Improving the Reliability of a Medical Device Component through Comprehensive Material Characterization

Background:

A medical device manufacturer experienced an unexpected problem during the assembly of a plastic device component. The part – a polymer syringe adapter – was found to fracture and crack shortly after a secondary assembly step. The assembly involved exposing the part to an adhesive solvent and UV light for curing. Despite using a well-known medical-grade polymer and having consistent manufacturing processes, several batches showed a brittle failure in this component. Both the polymer supplier and the molding contractor insisted nothing had changed in materials or process, leaving the device company puzzled and concerned. They needed to identify the root cause of the failure: Was the material inherently flawed or contaminated? Did the solvent or UV exposure during assembly weaken it? Or was there an unknown issue in the molding process? The company turned to a comprehensive characterization study to find answers and prevent this failure from occurring in the field.

Analysis: 3 samples were processed for investigation – a failed component (after assembly, showing cracks), an unused “good” component from the same batch (not yet assembled, no cracks), and a sample of the raw polymer pellets used to mold the component. A team of materials scientists designed a battery of characterization tests to compare these samples and pinpoint differences. Key techniques applied included:

• Scanning Electron Microscopy (SEM): to closely examine the fracture surfaces of the failed component. SEM provided high-magnification images of the crack morphology. These revealed patterns indicative of stress crazing – tiny micro-cracks and rough texture suggesting the material had become embrittled. By contrast, the unused component’s surface appeared ductile and smooth under SEM, confirming a significant change in the material’s fracture behavior had occurred during processing or assembly.
• Differential Scanning Calorimetry (DSC): to analyze the thermal properties of the polymer in the failed part vs. the raw material. DSC scans showed a lower glass transition temperature (Tg) and signs of a broad thermal degradation in the failed component compared to the raw polymer. This was a red flag: a lowered Tg and extra heat flow events suggested that the polymer’s molecular weight might have dropped (a sign of polymer degradation). Essentially, the material in the failed piece was no longer the same as the pristine material – it had broken down either during molding or assembly.
• Thermogravimetric Analysis (TGA): to complement DSC by checking the thermal stability and decomposition behavior. TGA indicated that the failed part began losing mass at a lower temperature than the raw polymer, consistent with a degraded polymer that would start to break apart (emit volatiles, etc.) sooner. This supported the theory that the polymer had undergone some thermal or chemical breakdown.
• Fourier Transform Infrared Spectroscopy (FTIR) is a fast, nondestructive method that identifies materials by their unique infrared absorption signatures. Each molecular bond absorbs IR light at specific frequencies, creating a distinctive “fingerprint” spectrum that can be matched against libraries to confirm polymer types, coatings, or contaminants. FTIR is particularly useful for failure investigation: for example, detecting the appearance of carbonyl peaks can signal oxidation in polymers—a common reaction seen in UV-exposed or aged implant materials. FTIR microscopy allows analysis even when particulate residues or small fibers are found on device surfaces, enabling precise identification of manufacturing or environmental contaminants. Our specialized FTIR services pair microscopic imaging with spectrum analysis to confirm material identity and detect chemical changes, ensuring your device components are pure, stable, and free from harmful degradation.

Conclusion

Comparative investigations using DSC and FTIR suggested that the polymer’s degradation occurred before the component reached assembly. DSC revealed a notably lower glass transition temperature (Tg) compared to fresh material, signaling chain scission – a hallmark of thermally aged polymers. FTIR spectra further confirmed oxidative damage through newly emerged carbonyl peaks, that are accordant with photo-oxidative cleavage induced by UV exposure and solvent stress. SEM images showed fine surface crazing – micro-crack networks typical of polymers that have undergone embrittlement through environmental stress cracking. These microscopic features indicated that thermal degradation had compromised the polymer, making it vulnerable to cracking under solvent exposure and mechanical load.

Nishka Research has suggested to adjust the production parameters like molding temperatures and cycle duration were lowered and the polymer grade was switched to one containing stabilizer.