Research Notebook: Carmell Therapeutics’ PBMs—A new paradigm for healing tissue and bone

Carmell Therapeutics’ PBMs: A new paradigm for healing tissue and bone

Editor’s Note: This article was condensed and adapted for The Link magazine from “Biologically Active Blood Plasma-Based Biomaterials as a New Paradigm for Tissue Repair Therapies,” a copyrighted paper published in Disruptive Science and Technology, Volume 1, Number 3, and written by Jason D. Smith, Lee E. Weiss, James E. Burgess, Alan I. West and Phil G. Campbell. To read the original paper, please visit To learn more about Carmell Therapeutics, visit The Link is grateful to the authors for allowing us to share a portion of their research.


When a person receives a traumatic injury to bone or tissue, platelets circulating in their blood are responsible for beginning the healing process. An array of growth factors and other signaling molecules are released into the injury site upon platelet activation, providing the cues needed to help orchestrate self-repair by the body.

It seems logical that collecting a patient’s own blood plasma, concentrating the platelets, and then injecting the concentrated plasma back into the injury site should accelerate healing and overcome the body’s limitations to tissue repair caused by age, disease or when tissues lack a sufficient blood supply.

This type of therapy uses what is called concentrated platelet-rich plasma, or PRP. It is an exciting but somewhat controversial new treatment option for a variety of orthopedic and sports medicine applications. The highly publicized use of PRP therapies by professional athletes, including former Pittsburgh Steelers wide receiver Hines Ward, has created significant hype.

Unfortunately, with few controlled studies, evidence in many instances has been anecdotal, and a number of published studies have called into question PRP’s effectiveness. One widely reported study examined the effectiveness of PRP to heal chronic Achilles tendon injuries, and found that PRP treatment was no more effective than the control treatment of saline. These mixed reports have created a skepticism regarding the use of PRP and any new PRP treatment.

In addition, PRP is not a simple, off-the-shelf treatment. It must be manufactured for each patient at the time of the procedure. Controlling the delivery of PRP at the site of injury is also highly problematic. There is also a great deal of clinical variability—patients’ blood plasma varies widely in both the quantity and quality of platelets and growth factors.

An engineered material that can reduce this variability, and also be provided as a cost-effective, off-the-shelf product, can overcome the limitations of PRP while still augmenting healing in a safe and natural manner.

What are PBMs?

With these goals in mind, Carmell Therapeutics, a CMU spinoff company based in Pittsburgh, has developed solid, biologically active materials called plasma-based biomaterials, or PBMs.

PBMs are designed to take advantage of the regenerative potential of PRP, but reduce its drawbacks. PBMs are made with pooled plasma units from multiple donors, collected in U.S. blood banks, and processed into plastic-like materials that remain bioactive. Pre-clinical data supports PBM biocompatibility and retention of growth factor activity, while clinical data described below support its safety and efficacy.

PBMs are inexpensive to manufacture. They are safe and can be supplied as an off-the-shelf product. They are also formable into complex 3D shapes, and biodegradable with tunable biomechanical and degradation properties. Overall, PBMs represent a platform technology with significant potential to be a disruptive new therapy option in a variety of clinical applications, not only in major clinical markets, but also in developing countries, where the need is high, but the cost is a barrier to treatment.

The need for new healing products

There is a great need for effective, consistent, and cost-effective products that can biologically enhance tissue healing. Injuries to connective tissue—tendons, ligaments and cartilage—are difficult to heal, requiring months of recuperation, and they often result in poor clinical outcomes. For example, one of the most common orthopedic repairs involves surgery to repair the meniscus, the cushioning cartilage in the knee.

But only the outer 30 to 40 percent of the meniscus has a capillary blood supply, and thus a good chance of healing after surgery. Tears involving the area without a blood supply are rarely good candidates for repair. Bone repair is another area in need of biologic augmentation. Biologics are used to augment the healing in only 10.5 percent of the more than 1.2 million fractures to the arms and legs.

Physicians have begun to look for ways to improve the healing of soft tissue and bone, and are rapidly embracing the use of autologous PRP—that is, PRP made from a patient’s own blood plasma—manufactured in the operating room, as it contains a concentration of natural growth factors and other proteins that appear to accelerate healing. However, as noted above, there are a number of questions and problems surrounding the use and effectiveness of PRP. While the concept of using a concentration of the body’s own regenerative factors to heal itself is very attractive, the high number of uncontrolled variables makes the true role of autologous PRP in soft and hard tissue repair difficult to determine.

If PBMs can mitigate the issues surrounding traditional PRP, they have the potential to be the basis for highly effective treatment options for bone and tissue repair and regeneration.

