The W8 Physical Cytometer is based on a ground-breaking flow-technology that measures the physical properties of spherical biological samples through a combination gravimetric and dimensional analysis. This novel approach provides an analysis of 3D cells, particularly spheroids and organoids, to measure mass density, weight, radius and their derivatives. This cytometer allows the operator to perform physical-based sorting of a target population under sterile conditions.

The analysis is performed inside the specifically designed PMMA W8 chip, where samples are analysed using a bright-field imaging setup in combination with a tracking algorithm.

The instrument tracks the sample during its free-fall movement along the vertical analysis channel of the central chip, with the W8 analysis solution at rest. Using Stokes’ law, the system measures the terminal velocity of the sample during its free fall to extract the mass density value. The free-fall movement of the sample can be repeated in order to increase the data precision.

The W8 software (Libra) calculates the radius of the spherical sample by approximating the circle that best describes its sphericity. The software then estimates the volume of the sample and relates the weight to the density value determined.

The W8 Physical Cytometer is designed to measure the density, size and weight of 3D cell models, such as small groups of cells, cancer spheroids and organoids.

The resulting physical characterisation provides a new, rapid method for:

• the control of the uniformity and homogeneity of the 3D cell culture;
• the monitoring of growth kinetics for process optimisation in cell cultures;
• quantifying the in vitro effectiveness of cell- and drug-based therapies through physical characterisation of preclinical 3D cell models;
• the selection and separation of samples within a specific diameter or density range and the differentiation and recovery of specific sample subpopulations.