Cartilage Cells from Cow Knee Joints Grow New Cartilage Tissue in Laboratory

A research team from Umeå University in Sweden has used cartilage cells isolated from the knee joints of cows engineer joint-specific cartilage. Such a technique might lead to a novel stem cell-based tissue engineering treatment for osteoarthritis.

Hyaline cartilage is a specific type of cartilage found at joints where bones come together. Hyaline cartilage is a tough, pliable shock absorber, but because it is poorly supplied by blood vessels its capacity to regenerate is also poor. Knee injuries and the everyday wear-and-tear wear down cartilage tissue and might lead to a condition called osteoarthritis. In Sweden along, 26.6 percent of all people age 45 years or older were diagnosed with osteoarthritis. According to the Centers for Disease Control, in the United States, osteoarthritis affects 13.9% of adults aged 25 years and older and 33.6% (12.4 million) of those older than 65 in 2005; an estimated 26.9 million US adults in 2005 up from 21 million in 1990 (believed to be conservative estimate). Serious osteoarthritis cases can involve the loss of practically the entire cartilage tissue in the joint. Osteoarthritis causes pain and immobility in patients, but it also burdens society with accumulated medical costs.

“There is currently no good cure for osteoarthritis,” says Janne Ylärinne, doctoral student at the Department of Integrative Medical Biology. “Surgical treatments may help when the damage to the cartilage is relatively minor, whereas joint replacement surgery is the only available solution for people with larger cartilage damage. However, artificial joints only last for a couple of decades, making the surgery unsuitable for young persons. So we need a more permanent solution.”

Fortunately, tissue engineering might provide way to successfully treat osteoarthritis. Ylärinne and his colleagues developed new methods to produce cartilage-like “neotissues” in the laboratory.

Normally, tissue engineering methods that grow cartilage use cartilage-making cells, signaling molecules such a growth factors, and some sort of three-dimensional scaffold that acts as an artificial support system that makes the culture system more realistic for the cells. Unfortunately, such protocols are difficult, inexact, and generate respectable variation in what they produce. Consequently, it is also unclear whether stem cells or primary cells are best suited for cartilage tissue engineering experiments.

In these experiments, Ylärinne and others used primary cow chondrocytes (cartilage-making cells from cows) to which they successfully devised improved methods for growing cartilage tissue in a laboratory environment. The cartilage made by Ylärinne and others is similar to that normally present in the human joints.

Bovine cartilage made in laboratory

In the future, protocols like this one might help the development of neocartilage production for actual cartilage repair. If this protocol or others like it can be adapted to stem cells rather than primary cartilage cells, then perhaps these cells can be grown to provide unlimited amount of material for tissue engineering. However, despite the hopefulness of this research, more research is needed to improve the tissue quality and make it more structurally similar to the hyaline cartilage found at human joints.

Stem Cell Treatments to Repair Cartilage Defects in the Knee

Erosions of the cartilage that covers the surfaces at the ends of our leg bones has motivated several laboratories to undertake clinical studies to test new techniques to heal lost cartilage, particularly at the knee. Many of these techniques have their share of drawbacks and advantages, but the number of clinical trials to deal with cartilage lesions of the knee are increasing. Unfortunately, more work remains to be done, but much more is known about several of these techniques than before. This article will summarize many of these techniques.

Microfracture is a procedure in which several small holes are drilled into the end of the bone to enhance the migration of mesenchymal stem cells from the bone marrow to the site of the cartilage defect. These MSCs then differentiate into chondrocytes and make cartilage that fills the lesion with new cartilage. Unfortunately, the cartilage made in these cases is fibrocartilage and not hyaline cartilage. Fibrocartilage lacks the biomechanical strength and durability of hyaline cartilage and it typically deteriorates 18-24 months after surgery. When used to treat large lesions, 20-50% of all cases develop intralesional osteophytes and the sclerotic bone increases the failure rate of autologous chrondrocyte implantation 3-7X. Thus microfractionation is only performed under very specific conditions and only in young patients, since this technique does not work in older patients.


Autologous Chondrocyte Implantation or ACI uses a full-thickness punch biopsy from a low-weight-bearing region of the joint taken during an arthroscopic surgery. This biopsy contains chondrocytes that are grown in cell culture to a population of about 12-48 million chondrocytes, which are troweled into the lesion during a second arthroscopic surgery. Clinical trials have established that ACI is safe and effective for large knee lesions. Peterson and others and Minas and others have established that even after 10 years, patients who have been treated with ACI show good relief of pain and increased knee function.

