Preparation, characterization and powder-bed laser sintering of biodegradable composite powders

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Additive manufacturing processes such as powder bed-fusion laser beam melting are becoming increasingly important for the production of complex components with individualized shapes and properties. Such processes are especially promising in the biomedical sector to produce personalized implants with patient-specific properties and exact fit. A major current limiting factor in this field is the availability of suitable composite powder materials that combine biodegradable polymers with functional additives. The aim of our project is to expand the available range of materials for by developing a new platform for the production of defined composite powders. Our approach uses supraparticles as powder materials, which can be produced from the controlled self-assembly of defined primary particle mixtures. These supraparticles offer several important advantages for the powder bed fusion laser beam melting process: i) a wide range of polymeric materials becomes accessible as powder systems by established methods such as miniemulsion-based techniques; ii) the composition can be precisely adjusted via the primary particles and leads to homogeneous distributions of the components in the final material; iii) a defined and adjustable surface roughness results from the size of the primary particles and promotes flowability and thus a homogeneous and dense powder bed. We will demonstrate the advantages of this process for a biomedically relevant material system consisting of biodegradable polyactide polymers with functional additives. An effective processing of these new powder systems and the realization of the different degrees of freedom in the powder design requires the development of a materials-effective printing process. This requires the development of a desktop laser beam melting system for processing small powder quantities. Furthermore, the interaction between the laser beam source and the structure of the powder particles plays a key role for the resulting component properties. As a standard, CO2 lasers (10.6 µm) are used for laser beam melting of thermoplastics, since polymers effectively absorb in the IR. However, this leads to a high heat input and therefore risks the degradation of thermolabile biopolymers such as PLA and added therapeutic molecules. Therefore, the project aims at changing the laser source to a diode laser system (445nm), which enables the volume-like coupling of the laser radiation directly via embedded, absorbing nanoparticles and thus requires less energy to be introduced into the powder. The overall goal of the project is to establish fundamental process-structure-property relationships that will enable the optimization of the powder bed fusion process and the resulting properties via the structure, morphology and composition of the supraparticle powders.