An Interview with Stephen Spiegelberg on Rheological Characterization

Interview conducted by Beth Ellison

BE: Please provide a brief overview of Cambridge Polymer Group and the services you provide.

SS: We like to think of ourselves as a one-stop resource for our clients, working everywhere in the product lifecycle from concept through launch and (hopefully not) root-cause analysis.
We are a well-established contract research laboratory that has been operating since the mid-1990’s specializing in polymer science. Our scientists are experienced in analytical testing, polymer chemistry, and product development, testing and analysis. We often serve as either an external routine analytical testing laboratory, or an external research and development facility for our clients.

BE: What does rheological testing involve?
SS: Rheology is the study of the flow of matter. Most people are familiar with the concept of viscosity, and how it relates to how easy it is to pour or spread liquids. Viscosity is one of the parameters that comes out of rheological characterization, but we do much more than that.
We can determine the viscoelastic nature of material, which tells you how the material will respond to different rates of deformation, which is important in polymer processing and end use. We can also (almost uniquely) characterize the response of fluids to extensional deformation, such as found in fibre spinning, coating or injection molding.

BE: What type of materials can you test?
SS: Polymers are, of course, our main source of testing, but the word ‘polymer’ extends beyond standard synthetic polymers. We do a lot of testing of natural polymers, such as collagen and hyaluronic acid, as well degradable polymers.
These polymers can be on their own, or as blends or composites, or functionally part of a larger device, so you can see that the scope of devices and products that “polymers” covers is far broader than the image that “plastics” alone might conjure up.
In the medical field, we also do a fair amount of testing on the cleanliness of devices, which can include both polymeric and metallic devices. In particular, in rheological testing we can of course test the melt-flow properties of the base resins, but we also have extensive experience in understanding and testing the solution and blend properties of these high molecular weight materials.
The rich and varied response of polymers in solution makes for challenging rheological testing, and understanding the end-use and requirements of the test is critical to get useful results.

Link to full Azom Interview

Call for Abstracts: ASTM Workshop on Reprocessing of Re-usable Medical Devices

A Workshop on Reprocessing of Re-usable Medical Devices will be held Tuesday, November 15, 2016. Sponsored by ASTM Committee F04 on Medical and Surgical Materials and, the workshop will be held at the Renaissance Orlando at SeaWorld in Orlando, FL, in conjunction with the November standards development meetings of the committee.
Objectives:
A recent article in Medical Processing Outsourcing (June 2, 2015) estimates that reprocessed medical devices will grow by 19% annually to reach $2.58 billion in 2020. A key element of this successful growth is assurances of cleanliness and safety standards.
Recently, the FDA released a guidance document on reprocessing of reusable devices (March 12, 2015) and held a public meeting on May 14-15, 2015 to discuss infections associated with the use of duodenscopes.
The workshop is intended to bring thought leaders together on the issues involving cleaning of re-usable medical devices to determine the areas of standardization that ASTM should focus on in the next few years.

Topics to be discussed include the following:

1. History of reprocessing issues
2. Review of relevant existing ASTM, ISO, AAMI, and FDA standards/documents
3. Designing of medical devices for reprocessing
4. Reprocessing
   1. Reprocessing work instructions
   2. 3rd party reprocessors experiences
   3. Manufacturers of reprocessing equipment
5. Testing for biological residues
   1. Test methods
   2. Test soils
   3. Instrumentation
6. Sterilization of residual soil
7. Biocompatibility of residual soil/limits
8. Discussion of new standards development for ASTM to consider

Please contact CPG researcher and workshop co-chair Stephen Spiegelberg with any questions or to submit an abstract.

More details on the workshop can be found on the ASTM web site.

Biomed Device Exposition in Boston

Cambridge Polymer Group will be exhibiting at the Biomed Device Exposition in Boston on May 6-7th.

Come visit us at booth 1147 to see the new analytical tools, formulation capabilities, and project assistance we can provide. If you would like to visit our lab while you are in town, please contact us at info@campoly.com.

