Harnessing expertise in polymer chemistry, molecular biology and medicine to develop important solutions in tissue regeneration and repair, Professor JÖns Hilborn shares his team’s work

To start, could you explain what you hope to achieve through your current research project?

We aim to develop materials that promote regeneration of missing human tissue by instructing our body to repair just as naturally growing or added cells grow and develop. We also aim to produce materials that assist in the correction of genetic defi ciencies (‘correcting errors in the DNA’) or incorporating genes with the aim of treating diseases like cancer, arthritis, cystic fi brosis but also for developing vaccines against eg. HIV and infl uenza.

What types of injuries and diseases might benefi t most from the use of biodegradable polymers?

Today we fi nd their use for regeneration of bone, cartilage and skin while the future holds hope for muscle and more vital organs. For drug delivery, we predict major advances with today’s more effi cient medicine and potentially addressing genetic diseases tomorrow. From the polymer standpoint, the advantage of synthetics is that they are controlled in terms of composition, origin, etc. to assure safety. Commonly used

synthetic polymers (suture threads) are useful when designing structures that should carry mechanical load. Our fi ndings, however, show natural polymers in the human body have an advantage over synthetic ones since, through evolution, they have become the matter that communicates with our cells and provide the stem cell niche.

Is there a limit to the amount of regeneration of bone, cartilage or soft tissue that can be achieved using biomedical materials?

If we use the approach of adding cells to regenerate the organ, the survival of the added cells depends on the distance to a blood (or nutrient) supply, which is usually limited to sub-millimetres. Other approaches use strategies based on recruitment of cells from our own body to the site of implantation. We have repaired a larger than 20 cm3 defect in a pig model where bone was regenerated, but we do not believe that this is a limit in the future. It is likely that signifi cant amounts of tissue can be regenerated, but the quality and function of the new tissue may be limited.

To what extent do you adopt a multidisciplinary approach in your research?

Our laboratory falls under the label of polymer chemistry, in that we work to understand how polymers are synthesised both synthetically and in vivo. Polymers of human origin are of particular interest for us and include proteins, polysaccarides, DNA and mRNA. These create natural bridges to molecular biology. We evaluate these in cell culture and in animal models with the aim of bringing new therapies to commercial applications and to patients. Therefore, with our competences from diverse fi elds, we collaborate in what we could call ‘biomedical engineering’, ie. research that aims to construct useful materials rather than research that aims to explain how the world functions.

Have you faced any challenges or setbacks to date?

We face challenges almost every day and many of our experiments and attempts fail. This is, however, a part of research where results cannot be predicted. Learning from these experiments can sometimes be even more rewarding than the original plan. To learn, however, you need to try. A major challenge in research today is the extensive and increasing requirements of detailed reporting. Together with proposal writing this consumes more and more time that could be spent on research.

One setback has been the observation that BMP-2 itself – even at lower doses – caused unacceptable temporary swelling of tissues in human patients in a recent alveolar cleft trial. It required signifi cant efforts to develop a safe and easy to use carrier, but we fi nd that the doses of BMP-2 required for adequate bone formation result in swelling. For other applications this might still be acceptable but the take-home message is to revert to the design of new systems that will give improved outcome.

What has been your most important development during the course of your research?

I think that the most important development has been the transition from expertise in polymer synthesis to a multidisciplinary team. Many of the questions for life sciences are found in the biology that needs to be understood in order to develop the right chemical solution. To point out a single step in development I would like to state the fi nding that we can make injectable materials from components that are found in our own body. Compared to injectables made from most other substances, these demonstrate signifi cant advantages in terms of biocompatibility. Just the gel made from hyaluronan proves this by successful transfer from the bench to the clinic of a material that is now commercially available.

New possibilities intissue regeneration

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Mimicking the body’s healing responseTransplantation and plastic surgery allow surgeons to repair and rebuild missing tissues, but using non-degradable materials that need to be removed can cause problems. Work at Uppsala University involves polymers that degrade within the body and replicate the body’s own repair mechanism may offer a smart alternative

ADVANCES IN SURGICAL techniques in the past decades have meant that the repair and reconstruction of missing tissue is possible for many patients with acute or congenital conditions. However, despite the success of such techniques, these procedures have traditionally used non-degradable repair materials (such as metal implants), which need to be left in the body, often causing problems such as scarring, pain, formation of harder tissues and infections. Removal at a later date is often the only solution, but this involves further surgery and can cause additional complications.

