Human Cartilage can be 3D-printed

We’ve already discussed about the importance of cartilages in the human body. Two examples are the knee menisci and the thyroid cartilage that origins the Adam’s apple. We’ve also understood that 3D printing would probably represent a great revolution in the world of medicine, with the possibility of reproducing human body parts or fabricating new-generation assistive tools. Put the two things together and you’ll be able to print human cartilage by means of a 3D printer. I simply copy-paste here the content of this interesting webpage (to which all rights belong).

Dr. Darryl D’Lima and the members of his team at the Scripps Clinic in La Jolla, California, say they’ve unlocked the secrets of bioprinting human cartilage. That’s big news as the current best practice medical technique to replace lost cartilage is implantation of an artificial joint. Even though that sort of operation is painful, requires a long stretch of rehabilitation and artificial joints can often need replacement as time goes on, such procedures are the industry standard.

dr-darryl-dlima-bioprinting-cartilageThe global market for knee replacements amounts to nearly $7 billion annually, and experts say it will climb to nearly $11 billion within the next few years. Somewhere around 773,000 Americans have a hip or knee replaced each year. That’s big business and a lot of pain. But D’Lima says the design of his latest prototype bioprinter will print living cartilage, and that would mark a great leap forward for those suffering from painful knee and joint damage. Taking a Hewlett-Packard inkjet printer as his starting point, D’Lima says his bioprinter uses cartilage progenitor cells suspended in a biocompatible liquid. Once the solution is exposed to ultraviolet light, it takes a permanent shape.

cartilageThe extremely tiny drops of material provide other benefits as well. Measuring just one picoliter in diameter (or one-billionth of a liter), the droplets output by the bioprinter are compact enough to fill microscopic pits on the surface of cartilage or bone. “It would be the equivalent of filling a pothole,” D’Lima says. “It would automatically fill the defect as you’re printing it. You’re getting a fairly good mechanical integration into the tissue, which is very difficult for us to do when we do traditional transplants.”

Patients suffering with arthritis or  knee injuries are often plagued by a lack of cartilage. That means bones begin to grind against bones, and that means extreme pain and constant discomfort for patients. Using D’Lima’s bioprinting method, cartilage can be applied directly into the knee joint to provide a custom fit impossible to achieve by cutting pre-made cartilage to the particular patient. And one day, D’Lima says he’s confident that the process will involve printing the cartilage material directly onto a patient on the operating table. “We wouldn’t have to prepare (material) in advance,” D’Lima said. “All of this would be done on the day of surgery, on demand.”

knee-worn-cartThe major hurdle, according to D’Lima, is that as there’s currently no printer which can print directly onto a patient. His technique needs some refining. D’Lima says he’s working on those tweaks now with biotech firms Invetech and Organovo. And D’Lima also says he’s certain the method will work in practice as cartilage, due to its simpler cellular structure and lack of a complicated network of blood vessels, will be less challenging to create than some other tissues. Cartilage, flexible connective tissue found in various areas of the body, is not as rigid as bone but can be stiffer and less flexible than muscle. Composed of specialized cells called Chondrocytes, cartilage (unlike other connective tissues) doesn’t contain blood vessels. The chondrocytes are supplied with nutrients by diffusion as a result of the pumping action generated by compression, so in comparison with other connective tissues, cartilage grows and repairs much more slowly. “(Cartilage) is complex enough that you need technology like 3D printing, but at the same time, it’s not so complex that it’s extremely challenging,” he said. “We’ve gotten interest from other researchers, wanting to print retinal cells. The retina has some similarities to cartilage in that the photoreceptors and the neural cells of the retina don’t require a blood supply, so we don’t have to print microvasculature. And the retina is a mature tissue in that if you lose a photoreceptor, that’s it. You don’t grow a new one. So it’s fairly attractive for 3D printing.”

Knee Replacement : some hints

Knee Replacement is a surgical procedure that aims to replace the weight-bearing surfaces of the knee joint. The proximal part of the tibia and the distal part of the femur may turn out to be damaged, either because of rheumatoid arthritis, osteoarthritis, or traumatic injury. Such suboptimal conditions of the knee articulation (the largest joint in the human body) lead to pain and disability for the patient. In order to restore perfect mobility conditions, after a bone cut procedure the orthopaedic surgeon removes the damaged bone parts and most of the cartilages and knee soft tissues. The geometry of the bones, which plays a key role for the joint stability and mobility, is completely restored by means of the installed prosthetic components. A common knee prosthesis consists of a femoral and a tibial component, a patellar cap and a polyethylene insert (that replaces the menisci). Components are designed so that smooth movements and minimal wear are always ensured. In order to make the components better join to the cut bones, a specific acrylic cement can be employed during the installation.


