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CPG Webinar - Thursday, October 5, 2 p.m. EST 

LC-MS is a widely used analytical technique for characterization of polymer additives, extractables and leachables, degradation products, APIs, drug release studies, and material stability. Typical LC-MS studies however usually focus on small molecules rather than the polymer or excipient components themselves. Structured appropriately, methods for the LC-MS analysis of polymers can yield large, complex datasets that can reveal valuable structural information about polymers and oligomers present in a medical device or pharmaceutical product. Such techniques can help identify the root cause for lot to lot variability or underlying reasons for why polymer blend A is “good” while polymer blend B is “bad.”

Join us for a CPG webinar that will walk through the basic principles and limitations of conducting LC-MS on polymers and oligomers for the purpose of performing structural characterizations, repeat unit analysis, charge state analysis, and molecular weight determination. Key variables such as material ionizability, separation mode, and mobile phase considerations will be discussed, as well as mass spectral data analysis techniques such as two dimensional contour plot visualizations, which can reveal a wealth of data “buried” under the total ion chromatogram. The presentation shall cover specific applications for complex polymer systems such as ethoxylates and hydrogel precursors/degradation products.

Your webinar presenter, Adam Kozak, is a research scientist and biomedical engineer at Cambridge Polymer Group, where he specializes in the chemical analysis of polymer materials. He has substantial experience in chromatography techniques including trace impurity/contaminant analysis, residual monomer/solvent content, extractables/leachables, cleanliness analysis, unknown compound identification, deformulation, migration analysis, molecular weight analysis, and odor analysis. He has managed the development and validation of many custom analytical methods, including extraction and recovery of target analytes from complex polymer and biological matrices.

This 40 minute webinar is targeted towards:

• Material Engineers
• Medical Device Engineers
• Product Designers
• Pharmaceutical Developers
• Regulatory Personnel

For more information and to register for the webinar, visit: https://attendee.gotowebinar.com/register/4618685894792158978

The certificate of analysis for polymer resins often includes a melt flow index (MFI) or melt flow rate (MFR), reported as grams of material/10 min under a specified temperature and load. This testing is normally performed per ASTM D1238 or ISO 1133 using a plastometer. A plastometer consists of a temperature-controlled cylindrical annulus through which a polymer melt is extruded by pressurization with a weight-loaded piston. The amount of material extruded through the die at the bottom of the annulus is measured by weight for a measured period of time. This mass, normalized by time, provides the MFI. It is easy to see that lower viscosity materials will result in a higher MFI, since more material can be extruded for a given amount of time.

How does MFI correlate to the molecular weight of a polymer? At CPG, we often measure molecular weight by gel permeation chromatography or dilute solution viscometry. Both these techniques involve dissolving the polymer in a good solvent to form a dilute solution, so that individual polymer chains can be interrogated directly (in the case of GPC) or indirectly (in the case of viscosity modification in dilute solution viscometry). In MFI testing, the polymer is not dissolved in a solvent, but rather is tested in the melt state. As a result, the MFI has a direct correlation to the polymer's melt viscosity. For polymer melts, the zero-shear viscosity h₀ (or the viscosity at very low shear rates) has a relationship to the weight averaged-molecular weight as follows:

Given the inverse relationship between MFI and viscosity, it is logical to see that the MFI has a relationship to molecular weight as follows, which has been shown empirically for linear polymers:[1]

Bremner and Rudin found values of LLDPE had G values ranging from 2x10^-20 to 1x10^-24 (10 min/g^(x+1)(mol^x)), and x ranged from 3.9-4.6. In a later article, Bremner found x values between 3.4 and 3.7.[2] The authors cautioned that this relationship becomes tenuous with polymers having variability in branching and polydispersity index. In order for the equation above to be valid, the authors’ note, the viscosity at the MFI conditions normalized by the zero shear viscosity should be a constant for the polymers in a given family. If not,  gel permeation chromatography is warranted.

Vitrum Flexile, or flexible glass. Although lost in legend, three different authors provided an account of a glass that could be dented and then repaired in Rome’s first century. According to the Corning Museum of Glass, Petronius (who died in 63 A.D.) told of a drinking vessel presented to Emperor Tiberius (reign 14-37 A.D.). The vessel was thrown to the ground, and though dented, the glassmaker was able to remove the dent with a hammer.

Pliny told a similar story in his encyclopedia, completed around 78 A.D., although his story goes on to say that the glassmaker's workshop was destroyed so that the value of copper, silver and gold would not be affected by the vitrum flexile. 

Dio Cassius provides the third story, in which an architect, who fell out of favor with Tiberius, provided the aforementioned demonstration of denting a glass vessel, then repairing it with his hands.

Unfortunately, no other accounts of vitrum flexile exist beyond these stories. As polymer scientists, we naturally assume that the vitrum flexile was not glass, but rather an early form of plastic, given its mechanical behavior and appearance. Perhaps it was formed of a natural resin, or from a crude polymerization. Ethylene gas was known to be in the Mediterranean around this time (the suspected source of the Oracle of Delphi’s visions). Did a resourceful Greek manage to perform some early free radical polymerization?

