Acknowledgements
5.5 Applications of Conductive Materials for Tissue Engineering
5.5.2 Applications for Bone Tissue Engineering
conductive film on neurite growth and branching.192 Conductive electrospun random and aligned scaffolds made of copolymer pVdF–trifluoroethylene (pVdF–trFe) showed good cell adhesion for drg neurons. however, only aligned scaffolds supported directed neurite outgrowth other than radial extension.193 human neural stem cells (hnsCs) cultured on these pVdF–
trFe substrates differentiated towards β-iii tubulin-positive cells, indi- cating neuronal cell differentiation for potential nerve tissue engineering applications.194
Cnts possess a unique array property allowing them to interact with neu- rons at a nanoscale level, and have been utilized in nerve-related research.
huang et al. developed a Cnt rope substrate to investigate the response of nsCs on the conductive substrate after electrical stimulation. the results show that the orientation of the spiral topography on the Cnt rope contrib- utes to neurite extension, and nsCs seeded on Cnt rope are differentiated towards neurons when compared with tissue culture plates (tCp). Moreover, electrically stimulated nsCs on the Cnt rope showed enhanced neuronal maturity and increased neurite outgrowth speed. their findings suggest a synergistic effect of the conductive Cnt rope substrate and electrical stimulation on promoting neurite extension as well as oriented differenti- ation of nsCs to mature neuronal cells in the application for nerve tissue engineering.195
park et al. reported a graphene substrate that showed a promotional effect on the differentiation of hnsCs into neurons. the graphene substrate was found to be a great cell-adhesion layer for persisting differentiation of hnsCs;
also, the hnsCs were more likely to differentiate toward neurons than glial cells (Figure 5.7). Moreover, the differentiated cells showed neural activity with electrical stimulation on the graphene substrate.123
Li and group’s work demonstrated that graphene films possess excellent biocompatibility for mouse hippocampal neurons. the number and average length of neurites on graphene were significantly enhanced compared to that on tCp; suggesting the potential of graphene as an implanted material for nerve tissue engineering.154 they further utilized graphene foams to fab- ricate a novel 3d porous scaffold for nsCs in vitro. the 3d graphene foam scaffold not only provides a better support for nsC growth and proliferation than two-dimensional (2d) graphene films, but also promotes the differen- tiation of nsCs to astrocytes as well as neurons. Moreover, the 3d graphene foams show good electrical coupling with differentiated nsCs for electrical stimulation. these findings indicate that the 3d graphene foams have great potential for nerve tissue engineering.127
of osteoblasts.196,217–219 therefore, a reasonable design and fabrication of 3d conductive scaffolds for bone defects, which can locally transport electrical stimuli, is eminently necessary for the development and clinical applications of bone tissue engineering.
Meng et al. synthesized a conductive membrane made of biodegradable pLLa and conductive ppy with heparin (ppy/heparin/pLLa) for the culture of osteoblast-like saos-2 cells. electrical stimulation can enhance the adhesion and proliferation of osteoblasts, and obviously increase calcium and phos- phate amounts in the mineral deposition of the membranes (Figure 5.8).
Figure 5.7 enhanced neural differentiation of hnsCs on graphene films. all scale bars represent 200 µm: (a) bright-field images of the hnsCs differenti- ated for three days (left), two weeks (middle), and three weeks (right). (b) Bright-field (top row) and fluorescence (bottom row) images of hnsCs differentiated on glass (left) and graphene (right) after one month’s dif- ferentiation. the differentiated hnsCs were immunostained with gFap (red) for astroglial cells, tuJ1 (green) for neural cells, and dapi (blue) for nuclei. (c) Cell counting per area (0.64 mm2) on graphene and glass regions after one month’s differentiation (n = 5, p < 0.001). (d) percent- age of immunoreactive cells for gFap (red) and tuJ1 (green) on glass and graphene (n = 5, p < 0.05). adapted from ref. 123 with permission from John Wiley & sons, inc.
