3D Printers in Medicine: Exciting Uses and Potential Applications
3D printing is an exciting innovation in technology that has many useful applications. One fascinating and potentially very important application of 3D printers is the creation of materials that can be used in medicine. These materials include implantable medical devices, artificial body parts or prosthetics, and customized medical instruments. They also include printed patches of living human tissue as well as mini organs. In the future, implantable organs may be printed.
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 powdered metal and "inks" containing living cells.
The ability of 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 three dimensional 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 as 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 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. Other types of printing media are available for special purposes.
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
In February 2013, scientists at Cornell University in the United States announced that they had been able to make an ear pinna with the aid of 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 then 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.
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 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 ones 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.
In March 2013, a company called Oxford Performance Materials reported that they had replaced 75% of a man's skull with a 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.
Printed structures are also being used in medical training and in pre-surgical planning. A three dimensional model created from a patient's medical scans can be very useful for surgeons, since it can show the specific conditions inside the patient's body. This may simplify complex surgery.
Prosthetics and Implantable Items
The metal jaw described above is a type of prosthetic, or artificial body part. The production of prosthetics is an area in which 3D printers are becoming important. Some hospitals now have their own printers or are working in cooperation with a medical supply company that has a printer.
The creation of a prosthetic by 3D printing is often a quicker and cheaper process than the creation by conventional manufacturing methods. In addition, it's easier to create a customized fit for a patient when a device is specifically designed and printed for the person. Hospital scans can be used to create tailored devices.
Replacement limbs are often 3D printed today, at least in some parts of the world. Printed arms and hands are often considerably cheaper than those produced by conventional methods. One 3D printing company is working with Walt Disney to create colourful and fun prosthetic hands for children. In addition to creating a cheaper product that is more affordable, the initiative aims "to help kids view their prosthetics as a source of excitement rather than embarrassment or limitation".
In late 2015, printed vertebrae were successfully placed in a patient. Patients have also received a printed sternum and a ribcage. 3D printing is used to produce improved dental implants. Replacement hip joints are often printed. Catheters that fit the specific size and shape of a passage in a patient's body could soon be common. 3D printing is often involved in the manufacture of hearing aids.
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 likely be stem cells, which are unspecialized cells that are capable of producing other cell types when they are stimulated correctly. The different cell types would be deposited by the printer in the correct order. Researchers are discovering that at least some kinds of human cells have an amazing ability to self-organize when they are deposited, which would be very helpful in the process of creating an organ.
A special type of 3D printer known as a bioprinter is used to make living tissue. In a common method of making the tissue, 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 a living body.
In medicine, a transplant is the transfer of an organ or tissue from a donor to a recipient. An implant is the insertion of an artificial device into the patient's body's. 3D bioprinting falls somewhere between these two extremes. Both "transplant" and "implant" are used when referring to items produced by a bioprinter.
Bioprinting Successes So Far
Non-living implants and prosthetics 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 yet been implanted into humans. In 2017, scientists presented a prototype of a printer that can create human skin for implantation, however, and in 2018 other scientists printed corneas in a process that may one day be used to repair damage in eyes.
Some hopeful discoveries 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 implanted structures were able to stay alive until the blood vessels had developed. This feat was accomplished by the existence of tiny pores in the structures that allowed nutrients to enter them.
Printing Parts of the Heart
Creating a Cornea
Scientists at Newcastle University in the UK have created 3D-printed corneas. The cornea is the transparent, outermost covering of our eyes. Serious damage to this covering can cause blindness. A corneal transplant often solves the problem, but there aren’t enough corneas available to help everyone who needs them.
The scientists obtained stem cells from a healthy human cornea. The cells were then placed in a gel made of alginate and collagen. The gel protected the cells as they travelled through the single nozzle of the printer. Less than ten minutes were needed to print the gel and the cells in the correct shape. The shape was obtained by scanning a person's eye. (In a medical situation, the patient's eye would be scanned.) Once the gel and cell mixture was printed, the stem cells produced a complete cornea.
The corneas made by the printing process have not yet been implanted into human eyes. It will probably be some time before they are. They have the potential to help many people, however.
Benefits of Mini Organs, Organoids, or Organs on a Chip
Scientists have been able to create mini organs by 3D printing (and by other methods). "Mini organs" are miniature versions of organs, sections of organs, or patches of tissue from specific organs. They are referred to by various names in addition to the term mini organ. The printed creations may not contain every type of structure found in the full-size organ, but they are good approximations. Research indicates that they could have important uses, even though they aren't implantable.
Mini organs are not always produced from cells supplied by a random donor. Instead, they are often made from the cells of a person who has a disease. Researchers can check the effects of medications on the mini organ. If a drug is found to be helpful and not harmful, it may be given to the patient. There are several advantages to this process. One is that a medication that is likely to be beneficial for the patient's specific version of a disease and for their specific genome can be used, which increases the likelihood of a successful treatment. Another is that doctors may be able to obtain an unusual or normally expensive drug for a patient if they can demonstrate that the drug is likely to be effective. In addition, testing drugs on mini organs may reduce the need for lab animals.
Some Challenges for Bioprinting
Creating an organ that is suitable for implantation 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.
Though it's likely to be years before bioprinted organs are available for implants, 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.
- An artificial ear created by a 3D printer and living cartilage cells from the Smithsonian Magazine.
- Transplant jaw made by a 3D printer from the BBC (British Broadcasting Corporation)
- Colourful 3D printed hands from the American Society of Mechanical Engineers
- Bioprinter creates bespoke lab-grown body parts for transplant from The Guardian
- First 3D-printed human cornea from the EurekAlert news service
- 3D printer makes tiniest human liver ever from New Scientist
- Mini 3D printed organs mimic beating heart and liver from New Scientist
- New 3D printer makes life-sized ear, muscle, and bone tissue from living cells from Science Alert
- 3-D bioprinter to print human skin from the phys.org new service
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
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© 2013 Linda Crampton