why in the real application, charcoal-based sorbents are associated with lingering odor (Zhang et al., 2017).

As expected, thanks to the covalent immobilization mechanism (imine formation, see Figure 1D), the AFC (solid circle) desorbed ten times less cadaverine into the solution than the charcoal, suggesting that the reversible Schiff-base reaction favors the formation of imines. As a result, the reactive sorbents had a much stronger capability to retain the cadaverine on the sorbents than the physisorption-based sorbents. In comparison, the AFC-charcoal pair (solid triangle) desorbed less cadaverine than charcoal, even though it contained more cadaverine (see Figure 3D). Based on the desorption behavior of the individual charcoal and AFC, it was likely that the desorption from the pair was mainly caused by the charcoal.

To test this hypothesis, after sorption of cadaverine (4.7 mM for 4 h) the sorbent pair was separated into charcoal only and AFC only and then tested for desorption individually. While the charcoal from the pair (open square) showed a slightly higher desorption level than the pair (solid triangle), the AFC from the pair (open circle) desorbed much less, confirming that the desorption of the pair was mainly due to the release of cadaverine from charcoal. Moreover, at each time point, the sum of the desorption amount from AFC alone and charcoal alone (when the desorption happened individually) was always higher than that from the pair (when the desorption occurred with the presence of both charcoal and AFC). This finding suggests that when charcoal and AFC are combined, part of the cadaverine desorbed from charcoal could be resorbed by AFC. Thus, the AFC could “catch” the released odor molecules from the sorbent pairs, making it even more attractive for various applications, particularly when combined with other classes of dressing materials such as charcoal.

3.5. Biocompatibility

A colorimetric XTT assay was used to evaluate the biocompatibility of the sorbents following ISO 10993-5:2009 in the direct contact mode. Figure 6 showed the metabolic activities of the mouse fibroblasts after 24 h of direct contact with the sorbents. The viabilities of the mouse fibroblasts were not significantly affected by either of the materials, pointing to excellent biocompatibility. The results for cotton and charcoal were not surprising as both have been widely used as wound-dressing materials (Errezma et al., 2018; Gethin et al., 2014; Plappert et al., 2018; Tang et al., 2017; Zhang et al., 2017). There are reports that aldehydes are cytotoxic to humans, which can form covalent adducts with cellular biomacromolecules such as DNA and proteins (Ahmed Laskar & Younus, 2019; LoPachin & Gavin, 2014; Rwere, Yu, Chen, & Gross, 2022; Sinharoy, McAllister, Vasu, & Gross, 2019). Nonetheless, these results were obtained from small molecules that were freely mobile. In our design, the aldehyde moieties were covalently bonded to the AFC fabrics and no release/diffusion occurred (Figure 1E), which could limit their access to cellular biomacromolecules, resulting in good biocompatibility.

Figure 6.

Effect of various sorbent materials on the viabilities of L929 mouse fibroblasts after direct contact for 24 hours. Data were normalized to mouse fibroblasts in culture medium only without sorbent materials (blank control=100% cell viability)

4. Conclusion

AFC was synthesized through periodate oxidation of cellulose and used to covalently immobilize cadaverine, a representative polyamine-based odor molecule associated with chronic wounds.

The Schiff-base reaction between AFC and cadaverine was confirmed by FT-IR, visual observation, CHN analysis, and the ninhydrin test. The cadaverine sorption efficiency was quantified by LC/MS. AFC rapidly reacted with cadaverine and showed much better retention of the odor molecule than charcoal, a widely used odor-control sorbent. Combining AFC and charcoal significantly improved the performance in both sorption and retention. These results confirm our hypothesis about the new reactive sorbent approach in controlling odors associated with chronic wounds to enhance the quality of palliative care.

This novel reactive sorbent strategy will be the first odor management approach in which the sorbents, in addition to their capacity for physical sorption, chemically react with odor compounds to immobilize them. This concept has never been reported before in the palliative care of end-of-life cancer patients and opens great opportunities to improve the management of chronic wound malodor. AFC is prepared from sustainable cellulose. The novel use of Schiff-base reaction for odor control occurs at room temperature under very mild conditions. No special equipment or devices are needed, and no organic solvents are involved for palliative care. Further, the new technology aims at managing the odor that is associated with chronic wounds, not treating, or healing the wounds, to improve the quality of life of patients with advanced cancer. This design is intended to be practical for the palliative care of end-of-life cancer patients and is not hindered by regulatory barriers. That is, this strategy is not a ‘treatment device’ that requires FDA (or other government agencies) clearance or approval and thus can have a rapid and real impact on patient care, using well-known cellulose-based materials and well-established mild immobilization reactions.