Spotlight on Chemists

Helmut Cölfen: Bone Biomaterials and Sea Urchin Cement

Biomaterials

Biominerals and Biologically-Based Materials 

Biominerals are natural composite materials based upon biomolecules (such as proteins) and minerals produced by living organisms via a process known as biomineralization [1]. Essentially, biominerals are minerals formed by living organisms – and can range from tiny microorganisms all the way upto humans. Some of the most common examples in the human body include bones, made of calcium phosphates – a kind of apatite biomineral – and teeth, which are made of ivory, another type of apatite. The shells of oysters, mussels, and snails are also composed of this diverse class of minerals [2]. It is exactly these biominerals that Dr. Helmut Cölfen researches.

In addition to helping organisms function in many ways, biominerals hold key information about their surrounding environments. Examining the chemical structures in biomaterials can reveal clues about Earth’s changing climate throughout time: If we can understand how biomineralization mechanisms operated back then, maybe we can use them as general rules when studying the future [3]. 

It was after looking at pictures of these wonderful biominerals that Dr. Helmut Cölfen decided to base his research on biominerals and how the biomineralization process could be used to construct useful synthetic systems. In particular, his lab conducts research into biominerals such as nacre, seashells and mussel shells, sea urchin spines and, more recently, bones and teeth. These are used as the basis for the manufacture of biomaterials, having wide-ranging applications in medicine, dentistry, and construction [4].

Figure 1: Application of biomaterials as implants in different areas of the human body. 

Source: Manivasagam et al. (2010). 

Bone and Teeth Biomaterials

Bone Grafting and Implants

As an important tissue/organ in the human body, bone plays a vital role in not only protecting the organs inside the body but also providing mechanical support. Moreover, it can coordinate with muscular tissue to accomplish various movements and respond to environmental changes. Although bone has a certain capability for regeneration and self-repair, large bone defects caused by severe trauma, cancer, or congenital diseases can only be repaired by bone grafting.

Bone biomaterials play a vital role in bone repair, and are now facing increasing demand. The specific biomaterial and porous structure can guide and control the type, structure, and function of regenerated tissue [5]. The bone implants used consist of layers that mimic the body’s natural bone to a better degree, causing the cells to connect to these implants much faster as compared to traditional ones made of titanium [4]. The biomaterials used in bone and joints, therefore, reconstruct or regenerate the musculoskeletal system and have vast application in the fields of orthopaedic, dental and neurosurgery.

Tooth-Filling Biomaterials

Figure 2: Application of biomaterials for tooth-filling 

Dental caries (or cavities) is one of the most widespread diseases in humans and has become a heavy economic burden; it is also a notoriously painful procedure that involves the dentist drilling holes in the teeth. Recently, some novel biomaterials have been developed in caries prevention and treatment and show broad prospects of application. 

Dr. Helmut Cölfen describes two branches of treatment: the first takes place before the caries actually develops, and thus does not require the aforementioned procedure yet. This usually is the case for micrometre-sized holes in the teeth. In this first route of treatment, the hole is filled with a liquid precursor that solidifies into calcium phosphate – this closes the cavity and prevents further caries from developing.

In case of developed caries that necessitates drilling, dental amalgam is generally used by dentists, owing to its suitability as a material and low cost. However, the presence of mercury – which is potentially toxic if leakage takes place – in dental amalgam calls for the synthesis of safer and more sustainable alternatives. Dr. Cölfen suggests using a dental paste composed of biomaterial – composed of calcium phosphate and gelatin, its consistency can be varied depending on the amount of water added by the dentist [4]. 

The Curious Case of Sea Urchins

Figure 3: A closer look at sea urchin spines

While stepping on a sea urchin’s spines is a less-than-pleasant experience, the spiky structures are actually vital protective elements for the organism and prevent it from getting flattened by our foot. Sea urchin spines are made from hard but brittle calcite – essentially chalk – that is normally broken easily. But the calcite in sea urchins is super strong because it is monocrystalline; that is, it is regularly ordered like rows of bricks, while thin amorphous layers in between them function as a mortar that stops cracks from developing [6]. 

Inspired by this property, Dr. Helmut Cölfen and his team developed a new form of concrete – essentially, a modification of cement that allowed it to be more elastic and crack-resistant by giving it a structure that mimics the nanoscale architecture of sea urchin spines. Traditional cement, while strong and stress-resistant, has the tendency to crack when bent; these cracks are exacerbated by water. The variant created by Dr. Cölfen addresses this issue, creating a fracture-resistant material. Amazingly, this new cement could create concrete that is between 40 and 100 times stronger than current mixes.

Learn More

If you’d like to hear more about the fascinating world of biomaterials and their applications, visit us on Spotify to listen to our ChemTalk podcast with Dr. Helmut Cölfen, Professor of Physical Chemistry at University Konstanz, to learn more about the benefits of sea urchin cement, how he first stumbled onto biomaterials, and what he considers essential for those pursuing a career in the sciences. 

Find the ChemTalk podcast here.

Works Cited

[1] ​​CURRAN, M. A. BIOBASED MATERIALS. Kirk-Othmer Encyclopedia of Chemical Technology, ISBN: 9780471238966. John Wiley & Sons, Inc., Hoboken, NJ, , 1-19, (2010).

[2] “Biominerals.” Youtube, uploaded by L’ÉCOLE, School of Jewelry Arts, 28 April 2020, https://www.youtube.com/watch?v=W1bNsgIemFQ

[3] Eisenstadt, Abigail. “How Biominerals are Stepping Stones for Climate Change Research.” Smithsonian Magazine. 22nd April 2021. 

[4] Cölfen, Helmut. Personal Interview. Conducted by Olivia Lambertson. December 2022. 

[5] Gao, C., Peng, S., Feng, P. et al. Bone biomaterials and interactions with stem cells. Bone Res 5, 17059 (2017). https://doi.org/10.1038/boneres.2017.59

[6] Urquhart, James. “Sea Urchin Spines Inspire Elastic Concrete.” Chemistry World. 5th December 2017.