A cross-disciplinary team has discovered that nanodiamonds (NDs) may be a highly effective agent in battling oral infections, a discovery which could open up new opportunities for improving oral health worldwide and provide a real alternative to the customary antibiotics route. Dental caries effect approximately half the world’s population – about 3 billion people – and can lead to a variety of other problems including Alzheimer’s, obesity and cardiovascular diseases, as well as having farreaching financial implications. The path to discovery began when Dr Chu Zhiqin, Assistant Professor of the Department of Electrical and Electronic Engineering and Dr Prasanna Neelakantan, Clinical Assistant Professor in Endodontology, began discussing the possibilities for NDs and joined forces to be co-principal investigators in the study. “We had noticed that a lot of work had been done using NDs in cell suspensions, but surprisingly, we couldn’t find any trail in biofilms,” said Dr Chu. “As Dr Neelakantan is an expert working in this direction, we decided to give it a try and see what’s going on there.” Dental caries is caused by a dominance of acid-producing bacteria – particularly Streptococcus mutans – that form biofilms on the surface of the teeth, while periodontal disease, commonly known as gum disease, is induced by Porphyromonas gingivalis, a Gram-negative bacterium. “Microbes demonstrate high resistance to conventional antibiotics, and there has been little significant development in therapeutic drugs for fighting fungal infections, another major infection affecting human beings. In fact, patients with COVID-19 have been shown to have an increased prevalence of fungal infections,” said Dr Neelakantan. Battling biofilms The team’s work using high-pressure hightemperature NDs to inhibit the formation of oral pathogenic biofilms, may change all that. The research, which has been published in Biomaterials Science, shows that the NDs are effective against both the free-floating cells (planktonic cells) and the attached cells (biofilm) of bacteria and fungi that frequently cause oral and systemic infections, and that they can also disrupt preformed biofilms in certain orally and systemically important organisms. “Our study provided the first laboratory evidence that a simple coating of According to Dr Neelakantan, the team’s next aim is to “develop a cost-effective, multifunctional coating on both natural (for example, teeth) and artificial dental substrates (for example dentures or implants, both of which often fail due to infections, especially in the elderly population).” Preventative measure The implications are that NDs could be used globally as a preventative measure against caries. “We envision a coating that can simply be placed on teeth or on prosthesis including dental fillings,” he continued. “Currently, dental fillings fail because bacteria grow on them and in-between the filling and the tooth. Because of this, the average life of these fillings is currently not more than five years and this represents a huge financial burden for patients.” nanodiamonds can inhibit the formation of attached communities of bacteria and fungi. These attached communities are called biofilms and it is shocking to know that at least 70 to 80 per cent of human infections are caused by biofilms,” said Dr Neelakantan. “Most pathogens are resistant to almost all antibiotics. So, in terms of impact for biomedical applications, this is significant because we are introducing an inexpensive, simple, non-antibiotic strategy.” Synthesising NDs using high-pressure hightemperature methods is one of the leading approaches for fabricating NDs on a large scale. “In general, the resulting nanomaterials have a lot of unique features which are missing in their bulk counterpart,” said Dr Chu. “We attributed the effects of NDs to their hardness, irregular shapes, faceted surfaces, etc, all of which lead to the destructive results in biofilms.” “Similarly, we would expect to investigate the effects of NDs as an anti-pathogen coating or spray in different environments. This is particularly important for tackling the current challenge of the pandemic.” As far as costs go, NDs are a viable proposition. “NDs are very cheap (approximately USD10 per gram), and this is one of the most attractive features for practical applications,” said Dr Chu. Asked where does the research go from here, Dr Chu said: “Our next step is to carry out a systematic study of how the properties of NDs, including their surface chemistry, shapes and other parameters may affect the interaction with biofilms.” Nanodiamonds could be key to finding an alternative to the usual antibiotics strategy for battling oral infections. DIAMONDS ARE A TOOTH’S BEST FRIEND Co-principal investigators of the study – Dr Prasanna Neelakantan (left) and Dr Chu Zhiqin (right). This study provided the first laboratory evidence that a simple coating of nanodiamonds can inhibit the formation of attached communities of bacteria and fungi. This image depicts the biofilm inhibition in oral pathogens by nanodiamonds: bacteria can’t stick to the substrate covered with nanodiamonds, and biofilm only forms in the substrate without any nanodiamonds. DR PRASANNA NEELAKANTAN Most pathogens are resistant to almost all antibiotics. So, in terms of impact for biomedical applications, this is significant because we are introducing an inexpensive, simple, non-antibiotic strategy. 24 RESEARCH The University of Hong Kong Bulletin | May 2022 25
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