Biomaterials, implants and tissue engineering

Molecular dynamics at cell-biomaterial interface

Prof. Dr. Altankov, George
(ICREA Research Professor)
Group Leader


Pavelló Govern 1ª Planta | Campus de Bellvitge | Feixa Llarga, s/n | 08907 | L'Hospitalet de Llobregat
Email : george.altankovicrea.cat

Research Topics

We are interested on cell-biomaterials interaction, and more specifically, on the dynamic formation of provisional extracellular matrix (ECM) – the tin protein layer that cells recognize, produce, and remodel at the materials interface. We aim to learn how this process affects the biocompatibility of materials, and if can be controlled by engineering the materials surface properties. For that purpose, we perform systematic studies in the following directions.


Remodeling of ECM proteins at cell-biomaterials interface

ECM remodeling occurs in various physiological and pathological processes, such as normal development, wound healing and angiogenesis, but also in atherosclerosis, fibrosis, ischemic injury and cancer. It consists of two fundamental processes; assembly and degradation. The organization of ECM is fundamental for biology and medicine, and it proteolytic degradation is a physiological mechanism for the removal of excess ECM. Although matrix remodeling is a subject of extensive biomedical research, the way it is related to the biocompatibility of materials is poorly understood and is therefore a hot topic of our research.

ECM organization at the biomaterial interface depends on the allowance of cells to rearrange adsorbed matrix proteins. We anticipate that materials that bind proteins loosely will support the arrangement of a provisional ECM, while stronger binding provokes its degradation.

Image: Pericellular proteolysis of adsorbed FITC-labeled vitronectin (dark zones) by HUVECs adhering for 5 hours on CH3 functionalized substrata. Part of the protein is rearranged in a linear pattern


Materials surface driven assembly of ECM proteins at the nanoscale

Upon adsorption at material interfaces, proteins may assemble spontaneously, and this interaction has significant consequences for their biological response. Recently we have employed distinct silane-inspired chemistries and polymer compositions to create model substrates with tailored densities of -OH, -COOH, -NH2 and -CH3 groups, thus varying the chemistry, charge and hydrophilic/hydrophobic balance. In a series of communications combining AFM and other nanoindentation techniques, we have described a novel phenomenon of substratum-driven protein assembly depicting the fate of various matrix proteins such as fibronectin, collagen IV, vitronectin and fibrinogen at the biomaterials interfaces of the model described above. Specifically, we show that by varying the density of chemical functions, one can tailor both the assembly and degradation of proteins. Following these findings we aim to control ECM remodeling by engineering specific material properties. Understanding the behavior of ECM proteins on flat biomaterials interface further boosts an important bioengineering target - the biohybrid organ technologies based on two-dimensional protein layers that mimic the arrangement of the natural basement membrane.

Image: AFM images of adsorbed native collagen type IV from a solution of 50 mg/ml for 30 minutes on NH2 (A) and COOH (B) functionalized surfaces, showing cellular network-like protrusions on the NH2 and aggregated morphology on COOH. It results in a distinct difference in the efficiency of cellular interaction: endothelial cells are better spread on NH2 (C, E) while rounded on COOH (D, F). (Coelho et al., 2010)

 

Electrospinning of nanofibers from natural and synthetic polymers for guiding cellular behavior

In solution, proteins can form structures of various shapes, including fibers with a diameter of only a few nanometers and with lengths up to centimeters. A fascinating possibility to mimic similar ECM structures is to engineer protein-like or matrix protein-containing nanofibers via electrospinning technology. For that purpose we are developing electrospun nanofibers from natural (e.g., fibrinogen) and synthetic polymers (e.g. PLA, PEA) in order to direct desired cellular response via spatially organized cues (e.g. fiber size and geometrical organization) as well as by tailoring their chemical and mechanical properties.

Image: Hybrid nanofibers of PLA and fibrinogen deposited in random (A) and aligned (B) configurations. Human mesenchymal stem cells adhere to the fibers and acquire a stellate-like (C & E) or elongated (D & F) morphology, depending on the fiber orientations (vinculin is immunostained in red and actin in green)

 

 


Nanofibers-based 3D constructs to provide cells with spatially organized stimuli

Examining hierarchical biology in only two dimensions (i.e. cells confined to a monolayer) is in most cases insufficient, as cells typically exhibit unnatural behavior if excised from native three-dimensional (3D) tissues. Within the European STRUCTGEL project (under our coordination) we are involved in developing an advanced multilayered 3D biohybrid construct that combine the structural and biological properties of electrospun nanofibers with the specific mechanical properties of hydrogels in order to provide stem cells with relevant spatial orientation in 3D.

Image: Schematic illustration of the STRUCTGEL concept

 

 

 

 

 

Creating dynamic stem cell niches using stimuli-responsive biomaterials

In addition to engineering the spatial configuration of cellular microenvironments, we are also interested in addressing the dynamic (i.e. temporal) aspects of the stem cell niche. To do that we take advantage of stimuli-responsive polymers to obtain control over an artificial cell-adhesive environment via dynamically altering either cell-cell (using cadherin-like ligands) or cell-matrix (using ECM proteins) interactions. By modulating the strength of adhesive protein-to-substratum interactions we aim to control the stem cell adhesive machinery, and which allows us to mimic the dynamic conditions of the stem cell niche.

Image: Stimuli-responsive polymers are used to spatio-temporally control cell-cell and cell-ECM interactions in the microenvironment