Periodic Reporting for period 1 - SIMPPER_MedDev (Surface Integrity for Micro/Nano Processing of Polymers: A European Research Training Network for High-Performance Medical Devices)
Reporting period: 2021-01-01 to 2022-12-31
This project focuses on micro/nano surface integrity issues when processing polymers for high performance medical devices. Micro/nano-scale precision manufacturing processes are being developed (moulding and forming, and additive and subtractive processes) for six classes of medical devices with specific industry-defined requirements: drug delivery devices, cardiovascular stents, microfluidic chips, organ-on-a-chip, acetabular cups and hearing aids. The surface integrity of these materials and devices are studied at a fundamental level and correlated with functionality, allowing for efficacy and performance to be optimised. Our training ensures that twelve outstanding ESRs will become experts in design and the precision micro/nano processing of polymers for medical devices, thereby improving their career prospects. Our ESRs undertake interdisciplinary and intersectoral research on polymer micro/nano processing for medical devices and obtain international work experience with industry. They receive specialised technical training and transferable skills structured around state-of-the-art individual research projects to provide them with pathways to engineering and manufacturing careers in Europe’s world leading industry.
During the first 24 months of the project, twelve ESRs were hired, four training modules were completed and the following work was carried out by each of the ESRs:
ESR1 is developing high strength bonding of polymer to magnesium with micro/nano structures for resorbable stents. The corrosion behaviour, roughness and hydrophilicity of WE43 Mg alloy are modified by means of anodization and stearic acid treatment. This limits corrosion of the alloy surface and also increases adhesion and the useful life of bonded polymer layers.
ESR2 focuses on developing micro/nanostructures for pathogen detection by immobilising DNA (not proteins, as stated in GA). For this purpose, a digital LAMP (loop-mediated isothermal amplification) platform comprising extraction and partitioning components (for DNA amplification) has been designed. Based on different selection criteria, PMMA and COC were chosen for injection moulding the functional devices.
ESR3 is developing a novel high-resolution DLP printing system for 3D bioprinting and microfluidics applications. The hardware and control software have been realised and validated. Background work for preparing photopolymer resin components has begun. The 3D printing system has been validated and its resolution limits were determined by digital microscopy.
ESR4 aims to develop microstructures for low friction polymer surfaces in medical device applications with particular emphasis on injection moulding systems. Material selection has been completed (POM, PC, PP, PBT and thermoplastic polyester) and microstructures have been designed based on a thorough state-of-the-art review. Sample parts have been designed.
ESR5 investigates the use of soft polymers in additive manufacturing to digitally produce hearing aid ear moulds and domes. Hydrophobicity and antifouling effects are induced by using suitable surface topographies in the 3D printing process. Strategies followed include integrating porogen into the photoresin, directly printing biocompatible soft resins and PDMS cast from 3D printed moulds. Initial studies were carried out on flat surfaces featuring hydrophobic micro-/nanostructures. Water contact angles of up to 160° have been achieved.
ESR6 investigates precision injection moulding with biobased polymers for medical device applications. Material characterisation (thermal properties and rheology) has been completed for selected poly(hydroxy alkanoates) and preliminary micro-structure replication trials have been achieved with two biopolymer grades. Injection moulding, particularly of micro-pillars, is challenged by the narrow processing window (high fluidity and strong temperature dependence of melt viscosities) and the risk for thermal degradation during processing.
ESR7 uses precision laser micro-machining to manufacture prototype thermoplastic mould inserts suitable for low volume fabrication of functional microfluidic devices by injection moulding. Four polymers (PI, PEI, PC and PEEK) have been analysed (optical, thermal and mechanical properties) and single pulse experiments have been carried out to determine the threshold fluence and the parameter regions for linear ablation. Laser micro-machining of microfluidic masters has been initiated.
ESR8 is exploring the feasibility of laser-assisted deposition of electrical conductors and insulators for medical micro-electro-mechanical device (MEMS) applications with a particular focus on the interaction of metals and medical-grade polymers as examples of these classes of materials. As a method, the process of laser-induced forward transfer (LIFT) was identified, allowing the deposition of metals and potentially polymers at the same time.
ESR9 investigates the formation of laser-induced periodic surface structures (LIPSS) on cyclo-olefin copolymers (COC) to modify wetting behaviour, adjust cell response, reduce friction or possibly induce antimicrobial effects. Laser experiments at UV wavelengths have been carried out to determine the parameter space in which LIPPS form on uncoated and Au-coated COC. The resulting surface morphology is being analysed by scanning electron microscopy. LIPSS experiments with IR wavelengths and deep UV have commenced.
ESR10 explores the potential use of lasers for sealing microfluidic devices based on transparent polymers, focusing on two grades of cyclo-olefin copolymers (COC), differing in glass transition temperature, widely used in diagnostic applications. The laser welding process being developed will be compared to standard thermal and ultrasonic bonding processes. Successful sealing of microfluidic devices with a black substrate and transparent cover was achieved with a nanosecond laser normally used for engraving.
ESR11 focuses on fabricating silicone-free prefilled syringes by injection moulding, making use of functional surface topographies that decrease friction to replace current coating technologies used in such systems. To screen a wide variety of dimple microstructures, the use of direct laser writing (DLW) based on two-photon polymerization is used to fabricate micro-structured surface prototypes to establish optimal low-friction surfaces.
