Development of Sharps Waste Device for Sustainable Healthcare Waste Management in Nepal

Abstract

The project's purpose was to investigate the development of a medical sharps waste device appropriate for use and manufacture in Nepal. Medical sharps waste management in Nepal is still somewhat dangerous, despite the physical and environmental dangers.

After considering several design directions, it was determined to create a mechanism capable of mechanically pulling the needle tube out of the hub. A device like this will render needles unusable while simultaneously opening up possibilities for the recycling of the materials of needle waste. Additionally a device that mechanically separates the materials of needles does not currently exist.

Tensile tests were performed with various needle sizes and temperatures to better investigate this. There were no statistically significant differences between temperatures, although the results from 16 G needles differed significantly from the results from 20 G and 23 G needles. It was discovered that the device's minimum pulling force should be 500 N; this, along with information taken from several set standards and previous projects on needle devices, was then included into a set of requirements for the device.

After exploring several clamping, pulling, and combined mechanisms, a roller mechanism was chosen for the device. A functional prototype capable of extracting a needle tube from its hub was created. This prototype was then tested, and various experiments were carried out to try to enhance the design because needle tubes were still slipping in between the rollers on occasion, and some needle tubes broke off.

Adding other structures or a different material like rubber on the rollers did not result in better performance, and a knurling pattern worked best for creating grip on the needle tube. Adding a ridge did not improve the performance, however removing some material from both sides of the gap in Roller A did enhance performance temporarily. Making the rollers out of stainless steel 431 rather than 316 did not increase their performance; however, stainless steel 431 with a heat treatment did improve the performance and showed consistent test results. This final prototype, including the rollers made out of stainless steel 431 with a heat treatment was then used to do final verification and validation.

20 G needles could be pulled with the device consistently at a needle length of 33.8 mm, both wet and dry. 27 G needles however kept breaking off, both wet and dry. A design choice should be made here about if the device should be aimed at a smaller range of needles or a redesign should be made where different spring forces could be applied. The device showed not springback and no parts became trapped in the mechanism.

It was impossible to insert needles of various diameters at greater angles from the vertical of the aperture and 16 G needles did not fit into the device at all. A redesign is needed for this.
The average activation force of the device was 14.72 N and the distance from the hand holding the needle to the hand operating the device did not exceed 50 mm.
The cycle time per needle was still too long for the device. Further research is required to improve these parameters. The prototype did meet the weight and size requirements. The device did not have a sharps box attached to it, this should be added in a redesign.

If the rollers of the device are to be constructed of stainless steel 431, they should be made in India, since stainless steel 431 was not available in Nepal. The case, cubes, pushing plate, socket, spring axis, and lever may all be made in Nepal. Standard components, such as springs and bearings, may be obtained in India. However still choices and more research is needed in the area of where exactly the product should be produced and assembled.
More research is needed to determine how the metal components of needles may be recycled and how a device like this would work with different types of needles. Also researching if applying force to both rollers and a redesign either with a different spring of multiple spring forces should still be done.

More testing is needed to determine the pulling force and how many cycles the device can sustain. As well as a drop test, a tipping test on an angular surface and users tests.
Lastly research into how to incorporate a redesign where the syringe is also rendered unusable is needed, since this study only focused on making the needle part unusable by separating the materials.