You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Fabrication of 3-dimensional cellular constructs via microstereolithography using a simple, three-component, poly(ethylene glycol) acrylate-based system. A novel method for the production of inhibitor- and solvent-free resins suitable for three-dimensional (3D) microstereolithography is reported. Using an exemplar poly(ethylene glycol)-based resin, the control of features in the X, Y, and Z planes is demonstrated such that complex structures can be manufactured. Human mesenchymal stem cells cultured on the manufactured scaffolds remained viable during the 7 day assessment period, with proliferation rates comparable to those observed on tissue culture polystyrene. These data suggest that this novel, yet simple, method is suitable for the production of 3D scaffolds for tissue engineering and regenerative medicine applications.
{"Chemical": ["poly(ethylene glycol) acrylate", "polystyrene", "poly(ethylene glycol)"]}