What is CRISPR? A Primer

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CRISPR is known as a cutting-edge tool for gene editing. Would you be surprised to learn that  that CRISPR originally evolved within single-celled organisms such as bacteria, as their own immune response to viruses? When viruses attack a bacterial cell, they inject their genome—their own viral DNA—into the cell. The bacterial cell, in turn, responds by deploying CRISPR: a scissor-like enzyme called CRISPR-associated protein, or Cas, hooked to a strand of RNA.3 The RNA recognizes the viral DNA, and Cas completely inactivates the targeted gene by making a precise cut in the gene, disabling the viral attack.1

CRISPR is an acronym for “clustered regularly interspaced short palindromic repeats,” which refers to the unique gene organization of bacteria and other microorganisms with short, partially palindromic repeated DNA sequences.2  Since its discovery in bacteria in 2012, scientists have been working in the lab to reproduce the CRISPR method to target plant or animal DNA, rather than viral DNA. CRISPR has the potential to “knock out” specific, targeted genes in plant, animal, or even human cells and, if a strand of DNA coding for a new gene is added, CRISPR can potentially provide a patch in the new gene between the severed ends. If it works, it would actually be fairly simple to design—all a researcher needs is a piece of RNA that can lock on to the targeted gene, attach it to a Cas enzyme, like Cas9, and you have a precision DNA editing tool.1

CRISPR editing technology has the greatest medical potential in humans in utero, to edit genes before birth and prevent the transmission of deadly genetic diseases like Tay-Sachs. Once a person is born with a disease like Tay-Sachs or Huntington’s disease, it’s much more difficult to use CRISPR to treat it.3 Gene editing is also being tested to treat conditions like cancer, blindness, sickle cell, thalassemia, and liver disease—among others.3,4

CRISPR has potentially broad applications that could impact allografts and human tissue engineering. It’s already being used to edit the genomes of mosquitoes, in the hopes of being able to prevent their ability to carry infectious diseases like Zika.3 And CRISPR/Cas is being applied directly within the field of tissue engineering, where it has been used to modify the expression of bone morphogenetic proteins (BMP) improve the osteogenic potential of adipose-derived stem cells (ASC).5

Another application of CRISPR is to edit induced pluripotent stem cell (iPSC) genomes to create special cell lines for use in tissue engineering.5 As techniques are developed to aid in homing and differentiation of stem cells, these customized iPSCs  may allow for the creation of multi-layered tissue scaffolds; cardiovascular grafts, whole organs, and other complex tissues could then be created.

For now, however, medical applications are confined to laboratories.1 Two recent studies have raised concerns that edited cells, designed to treat disease, might trigger cancer, demonstrating the need for further research and refinement before the technique is deployed. Experts describe the cancer risk as “plausible,” but not a “deal-breaker.”4  Considering the potential benefits to humankind, we’ll be staying tuned as the research evolves.

References

[1] Richter, V. (2016, 18 April). What is CRISPR and what does it mean for genetics? COSMOS: The science of everything. Retrieved from: https://cosmosmagazine.com/biology/what-crispr-and-what-does-it-mean-genetics

[2] Pak, E. (2014). CRISPR: A game-changing genetic engineering technique. Harvard: Science in the News. Retrieved from: http://sitn.hms.harvard.edu/flash/2014/crispr-a-game-changing-genetic-engineering-technique/

[3] Delviscio, J. (2018, April 4). How CRISPR works, explained in two minutes. STAT. Retrieved from: https://www.statnews.com/2018/04/04/how-crispr-works-visualized/

[4] Begley, Sharon. (2018, June 12). CRISPR-Edited cells linked to cancer risk in 2 studies. Scientific American. Retrieved from: https://www.scientificamerican.com/article/crispr-edited-cells-linked-to-cancer-risk-in-2-studies/

[5] Pulgarin, D. A. V., Nyber, W. A., Espiinosa, A. (2017, July). CRISPR/Cas systems in tissue engineering: A succinct overview of current use and future opportunities. Current Trends in Biomedical Engineering and Biosciences, 5(4), 001-004. doi:10.19080/CTBEB.2017.05.555670