In the Peterson study, questionnaires were sent to 341 patients. 224 of 341 patients replied to the questionnaires, and of these respondents, 74% of the patients reported their status as better or the same as the previous years 10-20 years after the procedure (mean, 12.8 years).  92% were satisfied and would have ACI again.  Knee function and pain levels were significantly better after the procedure than before.  From this study, Peterson and others concluded that ACI is an effective and durable solution for the treatment of large full-thickness cartilage and osteochondral lesions of the knee-joint, and that the clinical and functional outcomes remain high even 10 to 20 years after the implantation.

Minas and others analyzed data from 210 patients treated with ACI who were followed for more than 10 years. ACI provided durable outcomes with a survivorship of 71% at 10 years and improved function in 75% of patients with symptomatic cartilage defects of the knee at a minimum of 10 years after surgery. A history of prior marrow stimulation as well as the treatment of very large defects was associated with an increased risk of failure.
In comparison studies by Bentley and others, ACI produced superior results to mosaicplasty (osteochondral transplantation or cylinders of bone drilled form low-weight-bearing parts of the knee that are implanted in a mosaic fashion into the knee).  In the Bentley study, 10 of 58 ACI patients had failed grafts after 10 years, but 23 of 42 mosaicplasty patients had failed cartilage repair.  According to studies by Based and others, and Saris and others, ACI is also superior to microfractionation in the repair of large cartilage lesions (>3 cubic cm), but seems to provide the same outcomes as microfracture for smaller lesions, according to Knudsen and others.  There are drawbacks to ACI.  The tissue flap used to seal the cartilage implant sometimes becomes pathologically enlarged.  Other materials have been used to seal the patch, such as hyaluronic acid, or collagen types I and III, but the use of these materials increases the expense of the procedure and the likelihood that the immune system will response to the covering.  Also, ACI outcomes vary to such an extent that the procedure is simply too unstandardized at the present time to be used consistently in the clinic.

Autologous Cartilage Implantation

In an attempt to standardize ACI, several orthopedic surgeons have tried to add a supportive scaffold of some sort to the chondrocytes harvested from the patient’s body.  Several studies in tissue culture have shown that chondrocytes not only divide better, but also keep their identities as chondrocytes better in a three-dimensional matrix (see Grigolo et al, Biomaterials (2002) 23: 1187-1195 and Caron et al, Osteoarthritis Cartilage (2012) 20; 1170-1178).  Therefore, ACI has given way to MACI or Matrix-Induced Autologous Chondrocyte Implantation, which seeds the chondrocytes on an absorbable porcine-derived mixed collagen (type I and III) prior to implantation.  The implant is then secured into the debrided cartilage lesion by means of a fibrin cover.

Several case studies have shown that MACI has substantial promise, but individual case studies are the weakest evidence available.  To prove its superiority over ACI or microfracture surgery, MACI must be compared in controlled studies.  In the few studies that have been conducted, the superiority of MACI remains unproven to date.  Patients who received MACI or ACI showed similar clinical outcomes in two studies (Bartlett and others, Journal of Bone and Joint Surgery (2005) 87: 640-645; and Zeifang et al, American Journal of Sports Medicine (2010) 38: 924-933), although those who received MACI showed a significantly lower tendency for the graft to enlarge.  MACI is clearly superior to microfracture surgery (Basad, et al., Knee Surgery, Sports Traumatology and Arthroscopy (2010) 18: 519-527), but longer-term studies are needed to establish the superiority of MACI over other treatment options.

A slight variation of the MACI theme is to embed the chondrocytes in a gel-like material called hyaluronic acid (HA).  HA-embedded chondrocytes have been shown to promote the formation of hyaline cartilage in patients (Maracci et al., Clinical Orthopedics and Related Research (2005) 435: 96-105).  Even though the outcomes are superior for patients treated with HA-MACI, the recovery period is longer (Kon E, et al., American Journal of Sports Science (2011) 39: 2549-2567).  MACI is available in Europe but not the US to date.  FDA approval is supposedly pending.  Long-term follow-up studies are required to establish the efficacy of this procedure.

