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Good Tissue Bank Standards of Practice

What helps make a tissue bank good?

Following Standards of Practice (SOPs) in tissue banking is vital to ensure that every step of human tissue procurement, preparation, and distribution is held to the highest standards. This is done to ensure the safety, quality, and traceability of tissues for surgical use.

The internal Standards of Practice for tissue banks include documents that cover every aspect of this process. These standards cover topics including monitoring tissue recovery sites, the audit of tissue recovery partners, necessary body cooling protocols, microbiological surveillance programs, providing service to tissue donor families, prevention of contamination and cross-contamination at recovery, and many more.

However, the most relevant guide to understanding what makes a “good tissue bank” are the factors that govern “Good Tissue Practice,” defined by the steps that the FDA defines in the manufacturing of human allografts for surgical use: recovery, donor screening and testing, packaging, labeling, distribution, processing, and storage.1 Detailed guidelines for these areas of “Good Tissue Practice” have been developed by the national organization which audits and accredits participating US tissue banks.2

Recovery of Allografts

Recovery is the process of obtaining from a donor either cells or tissues that are intended for human use via implantation, transplantation, infusion, or transfer.1 It is the responsibility of the donor recovery agency to have a program in place that ensures donor information is received, investigated, evaluated, documented, and shared with all agencies that receive tissues from the donor to ensure donor suitability. There are specific SOPs in place to ensure that all recovery personnel are well trained and competent.

There are very specific steps that are taken by the donor recovery operation to control contamination and cross-contamination during retrieval. These steps include adherence to appropriate donor eligibility guidelines such as specific body cooling parameters and time limits for retrieval; ensuring a suitable location for recovery site activities; using clean techniques appropriate to the specific cells/tissues being recovered; cleaning, disinfecting, and sterilization of equipment, supplies, and instruments; monitoring recovery activities for microorganism contamination, such as by culture results; and sharing of all records related to donor eligibility determinations.

Donor Screening and Testing

The main step to prevent potential infectious diseases in the donor tissue supply is primary prevention, which comes from donor screening and testing, first in the form of the detailed medical-social interview (Donor Risk Assessment) of the donor and exhaustive review of their medical records and sexual history. There are multiple levels of review of every record, including by an independent medical doctor specializing in cytopathology. All tissues are also required to be tested by a range of FDA-licensed, cleared, or approved donor screening tests, as applicable by tissue type, such as for HIV, HBV, HCV, syphilis, HTLV, CMV, etc.3 Testing laboratories must also be registered as tissue establishments by the FDA, and are subject to the same rigorous oversight as tissue banks and procurement organizations.

Processing and Storage

Processing is defined by the FDA as “any activity performed on an HCT/P, other than recovery, donor screening, donor testing, storage, labeling, packaging, or distribution, such as testing for microorganisms, preparation, sterilization, steps to inactivate or remove adventitious agents, preservation for storage, and removal from storage.”4 Generally, processing includes cutting, grinding, shaping, culturing, enzymatic digestion, and decellularization of recovered tissues to make them suitable for surgical use.3 Processing must be conducted in a suitable clean room environment with appropriate environmental controls and monitoring.

Processing may also include a sterilization step such as gamma or e-beam radiation. Both are validated, controlled methods of improving allograft tissue safety. Most tissue banks employ a sterilization step in the face of infectious disease risks. To learn more about sterilization through radiation, see this post: Understanding Tissue Sterilization, Part 2: Radiation Round-up.”

Storage of allografts must be maintained at appropriate temperatures within each tissue’s tolerance limits. A temperature monitoring system must be in place to document storage temperatures and alert staff of deviations before straying outside of acceptable limits. Each unit of stored tissue should be packaged to facilitate sterile storage and prevent contamination or cross-contamination.

