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A group of scientists from ETH Zurich, the University of Colorado, and UC San Diego have built a 3D printed model of human breast tissue that secretes milk-like proteins, offering a new way to study lactation and hormone response at the cellular level.
Using 3D printing and cells sourced from donated breast milk, the team created structures that replicate the shape and behavior of natural milk-producing glands. Their findings were published in Science Advances, with ETH Zurich’s Professor of Tissue Engineering and Biofabrication Marcy Zenobi-Wong leading the project.
The printed model is designed to mimic the ducts and alveoli of the human breast, which are responsible for milk production and transport. To construct these shapes, researchers used volumetric 3D printing and a specialized bioink made from decellularized bovine mammary tissue.
This bioink retained more than 1,300 proteins, including key structural and biochemical components such as collagens, elastin, and glycosaminoglycans. Type I collagen, in particular, made up over half of the collagen content, helping the printed scaffold behave like real breast tissue.
Lab-grown tissue shows hormone response
To fine-tune the material’s physical characteristics, the researchers added 4 mg/mL of additional type I collagen, producing scaffolds with a stiffness close to 1,000 pascals. This is lower than the typical stiffness range of natural breast tissue, which falls between 3,000 and 5,000 pascals, but suitable for culturing cells in a controlled environment. The printed structures remained intact and usable in the lab for more than a month.
Instead of relying on biopsies, the team extracted mammary epithelial cells from donated breast milk. These cells made up only 11% of the initial sample but expanded to over 90% after just one round of culture. They included both major subtypes of mammary epithelial cells and retained receptors for prolactin, a hormone essential for milk production.
Once introduced into the 3D printed scaffolds, the cells formed cohesive epithelial layers within a week. They remained highly viable and began expressing cytokeratins CK8 and CK14, forming tight junctions, and producing milk proteins such as β-casein and lactalbumin. They also developed lipid droplets resembling those found in natural milk. Tests showed that β-casein was secreted into the culture medium, regardless of whether prolactin was added externally.
To study how the physical environment affects cell behavior, researchers printed scaffolds with different stiffness levels. On the softer version, cells formed branching networks that extended into the surrounding material. On stiffer scaffolds, the cells stayed within the printed structure. This suggested that the rigidity of the surrounding environment influences how the tissue organizes itself and how far the cells spread.
Gene analysis confirmed the presence of several important regulators of milk production, including STAT5, STAT6, ELF5, GATA3, and PRLR. The team also detected activated STAT5 protein, a sign that the prolactin signaling pathway was functioning. Though secretion levels differed between donors, every sample showed the ability to respond to hormones and produce milk-related proteins.
Unlike organoid models, which are often inconsistent in shape and hard to monitor, the printed scaffolds allowed for precise control over structure and easier observation of secreted materials. Because the scaffolds are cell-free until seeded, they can be used with donor-specific cells, including those from healthy individuals or patients.
Future improvements may include adding perfusion systems to simulate blood flow and enable real-time delivery of nutrients and hormones. Coating the internal surfaces of the scaffolds with proteins like laminin or collagen IV could further support long-term cell growth and organization.
This model offers a reproducible and accessible way to study human lactation, hormone responses, and breast tissue development. It could be valuable not only for biological research but also for investigating the effects of medications, environmental exposures, and disease on milk production.
3D printing supports nursing research
From studying how milk is made to developing protective tools for nursing, 3D printing is offering new ways to explore and improve breastfeeding, especially in medically complex or underserved settings.
For instance, antimicrobial material developer Copper3D developed a 3D printed device to reduce the risk of HIV transmission during breastfeeding, using its antimicrobial PLACTIVE material. Infused with nano-copper additives, the material disrupts HIV by degrading its membrane and genetic material.
In lab tests, HIV-1 samples exposed to 3D printed PLACTIVE surfaces showed a 58.6% drop in viral replication after just 15 seconds. Based on these results, researchers projected near-total inactivation with greater contact surface and time. Designed as a layered interface between mother and child, the device aimed to offer a practical solution in regions where access to treatment and prevention is limited.
Elsewhere, researchers from University College London (UCL), Imperial College London (ICL), and Universitá Campus Bio-Medico di Roma developed a 3D printed device to study facial touch in newborns, aiming to better understand breastfeeding difficulties in premature babies. Designed with Eagle CAD and produced by OSH Park, the compact circuit board was enclosed using a Stratasys Objet30 Pro 3D printer.
Worn on a finger and covered with a clinical glove, the device delivered gentle taps to an infant’s cheek while EEG recorded brain responses. In tests on seven infants, the device was well tolerated and accurately measured applied force, offering a safe, noninvasive method to study early sensory processing.
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Featured image shows Volumetric printed biomimetic scaffolds support in vitro lactation of human milk-derived mammary epithelial cells. Image via ETH Zurich.
