Figure 1: Chinese woodprints of the papermaking process (Wikimedia Commons)
Cellulose is one of the most abundant organic compounds on earth and utilized in applications as diverse as textiles, papermaking, food packaging, filtration, drug delivery systems, wound care products, nanocomposites, bone tissue engineering, and countless others. Cellulose is a fibrilar and semi-crystalline biopolymer which may be plant-derived or bacterial-derived, and generally exhibits remarkable mechanical properties as well as desirable biodegradability, biocompatibility, renewability, chemical stability, and cost effectiveness. [1]
Cellulose is notoriously difficult to process. Up until approximately 300 million years ago, there were no significant microorganisms capable of digesting cellulose—resulting in a high accumulation of organic matter. During this “carboniferous” period, the production of coal derived from biomass was 600 fold higher than estimated rates of production in modern day. [2]
Molecular Weight Analysis of Cellulose
As polymer and material scientists, we rely in fundamental measurements of polymer properties to understand the material performance in demanding circumstances. Typically, this includes measurement of the polymer molecular weight—however, this is a highly challenging measurement to obtain for un-modified cellulose materials. Simply put, cellulose doesn’t dissolve in most solvents as a consequence of its crystalline structure, hydrogen bonding, and hydrophobicity.
CPG has developed workflows for the molecular weight analysis of cellulose materials, including un-modified cellulose. Samples are carefully prepared in a series of matrix-modifying steps before ultimately being dissolved in an aprotic solvent and in the presence of high inorganic salt concentrations. Once in solution, the cellulose materials are analyzed by triple detection GPC for absolute measurement of the polymer molecular weight as well as structural characterization. By obtaining such fundamental measurements of molecular weight and structure, cellulose products may be evaluated for (bio)degradation, aging, failure analysis, material compatibility, lot-to-lot consistency, among other properties. Contact CPG for additional information on the material characterization of cellulose or other biopolymers.
[1] A. Amalraj, S. Gopi, S. Thomas, and J. T. Haponiuk, “Cellulose Nanomaterials in Biomedical, Food, and Nutraceutical Applications: A Review,” Macromolecular Symposia, vol. 380, no. 1, p. 1800115, 2018.
[2] P. Ward and J. Kirschvink, A New History of Life: The Radical New Discoveries about the Origins and Evolution of Life on Earth. Bloomsbury Publishing, 2015.
Is it appropriate to perform extractables testing and chemical risk assessment on metallic components?
As such evaluations are most commonly associated with polymeric constructs, it may seem strange to evaluate a solid metallic component in this way.
ISO & FDA Medical Device Guidance
For clarity on this issue, we turn to ISO 10993-1:2018 and the FDA 2016 guidance on biocompatibility assessment. These documents emphasize that the first step in assessing a device’s biocompatibility is in compiling a detailed understanding of the physical/chemical properties and chemical composition of the device. Only once this information is in hand can an evaluation and risk assessment be performed with regard to toxicological endpoints such as carcinogenicity, genotoxicity, etc.
Base Alloy vs. Surface Residue
For a metallic device, the question of chemical composition may seem straightforward: is it simply the alloy the device is machined or otherwise manufactured from? Unfortunately, considering only the base alloy does not take into account the processing aids which are used in the manufacture of the device and which may be left behind as residues on the surface of the part. These may include polishing compounds, lubricants, machine oils, cleaning agents, or adhesive residue from tape used to ‘mask off’ regions of the device. Inorganic residues (particulates, ions, elemental impurities, etc) that may be released should also be considered separately from the base material. An additional factor to consider is if the component has highly porous regions (e.g. to facilitate osseointegration) which may make the device more difficult to clean and in which manufacturing residues may linger.
Chemical Risk Assessment or Cleanline Validation?
In some regards, extractables and chemical risk assessment on metallic components blurs the line with the scope of work performed as part of a cleanliness assessment or clean-line validation – the workflows are in many ways similar and involve extracting the device in solvents of varied polarity and analysis of resultant extracts using techniques such as GC-MS, LC-MS, and ICP-MS. The results of this testing are a list of the identified organic and inorganic extractables which may then be inputs into a toxicological risk assessment. Often this process–other than being a key starting point of the ISO 10993-1 biocompatibility assessment– may mitigate the need for more extensive (and expensive!) animal testing.
Overheard at a recent conference: “Oh, our device isn’t a permanent implant, so we don’t need to do extractables testing.”