After the surgical operation the patient normally undergoes a rehabilitation period of about 6 months. The patient slowly “learns” how to perform daily activities with their brand new knee. The ideal surgical outcome consists, in the long term, in the possibility to live a normal life without being limited by the prosthesis for most daily activities.

total vs unicompartmentalThere are many different types of implants. When Knee Replacement is found to be necessary, the surgeon discusses with the patient about the clinical needs and all the possible implants. The basic principle is to reduce as much as possible the bone volume interested by the bone cut stage. Some people can benefit from just a partial (or unicompartmental) knee replacement, that is when the prosthesis replaces only one knee compartment (medial or lateral).

Concerning the material which prosthetic components are made of, there are many constraints. As already said, the set up of a proper compromise between stability and mobility of the prosthetic joint is a great surgical challenge. Thus, each component must be at the same time strong (enough to take weight-bearing loads) and flexible (enough to avoid undesired deformations and mechanical failure). But the most important constraint is represented by biocompatibility: the risk of rejection must be avoided. Biocompatibility strongly reduces the choice of usable materials (nowadays, prostheses are mainly in titanium or cobalt-chrome alloy).

revision surgery radioIn normal conditions, knee implants ensure a 15-20 years lifespan. When pathologies or suboptimal balance conditions occur on a prosthetic knee, this value is no longer ensured and risks being strongly reduced. In such cases, the only solution is represented by revision surgery. The patient undergoes a second Knee Replacement surgery in order to remove the suboptimal prosthesis and install a new one. This leads to a new hospitalisation period, a further bone cut procedure (revision components usually have longer stems that insert into the bones, as shown by the figure) and, of course, to a second rehabilitation period. Revision surgery always turns out to be more stressful than the first one: human body doesn’t appreciate when someone is playing with its parts, thus the probability of rejection increases and the recovery period gets harder.

My PhD project aims to develop a new generation of knee implants, able to compensate for suboptimal balance conditions without the need for revision surgery 🙂

sources: uno y dos

let’s take stock of … the lower limb !

Hello everybody! Since the number of daily readers (and followers) of my blog is (surprisingly) increasing day after day (Thank you everybody!), I thought it could be useful to take stock of some important posts I wrote about the lower limb. Let’s start from the top -the hip- and go down to the bottom -the ankle-, with 9 posts that got many views and some funny comments 🙂

Obviously, since my PhD project is about a knee prosthesis, most of the posts (5 out of 9) are about the knee joint. But in general I tried to give an overall view of some interesting topics related to the biomechanics of the lower limb. Enjoy! 🙂

leg skeletal anatomythe Hip Joint: some hints

hammers, screws and Intramedullary nails

the Knee Bursae: some hints

the Meniscus: some hints

the Patella: some hints

Knee Alignment Conditions

Patellar Reflex

How many limbs do you actually perceive?

the Ankle Joint: some hints

the Knee Bursae: some hints

The bursae of the knee can be defined in a very simple way: they are fluid sacs, or synovial pockets. This second definition comes from the sinovial fluid that fills them.

Synovial fluid is made of hyaluronic acid and lubricin, proteinases and collagenases. Its main functions are reducing friction by lubricating the joint, absorbing shocks and properly “feeding” joint cartilage. In the case of the knee, the Knee Capsule encloses the Knee Cavity which is filled with synovial fluid. Knee Bursae surround and sometimes communicate with the Knee Cavity, as we can see in the picture.

Usually Knee Bursae are thin-walled and represent the weak point of the joint. At the same time, their presence is really important since they enlarge the joint space. They can be grouped according to:

  • their characterization as communicating and non-communicating bursae. A communicating bursa is when a bursa is located adjacent to a joint, thus having the synovial membrane in communication with the joint itself.
  • their location (frontal, lateral, medial).

