Dehydration sensors having polymeric base-buffered inks

Abstract

A dehydration sensor having a stable, printable, buffered-ink composition that enables one to miniaturize the detection zone and permits both buffer and indicator dye to be applied in the same area of a detection zone, without need for a conventional, large buffer pad region. The ink composition includes a weak polymeric base as its primary buffering agent.

Description

CLAIM OF PRIORITY TO RELATED APPLICATION[0001]The present application is related to U.S. patent application Ser. No. 12 / 858,234, filed Aug. 17, 2010, and claims benefit of priority to the contents disclosed in the earlier application.FIELD OF INVENTION[0002]The present invention pertains to dehydration indicators for use in an absorbent, personal-care product. In particular, the invention describes a dehydration sensor which incorporates buffered inks.BACKGROUND[0003]Dehydration is the depletion of fluids, mostly water, and associated electrolytes from the body. Normally, a person's daily, total fluid amount is regulated to be within about ±0.02% of body weight, and water in the body may comprise approximately 63% of the entire body mass. A balance of bodily fluids is achieved and maintained by matching the input and excretion of liquid from the body, and an imbalance in fluids can be linked to either dehydration or hypohydration.[0004]Although dehydration can occur in persons of al...

AI Technical Summary

Benefits of technology

[0025]The invention discloses a dehydration sensor that utilizes a buffer system composed of a dye solution and a poly-allyamine solution in de-ionized water (DI H2O). In a desired embodiment, the dye and poly-allyamine solution are mixed together and deposited on the surface of a substrate of an assay device. The solution does not require the addition of any other additional buffering component, such as a poly-acid. In other words, one can apply the dye and polyallyamine solution alone. The dye and polyallyamine-based system has a buffer capacity comparable to other single buffer component systems, thus only a small quantity of buffer is needed to achieve similar efficacy as to conventional assay devices. The present buffer system can serve as both an enhanced buffering agent and can immobilize effectively the dye on a printed substrate to prevent the dye from leaching across the substrate during a urine testing or assay process. Conventional dehydration sensors require a relatively large area of the substrate to serve as a buffer pad so that they can optimize their sensitivity. Unlike conventional dehydration sensors that are prepared using a single buffer, the present invention is much more sensitive to the changes in ion concentration in urine sample. This feature permits one to create dehydration sensors that do not, the combined buffer system of the present invention enables one to employ a much smaller substrate (i.e., at least one-half or one-third the size of previous buffer pads). This advantage allows one to deposit or print the sensing components (i.e., dye and buffer) on a single spot due to its significantly increased buffer capacity. The spot can have a linear or diameter / cross-sectional dimension of about 1 mm to about 30 mm, more typically about 2 or 3 mm to about 20-25 mm, or about 4 or 5 mm to about 10 mm or 12-17 mm, and preferably between about 1-5 mm, inclusive of various combinations of ranges therein. In comparison a conventional buffer pad commonly requires linear dimensions of about 3-4 cm×28-30 cm or an area of about 84-120 cm2. One does not need to have a relatively long buffer pad section between the sample deposit zone and the detection zone, which allows the urine to travel to the detection zone. Hence, an advantage of the present invention is its ability to maintain good sensitivity to ion concentrations in urine while allowing one to miniaturize the buffer pad section of the sensor.

[0026]Furthermore, in the present invention, the pH indicating dyes can be directly immobilized to a cellulosic buffer pad, which minimizes the potential uncontrolled diffusion of the dye from the detection zone. This advantage simplifies and reduces costs for the manufacture of the dehydration sensor device and enhances the user-friendly application, eliminating additional fabrication steps. For instance, compared to some conventional dehydration sensors included a dye on a nylon carrier pad to support the dehydration zone, the invention eliminates the need for a separate relatively expensive nylon carrier pad like in some prior devices.

