Med-Tech Innovation Nanotechnology
their biocompatibility.5
Devices with a certain degree of
nanoscale roughness function better in vitro than those with smooth or microrough surfaces.6,7
In addition,
nanostructured materials show superior mechanical, electrical, magnetic, optical and biomechanical properties compared with micron-sized materials.8
Focus on porous polymers
Many biological systems display self-organising patterns, including the physiological development of living organisms as they grow.9
Biomimetics is the study
and development of synthetic systems that imitate biological structures and processes. Work on porous polymers developed by CRANN is aimed at exploiting self-organisation biological principles with the ambition of influencing much broader technological applications (Figure 2). Modern techniques have allowed us to use complex scientific methods to examine and produce features of ever decreasing dimensions, however, direct material machining approaches face increasingly significant challenges. The requirement for complex, patterned and controlled three-dimensional structures enforces strict design criteria that result in ever increasing energy and monetary costs. Nanomaterials differ in their production from conventional materials because they are preferably manufactured by a “bottom-up” additive process, as opposed to a “top-down” subtractive approach, as seen with traditional manufacturing techniques.10
This has led
scientists to look to nature for ways to solve the problem of complex top-down approaches by seeking to mimic self-organising mechanisms observed throughout the natural world.
New coatings for medical devices are continuously being developed. These have lead, for example, to improvements in implant technology through the design and development of drug eluting stents; however, problems have arisen. Coatings that allow drugs to be embedded can have adverse drug interactions, incomplete stent apposition and increased in-stent thrombosis rates.11
A solution could come in the form of
nanopatterned coatings that would lie beneath the drug eluting external layer. A porous polymer superhydrophobic coating could help to repel biomolecules and cells, thus leaving the stent clear and free from clotting.
Applications Porous polymers have the potential to deliver new biocompatible nanodevices or nanotemplates for medical applications. Creating 2D and 3D ordered porous polymer films is of great interest in the biomedical field,12
where
they enable a variety of applications, including: • drug infused films to treat wounds, or as surface coatings on heart stents or catheters
• transdermal drug delivery • hydrophobic surfaces capable of repelling liquids • tissue scaffolds to promote cell growth • coatings that have the ability to elicit positive cell behaviours, depending on the use of the coated medical device (Figure 3).
A study published in 2011 has used nanopores to test 14 ¦ November/December 2011
Figure 3: Microspheres on structured film. The polymer substrate is made using the self-organisation technique described herein. The SiO2 spheres are positioned extremely close, but not touching, which is essential for observations of photonic coupling between the spheres. This work was part of a collaboration between the groups of Professor John Boland and Professor John Donegan. Image supplied by Dr Ronan Daly
www.med-techinnovation.com
and measure how proteins move into a cell nucleus.13 This type of work can be used to look at how our innate natural systems select proteins to interact with, and could be used as a test platform for drug delivery studies. Currently, many ordered porous polymer surface production methods require costly, complex, multistage processing. For example, a multistage production method may utilise microspheres as a pore template followed by solvent washing to reveal the pores. This technique is limited in its control in terms of the total porosity and pore geometry, due to the use of a solid template. Other techniques use thermally induced phase separation, where after freeze drying, a highly porous but disordered product remains.
Figure 2: Scanning electron microscopy image of ordered porous polymer surface
Images supplied by Dr Ronan Daly
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