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Type III is the most common. [Image: Stanford Ear Institute]

Unilateral microtia is a congenital deformity that impacts the function and shape of the ear, and according to the Stanford Ear Institute, it’s estimated to occur in roughly one out of every 5,000 live births, depending on ethnicity. The condition causes an undersized and malformed outer ear due to structural abnormalities, and can even result in hearing impairment; the prevalence for microtia in higher in Andean, Asian, Hispanic, and Native American populations.

Treatment options typically involve reconstructive surgery, and 3D printing technology has also been helpful in treating the condition, particularly when it comes to making accurate, 3D printed models of ears, which can be used to manufacture patient-specific implants. Now, a team in China has released a new study that details their work in using 3D printing and cultured cells to grow new ears for five children with microtia. Even more exciting, they are reportedly the first to receive ear implants made from their own cells.

Lawrence Bonassar, a professor at Cornell University who was not involved in this study but has previously studied 3D printed ears in microtia patients, said, “The delivery of shaped cartilage for the reconstruction of microtia has been a goal of the tissue engineering community for more than two decades.

“This work clearly shows tissue engineering approaches for reconstruction of the ear and other cartilaginous tissues will become a clinical reality very soon. The aesthetics of the tissue produced are on par with what can be expected of the best clinical procedures at the present time.”

Preparation of the patient-specific ear-shaped scaffold.

The results of the study were recently published in a paper in EBioMedicine. In the study, which followed the children for up to 2.5 years post-op, the researchers wrote:

“In summary, we were able to successfully design, fabricate, and regenerate patient-specific external ears. The first clinical study of translating the well-known human-ear-shaped cartilage from nude mouse to human may represent a follow-up significant achievement in the field of tissue engineering after its original experimental study (Cao et al., 1997). Nevertheless, further efforts remain necessary to eventually translate this prototype work into routine clinical practices. In the future, long-term (up to 5 years) follow-up of the cartilage properties and clinical outcomes after complete degradation of the PCL inner core will be essential. In addition, further optimization and standardization in scaffold fabrication, cell expansion, in vitro cartilage engineering, surgical procedures, as well as multi-center clinical trials would also be the targets for the future investigations. 3D bioprinting (print with cells) for direct fabrication of ear-shaped cartilage may also be a future direction (Kang et al., 2016).”

For years, medical researchers have been experimenting with using a person’s own chondrocytes (cartilage cells) and a structural scaffold to create functional ear replacements, so the concept behind the study is not a novel one.

“Surgeons have been toying with the idea of removing cartilage tissue from a patient and distilling that tissue into individual cellular components and then expanding those cellular components. In other words, having the cells divide so you have a bigger piece or more cells to make a new part with,” explained Dr. Tessa Hadlock, the chief of facial plastic and reconstructive surgery at Massachusetts Eye and Ear in Boston, who was not involved in this study.

“The thing that is novel about this is that for the first time, they have done it in a series of five patients, and they have good long-term followup that shows the results of the ears that were grown from that harvested cartilage.”

Progress of the study’s first patient after receiving an autologous cartilage implant. [Image: Zhou et al., EBioMedicine, 2018]

The study involved five children with unilateral microtia: a 6-year-old girl, a 9-year-old girl, an 8-year-old girl, a 7-year-old boy, and a 7-year-old girl. The researchers first took detailed CT scans of each patient’s healthy ear, and used 3D design software to mirror the images and convert them into a 3D printable mold, which was cast with porous, biodegradable PGA material; rigid PCL reinforced the core of the scaffold.

Next, cartilage-producing chondrocyte cells were derived from each patient’s malformed ear tissue, seeded onto the scaffold molds, and cultured for three months. Thanks to a diet of growth factors, the chondrocyte cells started to form elastin fibers and collagen within the PGA lattice. As the cell matrix for each ear continued to grow, the PGA slowly degraded, so by the time the three months were up, each implantation-ready ear was composed mainly of the patient’s native tissue.

A flowchart depicting the ear reconstruction process using in vitro, tissue-engineered human ear-shaped cartilage. [Image: Zhou et al., EBioMedicine, 2018]

When the cultured cartilage framework had finished growing into the shape of the patient’s ear, plastic surgeons carefully implanted the engineered ear implants and performed ear reconstruction surgery.

Patient one, the 6-year-old girl, was monitored for 2.5 years post-implantation, and during that time period underwent multiple cosmetic adjustments. In each one, the surgeon removed tiny tissue samples, which showed that the chondrocytes were still healthy and producing cartilage that was similar to a natural ear. She has not suffered any serious side effects and has a realistic-looking ear; in addition, the only artificial substance that’s still in the engineered ear implant is, as intended, a part of the PCL core. However, the long-term integrity of the ear, as this core continues to degrade until is completely gone by the fourth year, is still unknown.

The other four patients showed less consistent results. Four showed cartilage formation six months later, and only three of the new ears had angles, shapes, and sizes that matched the healthy ear. In addition, two of the engineered ears were slightly distorted.

While the researchers describe their results as “a significant breakthrough” in the field of reconstructive medicine, several challenges still remain before this approach can be widely used, including scaling up the treatment and bringing down the cost.

“The main challenges for the widespread use of this particular approach for microtia are manufacturing and regulatory surveillance. The method for making these constructs is quite complicated, involving three distinct biomaterials that are combined into a scaffold, seeded with cells, then cultured for three months before implantation to ensure proper cell distribution throughout the construct,” Bonassar said.

“Secondly, the materials that are used for these scaffolds remain in the body for a long time: up to four years. Such implants would likely need to be monitored for four or five years before the ultimate fate of these materials in the body is known.”

The patients will continue to be monitored for a total of five years.

Discuss this and other 3D printing topics at 3DPrintBoard.com or share your thoughts below. 

[Source: CNN]

 

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