Tissues or organs of the body often undergo damage during the course of various diseases or due to external injury caused during accidents. Most of the time, these are treated using tissue or organ transplants from healthy donors. In some cases, devices (such as pacemakers for heart) can compensate for a loss of function of these organs. However, the focus of today’s cutting edge research is in making materials that the body’s own cells can grow on and repair the damage. The field of ‘tissue engineering’ involves the use of a synthetic material as a 3-D support structure to help the cells grow and subsequently heal and restore the original tissue.
In this context, a recent study by scientists at the Indian Institute of Science suggests that 3-D scaffolds of graphene composites are a suitable template for bone tissue regeneration as they mimic the environment of the bone. Dr. Kaushik Chatterjee, at the Institute’s department of Materials Engineering, and his students have investigated how and why do cells respond differently to 2D versus 3D scaffolds.
Polycaprolactone (PCL) is a biodegradable polymer and by itself is a very soft scaffold. This makes it unsuitable for use as a template for bone engineering. In this recent study, Dr. Chatterjee and his students attempted to make the PCL scaffold stronger by the addition of Graphene (known for its high mechanical strength). The resulting Graphene+ PCL scaffold was found to be stronger than PCL alone. They also investigated the response of osteoblast cells (bone precursors) to Graphene based polymer nanocomposites in 2-D substrates and 3-D scaffolds.
Graphene based polymer nanocomposites are processed differently while making 2-D substrates and 3-D scaffolds. The physical and chemical properties of these scaffolds differ depending on the kind of graphene used and the nature of the processing involved. Dr. Chatterjee’s group shows that bone cell precursors (osteoblasts) behave differently depending on the nature (2-D versus 3-D) of the scaffold. This difference in behaviour is due to the chemical difference in the method of preparation of the scaffold and the graphene used, which in turn affects the nature of the surface generated for housing the cells.
Another disadvantage of using PCL alone as a scaffold in tissue engineering is its inherent hydrophobic (water-hating) nature, making it a difficult home for cells (cells prefer a more hydrophilic i.e. water-loving environment). A solution to this problem is to mix PCL with other substances to make it more hydrophilic. In this study, the addition of graphene increased the wettability (the degree to which a substance absorbs or can be made to absorb moisture) of the scaffold making it a better home for osteoblasts. They also find that cells in 3-D scaffolds have a compact arrangement similar to what is seen inside bone tissue, in contrast to the random distribution seen in case of 2-D substrates. In addition to this, bone mineralization (process needed for strengthening the bone) was found to be higher in 3-D scaffolds as compared to 2-D substrates.
“The purpose of the scaffold is to provide only a temporary home for the regenerating cells. The scaffold should degrade slowly over time allowing for healthy tissue to eventually replace the scaffold. An ideal scaffold is one that is not only non-toxic to the body and non-immunogenic (does not incite an immune reaction from the body) but also supports attachment of cells and actively encourages healthy cells surrounding the damaged tissue to grow into the scaffold and repair the damaged area” says Sachin Kumar, the lead author of this study.
This study conclusively shows that 3D graphene based polymer nanocomposites fulfil the above requirements for a good scaffold for bone tissue repair. However, he states that “while 3-D scaffolds are the way to go in case of bone tissue engineering, 2-D scaffolds (where cells are provided on a solid block) may also find use in bone tissue repair. One isn’t necessarily better than the other. The kind of scaffold to be used will depend on the nature of the damaged tissue”. Most importantly, Dr. Chatterjee’s work highlights the importance of the processing method for making a scaffold as it affects its ability to be a surrogate home for the intended target cells.
About the authors: Dr. Kaushik Chatterjee is an Assistant Professor at the Department of Materials Engineering, Indian Institute of Science. Sachin Kumar (PhD research scholar), Md. Dilkash Azam (a former ME student), Shammy Raj (project assistant) and Elayaraja Kolanthai (postdoc) are members of Dr. Chatterjee’s lab. Prof A. K Sood is a Professor at the Department of Physics and K. S. Vasu is a former PhD student in his group.
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About the study: The paper “3D scaffold alters cellular response to graphene in a polymer composite for orthopedic applications” was published online in the Journal of Biomedical Materials Research B: Applied Biomaterials (October, 2015).