3D Printers in Medicine: Amazing Technology and Uses
3D printing is an exciting innovation in technology and has many useful applications. One fascinating and potentially very important use of 3D printers is the creation of materials that can be used in medicine. These materials include medical devices, artificial body parts and body structures made of living cells. In the future, entire organs may be created by 3D printers.
3D printers have the ability to print solid, three dimensional objects based on a digital model stored in a computer's memory. A common printing medium is liquid plastic that solidifies after printing, but other media are available. These include "inks" containing living cells.
The ability of 3D printers to produce materials that are compatible with the human body is improving rapidly. Some of the materials are already used in medicine while others are still in the experimental stage. Many researchers are involved in the investigation. 3D printing has the tantalizing potential to transform medical treatment.
A 3D Printer in Action
How Does a 3D Printer Work?
The first step in the creation of a 3D object by a printer is to design the object. This is done in a CAD (Computer Aided Design) program. Once the design is finished, another program creates instructions for producing the object in a series of layers. This second program is sometimes known as a slicing program or slicer software, since it converts the CAD code for the entire object into code for a series of slices or horizontal layers. The layers may number in the hundreds or even in the thousands.
The 3D printer creates the object by depositing layers of material according to the slicer program's instructions, starting at the bottom of the object and working upwards. Successive layers are fused together. The process is referred to as additive manufacturing.
Plastic filament is often used as a medium for 3D printing, especially in consumer-oriented printers. The printer melts the filament and then extrudes hot plastic through a nozzle. The nozzle moves in all dimensions as it releases the liquid plastic in order to create an object. The movement of the nozzle and the amount of plastic that is extruded are controlled by the slicer program. The hot plastic solidifies almost immediately after it's released from the nozzle.
Structure of the Ear
The part of the ear that is visible from the outside of the body is known as the pinna or auricle. The rest of the ear is located in the skull. The function of the pinna is to collect sound waves and send them to the next section of the ear.
Making an Ear by 3D Printing
In February 2013, scientists at Cornell University in the United States announced that they had been able to make an ear pinna by 3D printing. The steps followed by the Cornell scientists were as follows.
- A model of an ear was created in a CAD program. The researchers used photographs of real ears as the basis for this model.
- The ear model was printed by a 3D printer, using plastic to create a mold with the shape of the ear.
- A hydrogel containing a protein called collagen was placed inside the mold. A hydrogel is a gel that contains water.
- Chondrocytes (cells that produce cartilage) were obtained from a cow's ear and added to the collagen.
- The collagen ear was placed in a nutrient solution in a lab dish. While the ear was in the solution, some of the chondrocytes replaced the collagen.
- The ear was implanted in the back of a rat under its skin.
- After three months, the collagen in the ear had been completed replaced with cartilage and the ear had maintained its shape and distinction from the surrounding rat cells.
A 3D Printer Helps to Make an Ear
Difference Between a Mold and a Scaffold
In the ear creation process described above, the plastic ear was an inert mold. Its sole function was to provide the correct shape for the ear. The collagen ear that formed inside the mold acted as a scaffold for the chondrocytes. In tissue engineering, a scaffold is a biocompatible material with a specific shape on and in which cells grow. The scaffold not only has the correct shape but also has properties that support the life of the cells.
Since the original ear creation process was performed, the Cornell researchers have found a way to print a collagen scaffold with the correct shape needed to make an ear, eliminating the requirement for a plastic mold.
Potential Benefits of Printed Ears
Ears made with the aid of 3D printers could be useful for people who have lost their own ears due to injury or disease. They could also help people who were born without ears or have ears that haven't developed properly.
At the moment, replacement ears are sometimes made from cartilage in a patient's rib. Obtaining the cartilage is an unpleasant experience for the patient and can damage the rib. In addition, the resulting ear may not look very natural. Ears are also made from an artificial material, but once again the result may not be completely satisfactory. Printed ears have the potential to look more like natural ears and to work more efficiently.
Human Skull Bones
In March 2013, a company called Oxford Performance Materials reported that they had replaced 75% of a man's skull with a 3D printed polymer skull. 3D printers are also used to make health care appliances, such as prosthetic limbs, hearing aids and dental implants.