Published on 03 May 2017 on http://pubs.rsc.org | doi:10.1039/9781788010542-00110
as well, the expression level of several osteoblast-specific markers was upreg- ulated after electrical stimulation, indicating that an electrical stimulation through a conductive substrate could be applied for bone regeneration.219 they further investigated the influence of electrical stimulation intensity on the gene activation and protein expression of two essential osteoblast mark- ers, alkaline phosphatase (aLp) and osteocalcin (oC). an electrical stimula- tion intensity of 200 mV mm−1 was found to significantly activate the gene and the relevant protein production. however, electrical stimulation of 400 mV mm−1 decreased gene production. these results suggested that specific electrical stimulation parameters, such as intensity through conductive poly- mer materials, may be utilized to regulate osteoblast markers’ production for bone tissue engineering.196
shahini et al. fabricated a 3d conductive scaffold by including a biocom- patible conductive polymer pedot:poly(4-styrene sulfonate) (pss) in the composition of bioactive glass and gelatin (Bag/gelatin). incorporation of pedot:pss strengthened the stability of the scaffold, producing enhanced Figure 5.8 nodule formation under es. Calcium stained by alizarin red s (ars) shows the formation of the mineralized nodules at week 2 and the significant growth of the nodules at week 4. the controls show fewer and smaller nodules (bar 10 µm). reprinted from Journal of Bone and Mineral Metabolism, accelerated osteoblast mineralization on a conductive substrate by multiple electrical stimulation, 29, 2011, 535–544, s. Meng, Z. Zhang and M. rouabhia, with permission from the Japanese society for Bone and Mineral research and springer.
Published on 03 May 2017 on http://pubs.rsc.org | doi:10.1039/9781788010542-00110
mechanical properties and biodegradation resistance. adult human mes- enchymal stem cells’ (hMsCs) viability was enhanced when increasing the concentration of pedot:pss in the scaffold; indicating that the as-prepared Bag/gelatin/pedot:pss scaffold is not only biocompatible but also can well support the hMsCs’ growth.197
another promising scaffold being explored for bone tissue engineering is pVdF due to its electroactivity-confirmed biocompatibility. positively charged pVdF films coated with a thin titanium layer exhibit higher cell adhesion and proliferation of MC3t3-e1 osteoblasts than uncharged pVdF films; indicat- ing the surface charge could enhance osteoblast growth.198 hMsCs cultured on electrospun pVdF scaffolds with specific electrical stimulation possess better alkaline phosphatase activity and earlier mineralization in compar- ison to tCp.199 pärssinen et al. found that the surface charge of the poled pVdF films could influence the hydrophobicity of the substrates, further inducing the conformation changes of adsorbed extracellular matrix pro- teins, which finally can be used for the regulation of stem cell adhesion and directionally osteogenic differentiation.200,201 human alveolar bone-derived cells cultured on a novel pVdF–trFe/barium titanate (Bt) membrane showed a noticeably higher mrna expression for all markers compared to those on polytetrafluoroethylene (ptFe), indicating support for the acquisition of the osteoblastic phenotype as well as upregulation of expression of apoptotic markers. these results are obtained in vitro, whereas in vivo research should be undertaken in the future to prove the promotional effect of pVdF–trFe/Bt membranes on bone formation.202 pVdF–trFe blends were subcutaneously implanted into rats, showing normal inflammatory patterns and regression of the chronic inflammatory process over 60 days, which indicate its poten- tial application for bone regeneration.84
random and aligned conductive nanofibers via embedding multiwalled carbon nanotubes (MWCnts) in biodegradable poly(d,l-lactide) (pdLa) were fabricated by shao et al. non-stimulated neonatal rat osteoblasts on the aligned nanofibers showed enhanced cell extension and better directed cell outgrowth than those on random ones. electrically stimulated osteoblasts on nanofibers grew along the electrical current route, with no difference between random and aligned fibers (Figure 5.9). these results show the syn- ergistic effect of topography and electrical stimulation of conductive sub- strates on osteoblast outgrowth for bone tissue engineering.204