Is that right? If a device is implanted for less than 30 days (or even less than 24 hours), is extractables and chemical characterization unnecessary?
For clarity on this issue, we turn to ISO 10993-1:2018 and the FDA 2016 guidance on biocompatibility assessment. Each of these references contains a table which breaks down the biocompatibility evaluation endpoints associated with different implantation durations and the nature of body contact. Even in the case of a “limited” contact duration of less than 24 hours, these documents indicate that a biocompatibility assessment be performed. What does that entail, however?
The first step in performing any extent of biocompatibility assessment is to compile a detailed understanding of the physical/chemical properties and chemical composition of the device. Only once this information is in hand can an evaluation and risk assessment be performed with regard to toxicological endpoints such as carcinogenicity, genotoxicity, etc. For short term implants, the number of biocompatibility evaluation endpoints is generally less extensive than long term implants.
If the chemical composition of the device (both the raw materials as well as any manufacturing residues) are unknown or have not been previously characterized, an extractables assessment is typically necessary to determine the composition. Unless the device manufacturer has previous experience characterizing the material/manufacturing process by extractables, sufficient information on the device composition (including impurities, manufacturing residues, etc) is generally not available for this to be a pure paper exercise.
Note that from an analytical perspective, given the short term nature of the device, the analytical evaluation threshold (AET) employed will be less stringent than for a permanent implant. This means that when evaluating extractables data from techniques like GC-MS, and LC-MS, the number of peaks which must be identified and submitted for toxicological risk assessment is significantly lower than for a permanent implant–translating to generally lower cost and faster turnarounds.
As summer sets in, it’s not unusual to leave a water bottle in the car and forget about it. In the summer heat with the car windows down, it is possible for that PET (polyethylene terephthalate) water bottle to become a lens, concentrating the sun’s energy onto your car cushions (or that stack of junk mail you tossed into the backseat) and starting a fire.
Into Focus
Water is usually associated with putting out fires, rather than starting them. Much like a kid burning ants with a magnifying glass, the clear, spherical bottle full of clear liquid converges the sunlight onto a flammable point. Although your car cushion fabric is engineered to be as flame-retardant as possible, the pile of junk mail is not as well designed. Is it really likely that your forgotten water bottles will be optimally positioned to produce a focused beam capable of combustion? It is rare, but it can happen; some fire departments are urging the public not to leave bottles in cars.
Leachables in Your Bottled Water
Depending on how long the bottle has been sitting in your car, exposure to sunlight may accelerate the breakdown of the PET, releasing BPA and antimony into that disgustingly warm drink of water. As unappetizing as the leachables may sound, current research[1] has put those levels well below the safe limit, even for bottles stored in hot conditions for long periods of time. The FDA evaluates new research on BPA, but has not changed the acceptable levels of the material in food containers and packaging.
At Cambridge Polymer Group, we test leachables for packaging, pharmaceuticals, medical devices, food products, and cosmetics. Leachables aren’t always as harmless as the insignificant amount of BPA in your bottled water, and testing for them in the development stage of your product can reduce your litigation risk.
The odds of your car water bottle starting a fire or leaching unsafe levels of BPA and antimony are small, but it’s better to be safe than sorry. Keep calm and clean your car.
Their process makes use of a heat-curable monomer (DCPD) that, after curing has started by an external heat source, generates sufficient heat from the exothermic polymerization to sustain the curing process, producing a thermoset. The process is called frontal polymerization, so-named because the reaction moves as a front through the monomer.
Energy Efficient Custom Shapes in 3D Printing
Typically, these types of resins require the application of pressure and heat to effect the cure throughout the entire curing process, which requires much more energy and equipment. The FROMP (ruthenium-catalyzed frontal ring-opening metathesis polymerization) approach requires less energy and time and eliminates the need for large curing ovens.
Previous to this research, the FROMP technique was not industrially useful because the unheated DCPD resin cured in 30 minutes. By using alkyl phosphite inhibitors, the University of Illinois, Urbana-Champaign researchers were able to extend that time period to 30 hours, allowing enough time to shape the material before starting the frontal polymerization process.
These researchers generated quick-curing, high-quality spiral shapes and carbon-reinforced composite panels, and demonstrated similar mechanical properties to conventionally manufactured materials. Although the FROMP process has not yet been commercialized, this rapid fabrication of parts has a myriad of potential applications, including in the space, aircraft, and automotive industries.
