Optimizing the osteogenicity of nanotopography using block co-polymer phase separation fabrication techniques

Biological effects of apatite nanoparticle-constructed ceramic surfaces in regulating behaviours of mesenchymal stem cells

HCA nanoparticle-constructed nanotopography in vivo mediates bone marrow MSCs to condensate and spontaneously differentiate towards the osteogenic lineage.

Individual construction of freeform-fabricated polycaprolactone scaffolds for osteogenesis

The construction of engineered bone mostly focuses on simulating the extracellular matrix (ECM) for proper biological activity. However, the complexity of architecture and the variability of the mechanical properties of natural bones are related to individual differences in age, nutritional state, mechanical loading and disease status. Defect substitutions should be normed with the host natural bone, balancing architectural and mechanical adaption, as well as biological activity. Using a freeform fabrication (FFF) method, we prepared polycaprolactone (PCL) scaffolds with different architectures. With simulation of structural and mechanical parameters of rabbit femur cancellous bone, individual defect substitution with the characteristics of the rabbit femur was obtained with high porosity and connectivity. Biological adaption

NanoTopoChip: High-throughput nanotopographical cell instruction

Surface topography is able to influence cell phenotype in numerous ways and offers opportunities to manipulate cells and tissues. In this work, we develop the Nano-TopoChip and study the cell instructive effects of nanoscale topographies. A combination of deep UV projection lithography and conventional lithography was used to fabricate a library of more than 1200 different defined nanotopographies. To illustrate the cell instructive effects of nanotopography, actin-RFP labeled U2OS osteosarcoma cells were cultured and imaged on the Nano-TopoChip. Automated image analysis shows that of many cell morphological parameters, cell spreading, cell orientation and actin morphology are mostly affected by the nanotopographies. Additionally, by using modeling, the changes of cell morphological parameters could by predicted by several feature shape parameters such as lateral size and spacing. This work overcomes the technological challenges of fabricating high quality defined nanoscale features on unprecedented large surface areas of a material relevant for tissue culture such as PS and the screening system is able to infer nanotopography - cell morphological parameter relationships. Our screening platform provides opportunities to identify and study the effect of nanotopography with beneficial properties for the culture of various cell types.

STATEMENT OF SIGNIFICANCE

The nanotopography of biomaterial surfaces can be modified to influence adhering cells with the aim to improve the performance of medical implants and tissue culture substrates. However, the necessary knowledge of the underlying mechanisms remains incomplete. One reason for this is the limited availability of high-resolution nanotopographies on relevant biomaterials, suitable to conduct systematic biological studies. The present study shows the fabrication of a library of nano-sized surface topographies with high fidelity. The potential of this library, called the 'NanoTopoChip' is shown in a proof of principle HTS study which demonstrates how cells are affected by nanotopographies. The large dataset, acquired by quantitative high-content imaging, allowed us to use predictive modeling to describe how feature dimensions affect cell morphology.

Human mesenchymal stromal cell-enhanced osteogenic differentiation by contact interaction with polyethylene terephthalate nanogratings

Among the very large number of polymeric materials that have been proposed in the field of orthopedics, polyethylene terephthalate (PET) is one of the most attractive thanks to its flexibility, thermal resistance, mechanical strength and durability. Several studies have been proposed that interface nano- or micro-structured surfaces with mesenchymal stromal cells (MSCs), demonstrating the potential of this technology for promoting osteogenesis. All these studies were carried out on biomaterials other than PET, which remains almost uninvestigated in terms of cell shaping, alignment and differentiation. Here, we study the effect of PET 350-depth nanogratings (NGs) with a ridge and lateral groove size of 500 nm (T1) or 1 μm (T2), on bone marrow-derived human MSC (hMSC) differentiation in relation to the osteogenic fate. We demonstrate that these substrates, especially T2, can promote the osteogenic phenotype more efficiently than standard flat surfaces and that this effect is more marked if cells are cultured in osteogenic medium than in basal medium. Finally, we show that the shape and disposition of calcium hydroxyapatite granules on the different substrates was influenced by the substrate symmetry, being more elongated and spatially organized on NGs than on flat surfaces.

