How miniaturized liquid flow sensors are revolutionizing subcutaneous drug delivery

The COVID-19 pandemic has strengthened the push toward digitalization and patient-centric solutions in healthcare. The increasing demand for self-treatment, as well as the rise of biotechnology and precision medicine, give new meaning to smart drug tracking. By implementing miniaturized liquid flow sensors in wearable devices, subcutaneous drug delivery will reach the next level. This will result in a benefit for patients, doctors, nursing staff, pharmaceutical companies and the healthcare system.

Smart injectors, infusion pumps or digital pills – digital drug delivery is revolutionizing the medical and pharmaceutical industry and accelerating self-care at a rapid pace. As demographic change leads to an increase in patients with chronic diseases, the need for a larger number of digitalized home care therapies is strongly noticeable.

Digitalization trends have been relieving the healthcare system that was suffering from a nursing shortage even before the COVID-19 pandemic. But since its onset, the shift towards self-administration in healthcare has accelerated.

COVID-19 accelerating patient-centricity

As we learned, the pandemic has challenged hospitals all over the world. Scheduled surgeries and therapies have been put on hold due to a shortage of beds, over-burdened personnel and fear of infection. Patients became wary about visiting doctors’ offices and hospitals and resorted to telemedicine appointments where possible.

However, the healthcare system must be rethought, not only to deal with future diseases. Reducing hospital visits for routine checks and treatments of chronically ill patients is a key part of the transformation, just like improving efficiency of medical staff to help reduce overall treatment costs. Digital helpers can play an important role by improving collaboration between nurses, doctors and management, providing additional safety by monitoring drug delivery and treatment and allowing more data-driven interpretation of treatment plans and a faster response to changing patient conditions.

Nevertheless, it is assumed that the COVID-19 experience will continue to speed up and ease barriers to the development of modern healthcare solutions. New portable or wearable designs enable patients to manage their conditions safely at home, with more individualized, flexible treatment options supported by remote monitoring.

From a macroeconomic viewpoint, digitalization is associated with decreasing prices for electronic components. This not only justifies new equipment pricing, but also enables medical device manufacturers to invent new designs by adding new value to them. Directly documented feedback about ongoing treatment for patients and doctors is an example. For example, the electronic health record (EHR) of hospital treatments and diagnosis is also likely to become mandatory in home care someday.

Another factor is the increasing trends from health insurers. Pharmaceutical and insurance companies have been moving towards proof of use or effectiveness of therapy (e.g. for continuous positive airway pressure devices - CPAPs) and drugs, in order to receive full payment or reimbursement. Smart inhalers  that measure the inhaled flow profile and dose actuation, for example, are already able to prove that the drug was taken correctly. Overall, digital data like this is helping to build the Internet of Medical Things (IoMT) for the benefit of patients, caregivers and payers.

Biopharmaceuticals as a driving force

Whether for personalized or participatory patient care, precision medicine and advancements in biotechnology also have an impact on self-care trends. Compared to conventional medicines, the use of high-value drugs enables diseases to be treated in a more targeted way with fewer side-effects.

Unlike chemically synthesized drugs, biopharmaceuticals are made of complex structures from microorganisms, mammalian cells or plant extracts. For example, they include proteins that stimulate blood cell formation, insulin or antibodies that inhibit the growth of cancer cells. These high-value drugs also improve the opportunities to cure other previously untreatable diseases like autoimmune disorders, cardiovascular diseases, diabetes or neurological disorders.

However, because they must be administered parenterally, biopharmaceuticals are still not well accepted. Due to the large size of the molecules, the most prevalent mode is intravenous infusion. Large-volume administration requires clinical support, which means that therapy costs are added to already high production costs.

Another shortcoming is the elaborate handling of high-volume and viscous formulations that conventional drug delivery devices are not capable of. Some new drugs require specific dose timing concerning starting time or flow rate, while others are in a lyophilized state and require reconstitution. To overcome these administration-related challenges, new drug delivery mechanisms are required.

Connected large-volume injectors

For a few years already, large-volume injectors (LVIs) – also called on-body delivery systems, patch pumps or wearable drug-delivery devices – have been replacing intravenous infusion with subcutaneous injection. They are less painful to apply and enable chronic disorders to be treated at home by patients themselves. In particular, prefilled drug-device combinations provide a convenient and reliable alternative to outpatient treatment.

Wearable smart injectors

  • enable patients to receive therapeutics at home
  • enable therapy to be monitored in real time and remotely
  • reduce effort and cost for patients, healthcare providers and insurers.

