Sunday, August 14, 2016

Green Olympic Pool Chemistry

If you have watched the 2016 Summer Olympics in Rio, you have probably seen the diving pool which turned a mysterious green midway through the games. Athletes have complained that it was difficult to see in the murky water, and some complained of irritated eyes. The director of the Olympic venues at Rio finally indicated that someone had mistakingly added 160 liters of hydrogen peroxide to the pool, which neutralized the chlorine already in the pool. Subsequent algae growth resulted in the green color pictured above.

We were interested in this from a chemistry point of view. Chlorine is often used to disinfect municipal water, killing microorganisms in the water to make it potable. However, the chlorine itself could be unacceptable if the levels are too high. As a result, de-chlorination is often required before reintroduction of the treated water into the public water supply. And de-chlorination is often accomplished by the addition of hydrogen peroxide.

To disinfect water, chlorine gas can be added to water, and is hydrolyzed to form hypochlorous acid (HOCl). The hypochlorous acid can further ionize into hydrogen and a hypochlorite ion. The extent of the ionization depends on the pH of the water.

The hypochlorite is an oxidizer, which will oxidize bacteria, viruses, and fungi, thus killing these microorganisms.  Sodium hypochlorite (NaOCl) is often added directly into swimming pools, and undergoes the same ionization reaction shown above.

If peroxide is (H2O2) added to a chlorine-stabilized pool, it will react rapidly with the hypochloride ion to produce a chlorine ion, oxygen, and water.

So not only will the hydrogen peroxide deplete the hypochlorite ion level in the water, removing its biocidal efficacy, the reaction will also produce oxygen, providing a beneficial environment for growing algae. So although hydrogen peroxide is also a disinfectant, its use with another disinfectant (sodium hypochlorite) effectively cancelled each other out, allowing the algae to grow in the diving pool in Rio.
Others have suggested that the green color is not the result of hydrogen peroxide use in conjunction with a chlorine disinfectant, but rather an excess of copper sulfate, which can impart a green color to water, and is sometimes use as a biocide in swimming pools.  Whether or not the green color is due to precipitated copper or algae growth is to be determined. Algae growth can occur rapidly, often within 48 hours, if there is insufficient biocide present. Similarly, copper sulfate has been implicated in changing the hair color of swimmer to a a greenish hue. In either case, chemistry has played a key role.

Thursday, June 23, 2016

CPG Celebrates 20 Years

Cambridge Polymer Group is proud to be celebrating its 20th anniversary this summer. Started in the front room of an apartment in Arlington, MA by three MIT alumni, CPG has established an international reputation as a contract research and testing laboratory, with almost 900 clients. All three founders are still actively involved with the company.  Over the subsequent years, we have had the pleasure and opportunity to work and collaborate with many excellent employees, but we now have one of the best collections of researchers assembled in the history of the company.

CPG started with an NIH SBIR grant to develop an add-on feature for a rheometer, and have used this funding mechanism occasionally over the years to help fund speculative internal research.  We quickly realized that instrumentation was not where our primary interests lay and we soon began providing testing and consultation in orthopedics materials and devices. This work translated into other biomedical fields, including cardiovascular, ophthalmology, spine, women's health, gastro-intestinal, and general soft tissue applications. Our clients grew to rely on our expertise in test design coupled to our deep fundamental material understanding, all presented in detail-oriented, clear written, reports. CPG researchers also began to innovate on test methods and materials as part of our internal research efforts, and invented extensional rheometers, hydrogel formulations and constructs, surgical tools, and polyethylene formulations for total joint replacements. Many of these inventions have been licensed and are on the market.

We have continuously added on new capabilities and expertise to help our clients and to support our internal research efforts. In the past 5 years, we have built a chromatography lab to support our work in product formulation, medical device cleaning assessment, unknown analysis, and degradable polymer characterization. Our hydrogel team has developed expertise in tissue phantom development, and have created realistic tissue models for training and testing. Our chemistry team has developed new polymer systems for clients. Our engineers have assisted clients with the design and development of new tools, instruments, and medical devices, from original concept, to material selection, to proof-of-concept testing. And our testing team, arguably the core of CPG, continues to provide rapid, high quality and value added testing services to our clients.

We are pleased to be celebrating 20 years with our clients, and look forward to many more years of service.

Thursday, April 28, 2016

Sterilization by Vaporized Peracetic Acid

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.

Monday, April 4, 2016

MIT Polymer Day

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

Wednesday, March 30, 2016

Patent on Mosaicplasty Implants issued to CPG researchers

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.

Tuesday, March 29, 2016

FDA draft guidance document on UHMWPE

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.

Potential FDA ban on powdered gloves

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.