Future prospects for treating knee cartilage lesions include culturing collagen-seeded chondrocytes for a longer period of time than the three days normally used for MACI.  During these longer culture periods, the seeded chondrocytes mature, and make their own scaffolds, which ensure higher-quality cartilage and better chondrocyte engraftment (see Khan IM and others, European Cell Materials (2008) 16: 26-39).  Alternatively, joint cartilage responds to stress by undergoing cell proliferating and increasing in density.  This response is due to the production of growth factors such as Transforming Growth Factor-β1 and -β3 (TGF-β1 and TGF-β3).  This motivated some enterprising tissue engineers to use recombinant forms of these growth factors to grow cartilage in bioreactors under high-stress conditions.  Such a strategy has given rise to NeoCart, a tissue-engineered product that has gone through Phase I and II trials and has been shown in two-year follow-up studies to be safe and more effective than microfracture surgery (Crawford DC and others, Journal of Bone and Joint Surgery, American Volume. 2012 Jun 6;94(11):979-89 and Crawford DC, and others, Am J Sports Med. 2009 Jul;37(7):1334-43).

Mesenchymal stem cells (MSCs) from bone marrow and other sites have also been used to successfully treat cartilage lesions.  These types of treatments are less expensive than ACI and MACI, and do not require two surgeries as do ACI and MACI.  The studies that have been published using a patient’s own MSCs have been largely positive, although some pain associated with the site of the bone marrow aspiration is a minor side effect (see Centeno and others, Pain Physician (2008) 11:343-353; Emadedin, et al., Arch Iran Med (2012) 15: 422-428; Wong RL, et al., Arthroscopy (2013) 29: 2020-2028).  Fat-based MSCs have been tested as potential cartilage-healers in elderly patients (Koh YG, et al., Knee Surgery, Sports Traumatology, and Arthroscopy (Dec 2013, published on-line ahead of print date).  While these initial results look promising,, fat-based, MSCs have only just begun to be tested for their ability to regenerate cartilage.  Fat-based MSCs show different properties than their bone-marrow counterparts, and it is by no means guaranteed that fat-based MSCs can regenerate cartilage as well as MSCs from bone marrow.

Fresh cartilage grafts from donors (aka – cartilage allografts) use transplanted cartilage that has been freshly collected from a donor.  Fresh cartilage allografts have had positive benefits for young, active patients and the grafts have lasted 1-25 years (Gross AE, et al., Clinical Orthopedics and Related Research (2008) 466: 1863-1870).  Particulate cartilage allografts takes minced cartilage and lightly digests it with enzymes to liberate some of the cartilage-synthesizing chondrocytes, and then pats this material into the cartilage lesion, where it is secured with a fibrin glue plug.  The cartilage provides an excellent matrix for the synthesis of new cartilage, and the chondrocytes make new cartilage while seeded onto this cartilage scaffold.  Clinical experience with this technique includes a two-year follow-up in which MRI evidence showed good filling of the lesions (Bonner KF, Daner W, and Yao JQ, Journal of Knee Surgery 2010 23: 109-114 and Farr J, et al., Journal of Knee Surgery 2012 25: 23-29).  A variation on this technique uses a harvested hyaline cartilage plug that is glued into an absorbable scaffold before transplantation into the cartilage lesion.  This procedure had the same safety profile as microfracture surgery, but resulted in better clinical outcomes, high quality cartilage, and fewer adverse side effects (Cole JB et al., American Journal of Sports Medicine 2011 39: 1170-1179).  A clinical trial that tested this procedure remains uncompleted after the company suspended the trial because of conflicts with the FDA (Clinical Trial NCT00881023).

AMIC or Autologous Matrix-Induced Chondrogenesis is a cell-free treatment option in which the cartilage lesion is cleaned and filled subjected to microfracture, after which the lesion is filled with a mixed collagen matrix that is glued or stitched to the cartilage lesion.  The MSCs released by the microfracture procedure now move into a scaffold-laden cartilage lesion that induces the formation of hyaline cartilage.  This technique appears to aid the filling of full-thickness cartilage defects, and follow-up examinations have revealed that after 5 years, patients showed substantial improvements in knee function, pain relief and MRI analyses of knee cartilage showed high-quality cartilage in repaired lesion (Kusano T, et al., Knee Surgery, Sports Traumatology, and Arthroscopy 2012 20: 2109-2115; Gille J, et al., Archives of Orthopedic Trauma Surgery 2013 133: 87-93; Gille J, et al., Knee Surgery, Sports Traumatology, and Arthroscopy 2010 18: 1456-1464).

These are just a few of the new treatments of cartilage lesions of the knee and other joints.  As you can see, all of this will lead to greater repair of knee lesions and it is all being done without embryonic stem cells or destroying embryos.

