Investigation and characterization of the additive manufacturing of polycaprolactone/bioactive glass hybrid scaffolds for bone tissue engineering via material extrusion processing

Thanks to its versatility and effectiveness, additive manufacturing is expected to completely revolutionize the biomedical science field. In bone regenerative medicine, in particular, additive manufacturing has the great potential of opening new avenues of development for patient-specific ad hoc therapies. In theory, a defect could be scanned and precisely replicated, thus offering the best fitting for each patient. The main bottleneck to date is the relatively scarce availability of materials that can be printed reliably and consistently. This is the case for organic/inorganic hybrids, materials produced by sol-gel chemistry that combine the advantages of polymers and bioinorganics at the molecular scale. Due to their complex structure and unique rheological and mechanical properties, the printing of hybrids remains challenging. With this study, we aim to investigate the rheological, thermal and molecular properties of a class I polycaprolactone/bioactive glass hybrid and discover how they correlate with the printability of the material. The molecular weight distribution (gel permeation chromatography), thermal properties (thermal gravimetric analysis, differential scanning calorimetry) and rheological properties of each hybrid material were investigated at all stages of processing. Printing trials via direct material extrusion processing followed by morphological characterization were performed on both polymers and hybrids. Their apatite-forming ability in simulated body fluid was evaluated by scanning electron microscopy and particle-induced X-ray emission. Results confirmed the successful manufacturing of organic/inorganic hybrids using direct material extrusion processing for the first time. Three-dimensional scaffolds were successfully produced without the need for further processing. No additional solvents or convoluted indirect approaches were necessary. Thanks to the thermal analysis, an ideal temperature window for printing was identified. SBF immersion assays confirmed that the material's bioactivity is retained after printing. Considering the presented findings, material extrusion processing might develop into an essential technique for fabricating superior 3D bioactive scaffolds for bone tissue engineering.