Accuracy and reliability are key issues in the medical device industry — especially regarding administration of medical fluids or gases. Many medical fluid administration sets are provided with a flow restrictor. So far, a glass capillary is usually applied. However, this component has many shortcomings. The multi bore flow restrictor presented here solves many of these shortcomings as experienced with the present flow restrictors, and provides cost advantages.

The multi bore flow restrictor is a plastic tube with an integrated membrane with multiple micro holes drilled in it. The holes are drilled with an excimer laser. By varying the diameter and the number of holes, any resistance value can be obtained.

Fig. 1 – Multi bore flow restrictor integrated in an IV filter

The multi bore flow restrictor has been developed to generate accurate and reliable liquid and/or gas flows at low cost and in big quantities. It is a single injection-molded plastic duct, shut off by an integrated baffle. Micro bores have been drilled in that baffle by laser drilling to enable fluid passage. The number and diameter of the holes and the thickness of the baffle determine the resistance of the multi bore flow restrictor. By using a mask, all holes can be laser drilled simultaneously. Due to the accuracy of the holes and the linear relation with pressure, it is easy to generate pressure controlled flows. The baffle is situated robustly and well protected within the plastic part. The outside of the part can have any shape, which can be used for identification purposes.

Details for assembling this part in a duct system can also be integrated. In an embodiment of the multi bore flow restrictor, for example, one end can be made for plastic tubing to be glued in, and the other end can have an ISO standard cone, for medical applications. There are many possible applications, e.g., medical, domestic, agricultural, industry, and laboratories.

Apart from the accuracy and reliability, ultra low pressure controlled flows can be generated (e.g., a continuous flow of less than 1 mL of water per hour). There is no limitation for the upper limit. The design is robust and easy to handle in production. In case of different restriction values, the possibility of proper identification (shape, color, print, etc.) can prevent mix-up problems in production and administration failures. There are no particles released as can happen with the current state-of-the-art technology of glass capillaries. The applied material is biocompatible and can be sterilized by different methods such as EO, gamma, and steam. Due to integration of the baffle in the plastic part, a significant reduction of the number of connections is obtained as compared with existing technologies. This saves time in production and reduces the chance of failures such as leakage and occlusion. After drilling the holes in the baffle, this baffle is not touched by hands, which prevents contamination and the risk of occlusion.

Fig. 2 – Prototype samples of the multi bore flow restrictor were tested with sterile water for injection.

Benefits of this process include: much more accurate than the present glass capillary flow restrictors; more reliable than the present glass capillary flow, due to a much lower risk of occlusion; and lower manufacturing cost.

Several aspects can be integrated into the flow restrictor, which reduces the number of connections and the risk of leakages associated with such connections.

There are many medical applications for this technology, such as ambulatory pain pumps, hemo-dynamic monitoring flush systems, oncology, antibiotics, insulin administration, side lines in IV administration sets, standard IV lines, MRI drug administration, CO2 administration for laparoscopy, and wound care systems. The multi bore flow restrictor can be a key component for a broad administration platform. Some examples are: pressure controlled administration, miniaturization by integration, low flow rates to enable higher drug concentrations, an integrated flow restrictor-IV filter, and a modular restrictor system. While the technology has been developed for usage as a medical device, the use of the multi bore flow restrictor technology can be expanded to a wide variety of applications that require an accurately controlled flow.

An injection molding tool has been made for the production of high-quality prototype samples of the multi bore flow restrictor. These samples have been used to demonstrate functionality and to validate the conceptual assumptions. The prototype sample is a so-called male luer lock (standard cone for many medical applications), made of an FDA-approved lipid and gamma resistant PC grade. In each sample, 10 holes, with a diameter of approximately 10 micrometers, were made with an excimer laser, using a mask to drill five holes at a time. Laboratory tests show promising results. It is expected that a restriction with a standard error of 1% can be feasible.

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