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Pencil Plasma Device Brings Hopes of Healing Critical Bone Defects

For the first time, the direct application of non-thermal atmospheric plasma has been shown to induce positive therapeutic effects by promoting bone regeneration.

The incidence of bone fractures in those over 50 years old is 116.5 per 10,000 people. While most cases of fractures heal by restoration of the alignment and stable fixation of the fracture, roughly 5 per cent of cases fail to heal resulting in non-union, which can cause long-term pain, physical disability, and other consequences. To enhance fracture healing capacity, scientists have innovated numerous biophysical and biological therapeutic approaches such as the use of electromagnetic fields and parathyroid hormone respectively.

Recently, technological advancements have enabled scientists to generate plasma at room temperature and at ambient atmosphere in what is called non-thermal atmospheric pressure plasma (NTAPP). Studies have shown that plasma treatment in biomaterials has the potential to improve bone and cartilage regeneration. Going one step further, scientists from the Graduate School of Medicine and the Graduate School of Engineering at Osaka City University have applied the therapeutic properties of this “fourth state of matter” to bone regeneration using a pencil-type NTAPP in animal bone defect models.

“NTAPP is considered a new therapeutic method as it has been shown to accelerate cell growth when applied at low enough levels,” stated first author Akiyoshi Shimatani. In an ambient atmosphere, it can generate highly reactive oxygen and nitrogen species (RONS) that can be directly exposed to biological targets like cells and tissues.

While previous indirect treatments have shown the potential advantages of plasma in supporting the creation of stem cells that cause reactive oxygen species generation and in inducing osteogenic differentiation and bone formation, the team noted that there were no reports on directly using NTAPP for bone fracture therapy. Therefore, the researchers seized the opportunity to innovate a pencil-type plasma device that can “generate and deliver RONS to areas of the bone defect ‘effectively’,” as explained by Jun-Seok Oh, professor at the university’s Graduate School of Engineering and advisor to the study, effectively facilitating direct exposure.

To determine the optimal irradiation conditions, the team tested the pencil-type plasma device on an animal model with a well-established critical bone defect. They compared groups that were irradiated with NTAPP for 5, 10, and 15 minutes to control groups where no plasma was administered. After eight weeks, micro-CT images revealed that the 10-minute treatment time resulted in the most successful bone regeneration with 1.51 times larger bone volume than the control group.

“However, micro-CT images cannot determine whether a bone defect has been filled with a new bone, tissue, or both,” said Hiromitsu Toyota, associate professor at the Graduate School of Medicine and supporting author of the study. Consequently, the team also had to run a histological analysis before confirming that “bone defects in the groups treated with plasma were filled with new bone and there was no inclusion, such as fibre tissue and gap that was observed in the control group.”

As in all other therapeutics, the biological effect of plasma is highly dependent on the treatment dose delivered into the targets. Although future research will be needed to clarify why the 10-minute treatment period best-supported bone regeneration, scientists speculate that something akin to surface wettability may be an important factor as it promotes greater cell spreading and adhesion to biomaterials and implants.

“We wondered if something similar was occurring where we saw a strong regeneration of new bone and we found that compared to the control group, bone surface of the plasma-treated group as statistically and significantly more hydrophilic,” explained Hiroaki Nakamura, professor at the Graduate School of Medicine and advisor of the study.

There is still much to be explored and understood in terms of treatment dose. However, this novel study has demonstrated, for the first time, the positive results of the direct application of room temperature, atmospheric plasma to a living body. The researchers are hopeful that their newly developed plasma device can be used during surgery to bring the bone regeneration effect of NTAPP to various medical fields. [APBN]

Source: Shimatani et al. (2021). In vivo study on the healing of bone defect treated with non-thermal atmospheric pressure gas discharge plasma. Public Library of Science (PLOS) One, 16(10), e0255861.