1. A method of printing a three-dimensional (3D) structure, the method comprising: (a) providing a 3D printer, the printer comprising: i. one or more printer heads, wherein a printer head comprises a means for receiving and holding at least one cartridge, wherein the cartridge comprises at least one deposition orifice and contents comprising a bio-ink, wherein the bio-ink comprises cell solutions, cells suspensions, or cell concentrations; ii. a means for dispensing the contents of at least one cartridge; iii. a receiving surface for receiving a first layer of the materials dispensed from the at least one cartridge; iv. a programmable computer processor communicatively connected to the means for dispensing, the programmable computer processor for positioning the one or more printer heads in three dimensions and regulating the dispensing of the contents of the at least one cartridge; and v. a means for calibrating the position of the at least one cartridge or the at least one deposition orifice; (b) providing the materials to be dispensed; (c) encoding the printer with a 3D structure to be printed, wherein the 3D structure is a tissue construct; (d) dispensing from the deposition orifice the materials to be dispensed, wherein the materials to be dispensed comprise cell solutions, cells suspensions, or cell concentrations, wherein the dispensing is by extrusion; (e) depositing a first layer of the dispensed materials on the receiving surface; and (f) repeating the depositing step by depositing subsequent dispensed material on the first and any subsequent layers of deposited material, thereby depositing layer upon layer of dispensed materials in a geometric arrangement according to the 3D structure.