37th International Conference on Science and Technology of Complex Fluids

The Invited Speakers

Norma Alcantar

Nature‑Evolved Complex Fluids: Cactus Mucilage as a Sustainable Platform Material

Materials evolved for survival in extreme environments offer a largely untapped design space for complex fluids and soft matter engineering. One such material is the mucilage produced by the prickly pear cactus (Opuntia ficus‑indica), a polysaccharide‑rich hydrogel that enables water retention and resilience in arid climates.

This talk explores cactus mucilage as a naturally occurring complex fluid whose structure–property relationships can be leveraged for engineered water treatment and related applications. We examine how extraction conditions, molecular composition, and solution chemistry govern its colloidal interactions, and functionality as a flocculant and dispersant in aqueous systems.

Through systematic studies spanning natural and industrial water matrices, we evaluate performance using engineering‑relevant metrics such as flocculation kinetics, turbidity removal, and contaminant separation efficiency. Under optimized conditions, cactus‑derived hydrogels demonstrate performance comparable to conventional chemical flocculants across selected regimes, while exhibiting distinct transport and aggregation behaviors characteristic of biodegradable, polymeric complex fluids.

Beyond efficacy, cactus mucilage presents a compelling materials platform from a sustainability and systems perspective. It is non‑toxic, fully biodegradable, biocompatible, and sourced from a drought‑tolerant plant that can be cultivated with minimal inputs—attributes that align performance with environmental responsibility.

Overall, this work illustrates how plant‑derived hydrogels can be rigorously characterized and intentionally engineered, bridging bioinspired soft matter science with practical technologies for water treatment, materials engineering, and emerging biomedical applications.

Ryan McGorty

Dynamics and rheology of active biomaterials and gels quantified with optical microscopy tools

How can we quantify the microscale dynamics and mechanics of soft materials that are quickly restructuring in time, exhibit spatial and temporal heterogeneities, and move in all three dimensions? Here, I will discuss optical microscopy techniques that can capture such complex dynamics observed in active soft materials. I will highlight the image analysis technique of differential dynamic microscopy and recently developed microscopy modalities and their applications to cytoskeleton networks driven by molecular motors, to active fluids of swimming nematodes, and to suspensions and gels of colloidal rod-shaped particles. Through optical tweezers microrheology and bulk rheology used in combination with video microscopy, we connect observed microscale dynamics with a material's mechanical properties. I will present new methods we are developing to extend differential dynamic microscopy to achieve finer temporal resolution and improved detection of 3D motion.

Claribel Acevedo Vélez

Nanoparticle-Stabilized Liquid Crystal Droplets: New Strategies for Optical Detection of Amphiphilic Analytes

Microscale droplets of thermotropic liquid crystals (LC) dispersed in water (i.e., LC-in-water emulsions) provide versatile platforms for the design of droplet-based sensors capable of detecting a wide range of amphiphilic analytes, including surfactants, biosurfactants, and phospholipids, in aqueous environments. However, the broader practical application of LC emulsions has been limited by their poor colloidal stability, as bare (unprotected) LC droplets tend to coalesce over time. In this presentation, we describe our recent efforts to address these limitations through the development of Pickering stabilization strategies using surface-modified nanoparticles adsorbed at LC-water interfaces to prevent droplet coalescence and enhance emulsion stability. Our approach enables the preparation of colloidally stable thermotropic LC emulsions with significantly improved shelf-life, yielding LC droplets that remain stable for periods ranging from at least three months up to one year. Importantly, the nanoparticle-stabilized LC droplets retain their ability to respond to amphiphilic analytes in aqueous solutions by undergoing characteristic LC ordering transitions and “bipolar-to-radial” configurational changes that can be readily observed and quantified in real time using polarized light microscopy. These responses are similar to those observed in bare LC droplets, demonstrating that Pickering stabilization preserves the sensing functionality of the LC emulsions while substantially improving their practical utility. We further demonstrate that the sensitivity and potential selectivity of the stabilized LC droplets can be tuned through the choice of nanoparticle system used to prepare the Pickering LC emulsions. Overall, our results highlight Pickering-stabilized LC emulsions as promising, colloidally stable, and tunable platforms for the development of practical LC droplet-based sensors and biosensors for aqueous analyte detection.

José Campos

Alginate-Chitosan Hybrid Scaffolds for Regenerative Applications: Enhancing Wound Healing Through Nanofunctionalization

Wound healing is a complex and dynamic process involving coordinated inflammatory, proliferative, and remodeling phases, and remains a major clinical challenge. In this context, sustainable biomaterials derived from natural polymers and conductive nanomaterials offer promising strategies to increase properties that favor cell growth, maturation and functionality that enhance tissue regeneration and its therapeutic application.

Here, we report the development of a hybrid alginate–chitosan (Alg–CS) scaffold. This biodegradable and biocompatible system combines the high water-retention and gel-forming capacity of alginate with the antimicrobial and mechanical properties of chitosan, resulting in a highly porous matrix that promotes cell–material interactions. To further enhance its functionality, the scaffold was biofunctionalized with gold nanoparticles (AuNPs) and a combined AuNP–alginate system. A physicochemical characterization of the scaffolds was carried out by means of swelling, degradation and infrared spectroscopy studies. The results show that the scaffolds obtained are highly porous (>90%) and hydrophilic, with swelling percentages around 3000%.

The regenerative potential of these hybrid materials was evaluated using an in vivo wound healing model. Four experimental groups were analyzed: untreated control, Alg–CS scaffold, AuNPs alone, and AuNP–Alg functionalized scaffolds. Results demonstrate that treated groups exhibited improved healing compared to controls. Increased fibroblast density and collagen deposition at day 7 suggest an accelerated transition from the inflammatory to the proliferative phase. Moreover, enhanced TGF-β3 expression and angiogenic activity indicate improved tissue remodeling and vascularization.

