Shear flow assay platform for quantifying molecular surface interactions in alginate capsules

Overview

This research proposes a scalable shear flow assay that quantifies molecular interactions between encapsulated compounds and polymer surfaces. By encapsulating hydrophobic molecules within eco-friendly alginate capsules and applying controlled pressure-driven flows in millifluidic capillary devices, the platform measures the shear stress required to detach capsules from opposing surfaces. This approach enables the inverse design of polymer surface groups based on quantified adhesion and sorption energies, offering a faster and less labor-intensive alternative to traditional methods such as atomic force microscopy.

The technology addresses a critical need in controlled release, encapsulation, and surface functionalization across industries including agrochemicals, pharmaceuticals, and specialty chemicals. By replacing labor-intensive measurement techniques with a facile flow-based method, the platform accelerates the characterization of how active ingredients interact with surrounding materials.

Technical specifications

Core methodology:

• Compounds are encapsulated within fluorescent alginate capsules via drip centrifugation into a calcium crosslinking bath, producing cargo-laden capsules with diameters ranging from 50 to 500 micrometers
• Capsules are deposited onto polymeric surfaces of interest and given waiting time for encapsulated molecules to diffuse and interact with surface groups
• Capsules are incorporated into glass capillary devices connected to precision millifluidic pumps
• Varying pressure-driven flows generate different shear rates, and the shear stress required to detach capsules from channel walls is measured
• Detachment data is used to compute molecular interaction and sorption forces between the encapsulated compounds and the opposing surface

Key features:

• Preliminary FTIR analysis has confirmed that 1-2 wt% PEG-PDMS copolymers migrate through bulk PDMS elastomers when contacted against glass or aqueous environments over days due to thermodynamic driving forces
• Time-dependent release kinetics of hydrophobic active ingredients from 3D printed organohydrogels have been modeled using transient mass transport equations for compounds such as Coumarin 6 (MW 350 Da, D = 2.6 ug²/h) and methylene blue (MW 320 Da, D = 0.01 ug²/h)
• Prior experience with photolithography for patterned PDMS and centrifugal synthesis of alginate capsules supports rapid prototyping

Technology readiness level

The technology is currently at an early-to-mid stage of development. Preliminary validation has been completed, including FTIR confirmation of copolymer migration through PDMS elastomers and modeling of release kinetics from organohydrogel formulations. The research team has established core competencies in capsule synthesis via centrifugal drip methods and photolithographic fabrication of patterned polymer surfaces.

Future validation will focus on encapsulating the compounds etoxazole and pyriproxyfen within fluorescent alginate capsules, depositing them onto various polymeric surfaces, and measuring shear-induced detachment forces in glass capillary millifluidic devices. This next phase will demonstrate the assay's ability to quantify molecular interaction energies across different polymer surface chemistries, advancing the technology toward broader applicability in surface characterization and controlled release system design.