Here is another post in the series called Caleb’s Corner, where our company president Caleb Horst pens some original content related to biomaterials based on his insights and experience.

Tension Testing for Biomaterials

At CellScale we have supported researchers as they develop test methods for a wide variety of biomaterials. Along the way we have picked up some tricks we would like to share.

Fixation

To pull on something, you need to be holding on. Compression grips are the most common choice. We find that spring closures are best for peak forces less than 20N. They deliver a consistent clamping force that can be tailored for have the ideal force to hold but not damage the specimen. Screw closure grips are best for peak forces greater than 100N. In the 20 to 100N range both options work well.

Generally, tissue paper works well as a gripping surface for delicate tissues, sandpaper works well for soft tissues, and metal serrated jaws work well for stiff tissues. Sometimes gluing the specimen to plastic tabs and then gripping the tabs during the test works well.

For soft rope-like tissues, a 3-point bend jig can be used to create a tension test, as the forces required to bend the tissue are negligible. This makes specimen mounting easier and the force/displacement vectors along the specimen axis can be calculated using trigonometry.

Zero Stress/Strain Determination

Many soft biomaterials are highly non-linear. Determining a displacement at which there is zero load on the specimens is difficult. In these cases, it is best to use a defined pre-load at a point where there is a measurable slope to the force/displacement curve. As a rule of thumb, the preload should be no more that 10% of the peak force.

Strain Measurement

Assuming that the grip motion directly translates into specimen deformation is never ideal. For stiffness measurements on soft materials, non-contact strain measurement is the way to go. For peak force measurements or tests with very large strains, it may not be necessary. Images are always useful for presentations and understanding anomalies that become apparent during data analysis.

Other factors

This post covers some of the most significant aspects of biomaterials testing, but there is so much more! It may be necessary to consider non-uniform specimen geometry, hydration, temperature, material non-uniformity, failure modes, preconditioning, rate dependence, fatigue, and other factors. Testing biomaterials in interesting, and there is much still to learn.

CellScale has been in this business for over 15 years so we know a thing or two, and we’d like to help! Drop me a line at caleb.horst@cellscale.com.

Happy researching!

Caleb Horst 

President

CellScale Biomaterials Testing

To read Caleb’s advice on taking a product to market, click here.

Here is another post in the series called Caleb’s Corner, where our company president Caleb Horst pens some original content related to biomaterials based on his insights and experience.

After years of sweat and tears in research, you’ve invented a new technology! Brilliant and congratulations! You know most people have no idea what you’re talking about (including most of your own family), but you believe in the impact this technology will have in your field. Taking your technology to market is a whole new ball game. Since you are considering it, here are a few things to think about.

Market

Your potential customers’ needs are being met by an existing solution, but your technology is going to be an improvement. You need to research the current commercial entities. How big are they (associated employees on LinkedIn)? Are they new or mature (company age, Crunchbase funding history, publication history referencing their products on Google Scholar)? Are they innovating (new products)?

You should also try to estimate your potential revenue stream with some simple calculations. Take the potential number of customers and multiply by the price point of your product. If this number doesn’t get you excited, then that’s a red flag.

Costs

There is a gap between the product you have built for your own use and the product that you will need to take to market. In reality, it is less of a gap and more of a chasm. Whatever your cost/time estimates are, multiply them both by 4. I don’t mean to be negative here, but I have found this to be true and I know many others have as well. Whatever steps you take next, make sure you are prepared for this reality.

Product

Determine the simplest embodiment of your technology that can achieve the intended function. Bells and whistles are for carnivals. There may be some features you put a lot of time into that are not critical. Don’t let your pride get in the way. If they are not critical, put them on the shelf for now.

Make the product easy to use, hard to break, and cheap to operate. Customers may be wary of long learning curves, repair costs, and ongoing expenses.

Presentation

As a technical person, aesthetics of your product may not be top of mind. Think hard about how you can make it look better – even if the potential changes have a neutral or slightly negative impact on the functionality and cost.

Likewise, you may not yet fully appreciate just how critical sales and marketing are to a business. Even if your product is great, customers are not going to beat a path to your front door. Consider hiring someone to help with your graphics and website (upwork.com is a great place to start).

Licensing

Any entrepreneur will tell you that starting a new venture is not for everyone. Licensing can offload much of the business activities and still result in financial benefits. Be sure to work with a partner that understands your technology and is committed to getting it to market.

Time to start selling? In the end, every situation is unique, and the decision is yours. If you can relate to this article and would like to talk further, please let me know. I am always interested in helping others on their journey.

Happy researching!

Caleb Horst 

President

CellScale Biomaterials Testing

To read his take on mechanical testing for non-engineers, click here.

Here is another post in the series called Caleb’s Corner, where our company president Caleb Horst pens some original content related to biomaterials based on his insights and experience.

