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'Smart' biomaterials for drug delivery, biomedical applications

June 14th, 2011 By Eugene Low

First-of-its-kind hydrogel and new mix-and-match block copolymer 'smart' biomaterials for drug delivery and biomedical applicati — Photograph illustration of the hydrogels formation controlled by pH as it changes from solution (a) to hydrogel at pH 12 (b) to compact hydrogel with time (c). The process can be stopped and restored by adjusting pH to 7 and 12 respectively (b*). Credit: IMRE

Researchers from Institute of Materials Research and Engineering (IMRE), an institute of Singapore’s Agency for Science, Technology and Research (A*STAR) have invented new ‘smart’ biomaterials including a unique hydrogel that has an on-off switch to precisely control its density and a new modular block copolymer that can be tailored to be triggered by specific temperatures.

1. Singapore, 13 June 2011 - Medical ointments that could be thick outside the body but be made less dense for use in the body. Easy-to-make, new drug delivery vehicles that can be triggered multiple times at different temperatures. Science fiction? Not anymore. Researchers from A*STAR’s IMRE have developed two new ‘smart’ biomaterials that can be used for unique drug delivery and biomedical applications.

2. One of the new ‘smart’ biomaterials that IMRE scientists have developed is the first ever hydrogel with a gelation process that can be started, stopped and resumed at any time, which cannot be done with any of today’s hydrogels. These special properties mean that a single hydrogel can now be used in many different applications, for instance thicker for use as ointments outside the body or thinner for delivering drugs inside. The revolutionary hydrogel gelation process creates a single hydrogel that can vary in thickness, shape and size. More importantly, the gelation process, or change in hydrogel density, can be precisely controlled and turned on and off by specific pH levels. This means that one hydrogel dose could be loaded with different drugs that could be released at different densities at different pH levels, which are conditions that could happen on sweaty versus non-sweaty skin, or in the oral cavity versus the stomach, for example.

3. “As far as we know, we are the first ones to have this degree of control in a hydrogel system,” said Dr. Liu Ye, the IMRE scientist who heads the research. “It is difficult to control the cross-linking degree, or how viscous the hydrogel can get in other methods once the reactions have started.” The importance of the innovation is that it can be exploited to prepare ‘block’ hydrogels, micro-/nano- hydrogels, hydrogel fibres and capsules incorporating active agents for drug delivery, tissue engineering and other biomedical applications. Hydrogels are a unique class of materials with cross-linked polymer chains that can hold large amounts of water. They are currently used to make contact lenses, wound dressings and used in a host of other biomedical applications.

4. The other discovery by IMRE scientists is a novel way to make temperature-sensitive block copolymers that allows researchers to create new biomaterials by combining different block copolymers, much like mixing and matching LEGO toy building blocks. The newly created supramolecular block copolymer is made up of multiple chemical sequences, or blocks, arranged in an alternating series of two or more different chemical blocks. The uniqueness of IMRE’s block copolymers are the mix-and-match options that allow many new properties to be manifested through a combination of different polymers in such block structures. The scientists have already created a new block copolymer that can be triggered to change its nanostructure in two stages at different temperatures so that different active contents such as medicines can be released at those specific temperatures.

5. “Our new block copolymers are special as we can change the combination of its components to make many different block copolymers just like how LEGO blocks are used,” said Dr. Li Jun, the IMRE senior scientist whose team has already demonstrated a temperature-sensitive polymer that can be triggered not once but twice, and at different temperatures. Added Dr. Li Jun, “Such a polymer allows us to create new smart controlled release tools for medicines, where multiple drugs could be incorporated into the polymer and released stepwise at different locations where the temperature is different.” Block copolymers have many potential applications in pharmaceuticals, biomaterials, consumer care and cosmetics.

6. The research paper about Dr. Liu Ye’s new method, “‘Living’ Controlled in Situ Gelling Systems: Thiol−Disulfide Exchange Method toward Tailor-Made Biodegradable Hydrogels” was published in the Journal of the American Chemical Society. Dr. Li Jun’s work on block copolymers, “Self-Assembly and Micellization of a Dual Thermoresponsive Supramolecular Pseudo-Block Copolymer” was featured recently in the journal Macromolecules as one of its top ten most read articles for the first quarter of 2011.

Provided by Agency for Science, Technology and Research (A*STAR)

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