Provocatively Titled Study Explores “All Plastics Ever Made”

A recent study by Geyer et al published in Science Advances takes a wide-ranging look at the production and fate of all plastic produced to date, based on data collated from a range of market research and consulting groups.

Some key observations from the authors’ study are as follows:

The total amount of polymer resin produced from 1950-2015 is approximately 7800 Mt. Production growth has been accelerating with a compound annual growth rate of 8.4%—for perspective, half of the 7800 Mt has been produced in last 13 years!

Assuming an average pellet mass of 25 mg, the total amount of resin produced through 2015 is the equivalent of 3.12 * 10¹⁷ pellets.

Plasticizers, fillers, and flame retardants account for approximately 75% of all produced additives between 2000-2014. Antioxidants and heat stabilizers account for approximately 11% of additives produced.

Industrial Use of Plastics 

The largest industrial use sector for plastics is packaging. In fact, 42% of all produced nonfiber plastics are used for packaging purposes. The second largest use sector is construction, which makes use of 69% of all PVC produced.

fig. S1. Global primary plastics production (in million metric tons) according to industrial use sector from 1950 to 2015.  [1]

The most commonly produced plastics are polyethylene and polypropylene, which make up 57.3% of all polymer resins produced from 2002-2014.

              fig. S2. Global primary plastics production (in million metric tons) according to polymer type from 1950 to 2015. [2]

Where Is All That Plastic Now? 

It is estimated that 30% of all plastics ever made are currently in use—the rest having been disposed in one way or another. It is estimated that 12% of all plastics disposed of have been incinerated, and only 9% have been recycled. The remainder are in landfills or the natural environment. Note that none of the commonly used plastics are naturally biodegradable; the vast majority are derived from petroleum hydrocarbons.

In addition, there is an increased attention of to the ultimate fate of polymer fibers (such as those used in textile/clothing applications). Environmental accumulation of polymer fibers is in many respects analogous to recent concerns about the deliberate addition of polymer microparticles to consumer products—recall the Microbead-Free Waters Act of 2015 which banned the manufacture and sale of rinse-off cosmetics containing polymer microbeads.

How CPG Can Work With You

At Cambridge Polymer Group, our expertise and analytical capabilities intersect with the topics raised by such studies in multiple ways. We can assist your team in:

1. Material selection and screening
2. Resin equivalency studies
3. Identification of unknown polymers
4. Characterization of material stability and polymer degradation
5. Identification/quantitation of chemical degradation products
6. Impact of additive packages on polymer and device functional properties

CPG is an ISO 9001 certified, 17025 accredited contract R&D and analytical testing lab. Contact us to see how we can work with you.

Most traditional machined components involve starting with a standard block of material, and then machining away material to form the final finished device. The advent of 3D printing systems has allowed the opposite approach to machining, where material is sequencing added to a part, in effect growing it from raw material with little scrap material generated, hence the term ‘additive manufacturing’. 3D printing allows generation of more complex geometries, such as porous structures, fully-enclosed hollow features, and finer structure than may be achievable with more conventional milling, lathing, or molding processes. Additionally, 3D printing provides the opportunity for patient-specific implants derived from X-rays or MRIs of the patient’s anatomy.

A variety of materials have been used for 3D printed medical devices, including titanium powder and its alloys, calcium phosphate powder, thermoplastics such as polyether ketone ketone, and UV or light-curable resins. Since 2013, the FDA has been clearing medical devices and drugs made from 3D printing technologies through either the 510(k) process or the emergency need process. In the 510(k) process for a device, a device is cleared by the FDA if it is shown to be as safe and effective as a legally marketed predicate device to which it is substantially equivalent (same intended uses, comparable design and materials). The same tests conducted on machined or molded devices required for clearance, such as biocompatibility, leachables/extractables, mechanical behavior, cleanliness, and functional performance, all apply to 3D printed devices, and currently no additional regulation specific to 3D manufacturing has been established. As of 2016, more than 85 devices manufactured using 3D manufacturing processes have been cleared by the FDA.

3D Printed Medical Devices

Some examples of 3D printed devices that were cleared are shown below, spanning a variety of medical application areas.

2013

• Oxford Performance Materials received 510(k) clearance for a 3D printed cranial-facial device made from laser sintering polyether ketone ketone (PEKK), granted in 2013.

2015

• DENTCA, a 3D printed denture system, received 510(k) clearance in July of 2015. DENTACA is made from a light-cured resin, and underwent biocompatibility testing per ISO 10993, in addition to human mouth tissue sensitivity contact.
• The first 3D printed drug to be cleared by the FDA was Aprecia Pharmaceuticals Co.’s epilepsy drug, Spritam® (levetiracetam) tablets in 2015. Spritam is for treating seizures in patients with epilepsy, and is printed using a method called ZipDose technology, which produces a porous pill that dissolves rapidly with liquid.
• MedShape received 510(k) clearance on a Ti6Al4V 3D printed bunion correction system in 2015.

