Multiple initiators and dyes for continuous Digital Light Processing (cDLP) additive manufacture of resorbable bone tissue engineering scaffolds

Abstract

The formulation of resorbable polymer resins for light-based additive manufacturing of tissue engineered scaffolds goes beyond resin chemistry. There are at least four parameters that allow the transition from individual layer curing to 3D printing; they are: layer thickness, overcuring, step size, and inter-layer binding. Overcuring is the thickness of the layer minus step size. Overcuring distance limits surface feature resolution in the between-layer direction. Strength is an indication of crosslinking density and a function of inter-layer binding or ‘stitching’. 3D printed scaffolds must be sufficiently strong to endure cleaning of unpolymerised polymer from internal pore spaces without deforming. We report our study of the effect of exposure time on strength and layer thickness while holding step size constant. Increased overcuring dramatically increases scaffold strength. High resolution implants depend on sufficient energy from the light source and a well-tuned resin consisting of: polymer, initiator(s), and perhaps dye(s), solvent(s), and biologic(s).

Keywords:

• continuous Digital Light Processing (cDLP)
• dye-initiator package
• poly (propylene fumarate (PPF)
• titanium dioxide (TiO₂)
• oxybenzophenone
• additive manufacturing
• bone tissue engineering
• dark cure
• green strength

Acknowledgements

We would like to thank Jonathan Wallace (Department of Biomedical Engineering, CWRU) for his assistance in preparing and testing different resin formulations. We are also grateful to Jay Bensusan (Department of Mechanical and Aerospace Engineering (DMAE), CWRU) for his assistance in collecting the modulus data presented here. Those data were collected in the laboratory of Dr. Clare Rimnac (DMAE, CWRU). This paper was improved through the process of our responding to Reviewer comments.

Funding

This research was partially supported by the Research Foundation of the Department of Neurological Surgery, Case Western Reserve University (CWRU), Cleveland, OH [NIH grant number R01-DE013740], [NIH grant number R01-AR061460].

Disclosures

Financial Disclosure: Several of the authors (DD, EM, MOW, AS, and JPF) are inventors on a patent application that includes the material in this manuscript. DD has received compensation from, and has an ownership stake in, Osteoplastics, LLC (Shaker Heights, OH), an entity with an interest in this patent.

Additional information

Funding

Funding: This research was partially supported by the Research Foundation of the Department of Neurological Surgery, Case Western Reserve University (CWRU), Cleveland, OH [NIH grant number R01-DE013740], [NIH grant number R01-AR061460].