This work aimed to determine the influence of two hydrogels (alginate, alginate-di-aldehyde (ADA)/gelatin) on the mechanical strength of microporous ceramics, which have been loaded with these hydrogels. For this purpose, the compressive strength was determined using a Zwick Z005 universal testing machine. In addition, the degradation behavior according to ISO EN 10993-14 in TRIS buffer pH 5.0 and pH 7.4 over 60 days was determined, and its effects on the compressive strength were investigated. The loading was carried out by means of a flow-chamber. The weight of the samples (manufacturer: Robert Mathys Foundation (RMS) and Curasan) in TRIS solutions pH 5 and pH 7 increased within 4 h (mean 48 ± 32 mg) and then remained constant over the experimental period of 60 days. The determination surface roughness showed a decrease in the value for the ceramics incubated in TRIS compared to the untreated ceramics. In addition, an increase in protein concentration in solution was determined for ADA gelatin-loaded ceramics. The macroporous Curasan ceramic exhibited a maximum failure load of 29 ± 9.0 N, whereas the value for the microporous RMS ceramic was 931 ± 223 N. Filling the RMS ceramic with ADA gelatin increased the maximum failure load to 1114 ± 300 N. The Curasan ceramics were too fragile for loading. The maximum failure load decreased for the RMS ceramics to 686.55 ± 170 N by incubation in TRIS pH 7.4 and 651 ± 287 N at pH 5.0.

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The objective of this study was to vary the wall thicknesses and pore sizes of inversely printed 3D molded bodies. Wall thicknesses were varied from 1500 to 2000 to 2500 µm. The pores had sizes of 500, 750 and 1000 µm. The sacrificial structures were fabricated from polylactide (PLA) using fused deposition modeling (FDM). To obtain the final bioceramic scaffolds, a water-based slurry was filled into the PLA molds. The PLA sacrificial molds were burned out at approximately 450 °C for 4 h. Subsequently, the samples were sintered at 1250 °C for at least 4 h. The scaffolds were mechanically characterized (native and after incubation in simulated body fluid (SBF) for 28 days). In addition, the biocompatibility was assessed by live/dead staining. The scaffolds with a strand spacing of 500 µm showed the highest compressive strength; there was no significant difference in compressive strength regardless of pore size. The specimens with 1000 µm pore size showed a significant dependence on strand width. Thus, the specimens (1000 µm pores) with 2500 µm wall thickness showed the highest compressive strength of 5.97 + 0.89 MPa. While the 1000(1500) showed a value of 2.90 + 0.67 MPa and the 1000(2000) of 3.49 + 1.16 MPa. As expected for beta-Tricalciumphosphate (β-TCP), very good biocompatibility was observed with increasing cell numbers over the experimental period.

The aim of this study was to produce a composite of microporous β-TCP filled with alginate-gelatin crosslinked hydrogel, clindamycin and bone morphogenetic protein (BMP-2) to prolong the drug-release behaviour for up to 28 days. The most promising alginate-di-aldehyde(ADA)-gelatin gel for drug release from microcapsules was used to fill microporous β-TCP ceramics under directional flow in a special loading chamber. Dual release of clindamycin and BMP-2 was measured on days 1, 2, 3, 6, 9, 14, 21 and 28 by high performance liquid chromatography (HPLC) and enzyme-linked immunosorbent assay (ELISA). After release, the microbial efficacy of the clindamycin was checked and the biocompatibility of the composite was tested in cell culture. Clindamycin and the model substance FITC-protein A were released from microcapsules over 28 days. The clindamycin burst release was 43 ± 1%. For the loaded ceramics, a clindamycin release above the minimal inhibitory concentration (MIC) until day 9 and a burst release of 90.56 ± 2.96% were detected. BMP-2 was released from the loaded ceramics in low concentrations over 28 days. The release of active substances from β-TCP and hydrogel have already been extensively studied. Directional flow loading is a special procedure in which the ceramic could act as a stabilizer in the bone and, as a biodegradable system, enables a single-stage surgical procedure. Whether ADA-gelatin gel is suitable for this procedure as a more biodegradable alternative to pure alginate or whether a dual release is possible in this composite has not yet been investigated. Graphical Abstract

The aim of the present work was to develop a dual staged drug release of an antibiotic (clindamycin) and a growth factor: bone morphogenetic protein-2 (BMP-2) from a biodegradable system consisting of hydrogel and gelatin nanoparticles (GNP). Two-step de-solvation allowed us to prepare GNPs (~100 nm) as drug carriers. Fluorescein isothiocyanate (FITC)-conjugated protein A was used as a model substance for BMP-2. A 28-day release experiment was performed to determine the release kinetics from GNP for both FITC-protein A and BMP-2, and for clindamycin (CLI) from the hydrogel. The size, structure, and overall morphology of GNP samples (empty, loaded with FITC-protein A and BMP-2) were examined using an environmental scanning electron microscope (ESEM). Cell culture assays (Live/dead; cell proliferation; cytotoxicity) were performed with MG-63 cells and BMP-2-loaded GNPs. Drug release experiments using clindamycin-loaded alginate-di-aldehyde (ADA) gelatin gels containing the drug-loaded GNPs were performed for 28 days. The resulting GNPs showed an empty size of 117 ± 29 nm, 176 ± 15 nm and 216 ± 36 nm when containing 2% FITC-protein A and 1% BMP-2, respectively. No negative effects of BMP-2-loaded GNPs on MG-63 cells were observed in live/dead staining. In the proliferation assay, an increase in cell proliferation was observed for both GNPs (GNP + BMP-2 and controls). The cytotoxicity assay continuously showed very low cytotoxicity for GNPs (empty; loaded). Clindamycin release showed a concentration of 25-fold higher than the minimum inhibitory concentration (MIC) against Staphylococcus aureus throughout the 28 day period. BMP-2 showed a reduced burst release and a steady release (~2 µg/mL) over a 28 day period.