First Commercial Induced Pluripotent Stem Cell Plant Opens in Japan

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The first commercial facility to produce induced pluripotent stem cells (iPSCs) opened on March 22, 2018. The $340 million, 30,000 square foot facility was built by Sumitomo Dainippon Pharma and is designed to produce stem cells for therapeutic applications.1  Sumitomo Dainippon is currently involved in using iPSCs to create treatments for conditions including macular degeneration, Parkinson’s disease, retinitis pigmentosa, and spinal cord injuries. The plant’s function, initially, will be to produce stem cells for use in clinical trials and early-stage commercial production.2 The more than 30,000 square feet of floor space is divided in three autonomous zones, each producing different types of stem cells. The iPS cell lines come from those produced by Kyoto University’s Center for iPS Cell Research and Application (CiRA).1

The Sumitomo Dainippon Manufacturing Plant for Regenerative Medicine & Cell Therapy is the only facility designed for commercial purposes that exists worldwide. Existing facilities, including the National Institutes of Health’s Center for Regenerative Medicine and the UK Stem Cell Bank, have made stem cells available to researchers, but to date no facility has provided stem cells for commercial purposes. This demonstrates what Masayo Tada, the president of Sumitomo Dainippon, claims is an “overwhelming advantage in the market of medical and pharmaceutical products” that will help the company “occupy a definite position in the field of regenerative medicine.” Sumitomo Dainippon intends to make regenerative medicine one of its core business strategies, and has plans for significant market growth in the coming decade.1

References

  1. Daley, J. (2018, March 23). World’s first commercial iPSC cell plant opens in Japan. The Scientist. Retrieved from: https://www.the-scientist.com/the-nutshell/worlds-first-commercial-ipsc-cell-plant-opens-in-japan-29915
  2. Sumitomo Dainippon Pharma. (2018, March 1). Sumitomo Dainippon Pharma completes manufacturing plant for regenerative medicine and cell therapy. IR News. Retrieved from: https://www.ds-pharma.com/ir/news/2018/20180301-3.html
  3. Photo: Immunocytochemistry of Kindey Tubular Epithelial Cells derived from induced pluripotent stem cells. By Ugnezija7, from Wikimedia Commons

 

Understanding Stem Cells Part 2: Ready for the Clinic?

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With advances in research and technology, using stem cells for their regenerative potential has become a reality. But many stem cell treatments on the market have been marketed to the public and applied clinically without scientific evidence of efficacy. Worse, some treatments with stem cells have caused serious adverse events.

Provided that cell and tissue products fall into the “minimally manipulated” classification established by the Food and Drug Administration (FDA) under Title 21 of the Code of Federal Regulations Part 1271, studies to prove efficacy and safety are not required. This makes it possible to promote stem cell treatments for any use, without scientific or medical evidence that they work. Medical practitioners and patients alike must be aware that stem cell treatments are generally not “FDA approved.”

Draft guidance for industry was issued by FDA in 2017, proposing guidelines for evaluating and approving regenerative therapies which have demonstrated safe and efficacious use in serious conditions. These products could achieve a designation of “Regenerative Medicine Advanced Therapy” or “RMAT” in several ways. While the actual policy is still being formulated, this guidance initiated discussion with industry stakeholders and signaled increasing attention by FDA to regulating products touted as “regenerative,” including stem cells.

Cells for stem cell treatments are often autologous, extracted from the patient through bone marrow aspiration, a blood draw and centrifuge process, or liposuction (for adipose stem cells). There are also stem cell products available commercially that are allografts (cells or tissue from a human donor), including umbilical cord blood stem cells, allograft fat, and cell-based bone grafts. The number and type of stem cell varies based on the tissue of origin and the processing of the product, and both of these factors can be expected to affect outcomes.

Stem cell clinics often charge very high prices for stem cell treatments, from $1,500 for a joint injection to $25,000 for a systemic treatment. Insurance typically does not cover these treatments because they are considered experimental. Patients range from injured athletes and weekend warriors who want to avoid surgery, to desperate and terminally ill patients who are struggling with incurable conditions.

One unfortunate example of stem cell treatment gone wrong occurred at a Florida clinic. Three elderly women received stem cell injections to treat age-related macular degeneration and were blinded by the procedure. One of the women was apparently misled into believing that she was taking part in a clinical trial. The clinic which performed the injections, Bioheart Inc., had not conducted any pre-clinical or clinical trials. Today, Bioheart Inc. is doing business as US Stem Cell, which received a warning letter from FDA in August 2017, citing a multitude of deviations from current good manufacturing processes as well as inappropriate marketing claims and clinical uses. Read about it here.

