Sandwich-like Microenvironments to Harness Cell/Material Interactions

Cell culture has been traditionally carried out on bi-dimensional (2D) substrates where cells adhere using ventral receptors to the biomaterial surface. ...

Universitat Politècnica de València

Biomedical Research Networking Center in Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN)

Cartilage tissue engineering using synthetic scaffolds allows maintaining mechanical integrity and withstanding stress loads in the body, as well as providing a temporary substrate to which transplanted cells can adhere.

In vivo evaluation of 3-dimensional polycaprolactone scaffolds for cartilage repair in rabbits.

Fibronectin (FN) assembles into fibrillar networks by cells through an integrin-dependent mechanism. We have recently shown that simple FN adsorption onto poly(ethyl acrylate) surfaces (PEA), but not control polymer (poly(methyl acrylate), PMA), also triggered FN organization into a physiological fibrillar network. FN fibrils exhibited enhanced biological activities in terms of myogenic differentiation compared to individual FN molecules. In the present study, we investigate the influence of topological cues on the material-driven FN assembly and the myogenic differentiation process. Aligned and random electrospun fibers were prepared. While FN fibrils assembled on the PEA fibers as they do on the smooth surface, the characteristic distribution of globular FN molecules observed on flat PMA transformed into non-connected FN fibrils on electrospun PMA, which significantly enhanced cell differentiation. The direct relationship between the fibrillar organization of FN at the material interface and the myogenic process was further assessed by preparing FN gradients on smooth PEA and PMA films. Isolated FN molecules observed at one edge of the substrate gradually interconnected with each other, eventually forming a fully developed network of FN fibrils on PEA. In contrast, FN adopted a globular-like conformation along the entire length of the PMA surface, and the FN gradient consisted only of increased density of adsorbed FN. Correspondingly, the percentage of differentiated cells increased monotonically along the FN gradient on PEA but not on PMA. This work demonstrates an interplay between material chemistry and topology in modulating material-driven FN fibrillogenesis and cell differentiation.

Effect of topological cues on material-driven fibronectin fibrillogenesis and cell differentiation.

Cells behave differently between bidimensional (2D) and tridimensional (3D) environments. While most of the in vitro cultures are 2D, most of the in vivo extracellular matrices are 3D, which encourages the development of more relevant culture conditions, seeking to provide more physiological models for biomedicine (e.g., cancer, drug discovery and tissue engineering) and further insights into any dimension-dependent biological mechanism. In this study, cells were cultured between two protein coated surfaces (sandwich-like culture). Cells used both dorsal and ventral receptors to adhere and spread, undergoing morphological changes with respect to the 2D control. Combinations of fibronectin and bovine serum albumin on the dorsal and ventral sides led to different cell morphologies, which were quantified from bright field images by calculating the spreading area and circularity. Although the mechanism underlying these differences remains to be clarified, excitation of dorsal receptors by anchorage to extracellular proteins plays a key role on cell behavior. This approach--sandwich-like culture--becomes therefore a versatile method to study cell adhesion in well-defined conditions in a quasi 3D environment.

Dorsal and ventral stimuli in cell-material interactions: effect on cell morphology.

Scaffolds for cartilage tissue engineering should promote both adequate biomechanical environment and chondrogenic stimulation. Hyaluronic acid (HA) has been used in cartilage engineering for its chondrogenic and chondroprotective properties, nevertheless its mechanical properties are limited. Influence of HA microstructure in chondrocyte response has not been addressed yet. In this work, polycaprolactone (PCL) scaffolds were modified using HA following two coating strategies: coating in one step (PCL-HA1s) yields a gel-like phase within the scaffold, whereas a two-step reaction (PCL-HA2s) yields a thin HA layer coating internal surfaces of PCL structure. Chondrocytes were seeded in the scaffolds and cultured in dedifferentiating conditions up to 3 weeks and analyzed using a total DNA assay and sulfated glycosaminoglycan (sGAG) determination assay; cell morphology and extracellular matrix secretion were assessed by electron microscopy as well as immunofluorescent imaging (collagen I, collagen II, aggrecan, CD44). Cells proliferate in all samples and no cytotoxicity is observed. PCL-HA1s shows higher sGAG production per cell than PCL and PCL-HA2s at all times. Presence of hyaluronic acid promotes qualitative expression of CD44 surface markers and aggrecan (more visible in PCL-HA1s than PCL-HA2s), whereas in dedifferentiating conditions, expression of CD44 and aggrecan can hardly be detected in pure PCL scaffolds. Collagen type II seems more prominent in PCL-HA2s; although PCL-HA2s shows markers for COL II, aggrecan and CD44, quantitative ECM production is not improved with respect to PCL. It is thus likely that CD44 activation is not sufficient for explaining the better response in PCL-HA1s.

Different hyaluronic acid morphology modulates primary articular chondrocyte behavior in hyaluronic acid-coated polycaprolactone scaffolds.

The aim of this work is to compare the effect of hydroxyapatite (HAp) or bioglass (BG) nanoparticles in a polycaprolactone composite scaffold aimed to bone regeneration. To allow a comparison of the influence of both types of fillers, scaffolds made of PCL or composites containing up to 20 % by weight HAp or BG were obtained. Scaffolds showed acceptable mechanical properties for its use and high interconnected porosity apt for cellular colonization. To study the effect of the different materials on pre-osteoblast cells differentiation, samples with 5 % mineral reinforcement, were cultured for up to 28 days in osteogenic medium. Cells proliferated in all scaffolds. Nevertheless, differentiation levels for the selected markers were higher in pure PCL scaffolds than in the composites; inclusion of bioactive particles showed no positive effects on cell differentiation. In osteogenic culture conditions, the presence of bioactive particles is thus not necessary in order to observe good differentiation.

