The effect of varying percentage hydroxyapatite in poly(ethylmethacrylate) bone cement on human osteoblast-like cells

Protein Expression of STRO-1 Cells in Response to Different Topographic Features

Human skeletal stem cells (STRO-1 positive) display distinct responses to different topographical features. On a flat surface, skeletal cells spread, and in vitro, they typically display a polarized, fibroblast-like morphology. However, on microgrooved surfaces, these cells prefer to stretch along the grooves forming a similar morphology to in vivo, bipolarized fibroblasts. In contrast, on nanopits, these cells display a polygonal and osteoblastic phenotype. We have examined mechanotransduction events of STRO-1 positive in response to fibroblastic, microgrooved and osteogenic, controlled disorder nanopit, topographies using proteomics after 3 days in culture. Protein expression profiles were analyzed by difference gel electrophoresis to identify proteins that showed modulation of expression in response to different topographic features to assess early decision events in these cells on these discrete topographies. After only 72 hours in culture, STRO-1 positive displayed differential regulations of families of proteins involved in cell migration and proliferation. The current study indicated that osteogenic decision specific events had already occurred. Runx2 was localized in nuclei of the skeletal stem cells on the osteogenic nanopits; however, few signaling pathway changes were observed. This study demonstrated that micro- and nanotopographies activated skeletal stem cells at different times and with distinct mechanotransduction profiles.

Exposed hydroxyapatite particles on the surface of photo-crosslinked nanocomposites for promoting MC3T3 cell proliferation and differentiation

We present a systematic study for investigating the role of exposed hydroxyapatite (HA) nanoparticles in influencing surface characteristics and mouse pre-osteoblastic MC3T3-E1 cell behavior using nanocomposites prepared by photo-crosslinking poly(ε-caprolactone) diacrylate (PCLDA) with HA. PCLDA530 and PCLDA2000 synthesized from poly(ε-caprolactone) diol precursors with nominal molecular weights of 530 and 2000 g mol(-1) were used as the polymer matrices. Crosslinked PCLDA530 was amorphous while crosslinked PCLDA2000 was semi-crystalline. Crosslinked PCLDA/HA composites with different compositions of HA (10%, 20% and 30%) as well as crosslinked PCLDAs were characterized in terms of their composition-dependent physicochemical properties. The tensile, compressive and shear moduli were greatly enhanced by incorporating HA nanoparticles with the polymer matrices. The disk surfaces of original crosslinked PCLDA/HA nanocomposites were removed by cutting using a blade to expose HA nanoparticles that were embedded in the polymer substrates. The composition of HA was much higher on the cut surface, particularly in semi-crystalline crosslinked PCLDA2000/HA nanocomposites. The surface characteristics of original and cut crosslinked PCLDA/HA nanocomposites were compared and correlated with cell behavior on these nanocomposites. MC3T3-E1 cell attachment, proliferation and differentiation were significantly enhanced when the HA composition was increased in original crosslinked PCLDA/HA nanocomposites due to more bioactive HA, higher surface stiffness and rougher topography. More exposed HA on the surface of cut semi-crystalline PCLDA2000/HA nanocomposites resulted in improved hydrophilicity and significantly better MC3T3 cell attachment, proliferation and differentiation compared with the original surfaces. This study suggests that HA nanoparticles may not be fully exploited in polymer/HA nanocomposites where the top polymer surface covers the particles. The removal of this polymer layer can generate more desirable surfaces and osteoconductivity for bone repair and regeneration.

Effect of Surface Modification on Properties of Natural Hydroxyapatite/Polypropylene Composites

Cattle bone-based hydroxyapatite (HA) powders were prepared. Three types of silane coupling agents, i.e. γ-aminopropyl triethoxysilane (APES), methyl trimethoxysilane (MTMS), and γ-glycidoxypropyl trimethoxysilane (GPMS) were used to modify the HA surface. Untreated HA powders and silane-treated HA powders were utilized to produce HA/polypropylene (PP) composites containing a 60% (w/w) of HA content. Effect of filler surface modification on properties of HA/PP composites were investigated. The results suggested that treating HA surface with a silane coupling agent enhances interaction at HA-PP interface. Among the silane coupling agents used in this study, APES is, on average, the most effective agent for enhancing stiffness of HA/PP composites.

Changes in fibroblast morphology in response to nano-columns produced by colloidal lithography

In designing new biomaterials, specific chemical and topographical cues will be important in guiding cell response. Filopodia are actin-driven structures produced by cells and speculated to be involved in cell sensing of the three-dimensional environment. This report quantifies filopodia response to cylindrical nano-columns (100 nm diameter, 160 nm high) produced by colloidal lithography. Also observed were actin cytoskeleton morphology by fluorescence microscopy and filopodia morphology by electron microscopy (scanning and transmission). The results showed that the fibroblasts used produced more filopodia per microm of cell perimeter and that filopodia could often be seen to interact with the cells' nano-environment. By understanding as to which features evoke spatial reactions in cells, it may be possible to design better biomaterials.