Details about the trade show can be found here.

Molecular Weight Characterization to Assess Aging in Ultra High Molecular Weight Polyethylene

Ultra high molecular weight polyethylene (UHMWPE) is commonly used as a bearing surface in hip, knee, shoulder, and other total joint replacement arthroplasties. Aging of UHMWPE that has been irradiated without additional treatment to stabilize the residual free radicals can result in oxidation followed by chain scissioning. Researchers will usually measure oxidation index to characterize shelf‐life, but this technique does not capture the actual degradation due to oxidation. In this study, gamma sterilized UHMWPE was accelerated aged, and the molecular weights of extractable material were characterized with gel permeation chromatography in an attempt to see if this technique can be used to characterize shelf life of the aged material.

The extraction of the polyethylene material in this study shows that there is a molecular weight difference between the unaged and aged material, with the aged material showing broadening in the molecular weight distribution. This change can be explained by oxidative degradation, which is supported by the oxidation index. The test methodology shows that a larger ratio of solvent to sample is required to ensure extraction without gelation of the extracted material, and that 4 hours is sufficient to extract the larger molecular weight species. The impact of the molecular weight change on in vivo performance, however, cannot be discerned from this test.

See the poster presented at the Orthopedic Research Society in March, 2015 here.

Choc Full of Information

Chocolate is a complex structure containing consisting of cocoa powder, sugar, fat solids (primarily cocoa butter). The cocoa powder and cocoa butter both come from the cocoa bean following roasting, grinding, and liquification. The flavor and mouth feel of chocolate will depend on the ratios of these components, as well as their size and structure. For the cocoa butter alone, there are six different crystalline structures that it can assume depending on its processing, which will impact how shiny the finished product is, how it melts in your mouth, and if it will undergo blooming, the development of a gray coating on some inferior brands of chocolate.

Cambridge Polymer Group analyzed multiple types of chocolates, looking at their chemistry, morphology, rheology, and mechanical behavior. Alkaloid content, primarily caffeine and theobromine, was analyzed with chromatographic techniques, along with microstructural information by scanning electron microscopy.

The full application note can be found here.

Bubble Point for Pore Size Measurements

The pore size in filters, membranes, and fabrics can be determined at Cambridge Polymer Group by a variety of methods, including optical and scanning electron microscopy, mercury porosimetry, and particle size exclusion. A commonly used method is ASTM F316 “Pore size characteristics of membrane filters by bubble point and mean flow pore test.” This standard describes two test methods to obtain pore size in filtration media by making use of gas transmission through the filtration media. In both methods, the filtration media (in the form of a sheet) is cut into a disc, which is then placed in a filter holder. One side of the filter holder is connected to a gas line with a pressure regulator. The other side is vented to the atmosphere. In Method A, a fluid of known surface tension is placed on top of the filtration media on the vented side. The gas pressure on the other side of the filtration media is slowly increased, and the experimenter looks for the lowest pressure where gas bubbles begin to rise from the filter, indicating that the gas pressure has overcome the interfacial tension of the liquid in the pores. The maximum pore size can be calculated from this pressure and the surface tension of the fluid. In Method B, the same apparatus is used, but with the addition of a gas flow meter. In this variation, the gas pressure is also slowly increased, and the flow rates of gas through both a wet filter (using the fluid of known surface tension) and a dry filter are recorded. The percentage of filter flow rate can then be determined as a function of pressure, which in turn is related to the pore size.

Contact CPG for more information on performing this test on your filtration media.

MIT Polymer Symposium

CPG was a sponsor of MIT’s 5th annual Polymer Day Symposium, held on March 11, 2015 at MIT. The event is hosted by MIT’s Program in Polymers and Soft Matter. A poster session was held in the morning, and two CPG scientists, Svirkin and Kozak, acted as judges, and awarded prizes to the top posters. More information on the Symposium can be found here.