Packaging and Labeling

Packaging and shipping are not part of processing, and are therefore not required to be validated or verified in the same way as manufacturing. However, appropriate procedures must be in place to ensure the tissues are protected from contamination and cross-contamination, and that appropriate storage parameters are maintained during transport, particularly that temperature ranges are kept within acceptable limits.

Tissue labeling must make appropriate claims that are supported by verification and validation data to ensure that they are true and accurate. This could include information on sterilization procedures. Labeling also must include a method of internal donor identification, usually a lot-based identifying number on the label to allow for tracking and traceability of every tissue.

Distribution of Allografts

Strict regulations govern the transport and distribution of allografts, including an expiration date for their use. The expiration date is the maximum allowable storage period for the tissue, and expired tissues should not be transplanted. It is also critical to ensuring a safe allograft supply that the distribution of tissues be completely traceable from the original donor, to the retrieval agency, to the intermediary or processor, and on to any other tissue manufacturer or distributors to the ultimate end-user. The information that should travel with an allograft includes tissue ID numbers, tissue type, quantity, time of transport and delivery, recipient of delivery, and who transported and accepted tissues.

If you need help developing a tracking process for your surgical facility, there are resources available to guide you. In addition to the information above, a tissue tracking log should reflect the date of implantation and recipient of every graft. More information on tracking requirements can be found at the FDAs website .

 

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Hot Topics: Zika Virus and Allografts, Part 1

Background

Since the Zika outbreak first began in Brazil in late 2015,1 its spread has been of significant concern to the medical community. First identified due to the significant rise in microcephaly among newborns in Brazil, Zika infection has also been associated with other major birth defects including neural tube defects, eye abnormalities, brain abnormalities, and central nervous system dysfunction unrelated to microcephaly.

Studies have estimated the rate of birth defects among completed pregnancies with Zika infections to be 1 in 20, or 5%, with a higher risk of birth defects when infection occurs earlier in pregnancy.2 In addition to complications during pregnancy, Zika infection also has been shown to cause Guillain-Barré syndrome in adults and may result in other lasting neurological complications.3

Spread in the United States

The Zika virus is spread by two species of mosquito, Aedes albopictus and Aedes aegypti. Both of these vectors are native to the United States, but they are at the northernmost range of their territory and are therefore not found in every state. Ten states do not fall into the estimated range of either vector species and are therefore believed to be free of any native Zika transmission risk. The other states, as seen in the maps below, have at least small areas of potential mosquito transmission, though only Florida and Texas are known to have had local mosquito transmission of Zika to date.

Estimated range of Aedes albopictus and Aedes aegypti in the United States, CDC 2016*
*Maps are not meant to represent risk for spread of disease.

Zika became a nationally notifiable disease in 2016, which mandates reporting of cases to the CDC.4 As a result, there is very good surveillance of the disease in symptomatic patients, though many adults infected with Zika may remain asymptomatic or have only mild, flu-like symptoms.5

In 2016, the United States had 5,102 symptomatic cases of Zika reported to the CDC. Of these, only 224 were acquired through domestic mosquito-borne transmission (218 in Florida and 6 in Texas).4 There is a significantly declining prevalence of Zika virus disease in both North and South America, primarily due to the success of robust mosquito control measures and the public’s attention to preventing exposure.2

As of July 26, 2017, the United States has only had 181 symptomatic cases of Zika reported to the CDC for 2017. None were due to domestic transmission.6 It is believed that all prior areas of local mosquito transmission have been eliminated within the United States.

