Free Newsletters - Space News - Defense Alert - Environment Report - Energy Monitor
. Medical and Hospital News .




INTERN DAILY
Biomedical applications of shape-memory polymers: How practically useful are they?
by Staff Writers
Beijing, China (SPX) Apr 29, 2014


This is a schematic presentation of generalized shape-memory polymer architecture. Image courtesy Science China Press. For a larger version of this image please go here.

Polymers that exhibit shape-memory effect (SME) are an important class of materials in medicine, especially for minimally invasive deployment of devices. Professor Subbu Venkatraman and his group from School of Materials Science and Engineering, Nanyang Technological University presented a review article surveying the clinical applications of the SME and addressing critically the question of its utility in implantable devices.

Their work, entitled "Biomedical applications of shape-memory polymers: How practically useful are they?", was published in SCIENCE CHINA Chemistry.2014, Vol 57(4).

The shape-memory effect, as exhibited by metal alloys such as nitinol as well as many polymers, is the ability of a material to change its dimension in a predefined way in response to an external stimulus.

For the many medical implants that can be deployed in the body using minimally invasive means, the implant dimension should be small during deployment and must regain a larger shape after deployment. Examples of such devices include stents, heart valves and septal defect occluders.

As the range of available materials expands, so will the range of applications. Although the filed has been long dominated by one single material, nitinol (an alloy of nickel and titanium), polymers are challenging this dominance because they offer more functionality than simple ease of deployment.

For instance, a polymer that exhibits the SME could be biodegradable as well as drug-eluting, two functions that are impossible to achieve with nitinol. Thus, a biodegradable implant made of SMP loaded with therapeutic agent could be compressed and delivered inside the body, still in its compact form, via minimally invasive surgery.

Once the implant is placed in the targeted site, it can be simultaneously recovered to its larger primary shape (triggered by body heat or other means) and one or more drugs can be released from the SMP matrix.

Finally, the implant degrades, which eliminates the need for a second surgery for explanation. Developing this novel concept into practice has engaged the attention of researchers from both academia and industry, as reflected in the rapidly increasing number of publications on SMPs since 2003.

Over the past decade, various types of SMPs have been developed. A generalized SMP architecture is depicted in figure below. Based on this diagram, SMPs can be typically broadly categorized by their stimulus into two main streams: thermally and athermally induced SMEs. A thermoresponsive SMP can be thermally actuated by increasing the environment temperature above its thermal transition by either direct or indirect (i.e. magnetic or electrical) heating. Athermoresponsive SMP, however, can be actuated by stimuli other heat (e.g. light and solvent).

Despite of the numerous SMPs being developed, the kinetics of shape recovery is one of issues needed to be addressed to accelerate the rate of translation of the concept to approved products. Stent is one of the main targets for SMPs development in medical devices.

For instance, a laser-actuated SMP stent prototype fabricated from polyurethane was developed by Baer et al. The stent was crimped over a fiber-optic light diffuser coupled to an IR diode laser for photo-thermal actuation of the stent. Under zero flow condition, the stent was fully recovered / expanded within 6 minutes in vitro. In general, the speed of recovery is more important than the extent of recovery for SMP stents.

The crimped (or sheathed) stent must recover to anchor itself in the vessel within 1-2 min. Therefore, options such as water-induced or light-induced SMEs are not the best options for stents. Generally, the SMP stents based on nitinol are pre-recovered but constrained in a sheath until deployment at the site by slow sheath removal. This is the best way to meet the rate-of-recovery requirements.

Another issue to be addressed is sterilization for SMP-based medical devices. All medical devices must undergo sterilization before they can be used clinically. Conventional methods of sterilization listed in the US FDA guide include exposure to steam, ethylene oxide (EtO), irradiation (gamma or e-beam) and plasma treatment. Virtually all methods have their own merits and disadvantages, depending on the mode of SME activation that is envisaged.

Therefore, identifying an appropriate process that can achieve the required sterility without compromising the SMP properties is challenging. In general, autoclave (steam) sterilization is not suitable for use with thermal SMPs due to its high temperature range, which can delete the shape-memory effect and also damage drugs that are embedded within the polymer matrix.

By far, EtO sterilization is the gold standard of the low-temperature sterilization methods. Numerous research teams have studied the impact of EtO sterilization of various polymeric materials and have obtained promising results, with maintenance of the shape-memory effect.

However, due to moisture ingress during EtO sterilization due to the high humidity levels usually employed, this method is not suitable for water-activated SMPs. Currently, unconventional low-temperature sterilization methods are under development such as noxilizer (room temperature NO2-based sterilization technology) and dense carbon dioxide gas sterilization.

Both techniques can be performed at even lower temperatures (25-34 C) than the conventional sterilization methods. This possibility would eliminate any potential for premature activation of SME during sterilization, even when the activation temperature is at body temperature.

Overall, SMPs are an important class of materials in medicine. Nevertheless, we find that the rate of translation of the concept to approved products is extremely low, with mostly nitinol-based devices being approved. Further success will depend upon overcoming the problem of shape-memory loss during storage and sterilization, as well as upon improving the kinetics of shape recovery.

Wong Y S, Kong J F, Widjaja L K and Venkatraman S S. Biomedical applications of shape-memory polymers: how practically useful are they?. SCI CHINA Chemistry, 2014 Vol. 57 (4): 476-489

.


Related Links
Science China Press
Hospital and Medical News at InternDaily.com






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News





INTERN DAILY
Building 'Smart' Cell-Based Therapies
Chicago IL (SPX) Apr 22, 2014
A Northwestern synthetic biology team has created a new technology for modifying human cells to create programmable therapeutics that could travel the body and selectively target cancer and other sites of disease. Engineering cell-based, biological devices that monitor and modify human physiology is a promising frontier in clinical synthetic biology. However, no existing technology enabled ... read more


INTERN DAILY
Nepal counts cost of damaging Everest debacle

Italy cruise ship removal project halted: media

Captain says warnings over Korean ferry ignored

How costly are natural hazards?

INTERN DAILY
Glonass Failure Caused by Faulty Software

Homegrown high-precision positioning system put to use

Russia eyes building Glonass stations in 36 countries

Turn your satnav ideas into business

INTERN DAILY
Genomic diversity and admixture differs for Stone-Age Scandinavian foragers and farmers

British designer Heatherwick seeks cities with 'human scale'

Prehistoric caribou hunting site discovered under Lake Huron

It's a bubble, but not as we know it

INTERN DAILY
Iconic Galapagos bird suffering population decline

Australian marine reserves provide safe passageway for endangered species

How a fish can fry

Important migratory corridor for endangered marine species off north-west Australia

INTERN DAILY
Mystery of the pandemic flu virus of 1918 solved by University of Arizona researchers

Two antibodies show promise blocking MERS virus

Decrease in large wildlife drives rodent-borne diseases

Re-Emergence of Ebola Focuses Need for Global Surveillance Strategies

INTERN DAILY
Church demolition illuminates China's religious tensions

US lawmaker urges China to expand religious freedoms

Most back to work after China shoe factory strike

China offers cash in Xinjiang for tips on beards: report

INTERN DAILY
Vietnam says 7 killed in shooting on China border

Kidnappers demand $11 mln for Chinese tourist

Malaysia kidnappers telephone Chinese victim's family

China presses Malaysia to rescue kidnapped tourist

INTERN DAILY
China poised to overtake US economy: World Bank ranking

US economy slows to a near-stall in first quarter

China house price increases slow in April: survey

Fujitsu swings back into the black




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.