2D and 3D control of photopolymerized polycaprolactone scaffolds for cell replacement therapy in retinal disease

Obstacles to the realization of polymer scaffolds to be used for cell replacement therapies often include the challenges in controlling the microstructure of biocompatible molecules in three dimensions at cellular scales. Two-photon polymerization (TPP) of acrylated poly(caprolactone) (PCL) offers a means of achieving precise microstructural control of a material in a biocompatible and biodegradable platform. Two obstacles inhibit the efficient development and research of this method: there is not a commercially available acrylated PCL and the fabrication time using TPP can be lengthy. Initially in this work, TPP parameters and molecular structures were varied to find the ideal relationship for our prototype. Increasing the concentration of reactive groups, either by increasing number of acrylate groups per molecule or decreasing molecular weight, was found to increase the similarity of the scaffold to the computer generated model. Sub-retinal implantation of TPP PCL scaffolds in a porcine model of retinitis pigmentosa was well tolerated, and did not cause inflammation, infection, or local or systemic toxicity after one month. However, this acrylated PCL was not as pure as originally thought; there were remaining reactants present that prevented accurate quantification of reaction success. Without the ability to measure the number of acrylates that were bonded to the molecule we could not ensure that batches were consistent, preventing a standard to be developed for quality and control. A method to purify the products of our PCL synthesis was delineated; a series of washes and separations with concentrated sodium bicarbonate successfully purified the PCL. The more thoroughly the phases were combined during these washes, the more effectively the reactant was removed. To address the time scale issues of TPP, the implementation of a two-dimensional photo-masked (PM) polymerized PCL film was adopted. Since films are faster and simpler to make, they can be developed and tested first and used as a predicate device for FDA approval of TPP PCL scaffolds. Therefore, the PM scaffolds were formulated similarly to the TPP materials and then the minimum intensity of light and time necessary to polymerize a film was determined. Time and light intensity displayed an inverse relationship, and the films at each intensity and exposure require more research into their quality and elastic modulus . A representative film was selected, seeded with dissociated retinal organoids, and, after one week, the cells that successfully adhered to the scaffold maintained their neuronal lineage. The density of cells seeded using 16 retinal organoids was estimated and will provide insight into how many organoids to use in the future. These results represent an important step towards understanding how photopolymerization can be applied to a wide range of biologically compatible chemistries for various biomedical applications.