Comparative study of PCL-HAp and PCL-bioglass composite scaffolds for bone tissue engineering.

While most of the in vivo extracellular matrices are 3D, most of the in vitro cultures are 2D--where only ventral adhesion is permitted--thus modifying cell behavior as a way to self-adaptation to this unnatural environment. We hypothesize that the excitation of dorsal receptors in cells already attached on a 2D surface (sandwich culture) could cover the gap between 2D and 3D cell-material interactions and result in a more physiological cell behavior. In this study we investigate the role of dorsal stimulation on myoblast differentiation within different poly(L-lactic acid) (PLLA) sandwich-like microenvironments, including plain material and aligned fibers. Enhanced cell differentiation levels were found for cells cultured with dorsal fibronectin-coated films. Seeking to understand the underlying mechanisms, experiments were carried out with (i) different types of dorsal stimuli (FN, albumin, FN after blocking the RGD integrin-binding site and activating dorsal cell integrin receptors), (ii) in the presence of an inhibitor of cell contractility, and (iii) increasing the frequency of culture medium changes to assess the effect of paracrine factors. Furthermore, FAK and integrin expressions, determined by Western blotting, revealed differences between cell sandwiches and 2D controls. Results show a stimuli-dependent response to dorsal excitation, proving that integrin outside-in signaling is involved in the enhanced cell differentiation. Due to their easiness and versatility, these sandwich-like systems are excellent candidates to get deeper insights into the study of 3D cell behavior and to direct cell fate within multilayer constructs.

Dorsal and ventral stimuli in sandwich-like microenvironments. Effect on cell differentiation.

Currently, cell culture systems that include nanoscale topography are widely used in order to provide cells additional cues closer to the in vivo environment, seeking to mimic the natural extracellular matrix. Electrospinning is one of the most common techniques to produce nanofiber mats. However, since many sensitive parameters play an important role in the process, a lack of reproducibility is a major drawback. Here we present a simple and robust methodology to prepare reproducible electrospun-like samples. It consists of a polydimethylsiloxane mold reproducing the fiber pattern to solvent-cast a polymer solution and obtain the final sample. To validate this methodology, poly(L-lactic) acid (PLLA) samples were obtained and, after characterisation, bioactivity and ability to direct cell response were assessed. C2C12 myoblasts developed focal adhesions on the electrospun-like fibers and, when cultured under myogenic differentiation conditions, similar differentiation levels to electrospun PLLA fibers were obtained.

Robust fabrication of electrospun-like polymer mats to direct cell behaviour.

Due to the attractive properties of poly(L-lactic acid) (PLLA) and chitosan (CHT) for tissue engineering applications, this study is aimed at analyzing the chondrogenic potential of human bone marrow-derived mesenchymal stem cells (BM-MSCs) derived from osteoarthritic (OA) patients, in pure or CHT-coated PLLA, using different coating methodologies. Although PLLA scaffolds coated in one-step (PLLA-CHT1) yielded CHT smooth pellicles filling the PLLA macropores, a two-step strategy resulted in a CHT fiber-like thin coating covering PLLA pore walls (PLLA-CHT2). Both strategies led to the incorporation of similar content of CHT and a two-fold increase in the scaffold's water uptake capacity, providing elastic moduli values comparable to the ones found for human articular cartilage. After confirming OA-derived BM-MSCs, metabolic activity in the scaffolds, the chondrogenic potential was tested at 30 and 60 days, in a chondrogenic differentiation medium. PLLA scaffolds improved the chondrogenic differentiation of BM-MSCs, regarding cell pellet conventional culture and presented a typical cartilage zonal distribution, although was not able to revert a terminal differentiation. In PLLA-CHT1, on a short term, a rather heterogeneous tissue was formed, with confined areas of either slower cell infiltration or a faster maturation, with enhanced chondrogenic phenotype. In PLLA-CHT2, a similar tissue to PLLA was obtained, albeit on the long term, these scaffolds helped to maintain a hyaline-like phenotype and prevented the advance of the hypertrophic process. These results demonstrate the importance of the scaffolds microenvironment on the cellular events of chondrogenesis.

Effect of the physicochemical properties of pure or chitosan-coated poly(L-lactic acid)scaffolds on the chondrogenic differentiation of mesenchymal stem cells from osteoarthritic patients.

Cancer research focuses increasingly on cancer stem cell study as those cells are thought to be the root of chemo and radioresistance of the most aggressive cancer types. Nevertheless, two-dimensional (2D) cell culture and even three-dimensional (3D) spheroid models, with their limited ability to reflect cell-extracellular matrix interactions, are not ideal for the study of cancer stem cells (CSCs). In this study, we establish a 3D in vitro cancer model using a synthetic and natural scaffold with tunable features and show that U87 cells cultured in this system acquire a stem-cell like phenotype.

Three-dimensional constructs using hyaluronan cell carrier as a tool for the study of cancer stem cells.

We introduced sandwich-like culture as a tool to engineer the cellular nanoenvironment by tuning protein presentation and activation of dorsal and ventral receptors. We aim at studying cell migration under more similar conditions to the 3D physiological one.

Myriam Lebourg

Center for Biomaterials and Tissue Engineering

Universitat Politècnica de València

Sandwich-like Microenvironments to Harness Cell/Material Interactions

Myriam Lebourg

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Universitat Politècnica de València

Sandwich-like Microenvironments to Harness Cell/Material Interactions

Center for Biomaterials and Tissue Engineering