Yet, there are many reasons to be excited about stem cells which are produced, processed, and applied appropriately. The California Institute for Regenerative Medicine (CIRM) has pioneered stem cell treatments to cure children afflicted with Severe Combined Immunodeficiency Disease (SCID), and they are now entering Phase 2 clinical trials for this clinical application. CIRM has over 40 trials running at this time, all targeting devastating medical problems.

In more common clinical scenarios, studies have shown that stem cell injections can improve osteoarthritis symptoms, and many sports medicine and orthopedic specialists are using them to help patients avoid surgery.

Future cardiac applications may become possible, too. In an article published in Nature Communications by Shadrin and colleagues (2017), scientific work investigated the development of a scaffold composed of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), which are heart cells derived from adult human stem cells. The scientists developed a “cardiopatch”, essentially a network of organized heart cell tissue, and conducted experiments in a rodent model. The cardiopatches became vascularized, showed specific characteristics of adult heart tissue, and conducted the heart’s electrical charge. The researchers believe that their 4x4cm cardiopatches could eventually be scaled to create larger sections of functioning tissue for myocardial repair.

Validated treatments using stem cells have the potential to improve countless lives. But, for most conditions, we are years away from establishing proper protocols and doses. It’s appropriate for practitioner and patient alike to weigh the risks and benefits of any treatment, including (and, perhaps, especially) those promising stunning disease reversals and health advancements. Meanwhile, research continues to bring the promise of stem cells closer into focus and, step by step, safely into the clinic.

 

References

Begley, Sharon. (2017, March 15). Three patients blinded by stem cell procedure, physicians say. STAT. Retrieved from https://www.statnews.com/2017/03/15/stem-cell-patients-blind-macular-degeneration/.

Doheny, Kathleen. (2017, April 14). Stem cells for knees: promising treatment or hoax? WebMD. Retrieved from https://www.webmd.com/osteoarthritis/news/20170407/stem-cells-for-knees-promising-treatment-or-hoax#1.

GEN News Highlights. (2018, January 29). Stem cells: On your mark, get set, don’t go. Genetic Engineering & Biotechnology News. Retrieved from https://www.genengnews.com/gen-news-highlights/stem-cells-on-your-mark-get-set-dont-go/81255432.

McFarling, Usha Lee. (2016, February 8). FDA moves to crack down on unproven stem cell therapies. STAT. Retrieved from https://www.statnews.com/2016/02/08/fda-crackdown-stem-cell-clinics/.

Shadrin, Ilya Y., Allen, Brian W., Qian, Ying, Jackman, Christopher P., Carlson, Aaron L., Juhas, Mark E., & Bursac, Nenad. (2017, November 28). Cardiopatch platform enables maturation and scale-up of human pluripotent stem cell-derived engineered heart tissues. Nature Communications, 8: 1825. doi:10.1038/s41467-017-01946-x

Uygur, Aysu, & Lee, Richard T. (2016, February 22). Mechanisms of cardiac regeneration. Developmental Cell, 36: 362-374. https://doi.org/10.1016/j.devcel.2016.01.018

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Understanding Stem Cells, Part 1: Stem Cells 101

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Stem cells are a promising regenerative medicine tool and treatment. So much information on stem cell research exists that sorting through the facts and the hype can be daunting. This post will focus on explaining stem cell basics: What are stem cells, and what are the different types? Here, we will focus on adult stem cells, also known as somatic stem cells, since these are most relevant to medical research and clinical use today.

Nearly every cell in the body has a specific purpose. When a fetus begins to develop, cells become specialized (or differentiated), developing structure and characteristics specific to carrying out a special function in the body.1 For example, heart muscle cells generate movement (i.e., heartbeat), and red blood cells contain hemoglobin so that they can transport oxygen throughout the bloodstream. Stem cells, on the other hand, are unspecialized (undifferentiated); they have the potential to become any type of cell.