The history of biological plastics

Although PBMs represent an innovative and disruptive platform technology, the concept of making biological plastics from blood components is not a new idea. Fibrin-based plastic scaffolds were developed in the 1940s and successfully used during World War II as part of a U.S. defense research program to develop medical strategies for treating wounded soldiers.

Fibrin was refined from pooled, donated human plasma using methods developed by Edwin Cohn at Harvard. John Ferry, then at Woods Hole, led the effort to develop methods to form fibrin into 3D plastics. From the 1950s onward, development and commercialization of fibrin-based plastics shifted to Hungary, and was based on more readily available fibrin from bovine-sourced blood plasma.

The purpose of these materials was to create bio-inert, biodegradable plastic components across a range of clinical applications, ranging from non-adherent barrier membranes for neurosurgery, to plates and materials for orthopedics. The high-temperature molding processes used to make most of these fibrin-based plastics, as well as their sterilization by autoclaving, destroyed any bioactivity.

Furthermore, formaldehyde, sometimes used as a cross-linking agent to decrease the body’s absorption of these materials, was relatively toxic.

Nevertheless, various forms of these plastics were successfully used over a broad range of clinical applications, including implants for bone resurfacing, neurosurgical applications, burn treatments and peripheral nerve regeneration.

Motivated by the idea that bioplastics could be made from blood components, as well as by the potential for PRP-based therapies, Carmell has set out to combine these ideas and to overcome the limitations of the WWII-era plastics and current PRP therapies.

About Carmell Therapeutics

Carmell was founded in 2007 to commercialize technology developed jointly at Carnegie Mellon University and Allegheny General Hospital. The company’s primary focus is on musculoskeletal trauma with products designed to accelerate healing and produce better clinical outcomes in treating injuries to all musculoskeletal tissues (bones, tendons, ligaments, cartilage and muscles).

The co-inventors of PBM technology and the founders of Carmell—whose name is derived from “Carnegie Mellon”—are James Burgess, a staff neurosurgeon at Allegheny General Hospital in Pittsburgh who has an academic appointment at Drexel University and adjunct appointments at CMU’s Robotics Institute as well as George Mason University’s Krasnow Institute; Phil Campbell, a research professor in CMU’s Institute for Complex Engineered Systems; and Lee Weiss, a research professor in CMU’s Robotics Institute. Campbell also currently serves as the company’s chief scientific officer.

Weiss’ research focuses on development of advanced manufacturing processes such as bioprinting technology to create implantable scaffolds with spatially defined patterns of growth factors to aid musculoskeletal tissue repair. Campbell’s research involves bioavailability of growth factors, growth factor association and dissociation with various interstitial components, biopatterning stem cell behavior and tissue repair, biomimetic tissue engineered materials, musculoskeletal tissue repair and regeneration. Burgess is director of the clinical trials program for the Allegheny Health Network of hospitals and specializes in treatment of spine diseases and injuries.

In May 2014, Carmell was awarded a second Phase I Small Business Innovation Research grant in the amount of $157,000 from the National Institutes of Health to fund further research into PBMs.

How PBM is manufactured

Carmell manufactures PBM at its laboratory located within the Institute for Transfusion Medicine in Pittsburgh. Commercial PRP preparations, currently promoted for autologous-based therapies—that is, PRP using a patient’s own donated blood—are based on removal of red blood cells and the concentration of platelets within a minimum volume of plasma. This process discards the bulk of the plasma that contains its own growth factors and other wound-healing constituents. The PRP used for PBMs fully utilizes both plasma and platelet fractions, thus maximizing the growth factors from both fractions.

Blood plasma and platelets, representing pooled lots from multiple donors, are clotted, freeze-dried, ground, mixed with other components and compression-molded into PBMs. These PBMs can take a variety of forms and physical properties, including flexible sheets, putties and even complex shapes, such as screws.

Any material derived from living tissue has the potential to vary greatly from lot to lot. This is especially evident in autologous PRP therapy; variability in the number of platelets and growth factors make it difficult to predict which patients may respond well to PRP therapy. Additionally, certain growth factors are known to decrease with age, making it more likely that older patients will not respond well to PRP therapy; it is these older patients, however, who could benefit the most from a biologic acceleration of healing. With PBM products, the potential for lot-to-lot variability is reduced through the pooling of multiple units of plasma and platelets, sourced from a healthy, age-controlled donor population. 

Current PRP liquid-based therapies have a relatively short-lived delivery, which calls into question the time frame of effectiveness, and has led some to utilize multiple PRP injections over several weeks. Because PBM is an engineered material, the release rate of its growth factors can be controlled.

