Better material for bone tissue regeneration
A new study suggests how to cover biodegradable implants with a material similar to human bone. Bone tissue regeneration is a research area for Dmitry Gorin, a leading research fellow at the RASA Center in Tomsk Polytechnic University. His group has developed a new vaterite-based coating for nanofiber material used as a scaffold to grow bone tissue cells in a shorter time.
The process of porous calcium carbonate (CaCO3) covering on electrospun poly(ε-caprolactone) (PCL) fibers was described in this study. The cytocompatibility test demonstrates the suitability of PCL/CaCO3 scaffolds for cell culturing.
The scientists produced non-woven PCL (poly (e-caprolactone) fiber by an electrospinning technique. This technology was first developed in the USSR in the 1930s, but has long been classified; it was subsequently rediscovered in the U.S. In regenerative medicine, nonwoven materials fabricated by an electrospinning technique can be successfully used as scaffolds for tissue engineering materials because of their unique physical chemical properties and nanostructured nature.
"We had a well-known polycaprolactone matrix, and have grown a coating of one of the polymorphic calcium carbonate modifications (CaCO3)—vaterite—a very interesting material in terms of drug delivery since it has a porous structure. Furthermore, under certain conditions, vaterite may recrystallize in bone components in vivo. Therefore, a vaterite-PCL composite is a promising material for bone implants," says Gorin.
In nature, vaterite is a rare mineral due to the fact that its structure is unstable. Vaterite has two much more common counterparts with the same chemical formula (CaCO3): aragonite and the most commonly occurring calcite. Substances with the same chemical formula but different crystal structure types are said to exhibit "polymorphism" in mineralogy. Vaterite is found in nature as a component part of the skeleton of some gastropods (e.g. snails).
In order for cells to grow, they need a basis. The basis can be different: you have to pick up the one which properties ensure the rapid growth of cells, and therefore faster regeneration of tissues. This material must meet certain requirements as the permeability of medium for various substances and water vapor permeability. After transplantation scaffolds trigger cell growth process, and then degrade. According to Dmitry Gorin, when it deals building a future bone tissue, in this case, the composite basis degradation will go slowly enough, about a month or more, which is enough to substitute the implant with the newly-formed bone tissue.
The basis is a nanostructured polycaprolactone PCL matrix, wherein the fibers surface was precipitated with polycrystalline vaterite aggregates (CaCO3), which upon recrystallization in the body is transformed into hydroxyapatite (Ca5 (PO4) 3 (OH)) – a mineral, of which the human skeleton consists. This transformation is possible due to the interaction of the implant with blood and other body fluids. If blood is considered from the standpoint of ion composition, it contains a phosphate ion (PO4) 3- (in a phosphate buffer system). It is this phosphate ion reacts with coating vaterite particles, thereby recrystallizing the reaction to form hydroxyapatite. The mechanism of vaterite recrystallization in hydroxyapatite has been reviewed in detail by scientists in their previous work.
"The bone implants are relevant when it comes to a defect in the bone, which can't recover itself. Now we are working on the creation of bone implants, together with colleagues from Saratov Scientific Research Institute of Traumatology and Orthopedics," said Dmitry Gorin.
PCL fibers obtained as mentioned above, by electrospinning. The method is that under pressure polymer solution is fed through the needle and due to the potential difference applied between the second electrode and the needle, the thread is formed with a submicron diameter. The thread falls freely onto the substrate, which is the second electrode, and forms a non-woven fabric.
The obtained threads can be directed, but for the tasks described in the article they were to be arranged randomly. Modern membrane materials used in cloth manufacturing are permeable to steam but do not to water, and made by the same technology.
Later the researchers plan to study the behavior of the new implant material in vivo in order to investigate the possibility of using this material for bone tissue regeneration.
More information:
Maria S. Savelyeva et al. Vaterite coatings on electrospun polymeric fibers for biomedical applications, Journal of Biomedical Materials Research Part A (2017). DOI: 10.1002/jbm.a.35870
Provided by Tomsk Polytechnic University
