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The influence of external factors, including temperature, storage, aging, time, and shear rate, on the general rheological behavior of raw human milk is investigated. Rotational and oscillatory experiments were performed. Human milk showed non-Newtonian, shear-thinning, thixotropic behavior with both yield and flow stresses. Storage and aging increased milk density and decreased viscosity. In general, increases in temperature lowered density and viscosity with periods of inconsistent behavior noted between 6–16 ∘ C and over 40 ∘ C. Non-homogeneous breakdown between the yield and flow stresses was found which, when coupled with thixotropy, helps identify the source of nutrient losses during tube feeding. 

The interaction between breast and infant's mouth, during breastfeeding, is a complex dynamic mechanism. It remains unclear which factor plays the key role in removing milk from the breast: the intra-cavity vacuum pressure or the compressive pressure of the tongue. While there are extensive clinical data on collection of vacuum pressure, limited data exist for the positive pressure values on the breast areola exerted by infant's mouth. The goal of this study is to use a methodology to capture these positive pressure values exerted by maxilla and mandible on the breast areola during breastfeeding. In this study, the positive and negative (vacuum) pressure values are obtained simultaneously on seven lactating mothers successfully. Parallel to the pressure data measurements, ultrasound images are captured and processed to reveal the nipple deformations and the displacements of infants' tongues and jaw movements during breastfeeding. At the end, motivated by the significant differences in composition between the tissue of the breast and the nipple-areola complex, the Poisson's ratio values of the lactating nipples are obtained using these deformation measurements. 

Breastfeeding provides both nutrients and immunities necessary for infant growth. Understanding the biomechanics of breastfeeding requires capturing both positive and negative pressures exerted by infants on the breast. This clinical experimental work utilizes thin, flexible pressure sensors to capture the positive oral pressures of 7 mother-infant dyads during breastfeeding while simultaneously measuring vacuum pressures and imaging of the infants oral cavity movement via ultrasound. Methods for denoising signals and evaluating ultrasound images are discussed. Changes and deformations on the nipple are evaluated. The results reveal that pressure from the infant’s maxilla and mandible are evenly distributed in an oscillatory pattern corresponding to the vacuum pressure patterns. Variations in nipple dimensions are considerably smaller than variations in either pressure but the ultrasound shows positive pressure dominates structural changes during breastfeeding. Clinical implications for infant-led milk expression and data processing are discussed.