SMART TECHNOLOGY
The significance of sweat
Among many bodily fluids, sweat provides a significant amount of information about a patient’s health status and is readily accessible, making it suitable for wearable, noninvasive biosensing. Sweat contains important electrolytes, metabolites, amino acids, proteins, and hormones, which allow monitoring of metabolic diseases, physiological conditions, or a person’s intoxication level. Stress plays an important role in the overall health of a patient. When under stress, the adrenal gland releases cortisol and adrenaline into the bloodstream. The cortisol levels in various bodily fluids can range from 4pM to 70 M depending on the fluid. In sweat, the optimum level of cortisol ranges from 0.02 to 0.5 M. Increased levels of cortisol have a detrimental effect on the regulation of various physiological
caused by remaining in a hospital bed for too long. However, they also typically produce simpler data sets than the full 12-lead standard monitor and offer less control over the quality of the data produced. These competitive landscapes drive positive product development but it is often the central regulatory and funding bodies that have the power to drive change. Previously, these mobile cardiac telemetry products have benefited from a favourable reimbursement scenario in the US, defined under a Category 3 CPT code for “extended Holter monitoring.” This code entitles them to twice the amount of reimbursement as “event monitoring” and more than eight times the amount afforded to generic “Holter monitoring” (both Category 1 CPT codes). If the reimbursement situation were to change, the entire revenue structure for these devices will change with it. Should reimbursement strategies be allowed to shape developments rather than consumers and effectiveness?
processes such as blood pressure, glucose levels, and carbohydrate metabolism, and sustained stress can disrupt homeostasis in the cardiovascular, immune, renal, skeletal, and endocrine systems, leading to development of chronic diseases. Therefore, continuous monitoring of cortisol levels in bodily fluids has great relevance in maintaining healthy physiological conditions. As a result, there is much interest in devising wearable devices able to monitor stress levels. Most stress sensors are based on physical sensing and mainly focus on monitoring skin perspiration or conductivity, heart rate, and temperature. These approaches are promising in terms of fabrication, using novel functional materials having desirable mechanical properties such as stretchability, flexibility, and high durability. However, the
alteration of bodily physical parameters can also be induced by nonstress-related causes such as weather conditions and fever, making these sensors generally vulnerable to false positives. Furthermore, recent devices often show poor performance in terms of invasiveness, stability of recognition, selectivity, and sample acquisition. However, in one recent study, Jang et al. demonstrated a field- effect transistor-based cortisol sensor by embedding a cortisol antibody into the synthetic polymer matrix to generate a cortisol-selective/sensitive membrane. The designed sensor shows high sensitivity and a low limit of detection (down to 1 pg/ml). A wearable biosensor has recently been developed, using an organic electrochemical device for the detection of stress by selectively sensing cortisol in sweat.
Skin patch sensors have been used to detect the chemical composition of sweat for some time, and different application options from assessment of athlete hydration, through to proposals for detection of potential higher value sensing (for example, detection of hormones such as cortisol.
Diabetes management reveals a confusing system
One of the biggest revenue generators in the electronic skin patches market has been continuous glucose monitoring (CGM) for diabetes management, which posted annual revenues of over $2.5 bn in 2018. The US Food and Drug Administration (FDA) has
given four companies approval to sell CGM products, three of the four companies offer a skin patch with a small needle to test glucose levels in interstitial fluid. Only one organisation offers a subcutaneous implant which is then read using a skin patch as a communication hub. In such a closed market, regulations and reimbursements are shaping its course.
The three large players offering a needle- based skin patch have benefited from multiple geographies now offering partial - or full - reimbursement for CGM products under national healthcare schemes. Yet each of the three products is treated under a single regulatory category and receive the same reimbursement per device, regardless of performance, longevity or functionality. This opens up the potential for a closed market which favours devices because of simplicity and cost rather than effectiveness. The fourth player is a new market entrant with lower revenue but offers a much longer- lasting CGM solution with significant differentiation from its rivals, but because of limited regulation and reimbursement, however, it may struggle to break the market stranglehold from larger players with cheaper solutions. New entrants need to be encouraged
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WWW.CLINICALSERVICESJOURNAL.COM NOVEMBER 2019
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