Determination of resin components for continuous Digital Light Processing (cDLP) additive manufacture of resorbable tissue engineering scaffolds

摘要

The formulation of resorbable polymer resins for light-based 3D printing (additive manufacturing) of tissue engineered scaffolds (i.e., an implant that guides tissue formation and then resorbs) goes beyond resin chemistry. First, individual layers must have a sufficient density of crosslinks to be both thick enough and strong enough to bind to the next layer. Next, there must also be a sufficient density of crosslinks between adjacent layers to form a seamless 3D scaffold. 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 layer strength. Overcuring is the thickness of the layer minus step size. Overcuring distance is a limiting factor for surface feature resolution in the between-layer direction (i.e., resolution in the "Z" direction). Strength is an indication of crosslinking density and a function of inter-layer binding or "stitching". These parameters are directly affected by the energy imparted from the printer's light to the polymer via the initiator during the 3D printing process (i.e., polymerization). The resulting scaffold needs to be sufficiently strong to endure cleaning of unpolymerized polymer from its internal pore space without deforming. We report here on a study of the effect of exposure time on strength and layer thickness while holding step size constant (i.e., increasing the overcure dimension). Increasing overcure was found to dramatically increase scaffold strength. Extremely high resolution implants depend on sufficient energy from the light source and a well-tuned resin consisting of: polymer, initiator(s), and perhaps other constituents such as dye(s), solvents, and biologics.