Polymer based biomaterials offer an alternative, since they degrade inside the body, circumventing the need for removal. Such materials can also be designed to trigger specifi c biological responses to aid the body’s own healing process. These biomaterials are the subject of new research at Uppsala University in Sweden, where scientists are exploring questions of tissue regeneration and drug delivery where new materials are synthesised and evaluated in vitro and in vivo. “In our work we are aiming for regeneration of tissues where traditional approaches often had been transplantation or plastic surgery,” says Professor JÖns Hilborn, the lead researcher. “These methods are limited by availability of suitable donors or the amount of tissue that can be moved from one site of the body to repair another site eg. bone harvested from the hip to repair skull defects.”

By developing new materials that instruct for self-repair of tissues, the researchers hope to provide clinicians with an improved source of ‘artifi cial tissue’, without damaging any healthy tissue. Such materials are also designed to be compatible with the body’s own tissues, mimicking their functions: “The development of synthetic polymers is only slowly moving towards performances shown by the body’s own natural polymers,” explains Hilborn. Such polymers may be designed to carry mechanical load and can be used in the construction of implants and will avoid many of the risks associated with possible rejection of the material by the host’s immune system.

The materials will degrade naturally inside the body, which has a two-fold benefi t: removing the need for a second surgical intervention to remove the implant; and that the materials progressively increase the load on the tissue as they degrade, thereby ‘training’ the tissue to support weight via a process known as mechanotransduction. “Mechanotransduction refers to the many mechanisms by which cells convert mechanical stimulus into biochemical activity. Tissues like bone and muscles that have the purpose of carrying load grow stronger and larger upon loading and weaker and smaller if not loaded,” he notes.

This process is of major importance for tissue regeneration. For example, a fractured bone that has been fi xated with a stainless steel implant is not being ‘trained’ to bear load as it heals, since the implant is carrying all the weight. This causes imbalance in load bearing which results in fractures at other parts of the body. If an implant is made using biomaterials, it degrades slowly and naturally throughout the healing process, decreasing the risk of fracture. The composition and properties of the biomaterials can be controlled so that implant can be engineered according to the specifi c requirements of the application.

JOINT EFFORT

Such challenges, encompassing organic and polymer synthesis, materials chemistry, biology and medicine, necessitate a multidisciplinary approach. The focus of the team at Uppsala is broadly split into three key areas. The investigation of biodegradable synthetic

48 INTERNATIONAL INNOVATION

BONE FORMED BY INJECTION IN RAT MODEL (LOWER PIECE) COMPARED TO NATIVE RAT FEMUR (UPPER)

PROFESSOR JÖNS HILBORN

INTELLIGENCE

INJECTABLE BIOMEDICAL MATERIALSOBJECTIVES

The project focuses on (i) biodegradable synthetic polymers that function as mechanical support or protection for regenerating tissues, (ii) soft materials/gels mimetic of the extracellular matrix designed to allow injection and (iii) materials that enable delivery across the cell membrane and to intracellular targets. Specifi c applications include regeneration of bone, cartilage, neural repair, soft tissue regeneration in urology and the treatment of diabetes.

KEY COLLABORATORS

Professor Wout Feitz, Nijmegen Centre for Molecular Life Sciences, The Netherlands • Dr Jerónimo Blanco, Cardiovascular Research Center (CSIC-ICCC), Barcelona, Spain • Professor Olle Korsgren, Professor Bo Nilson, Clinical Immunology, Uppsala University, Sweden • Professor David Sassoon, Myology Group, INSERM, University of Marie and Pierre Curie, Paris, France • Professor Henrik Semb, The Danish Stem Cell Center, University of Copenhagen, Denmark • Professor Bhuvanesh Gupta, Indian Institute of Technology, New Delhi, India • Professor Peter Frey, Institute of Bioengineering (IBI), School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland • Professor Sune Larsson, R&D Director, Uppsala University Hospital, Akademiska sjukhuset, Sweden

FUNDING

Swedish Research Council • Swedish strategic research in stem cells and regenerative medicine • European Comission

CONTACT

Professor Jöns HilbornResearch Leader

Head of Polymer Chemistry ProgramScience for Life LaboratoryDepartment of Chemistry - ÅngstrÖm LaboratoryUppsala University75121 Uppsala, Sweden