In pathological conditions, such as excessive local friction, infection, arthritides or direct trauma, fluid and debris collect within the bursa or fluid extends into the bursa from the adjacent joint. As a consequence, the walls of the bursa thicken as the bursal inflammation becomes longstanding. The term bursitis refers to pathological enlargement of the bursa. Clinically, bursitis mimics several peripheral joint and muscle abnormalities.


<–prepatellar bursitis

          elbow bursitis–>



sources: Wikipedia and this website

accepted for publication


Towards a Dynamic Tibial Component for Postoperative Fine-tuning Adjustment of Knee Ligament Imbalance


Andrea Collo, Shaban Almouahed, Chafiaa Hamitouche, Philippe Poignet, Eric Stindel

Accepted for Publication at:

BIODEVICES 2013 – 6th International Conference on Biomedical Electronics and Devices (conference official website)

Patellar Reflex

definition _

Patellar Reflex, also called knee-jerk, is a stretch reflex associated with quadriceps femoris muscle stretching.

how it works _

The stretch is created by a blow upon the patellar tendon (positioned just below the Patella). This blow, usually performed with a specific tendon hammer, activates the muscle spindle in the quadriceps femoris muscle.

Muscle spindle is a particular type of sensory receptor, normally embedded in muscle fibers, able to detect changes in the length of the muscle itself. Once “activated” by the external blow, this receptor sends a signal to the spinal cord. Instead of involving higher nervous centres (it would take too long), at the level of the spinal cord an alpha-motor neuron is immediately activated.

The alpha-motor neuron conducts an efferent impulse directly back to the quadriceps femoris muscle, leading to its contraction. At the same time, an inhibitory interneuron relaxes the hamstring muscle, which is the quadricep’s antagonistic muscle.

The result of such coordinated contraction-relaxation, causes the “kick movement” of the leg. In normal health conditions, the leg extends once and then comes back to rest. It only takes about 50 milliseconds between the tap and the start of the leg kick.

why it is useful _

Patellar Reflex is a proprioceptive reflex which helps keeping posture and balance. The fact that everything “happens” at the level of the spinal cord, without involving higher nervous centres, allows for instance to keep balance without effort (actually, one does not have to focus on keeping an upright position). Energies are saved for more complex activities. Moreover, Patellar Reflex helps avoiding strong muscle contractions which could tear the tendon.

clinical interest _

As said, there is no interneuron in the pathway leading to contraction of the quadriceps muscle. Patellar Reflex can be used, for example, to check the conditions of the connections between the spinal cord and the muscles.

The absence or decrease of the Patellar Reflex is known as Westphal’s sign. On the other hand, multiple oscillation of the leg following the blow may be a symptom of cerebellar diseases.

source: contents taken from Wikipedia’s page

the Patella: some hints

The patella (also known as knee cap) is a thick, circular-triangular bone which articulates with the femur and covers and protects the anterior articular surface of the knee joint.

It is the largest sesamoid bone in the human body. In the adult the articular surface is about 12 cm2 and covered by cartilage, which can reach a maximal thickness of 6 mm in the centre at about 30 years of age.

The patella is attached to the Quadriceps tendon (of the quadriceps femoris muscle), which contracts to extend/straighten the knee. The vastus lateralis and vastus medialis are attached to lateral and medial borders of patella respectively. The vastus intermedialis muscle, not showed in this picture, is attached to the base of patella.

The patella is stabilized by the insertion of vastus medialis and the prominence of the anterior femoral condyles, which prevent lateral dislocation during flexion. The retinacular fibres of the patella also stabilize it during exercise.

The primary functional role of the patella is knee extension. The patella increases the leverage that the Quadriceps tendon can exert on the femur by increasing the angle at which it acts.

Patellar problems are among the most common causes of knee pain. This disease may be associated with other symptoms, such as instability or giveaway, dislocation, catching, grinding (crepitation), and/or swelling. These symptoms may present spontaneously or following injury (such as subluxations, blows to the front of the knee etc.). In general terms, patellar problems can be organized as:

  1. Pain alone – “patellofemoral syndrome”,
  2. Pain from malalignment – tilt and/or displacement,
  3. Instability – subluxation and dislocation,
  4. “Wear and tear” – arthritis,
  5. Other problems – synovial plica, tendonitis, bursitis, Osgood Schlatter’s disease, etc.