The manufacture of PBMs offers unique challenges. For instance, higher molding temperatures typically increase mechanical strength, but they also decrease the biological activity of the material, and thus its potential for healing. In addition to growth factor retention and release, growth factor fate is also a significant focus of the company’s ongoing research. Each factor may be uniquely susceptible to the various processing conditions employed in manufacturing PBMs.

Determining individual growth factor fate requires not only the isolation and total recovery of each individual factor, but also determining the total individual growth factor activity. Unfortunately, recovering individual growth factors bound by the PBM matrix is nontrivial and the paucity of growth factor-specific activity assays impedes this work. As a result, aggregate biological activity as measured in a laboratory environment is used to evaluate PBM formulations. Because this only measures the freely released aggregate growth factor activity and not the potential activity retained in the PBM matrix, it is an incomplete measure of total PBM activity.

Clinical trial of Carmell’s bone putty

For a new technology to be truly disruptive, it must not only be functionally unique, addressing unmet clinical challenges, but also be cost effective, to be available to the masses. The rising cost of healthcare has become a central problem for hospitals, and represents a major barrier for new and expensive technologies, regardless of their effectiveness.

PBM materials can be offered at relatively low cost, allowing this important new technology to benefit a wide population of patients. Not only is this an important consideration in the United States, where pricing pressures are limiting the adoption of expensive new technologies, it also means that low-cost PBMs could be practical options for developing and underprivileged nations. By means of comparison, biologic products manufactured from recombinant proteins cost hospitals approximately $9,000 for the treatment of a single patient. Tissue-engineered approaches for treating cartilage defects average $26,000 per procedure. In contrast, putty formulations of PBM can cost under $20 to produce.

In September 2014, David North, a registrar (equivalent to a U.S. resident) orthopedic trauma surgeon at South Africa’s University of Cape Town, presented a paper describing the results of the first clinical trial sponsored by Carmell. The paper described the use of Carmell’s REPAIR Bone Putty in a clinical trial involving 30 patients who suffered open fractures of the tibia—the larger and stronger of the two bones below the knee. Twenty-one of the patients suffered severe type IIIA and type IIIB fractures, with damage to surrounding tissue, high levels of contamination in their wounds and bone fragments that were splintered and crushed. Patients were randomly selected for either a treatment group or a control group.

The REPAIR putty, made with PBM material, was placed directly into the wound site of the patients in the treatment group while their fractures were being reduced. North reported that after 30 days, patients who were treated with REPAIR putty had more rapid wound closure. The patients in the treatment group also reported fewer infections during the one-year follow-up—22 percent, versus 80 percent for the control group. Additionally, after 180 days, the fractures that were treated with the bone putty had healed faster.

In October 2014, as a result of this clinical trial, the South African Orthopedic Association presented North with the G.T. du Toit Registrar Prize for the best paper presented by any registrar at a South African hospital.

Safety of pooled products

Safety is a primary concern when dealing with human tissue. This is one reason why PRPs using a patient’s own blood plasma, instead of from donor patients, are an attractive treatment option.

In manufacturing PBMs, Carmell incorporates pooled plasma, which carries with it not only the burden of demonstrating safety quantitatively, but also overcoming perceptions or even fears of non-safety—this may be, especially, an issue with orthopedic physicians who have been taught that human tissues should never be pooled.

The blood plasma used by Carmell is prescreened for known blood-borne pathogens. The pool is then rescreened for known viral contaminants by using sensitive nuclear amplification technology assays. Additionally, multiple proprietary viral inactivation steps are employed to reduce potentially unknown enveloped and non-enveloped RNA and DNA viruses.

Due to their novel nature as well as their blood derivation, Carmell expects that PBM materials will be carefully reviewed and scrutinized by regulators in both the United States and Europe before clearance to market PBM products will be granted. While the regulatory pathway always represents an expensive and time-consuming barrier, it is an important and necessary one.


Manufacturing novel biomaterials from human platelet-rich blood plasma represents a unique, but simple value proposition with a material that encourages the safe and natural healing of damaged tissue.

PBM products have the potential to accelerate healing and reduce pain and complications, reducing the need for costly secondary procedures and enabling patients to return to work and their daily lives more quickly. The PBM technology enables the manufacture of products incorporating a concentration of natural growth factors at a relatively low cost—unique for any product containing a biologic, and truly disruptive.

Editor’s Note: This article was condensed and adapted by The Link magazine from “Biologically Active Blood Plasma-Based Biomaterials as a New Paradigm for Tissue Repair Therapies,” a copyrighted paper published in Disruptive Science and Technology, Volume 1, Number 3, and written by Jason D. Smith, Lee E. Weiss, James E. Burgess, Alan I. West and Phil G. Campbell. To read the original paper, please visit To learn more about Carmell Therapeutics, visit The Link is grateful to the authors for allowing us to share a portion of their research.

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