Mesenchymal Stem Cell Fate: Applying Biomaterials for Control of Stem Cell Behavior

The materials pipeline for biomaterials and tissue engineering applications is under continuous development. Specifically, there is great interest in the use of designed materials in the stem cell arena as materials can be used to manipulate the cells providing control of behavior. This is important as the ability to "engineer" complexity and subsequent in vitro growth of tissues and organs is a key objective for tissue engineers. This review will describe the nature of the materials strategies, both static and dynamic, and their influence specifically on mesenchymal stem cell fate.

Analysis of Osteoclastogenesis/Osteoblastogenesis on Nanotopographical Titania Surfaces

A focus of orthopedic research is to improve osteointegration and outcomes of joint replacement. Material surface topography has been shown to alter cell adhesion, proliferation, and growth. The use of nanotopographical features to promote cell adhesion and bone formation is hoped to improve osteointegration and clinical outcomes. Use of block-copolymer self-assembled nanopatterns allows nanopillars to form via templated anodization with control over height and order, which has been shown to be of cellular importance. This project assesses the outcome of a human bone marrow-derived co-culture of adherent osteoprogenitors and osteoclast progenitors on polished titania and titania patterned with 15 nm nanopillars, fabricated by a block-copolymer templated anodization technique. Substrate implantation in rabbit femurs is performed to confirm the in vivo bone/implant integration. Quantitative and qualitative results demonstrate increased osteogenesis on the nanopillar substrate with scanning electron microscopy, histochemical staining, and real-time quantitative reverse-transcription polymerase chain reaction analysis performed. Osteoblast/osteoclast co-culture analysis shows an increase in osteoblastogenesis-related gene expression and reduction in osteoclastogenesis. Supporting this in vitro finding, in vivo implantation of substrates in rabbit femora indicates increased implant/bone contact by ≈20%. These favorable osteogenic characteristics demonstrate the potential of 15 nm titania nanopillars fabricated by the block-copolymer templated anodization technique.

Assessing the hierarchical structure of titanium implant surfaces

The physical texture of implant surfaces are known to be one important factor in creating a stable bone-implant interface. Simple roughness parameters (for e.g., Sa or Sz) are not entirely adequate when characterizing surfaces possessing hierarchical structure (macro, micro, and nano scales). The aim of this study was to develop an analytical approach to quantify hierarchical surface structure of implant surfaces possessing nearly identical simple roughness. Titanium alloys with macro/micro texture (MM) and macro/micro/nano texture (MMN) were chosen as model surfaces to be evaluated. There was no statistical difference (p > 0.05) in either Sa (13.56 vs. 13.43 µm) or Sz (91.74 vs. 92.39 µm) for the MM and MMN surfaces, respectively. However, when advanced filtering algorithms were applied to these datasets, a statistical difference in roughness was found between MM (Sa = 0.54 µm) and MMN (Sa = 1.06 µm; p < 0.05). Additionally, a method was developed to specifically quantify the density of surface features appearing similar in geometry to natural osteoclastic pits. This analysis revealed a significantly greater numbers of these features (i.e., valleys) on the MMN surface as compared to the MM surface. Finally, atomic force microscopy showed a rougher nano-texture on the MMN surface compared with the MM surface (p < 0.05). The results support recent published studies that show a combination of appropriate micron and nano surface results in a more robust cellular response and increased osteoblast differentiation. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1083-1090, 2016.