There are different categories of stem cells. Most current research focuses on these stem cell types:

  • Totipotent—can form all cell types in the body. During embryonic development, totipotent stem cells differentiate into all of the different cell types in order to form a whole organism. Researchers have been able to take differentiated cells and return them to a state of totipotency. More work is needed to make totipotent cells clinically useful.
  • Pluripotent—are descended from totipotent stem cells and can form into almost all cell types. Pluripotent stem cells can form any type of cell derived from the three germ layers: endoderm (forms the inside lining of stomach, digestive tract, and lungs), mesoderm (forms blood, muscle, and bone), and ectoderm (forms the skin and nervous system.) Pluripotent stem cells naturally exist in the embryo.
  • Multipotent—more specialized than totipotent and pluripotent stem cells, multipotent cells can develop into several different somatic cell types. Multipotent stem cells give rise to various tissues and organs during development, and some of these stem cells remain in a state of dormancy (“quiescence”) within their specific tissue niches of the adult human body. Types of multipotent stem cells include:
    • Hematopoietic stem cells—form the components of the blood.
    • Mesenchymal stem cells—form bone, cartilage, muscle, and fat cells.
    • Neural stem cells—form the nervous system.
    • Epithelial stem cells—form cells in the digestive tract lining.
  • Oligopotent—can form a few different cell types. They are derived from multipotent stem cells, descending from hematopoietic stem cells. Examples:
    • Lymphoid cells—form several types of immune cells, such as B cells and T cells.
    • Myeloid cells—form red blood cells and white blood cells, among others.

As mentioned above, stem cells are found in the adult body within tissues such as blood, bone, skin, heart, and gut, as multipotent cells. It’s believed that the cells are located in a stem cell niche, or a specific area of each tissue. The number of niche-dwelling stem cells is relatively small. These cells may remain quiescent (undifferentiated) for a long time, until disease, injury, or normal body processes cause the need for differentiation.

Three main sources of these adult somatic stem cells are bone marrow, blood, and adipose, tissue. Research is being conducted on ways to grow larger numbers of adult stem cells outside the body. When experimental conditions in the laboratory are right, stem cells can be induced to become specialized cells that perform specific functions. This has important implications for regenerative medicine.

Inducing cells from a patient’s own body to grow into the specific tissue they need to receive could lead to tremendous medical advances, someday eliminating the need for allografts and organ transplants. In the lab, researchers have been able to manipulate adult somatic stem cells to become induced pluripotent stem cells, or iPSCs. Through forced expression of specific genes, transcription factors, and epigenetic factors, differentiated somatic cells can be de-differentiated or induced to return to a pluripotent state. Advances have been made in scientific research on therapeutic implications of iPSCs.

Another source of pluripotent stem cells is umbilical cord blood. Stem cells from umbilical cord blood can be saved just after birth, cryopreserved for later use, and stored in an umbilical cord blood bank.2 There are now commercialized injectable therapies using umbilical cord blood stem cells.

There are many exciting possible applications of the stem cell research now being performed in laboratories worldwide. One example of this involves limbal stem cells, or LSCs. LSCs are found in the limbus, the part of the eye where the cornea meets the sclera. Normally, these cells are used to regenerate the cornea, which has a very fast turnover rate of 1-2 weeks in the human body. If a person’s LSCs deteriorate or they do not have enough LSCs, their corneas degenerate and they will go blind. However, research suggests that if LSCs were transplanted into such an eye, the entire cornea would regenerate.3 Researchers have studied LSCs using experiments with mice, and were able to restore the cornea of mice with experimental blindness. These results are promising for regenerative medicine in humans. For more information about the applications of stem cell research, check out Part 2.

References:

Stem Cell Basics (2016). National Institutes of Health. Retrieved from https://stemcells.nih.gov/info/basics.htm.

Jawdat, Dunia (2016). Banking of Human Umbilical Cord Blood Stem Cells and Their Clinical Applications. In Abdelalim E. (ed.) Recent Advances in Stem Cells. Humana Press. Retrieved from https://link.springer.com/chapter/10.1007/978-3-319-33270-3_8.

Limbal Stem Cells for Treatment of Corneal Blindness (2017). Advanced Science News. Retrieved from http://www.advancedsciencenews.com/limbal-stem-cells-treatment-corneal-blindness/.

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3D Printed Tissues From Bench to Bedside

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3D bioprinting has the potential to provide significant medical advances. For example, 3D printing of functional tissues and organs could someday alleviate shortages in organ availability and the problem of organ incompatibility. But where does the field stand today?