How To Determine If Your Medical Devices Are Clean

The success of a medical device depends on both the details of its design and the proper selection of materials from which it is fabricated, taking in to account its final use and regulatory requirements. Success also depends on how it is manufactured, and a critical feature of medical device manufacturing is ensuring a suitably clean product. Cleaning is almost always performed in the final stages of manufacturing, but some manufacturing processes may include intermediate cleaning steps.

To ensure that the cleaning process is doing its job, manufacturers will perform cleanliness measurements on their devices to determine how much manufacturing residue remains on the part, and the nature of that manufacturing residue. Simply quantifying the presence of residues is not sufficient however, because this does not account for how sensitive the design is to that residue. For example, residual sodium chloride may be acceptable at gram quantities, whereas arsenic may not be acceptable at any level. A critical step in clean-line validation that is often missed is therefore to assess what is an allowable amount of residue while still ensuring a good clinical outcome of the device. Often this involves are considered cost-benefit analysis between the effort to clean, and the risk associated with that residue.

Cleanliness measurements are either performed by removing the residue from the part and quantifying the residue with various analytical assays, or by measuring the residue in situ on the part. The latter technique is less suitable for quantification measurements, but is useful for identifying where on the part the residue is residing, which may assist in modifying either the cleaning process or the part design. Cleanliness measurements include residue weighing, FTIR, GC and LC/MS, ICP, UV-Vis, and SEM-EDS to quantify and identify sources of residue.

To assess what levels of residues may remain on the part without impacting the clinical performance, manufacturers often look at devices on the market already in the same application area with good clinical history, and measure their residue levels. These levels can serve as guidance for establishing acceptable manufacturing residues. Alternatively, toxicological studies can be carried out, or some animal studies.

The manufacturers clean-line can then be validated using the cleaning assays discussed above, along with the allowable residue levels the manufacturer previously determined. To validate a clean-line, a representative number of devices are tested under normal operating conditions as well as the extremes of the operating conditions, to see if the process is in control.

ASTM offers several standards for testing the cleanliness of medical devices, and new standards are being developed for clean-line validation and establishing allowable residue levels. Cambridge Polymer Group performs these standards for clients, and assists with clean-line validation.

Case studies on medical device cleanliness can be found here.

Using Free Radicals To Monitor Engine Oil Age

Car owners are advised to change their engine oil every 3000-5000 miles. But what is actually happening to the oil over time in the engine? We have heard about the benefits of antioxidants in the body. Antioxidants also help engine oil. In use, engine oil is subjected to high temperatures and high shear stresses which can act to break apart the oil molecules, affecting its viscosity and performance. This chemical reaction occurs through the generation of free radicals, or unpaired electrons on the oil molecules. By monitoring the free radical content, it is possible to monitor the change in the oil.

CPG used electron spin resonance spectroscopy to monitor the change in oil in a 6 cylinder gasoline engine, taking samples every 500-1300 miles. Free radical production started around 400 miles, and changed as the free radicals were either stabilized by the antioxidant package in the oil, or reacted to form other radical species. This method is useful for monitoring the chemical changes in the oil, and to see the efficacy of the additives package.

Read the application note for more details.

The Rheology of Beer

Princeton scientists Alban Sauret, Francois Boulonge, Emilie Dressaire, and Howard Stone have applied fluid dynamics and rheology to help long-suffering beer drinkers understand why beer with a head of foam are less likely to slosh and spill compared to their counterparts with less foam. Simple experiments, like the images shown above, indicate that reducing the thickness of the head of foam increases the sloshing potential when the glass is agitated. Stone and colleagues modeled this behavior, and demonstrated that the foam in beer dampens the sloshing effect of the beer through viscous dissipation. The viscous force scales with the Capillary number, which relates the relative contributions of surface tension and viscosity. The viscosity of the foam is related to the velocity of the bubbles in the foam. The foam dissipates the energy of sloshing to the walls of the glass. Stone and colleagues suggest this is why it is easier to carry a glass of beer versus a cup of coffee without sloshing, although the study would suggest that cappuccinos may be recommended for those on the go.