A breakthrough technology uses sunflower pollen to produce 3D ink used for human-tissue engineering, drug delivery and toxicity testing.

In a new study, scientists developed an ink derived from sunflower pollen that holds its shape while remaining flexible. It offers an alternative to 3D printing inks used in the biomedical field, also known as bioprinting.

The NTU scientists tested their pollen-based 3D ink by printing a scaffold used to grow biological tissue. They found it supported both cell adhesion and growth, which are essential for tissue regeneration.

“Bioprinting can be challenging because the material of the inks used is typically too soft, which means the structure of the envisioned product may collapse during printing,” said co-lead author Cho Nam-Joon of the Nanyang Technological University (NTU) in Singapore.

“Through tuning the mechanical properties of sunflower pollen, we developed a pollen-based hybrid ink that can be used to print structures with good structural integrity,” Cho said. This novel use for pollen, described in Advanced Functional Materials, has potential as a sustainable and affordable alternative material to current bioprinting inks.

Use in cell cultures platforms

“Pollen microgel particles have a hollow shell structure, which means they could potentially be used to carry drugs, cells, or biomolecules in drug delivery platforms with customized 3D structures. We are now looking at how we can use these pollen microgel scaffolds for 3D cell culture platforms in various biomedical applications,” Cho said.

“Our findings could open new doors to customized flexible membranes that fit the human skin’s contours exactly, such as wound-dressing patches or facial masks,” said co-author Song Juha.

Scientists at NTU Singapore have found a way to use sunflower pollen to develop a 3D printing ink material that could be used to fabricate parts useful for tissue engineering, toxicity testing and drug delivery. (NTU Singapore)

Soft and flexible membranes are usually manufactured based on flat geometry, resulting in problems such as fractures in the layers or a poor fit when applied on large surface areas of skin or areas that see frequent movement, like the joints.

“Using our pollen-based 3D printing ink, which is biocompatible, flexible and low in cost, we can fabricate membranes that are tailored to the contours of the human skin and are capable of bending without breaking,” said Song.

Previous research sought to develop bio-inks that mixed hydrogels (a polymer that can hold water) with fibers or particles to ensure printability. Hydrogel composite inks, however, clog printer nozzles, said the study’s authors.

“The pollen-based hybrid ink we have developed, in contrast, is mechanically strong enough to retain its structure without jamming the printer,” Song said.

Pollen-based scaffold for cell culture and drug delivery

The scientists printed a five-layer tissue engineering scaffold for culturing cells and added collagen to provide anchor points for cell adhesion and growth. When they seeded human cells on the scaffold, it had a high cell-seeding efficiency of 96 percent to 97 percent.

The researchers also tested their 3D scaffold as a drug delivery system. When a fluorescent red dye was dripped onto the scaffold, the pollen microgel particles released it into the scaffold gradually. The amount and rate of release increased with the addition of an acid, thus showing the scaffold’s potential as a controlled-release drug delivery system.

The soft and flexible pollen microgel particles can be used as a recyclable support matrix in freeform 3D printing in which soft ink is used. After curing inside the pollen microgel, the printed 3D silicone rubber mesh could adapt to the human elbow curvature. (From “Engineering Natural Pollen Grains as Multifunctional 3D Printing Materials” in Advanced Functional Materials)

“There is also potential for the pollen-based scaffold to be used as a smart drug carrier, given pollen’s stimulus-responsive nature. For instance, we can further slow down the release of drugs by coating the pollen-based scaffold with a thin layer of alginate and stimulate the release by introducing an acid,” said Cho.

Pollen-based support structure for soft 3D printing inks

The authors found the soft and flexible pollen microgel particles can be used as a recyclable support matrix in freeform 3D printing in which soft ink is used. This prevents the collapse of the printed structure as the ink cures. To test the concept, they fabricated a 3D printed silicon rubber mesh for the human elbow using pollen microgel as the support to retain the mesh’s shape as it printed.

The scientists found that after curing inside the pollen microgel, the printed 3D silicone rubber mesh could adapt to the human elbow curvature. They also found that the mechanical properties of the silicone rubber samples printed and cured in the pollen microgel supporting matrix were similar to samples fabricated via the traditional casting method.

“Given that there are numerous types of pollen species with distinct sizes, shapes and surface properties, pollen microgel suspensions could potentially be used to create a new class of eco-friendly 3D printing materials,” Cho said.

Edited by Fern Siegel and Kristen Butler

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