Swelling Meets Wicking: Harnessing Complementary Absorption for Synergistic Fluid Management under Clinically Relevant Conditions
Published: 27.08.2026
Why Maximum Absorption Alone Does Not Define Performance
In wound care applications, effective fluid management is not determined solely by how much liquid a material can absorb under ideal laboratory conditions. What matters most is how the material performs under clinically relevant conditions, where exudate must be transported by capillary forces, often against compression.
Despite the high demands encountered in clinical practice, a common approach for characterizing absorbent materials is the determination of the liquid binding capacity (LBC). Methods such as settling volume determination according to the European Pharmacopoeia measure the maximum liquid uptake at complete saturation. The method determines the sediment volume of a fully dispersed material after a defined settling time.
In this study, the LBC was determined using a modified approach in which the material was fully dispersed and subsequently centrifuged, preventing incomplete sedimentation during the measurement period. Absorptive behavior was evaluated using Solution A according to EN 13726:2023 Appendix L, simulating the ionic composition of wound exudate. To better compare materials and physical mixtures under clinically relevant conditions, the LBC was complemented by a measurement of liquid uptake under compression at 40 mmHg according to EN 13726:2023. This additional test mimics the pressure conditions encountered in wound care and provides a more representative assessment of practical absorption performance.
The following section introduces the investigated absorber materials evaluated using these complementary measurement methods.
The Importance of Fiber Morphology in Liquid Transport
Long hydrophilic fibers appear to provide superior liquid transport. In contrast, swelling and gel-forming polymers such as Sodium Starch Glycolate (SSG) often show higher overall liquid uptake capacities, but gel blocking may limit their performance under clinically relevant conditions.
Therefore, a more efficient wicking component appears to be necessary. In this study, the strongly swelling SSG Type C was either combined with croscarmellose sodium (CCS), a cross-linked carboxymethyl cellulose, or powdered cellulose (PC). While the fibrous CCS provides not only wicking but also some swelling capacity, powdered cellulose is primarily characterized by its strong wicking properties. In contrast to CCS, PC does not form a gel.
The morphology of the absorber materials under consideration can be seen in the electron microscope images in Fig. 1.
Fig. 1 Scanning electron microscopy images
A Comparison: Different Perspectives on Liquid Absorption
Fig. 2 Liquid binding capacity and liquid uptake under compression (40 mmHg) after 1 h measured for different materials and physical blends with Solution A (n = 3)
The liquid-binding capacity decreased linearly as the proportion of SSG was reduced. This trend was observed for both investigated material combinations, although the decrease is considerably more pronounced for CCS-based mixtures than for those containing PC.
At the same time, the standard deviation increased with higher PC content, indicating limitations and inaccuracies in the measurement method. In contrast to PC, both SSG and CCS formed a stable gel sediment, enabling more reliable measurements. The absence of such a stable structure in PC likely contributed to the higher variability observed in the results.
Despite these methodological limitations, the findings suggest that SSG possesses a very high liquid-binding capacity. The addition of fibrous, less-swelling materials generally reduces this capacity, with a stronger reduction observed for CCS-containing systems than for PC-based combinations. This behavior may seem contradictory, given that CCS has a higher swelling capacity than PC. However, this can be explained by the low density and fibrous structure of PC. Because of these properties, PC occupies a larger volume and can absorb greater amounts of liquid within its pore structure, without notable swelling.
Under idealized conditions, the addition of wicking agents may appear disadvantageous.
However, liquid uptake measurements performed under compression reveal a more differentiated picture. Hydrophilic fibers can reduce the gel-blocking effect, in which swollen particles hinder further liquid transport. This phenomenon becomes particularly relevant under mechanical load, where not only the maximum liquid retention but also the dynamic absorption behavior is critical.
While SSG exhibits excellent liquid retention properties, fibrous additives improve liquid transport pathways and help maintain absorption performance under pressure. It could be observed that when the proportion of wicking agent is too low, liquid transport is impeded, preventing the swelling potential of SSG from being fully utilized. After reaching an optimal mixing ratio, a subsequent decrease in liquid uptake could be observed with further increase of the wicking percentage, which is attributed to material saturation. Particularly noteworthy is that combinations containing CCS achieved higher liquid uptake under compression than systems containing PC.
This finding contradicts the results obtained from the idealized liquid binding capacity measurements. The difference can be explained by the fact that, unlike PC, CCS is capable of binding and retaining liquid under mechanical load, whereas PC behaves more like a sponge.
Furthermore, the optimal mixing ratio at which the material combinations outperform the individual components differed between the investigated systems, reflecting the distinct absorption mechanisms of the respective materials. The dynamic absorption measurements of capillary-driven liquid uptake presented in the recent poster supports this observation by showing that PC blends absorb liquid faster than CCS blends of the same ratio, yet exhibiting lower total capacity.1 The liquid uptake under compression measured after one hour provides a representative snapshot, demonstrating that tailored material combinations can generate synergistic effects and surpass the performance of the individual components alone.
Conclusion
This study demonstrates the versatility of plant-based absorber materials in meeting diverse requirements within the growing wound care market.2 The liquid uptake behavior of SSG-based systems strongly depends on the type and proportion of the applied wicking agent. While fibrous additives reduce the liquid binding capacity under idealized conditions, they improve liquid transport and reduce gel blocking under compression. PC mainly promotes rapid capillary uptake through its porous fibrous structure, whereas CCS additionally contributes to liquid retention under load, resulting in superior absolute liquid uptake under compression.
The results demonstrate that optimized mixing ratios can generate synergistic effects and outperform the individual components. These findings are particularly relevant for absorbent applications requiring fast and reliable liquid uptake under mechanical stress.
Literature
[1] Poster: Optimizing Liquid Absorption Through Tailored Material Combinations. JRS Pharma GmbH & Co. KG
[2] Blog: Exploring Plant-Based Biomaterials in Wound Care: A Sustainable Solution. JRS Pharma GmbH & Co. KG