A look at the research benches of top labs can give us an idea. In this post we’ll take a look at CELLINK’s innovative inks and printers, ORGANOVO’s functional bioprinted tissues, Dr. Anthony Atala’s Wake Forest Institute for Regenerative Medicine, and the 3D printed cortical fibers line by Xtant Medical, 3Demin®.

CELLINK is the world’s first bioink company. A Swedish company founded in 2016, CELLINK solved problems for the tissue engineering community by commercializing hydrogel bioinks which can be used to 3D print cartilage, bone, skin, or muscle. CELLINK is also a top provider of bioprinters. It’s likely to be one of CELLINK’s printers in a researcher’s lab being used to create 3D printed allografts during experiments, as was the case of the 3D printed cartilage mentioned in the prior post. With the right raw materials, it’s possible to create multiple biologics scaffolds and structures, and CELLINK is at the forefront of bioink development.1

ORGANOVO creates functional, responsive bioprinted human tissue models for preclinical testing and drug discovery research. Their 3D bioprinted tissues remain viable and dynamic for more than 28 days in vitro.2 Their key architectural and functional features mimic natural function and provide important information for scientists.

Pharmaceutical companies conducting research can examine the effects of new compounds on ORGANOVO’s ExVive™ 3D bioprinted human tissues. This allows tissue-specific data to be collected to better predict human outcomes, lower total development time, and reduce costs.

For example, liver and kidney tissues can be used to evaluate drug exposure for both acute and chronic toxicity and metabolism studies.2 ORGANOVO is also working on developing functional, 3D tissues for implantation or delivery into the human body, with the intention of creating these tissue for use for repair or replacement of damaged or diseased tissues.3

The Wake Forest Institute for Regenerative Medicine is one of the nation’s top research labs working to translate scientific discoveries in 3D printing into clinical therapies. Led by Dr. Anthony Atala, a pioneer in medical tissue engineering, this interdisciplinary team is engineering more than 30 different replacement tissues and organs to develop curative cell therapies.4 Wake Forest was the first institution to successfully engineer laboratory-grown organs and implant them into humans: these were engineered bladders grown from the patient’s own cells.5

The fact is, all living tissues are composed of many different cell types arranged in a specific order that is essential to function. Therefore, when using 3D printing to create a tissue, precision is critical.6 Researchers at Wake Forest have designed their own inkjet bioprinter that can print kidney cells, and the binders to hold the cells together, into a 3D kidney prototype. This bioprinter could potentially be used to create a custom organ based on a CT scan and patient data. Their bioprinter is also being tested in the creation of other structured tissue, such as the ear.7

While 3D bioprinting of living, functional, clinically applicable tissues and organs remains the Holy Grail, there are much simpler examples of the technology already commercialized and in use today.  Bacterin’s 3Demin® line of demineralized cortical bone fibers is bioprinted into different shapes and sizes designed for specific surgical applications. The bioprinting process creates a porous, interconnected allograft that contains BMPs and other growth factors necessary to promote new bone formation. It is an osteoconductive demineralized cortical fiber matrix with osteoinductive potential that can be used as a stand-alone graft, or in combination with autologous bone, bone marrow, DBM putty, and other products.8

Bacterin’s production of customized bone implants using 3D printing technology was applied clinically during a mission sponsored by the World Craniofacial Foundation. In Zambia, a child named Grace Kabelenga was born with the most severe facial cleft in 40 years (Tessier 0-14), and a total absence of the bones separating her brain from her oral cavity.9 3D printed plastic prototypes allowed the team to simulate surgery and to create molds for custom bone implants. Bacterin’s 3Demin® bone allograft material was used to create custom 3D printed bone to serve as a “bandeau” to define the superior orbital rims above her eyes.10 This was combined with other Bacterin allografts and rhBMP2 to reconstruct missing parts of Grace’s skull.

Multiple surgeries have allowed Grace to function as a normal child would. Allografts.com members can view a video about the WCF mission on our portal. A slide deck is also available here.

3D printing for tissue engineering has the potential to provide incredible benefits to humankind if the technology can be developed to its full potential for medical applications.

If you missed it, you can read more about the history and applications of bioprinting here: 3D Printing in Tissue Engineering.

