FBRM for Real-Time Particle Characterization in Bioprocessing

Monitoring particle size and distribution in bioprocessing is essential for optimizing yield, ensuring consistency, and maintaining efficiency. Traditional offline sampling methods can be time-consuming and may not accurately capture dynamic changes.

Focused Beam Reflectance Measurement (FBRM) addresses these limitations by providing real-time, in-situ particle characterization without disrupting the process. This enables immediate adjustments and better control over critical parameters.

Basic Mechanism Of Particle Detection

FBRM operates on the principle of laser backscattering to quantify particle size and distribution. A focused laser beam is directed into the process medium, where it interacts with suspended particles. As the laser scans across the particles, it reflects off their surfaces, generating backscattered light signals. The duration and intensity of these reflections correlate with the chord length of individual particles, serving as a proxy for size. Unlike imaging techniques that rely on two-dimensional projections, FBRM continuously measures particle size distribution without requiring sample extraction or dilution.

The system’s rapidly rotating laser beam enables thousands of measurements per second, capturing even transient changes in particle populations. The resulting chord length distribution (CLD) represents the statistical distribution of particle sizes within the sample. Since FBRM does not assume a specific particle shape, it is particularly useful for monitoring irregularly shaped or aggregated particles common in bioprocessing.

Signal processing algorithms refine the raw data by filtering noise and distinguishing between individual particles and clusters. The system differentiates between small and large particles based on the duration of the reflected signal, allowing real-time tracking of particle growth, breakage, or agglomeration. This capability is particularly advantageous in processes where particle size influences product quality, such as crystallization, fermentation, and cell culture. Continuous monitoring enables operators to make informed decisions to maintain optimal conditions.

Equipment Components And Optical Features

FBRM relies on precision-engineered optical and mechanical components designed for complex bioprocessing environments. At its core is a focused laser module that generates a highly collimated beam, typically in the near-infrared spectrum. This laser is directed through an optical window into the process medium, where it interacts with suspended particles. The window, typically made from sapphire or quartz, resists chemical degradation and maintains optical clarity under prolonged exposure to bioreactor conditions.

A key feature of the FBRM probe is its rapidly rotating optical assembly, which sweeps the laser across the sample at high frequency. This rotation, powered by a precision-engineered motor housed in a sealed compartment, prevents contamination. With speeds exceeding 2,000 revolutions per second, the system records vast numbers of particle interactions in real time. This high temporal resolution is critical for capturing transient changes in particle populations during dynamic bioprocesses.

The backscattered light from particle interactions is collected by a photodetector within the probe assembly. This detector differentiates signal intensities corresponding to various particle sizes. Optical filters and beam splitters refine the signal, minimizing interference from ambient light or vessel reflections. The processed signal is transmitted to a high-speed digitization unit, where proprietary algorithms convert raw backscatter data into chord length distributions.

Integrated temperature and pressure sensors provide additional context for data interpretation. Fluctuations in these parameters can influence particle behavior, making auxiliary measurements valuable for correlating physical changes with real-time particle size distributions. Some advanced systems incorporate automated calibration routines using reference particles to maintain measurement accuracy over extended periods.

Interpreting In-Situ Measurements

FBRM generates a continuous stream of particle size distribution data, but interpreting these measurements requires understanding how chord length distributions (CLD) reflect real-world particle dynamics. Unlike traditional particle sizing techniques that assume spherical geometry, FBRM captures chord lengths—straight-line distances across particles as intersected by the laser. This means the resulting distribution is a statistical profile rather than a direct representation of actual particle diameters.

The shape of the CLD curve provides insights into particle behavior. A shift toward longer chord lengths suggests particle growth, which could indicate successful crystallization or cell aggregation. Conversely, an increase in shorter chord lengths may signal fragmentation due to excessive shear forces. A broad distribution with multiple peaks suggests a heterogeneous population, which could be problematic in applications requiring precise particle size control. Continuous monitoring allows operators to adjust agitation speed, feed rates, or temperature profiles to maintain optimal conditions.

Beyond size tracking, the rate at which the CLD changes highlights process kinetics. Rapid shifts indicate instability, such as uncontrolled nucleation in crystallization or abrupt cell lysis in fermentation. Gradual changes reflect steady-state conditions where particle transformations occur predictably. This temporal aspect of FBRM data is particularly valuable in bioprocessing, where maintaining a controlled environment directly impacts yield and consistency. Integrating FBRM with other process analytical technologies (PAT) provides a more comprehensive view of system performance, enabling predictive adjustments rather than reactive corrections.

Use In Bioprocessing And Fermentation

Real-time particle monitoring has transformed bioprocessing, particularly in fermentation systems where maintaining optimal cell density and morphology is critical. FBRM tracks microbial growth, aggregation, and flocculation without the need for offline sampling, which can disrupt culture conditions. In fermentation processes involving bacteria, yeast, or filamentous fungi, cell clustering and morphology shifts directly impact productivity. By continuously measuring chord length distributions, operators can detect deviations that indicate suboptimal growth conditions or impending process failures.

One of FBRM’s most practical applications in fermentation is assessing biomass aggregation in high-cell-density cultures. In industrial-scale monoclonal antibody production using Chinese hamster ovary (CHO) cells, excessive aggregation reduces oxygen transfer and nutrient availability, leading to inconsistent yields. By monitoring changes in particle size distribution, bioprocess engineers can adjust agitation speed, optimize media composition, or introduce shear protectants to prevent excessive clustering. Similarly, in yeast-based ethanol production, excessive flocculation hinders substrate utilization, making real-time adjustments crucial for maintaining efficiency.