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Physical testing for 3D printed medical products

Image Credit: Stable Micro Systems Ltd

3D printing has become a niche manufacturing method, allowing consumers to design and manufacture their own products. As such, it now occupies an important place in the manufacturing industry. Objects can be constructed in almost any format the consumer desires, and this has overcome the early limitations of certain groups of polymers as a building material. It’s now a potential tool in many industries, including bone and organ replacements, meat manufacturing, and even customizable baking.

Stable Micro Systems manufactures instruments that measure the tensile and compressive properties of 3D printed parts. As with any manufacturing innovation, the final product must go through a quality control process to assess its physical properties. A Texture Analyzer is a crucial part of this procedure, providing a reliable way to test the mechanical properties of 3D printed objects by applying a choice of compression, tension, extrusion, adhesion, bending or cutting tests to measure the resistance of a product physical properties for example tensile strength, flexural modulus, fracturability, compressibility, to name but a few.

3D Printing Materials Test Example – Extrusion

The printability of materials used in extrusion 3D printing is one of the most important properties, especially when manufacturing objects with architectural complexities. This parameter is influenced by several factors (temperature, components and additives), which makes a thorough evaluation and classification difficult. Interest in 3D printing for biomedical applications is growing and the pharmaceutical industry is beginning to explore how 3D printing can help us deliver better medicines. Achieving reproducibility in 3D printing of biomaterials requires a robust polymer synthesis method to reduce batch-to-batch variation as well as methods to ensure thorough characterization throughout the manufacturing process. In particular, biomaterial inks containing large solid fractions such as ceramic particles, often required for bone tissue engineering applications, are prone to inhomogeneity from improper mixing or particle aggregation which can lead to inconsistent print results. The production of such ink can be optimized to ensure consistent and repeatable print results by using a TA.XTPlusC Texture Analyzer to perform extrusion force measurements to predict the printability of inks. To read a sample post of this texture analyzer app at ETH Zurich, Click here.

Direct extrusion test on a texture analyzer. Image Credit: Stable Micro Systems Ltd

3D Printing Materials Test Example – Compression

Due to the low price of 3D printing equipment and its versatility, materials such as antioxidant PLA composites containing lignin can be used in hospitals to print dressings for patients on demand. 3D printing can also benefit plastic and reconstructive surgeries by fabricating patient-specific tissue substitutes with tissue-like functions and mechanical properties. A texture analyzer can be used to perform compression test on samples to characterize their mechanical properties which are important for their structural integrity. To read a sample post of this Texture Analyzer app at the University of Nottingham, Click here.

Unconfined compression on a texture analyzer. Image Credit: Stable Micro Systems Ltd

3D Printing Materials Test Example – Bending and Bending

3D printing offers a new approach to the fabrication of drug-eluting implantable medical devices, as it allows complex and custom shapes of tissue scaffolds to be flexibly extruded. Given the simplicity, it can be easily transferred to a clinical setting, where implants could be designed on demand to meet patient needs after surgery. These implants may be suitable for administering drugs for localized treatment. For example, chemotherapy agents, antibiotics or local anesthetics. Alternatively, they could be adapted by coating them for prolonged administration of drugs for the treatment of chronic diseases.

Compared to other printable biomaterials, polyurethane elastomers have several advantages, including excellent mechanical properties and good biocompatibility. However, some intrinsic behaviors, especially high melting point and slow degradation rate, hinder their application in 3D printed tissue engineering. The development of a 3D printable amino acid modified biodegradable water-based polyurethane means that the flexibility of this material provides better tissue compliance during implantation and prevents high modulus grafts from scratching tissue surrounding. The use of a texture analyzer to perform flexibility measurements (three-point curvature) on 3D printed samples allows to evaluate if this can be used as an alternative biomaterial for tissue engineering with low temperature printing, biodegradability and compatibility. To read a sample post of this texture analyzer app at Beijing Science and Technology University, Click here Where Click here to see similar work at Queen’s University Belfast.

3-point flexibility and bending test on a texture analyzer. Image Credit: Stable Micro Systems Ltd

Example of testing 3D printing materials – Perforation, Elongation and Tension:

Orodispersible films (ODF) are promising dosage forms for children or the elderly who may have swallowing problems with solid oral dosage forms. By printing active pharmaceutical ingredients on orodispersible films, the flexibility of drug dosing is increased and offers potential for personalized drugs. Warfarin is an example of a drug with a narrow therapeutic index which requires a personalized dosage which is not currently achieved by marketed products. 3D printing by extrusion can be used to produce transparent, smooth and thin, yet flexible and resistant orodispersible films containing therapeutic doses. Using a texture analyzer, films can measure their properties of burst strength and flexibility as part of their critical physical characteristics that could impact their usability.

To read a sample post of this texture analyzer app at Heinrich Heine University Dusseldorf Click hereWhere Click here for similar work done at Åbo Akademi University.

Bursting strength, tensile strength and film flexibility on a texture analyzer. Image Credit: Stable Micro Systems Ltd

How a Texture Analyzer Can Assess the Flow of Base Powder

Texture analysis can also be used at other stages of the 3D printing process, not just to measure the properties of the final product. For example, the properties of the base powder used in selective laser sintering affect the sintering process as well as the properties of the final product. The flow of the powder is one of these properties. As each new layer of powder is swept over the sinter bed, the layer should be even and of the correct thickness and distribution. A Powder flow analyzer (PFA) is a very useful addition to a Texture Analyzer Plus to help measure these flow properties.

PFA proves to be an accurate and reliable method for measuring the flow characteristics of dry and wet powders, with the ability to measure cohesion, clumping and velocity flow dependence as well as bulk density and other properties. It can be quickly retrofitted to a TA.XTPlusC Texture Analyzer, allowing manufacturers to assess and avoid typical issues such as batch and source variation of ingredients, clumping during storage/transportation and problems unloading hoppers or bins, as well as 3D printing. specific properties of the powder. The powder is conditioned at the start of each test to eliminate any load variation and the patented precision blade is then rotated through the sample causing a controlled flow.

Image Credit: Stable Micro Systems Ltd

The need to measure dimensional profiles

If you designed a product and then print it, one of the concerns will be whether what was printed matches what you designed. In many cases you will need your printed object to be dimensionally accurate and printing iterations of your design are almost inevitable to adjust the print settings to achieve a dimensionally accurate product. A precise numerical evaluation of the physical dimensions thus becomes a necessity. A Volscan Profiler provides such a solution – a benchtop laser scanner that measures the volume, density and dimensional profiles of solid products. Rapid three-dimensional scanning of products allows for the automatic calculation of several detailed dimension-related parameters, the results of which can be mathematically manipulated for immediate use or future retrieval in a variety of data formats for your printed objects.

Volscan Profiler models for measuring volume, density and dimensional profiles. Image Credit: Stable Micro Systems Ltd

Bone sample ready for scanning and an archived scan of the sample. Image Credit: Stable Micro Systems Ltd

The medical industry is increasingly dependent on the TA.XTmoreC Texture Analyzer as a tool for measuring all types of physical/mechanical properties.

See a wider range of test and measurement possibilities in this area.

Joan J. Dean

The author Joan J. Dean