Clinical Testing for the Zika Virus

No diagnostic tests for the Zika virus are presently approved by the FDA for use in patients, though a number of tests have been developed. These tests are available due to an Emergency Use Authorization (EUA) for use in symptomatic patients residing in (or who have recently traveled to) an area with a risk of Zika infection. A total of 15 different tests are currently available under the Zika EUA, including molecular tests like real-time PCR and serological tests like ELISA. The Trioplex Real-Time RT-PCR assay (Nucleic Acid-based Testing) and the Zika MAC-ELISA (IgM antibody-based testing) are the only two tests that are in widespread use and distribution.7

Tests like these are important and clinically useful, but because of their newness and lack of FDA approval through the typical Premarket Application (PMA) process, concrete data on sensitivity, specificity, and predictive values are still being collected. Testing poses three primary challenges. First, the Zika virus is only transiently present in body fluids, which makes identifying the virus difficult using PCR NAT-based molecular testing. Second, serological testing for IgM antibodies using the MAC-ELISA cannot reliably pinpoint whether infection occurred during or prior to a pregnancy. Finally, serologic tests have been found to have cross-reactivity with other flaviviruses like dengue and are prone to false-positive results, which is a problem in zones where infection rates are high for the other flaviviruses.2

Current guidelines continue to recommend testing of symptomatic pregnant women with recent possible Zika exposure. However, the CDC now only recommends that asymptomatic pregnant women with ongoing possible Zika virus exposure be offered Zika virus NAT testing three times during pregnancy. IgM testing is no longer recommended for routine testing in pregnant women with ongoing Zika exposure, since IgM can persist for months after infection and therefore cannot reliably determine whether an infection occurred during the current pregnancy.2 The CDC also no longer recommends routine screening of asymptomatic pregnant women without ongoing Zika exposure, except in cases where prenatal ultrasound findings are consistent with congenital Zika virus syndrome to assist with establishing a diagnosis for the fetus.2

Testing for Zika in Human Allografts

Right now there is no test available to detect the Zika virus in human allografts, a category which includes placental tissues like the amniotic membrane and umbilical cord. The Procleix Zika Virus Assay is currently being tested under an Investigational New Drug (IND) protocol by manufacturer Gryfols and Hologic in conjunction with industry partners, but studies have not yet been completed to allow for FDA approval. The Procleix assay system, if proven effective, will be able to screen blood, plasma, and organ and tissue donations for the Zika virus.

You can read more about how tissue banks are managing risk for Zika virus in this blog post: Hot Topics: Zika Virus and Allografts, Part 2

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Hot Topics: Zika Virus and Allografts, Part 2

There is presently no test available to detect the presence of Zika virus in allograft tissues. This may change if the Procleix Zika Virus Assay now being investigated proves to be an accurate and reliable test. Until then, how are tissue banks managing the risks posed by this viral threat?

It’s important to understand that Zika is not the first virus to affect tissue banking, and the industry has specific protocols already established to protect the tissue supply. This begins with what happens before tissue procurement and acceptance, as the key to keeping Zika (and other viruses) out of the supply chain lies in primary prevention.

Tissue banks long ago implemented stringent donor screening methods and medical records review that form the basis of determining high risk for viruses such as HIV and hepatitis. These same screening methods are effective at assessing risk of Zika, along with other new contagious diseases such as West Nile, Dengue, and Chikungunya. Both deceased and living donors are screened for infectious disease risks routinely, although more public attention is focused on Zika at this time.

In the case of screening living donor mothers for Zika, Allografts.com owner Nikki Couloumbis turned to Craig Thomsen, the Director of Quality Systems for TissueTech, the Miami-based market-leading producer of cryopreserved placental tissues provided by Bio-Tissue and Amniox Medical.

Nikki: “Craig, can you discuss what TissueTech is doing to protect the placental tissue supply from Zika?”

Craig: “Absolutely. First, we do not work with any procurement partners that collect tissues within CDC-identified Zika transmission zones, including Miami-Dade, Broward, Palm Beach in Florida, and Brownsville, Texas. So, tissues potentially most at risk of infection are excluded, including the ones right in our backyard.

Second, we follow procedures that would disqualify outright those donors at risk of Zika. The main step to prevent potential infectious diseases has always been the Donor Risk Assessment Interview.”

Nikki: “In the case of deceased donors this interview is conducted with next-of-kin. But the same type of exhaustive review of risks is conducted with living donors. Can you explain some aspects of what you look for?”