Silk and Cellulose as Scaffolds for Stem Cell-Mediated Cartilage Repair

When two bones come together, they grind each other into oblivion. This results in inflammation, joint swelling and pain, and scar tissue accumulation, which eventually results in the immobilization of the joint. To prevent this, bone are capped at their ends with a layer of hyaline cartilage that acts as a shock absorber. However, cartilage regenerates poorly and the wear and tear on cartilage, particularly at the knee, causes it to degenerate. The loss of the cartilage cap at the end of long bones causes osteoarthritis . The only way to mitigate the damage of osteoarthritis is to replace the knee with a prosthetic knee-joint.

Stem cells can make a significant contribution to the regeneration of lost cartilage. The Centeno/Schultz group near Denver, Colorado has been using bone marrow-derived mesenchymal stem cells to treat patients for over a decade with positive results. However, finding a way to grow large amounts of cartilage in culture that is the right shape for transplantation has proven difficult.

One way to mitigate this issue is the use of scaffolds for the cartilage-making cells that pushes them into a three-dimensional arrangement that forces them to make cartilage that mimics the cartilage found in a living organism. However a problem with scaffolds is finding the right material for the scaffold.

A recent publication has formed scaffolds from naturally occurring fibers such as cellulose and silk. By blending silk and cellulose fibers together, researchers at the University of Bristol have made a very inexpensive and easily manufactured scaffold for cartilage production.

Silk scaffold
Silk scaffold

When mixed with stem cells, cartilage and silk coax connective tissue-derived stem cells to differentiate into chondrocytes or cartilage-making cells. In the silk/cellulose scaffold, the chondrocytes secrete the extracellular matrix molecules characteristic of joint-specific cartilage.

Wael Kafienah, lead author of this work from the University of Bristol’s School of Cellular and Molecular Medicine, said, “The blend seems to provide complex chemical and mechanical cues that induce stem cell differentiation into preliminary form of chondrocytes without need for biochemical induction using expensive soluble differentiation factors. Kafienah continued: “This new blend can cut the cost for health providers and makes progress towards effective cell-based therapy for cartilage repair a step closer.”

To make the blended silk/cellulose scaffolds, Kafienah and his colleagues used ionic fluids, which effectively dissolve polymers like cellulose and silk, but are also much more environmentally benign in comparison to the organic solvents normally used to process silk and cellulose.

Presently, the U of Bristol team to trying to fabricate three-dimensional scaffolds that can be safely and easily implanted into patients for future clinical studies. Before human clinical studies are commenced, however, they must first be extensively tested in animals and also, the nature of the interactions between the scaffold and the stem cells that drive the cells to form cartilage must be better understood.

A Co-culture System Makes Better Cartilage for Tissue Replacement

At joints, the bones are covered with cartilage to act as a shock absorber. Articular cartilage, or cartilage at joints, is usually characterized by very low friction, high wear resistance, but very abilities to regenerate. Articular cartilage is responsible for much of the compressive resistance and load bearing qualities of joints, and without it, even activities as simple and walking is too painful. Osteoarthritis is a condition that results from cartilage failure, and limits the range of joint motion, increases the bone damage and also causes a respectable amount of pain. When the cartilage of the articular surface erodes, the bone is exposed and grinding of the bone creates bone spurs, extensive inflammation and pain.

Treating osteoarthritis requires that one make new cartilage that has similar properties as articular cartilage. Unfortunately, mesenchymal stem cells that are differentiated into cartilage making cells (chondrocytes) and implanted into the knee tend to make fibrocartilage, which is different than the hyaline cartilage that composes articular cartilage. Fibrocartilage does not possess the high-wear resistance characteristics of hyaline cartilage and it tends to erode rather rapidly after formation. Therefore, directing mesenchymal stem cells (MSCs) to form proper cartilage is a genuine challenge.

A paper that appear in Stem Cell Translational Medicine from Gilda A. Barabino, who is a faculty member at the Wallace H. Coulter Department of Biomedical Engineering at Georgia Institute of Technology and Emory University, examines a technique to coax MSCs to make articular cartilage.

As Barbino points out, traditional protocols that direct MSCs to differentiate into chondrocytes uses culture systems of MSCs that have been treated with various growth factors, such as transforming growth factor-β. Unfortunately, these culture systems tend to fall short in meeting the needs of clinical applications, largely because they yield terminally differentiated cells that enlarge and then form bone.