ESR12 investigates the cryogenic machining of biomedical grade polymers to improve the surface integrity of acetubular cups and possible reduction of friction and wear. Biomedical grade PEEK has been selected and turning trials (cryogenic and conventional) have been conducted under different parameters, followed by inspection of the resulting surfaces and chip morphology with respect to surface texture, surface defects, crystallinity and hardness.
ESR1 is developing high strength bonding of polymer to magnesium with micro/nano structures for resorbable stents. The corrosion behaviour, roughness and hydrophilicity of WE43 Mg alloy are modified by means of anodization and stearic acid treatment. This limits corrosion of the alloy surface and also increases adhesion and the useful life of bonded polymer layers.
ESR2 focuses on developing micro/nanostructures for pathogen detection by immobilising DNA (not proteins, as stated in GA). For this purpose, a digital LAMP (loop-mediated isothermal amplification) platform comprising extraction and partitioning components (for DNA amplification) has been designed. Based on different selection criteria, PMMA and COC were chosen for injection moulding the functional devices.
ESR3 is developing a novel high-resolution DLP printing system for 3D bioprinting and microfluidics applications. The hardware and control software have been realised and validated. Background work for preparing photopolymer resin components has begun. The 3D printing system has been validated and its resolution limits were determined by digital microscopy.
ESR4 aims to develop microstructures for low friction polymer surfaces in medical device applications with particular emphasis on injection moulding systems. Material selection has been completed (POM, PC, PP, PBT and thermoplastic polyester) and microstructures have been designed based on a thorough state-of-the-art review. Sample parts have been designed.
ESR5 investigates the use of soft polymers in additive manufacturing to digitally produce hearing aid ear moulds and domes. Hydrophobicity and antifouling effects are induced by using suitable surface topographies in the 3D printing process. Strategies followed include integrating porogen into the photoresin, directly printing biocompatible soft resins and PDMS cast from 3D printed moulds. Initial studies were carried out on flat surfaces featuring hydrophobic micro-/nanostructures. Water contact angles of up to 160° have been achieved.
ESR6 investigates precision injection moulding with biobased polymers for medical device applications. Material characterisation (thermal properties and rheology) has been completed for selected poly(hydroxy alkanoates) and preliminary micro-structure replication trials have been achieved with two biopolymer grades. Injection moulding, particularly of micro-pillars, is challenged by the narrow processing window (high fluidity and strong temperature dependence of melt viscosities) and the risk for thermal degradation during processing.
ESR7 uses precision laser micro-machining to manufacture prototype thermoplastic mould inserts suitable for low volume fabrication of functional microfluidic devices by injection moulding. Four polymers (PI, PEI, PC and PEEK) have been analysed (optical, thermal and mechanical properties) and single pulse experiments have been carried out to determine the threshold fluence and the parameter regions for linear ablation. Laser micro-machining of microfluidic masters has been initiated.
ESR8 is exploring the feasibility of laser-assisted deposition of electrical conductors and insulators for medical micro-electro-mechanical device (MEMS) applications with a particular focus on the interaction of metals and medical-grade polymers as examples of these classes of materials. As a method, the process of laser-induced forward transfer (LIFT) was identified, allowing the deposition of metals and potentially polymers at the same time.
ESR9 investigates the formation of laser-induced periodic surface structures (LIPSS) on cyclo-olefin copolymers (COC) to modify wetting behaviour, adjust cell response, reduce friction or possibly induce antimicrobial effects. Laser experiments at UV wavelengths have been carried out to determine the parameter space in which LIPPS form on uncoated and Au-coated COC. The resulting surface morphology is being analysed by scanning electron microscopy. LIPSS experiments with IR wavelengths and deep UV have commenced.
ESR10 explores the potential use of lasers for sealing microfluidic devices based on transparent polymers, focusing on two grades of cyclo-olefin copolymers (COC), differing in glass transition temperature, widely used in diagnostic applications. The laser welding process being developed will be compared to standard thermal and ultrasonic bonding processes. Successful sealing of microfluidic devices with a black substrate and transparent cover was achieved with a nanosecond laser normally used for engraving.
ESR11 focuses on fabricating silicone-free prefilled syringes by injection moulding, making use of functional surface topographies that decrease friction to replace current coating technologies used in such systems. To screen a wide variety of dimple microstructures, the use of direct laser writing (DLW) based on two-photon polymerization is used to fabricate micro-structured surface prototypes to establish optimal low-friction surfaces.
ESR12 investigates the cryogenic machining of biomedical grade polymers to improve the surface integrity of acetubular cups and possible reduction of friction and wear. Biomedical grade PEEK has been selected and turning trials (cryogenic and conventional) have been conducted under different parameters, followed by inspection of the resulting surfaces and chip morphology with respect to surface texture, surface defects, crystallinity and hardness.
The deep involvement of world-leading industry partners in the training network will ensure that improvements beyond the state-of-the-art translate into the next generation of designs for medical devices and that 12 ESRs will be trained in the design, manufacturing, evaluation and commercial aspects of this interdisciplinary and intersectoral field. The ESRs key transferable skills are developed, helping to ensure that Europe remains at the forefront of the worldwide medical devices manufacturing industry.