Craig: “The DRAI is a very effective tool. It’s extremely in-depth, with very specific questions mandated by Federal and State authorities, supplemented by specific questions guided by company-specific exclusions. The interview addresses social behavior including drug and alcohol use, sexual partners, and tattoos and piercings. It includes a detailed family history, medical history, and travel history for the mother and her partner to known Zika transmission zones. Any living donor who has lived or traveled to an active Zika virus transmission zone within the last 16 months is not eligible to donate.”

“There are multiple levels of review of every record, including by an independent medical doctor specializing in cytopathology, and the exclusion criteria are very stringent, mandated by both the FDA and TissueTech Standards of Practice.”

Nikki: “I expect that in most cases, women at risk are self-identifying as well, so there is less likely to be a case that gets missed.  Furthermore, donors are uncompensated, so there is no incentive to donate if they pose a risk of transmitting Zika. Right?”

Craig: “That’s correct. The public’s high awareness of Zika makes it less likely that a tissue at risk will be donated to begin with. Donors with known infectious disease risks won’t be referred by their obstetricians for tissue donation, and pregnant women living in areas outside of transmission zones who believe they are at risk typically self-identify to their medical providers and request a test. This would be a part of their medical record, and it automatically excludes the mother from birth tissue donation.”

Nikki: “Clearly, it is highly unlikely that Zika-infected tissue will be processed with the extensive procedures that are in place. That’s good news. But let’s discuss your thoughts on sterilization methods. Irradiation has been used by some tissue banks to address concerns about other viruses in allografts.”

Craig: “While that is true, there is no validated method for destroying Zika virus in tissues. The amount of radiation required has not been quantified. So even radiated tissues would pose a risk if primary prevention procedures lapsed. And in the case of placental tissues, biologic value and quality would likely be affected. Truthfully, radiation is not necessary if strict exclusionary procedures are followed absolutely, and that is what we do at TissueTech.”

Nikki: “What is the news on a laboratory test for allografts down the road?”

Craig: “TissueTech has joined with leaders in the industry to jointly petition FDA to amend its recommended guidelines to include testing the donor mother’s blood as a screening tool. The FDA has already approved Zika blood tests for blood donation, so testing placenta donors would seem a logical extension of that. FDA has also approved an investigational study of an assay for Zika virus in tissues which would include placentas. So, yes, we expect progress this year and next year.”

Nikki: “Thanks, Craig, very informative. Our readers will appreciate your insights.”

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Tissue Banks: Standards and Accreditation

At present, there are about 167 tissue banks operating across the United States.1 Their role is vital to ensuring the quality, safety, and availability of allografts, as tissue banks are responsible for screening donors and preparing acceptable tissues for surgical use. While all tissue banks are expected to be registered with the FDA, there are no regulations for greater transparency and only limited federal standardization of policies and procedures.

Into this void of accountability stepped the American Assoc. of Tissue Banks. Established in 1976 by the same group of doctors and scientists who started the nation’s first tissue bank with the U.S. Navy, the association’s mission is “improving and saving lives by promoting the safety, quality and availability of donated human tissue.2

The association is responsible for establishing the highest level of modern day tissue bank operations and has created guidelines for standard practice. The areas covered by these guidelines include all tissue bank activities and operations from procurement to donor testing, from processing and sterilization to packaging. The association has helped quality tissue banks by crafting a framework to establish their own internal Standards of Practice (SOPs).

Only roughly 71% of tissue banks in the United States are actually accredited by the association. It is a voluntary process that requires a lengthy inspection and external review of the tissue bank’s policies and procedures. It is only those banks adhering to the high standards can achieve accreditation. Furthermore, this process must be repeated every three years during accreditation renewal to ensure that accredited tissue banks maintain those high standards of professional practice.

You can check if your tissue bank provider is accredited here and see which specific products and activities they are able to perform (e.g. acquisition, processing, storage, distribution).

