Traumatic bone injuries often require interventive measures in the form of bone stents. Other types of orthopaedical interventions, such as spine cages, frequently require metal implants that differ from the properties of bone. These metal bone stents and implants differ greatly from the modulus of bone in addition to various other mechanical properties. Recent developments in bioprinting and biocompatible printing materials make bioprinting a promising method for designing biodegradable scaffolds for these purposes as they match the properties of bone much closer.

Our primary objective was to develop a new methodology to create biodegradable scaffolds to be implanted in patients that suffer severe bone-related traumas or require orthopaedic implants. In order to do this with bioprinting, not only must we use materials that match the properties of bone, but we must also be able to create a print with osteogenic properties, sufficient structural integrity, and the capability to be vascularized in the future. We seek to fulfill the first two objectives by creating a PCL:HA scaffold framework. The polycaprolactone (PCL) provides structural integrity, while the hydroxyapatite (HA) promotes bone growth as it degrades.

Current printing methods are cytotoxic and expensive as they dissolve the PCL and HA using solvents such as chloroform to make the bioink sufficiently uniform and viscous for extrusion printing. In order to overcome the dangers associated with previous methods, we utilized a new PCL printing methodology that involved quantitative melting of the PCL and mixing in the HA.

We used this methodology to create PCL and HA cuboids of varying ratios of PCL and HA. The scaffolds also had various infill geometries so we could test that variable in addition to the PCL to HA ratio. We then conducted mechanical testing to determine the different stiffness values (N/mm) of varying compositions of PCL:HA and scaffold geometries. This data was then utilized to determine the optimal scaffold for the biodegradable implants.

Once we determined the optimal scaffolds, the printing methodology was applied to implants used in surgical applications. We decided to focus our efforts in two distinct aspects. The first was image-based biodegradable scaffolds for better bone stents and the second was biodegradable spine cages for spinal fusion surgeries.

For the image-based scaffolds, we focused on taking patient medical files in the form of DICOM files and converting them to STL files (the files used in bioprinting). We then printed these files to showcase our ability to model hard tissue like bone for future use in custom-fit bone stents.

For the spine cage project, we went with 80:20 PCL:HA ratios for ease of printing and set up designing the most optimal spine cage for TLIF surgeries (the most common type of spinal fusion surgery). We created several prototypes and then decided on a single scaffold to conduct mechanical testing on to see if it was a better alternative than currently utilized spine cages.