Bioplastics in domestic medical applications. The case study of the pH Meter Cup for urine pH monitoring.

The production of plastic has exponentially increased in recent decades, causing a serious impact on the environment and human health. One of the sectors where plastic use is daily is that of healthcare and caregiving. According to a study published in the AMA Journal of Ethics, healthcare in the United States generates 6.6 million tons of waste annually, of which 20% is made up of plastic materials (Jain & LaBeaud, 2022). The following research aims to investigate how the use of bioplastics can be introduced even in domestic healthcare contexts. Currently, bioplastics are used in biomedical applications for vascular grafts for soft tissue replacement, breast prostheses, intraocular lenses, artificial hearts, and more (Pattanashetti et al., 2017; Reddy et al., 2015). The proposed case study explores the possibility of using food waste for the production of bioplastics by identifying the different organoleptic varieties found among the investigated waste. The research focused on "red cabbage," a food that contains "anthocyanins," water-soluble substances that release pigments, which are extremely variable depending on the pH of the liquid they come into contact with. In the case of urine, the pH normally ranges between 4.6 and 8, and this is related to the individual's diet and health. Beyond these lower or upper limits, a condition considered pathological occurs. Urine pH, therefore, reflects the kidneys' ability to maintain a normal concentration of hydrogen ions in the blood plasma and extracellular fluids. Urine pH measurement is used to detect the presence of various pathologies, such as acid/base system disorders; respiratory disorders, metabolic problems, and urinary tract infections. The method for monitoring urine at home can be done using a plastic cup and litmus paper, exploiting the chemical sensitivity properties of the red cabbage pigment's pH. However, it should be noted that both the plastic cup and the litmus paper have drawbacks in terms of environmental impact, human health risks, and practicality of use. The traditional plastic cup used for urine pH control is made of HDPE plastic, while the use of litmus paper requires it to be immersed in the patient's urine, contained in the plastic cup, for a few seconds to detect the pH. The use of bioplastic cups offers greater ease of use, as the patient only needs to collect the urine in the cup, and the resulting chemical reaction changes depending on the urine pH. Additionally, the result's reading is automatic and objective, as the cup's color changes in a predetermined way depending on the pH. The pH Meter Cup is a container measuring 10cmx8cm with a shape similar to a plastic cup but with an irregular upper edge along the diameter curve, providing an ergonomic function for grasping the object. The initial color is purple, but during use, it can change from magenta/pink to blue/green depending on the urine pH. The experiments that led to the prototyping of the pH Meter Cup were carried out in a domestic area through a kitchen equipment that allowed quantifying, mixing, amalgamating, cooking, and drying the necessary components for bioplastic prototyping. Following various experiments in which quantities, cooking times, and drying methods were perfected, it was possible to prototype examples for each type of material and quantity ratio between the elements. In the first attempt, starch-based bioplastic was found to be too rigid and broke during the drying period. Later, the idea of using glycerin in addition to starch was developed, which increases bioplastic flexibility during the cooling phase. These problems are present due to the reduced thickness of the final object, which is only 2 mm. The final result was obtained through 24g of corn starch, 3.5ml of glycerin, and finally, 120ml of water pigmented with the red cabbage color (Fig.1). Fig. 1 - Production process. Further tests were carried out with Guar gum/gelatin, which did not allow obtaining a material that maintained its rigidity without generating cracks at the time of separation from the molds. The mold is composed of two parts connected by 4 joints at the corners and is closed only after inserting the freshly prepared bioplastic into the lower part of the mold. After closing the mold, the bioplastic must dry for several days, depending on the humidity and temperature of the environment. At the end of cooling, the object's dimensions have reduced due to water loss (Fig.2). Fig. 2 - Prototyping through a PLA mold. The experimental research then focused on evaluating the materials' biodegradability. The activity was carried out in a temperature range ranging from 18 to 20 degrees Celsius. Visual measurements of biodegradability in water over time were carried out over 4 days, always at the same time each day, using 3 pieces of different sizes of the same material. From the observations made, it was possible to understand that the material, within 30 seconds, began to change color from purple to blue, tending towards a lower pH. In the first 24 hours, it was possible to perceive the thinning of the material based on the size of the pieces placed in water. In the following 72 hours from the immersion of the elements, it was possible to validate their biodegradation due to the evident thinning of the material, the loss of Adel pigment, and the fragmentation of the elements immersed along the edges (Fig. 3). Fig. 3 - Biodegradability over 72 hours. Finally, an evaluation was carried out on the color change of the biodegradable material in various aqueous solutions ranging from pH 3 to pH 9.5 (Fig.4). All values were analyzed using a litmus paper. Upon insertion of the material into the various aqueous solutions, an instantaneous change in the color of the bioplastic was noted within 3-10 seconds, except for the solution with a pH of 7.5, which maintained its original color, responding faithfully to the need to keep the material's color unchanged under optimal user health conditions.