References:

1 CELLINK. (2017). BioX Printer. Retrieved from https://cellink.com/bioprinter/

2 ORGANOVO. (2017). 3D human liver tissue testing services. Retrieved from http://organovo.com/tissues-services/exvive3d-human-tissue-models-services-research/3d-human-liver-tissue-testing-services/

3 ORGANOVO. (2017). About ORGANOVO. Retrieved from http://organovo.com/about/about-organovo/

4 Wake Forest School of Medicine. (n.d.). Wake Forest Institute for Regenerative Medicine. Retrieved from http://www.wakehealth.edu/WFIRM/

5 Wake Forest Baptist Medical Center. (2006). Wake Forest physician reports first human recipients of laboratory-grown organs. Retrieved from http://www.wakehealth.edu/News-Releases/2006/Wake_Forest_Physician_Reports_First_Human_Recipients_of_Laboratory-Grown_Organs.htm

6 Wake Forest School of Medicine. (2017, September 6). Using 3D printing technology to print organs and tissue. Retrieved from http://www.wakehealth.edu/Research/WFIRM/Our-Story/Inside-the-Lab/Bioprinting.htm

7 Wake Forest School of Medicine. (2016, August 8). Replacement organs and tissues: Engineering a kidney. Retrieved from http://www.wakehealth.edu/Research/WFIRM/Research/Engineering-A-Kidney.htm

8 Bacterin. (2015). 3Demin Benefits. Retrieved from: https://xtantmedical.com/app/uploads/2016/09/3Demin_Brochure_Digital-14009B.pdf

9 3D Systems. (2016). Delivering the gift of a normal life. Retrieved from: https://www.3dsystems.com/sites/default/files/2016/cs_3ds_grace_kabelenga_0316_0.pdf

10 3D Systems. (2017). Delivering the gift of a normal life with 3D systems healthcare solutions. Retrieved from 3D Systems. Delivering the gift of a normal life with 3D systems healthcare solutions. Retrieved from https://www.3dsystems.com/learning-center/case-studies/delivering-gift-normal-life

3D Printing in Tissue Engineering

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Three-dimensional (3D) printing was developed in the early 1990s at MIT by by Sachs, Haggerty, Cima, and Williams.1 It is a freeform fabrication method that uses regular inkjet printheads to fabricate objects by printing binders onto loose powders in a powder bed.2 What can be made in 3D printing depends on what is used as the material which is either simply deposited or fused, and can include such things as plastics, metal, ceramics, or even living cells, which are applied in layers to produce a 3D object.3

The 3D printing process uses 3D computer models from CAD data sets to produce a physical object. The process is also referred to as rapid prototyping (RP), solid free-form technology (SFF), layered manufacturing (LM), additive manufacturing (AM), or computer aided manufacturing (CAM), depending on the kind of production method used.3,4 The primary advantage of this type of rapid prototyping and additive fabrication is that these layers, which correspond to the cross-sections from the CAD model, can create nearly any complex shape.4 This manufacturing of specific parts is done layer-by-layer without any part-specific tooling or dies, which offers unique advantages for part fabrication of small volumes or one of a kind product manufacturing.2 In general, a wide variety of ceramics, metals, polymers, and composites can be processed using 3D printing, though the keys to successful fabrication are binder selection and temperature parameters.2

3D printing has three primary biological applications: its use in prototyping models for surgery; its potential use in custom implants; and its use in bioprinting human tissues and tissue scaffolds.

The usefulness of 3D printing to create rapid prototypes has been utilized in the surgical arena as a tool to aid in presurgical planning using prototype models to simulate complicated surgeries. 3D models of the pelvis, brain, maxillofacial area, spine, heart, and other organs have all been created to aid in diagnosis and treatment planning. The use of this type of custom 3D models can potentially reduce operating time and complications.4

With 3D printing also comes the potential ability to make custom medical devices that are tailored to individual patients and specific clinical needs, though further process optimization is needed to truly accomplish this goal.2 In February of 2012, a woman received the “world’s first 3D printed jaw transplant,” a custom implant made from a scan of her jaw and produced with titanium powder in just a few hours. Coated in ceramic, the implant was heavier than a natural jaw, but otherwise identical in shape and size to her own, though unlike bioprinted tissue it did not have osteogenic properties.5

Bioprinting, the 3D printing of human cells, is on the forefront of 3D printing technology. In the same way that traditional 3D printing uses binders printed onto loose powders, bioprinting uses “bioinks” printed onto powdered extracellular matrix, in a layer-to-layer manner to create a tissue construct with or without scaffold support. Bioinks are defined as any ink formulation useful for printing human cells.6 The most common bioinks are cell-laden hydrogels, decellularized extracellular matrix-based solutions, and cell suspensions. Inorganic binders can sometimes be used for printing on demineralized bone matrixes.

