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.

An engineered multicomponent bone marrow niche for the recapitulation of hematopoiesis at ectopic transplantation sites.

BACKGROUND: Bone marrow (BM) niches are often inaccessible for controlled experimentation due to their difficult accessibility, biological complexity, and three-dimensional (3D) geometry. METHODS: Here, we report the development and characterization of a BM model comprising of cellular and structural components with increased potential for hematopoietic recapitulation at ectopic transplantation sites. Cellular components included mesenchymal stromal cells (MSCs) and hematopoietic stem and progenitor cells (HSPCs). Structural components included 3D ß-tricalcium phosphate (ß-TCP) scaffolds complemented with Matrigel or collagen I/III gels for the recreation of the osteogenic/extracellular character of native BM. RESULTS: In vitro, ß-TCP/Matrigel combinations robustly maintained proliferation, osteogenic differentiation, and matrix remodeling capacities of MSCs and maintenance of HSPCs function over time. In vivo, scaffolds promoted strong and robust recruitment of hematopoietic cells to sites of ectopic transplantation, vascularization, and soft tissue formation. CONCLUSIONS: Our tissue-engineered BM system is a powerful tool to explore the regulatory mechanisms of hematopoietic stem and progenitor cells for a better understanding of hematopoiesis in health and disease.

Degradation and swelling issues of poly-(d,l-lactide)/ß-tricalcium phosphate/calcium carbonate composites for bone replacement.

Recently a tri-phase material consisting of poly-(d,l-lactide) (PDLLA), ß-tricalcium phosphate (ß-TCP), and calcium carbonate (CC) was proposed as a novel bone substitute candidate. ß-TCP is suitable because of its bone-like mineral phase, PDLLA is introduced as a biodegradable adhesive phase, and CC is essential for buffering the acidic degradation of the lactate component. We hypothesize that the amounts of the three different components in the composite material must be carefully balanced in order to avoid issues such as accelerated degradation or pronounced volumetric swelling. To prove this, granulates made of different mixing ratios of the tri-phase compound were prepared by grinding. Specimens of the different compounds were manufactured by a hot pressing process. The bending strength of the specimens was determined before and after storing in demineralized water and phosphate buffered saline (PBS). The particle size of the compound granulates was smaller than 100µm. A ratio of 60wt% of the PDLLA component indicated the best compromise between stability of test specimens based on a strong melting network and bone-like properties. The specimens exhibited a bending strength up to 90MPa. The strength increased with an increasing ratio of ß-TCP to calcium carbonate (based on 60wt% PDLLA). A vast volumetric swelling up to 40%, and thus a huge reduction of the bending strength, was observed during the storage of specimens in PBS. A swelling and thus a volume increase could be critical, especially for using the tri-phase bone substitute compound as 3D scaffold with defined dimensions. This must be considered with regard to the composition of the compound and the scaffold design.