Measurement of internal diameters of capillaries and glass syringes using gravimetric and optical methods for microflow applications

Abstract

Objectives Microflow measurement devices are used in several science and health applications, mainly drug delivery. In the last decade, several new methods based on optical technology were developed, namely the front tracking and interferometric method, in which the knowledge of the inner diameter of the syringe or the capillary used is critical. Only a few National Metrology Institutes (NMIs) can perform inner diameter measurements below 1 mm, which requires expensive technology. Therefore, IPQ, in cooperation with CETIAT, CMI and UNIDEMI, under the EMPIR project 18HLT08 MeDDII – Metrology for Drug Delivery, developed new measurement methods for small inner diameter tubes based on the gravimetric principle and optical methods in order to simplify the apparatus used for this type of measurements without increasing uncertainty. Methods The gravimetric experimental setup consists of measuring the liquid volume on a specific length of the glass tube. The optical method used is based on the front track principle that uses a high-resolution camera and ImageJ software, to determine the diameter at both ends of each capillary. Results To validate the developed methods, a comparison was performed between CETIAT, CMI and IPQ and the results obtained were all consistent. Conclusions This work allowed the determination of inner diameter of syringes or capillaries using two different methods with relative expanded uncertainties from 0.1 to 0.5% (k=2), that can be applied for flow measurements using optical technology.

Rapid Calibration of Nanoliter per Second Flow Rate by Image Processing Technology

“…Upon achieving a stable flow, we recorded real-time images of the droplets and employed MATLAB to extract their edges. Given that the emitter was mounted nearly vertically, the droplet was assumed to be pendant and axisymmetric [15,18]. Using this axisymmetric model, we split the droplet into a collection of cylindrical volume elements along the vertical direction [19], as shown in Figure 3.…”

“…The high resolution of an HD camera is leveraged to calibrate the flow rate frame-by-frame, which enables precise and efficient measurements. This approach is distinct from liquid level measurement [ 15 ], as it calibrates the flow rate of the system by measuring the drop at the outlet, thus reducing the requirements on the flow supply system pipe and measurement environment. In comparison to conventional methods, such as traditional flow sensors, non-contact techniques, and contact measurement methods, the proposed approach overcomes limitations associated with achieving precision in the nanoliter per second range.…”

Optical Bubble Microflow Meter for Continuous Measurements in a Closed System

“…The need for precise measurement of slow liquid flows exists, for example, in cases such as measurement of the absolute blood flow in veins or flow through a peripheral organs [1], measurement of flow of lymph in lymph vessels [2], quantitative evaluation of the equipment for the target controlled infusion or drug infusion systems [3][4][5], flow rate measurement for calibration of microchannels used in liquid dosing applications [6,7], and testing of high-precision microfluidic flow controllers [8]. In addition to the appropriate sensitivity and accuracy of microflow meters, an important requirement that may be imposed on such devices, for example, in the context of clinical measurements, is the need for continuous or long-term monitoring of the flow process depending on other factors affecting the flow rate and measurement in a closed system, i.e., without contact of the liquid with the elements of the measuring apparatus.…”