Have you ever wondered what types of standards are for tissue procurement and processing? You can learn more about the Standards of Practice followed by America’s best tissue banks in our next blog post: What Makes a Tissue Bank “Good”?

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Introduction to Allografts

What is an Allograft?

An allograft is a tissue transplant between genetically dissimilar members of the same species1. An allograft is different from an autograft, which utilizes tissue from the same individual’s body and is therefore genetically identical. Examples of human allografts include: anterior tibialis tendon, frozen femoral head, freeze dried bone chips, DBM putty, acellular dermis, and amniotic membrane.

What are the Sources of Allografts?

Allografts are made possible through the generous gift of tissue donation after death by individual donors and through family consent. They are obtained after the donor’s death by procurement teams with specialized training in anatomy and surgical techniques to ensure viable soft tissue and bone grafts.

How are they Regulated?

Human tissue products are regulated by the FDA. Most allografts are regulated as Human Cell and Tissue Products (361 HCT/P’s). To qualify as 361 HCT/P, allografts must be considered “minimally manipulated” according to specific criteria under Part 21 CFR 1271.10(a) of the Public Services Health Act.

Allografts that qualify as minimally manipulated human cells and tissues are not required to undergo the same regulatory approval processes as those allografts that are considered medical devices. Examples of 361 HCT/P allografts include the tendon, femoral head, bone chips, dermis, and amniotic membrane mentioned above, but not the DBM putty.

When a tissue product is combined with a carrier, filler, polymer, or other non-human or synthetic ingredient, the combined product is considered more than minimally manipulated by the FDA. These products must obtain FDA 510K Clearance and premarket approval (PMA) like other medical devices. This approval process requires a preclinical study (using animal models) to demonstrate the safety, effectiveness, and equivalence to a similar product already on the market. Examples of allografts that are regulated as medical devices are DBM putties, which combine demineralized bone matrix with bovine or porcine material, or with non-tissue carriers such as carboxymethylcellulose, glycerol, or hyaluronic acid.

What are the Surgical Uses of Allografts?

Allografts are used for the repair, reconstruction, supplementation, or replacement of a recipient’s cells and tissues. For allografts to qualify as 361 HCT/P’s according to the FDA, the human cell or tissue product must perform the same basic function or set of functions in the recipient as in the donor, also known as “homologous use.” For example, tendons used for ACL reconstruction act as a connector in the recipient, as they did in the donor; connecting muscles to bones in the case of tendons is homologous to the function of connecting two bones, as ligaments do. In the same way, acellular dermis used for breast reconstruction acts as a soft tissue replacement, maintaining the same basic function as the original donor tissue.

Each year there are more than 1.75 million allografts performed in the United States from more than 30,000 donors.2  Since allografts were adopted into modern medicine 150 years ago, they have found increasing and widespread usage in a variety of medical fields, improving surgical outcomes and the quality of life of patients.

Tissue Banks

Tissue banks play a vital role, making it possible to perform life-saving, function-preserving medical transplants. Charged with qualifying donors and preparing and processing tissues for transplant, tissue banks must operate in a way that ensures the quality and safety of allografts.

But how do you know if you are working with a quality tissue bank? How can you tell if your tissue bank is adhering to the industry’s highest standards? What are some of those standards?

Get the answers in this post: Tissue Banks: Standards and Accreditation

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Understanding Tissue Sterilization, Part 2: Radiation Roundup

In Part 1, we reviewed the differences between aseptic processing and terminal sterilization. In this post, we explore two validated methods of tissue sterilization: gamma radiation and E-beam radiation.

Safety in tissue transplants is of critical importance. All potential donors are first subject to physical assessment, medical and social screening, and serological testing as the first line of defense against infectious disease transmission. To learn more about these standards of practice (SOPs), look at this post. Current Good Tissue Practice SOPs are established as recommendations by the FDA and are required as part of the accreditation process for tissue banks regardless of the processing and/or sterilization methods to be used.