Because of the high volumes and viscosities, biopharmaceutical delivery must be controlled, confirmed and tracked. Automatic drug-delivery systems with flow rates ranging from 1.5 to 300 milliliters per hour ensure continuous drug delivery out of a vial over a specific period of time. Large-volume injectors can also allow lyophilized drugs that need be delivered by the user shortly after reconstitution to be filled at the point of use.

Challenging device design

The market for large-volume injectors for non-insulin drugs is expected to grow at fast pace in this decade. Over 50 wearable products and more than 10 drug-device combinations with high storage capacities are either commercialized or in development. Whether selling devices including a medication or not, the drug-delivery industry is facing many design challenges: improving the handling of viscous formulations, optimizing usability as well as keeping devices small and costs low. Consequently, most large-volume injectors are made of disposable and reusable parts, which makes sense in environmental terms. Although the battery, motor, readout electronics, connectivity module and display are reusable, the needle, drug compartment, patch and wetted sensors are disposable.

As recent events have shown, large-volume injectors can also be designed for already existing drugs. Although a patent on a drug expires, for example Amgen’s Neulasta in 2015, the availability of a new on-body injector can lead to an extension of the drug’s lifetime and the related business for Amgen. Thus, new lifecycle management strategies in the pharmaceutical and medical industry can create new revenue streams.

Miniaturized, cost-effective and disposable sensors

Since there are various biopharmaceuticals with different properties, large-volume injector designers must individually guarantee reliable, precise function and high ease of use. Up to now, they equipped devices with visual, audio or tactile indicators for needle positioning and on-body attachment. Even failures like occlusions can be detected to some degree, but currently only in an indirect way, leaving the possibility of false positives.

Even more important is the direct flow measurement and delivered volumes as well as bidirectional measurement capability, which conventional sensors are not capable of. Sensirion’s sensor solutions allow miniaturized, disposable liquid flow sensors to be integrated into large-volume injectors to control, confirm and track subcutaneous drug delivery in real time. They enable precise dosing in terms of flow rate as well as administered volume and enable automatic failure detection such as occlusion or air-in-line in a cost-effective and direct manner.

Integrated into a connected large-volume injector, these next-generation sensors not only allow the administration to be monitored by the patient via a smartphone app, but additionally enable communication such as telemetry with stakeholders involved in the patient’s care, like family members, parents or relatives. Nursing staff, doctors, pharmaceutical companies (for research) and health insurers (for proof) receive updates as well as metrics about the administration and the device status. Programmable features could also adapt or optimize the subcutaneous drug delivery process. In case an injection device shows issues, a flow sensor can provide peace of mind to patients as well as their relatives. Put simply: implementing a tiny smart sensor improves therapy outcome, patient adherence and quality of life. Miniaturized liquid flow sensors address the above-mentioned market trends and provide a great value-to-cost ratio.

Miniaturized liquid flow sensors enable LVI to

  • measure the flow rate directly and bidirectionally to confirm the administered fluid volume in real time
  • monitor system performance and guarantee reliable failure detection
  • enable connected solutions for therapy monitoring and tracking by all stakeholders

Sensor, pump and beyond

Finally, in designing LVIs, it is recommended to view the liquid flow sensor and the pumping mechanism from a holistic point of view. To identify the ideal design of the flow control system in terms of size, performance, ease of integration, manufacturability and cost, medical device manufacturers should aim for the best possible combination.
Conventionally, pump technology is selected first and often independently of the flow sensor, especially when unique requirements and related intellectual property of the device manufacturer are involved. Combining a previously selected pump with a liquid flow sensor can be challenging, especially when the pump performance requires further improvement, failure detection and resilience, all to be provided by the sensor. The pump’s specific working principle, flow profile, mechanical design and fluidic connectors might further complicate the task.

Sensirion has put its extensive flow sensing experience to the test in a design study, assembling a small-footprint liquid flow sensor with a single-use micropump from Quantex Arc. The result was a highly compact flow controller providing a steady flow in different flow regimes and consuming very little energy.

Sensirion’s technology certainly works well with pumps from other manufacturers as well. Being merely a concept study, there is surely space for further improvements and customizations, also considering different device requirements. We are at the beginning of an exciting journey.

Test design

The used lightweight in-line pump CS-3 with barbed inlet and outlet connectors for easy fitting to tubing is ideal for precise microdosing at flow rates of up to 100 milliliters per hour. Taking up only 0.5 cm3 of space (12 x 6 mm), Sensirion’s liquid flow sensor stands out due to its millisecond-fast response times and direct as well as bidirectional flow rate measurement

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