Introduction

Cell-based in vitro assays play an increasingly important role in basic research and applied pharmacology and toxicology. These methods generate valuable data and help researchers better understand human physiology and pathophysiology.

To improve the predictive value of in vitro assays, researchers are moving from traditional two-dimensional cell culture models to more advanced three-dimensional systems. These include spheroids, organoids, and microfluidic platforms such as organ-on-a-chip systems. Both trends require robust and reproducible surface coatings to generate reliable data.

Challenges in 3D Cell Culture

Low-attachment U-bottom plates are widely used for spheroid generation. Most major laboratory suppliers offer such plates in different formats. However, many first-generation low-binding plates show clear limitations.

Researchers may observe multiple spheroids, irregular aggregates, or poor spheroid uniformity. These issues can reduce the reproducibility and reliability of assay results. In addition, many available plates are limited to standard microtiter formats and dishes. This restricts their use in more complex experimental setups.

Self-made coating systems, such as agarose-based approaches, offer more flexibility. However, they often increase variability and make handling more difficult. More standardized 3D cell culture workflows could therefore reduce data variability and improve the biological relevance of in vitro assays.

BIOFLOAT™ FLEX Coating Solution

To address these limitations, we developed the BIOFLOAT™ FLEX coating solution. This polymeric coating creates a highly protein- and cell-repellent surface on different laboratory consumables.

The coating generates a biologically inert surface on plastic and glass materials. Due to its strong anti-adhesive properties, the surface promotes cell-to-cell interactions rather than cell-to-surface attachment. As a result, cells form highly uniform spheroids that float freely in the medium.

BIOFLOAT™ FLEX can be used to treat different plate formats and microfluidic devices. This makes it suitable for 3D spheroid screening, organoid models, cancer research, and toxicology applications.

Surface Passivation on Plastic and Glass

The aim was to develop a polymer solution with three key properties. First, the coating should bind rapidly and strongly to the surface without complex pretreatment. Second, it should provide stronger protein- and cell-repellent properties than previously available systems. Third, it should remain stable under cell culture conditions.

QCM Analysis of Coating Performance

We characterized the physical properties of the coated surfaces using Quartz Crystal Microbalance analysis. QCM detects mass changes on a sensor surface and allows precise monitoring of protein adsorption and coating formation.

Protein adsorption occurs on many commonly used laboratory materials, including plastic and glass. In contrast, BIOFLOAT™ FLEX strongly reduces protein binding after surface coating.

During the QCM experiment, BIOFLOAT™ FLEX rapidly adsorbed to polystyrene within seconds after the solution passed through the flow cell. The adsorbed polymer layer reached approximately 600 ng/cm². This value corresponds to a monolayer of polymer molecules.

Because the coating forms only a very thin layer, it does not affect the geometry of the device. This is especially important for microfluidic systems, where channel diameter and flow rate must remain unchanged.

Protein-Repellent Properties

We analyzed the protein-repellent performance of BIOFLOAT™ FLEX on several commonly used substrate materials. These included polystyrene, quartz glass, polycarbonate, and polyethylene.

For this experiment, we introduced a casein solution into the QCM flow cell as a model protein. This allowed us to monitor protein loading on the different surfaces.

The control experiments showed strong casein adsorption on all uncoated materials. In contrast, BIOFLOAT™ FLEX prevented protein adsorption almost completely after surface passivation. The QCM study confirmed this result through minimal mass loading on the coated surfaces.