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22 - Endogenous stem/progenitor cell recruitment for tissue regeneration
- from Part IV - Biological factor delivery
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- By Mildred Embree, Columbia University Medical Center, Chang Hun Lee, Columbia University Medical Center, Ziming Dong, Zhengzhou University, Mo Chen, Columbia University Medical Center, Kimi Kong, Columbia University Medical Center, Hemin Nie, Columbia University Medical Center, Avital Mendelson, Columbia University Medical Center, Bhranti Shah, Columbia University Medical Center, Shoko Cho, Columbia University Medical Center, Takahiro Suzuki, Columbia University Medical Center, Rujing Yang, Columbia University Medical Center, Nan Jiang, Columbia University Medical Center, Jeremy J. Mao, Columbia University Medical Center
- Edited by Peter X. Ma, University of Michigan, Ann Arbor
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- Book:
- Biomaterials and Regenerative Medicine
- Published online:
- 05 February 2015
- Print publication:
- 24 July 2014, pp 405-418
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- Chapter
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Summary
Introduction: stem/progenitor cell recruitment vs. transplantation
The utilization of transplanted stem cells in regenerative medicine has been studied extensively as a potential therapy to repair or replace tissues that are lost due to trauma, congenital deformities, tumor resections, or infectious diseases [1–3]. The current cell transplantation model in regenerative medicine is founded on the principle that the application of transplanted stem cells could repopulate and regenerate damaged or diseased tissues, with restored tissue functions and homeostasis. However, cell transplantation is faced with a multitude of clinical and cell culture complications including the complexity of the multistep surgical procedures, donor-site trauma, immune rejection for allogeneic and xenogeneic cells, cell phenotypic variations due to in-vitro culture techniques, potential tumorigenesis associated with long-term cell expansion, failure of exogenous cell engraftment, and uncertainties and difficulties in the regulatory approval process [4–8]. The difficulties in the clinical application of stem cell transplantation are in strong contrast to the results of multiple experimental studies that demonstrate different levels of efficacy of cell delivery in a number of disease models such as Parkinson’s disease [9, 10], blood cancers and diseases [11, 12], and muscle and spinal disorders/injuries [13, 14].
For a number of regenerative medicine applications, the use of stem cell transplantation might not be competitive with the cost-effectiveness of current clinical treatment modalities in the dental and musculoskeletal fields, including titanium joint replacements, dental implants, and operative dental procedures [15–17]. Alternatively, the concept of endogenous stem/progenitor cell recruitment in regenerative medicine is based on the idea that native stem/progenitor cells that already reside within mature tissue can be stimulated and functionally enhanced to repopulate, repair, and/or regenerate damaged tissues [18]. Relative to stem cell transplantation, the application of endogenous stem cell recruitment in regenerative medicine is still in its infancy. The combination of the use of biological factors, release technology, biomaterials, and bioengineered scaffolds to enhance endogenous stem cell recruitment seems very promising for potential use in translational regenerative medicine. However, further scientific experimentation is warranted, since many scientific questions concerning the mechanistic details remain unresolved and it will be necessary to validate the efficacy of this approach for clinical application.
Metal ions incorporated titania nanotubes for hydrocarbon oxidation
- Huifang Xu, Ganesh Vanamu, Ziming Nie, Jonathan Phillips, Yifeng Wang
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- Journal:
- MRS Online Proceedings Library Archive / Volume 876 / 2005
- Published online by Cambridge University Press:
- 15 February 2011, R9.7/P6.7
- Print publication:
- 2005
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- Article
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Present work shows that simple, standard methods of metal addition, without the need for ion implantation or other complex and expensive processes, can dramatically improve the performance of titania based structures compared to P25 for (i.e. hydrocarbon oxidation) photocatalytic reactions. In this work, Au and Pt were incorporated into titania nanotubes, and their photocatalytic activities were investigated in detail. The samples were analyzed using a JEOL FEG-2010F field emission gun scanning transmission electron microscopy (STEM) with attached Oxford Instruments' X-ray energy-dispersive spectroscopy (EDS) system and Gatan imaging filtering (GIF) system. Both high-resolution TEM (HRTEM) images and high angle annular dark-field (HAAD) images were recorded for the specimens. The performance of the samples was tested for the oxidation of acetaldehyde using a continuous flow reactor. The pure nanotube is more photoreactive than commercial P25 titania. Both Au and Pt treated nanotube samples increased the photo reactivity. The most significant result of this work is that the activity of Pt (< 1 nm) containing nanotube is more than 10 times the rate of P25, and more than 6 times the rate of the pure nanotube. However, sizes of the Au and Pt nanoparticles on the nanotube surfaces likely affected the photo-reactivity. Large size of the Au and Pt particles decreased the photo-reactivity. Specifically, the addition of platinum without formation of obvious nanoparticles on the nanotube surfaces increased the maximum activity significantly, and increased the total yield.
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