Light delivery into the human body is important for certain treatment methods such as laser surgery, optical imaging, drug activation, diagnosing diseases etc. Light is used to manipulate neuron function in the brain in the field of optogenetics, an experimental field. Till now, light has been delivered into the body using optical fibres which are made of glass. The problem with glass optical fibres is that it is non-biodegradable, and brittle. If it is implanted into tissue, it might break and damage the tissue. Now, researchers are working on flexible fibres made from polymers, as an alternative. These polymers are biodegradable too, enabling them to be implanted into the body, without fear of damage.
Penn University’s research on optical fibres made from biomaterials
Penn University’s researchers – a biomaterials’ engineer and electrical engineer have collaborated and shared their knowledge of their respective fields, to develop a unique biodegradable optical fibre, which is flexible as well. This optical fibre will be used to deliver light to the human body, instead of glass optical fibre.
According to Professor Jian Yang, who is an expert in biomedical engineering, visible light can penetrate only up to certain depths, (could be hundreds of microns). Light which is almost infrared, may penetrate anywhere between few millimetres up to one centimetre, but this is not sufficient for doctors to diagnose the problem.
The organic solution
Professor Yang earlier had invented a particular polymer which is citrate based. Citrate is a key ingredient which occurs naturally in human body metabolism. This citrate based polymer, invented by Professor Yang, has been used as a sound platform for many biomedical applications, like scaffolds used in tissue engineering, bone screws to fix bones, and nanoparticles which are used to deliver therapeutic drugs into the body following time release mechanisms.
Now, he is working to create a unique step-index optical fibre, based on the citrate polymer to deliver light within the body. The new approach, which Professor Yang is working with Penn electrical engineer, Zhiwen Liu, is the step-index method for optical fibre to deliver light within the body.
In step-index method there is a material at the core, which transmits light, and a kind of cladding that gives protection to the core and stops the light escaping from the core. Professor Yang’s laboratory makes as well as tests the citrate based polymer and then it is taken to Professor Liu’s lab to convert it into a fibre. After the fibre has been tested and the required adjustments are made, Yang’s laboratory implants the optical fibre into biological tissue to test it further.
According to one of the researchers, the current work is an example of the citrate based biodegradable flexible polymer optical step index fibre. The citrate based polymer fibres enable the refractive indexes of the cladding and core layers to be tuned to a great extent.
Advantage of the biodegradable fibre over glass fibre
The cladding and the core of the new fibre have similar mechanical characteristics, due to which the fibre can stretch and bend, without the two layers pulling apart from each other, unlike materials which are not similar, as is the case with glass optical fibres.
The cladding and core, which are made of similar materials, will degrade in the same rate within the bodywithout harming the tissue.
According to the scientists, the new biocompatible and biodegradable, step index, low loss optical fibre will be able to facilitate even deeper light delivery, and can deliver organ scale light as well as enable light collection from within organs. Thus, it will be able to be used in a variety of biomedical applications, in which light delivery, sensing or imaging is required.
The step index fibre can create a unique transparent window, to peek into turbid tissues and enabling new imaging opportunities.
This new fibre is a path breaking invention, as it can be left inside the body for a long period of time in which it will dissolve inside the body, unlike glass optical fibres. There would be no need for a second surgery to remove this fibre from the body. Apart from imaging and sensing, this fibre can be used to deliver therapeutic drugs, biological molecules and chemicals to treat various diseases.