2016

• K2M received clearance for titanium printed porous spinal fusion devices made with laser fusion, designed to have surface roughness with feature sizes of 3-5 microns to encourage bone on-growth.
• Stryker received 510(k) clearance for a titanium printed lumbar cage to treat degenerative disk disease.
• ZB’s reconstructive wedges made from OsseoTi (titanium powder) for ankle fusion received clearance. 
• Additive Orthopedics cleared for titanium 3D printed devices for foot applications.  
• Bioarchitects received clearance for 3D printed titanium craniofacial implants.

2017

• OssDsign received 510(k) clearance for cranial plates 3D printed with a proprietary calcium phosphate composite reinforced with titanium in 2017. 

The Future of Additive Manufacturing 

3D printing of drugs could allow hospitals to customize the API dose in each tablet for individual patients, ushering in a new era of personalized medicine. Additive manufacturing may also make medication easier to swallow, both for adults due to improvements in swallow-ability and dissolution, and for children, in that the drug can be made in kid-friendly shapes. At this point, conventional large scale manufacturing continues to be more financially efficient for large quantities of medication, and FDA clearance of 3D manufactured drugs is not easy to obtain.

Additive manufacturing is becoming a more viable alternative manufacturing process for medical devices, since it offers solutions to designs that are unprocessable by conventional manufacturing approaches, readily allows custom device manufacturing, and may present options for on-demand manufacturing of implants. In addition to the standard tests for new medical devices, the areas that currently need addressing for additive manufacturing include process validation procedures and qualification of raw materials (new and potentially used).

Polymer scientists often use polarized light to optically examine features in polymers, such as crystallinity and residual stress, through the phenomenon of birefringence. White light, such as that coming from the sun and incandescent light bulbs, is comprised of multiple wavelengths of light traveling in multiple planes. When white light passes through a polarizer (which is a type of linear optical filter that only permits waves oriented in the same direction of the linear direction of the polarizer to pass through, and blocks all others, as shown in Figure 1), the randomly oriented light becomes plane-polarized in a single optical plane. 

Figure 1: Schematic of randomly oriented white light passing through a polarizer, becoming plane-polarized light with the principle axis indicated by the blue arrow.

A similar phenomenon occurs when white light is reflected off of a flat surface, such as a body of water or a metal or glass surface. You may have experienced this phenomenon when wearing polarized sunglasses while looking at the ocean or your smart phone. In some orientations of the glasses relative to the ocean or phone, the light intensity is greatly diminished (and you may not be able to see the images on your phone) because the polarizer in your glasses is blocking a percentage of the plane-polarized light reflecting off the surface of the object you are looking at. By rotating your head in a clockwise fashion, the light intensity will decrease or increase as angle of the plane-polarized light moves towards or away from 90º from the principle angle of your glasses.  More details on the math associated with light polarization can be found on our birefringence application note.

The use of polarization of light in nature is commonplace. It has been known for decades that insects (bees, ants, beetles) use the atmospheric polarization of light[1] to navigate to and from their home bases.[2] Whereas these insects do not have traditional polarizers, they do have specific arrangements of photoreceptors that maximize the absorption of polarized light. Using polarized light aids in the sky and in reflected light off the ground and off plants, the insects can ably navigate. In most cases, the photoreceptor systems are fixed relative to the animal’s eyes. However, it was recently discovered that the mantis shrimp is able to rotate its eyes independently, effectively adjusting the principle orientation of its ‘polarizer’ to maximize the signal of incoming polarized light (see Figure 2). What do they do with this information? Identify food sources, for one thing. Many of the jelly-fish and multi-cell organisms in the ocean are nearly transparent to the naked eye. However, to a creature tuned into polarized light, these amorphous organisms light up against the dark ocean back ground as the plane polarized sunlight passes through their bodies, making them easy targets for hunting by the shrimp (see Figure 3). 

Figure 2: Rotational degrees of freedom in Odontodactylus cultrifer.[3] 

Figure 3: Transparent organisms made visible with polarized light.[4]

But the shrimp have a secondary use for polarized light, namely communication. Scientists have noticed distinct color patterns on shrimp that are only visible when observed through a polarization filter. As shown in Figure 4, the male shrimp has a distinct red pattern visible when the polarizer is oriented horizontally. The female (on the right) does not have this pattern, suggesting that the pattern may be useful for shrimp courtship.

 Figure 4: Male (left) and female (right) mantis shrimps, showing a clear difference in polarizing signals (the arrows show the orientation of the camera polarizing filter). This method of communication  may be important for mating.[5]

Let’s hope that shrimp continue to use this optical power for food and mating, so that they don’t push us polymer scientists out of our jobs.