Direct ink writing (DIW) is the primary commercial bioprinting method. It is an extrusion-based printing that, like all additive manufacturing methods, builds the 3D printed model using cross sections. It is capable of handling high viscosity solutions, colloidal suspensions, and hydrogels.6 Inkjet 3D printing is also be suitable for bioprinting, but it has not yet been commercially adopted.6

Current bioprinting techniques allow printing of structures with similar composition to that of human tissue, but we are still a long way from printing truly functional organs. However, simple tissues like bone and cartilage are closer to being able to being able to be successfully printed, and 3D printed demineralized bone products are already in commercial use.2

The advantages of 3D printing for bone engineering comes from the fine control of features including interconnected porosity, lack of contamination from secondary materials, and direct printing abilities with both metallic and ceramic biomaterials.2 Overall, it is a popular and versatile tool that can fabricate scaffolds for bone tissue engineering with defined shapes and controlled, interconnected porous surfaces.2

Unfortunately, low mechanical strength is a major challenge in building porous scaffolds for tissue engineering, and so far 3D printed bone scaffolds have been limited in use to only no- and low-load bearing applications.2 However, studies attempting to build artificial cartilage have been more succesful, and human-derived induced pluripotent stem cells (iPSCs) have been successfully bioprinted into cartilage mimics using a nanofibrillated cellulose (NFC) composite bioink co-printed with human chondrocytes in the lab.7

Adding growth factors or drugs and personalizing implants to individual patients are all possible outcomes of 3D printing technologies. Although much work remains to be done to make 3D printed tissues clinically applicable,2  progress has been rapid and the future potential is very exciting.

You can read more about the emerging applications of bioprinting here: 3D Printed Tissues from Bench to Bedside.

References:

1 Sachs, E. M., Haggerty, J. S., Cima, M. J., Williams, P. A. (1993). Patent Identifier No. 5,204,055. Cambridge, MA: Massachusetts Institute of Technology. Retrieved from: http://patft.uspto.gov/netacgi/nph-Parser?Sect2=PTO1&Sect2=HITOFF&p=1&u=/netahtml/PTO/search-bool.html&r=1&f=G&l=50&d=PALL&RefSrch=yes&Query=PN/5204055

2 Bose, S., Vahabzadeh, S., Bandyopadhyay, A. (2013). Bone tissue engineering using 3D printing. Materials Today, 16(12): 496-504. https://doi.org/10.1016/j.mattod.2013.11.017

3 Ventola, C. L. (2014). Medical applications for 3D printing: Current and projected uses. Pharmacy and Therapeutics, 39(10): 704-711. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4189697/

4 Rengier, F. Mehndiratta, A., von Tengg-Kobligk, H., Zechmann, C. M., Unterhinninghofen, R., Kauczor, H.-U., & Giesel, F. L. (2010). 3D printing based on imaging data: Review of medical applications. International Journal of Computer Assisted Radiology and Surgery, 5: 335-341.https://doi.org/10.1007/s11548-010-0476-x

5 Dybuncio, M. (2012, February 6). Woman gets world’s first 3D printed jaw transplant. CBS News. Retrieved from https://www.cbsnews.com/news/woman-gets-worlds-first-3d-printed-jaw-transplant/

6 Ji, S. & Guvendiren, M. (2017). Recent advances in bioink design for 3D bioprinting of tissues and organs. Frontiers in Bioengineering and Biotechnology, 5(23). https://dx.doi.org/10.3389%2Ffbioe.2017.00023

7 Nguyen, D., Gagg, D. A., Forsman, A., Ekholm, J., Nimkingratana, P., Brantsing, C., … Simonsson, S. (2017). Cartilage tissue engineering by the 3D bioprinting of iPS cells in a nanocellulose/alginate bioink. Scientific Reports, 7(658). Retrieved from https://www.nature.com/articles/s41598-017-00690-y