Surgery is rarely necessary, and must be carefully considered. For example, for the “pain alone” case, surgery is rarely indicated since it may even make pain worse. In these terms, surgery is best used as a last resort, after all other techniques fail (normally: conservative care trials).

Arthroscopy is the very best way to evaluate the patella and surrounding portions of the knee joint. Surgery will vary depending upon the type of patellar problem.  Of course it has risks, such as infection, stiffness, continued instability, weakness, pain, blood clots, fracture, impaired bone healing, etc. Recovery ranges from 6 weeks to 6 months, or even longer, depending upon the type of surgery, healing rates and limitations, and patient rehabilitation and efforts.

sources: two websites, this one and this one

Knee Alignment Conditions

The lower limb Mechanical Axis is defined by a line running through the centre of the hip joint to the centre of the ankle joint.  This line should pass essentially through the centre of the knee joint.

The tangential distance of this line from the centre of the knee joint is referred to as the Mechanical Axis Deviation.

In a Varus knee, the axis passes through the knee medial compartment, while in a Valgus knee it crosses the knee lateral side.

Another key concept is the one of Anatomical Axis. The Anatomical Axis of a bone is represented by a line drawn down the centre of the medullary cavity of the bone.

In the femur, the mechanical and anatomical axes deviate whereas in the tibia the mechanical and anatomical axes are essentially represented by the same line.

The angle between the Anatomical Axis of the femur and the lower limb Mechanical Axis is normally 6° of Valgus.

source: this website

A day at the hospital

Last week I was invited to attend in a knee surgery at the Hospital Cavale Blanche, in Brest. For my PhD project, the research work that I am currently carrying on is actually closer to the mechanical side of Robotics (microactuators, tiny mechanical structures, wireless energy transfer techniques …). Although, since one of my supervisors is an orthopedic surgeon, I was invited to participate to TKA surgery. Basically, this meant two things: I had to put on specific sterilized clothes and, once in the operating room, I was allowed to watch and put questions 🙂

When I got here I was told that, for PhD students in the field of Robotic Surgery, half a day at the hospital was more useful, in terms of acquirable knowledge, than a month of theoretical study. Actually, one of the aspects I mostly appreciated was the “pedagogical approach” of the surgeon towards the observers. We were two, a sweet girl who’s completing her studies in Pharmacology and me. And the surgeon kept explaining each single step, motivating each procedure and answering all our questions. The confidence he showed while (literally) manipulating the patient’s knee and conducting the operation in front of younger and less experienced surgeons was simply amazing.

Before the surgery, the patient can decide to undergo either general or local anesthesia. Let’s say that the noises and, especially, the smells produced by hammers and saws are not the best way to stimulate one’s appetite 😉 But one thing is sure: after living the atmosphere of such a delicate surgical operation, and understanding that one can really trust expert surgeons, personally I wouldn’t be so worried/scared to undergo TKA as I was before 🙂

the Meniscus: some hints

Medically speaking, the “cartilage” is actually known as the meniscus. The meniscus is a C-shaped piece of fibrocartilage which is located at the peripheral aspect of the joint. The majority of the meniscus has no blood supply. For that reason, when damaged, the meniscus is unable to undergo the normal healing process that occurs in most of the rest of the body. In addition, with age, the meniscus begins to deteriorate, often developing degenerative tears. Typically, when the meniscus is damaged, the torn piece begins to move in an abnormal fashion inside the joint.

Because the space between the bones of the joint is very small, as the abnormally mobile piece of meniscal tissue (meniscal fragment) moves, it may become caught between the bones of the joint (femur and tibia). When this happens, the knee becomes painful, swollen, and difficult to move.

The meniscus has several functions:

  • Stability – As secondary stabilizers, the intact meniscii interact with the stabilizing function of the ligaments and are most effective when the surrounding ligaments are intact.
  • Lubrication and nutrition – The meniscii act as spacers between the femur and the tibia. By doing so, they prevent friction between these two bones and allow for the diffusion of the normal joint fluid and its nutrients into the tissue which covers the end of the bone. This tissue is known as articular cartilage. Maintenance of the integrity of the articular cartilage is critical to preventing the development of post-traumatic or degenerative arthritis.
  • Shock absorption – The biconcave C-shaped pieces of tissue known as meniscii (cartilage in non-medical terms) lower the stress applied to the articular cartilage, and thereby have a role in preventing the development of degenerative arthritis.

source: this website