Meet the editor

Dr. Brajesh Kumar is currently an assistant professor and head in the Department of Chemistry, TATA College, Kolhan University, Chaibasa, India. He received a Ph.D. in Chemistry from the University of Delhi, India, in 2009. His research interests include the development of sustainable and eco-friendly techniques for nanoparticle synthesis and their applications for environmental remediation, nanofibers, nanocomposites, nanomedicine,

sensors, active films of organic solar cells, natural product extraction, purification and analysis, natural polymers, peptide chemistry, microwave- and ultrasound-assisted organic synthesis, and organic synthesis. Dr. Kumar has several national and international fellowships to his credit and has worked as a faculty member in various universities throughout India, Ecuador, and South Korea. He has also published numerous research articles and is an active reviewer of more than seventy journals. He is also included in the top 2% of scientists (2021) ranked by Stanford University, USA, and Elsevier.

Contents

*and Ashwani Sharma*

*by Pradeep Sharma*

Wood Composites

*by Basel Younes*

**Preface XI**

**Chapter 1 1**

**Chapter 2 21**

**Chapter 3 57**

**Chapter 4 73**

**Chapter 5 95**

**Chapter 6 111**

**Chapter 7 133**

Eco-Friendly and Biodegradable Green Composites *by Kalmanje Mugdha Bhat, Jyothsana Rajagopalan, Rajeshwari Mallikarjunaiah, Nagashree Nagaraj Rao*

Opportunity of Non-Wood Forest Products in Biocomposites

Functionality Based Design of Sustainable Bio-Composite

*by Sushant Kumar, Swarnima Pandey and NV Satheesh Madhav*

Properties of High-Density Polyethylene-Polypropylene

Characterization, Modeling and the Production Processes

Medicinal Uses with Immense Economic Potential and Nutritional

*by Mourad Saddem, Ahmed Koubaa and Bernard Riedl*

*by MD Rajbanul Akhond and Ahmed Sharif*

Biopolymer: A Novel Bioexcipient

of Biopolymers in the Textiles Industry

Properties of *Aegle marmelos*: A Concise Review *by Harekrishna Mahato and Brajesh Kumar*


4.2 Normal and shear strength calibration for parallel bond

Normal strength and shear strength (σc and τc) for parallel bond are the two major micro-parameters contributing to the material's compressive strength. Three typical calibration tests were carried out: varying normal strength, varying shear strength, and varying both with a constant relative ratio. The relationship between compressive strength and microstrength is shown in the Figure 10.

Figure 10. Relation between macro-compressive strength and micro-strength.

As illustrated in Figure 10, the macro compressive strength depends on both normal and shear strength of the contact balls, while normal strength contributes a little more. An important feature for this case is that it is the smaller one of these two micro-parameters controls the upper limit of the macro-strength, i.e. the compressive strength cannot increase when either one of the micro strengths stay at a constant level.

For Young's modulus and Poisson's ratio, neither the normal nor the shear strength of particles has much contribution in the normal range. However, when both these two micro strengths decrease to very small values, the Young's modulus and Poisson's ratio have a little more influence.

The empirical discoveries found in the above calibration test can be used to form concrete target with the required mechanical property, although the calibration still needs to be conducted step by step. This is because different micro-variable changes may result in similar macro-property, and the changing magnitudes probably vary widely as other parameters vary.


5. Heat pipe experiments

structures made form Cu powder with grain size 50 μm and 100 μm and two wick structures

Figure 17. Influence of the wick structure on LHP cooling efficiency with working fluid water depending on loaded heat.

Comparing the results of dependence of temperature on input power of IGBT cooled by LHP with variants of sintered wick structure, the LHP with nickel wick structure does not show so good properties of heat removal than LHP with copper wick structure. Comparing the temperature curves of the LHP with first wick structure (made of Cu powder 50 μm) and LHP with second wick structure (made of Cu powder 100 μm), it is seen that both LHP have almost the same results at heat load of up to 200 W. At higher input power than 200 W loaded in to IGBT is

made from Ni powder grain size 20 μm and 10 μm were compared.

Figure 16. Influence of working fluid amount on LHP operation.