Last summer, we wrote about a hagfish accident that covered an Oregon highway in slime. Another sticky situation has come to our attention – on May 9 at 5:30 a.m., a tanker of liquid milk chocolate flipped over on the A2 in western Poland, spilling a dozen tons onto the six lane highway. Until authorities closed the motorway, drivers continued to drive over the spilled chocolate, tracking it a mile in either direction.
Cleanup crews sprayed the congealed chocolate with hot water to re-melt it and wash it off the road. Additionally, a bulldozer pushed chocolate sludge off the motorway – a technique also used to clear the Oregon highway of hagfish slime.
“Removing the chocolate will take a couple of hours. The chocolate congeals on the pavement, and it’s worse than snow,” one member of the fire brigade told TVN24.
At the time of the accident, the temperature in Slupca, Poland was 12 °C, a bit lower than the 20-25 °C usually considered room temperature but not nearly as cold as the 0° to -4°C of a Western Polish January. What if the temperature had been much lower? Could cars and people have been trapped in the sugary non-Newtonian fluid as it quickly cooled, like the victims of the 1919 Boston Molasses Flood?
The ease at which drivers sped through the spilled chocolate seems to indicate the muck was not impassably sticky. The air temperature must have been warm enough to keep the flow thin enough to allow for mobility. Fortunately, injuries from the May 9th accident were limited to the tanker driver’s broken arm and a reporter’s wounded pride after slipping into a chocolate-filled ditch.
Our CPG application note on chocolate mentions the importance of slow cooling for successful chocolate tempering. Did the change in temperature from tanker (>28 °C) to brisk morning air (12 °C) allow for proper tempering of the highway chocolate? The brown goo would have cooled too quickly for optimal confectionery quality. Probably a moot point, considering highway chocolate will never meet the quality standards of 21CFR163, Subpart B: Requirements for Specific Standardized Cacao Products or EU Directive 2000/36/EC. The only consumers of the Slupca spill are likely to be local wildlife.
The crystal would refract light depending on its orientation relative to the principle axis of the incoming light. When the crystal’s principle axis is aligned east-west, an image viewed through the crystal resolves from a double image into a single image, thus providing a means of orientation. Since magnetic compasses were not fully utilized until the end of the 16th century, the crystal may have been used to augment compasses.
Called “sunstones” in Viking sagas, these crystals were believed to be used by Vikings in the 10th century, well before the use of compasses in Europe, to navigate from Norway to Greenland, a journey of 1,600 miles. They can be used in cloudy weather to locate the sun, as well as the afore-mentioned east-west orientation. There is still not direct evidence that Vikings used the sunstones for navigation, but computer simulation has shown that Viking navigation with these crystals would have been possible.
Calcite crystals are still used today as polarizers for the more pedestrian use of examining crystal structure and stress concentration in polymeric materials.
ASTM F2459 Standard Test Method for Extracting Residue from Metallic Medical Components and Quantifying via Gravimetric Analysis
The latest draft of ASTM F2459 Standard Test Method for Extracting Residue from Metallic Medical Components and Quantifying via Gravimetric Analysis just published. The key difference in this version is the inclusion of the method to determine extractable residue by measuring the medical device before and after extraction. This approach is particularly useful for smaller parts, a method CPG routinely uses to assist clients in cleaning validation. Please contact us if you have any questions about this standard or the associated testing.
Of the estimated 95 million Americans celebrating with Christmas trees this December, 81% are expected to choose plastic trees. Why is plastic preferred? The cost of buying a live tree is 5%-10% higher this year, due to fewer trees planted during the Great Recession. Although the initial purchase of a plastic tree can cost as much as a live tree, plastic can be re-used, year after year.
In addition to thrift, allergies, ubiquitous needle spikes and fire phobia also play a role in tree material selection. However, an artificial tree is not fireproof. While not as prone to combustion as a dried-out pine, plastic trees can still burn when subjected to holiday hazards such as frayed light cords, candles, or discarded cigarettes.
Despite the benefits of plastic trees, 19% of American tree buyers opt for natural. For some, this decision is an environmental choice, since the purchase of a fresh-cut tree supports tree farms, conserving green space and farm land. Others simply love the smell of a live tree, a fragrance brought to you by the chemical pinene, from the terpene family. Recently, scientists at the University of Bath developed a renewable material from the fragrant beta-pinene that can be used in place of the petrochemical-derived caprolactone.