In conclusion, these sustainable hybrid alginate–chitosan scaffolds functionalized with gold nanoparticles promote accelerated wound healing and improved tissue regeneration, highlighting their potential for advanced regenerative medicine applications.

Leticia López

Charge Regulation Effects in Ionizable Colloidal Suspensions.

Charge regulation, driven by acid–base equilibria, strongly influences the electrostatic interactions, aggregation, and structural organization of ionizable colloidal and supramolecular systems. In this work, we investigate the effects of pH and salt concentration on charge dissociation and self-assembly using a hybrid Molecular Dynamics–Monte Carlo simulation framework. The model explicitly accounts for protonation and deprotonation of dissociable groups, allowing us to analyze cooperative charge-regulation effects in charged colloids. Our results show that charge regulation modifies the phase behavior of colloidal suspensions, promoting transitions from ordered to disordered structures and affecting network formation. In addition, preliminary studies on coloidal nanoparticles reveal that electrolyte concentration and intermolecular separation strongly influence the spatial distribution of charge and the effective interactions between neighboring particles. These findings provide insight into the role of pH-responsive electrostatic interactions in soft-matter self-assembly and functional materials design.

Ryan Toomey

Cellulose as Controlled Release Membranes: Overcoming Property and Processing Barriers

Most polymeric materials are derived from fossil fuel feedstocks. Pressures from climate change, plastic pollution, recyclability, and end-of-life issues lead to several challenges. Cellulose has emerged as a versatile biopolymer for hydrogels, membranes, fibers, and films. An underlying question, however, is whether cellulose-based materials can compete with conventional synthetic materials, especially in products where its replacement would put the cellulose-based product at a price disadvantage. This talk will focus on using cellulose as a controlled-release membrane for granular materials (such as fertilizer) where release is driven by osmotic pressure. The goal is to provide insights into the potential and the challenges in adapting cellulose to uses beyond what nature ever intended.

Samanvaya Srivastava

Complex Coacervate Microemulsions

This presentation will discuss our progress in creating stable membraneless water-water emulsions comprising complex coacervate microdroplets. Complex coacervation is a liquid-liquid phase separation phenomenon driven by the electrostatic association of oppositely charged multivalent macromolecules in water, resulting in coacervate microdroplets enriched with charged moieties. These aqueous membraneless microdroplets possess numerous attributes desired in colloidal reactors and protocell models. However, the membraneless coacervate-water interface that facilitates many of the bio(techno)logical functions of the coacervate microdroplets also promotes their coalescence, resulting in rapid coarsening and sedimentation. We will discuss our recently discovered strategy to stabilize complex coacervate microdroplets without introducing membranous sheaths around the droplets, using the assembly of anionic comb polyelectrolytes at the water (coacervate)-water interface. We will demonstrate the tunability of microdroplet size, its months-long stability, and its ability to withstand high-ionic-strength environments. Selective sequestration of charged (bio)molecules (proteins and enzymes) into the crowded environments of stabilized coacervate microdroplets is argued to significantly (up to 10-fold) and sustainably accelerate enzyme-mediated bioreactions. Aided by the low cost of the constituent polymers and the simplicity of the formulations, we will argue that stabilized coacervate emulsions serve as efficient enzyme encapsulants in economical, large-scale flow bioreactors.

Vivek Sharma

Surface Forces and Stratification in Micellar Foam Films

Ultrathin films of soft matter containing supramolecular structures such as micelles, nanoparticles, smectic liquid crystals, lipid bilayers, and polyelectrolytes undergo drainage via stratification, manifested as stepwise thinning in interferometry-based measurements of average thickness. We focus primarily on stratification in micellar foam films formed from aqueous solutions of small-molecule surfactants, including sodium dodecyl sulfate (SDS), above the critical micelle concentration (CMC). Foam films typically consist of fluid sandwiched between two surfactant-laden surfaces ~ 5 nm - 10 microns apart. The drainage in films occurs under the influence of viscous, interfacial, and intermolecular forces, including disjoining pressure. In reflected-light microscopy, the stratifying films (thickness < 100 nm) exhibit regions with distinct shades of grey, suggesting that domains and nanostructures with varying thicknesses coexist in the thinning film. Understanding and analyzing such nanoscopic thickness transitions and variations has been a long-standing experimental challenge due to the lack of techniques with the requisite spatio-temporal resolution and theoretical challenge due to the absence of models for describing hydrodynamics and thermodynamics in stratified thin films. We show that nanoscopic thickness variations in stratifying films can be visualized and analyzed with unprecedented spatial (thickness ~ 1 nm, lateral ~500 nm) and temporal ( < 1 ms) resolution using IDIOM (interferometry digital imaging optical microscopy) protocols we developed.

Stratification proceeds by forming thinner domains that grow at the expense of surrounding films. Using exquisite thickness maps generated using IDIOM protocols, we provide the first visualization of nanoridges and mesas that form at the moving front around expanding domains. We contrast the step size measured in stratification studies with the intermicellar distance obtained from scattering measurements. Most significantly, we develop a self-consistent theoretical framework, a nonlinear thin film equation model that explicitly accounts for the influence of non-DLVO supramolecular oscillatory surface forces and the physicochemical properties of surfactants.

Finally, we elucidate how surfactant type and concentration can be manipulated to enable molecular engineering of micellar foams. The ongoing efforts are directed at exploring the influence of surfactants and defoamers/ antifoamers in bioprocessing, proteins and lipids in food engineering, and biologically sourced/derived surfactants on drainage via stratification in foam films, and integrated examination of foamability and foam stability.

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