Tissue Engineering to Help Treat Complex Pathologies and Underpin Further Research

Skin transplantation and artificial bladder replacement are no longer science fiction but very much a reality. Such research is carried out and implemented into practice by scientists working in the interdisciplinary field of tissue engineering. By combining several branches of science, they are developing methods and products that will help treat complex pathologies and also become a driving force for further research, believes Prof. Daiva Baltriukienė, researcher at Vilnius University Life Sciences Center. In the latest episode of the Vilnius University podcast “Mokslas be pamokslų” (“Science without Sermons”), she explains how artificial tissues and organs are created and what problems they can solve.

‘Tissue engineering is an interesting and engaging interdisciplinary field, requiring knowledge of medicine, chemistry, and engineering. In our case, we even need certain skills in physics and laser physics, biology, biochemistry, as well as molecular biology. Tissue engineering spans an extensive range of sciences with the common goal of creating functional tissue to replace damaged tissues or even entire organs and, potentially, become an alternative to organ donation,’ says the VU Professor.

Science originating from the US

According to Prof. Baltriukienė, humanity has always been interested in the processes of its own origin. However, genetic engineering gained momentum as a scientific field only in the 1980s; this was due to several factors: firstly, stem cells being discovered back in 1961, and secondly, proactive researchers seeking to understand and apply them in practice.
‘Joseph and Charles Vacanti, brothers from the US, are considered pioneers in this field. In their daily medical practice, they noticed a strong need for new innovative treatment strategies. Therefore, they started collaborating with chemists and engineers in search of various materials that could be used to restore minor tissue damage. Having obtained some inspiring results, the tissue engineering community began to expand,’ the researcher comments.

As she mentions, tissue engineering also includes cell research because cells can be used for tissue regeneration: ‘The beginning of such research in Lithuania traces back to 1990, when Raimundas Širmenis, cardiac surgeon from the team led by Prof. Vytautas Sirvydis, addressed his colleagues Vigintas Domkus and Virginija Bukelskienė at the then Institute of Biochemistry, proposing the idea of extracting stem cells from muscle tissue to use them for treatment purposes in the future.’

However, studies in this field were postponed due to a lack of resources. Around 2004, when state funding became available, research on muscle-derived stem cells was resumed with the aim of applying them in the regeneration of cardiac tissue. At the time, many studies in Europe were already moving in this particular direction, and scientists were optimistic about the potential use of muscle-derived stem cells, e.g. in restoring cardiac tissue after a myocardial infarction. In Europe, this type of research even reached the stage of clinical trials. Unfortunately, it was then realised that we did not yet know enough about these cells. Researchers had to go back to their laboratories to study and understand better where and how they can be used. The further involvement of scientists from other disciplines – physicists, chemists, and medical professionals of various fields – finally led to the actual onset of tissue engineering.

Artificial skin as the first tissue engineering product

‘The first artificially created tissue was the skin – our largest organ that tends to be most vulnerable to burns and injuries. Another important area is cartilage tissue, such as joints. Scientists have first opted for simpler research subjects because it is always better to start with less complicated things so that we can later move on to more complex aspects and the most topical areas,’ says Prof. Baltriukienė.

According to her, although these are not routine treatments, there are quite a few examples of successfully produced tissue constructs around the globe: ‘I was most impressed by a project that combined both tissue and genetic engineering. In 2017, skin grafts were created, and a boy with a rare genetic disease that causes the epidermal layer of the skin to blister and tear off received a skin transplant. Such children do not usually reach adulthood and, if lucky, they can live at most to the age of 30. In this case, as much as 60 per cent of the boy’s skin was already lost. Therefore, researchers took his skin cells, replaced the faulty gene with a healthy one, encoding the correct version of the protein, created skin grafts and transplanted them onto the boy. A couple of years after the surgery, he was able to lead a normal life because his skin remained functional.’

Referring to other examples, the Professor mentions that a tissue-engineered bladder has also been created and transplanted. In such a way, the functions of damaged tissues can be partially restored in a laboratory environment, e.g. by replacing defective cells with new ones. It has been proven to work in restoring both heart and kidney functions. As an alternative to animal experiments, tissue engineering methods are also applied for in vitro drug safety testing, where human tissue prototypes are used to determine the effects of chemical compounds.

Key ethical aspect

‘Another significant thing to mention is the multiplication of these tissues. After creating an individual tissue, it takes a lot of resources to get mass production going. There are also certain regulatory issues because such aspects have to be universally agreed upon,’ emphasises Prof. Baltriukienė.

As explained by the Professor, not all cells are conducive to forming tissues. The most effective ones – embryonic stem cells, which can differentiate into all other types of cells – cannot be used, as they are obtained through the destruction of an embryo. This poses certain ethical challenges; therefore, such research has been banned in many countries, including Lithuania.

‘A major breakthrough in this field was made by isolating induced pluripotent cells from mice in 2007 and human somatic cells in 2008. They exhibit properties very similar to those of embryonic stem cells. However, even in this case, some questions still remain, as the production employs genetic engineering techniques,’ says the VU researcher.

According to her, there are, nonetheless, some countries with no prohibitions applied in this field, which is why intensive research is still ongoing there: ‘For example, we can mention the US. At the moment, when it comes to tissue engineering, they are focussing on adult stem cells because we still have so much to learn about embryonic ones. The latter have contributed greatly to understanding how the body and individual organs develop. On the other hand, both embryonic stem cells and induced pluripotent cells can form a tumour tissue called teratoma. Controlling cellular response in vivo is not an easy task. In vitro and in vivo results may significantly diverge since cells in a natural environment are exposed to a wide variety of factors that regulate cell multiplication and death, as well as their response to the same factors. Thus, these aspects are challenging to control in a complex environment.’
The same applies to artificial tissues: ‘We can see how a tissue works in vitro, but the question is how it will behave when implanted into a human body. Scientists still cannot provide an ultimate answer to that.’

How does tissue engineering work?

‘Tissue engineering requires three key elements: cells, a conducive environment, and stimulating factors. Cells are usually obtained from a small piece of donor tissue, which can yield billions of cells for researchers to work on. Of course, special factors are required to release the cell from the tissue and make it multiply. Another crucial factor is the scaffold – our way of referring to an artificially created environment,’ says Prof. Baltriukienė.

She also adds that 3D printing is now used to create such scaffolds: ‘We have started research in this field in collaboration with the Laser Research Center. 3D constructs have to be porous so that cells can migrate, integrate, and get nutrients.’

Although new-generation 3D printers are capable of printing quite large structures, it all started with tiny ones, of less than half a centimetre in size: ‘Engineering techniques have to be developed in such a way to ensure the easy creation of a cell-friendly environment. However, a so-called scaffold alone cannot be sufficient. It provides spatial orientation because cells in vitro usually grow on a flat surface, which is not physiologically specific to them. They must be implemented in an environment similar to a human body. All this may affect the cell properties, but it is still insufficient.’

Prof. Baltriukienė states that tissue engineering requires complex conditions – a combination of different factors that would steer the fate of cells in the right direction. In case of any imbalance between different bioactive substances, we will end up with cell characteristics other than those that should be found in a particular tissue. In this context, it is not only external factors that are important, but also understanding the cell itself: how it transmits signals to its nucleus, how this affects gene regulation and, subsequently, protein synthesis, since the protein plays a vital role here. For this reason, large research teams have pooled their intellectual resources to work on these issues.