Clinical and Experimental Study on the Biomechanics of Breastfeeding

Abstract

Breastfeeding benefits mothers and infants in both physical and mental health. An infant develops complex oral dynamics on the breast to extract milk. The present study aims to understand the breastfeeding mechanism through in vivo clinical analysis and in vitro experimental work, which can answer several bio-mechanical questions that arise from the infant’s oral interaction on the breast during breastfeeding. In the clinical study, the positive (compression) and negative (vacuum) pressure values were obtained simultaneously on multiple lactating mother-infant dyads. Parallel to the pressure data measurements, ultrasound images were captured and processed to reveal the nipple deformations and the displacements of infants’ tongues and jaw movements during breastfeeding. The results showed an oscillatory positive pressure profile on the breast under both maxilla and mandible, which differed from clinical observations that only the mandible of an infant moves during breastfeeding. The nipple deformations varied between mothers and indicated a large volume change in the anatomy. In the experimental work, a new and unique bio-inspired breastfeeding simulator (BIBS) was constructed to mimic infant oral behavior and milk extraction, with the intent to study the breastfeeding mechanism in vitro. The simulator replicated the intra-oral vacuum pressure, compression pressures from the infant’s jaw, tongue and upper palate, and nipple deformation on the breast areola area. All mechanisms were successfully coordinated to mimic the infant’s feeding mechanism during breastfeeding. Results were matched with the in vivo clinical pressure data and nipple deformation in ultrasound images. Integrated with graphical user interface and feedback controllers, the BIBS adjusted automatically based on vacuum magnitude and frequency and served as a physiologically accurate test-bed for studying the biomechanics of breastfeeding. Finally, the flow dynamics in the bifurcated milk ducts of a lactating breast model during breastfeeding simulation using BIBS was analyzed with a particle image velocimetry (PIV) system. A clear human milk-mimicking fluid (HMMF) achieved with composition of 15.69% NaI, 30.27% glycerin, 54.02% water and 0.02% xanthan gum by weight percentage provided a non-Newtonian density, viscosity, and refractive index matched fluid for use in PIV experiments. The oscillatory flow under vacuum pressure provided a higher maximum velocity magnitude at the outlet compare to when an infant applies both vacuum and oral compression pressures, however mean velocity was higher when compression was combined with vacuum. Additionally, the average milk flow rate of vacuum-only operation was less than that of vacuum plus oral compression, thus further explaining the effectiveness of applying compressive suckling dynamics on the breast in human lactation.