Biomaterials research teams often have members from engineering, biology, medicine, and other fields.  For non-engineers it can be easy to understand why mechanical properties are important, but testing can seem complex and confusing. Here’s a quick framework to help you get started.

understand your objectives

Do you need to test an entity with a particular geometry or the properties of a material? For entity testing, it is often important to mimic in vivo loading, perform comparison studies and establish benchmarks. For materials testing it is important to generate a specimen with a regular geometry such as a cylinder, sphere, or dog-bone. This will enable the determination of material properties (such as Young’s Modulus) that are independent of specimen geometry.

choose the right technology for your application

For applied forces 50mN-50kN, conventional load cells are the best choice and are available from most major equipment providers. For applied forces 1μN-50mN, consider cantilever-based force probes such as those used in the CellScale MicroTester or the Optics11 Piuma. In general, expect force accuracy of between 0.1% and 0.5% of the load capacity of the force sensor

For 2-10μm displacement accuracy, motor/screw actuation is used by most equipment providers. For higher accuracy consider piezo-driven or voice coil-driven actuation such as used in the CellScale MicroTester or the TA instruments Electroforce line.

consider fixturing/test environment

Biomaterials vary widely and often require special treatment. For gripping, consider jaw surfaces (serrations, sand paper coating), gripping force (screw, pneumatic, spring closure), or alternative methods such as multi-point puncture mounting or adhesively-applied gripping tabs. Some manufacturers are happy to help in this regard.

Also consider the importance of maintaining hydration and physiological temperatures. Most manufacturers can provide this, but often at additional cost.

plan for test validation

Most test systems will provide a means to calibrate system force and displacement. Many manufacturers have integrated imaging systems which can provide valuable qualitative and quantitative information. These images/videos can also be used effectively in presentations and publications.

Happy researching!

Caleb Horst 

President

CellScale Biomaterials Testing

To read the second post of Caleb’s Corner: Build or Buy, click here

We introduce to the CellScale Blog a series called Caleb’s Corner, where our company president Caleb Horst pens some original content related to biomaterials based on his insights and experience.

So, you’re an engineer, technologist, or DIY maker. You’ve designed and built THINGS before. Back in the day your capstone project won an award, your home is filled with IOT gadgets, and you’ve at least thought about building a robot to make some trivial aspect of your life soooo much better. 

And now you want to do some mechanical testing of biomaterials. You look around at the equipment out there, and you correctly surmise that you could probably buy what you need and build something yourself for less than 1/3 of the cost. 

I know who you are, and I know how you think. A little over a decade ago I WAS YOU. For over 10 years, I have been building and selling equipment to people JUST LIKE YOU. In these years, I have witness great DIY successes. Projects that stayed on schedule and systems worked reliably. Sadly, it is more common that DIY systems take longer than expected, cost more than expected, and in the end only work well under a narrow range of test conditions. 

Generally, I see more researchers succeeding with commercial equipment. It makes sense when you think about all the time and money that goes into building and supporting commercial systems. Our company’s first product, the BioTester, became commercially available in 2007. Every year since then we have continued to invest time and money to improve the system. From the product features, to the user interface, to the robustness of the system, to the documentation – every aspect has been continuously improved in response to the feedback from a large and diverse group of users. Not only does this level of investment improve this product, it has allowed us to create a level of experience and expertise that would not be possible for a part-time DIY system developer.

So back to the main question, build or buy? As with most difficult questions, the answer is… IT 

First, it depends on your budget. Commercial equipment is always more expensive AT THE START and if you don’t have the money then you may not have a choice. That being said, the costs may not as much as you think so it’s always worth a few inquiries.

Second, it depends on your priorities. If your goal is to develop your own engineering capabilities and/or educate as many students as possible on how to build mechanical devices, develop control circuits, and write software, then there has never been a better time to become a designer, maker, and coder. If your mandate is to efficiently complete your research goals and/or publish the most scientifically impactful journal articles as possible, then a well-chosen commercial system is usually the best

Third, it depends on the alignment between the testing you want to do and the capabilities of commercially-available test equipment. If what you want to do is standard (e.g. parallel plate compression) then your needs are well aligned. For cases where a small amount of customization is required, there are great options available. Some companies are willing to absorb some of the engineering costs associated with modifying their equipment for your application if they believe that there is a market for their newly-developed 

Build or buy? In the end, every situation is unique, and the decision is yours. If you can relate to this article and would like to talk things through, then please let us know. We have a knowledgeable and experienced team and we are happy to talk about your application with no obligation at all.

Happy researching!

Caleb Horst 

President

CellScale Biomaterials Testing

To read the first post of Caleb’s Corner: What Makes Mechanical Testing of Biomaterials Different from Manufactured Materials, click here

Check out a subsequent post from Caleb’s Corner: Build or Buy?