[0027]According to certain embodiments, the buffer ink-treated substrates according to the present invention can be laminated to overlay another kind of substrate that is selected from either a similar type or different type of material. The lead of the underlying substrate can serve as a wicking medium for the assay device, and the buffer-ink-treated overlying cellulose substrate functions as the sensing portion for urine ionic concentration. In this fashion, one can cost-effectively simplify the manufacture of urine ionic / dehydration sensors.

[0028]The present dehydration sensor allows one to accurately monitor either quantitatively or semi-quantitatively the specific gravity of urine. The sensor includes a porous substrate, with a buffered ink system that is directly deposited on a portion of the substrate. The substrate forms part of a buffering pad. The buffered ink system is composed 0.5 wt % to about 10 or 15 wt. % of a weak polymeric base and about 0.5 wt % to about 20 wt % of a pH-sensitive dye. The present invention can employ the buffering function of a weak polymeric base alone in the buffered ink composition.

[0029]According to the invention, the polymeric base can be, for instance, poly(allylamine), poly(ethyleneimine), poly(vinylamine hydrochloride), or a combination thereof. Optionally, one can also include polymeric stabilizers, for example, a polyvinyl alcohol or a polyethylene oxide.

[0030]The pH-sensitive dye employed in the dehydration sensor can be, for example, any one of the following, but is not limited to these dyes: bromocresol green, bromothymol blue, nitrazine yellow, meta-cresol purple, thymol blue, xylenol blue, cresol red, bromophenol blue, congo red, methyl orange, bromochlorophenol blue, ethyl orange, chrysoidin, methyl red, alizarin red S, cochineal, chlorophenol red, bromocresol purple, para-nitrophenol, alizarin, brilliant yellow, neutral red, rosolic acid, phenol red, meta-nitrophenol, or a combination of these dyes. The amount of dye in the composition may range from about 0.5 wt % up to about 15 wt % or 17 wt %. Typically, the amount is in a range between about 0.5, 0.7 or 1.0 wt % and about 6, 7, or 10 wt %, inclusive. More typically, the amount is between about 0.8 wt % and about 3 or 5 wt %.

Problems solved by technology

A balance of bodily fluids is achieved and maintained by matching the input and excretion of liquid from the body, and an imbalance in fluids can be linked to either dehydration or hypohydration.

Dehydration can pose serious consequences to a dehydrated person if not cared for properly.

These consequences can include muscle cramps, dizziness, fainting, and even death in extreme cases.

This early warning sign, however, is often missed in situations where the person cannot adequately communicate with their caregiver, such as infants and the disabled or elderly.

People who are incontinent also have high chance of missing this dehydration sign since they are more likely to restrict their liquid intake to avoid the chances of embarrassing accidents.

Problems, however, persist for all the commercially available dipsticks.

A major problem is that the user has to read a change in color within a few brief minutes after dipping in the sample because the color development is not stable under test conditions.

The signals that one may observe outside of the time window are often inaccurate, hence normally invalid.

This situation may not be a problem for a test that a user can constantly monitor; however, it becomes a problem when constant monitoring of the test is not feasible and sample introduction time is uncertain.

For instance, it is difficult, if not impossible, to predict accurately when a baby or incontinent adult will urinate to provide a sample for an assay device in a diaper or other personal care product.

However, conventional reagent strips for USG measurement suffer from major shortcomings, particularly for over-the-counter and point-of-care markets.

For instance, conventional reagent strips have a limited reading window because the signal produced by such strips begins to change only a short period of time after sample application.

Unless the strips are analyzed shortly after application of the sample, the signal change can lead to erroneous test results.

Multiple urine insults can lead to erroneous test results making such strips unsuitable for applications in absorbent articles where multiple urine insults cannot be controlled.

Finally, conventional reagent strips do not provide a way for a user to know if the test has been performed correctly or if enough sample has been applied.

Additionally, urine reagent strips which change color based on urine ionic strength are commercially available, but they are not applicable for personal care products due to their dye diffusion and color instability issues.

Thus, an unsatisfied need exists for an assay device that can provide such assurance to caregivers in a cost effective way to help monitor a user's hydration status.

However, the sensor design and manufacturing steps are quite complicated.