Once donor tissue is accepted, it is aseptically processed and tested for intrinsic bioburden, which is the population of microorganisms existing on the tissue before sterilization. Unfortunately, there have been incidents of infections transmitted to patients by aseptically processed allografts in the past, including Clostridium species (an anaerobic and spore-forming toxin), viral hepatitis, and the HIV virus. Because of this, the Centers for Disease Control and Prevention requires the use of sterilization technologies proven to kill sporicidal organisms for a tissue to be declared sterile.2

Both gamma and E-beam radiation are delivered in quantifiable doses validated to kill or inactivate specific harmful microorganisms including bacteria, viruses, and fungi. However, there are some differences between the two methods.

Gamma radiation is the exposure of tissue to continuous gamma rays, electromagnetic radiation similar to X-rays that are extremely high frequency. The radiation is delivered to a large number of grafts at once. The dose applied to the tissue is measured in kilograys (kGy). When gamma radiation first began to be used in the late 1950s, radiation doses between 30 and 50 kGy were most often used. Clinical outcomes suffered, and early studies showed that these high doses of radiation had negative effects on tissues by altering biomechanical properties of the collagen through the breakdown of the protein.

Modernized methods are now able to validate lower dose ranges (15 to 20 kGy) to achieve terminal sterilization.1 Techniques to prevent collagen damage are typically used during radiation protocols today, including delivering radiation to grafts while they are in a lyophilized state, irradiating tissues while they are kept frozen at ultra-low temperature, or using radioprotectant anti-oxidants.

Electron beam radiation, also called E-beam radiation, is another form of radiation used to sterilize allografts. With E-beam, tissue is irradiated using a beam of accelerated (high energy) electrons. E-beam irradiation is delivered as tissues pass in front of the beam on a conveyor belt.

As with gamma radiation, early studies using high doses of radiation found unwanted negative side effects on the sterilized tissue. However, modern sterilization utilizes low doses of radiation; E-beam sterilization of allografts at doses of 9-21 kGy has been shown to achieve a sterility assurance level (SAL) of 10-6, the highest level of terminal sterilization.

E-beam is more powerful irradiation than gamma radiation, so tissues are exposed to E-beam radiation for a shorter time (on the scale of minutes instead of hours) to achieve sterilization. However, E-beam radiation does not penetrate as deeply and delivers a less uniform dose than gamma radiation. E-beam radiation is well-suited to smaller items that are less densely packed, and it allows faster turnaround of the final product. In addition, E-beam irradiation can also be used on plastic packaging, allowing for sterilization of a final manufactured product.

Both gamma and E-beam radiation are extremely safe sterilization methods; neither method results in any lingering radioactivity in the sterilized allograft. Sterilization through irradiation is considered to be a clean and efficient process. It prevents the need to use harsh chemicals that can damage the collagen in allografts, and it leaves no solvent residue on the tissue. Also, tissues sterilized by irradiation need no quarantine period after terminal sterilization.

Modern irradiation methods have minimal effects on the biomechanical properties of allografts. In fact, studies have shown that most tissues sterilized with low-dose gamma or E-beam radiation are biomechanically similar those that don’t undergo irradiation. Additionally, a substantial amount of research has helped the tissue industry determine how to mitigate negative effects of radiation.

In summary, both E-beam and gamma radiation are efficient, safe, and result in terminal sterilization of tissue with minimal negative effects on structure and function.

References

Singh, Rita; Singh, Durgeshwer; and Singh, Antaryami. (2016). Radiation sterilization of tissue allografts: A review. World Journal of Radiology 8(4): 355-369. 10.4329/wjr.v8.i4.355

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Understanding Tissue Sterilization, Part 1: Aseptic Processing vs. Terminal Sterilization

When you need to procure allograft tissue, you want to be confident that it has gone through appropriate procedures to minimize the risk of infection. Any microorganisms present on a graft can cause infection in the patient, so reducing the chance of infection is crucial. You will see products labeled with phrases such as “aseptically processed” and “terminal sterilization.”

