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.

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)/β-tricalcium phosphate (β-TCP) composite powder with 50 wt% PDLLA and 50 wt% β-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/β-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.

Polyurethanes have the potential to impart cell-relevant properties like excellent biocompatibility, high and interconnecting porosity and controlled degradability into biomaterials in a relatively simple way. In this context, a biodegradable composite material made of an isocyanate-terminated co-oligoester prepolymer and precipitated calcium carbonated spherulites (up to 60% w/w) was synthesized and investigated with regard to an application as bone substitute in dental and orthodontic application. After foaming the composite material, a predominantly interconnecting porous structure is obtained, which can be easily machined. The compressive strength of the foamed composites increases with raising calcium carbonate content and decreasing calcium carbonate particle size. When stored in an aqueous medium, there is a decrease in pressure stability of the composite, but this decrease is smaller the higher the proportion of the calcium carbonate component is. In vitro cytocompatibility studies of the foamed composites on MC3T3-E1 pre-osteoblasts revealed an excellent cytocompatibility. The in vitro degradation behaviour of foamed composite is characterised by a continuous loss of mass, which is slower with higher calcium carbonate contents. In a first pre-clinical pilot trial the foamed composite bone substitute material (fcm) was successfully evaluated in a model of vertical augmentation in an established animal model on the calvaria and on the lateral mandible of pigs.

A promising therapeutic option for the treatment of critical-size mandibular defects is the implantation of biodegradable, porous structures that are produced patient-specifically by using additive manufacturing techniques. In this work, degradable poly(DL-lactide) polymer (PDLLA) was blended with different mineral phases with the aim of buffering its acidic degradation products, which can cause inflammation and stimulate bone regeneration. Microparticles of CaCO₃, SrCO₃, tricalcium phosphates (α-TCP, β-TCP), or strontium-modified hydroxyapatite (SrHAp) were mixed with the polymer powder following processing the blends into scaffolds with the Arburg Plastic Freeforming 3D-printing method. An in vitro degradation study over 24 weeks revealed a buffer effect for all mineral phases, with the buffering capacity of CaCO₃ and SrCO₃ being the highest. Analysis of conductivity, swelling, microstructure, viscosity, and glass transition temperature evidenced that the mineral phases influence the degradation behavior of the scaffolds. Cytocompatibility of all polymer blends was proven in cell experiments with SaOS-2 cells. Patient-specific implants consisting of PDLLA + CaCO₃, which were tested in a pilot in vivo study in a segmental mandibular defect in minipigs, exhibited strong swelling. Based on these results, an in vitro swelling prediction model was developed that simulates the conditions of anisotropic swelling after implantation.

Background: The aim of this experimental pilot study was to evaluate the effect of pore volume and material composition on bone ingrowth into a resorbable poly-L-lactide-CaCO₃/CaP scaffold. Methods: Cylindric scaffolds of 7 mm diameter and 5 mm height and two different degrees of porosity were produced using selective laser sintering of poly-L-lactide-powder containing 24% CaCO₃ spherulites with and without surface modification with 4% CaP. Six minipigs received the four types of macroporous cylindrical scaffolds, inserted press fit into trephine defects of the tibial metaphyses, and left to heal for 4 and 13 weeks in three animals each. The specimens were evaluated using µCT for pore volume fill, and histomorphometry for bone formation and immunohistochemistry for expression of osteocalcin. Results: After 4 weeks, newly formed bone ranged from 2.73 mm² to 5.28 mm² mean total area. Mean pore volume fill varied between 12.25% and 20.35% and the average level of osteocalcin expression ranged from 2.49 mm² to 4.48 mm² mean total area. No significant differences were found between the different scaffolds. After 13 weeks, bone formation and pore fill volume had significantly increased in all scaffold groups up to a mean value of 14.79 mm² and 96.04%, respectively. Again, differences between the groups were not significant. Conclusions: The tested SLS produced scaffolds allowed for bone ingrowth, almost completely filling the pore volume after 13 weeks. Newly formed bone was in direct contact with the scaffold walls. Differences in pore volume did not account for significant differences in bone formation inside the scaffolds. The addition of CaP likewise did not lead to increased bone formation, most likely due to low availability of CaP to the biological environment.

Aim: The aim of this experimental pilot study was to evaluate the effect of pore volume and material composition on bone ingrowth into a resorbable poly-L-lactide-CaCO3 / CaP scaffold. Materials and Methods: Scaffolds with 35.9 and 41.1% porosity were produced through selective laser sintering of poly-L-lactide-powder with 24% CaCO3 spherulites with and without surface modification with 4% CaP. Six minipigs received the four types of macroporous cylindrical scaffolds, inserted press fit into trephine defects of the tibial metaphyses and left to heal for 4 and 13 weeks in three animals each. Specimens were evaluated using µCT for pore volume fill and histomorphometry for bone formation as well as immunohistochemistry for expression of osteocalcin. Results: After 4 weeks, newly formed bone ranged from 2.73 mm² to 5.28 mm² mean total area. Mean pore volume fill varied between 12.25% and 20.35 % and the average level of osteocalcin expression ranged from 2.49 mm² to 4.48 mm² mean total area. No significant differences were found between the different scaffolds. After 13 weeks, bone formation and pore fill volume had significantly increased in all scaffold groups up to a mean value of 14.79 mm² and 96.04%, respectively. Again, differences between the groups were not significant. Conclusion: The tested SLS produced scaffolds allowed for bone ingrowth that almost completely filled the pore volume after 13 weeks and was in direct contact with the scaffold walls. Differences in pore volume and scaffold composition did not account for significant differences in bone formation inside the scaffolds.