BACKGROUND

There is a significant rise in three-dimensional fabrication devices. These are commonly referred to 3D printers. Presently, there are a limited amount of 3D printers that have the abilities to print living biologies, such as, but not limited to human cells. The technology and techniques to print a three-dimensional construct is well established. However, the abilities to print various forms of materials are limited. For examples, many 3D printers today would only print some form of a hard plastic. This plastic would be fed thru a nozzle, heated, and extruded. This works well, however, the temperature is usually well above what cells can survive. There are materials that be printed at room temperature with cells. However, these materials are very limited and does not always provides the best conditions for cells to attached, generate, and/or regenerate. Since cells can survive very low temperate conditions (cold), they can be printed where there print head is cold. There are lots of bio-materials that are commonly referred to reverse- polymers. Reverse polymers are one in which at room temperature are solid or gel-like. However, at colder temperature it becomes more liquid-like. A cold fabrication head on a 3D biologies printer would expand the library of materials that can be used to fabricate physiologically relevant tissue constructs.

This article presents a low temperature module for a biological printer's deposition system and build platform. This module is designed to be adaptive and integrative to current biological printer while providing the abilities to maintain a "cold" environment within the fabrication head. A "cold" environment is defined as changing and maintain the temperature within the printer's fabrication system of at least one degrees Celsius (1°C) below ambient temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and desired objects of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawing figures wherein like reference characters denote corresponding parts throughout the several views and wherein:

Figure 1 depicts the cold-body of the low temperature module for the fabrication head and its components;

Figure 2 depicts the Schematic of the heat exchanger showing the heat fins;

Figure 3 depicts a photo of the Thermoelectric Peltier Cooler (TEC) used;

Figure 4 depicts the system components of the low temperature module for the printer's fabrication system;

Figure 5 depicts the low temperature module is mounted on the fabrication system of an existing 3D biological printer;

Figure 6 depicts a schematic of the low temperature module for the build platform

DETAILED DESCRIPTION

This low temperature module has two components, namely; 1) the fabrication head module, and 2) the build platform module. The fabrication head module will only cool the materials in the fabrication head (Figure 1) while the build platform is primarily responsible for the build/fabrication process' integrity (Figure 6).

The fabrication head module is designed to operate integratively with the 3D printer's deposition system. This low temperature module has a proportional-integral - derivative (PID) temperature control unit, thermocouple, relay system, comprehensive heat exchanger (Figure 2), a Thermoelectric Peltier Cooler (TEC) (Figure 3), cold-body, and mounting apparatus.

The PID temperature control unit is integrated with the biological printer such that all settings and processes can be controlled by the end-user and/or with the printer's control system. The PID system provides a unique feedback control system that reduces error and over-shooting temperature settings. Over-shooting temperature can create an environment that is too hot or cold, hence causing cell dead or damaging the material in the fabrication system. Coupled with the PID system is the relay system. Together these two systems provides and maintain thermal equilibrium (set by the end user).

The TEC is an electrical device that has the unique ability to produce a thermal difference between its faces. On one side of the TEC device it's hot, while the other feels cold. Since this system is designed to harvest the energy on the cold face, a heat exchange is incorporated to remove the heat from the other face. The TEC device is controlled with the PID controller and a thermocouple provides a feedback to the control unit. The cold face of the TEC device is pushed against the "cold-body" which conducts and transfer the cold energy onto the fabrication system.

The heat exchanger's objective is to remove unwanted heat from the TEC to optimize a thermal difference to maintain a cold-body on the fabrication head. The heat exchanger is a liquid cooling system which operates with a pump, radiator reservoir, and heat fins. The heat fins are pushed/mounted on the hot side of the TEC and collects the unwanted energy from the TEC unit. This unwanted energy is then transferred onto the fluid flowing between the fins. The fluid then goes to the radiator where a convection cooling technique removes the unwanted energy (heat) from the fluid and distributes it into the environment. The chilled fluid returned back to the fins, where this process begins again.

The "cold-body" is defined as the device in which cold energy is collected and maintains a frigid environment for the printer's deposition system. The cold-body is design with 200 proof ethanol to enhance the unit's potential to maintain a frigid environment. The ethanol surround the deposition head, hence, maintain a constant temperature setting. The cold-body has a mount apparatus to ensure a tight and secure fit onto the fabrication system. Figure 4 shows the system components while Figure 5 shows the low temperature module mounted on an existing printer's fabrication head.

The low temperature module for the fabrication head is used to apply and maintain a cold environment for the material within the printer's deposition head. For many reverse polymers, at cooler/low temperature, the material becomes more liquid- like. While at room temperature the material is more rigid. These types of materials are of great interest in the field for tissue engineering, bio-printing. In order to fabricate any three-dimensional constructs, the fabrication device must be able to manipulate the deposited material. When using cells to print any tissue construct, there cannot be any material/chemicals present that may harm the cells. Reverse polymers are great for cell printing, because they do not require any chemical cross-linking to retain their fabricated architecture. Also, since cells are survive sub-zero conditions, printing them within a cold nozzle should not significantly cause death. This low temperature module for the fabrication head will provide a new opportunity to fabricate more physiologically relevant tissue constructs.

In addition to the low temperature module for the fabrication head, there is a low temperature module for the build platform. In some cases, the end-user may not want to cool the material in the print head, but at the build platform where the fabrication process is occurring. This module provides a low temperature environment similar to that of the low temperature module of the fabrication head. The module for the build platform can be using with or independent of the module with the fabrication head. When used with the fabrication head, it is maintaining a constantly cold environment from the fabrication head until the fabrication process is 100% complete. The build platform module can also present varying temperature to help with the gelation of the printed material.

The build platform is design to maintain the temperature within the build platform of at least one degrees Celsius (1°C) below ambient temperature. The build platform operates integratively with the printer's deposition system. This build platform module has a proportional-integral-derivative (PID) temperature control unit, thermocouple, relay system, a thermal heating element (TEC), comprehensive heat exchanger, and a cold- body. Together these components creates cold environment for cell printing.