Comparison of human olfactory and skeletal MSCs using osteogenic nanotopography to demonstrate bone-specific bioactivity of the surfaces

Recently we identified a novel population of mesenchymal stem cells (MSCs) from human olfactory mucosa (OM-MSCs), a tissue which promotes neurogenesis throughout life, and demonstrated that they promoted CNS myelination to a greater extent than bone marrow-derived (BM)-MSCs. Previous data demonstrated that nanotopographies with a degree of disorder induce BM-MSC osteogenic differentiation. Thus, using biomaterials as non-chemical tools, we investigated if MSCs from a completely different cellular niche could be induced to differentiate similarly to nanoscale cues alone. Both MSCs differentiated into bone when cultured on nanotopographically embossed polycaprolactone (PCL) with a disordered pattern and heights but not on a "smooth" non-embossed PCL control substrate, but OM-MSC changes were at lower expression levels. Both MSCs showed similar increases in differentiation markers at the protein and mRNA level when plated on the two patterned surfaces. Thus, topographical cues from substrates with disordered patterns can up-regulate several MSC resident genes in both BM-MSCs and OM-MSCs. Moreover, antibody purified BM-MSCs had similar properties to non-purified BM-MSCs. These data suggest that MSCs from a neural cellular niche express similar bone-induced cues to BM-MSCs, suggesting that MSCs that inherently support nervous tissue can differentiate along the bone lineage in a similar manner to MSCs from a skeletal environment.

Nanotopographical Surfaces for Stem Cell Fate Control: Engineering Mechanobiology from the Bottom

During embryogenesis and tissue maintenance and repair in an adult organism, a myriad of stem cells are regulated by their surrounding extracellular matrix (ECM) enriched with tissue/organ-specific nanoscale topographical cues to adopt different fates and functions. Attributed to their capability of self-renewal and differentiation into most types of somatic cells, stem cells also hold tremendous promise for regenerative medicine and drug screening. However, a major challenge remains as to achieve fate control of stem cells in vitro with high specificity and yield. Recent exciting advances in nanotechnology and materials science have enabled versatile, robust, and large-scale stem cell engineering in vitro through developments of synthetic nanotopographical surfaces mimicking topological features of stem cell niches. In addition to generating new insights for stem cell biology and embryonic development, this effort opens up unlimited opportunities for innovations in stem cell-based applications. This review is therefore to provide a summary of recent progress along this research direction, with perspectives focusing on emerging methods for generating nanotopographical surfaces and their applications in stem cell research. Furthermore, we provide a review of classical as well as emerging cellular mechano-sensing and -transduction mechanisms underlying stem cell nanotopography sensitivity and also give some hypotheses in regard to how a multitude of signaling events in cellular mechanotransduction may converge and be integrated into core pathways controlling stem cell fate in response to extracellular nanotopography.

Influence of polymer molecular weight in osteoinductive composites for bone tissue regeneration

In bone tissue regeneration, certain polymer and calcium-phosphate-based composites have been reported to enhance some biological surface phenomena, facilitating osteoinduction. Although the crucial role of inorganic fillers in heterotopic bone formation by such materials has been shown, no reports have been published on the potential effects the polymer phase may have. The present work starts from the assumption that the polymer molecular weight regulates the fluid uptake, which determines the hydrolysis rate and the occurrence of biological surface processes. Here, two composites were prepared by extruding two different molecular weight L/D,L-lactide copolymers with calcium phosphate apatite. The lower molecular weight copolymer allowed larger fluid uptake in the composite thereof, which was correlated with a higher capacity to adsorb proteins in vitro. Further, the large fluid absorption led to a quicker composite degradation that generated rougher surfaces and enhanced ion release. Following intramuscular implantation in sheep, only the composite with the lower molecular weight polymer could induce heterotopic bone formation. Besides influencing the biological potential of composites, the molecular weight also regulated their viscoelastic behaviour under cyclic stresses. The results lead to the conclusion that designing biomaterials with appropriate physico-chemical characteristics is crucial for bone tissue regeneration in mechanical load-bearing sites.