In this study Barbino and her co-workers co-cultured bone marrow-derived MSCs with juvenile articular chondrocytes. The rationale is that the MSCs would receive just the right growth factors in just the right concentrations and at the right time to drive MSC cartilage formation. Physical contact between cells can also do a better job of driving them to differentiate into various cells types rather than simply treating them with growth factors.

Barbino and others discovered that an initial chondrocyte/MSC ratio of 63:1 worked the best and the MSCs form chondrocytes that had the right cells shape, behavior, and characteristics of articular chondrocytes.

Next, Barbino and her team grew the MSCs in a three-dimensional agarose system. Three-dimensional systems are generally thought to more realistically recapitulate the cartilage-making system present at joints. In this 3-D culture system, when co-cultured with juvenile articular chondrocytes, bone marrow MSCs develop into robust neocartilage that was structurally and mechanically stronger than the same cultures that only contained chondrocytes.

There was another advantage to this culture system; cultured MSCs that are induced to form cartilage tend to cease all expression of a surface protein called CD44, which is an important regulator in cartilage biology. However, when cultured in the 3-D culture, the MSCs retained the expression of CD44, which suggests that these co-cultured MSCs, which cultured in a 3-D culture system form chondrocytes that make superior articular cartilage, but retain CD44, which allows cartilage maintenance.

This shows that making articular cartilage from MSCs is probably possible and only requires the right culture system. Also, co-culturing MSCs with articular chondrocytes in a 3-D culture system might be one of the better culture systems for developing clinically relevant cartilage for tissue replacements.

Induced Pluripotent Stem Cells Make Cartilage

Induced pluripotent stem cells (iPSCs) are made from adult cells through genetic engineering techniques that drive terminally-differentiated adult cells to revert into embryonic-like cells. iPSCs have the capacity to form any cell type in the adult body, and they may represent the future of regenerative medicine when it comes to treatment of some diseases.

On the 30th of October, 2012, scientists from Durham NC reported that they were able to make cartilage from iPSCs. The cartilage made by iPSCs was not simply the fibrous cartilage found in the ribs and between the connection at the pelvis, but the whitish, hyaline cartilage found at weight-bearing joints. Hyaline cartilage acts as a shock absorber at the hip and knee joints and has proven difficult to make in culture.

According the Farshid Guilak, professor of orthopedics surgery at Duke University Medical Center and senior author of this study: “This technique of creating pluripotent stem cells is a way to take adult cells and convert them so that they have the properties of embryonic stem cells.”

Dr. Guilkak continued, “Adult stem cells are limited in what they can do and embryonic stem cells have ethical issues.” What this research shows in a mouse model is that ability to create an unlimited supply of stem cells that can turn into any type of tissue – in this case cartilage, which has no ability to regenerate itself.

Hyaline cartilage, which is found at articular surfaces (the surfaces between joints, allows us to walk and climb stairs. However, the everyday wear-and-tear or an injury can degrade the cartilage, leaving bones to grind against bones. the result is bone fragmentation, extensive inflammation and pain (osteoarthritis), and the replacement of that joint with an artificial joint. Articular cartilage has a very limited ability to repair itself and damage and osteoarthritis are the leading causes of impairment in older people.

Guilak’s research group, led by postdoctoral research fellow, Brian Diekman, is an alternative to other procedures presently in use, which include the application of stem cells from bone marrow or fat to the damaged cartilage.

The main challenge in using iPSCs was differentiate the cells so that they provided a relatively pure population of cartilage-making cells (chondrocytes). To hone their protocol for making and selecting chondrocytes from iPSCs, Diekman devised a technique that caused only those iPSCs that had differentiated into mature chondrocytes to glow a fluorescent green color. This provided a tag that Diekman and his colleagues used to sort the mature chondrocytes from the other cells.

The isolated chondrocytes made beautiful cartilage that had all the strength and resilience of nature cartilage. As noted by Diekman, “This was a multi-step approach, with the initial differentiation, the sorting, and then proceeding to make the tissue (cartilage in this case). What this shows is that iPSCs can be used to make high quality cartilage, either for replacement tissue or as a way to study disease and potential treatments.”

According to Diekman and Guilak, the next step in this research is to use human iPSCS to test and ultimately refine their cartilage-growing protocol. Guilak summarized his work with these words: “The advantage of this technique is that we can grow a continuous supply of cartilage in a dish. In addition to cell-based therapies, iPSC technology can also provide patient-specific cell and tissue models that could be used to screen for drugs to treat osteoarthritis.”

This work was published in the Proceedings of the National Academy of Sciences USA, 2012, DOI: 10.1073/pnas.1210422109.