T +46 18 471 3839E Hilborn@mkem.uu.se

JÖNS HILBORN has served as Head of the Polymer Chemistry Program at the Department of Materials Chemistry, Uppsala University in Sweden, since 2001. He received his PhD from the Royal Institute of Technology in Stockholm, followed by seven years in industry before joining the Swiss Federal Institute of Technology. Hilborn is a frequently invited speaker at international events and has published more than 200 scientifi c papers, 26 patents and has started four companies.

polymers primarily explores how such polymers can function as mechanical support or protection for regenerating tissues. A second area of research looks at designing artifi cial 3D matrices – how materials can be designed to mimic the natural extracellular matrix and allow injection. Conversely to synthetic polymers that are mechanically strong, the extracellular matrix based polymers possess native cellular recognitions sites to provide suitable signals from the material to the cells and tissues. The challenge is to assemble these natural polymers without changing their native chemical structure.

Finally, the issue of how materials can be engineered to enable delivery across the cell membrane to intracellular targets is being explored. Recent fi ndings show that it is possible to ‘tag on’ to the native routes of cell entrance. Thereby it seems likely much higher specifi city for drug delivery will be addressed and therapies aiming to treat genetic defects (eg. cancer) and novel vaccination strategies will be developed. These different areas require a combination of skills to achieve successful practical outcomes, and for this the researchers also look outward to further collaborations: “A signifi cant part of the work is done in collaborations involving engineering, basic biology, mechanics and medicine both nationally and internationally,” says Hilborn.

Specifi c applications include the regeneration of cartilage and bone, neural repair, soft tissue regeneration in urology and the treatment of diabetes. One notable success so far has been an injectable hyaluronan hydrogel that the team are developing as a carrier for BMP-2, a protein used in bone repair. Hilborn describes how the team are engineering the material to achieve optimum results: “We have selected hyaluronan as this is one of the body’s own materials that doesn’t provoke immunological problems, ie. there are no rejection issues upon implantation. Furthermore it is degraded by the body’s own processes into compounds that the body is used to dealing with”.

CLINICAL TRIALS ARE UNDERWAY

These bone-repair materials have already been applied in clinical trials, and having begun to unlock the potential of such materials. The researchers are now developing clinical trials for other tissues. For more widespread application, however, they are turning to commercial partners. “We are actively involved in transferring technology to the industrial setting, but should point out that our group will not directly supply therapies to patients,” Hilborn recognises. “Our own research is more focused on addressing new medical challenges that currently involve new systems for delivery of drugs, materials that themselves possess biological activity such as anti-infl ammatory response, and materials that allow in vivo gene delivery using safe and effi cient routes.”

These important areas of interest have been established by young researchers, whose work is central to the team’s investigations. For instance, Dr Dmitri Ossipov has established the work on new drug delivery systems; bioactive materials that prevent or modulate the infl ammatory response are being explored by Dr Tim Bowden; and Dr Oommen Varghese is investigating in vivo gene delivery. “We can do many challenging things like delivering biologically active DNA and RNA inside living cells by mimicking nature,” says Dr Varghese. Through a collaboration with Dr JerÓnimo Blanco in Barcelona, it has been shown that it is possible to deliver biologically active cargo specifi cally to desired cells/tissue in mice. In the present scenario, only viruses have this unique ability to enter cells so effi ciently. This technology has far reaching signifi cance in medicine as it possesses the same effi ciency as classical viral delivery vector but unlike viruses these are completely non-immunogenic. They look forward to using it as a novel delivery platform for useful genes and nucleic acids in our body, which will open new avenues to treat lethal diseases like cancer and HIV.

Such challenging research loads are part of the ethos of the team: “In our group, taking personal responsibility is required. This also implies that our seniors delegate responsibilities. We expect young scientists to assume these and we encourage new ideas and creative thinking. Most young scientists fi nd this atmosphere and way of working highly rewarding, albeit demanding”.

The team’s multidisciplinary approach and integration into a larger mileu including medical nanomaterials and medical ceramics fosters an exciting research environment: “We are particularly excited about the possibilities we have to give training to young visiting researchers, a training that has proved to boost their careers,” Hilborn adds. They are focussing on the translation of fundamental molecular science into practical bioengineering that can be applied to living tissues. Working with commercial partners, the scientists at Uppsala are already beginning to turn their research into clinically available realities.

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LIGHT PRODUCTION BY MOUSE CELLS AFTER THREE DAYS POST-INJECTION OF LUCIFERASE DNA-HA COMPLEX, THE GENE RESPONSIBLE FOR THE FIREFLY TO GLOW IN THE DARK

COURTESY OF DR BLANCO