Inner strut morphology is the key parameter in producing highly porous and mechanically stable poly(ε-caprolactone) scaffolds via selective laser sintering.

Selective laser sintering (SLS) is an established method to produce dimensionally accurate scaffolds for tissue engineering (TE) applications, especially in bone. In this context, the FDA-approved, biodegradable polymer poly(ε-caprolactone) (PCL) has been suggested as a suitable scaffold material. However, PCL scaffold mechanical stability - an attribute of particular importance in the field of bone TE - was not considered as a primary target for SLS process parameters optimization so far. Here, we investigated the influence of SLS process parameters on the sintered scaffolds with the aim of producing highly porous (>70% porosity) PCL scaffolds with sub-mm geometrical features for bone TE. Specifically, we studied the influence of laser power, beam compensation and laser beam diameter on the dimensional accuracy and mechanical stiffness of the produced PCL scaffolds. We found that the ratio between the diameter of the molten cross-section within scaffold struts and the outer strut diameter (including partially sintered particles) depended on the SLS process parameters. By maximizing this ratio, the mechanical stability could be optimized. The comparison with in silico predictions of scaffold mechanical stiffness revealed that the diameter of the molten cross-section within struts and not the strut diameter controlled the mechanical behaviour of the scaffold. These observations should be considered when evaluating the quality of the sintering process based on dimensional accuracy, especially for features <1 mm. Based on these findings, we suggested an approach to evaluate the sintering outcome and to define SLS process parameters that enable the production of highly porous scaffolds that are both dimensionally accurate and mechanically stable. Moreover, the cytocompatibility of PCL scaffolds was evaluated by elution tests with primary human mesenchymal stromal cells. No evidence of cytotoxicity was found in any of the investigated scaffolds, confirming the suitability of SLS as production technique of PCL scaffolds for bone TE over a wide range of SLS process parameters.

Development of a solvent-free polylactide/calcium carbonate composite for selective laser sintering of bone tissue engineering scaffolds.

Since large bone defects cannot be healed by the body itself, continuous effort is put into the development of 3D scaffolds for bone tissue engineering. One method to fabricate such scaffolds is selective laser sintering (SLS). However, there is a lack of solvent-free prepared microparticles suitable for SLS. Hence, the aim of this study was to develop a solvent-free polylactide/calcium carbonate composite powder with tailored material properties for SLS. Four composite powders with a composition of approximately 75 wt% polylactide (PLLA as well as PDLLA) and 25 wt% calcium carbonate (calcite) were prepared by a milling process based on GMP standards. Four different grades of polylactide were chosen to cover a broad inherent viscosity range of 1.0-3.6 dl/g. The composite material with the lowest inherent viscosity (1.0 dl/g) showed the best processability by SLS. This was caused by the small polymer particle diameter (50 µm) and the small zero-shear melt viscosity (400 Pa·s), which led to fast sintering. The SLS process parameters were developed to achieve low micro-porosity (approx. 2%) and low polymer degradation (no measurable decrease of the inherent viscosity). A biaxial bending strength of up to 75 MPa was achieved. Cell culture assays indicated good viability of MG-63 osteoblast-like cells on the SLS specimens. Finally, the manufacture of 3D scaffolds with interconnected pore structure was demonstrated. After proving the biocompatibility of the material, the developed scaffolds could have great potential to be used as patient-specific bone replacement implants.

Influence of the material properties of a poly(D,L-lactide)/ß-tricalcium phosphate composite on the processability by selective laser sintering.

Complex 3D scaffolds with interconnected pores are a promising tool for bone regeneration. Such 3D scaffolds can be manufactured by selective laser sintering (SLS) from biodegradable composite powders. However, the mechanical strength of these scaffolds is often too low for medical application. We propose that the mechanical strength of laser-sintered scaffolds can be improved through composite powders with tailored properties (e.g., suitable powder particle size and melt viscosity for SLS). To prove this, two batches of a poly(D,L-lactide) (PDLLA)/ß-tricalcium phosphate (ß-TCP) composite powder with 50 wt% PDLLA and 50 wt% ß-TCP were synthesized. The two batches differed in polymer particle size, filler particle size, and polymer molecular weight. Both batches were processed with identical SLS process parameters to study the extent to which the material properties influence how well a PDLLA/ß-TCP (50/50) composite can be processed with SLS. In the SLS process, batch 2 showed improved melting behavior due to its smaller polymer particle size (approx. 35 µm vs. 50 µm) and its lower zero-shear melt viscosity (5800 Pa∙s vs. 17,900 Pa∙s). The better melting behavior of batch 2 led to SLS test specimens with lower porosity compared to batch 1. In consequence, the batch 2 specimens exhibited a larger biaxial bending strength (62 MPa) than the batch 1 specimens did (23 MPa). We conclude that a tailored composite powder with optimized polymer particle size, filler particle size, and polymer molecular weight can increase the achievable mechanical strength of laser-sintered scaffolds.

The former Iron Curtain still drives biodiversity-profit trade-offs in German agriculture.

Agricultural intensification drives biodiversity loss and shapes farmers' profit, but the role of legacy effects and detailed quantification of ecological-economic trade-offs are largely unknown. In Europe during the 1950s, the Eastern communist bloc switched to large-scale farming by forced collectivization of small farms, while the West kept small-scale private farming. Here we show that large-scale agriculture in East Germany reduced biodiversity, which has been maintained in West Germany due to >70% longer field edges than those in the East. In contrast, profit per farmland area in the East was 50% higher than that in the West, despite similar yield levels. In both regions, switching from conventional to organic farming increased biodiversity and halved yield levels, but doubled farmers' profits. In conclusion, European Union policy should acknowledge the surprisingly high biodiversity benefits of small-scale agriculture, which are on a par with conversion to organic agriculture.