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Biofouling, the adhesion of sea life to ships' hulls, is a serious problem for all marine vessels. The sticky stowaways significantly increase the hull's friction; the resulting drag decreases boat speed and increases fuel consumption by up to 40%. In the past, the most effective solution was to dry-dock the boat and manually remove the sea life, which is expensive and labor intensive. In addition to the financial toll of increased fuel usage and dry dock cleaning, marine fouling also contributes to the spread of invasive species.

Anti-Fouling Biocides vs. Non-Toxic Hydrogel

Many commercial anti-fouling agents are composed of toxic chemicals. The obvious drawbacks to a toxic approach are water pollution and the poisoning of non-fouling species. Additionally, anti-fouling biocides need to be replaced frequently, and do not always work well. 

The US Naval Coastal Systems Station contracted Cambridge Polymer Group to develop a slow-dissolving hydrogel formulation to clean ships' hulls underwater. Applied by divers using gun applicators, the hydrogel eliminates the need for dry dock manual removal. Simple dilution of the hydrogel makes it safe for marine life, providing a non-toxic, affordable solution for boat cleaning.

Mussel Attachment Issues

But what if the fouling itself could be prevented? Recently, Harvard researchers unveiled a lubricant-infused coating which stops mussels from attaching to underwater surfaces. Mussels are some of the worst biofouling offenders; they have evolved to stick under the severest of marine conditions. As part of that adaptation, mussels secrete adhesive filaments called byssal threads. These threads are tipped with adhesive plaques which remove water molecules from the wet surface, allowing the plaques to bind to it.

The researchers' lubricant-infused polymer coating fools the mussel into sensing the hull's surface as too soft for attachment. This trick discourages the mussel from secreting its adhesive filaments, preventing attachment of the mussel's foot. Even if a mussel attempts to deploy its byssal threads, this Slippery Liquid Infused Porous Surface (SLIPS) stops the threads from binding. Co-first author Shahrouz Amini speculates the liquid overlayer of the lubricant-infused surfaces resists displacement by mussels' adhesive proteins.

The amazing adhesive ability of mussels does have positive applications. UC Santa Barbara researchers have developed stronger, more durable dental fillings using catechols, the same chemical groups used by the mussel to promote adhesion on wet surfaces (wet surfaces except for SLIPS, that is). Purdue researchers have inserted catechol into a biomimetic polymer, creating an underwater adhesive that outperforms many commercial adhesives.

 Thursday, October 12, 2:10 p.m. EST

Adam Kozak, a senior research scientist at Cambridge Polymer Group, presents "Leachable Studies of Medical Devices in Complex Biological Environments" at Eurofins Lancaster Laboratories' Extractables and Leachables Symposium for Drugs and Devices in Pennsylvania.

Detailed Extractables/Leachables Studies

Extractables and leachables studies usually follow a two-step program. In the first step, an exaggerated extraction is conducted using simple solvent conditions more aggressive than those anticipated to be realized in a clinical setting in order to determine to determine the complete extraction profile and to identify the potential extraction compounds, desired or undesired. In the second step, a leaching study is conducted that attempts to simulate the clinical environment of the target application. The simulated leaching environment often comprises a more complex biological matrix than those used for extraction, which in turn complicates the chemical analysis assays used to identify and quantify the leaching materials. In this presentation, we show examples of studies that required a more detailed testing assay to identify and quantify compounds coming from implanted medical devices.

Biography

Adam Kozak specializes in the chemical and mechanical analysis of polymer materials and medical devices. He has substantial experience in the use of gas chromatography-mass spectroscopy (GC-MS) for leachables and extractables analysis, trace impurity/contaminant analysis, residual monomer content, unknown compound identification, migration levels, deformulation, and odor analysis by headspace GC-MS and other chromatographic techniques.

Figure 1: On left, flax seeds, the source of linseed oil. On right, a representative triglyceride found in a linseed oil.

Linseed oil is derived from flax seeds (Fig 1; typically via pressing and solvent extraction methods). In the presence of oxygen, it polymerizes to form a rigid and hydrophobic solid through a highly exothermic oxidation reaction. This is often misleadingly referred to as “drying”; the process does not depend on evaporation of water but rather on the presence of oxygen to form crosslinks between adjacent triglycerides at points of fatty acid unsaturation (Fig 2). The resulting material is an excellent example of a naturally derived, crosslinked polymer whose properties arise from a complex mixture of its constituents and the processing conditions under which it is formed.

Figure 2: Polymerized and hydrogenated linseed oil. Crosslinks between triglycerides (formerly double bonds) are indicated with arrows.

Due to its easy workability and advantageous “dry” properties, linseed oil is widely used in applications ranging from nutritional supplements (it is rich in Omega-3 fatty acids), as a binder in paint, and in linoleum. In fact, the name “Linoleum” derives from the Latin words for flax (“linum”) and oil (“oleum”). In its native state, linseed oil is a liquid composed of triglycerides (Fig 1) consisting of various combinations of fatty acids—the most common being linoleic acid, alpha-linoleic acid, palmitic acid, stearic acid, and oleic acid.

Figure 3: Example separation of 37 fatty acids by gas chromatography for subsequent quantitation.

The fatty acid fingerprint of a triglyceride-based oil (Fig 3) is a valuable analytical tool for material/compositional identification, correlation to functional properties, good/bad analysis, and quantitative analysis. CPG has a variety of methods which may be leveraged for the analysis of oils—this includes techniques such as gas chromatography (which may be coupled to mass spectrometry; GCMS) which can be used to determine the fatty acid distribution for a sample. 

Note that due to the highly exothermic nature of the polymerization process, linseed oil should be handled with care and is often treated as a fire hazard. Over the years many fires have been attributed to the spontaneous combustion of oil soaked rags, often abandoned after a painting job. Such rags are especially dangerous because they present a very high surface area and accelerate the oxidation reaction. If left balled up, temperatures may rise sufficiently high to ignite the entire mass. The Massachusetts Office of Public Safety and Security offers clear guidelines for the safe disposal of such materials.

Working with natural oils? Looking to better understand differences between performance of naturally derived materials? Contact us to see how our team may be able to assist in your project.

Cambridge Polymer Group has received notification of the award of their patent “Thiolated PEG-PVA Hydrogels” (14/328,176).  This patent describes a new way of creating hydrogels from a conventional biomaterial poly(vinyl alcohol).  The resulting hydrogels cure under physiological conditions with no toxic crosslinkers or bi-products and can be tuned to degrade over periods of weeks. 

They are therefore likely to see value in drug release, temporary tissue bulking or scaffold applications, and although they can be cured in vitro, they appear particularly well suited to in vivo applications.  In fact, we are already working to commercialize this material through the recent award of an NIH Phase 1 SBIR grant in the field of retinal detachment.  

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.