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Sterilization modalities for medical devices include ionizing radiation (gamma or electron beam), ethylene oxide (ETO), autoclaving (high temperature), and gas plasma. Gamma and ETO sterilization are the most popular techniques. Gamma has the advantage that devices can be sterilized in conventional packaging, and hidden surfaces in the devices can be reached by gamma. Gamma has the disadvantage that it can chemically alter some materials, such as some polymers, which may result in property changes. ETO does not have the issue with chemical modifications of most materials, but does involve the use of gas-permeable packaging. Additional ETO is a carcinogenic chemical, and residues must be carefully monitored following sterilization. Both ETO and gamma require custom facilities to perform the sterilization, which involves shipping and quarantine times.

Autoclaving and gas plasma can both be done at manufacturer's facilities. Autoclaving is not suitable for most polymeric devices, as the temperatures used would result in device distortion. Gas plasma does not have this issue, but is limited to surface sterilization.

Vaporized peracetic acid (VPA) sterilization is an alternative method to gas plasma. In VPA, the peracetic acid, which is produced by reacting acetic acid with hydrogen peroxide, acts as a strong oxidizer, and is believed to denature protein and oxidize sulfide bonds. It can also disintegrate the cell walls of bacteria. Similar to gas plasma and ETO, VPA is a surface sterilant only. An advantage of VPA over ETO is the lack of toxic compounds. VPA can be safely performed in conventional manufacturing spaces, and requires less time to remove the sterilization by-products compared to ETO.

Cambridge Polymer Group was a sponsor for MIT's 6th annual Polymer
Day on March 30th, 2016. CPG scientists Gavin Braithwaite and Brian Ralston were judges at the poster contest, where MIT researchers presented their latest research.


MIT Polymer Day Website

US Patent 9,289,302 was issued on March 22, 2016 to CPG researchers. The patent describes designs and methods for making implants for focal cartilage tears in load bearing implants, such as hips and knees. The construct designs make use of a surgical procedure termed mosaicplasty, whereby a plug of healthy osteochondral plug is removed from a non-load bearing portion of the joint, and placed in a drilled out cavity in the focal defect. In this patent, synthetic plugs are created based on hybrid structures of polymers and metal repair the focal defects.

The FDA issued a draft guidance document on the required testing for devices using ultra high molecular weight polyethylene (UHMWPE) in February 2016. The guidance document separates UHMWPE into four categories: (1) conventional UHMWPE; (2) highly crosslinked UHMWPE; (3) Vitamin E stabilized UHMWPE; and (4) other forms of UHMWPE, including porous UHMWPE. In each category, test methods are suggested, including fatigue crack propagation, crystallinity assessment, oxidation index measurements, crosslink density, free radical concentration, radiation by-products determination, and antioxidant concentration. The guidance document indicates that some properties, such as mechanical characterization through tensile and impact strength, need to meet minimum threshold values indicated by ASTM F648, whereas other properties should be compared to results obtained from a predicate material.

Cambridge Polymer Group has extensive experience in testing UHMWPE to this guidance document. Contact us for more information. Additional information on UHMWPE characterization can be found on our website.


The draft guidance document is available for public comments for 90 days. Comments can be submitted here.

The FDA recently released a statement proposing a ban on most powdered surgical gloves in the United States. The powder, usually in the form of corn starch, is added to facilitate putting on the gloves and taking them off, as well as providing some comfort. The FDA's concerns about the powder stems from its use in latex gloves, which are known to cause an allergic reaction in some people due to the presence of latex proteins. A 1997 study by the FDA showed that the powder used in latex gloves can act as an airborne carrier for these latex proteins, as the latex proteins can bind to the cornstarch. The resulting aerosolized powder can lead to respiratory allergic reactions. The powder could also potentially get into wound sites and cause dermal allergic reactions.

The proposed ban is currently available for public comment for 90 days. Comments can be made at this web site.

Residual solvents can sometimes be found in pharmaceuticals after processing. These solvents are sometimes used during manufacturing to synthesize, purify or blend the active pharmaceutical ingredient (API) with excipients, or may be used elsewhere in the manufacturing process, from  solvents to clean equipment or solvents used in the packaging process. Often, these solvents can be hazardous if present in levels above a critical threshold. USP provides three levels of solvent classes based on their potential risk. Class 1 describes solvents to be avoided, which includes known and suspected carcinogens (examples include benzene and 1,2 dichloroethane). Class 2 describes solvents to be limited in their use, and includes nongenotoxic animal carcinogens and other significant but reversible toxicities (examples include chloroform, toluene, ethylene glycol) . Class 3 describes solvents with low toxic potential (examples include acetone, isopropyl alcohol, ethyl acetate).   USP provides permitted daily exposure (PDE) thresholds for the individual solvents in each class.  Other residual solvents, for which no adequate toxicological data is available, are also discussed.

Analysis of pharmaceutical compounds for residual solvents is normally performed by gas chromatography with mass spectroscopy coupled to either a flame ionization detector or a mass spectrometer, often with a head-space system used for sample introduction. This analysis requires the optimization of test conditions to ensure adequate separation of the various compounds in the chromatography column. Limits of detection and quantification, along with linearity, precision, and percent recovery are then determined for the specific solvent and matrix. Depending on the solvent and matrix, limits of detection can be as low as several parts per billion.

CPG regularly performs residual solvent analysis. Contact us for more information, or visit our web page.