additives feature | Antimicrobials
10,000,000 1,000,000 100,000 10,000 1,000 100 10 1
% silver ppm
Design considerations Since the material is integrated with the polymer, proactively identifying the required lifetime and utilizing the silver load efficiently can lead to greater efficacy over time and possibly lower costs. These are some of the design considerations and requirements that need to be taken into when making such plans. Lifetime - Agion branded antimicrobial technology is
ppb Metal ion
FigurE 1: CoMparing ThE ELEMEnTaL EFFiCiEnCy oF diFFErEnT METaL ions
35% 30% 25% 20% 15% 10% 5% 0%
0
engineered to last for the lifetime of the product due to the controlled delivery. Specific applications for medical devices will dictate the required amount of material to use in order to last the duration of the required lifetime of the medical device. Efficacy - what problem is the customer trying to
solve? Are there specific goals for efficacy, including specific targeted organisms and minimum efficacy requirements? Testing - Sciessent has a staff of material scientists
dissolving ag Controlled release ag
and microbiologists accustomed to developing prototypes and testing antimicrobial efficacy during development. Materials - what are the required materials with which the antimicrobial must be integrated? Cost constraints and goals - custom formulations
rapid depletion over time
specifically engineered for medical device applications are essential, balanced with the lifetime and efficacy goals. Colour considerations - Sciessent has developed
colour-stable antimicrobial grades. Marketing and regulatory considerations - An
antimicrobial partner should offer medical devices files and expertise in FdA and global registrations.
12 24 36
FigurE 2: dissoLving siLvEr CoMparEd To ConTroLLEd dELivEry hours
mrSA, as it is against susceptible strains, such as mSSA, because of its multiple modes of action. There are three types of silver antimicrobials
typically incorporated into polymers for medical devices. These include: controlled-release silver incorporated in a silicate structure (zeolite); silver zirconium phosphate; and, micro- or nano-scale particulate silver and silver compounds that are integrated in dissolving carriers like glass or salt. Although all silvers work in essentially the same manner, with silver ions being the active ingredient in all cases, the method of ionic delivery can be a key design consideration for medical device manufacturers. For some technologies, the silver release can be faster than desired as shown in Figure 2, leading to early depletion of the silver reservoir.
34 compounding world | February 2012 48
Getting to market As part of determining the safety of a medical device, biological testing is conducted to evaluate the potential toxic effects the device might have on the body. most regulatory bodies around the world recognize the international Standards organization’s (iSo) standard for biological evaluation of medical devices, iSo 10993. The standard consists of 12 parts; part one provides
guidance for selecting the tests to be performed. Several factors must be considered when choosing which biocompatibility tests are necessary and appropriate for a given device. The chemical character- istics of the device material, along with the intended use and duration of use of the device must be taken into account to ensure adequate evaluation of the device’s potential toxicity. when evaluating an antimicrobial device, additional
factors to consider are the effects of the antimicrobial technology, its mechanism of action and if there are any known potential toxic effects of the active ingredient. For example, additional testing for specific target organ
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depletion of silver reservoir
Minimum inhibitory Concentration (MiC) (ug/L)
ag+
hg++ Cu++ Cd++ ni++ Co++ au+
pb++ Zn++
al+++ Fe++ h+
Mn++ Mg++ Ba++ Li+
sr++ Ca++ na+ K+
nh4+
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