The Power of Pinene
Bio-based polyesters like (polylactide) PLA are susceptible to brittleness and are often mixed with caprolactone to improve mechanical properties. Although the addition of caprolactone is essential to expanding the plastic’s suitability for medical and engineering applications, the resulting plastic is not renewable, since the caprolactone is made from crude oil. The University of Bath researchers’ pinene material allows for the creation of sustainable PLA. The chemical similarity between caprolactone and pinene (both are hydrocarbons) makes the possibility of pinene substitution more economically feasible for manufacturers.
Be not afraid, fans of the Tannenbaum au naturel; the researchers have no Grinchly designs on your trees. The concentration of b-pinene in individual trees is fairly low. However, the paper industry produces pinene in large quantities as a waste byproduct of crude sulfate turpentine, making it cheap and readily available.
Possible applications of the new plastic include food packaging, bags, and medical devices. Thus far, only a few grams of the material have been created, and researchers seek to make their production of the pinene-sourced material both scalable and green.
Sustainable Raw Materials
Even the abundant supply of b-pinene generated by the paper industry is still not enough to replace all caprolactone in products currently in use. University of Bath is also investigating how to manipulate bacteria into transforming their natural terpene stores into more useful chemical precursors. If successful, terpene could be produced in mass quantities by fermentation of plant sugars and cellulose waste.
Pinene is just one of many bio-based chemicals currently under consideration as a crude oil alternative. Limonene, from citrus fruit, is another terpene of interest that could be used to create terephthalic acid, a monomer essential to the production of PET – poly(ethylene terephthalate), from renewable sources. The market for PET is huge, so a breakthrough on this front would have a significant environmental impact.
The ability to use bio-based, renewable sources as starting materials could revolutionize the plastics industry and help to mitigate climate change.
It’s that time of year when the turkey takes center stage, er, table. Although many claim Ben Franklin lobbied for the turkey to become the United States’ national symbol, Franklin was taken out of context. Franklin neither publicly championed the turkey nor opposed the bald eagle, and he characterized the turkey as “a little vain and silly.” Although the wild turkey was never a candidate for national symbolism, it has played a significant role in the culture of many Native American tribes, from sacred warrior to fabric to favorite meal. Wild turkey was important to European settlers as well; historical record puts wild turkey on the menu at the first Plymouth Thanksgiving, unlike pumpkin pie, potatoes and cranberry sauce, which wouldn’t have been available to the Pilgrim colonists.
Better Color Through Chemistry
In addition to these cultural and culinary roles, Meleagris gallopavo has another claim to fame. Turkey feathers have inspired an international team of researchers to create a new type of structural coloring, a nanoparticle made of melanin and silica, called a “supraball.” Changing the thickness of the silica shell surrounding the melanin core determines the shade and intensity of color.
Chemical pigments, produced by the absorption of light by molecules, fade as they break down. Structural colors, created by the scattering of light by nanostructures, are resistant to bleaching and are less dependent on toxic materials than pigments. Although structural colors have obvious advantages to chemical pigments, obstacles remain to the mass production of structurally colored materials.
Many structural colors are iridescent and not practical for wide-angle displays. Non-iridescent structural colors often lack adequate color saturation due to incoherent scattering. Although a partial “solution” for non-iridescent colors has been found, it is not scalable; core-shell nanoparticles with a shell refractive index (RI) comparable to water have been used to tune core spacing to attain optimal scattering for non-iridescent colors, but only in solution.
The discovery of the supraball technique could overcome these challenges. Supraballs tune core spacing without the need for a solution, and yield a full spectrum of colors. Additionally, the reverse emulsion process used to create the supraballs is simple and scalable. The nanoparticles cluster into supraballs at room temperature in water and octanol, and can be extracted as a powder.
Paint It Black
Melanin is a dark biological pigment found in skin, hair, feathers (including turkey), scales, eyes, and some internal membranes. The use of melanin, with its high RI and broadband absorption of lights, increases the brightness and saturation of the supraballs. The spacing between the balls of melanin produces different colors, although only from normal distance; under a microscope, the supraballs are black.
The low RI clear silica shell forces the melanin cores farther apart or closer together, depending on the thickness of the shell. This color tuning technique, using high-RI cores and low-RI shells to increase reflectance and brighten colors, was inspired by the hollow, high RI contrast melansomes of wild turkeys, and the hexagonal nonclose-packed melansomes of green-winged teal.
Researchers believe this technology can be replicated at the industrial scale, and has many potential applications. Since melanin can dissipate 90% of UV radiation, supraballs could be used to color UV-resistant inks. Supraballs could also be used in paints, plastics, coatings, and, since melanin is biocompatible, cosmetics and food.