2D and 3D nanopatterning of titanium for enhancing osteoinduction of stem cells at implant surfaces

The potential for the use of well-defined nanopatterns to control stem cell behaviour on surfaces has been well documented on polymeric substrates. In terms of translation to orthopaedic applications, there is a need to develop nanopatterning techniques for clinically relevant surfaces, such as the load-bearing material titanium (Ti). In this work, a novel nanopatterning method for Ti surfaces is demonstrated, using anodisation in combination with PS-b-P4VP block copolymer templates. The block copolymer templates allows for fabrication of titania nanodot patterns with precisely controlled dimensions and positioning which means that this technique can be used as a lithography-like patterning method of bulk Ti surfaces on both flat 2D and complex shaped 3D surfaces. In vitro studies demonstrate that precise tuning of the height of titania nanodot patterns can modulate the osteogenic differentiation of mesenchymal stem cells. Cells on both the 8 nm and 15 nm patterned surfaces showed a trend towards a greater number of the large, super-mature osteogenic focal adhesions than on the control polished Ti surface, but the osteogenic effect was more pronounced on the 15 nm substrate. Cells on this surface had the longest adhesions of all and produced larger osteocalcin deposits. The results suggest that nanopatterning of Ti using the technique of anodisation through a block copolymer template could provide a novel way to enhance osteoinductivity on Ti surfaces.

Biophysical regulation of stem cell differentiation

Bone adaptation to its mechanical environment, from embryonic through adult life, is thought to be the product of increased osteoblastic differentiation from mesenchymal stem cells. In parallel with tissue-scale loading, these heterogeneous populations of multipotent stem cells are subject to a variety of biophysical cues within their native microenvironments. Bone marrow-derived mesenchymal stem cells-the most broadly studied source of osteoblastic progenitors-undergo osteoblastic differentiation in vitro in response to biophysical signals, including hydrostatic pressure, fluid flow and accompanying shear stress, substrate strain and stiffness, substrate topography, and electromagnetic fields. Furthermore, stem cells may be subject to indirect regulation by mechano-sensing osteocytes positioned to more readily detect these same loading-induced signals within the bone matrix. Such paracrine and juxtacrine regulation of differentiation by osteocytes occurs in vitro. Further studies are needed to confirm both direct and indirect mechanisms of biophysical regulation within the in vivo stem cell niche.

Topographically targeted osteogenesis of mesenchymal stem cells stimulated by inclusion bodies attached to polycaprolactone surfaces

AIM

Bacterial inclusion bodies (IBs) are nanostructured (submicron), pseudospherical proteinaceous particles produced in recombinant bacteria resulting from ordered protein aggregation. Being mechanically stable, several physicochemical and biological properties of IBs can be tuned by appropriate selection of the producer strain and of culture conditions. It has been previously shown that IBs favor cell adhesion and surface colonization by mammalian cell lines upon decoration on materials surfaces, but how these biomaterials could influence the behavior of mesenchymal stem cells remains to be explored.

MATERIALS & METHODS

Here, the authors vary topography, stiffness and wettability using the IBs to decorate polycaprolactone surfaces on which mesenchymal stem cells are cultured.

RESULTS

The authors show that these topographies can be used to specifically target osteogenesis from mesenchymal stem cells, and through metabolomics, they show that the cells have increased energy demand during this bone-related differentiation.

CONCLUSION

IBs as topographies can be used not only to direct cell proliferation but also to target differentiation of mesenchymal stem cells.

Novel anodization technique using a block copolymer template for nanopatterning of titanium implant surfaces

Precise surface nanopatterning is a promising route for predictable control of cellular behavior on biomedical materials. There is currently a gap in taking such precision engineered surfaces from the laboratory to clinically relevant implant materials such as titanium (Ti). In this work, anodization of Ti surfaces was performed in combination with block copolymer templates to create highly ordered and tunable oxide nanopatterns. Secondary ion mass spectroscopy (SIMS) and X-ray photoelectron spectroscopy (XPS) analyses showed that the composition of the anodized structures was mainly titania with small amounts of nitrogen left from the block copolymer. It was further demonstrated that these nanopatterns can be superimposed on more complex shaped Ti surfaces such as microbeads, using the same technique. Human mesenchymal stem cells were cultured on Ti microbead surfaces, with and without nanopatterns, in vitro to study the effect of nanotopography on Ti surfaces. The results presented in this work demonstrate a promising method of producing highly defined and well-arranged surface nanopatterns on Ti implant surfaces.