Printing a Lower Jaw
In February 2012, Dutch scientists reported that they had created an artificial lower jaw with a 3D printer and implanted it into the face of an 83-year-old woman. The jaw was made from layers of titanium metal powder fused by heat and was covered by a bioceramic coating. Bioceramic materials are compatible with human tissue.
The woman received the artificial jaw because she had a chronic bone infection in her own lower jaw. Doctors felt that traditional facial reconstruction surgery was too risky for the woman because of her age.
The jaw had joints so that it could be moved, as well as cavities for muscle attachment and grooves for blood vessels and nerves. The woman was able to say a few words as soon as she woke up from the anesthetic. The next day she was able to swallow. She went home after four days. False teeth were scheduled to be implanted into the jaw at a later date.
Bioprinting with Living Cells - A Possible Future
Printing with living cells, or bioprinting, is happening today. It's a delicate process. The cells mustn't get too hot. Most methods of 3D printing involve high temperatures, which would kill cells. In addition, the carrier liquid for the cells mustn't harm them. The liquid and the cells that it contains is known as a bio-ink (or a bioink).
Organ and Tissue Replacement
The replacement of damaged organs with organs made from 3D printers would be a wonderful revolution in medicine. At the moment there aren't enough donated organs available for everyone who needs them.
The plan is to take cells from a patient's own body in order to print an organ that they need. This process should prevent organ rejection. The cells would be stem cells, unspecialized cells that are capable of producing other cell types under certain conditions. Stem cell biology is another exciting area in medical research. A knowledge of stem cells is essential in order to create printed organs.
A special type of 3D printer known as a bioprinter is used to make living tissue. In general, a hydrogel is printed from one printer head to form a scaffold. Tiny liquid droplets, each containing many thousands of cells, are printed on to the scaffold from another printer head. The droplets soon join and the cells become attached to each other. When the desired structure has formed, the hydrogel scaffold is removed. It may be peeled away or it may be washed away if it's water soluble. Biodegradable scaffolds may also be used. These gradually break down inside the human body.
Organ Printing Research
Bioprinting Successes So Far
Non-living implants created by 3D printers are already used in humans. The use of implants containing living cells requires more research, which is being performed. Entire organs can't yet be made by 3D printing, but sections of organs can. Many different structures have been printed, including patches of heart muscle that are able to beat, skin patches, segments of blood vessels and knee cartilage. These haven't been implanted into humans yet, however.
Some hopeful research results were reported in 2016. A team of scientists implanted three types of bioprinted structures under the skin of mice. These included a baby-sized human ear pinna, a piece of muscle and a section of human jaw bone. Blood vessels from the surroundings extended into all of these structures while they were in the bodies of the mice. This was an exciting development, since a blood supply is necessary in order to keep tissues alive. The blood carries nutrients to living tissues and takes away their wastes.
It was also exciting to note that the transplanted structures were able to stay alive until the blood vessels had developed. This feat was accomplished by the existence of tiny pores in the transplanted structures that allowed nutrients to enter them.
Printing Parts of the Heart
Some Challenges for Bioprinting
Creating an organ that is suitable for transplantation is a difficult task. An organ is a complex structure containing different cell types and tissues arranged in a specific pattern. In addition, as organs develop during embryonic development, they receive chemical signals that enable their fine structure and intricate behaviour to develop properly. This signals are lacking when we try to create an organ artificially.
Some scientists think that at first - and perhaps for some time to come - we will print implantable structures that can perform a single function of an organ instead of all of its functions. These simpler structures may be very useful if they compensate for a serious defect in the body.
It's possible that bioprinted structures will be good enough for testing new medical treatments before they are ready for transplantation. This in itself could be an important breakthrough because it could reduce the use of lab animals.
The Future for Bioprinting
Though it's likely to be years before bioprinted organs are available for transplants, we may well see new benefits of the technology before then. The pace of research seems to be increasing. The future of 3D printing in relation to medicine should be very interesting as well as exciting.
References and Further Reading
© 2013 Linda Crampton
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