Ultralong Hydroxyapatite Micro-Tubes: Biomaterial with Potential in Dentistry



A new microtube array mimics the structure of your teeth – this new discovery could have significant implications for dental patients.

Researchers from the Shanghai Institute of Ceramics, Chinese Academy of Sciences  (Shanghai, China) prepared hydroxyapatite – Ca10(PO4)6(OH)2 – in the form of three-dimensional highly ordered microtube arrays with large sizes in the millimeter scale.

This material reproduces closely the structure of tooth enamel; because of this, it has great potential for use in dentistry for tooth repairs.

Hydroxyapatite – HAp

Hydroxyapatite – Ca10(PO4)6(OH)2, HAp – is a calcium phosphate compound with very important applications in the biomedical field. HAp is in fact the main component of human bones and teeth, and is highly biocompatible; because of this, we use synthetic HAp to make bone implants, as well as synthetic teeth enamel and pastes.

Reproducing the Structures of Teeth and Bones

Researchers have produced synthetic HAp with a number of methods and in different forms, which include thin films deposited on metallic surfaces and nanopowders.

To achieve the best functional properties, the structure of synthetic HAp should be as similar as possible to that of teeth and/or bones. Teeth, for instance, consist of HAp organized in the form of crystallites all aligned in the same direction and with dimensions in the millimeter scale; bones also possess an ordered structure.

Because of this, scientists tried to prepare HAp with these structural characteristics. This feat, however, was not easy. In order to prepare tube-structured HAp, for example, researchers must make HAp tubes longer than 100μm which is a great challenge.

Building New Teeth: Researchers Develop New Method

Scientists of the Shanghai Institute of Ceramics, Chinese Academy of Sciences achieved important innovations in this field; they developed a new method which allowed them to prepare three-dimensional bulk biomaterial made of highly ordered HAp microtube arrays with dimensions in the millimeter scale. Their results were published in Chemistry – AEuropean Journal on the 17th of April 2014.

This research group already has experience in HAp preparation and use; in fact some months ago, they presented a work about a new HAp-based paper, which was flexible, fire resistant and which could be used for both printing and writing.

Solvothermal Synthesis

Professor Ying-Jie Zhu, leading scientist of this research, explains to Decoded Science their research work:

“As HAp is a member of the calcium phosphate family,we need a chemical reaction between a calcium salt and a phosphorus saltto prepare it. In our case, the calcium compound was calcium oleate, which is a calcium salt of oleic acid (see the formula in the Figure).

The reaction to form highly ordered HApmicrotube arrays was performed using the solvothermal method. This is based on the chemical reaction(s) in an autoclave – i.e. at high temperature and pressure – but using a solvent different from water or mixed solvent. In our case, we adopted the solvothermal reaction between the calcium oleate, pressed in form of a 1 cm diameter pellet, and sodium dihydrogen phosphate (NaH2PO4·2H2O). We used mixed solvent of ethanol and water, and carried out the reaction at 180 oC in a Teflon-lined stainless steel autoclave.

SEM micrograph of HAp microtubes. The inset shows a single microtube. Photo by Ying-Jie Zhu.

SEM micrograph of HAp microtubes. The inset shows a single microtube. Photo by Ying-Jie Zhu, used with permission, all rights reserved.

Highly Ordered Tube-Structured HAp Arrays

The material prepared with this method has an oblate shape (like a flattened sphere) with 6 mm diameter. The array exhibits a core–shell structure with the shell composed of highly-ordered HAp microtube arrays.

According to Professor Zhu:

To the best of our knowledge,it is the first time that three-dimensional bulk biomaterial made of highly ordered HAp microtubearrays with dimensions in the millimeter scale has been prepared.”

The structure of the material is visible in the picture on the side. You can see that the ultralong HAp microtubes as the building blocks are self-assembled to form highly ordered arrays with sizes reaching the millimeter scale.

Tooth Enamel: New Potential Applications

“HAp with this highly ordered structure closely mimics the morphology of tooth enamel” Professor Zhu told Decoded Science, “it can, therefore, have a promising application in dentistry. Potentially, however, this material can also be used in other biomedical fields, bone defect repairs, for instance, could also be performed with this highly ordered ultralong HAp microtube material.”

This new technology could mean big things for the medical and dental industry – and for patients as well.

© Copyright 2014 Clara Piccirillo, PhD, All rights Reserved. Written For: Decoded Science

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