To define optimal molecular materials design for fused deposition modelling of mechanically integral polylactide parts, the effect of intrinsic local heat fluctuations on morphology and structure evolution is presented. Macroscopic fusion during melt deposition is governed by molecular dynamics of solidification and positively affected by low print speed, low molar mass. However, low molar mass and high L-enantiomeric purity induces melt crystallization during deposition, limiting interfacial

molecular diffusion. By increasing molar mass crystallization during melt deposition is suppressed, establishing interfacial molecular diffusion and mechanically effective interfaces. Despite the mutual interpenetration depth (bond thickness) is typically in the order of the molecular coil size, the mechanical strength suffers from low re-entangled state 1. Further structure evolution via cold crystallization is timed in successive annealing cycles. Adding more layers entails a progressive decrease (i) in heat transfer to the build plate and (ii) number of annealing cycles per layer, inducing variations in crystallinity and thus thermodynamic instability. Consequently, macroscopic mechanics and geometrical stability of fused deposition modelled polylactides remain compromised by judiciously timed crystallization and process design. However, the molecular understanding of the dynamics of fusion, chain diffusivity and crystallization in relation to print strategy and operational life-time is opportune in materials design exploiting positioning and directing local structure induced functionalities for tailored biomedical gradient performance.

Jules Harings is asst. Prof. Macromolecular Physics & Technology at Maastricht University. He received his PhD in Polymer Technology from Eindhoven Technical University under supervision of Prof. S. Rastogi and Prof. P.J. Lemstra in 2009. His thesis is entitled "Shielding and deshielding of amide-based (macro)molecules. After a four year's period as Research Scientist and project leader fiber physics and new product development at Teijin Aramid, where he received the Teijin global best R&D award in 2011, he returned to academics at Maastricht University in 2013. Besides coordinating and lecturing the UM undergraduate courses "Physical Chemistry", "Physical Chemistry for the Life Sciences", and UM BioBased Master courses "Introduction to Polymer Materials Science and Engineering" and "Bio-inspired Nano-structured Functional Materials", he is principle investigator in the Aachen Maastricht Institute for Biobased Materials (AMIBM). His focus is studying, understanding and technically exploiting the behaviour of macromolecules via his research lines: (i) molecular, structure and scaffold design of biomedical polymers for 3D printing and fiber spinning in regenerative tissue engineering, and (ii) water actuated structural refinement and enzymatic biodegradability for timed ultimate polyamide performance.

Maastricht University (UM) is the most international university in the Netherlands and, with 16,300 students and 4,300 employees, is still growing. The university stands out for its innovative education model, international character and multidisciplinary approach to research and education. The Faculty of Science and Engineering (FSE) is the incubator and home of several outstanding departments and prestigious institutions in education and research such as the Aachen Maastricht Institute for Biobased Materials (AMIBM). It is a cross-border cooperation between Maastricht University, RWTH Aachen and Fraunhofer IME acting on the missing link between fundamental and applied research, and the market in the field of biobased materials. Via an integrated, interdisciplinary research program novel, innovative, sustainable and socio-economically viable strategies AMIBM focuses on advanced biobased technical and biomedical materials.