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In an effort to improve the current method of urine collection from premature infants, we have manipulated the current diaper by inserting a polyethylene tube designed to collect and hold 5 ml of urine. The tube will extend out of the diaper where it can be easily accessed and the urine can be collected with ease.

Problem statement


  • To improve the method of urine collection from the diaper of pre-term infants that collects a high percentage of the total urine and improves the analysis of sodium/potassium levels.

Premature infants

Premature Infants

Age - 25 weeks

Weight - 1–2 lbs.

Length - 14 in.



  • Premature infants, around 25 weeks old, often have underdeveloped kidneys which lack the ability to regulate the body’s sodium and potassium levels.

  • If these levels stray too far from the acceptable levels the effect can be fatal.

Abstract 3909707

  • Due to their importance, sodium and potassium levels are measured from the infant’s urine

  • In the current process, urine is sent to the lab for analysis every 2 to 6 hours

  • Nurses squeeze the infant’s diaper to collect the needed urine. This collection process is cumbersome and needs improvement.



  • For analysis, the lab needs a minimum of 0.70 ml of urine.

  • An infant will produce anywhere from 5-15 ml of urine during a 2-6 hours period.

  • The urine can be directed into an area approximately 5 cm x 5 cm.

  • Premature infants do not have enough blood to provide for continuous blood testing.

Original goals


  • Initially our client desired a device which could replace the lab completely.

  • Device would require the use of electrodes within the diaper.

  • Consulting with analytical and physical chemists concluded a device of this nature would be extremely difficult to produce.

  • Next option, fix the collection process.

Product design specification

Product Design Specification

  • Ability to remove 5 ml and contain 25 ml

  • Feasibility

  • Simplicity

  • Cannot distort Na+/K+ concentration

  • Urine kept away from skin

  • Ergonomics

  • Thin and flexible (Plastic)

Final design


  • The inner channel design

  • An open, half elliptical shaped tube is placed inside the diaper underneath the thin exterior and a thin layer of cotton.

  • The tube runs lengthwise through the center of the diaper and exits the diaper in an enclosed tube, where the nurse can simply drain the tube and collect the urine.

Theoretical process


  • Urine from the infant will be directed into a marked 5 cm x 5 cm area.

  • The open tube, lying directly beneath this area, will collected a minimum of 2 ml of urine.

  • Excess urine will be absorbed by cotton in the diaper, avoiding an irritation to the infant’s skin.



  • Plastic

    • Low-Density Polyethylene instead of high-density used in prototype

  • Cotton Pieces (2)

    • Length of 5.5 cm along inner channel

    • Water needed to saturate diaper is proportional to square root of the weight of the cotton

    • Each piece approximately 0.35 g

Proe profile of the prototype

ProE Profile of the Prototype

Proe profiles of the prototype

ProE Profiles of the Prototype



Inside the diaper

Inside the Diaper



  • An absorbance to weight ratio for the cotton used in the diaper was determined by keeping the area of cotton constant while changing the weight. We found that the absorbance was proportional to the square root of the weight.

  • A second test, measuring % of liquid collected vs. amount of cotton in the diaper, displayed an obvious cut-off point.

Volume of water ml v s weight of cotton grams

Volume of Water (ml) v.s Weight of Cotton (grams)

Liquid collected vs cotton in diaper


Future work

Future Work

  • Plastic

    • Low-Density Polyethylene use instead of high-density

  • Other possible materials

    • Foam-like substance, soft flexible materials

  • “Wings”

    • Additional plastic to facilitate urine collection into inner channel

Future work cont

Future Work(cont.)

  • Future Testing

    • Test addition of the “wings” in urine collection

    • Test smaller versions of prototypes

    • Test with premature infants in hospital situations



  • Dr. Julie Kessel, and all the friendly nurses at Meritor Hospital

  • The University of Wisconsin-Madison Chemistry Department, specifically;

    • Pamela Doolittle Ph.D.

    • John Scrag Ph.D.

    • Claude Woods Ph.D.

    • Lyold Smith Ph.D.

    • Hyuk Yu Ph.D.

    • Arun Yethiraj Ph.D.

    • John Wright Ph.D.

  • Tim Osswald Ph.D. (plastics specialist)

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