What Does a Human Heart Need to Grow? Scientists Found the Answer in a Bioprinted Model

Heart problems that babies are born with, called congenital heart defects, often begin developing early in pregnancy. Approximately three weeks after fertilization, the human heart is still a simple, straight tube of cells and, over the course of about five weeks, this tiny structure must undergo a remarkable transformation to reshape itself into the complex organ that eventually pumps blood throughout the body.

For scientists studying heart development, there is a challenge: We cannot directly observe this process as it unfolds in a developing human embryo. For decades, researchers have turned to animal embryos to study early heart development. However, the genetic and physical signals that guide heart development can differ between animals and humans.

Now, researchers have built a human-based model that brings this difficult-to-study stage of development into the laboratory. A multi-university team led by Dr. Vahid Serpooshan, director of the Center for Innovation in Congenital Heart Disease at UTHealth Houston’s McGovern Medical School, used 3D bioprinting with multiple types of human cells to model the developing heart. The printed model recreates key features of the early-stage developing heart tube, including its layered structure.

In addition to replicating the structure of an early heart, researchers recreated one of the most important physical forces acting on the developing heart: fluid flow. The printed heart tube has a hollow interior through which a liquid containing what the cells need to survive and grow can be continuously circulated. This allowed the researchers to study the cells in a dynamic environment rather than on a flat laboratory dish, where many of the physical cues present during early heart development are missing.

Incorporating that flow turned out to be crucial. When the heart-tube models were exposed to fluid flow, the tissues became more organized and their cells beat in a more coordinated way. The fluid moving through the tiny heart tube did not simply carry nutrients around; it also provided physical signals that guided cell development. The researchers observed that cells exposed to flow matured further and took on more specialized roles.

Dr. Serpooshan  said in a department news post: "We are moving beyond simply observing development—we are beginning to recreate it." This matters because congenital heart defects can arise when the complex sequence of events involved in early heart development goes wrong. A human-based model that allows researchers to control the cells, 3D structure, and mechanical environment has the potential to provide a new way to investigate these processes in the lab, helping researchers explore potential therapies for developmental heart disorders without the use of animals.

It may be tiny, but this 3D-printed heart tube offers something that traditional flat cell cultures and animal experiments cannot provide: a window into the earliest stages of human heart development, built from human cells and shaped by the physical forces that guide a developing heart.

Lakshmi Menon is a PhD research candidate in Pharmaceutical Sciences and Technology at the Institute of Chemical Technology, Mumbai, India, and a SciComm Catalyst program participant. Her research focuses on 3D bioprinting and organ-on-chip models as human-relevant approaches for drug and cosmetic evaluation. Through her science communication work, she aims to bridge the gap between advances in animal-free research and the audiences who can benefit from them.