But what do these terms mean, and how are they related to contamination risk?

Aseptic processing minimizes the chance that donor tissues can be contaminated during preparation. Aseptic processing involves specific, validated protocols which include mechanically agitating the tissues to remove blood, lipids, and cells; cleaning them with detergents, antibiotics, antifungals, or chemical disinfectants; and cutting/shaping them in a clean room. These protocols are validated through biological testing of the tissues and environmental testing of the equipment and packaging used. While aseptically processed allografts are prepared and tested in ways which reduce the microorganisms that could be present, aseptic processing is not the same as terminal sterilization.

Terminal sterilization is an additional, final procedure completed by some tissue banks on some allografts. It’s good to know that terminally sterile allografts have also undergone aseptic processing. After aseptic processing, the grafts are placed in their final packaging before sterilization. Most often, sterilization is achieved through exposure to a validated low dose of gamma or electron beam radiation, which is administered by an ISO-certified third party.

Terminal sterilization destroys virtually all microorganisms that may be present, including sporicidal organisms and viruses which cannot be adequately destroyed by aseptic processing. Terminal sterilization is regarded as the highest safety standard for allograft tissue. A major difference between aseptically processed and terminally sterilized tissue is the risk of contamination. What are the chances of a microorganism surviving aseptic processing compared to terminal sterilization?

The Sterility Assurance Level (SAL) is the probability of one microorganism surviving on the tissue. According to the Centers for Disease Control and Prevention, terminally sterilized tissue has a SAL of 10-6. This means that there is a one in 1,000,000 chance that one microorganism will survive the sterilization methods and be present in the sterilized tissue. A SAL of 10-6 assures us that the chance of infection is literally “one-in-a-million.”

Aseptically processed and cleansed tissue has a SAL of 10-3, meaning that there is a one in 1,000 chance of a microorganism surviving on the tissue. While this risk is still quite low, it is technically a much higher risk than what is faced when using terminally sterilized tissue. The CDC has stated that potentially lethal sporicidal organisms are unaffected by aseptic cleansing alone. Why, then, aren’t all allografts sterilized?

Allografts used in procedures requiring living cells cannot be terminally sterilized without negatively impacting the tissue. In these cases, the surgeon, hospital, and patient must balance the risk of infection against the need for maximum preservation of the allograft’s cellular integrity and strength. This decision is usually influenced by the medical condition being treated and the needs of the patient.

Choosing the right allograft for a procedure without understanding the difference between aseptic processing and sterilization can be confusing. To add to this confusion, a certain sterility claim on many aseptically processed tissues states “sterile based on US Pharmacopeia Guideline 71 (USP <71>)”. USP <71> mandates that “for every 100 containers, ten percent or four containers, whichever is greater” must be tested for contamination. Products that undergo this testing successfully may be said to be “sterile based on USP <71>”, but they have only been aseptically processed, not terminally sterilized.

We’ll compare the methods of sterilization used by today’s tissue banks in Part 2. For all practical purposes, when you source tissue from an accredited tissue bank that adheres to the stringent guidelines of the tissue bank accrediting body1, the risk of infection is very low, whether the tissue is aseptically processed or terminally sterilized. However, it certainly helps to understand the difference when you are trying to make discriminating decisions on behalf of your patients!

Thanks for reading!

Click on this link to get to Understanding Tissue Sterilization, Part 2: Radiation Roundup.

References:

Guideline for Disinfection and Sterilization in Healthcare Facilities: Sterilization (2008). Centers for Disease Control and Prevention. Retrieved from https://www.cdc.gov/infectioncontrol/guidelines/disinfection/sterilization/index.html.

US Pharmacopeia Sterility Testing Guidelines <71>.

3D Printing in Tissue Engineering

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