158 Porosity - Process, Technologies and Applications

The next experiments were performed in frame scientific research of porous wick heat pipes, where the ability of heat transfer depending on wick structure and working fluid is investigated. The popularity of porous wick heat pipe and lack of experiments performed with them were the reason to realize experiment which deals with heat pipes with sintered wick structures made from copper powders. This section describes manufacturing process of wick heat pipe, experimental measurement of heat transfer ability of heat pipe, and mathematical calculation of heat transport limitation of heat pipes.


**Regulators of the Proliferation of Hematopoietic Stem and Progenitor Cells During Hematopoietic Regeneration**

Yasushi Kubota and Shinya Kimura

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/55639

#### **1. Introduction**

Adult hematopoietic stem cells (HSCs) ensure the maintenance of the HSC pool via their selfrenewal capacity, and replenish mature cells throughout life via their proliferation and differentiation into lineage-restricted cells [1, 2]. HSCs are the only stem cells that have been used in the clinic to treat diseases, such as leukemia, germ cell tumors, and congenital immunodeficiencies. Since HSCs were first proposed [3], advances in multicolor flow cytom‐ etry have allowed the purification of mouse HSCs close to homogeneity. Several groups have succeeded in long-term hematopoietic reconstitution by transplanting a single lineage of HSCs (e.g., CD34low/- Kit+ Sca-1+ lineage marker-negative cells and CD150+ CD48- Kit+ Sca-1+ lineage marker-negative cells), providing direct proof of the existence of HSCs [4-7]. More recently, two groups analyzed the cycling status of HSCs by monitoring their proliferation rate over several months in vivo. The results of these studies suggested the presence of dormant HSCs that divide only about five times throughout the mouse life span [8, 9].

In the bone marrow (BM), HSCs are located in a specialized microenvironment, called the niche. Under steady-state conditions, signals from niches maintain some HSCs in a dormant state. Acquisition of dormancy is critical for the preservation of the self-renewal ability of HSCs and for the prevention of premature stem cell exhaustion [10-12]. However, in response to external stresses, such as bleeding, myeloablative chemotherapy and total body irradiation, HSCs proliferate extensively to produce very large numbers of primitive progenitor cells, thereby enabling rapid hematological regeneration [13]. Once recovery from myelosuppres‐ sion or other stresses has been achieved, the activated HSCs return to a quiescent state via a number of negative feedback mechanisms [14]. This ability is a hallmark of HSCs and is

© 2013 Kubota and Kimura; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

fundamental for the maintenance of hematopoietic function throughout the life of the organ‐ ism. Although this property has long been recognized and is very important for organism survival, the molecular basis underlying how HSCs react to a hematologic emergency remains enigmatic. However, some key players have been identified. In this chapter, we briefly review the recent advances in our knowledge of HSC cell-intrinsic and cell-extrinsic regulators that are critical for hematopoietic regeneration under stress hematopoiesis.

**2.3. Necdin**

**2.4. Slug**

SLAM, and EPCR+

Necdin belongs to the melanoma antigen family of molecules, whose physiological roles have not been well characterized [25]. Necdin was originally identified as a gene product induced in neurally differentiated embryonal carcinoma cells [26]. Interestingly, recent genetic analyses demonstrate that aberrant genomic imprinting of *NDN* on the human 15q11-q13 chromosomal region is, at least in part, responsible for the pathogenesis of Prader-Willi syndrome [27-29], a disease associated with a mildly increased risk of myeloid leukemia [30]. Necdin interacts with multiple cell cycle-related proteins, such as SV-40 large T antigen, adenovirus E1A, E2F1, and p53 [31-34]. We reported that necdin is one of 32 genes that show higher expression in HSCs than in differentiated hematopoietic cells [35]. Other groups also found that necdin is highly expressed in HSCs [36, 37]. Necdin-deficient mice show accelerated recovery of hematopoietic systems after myelosuppressive stress, such as after 5-FU treatment and BM transplantation, whereas no overt abnormality is seen under conditions of steady-state hematopoiesis. As necdin is a potential negative cell cycle regulator, the enhanced hematologic recovery in necdin-null mice was suggested to result from an increase in the number of proliferating HSCs and progenitor cells. As expected, after 5-FU treatment, necdin-deficient mice had an increased number of HSCs, but this increase was transient and was observed only during the recovery phase [35]. These data suggest that the repression of necdin function in HSCs could form the basis of a novel strategy for the acceleration of hematopoietic recovery, thereby providing therapeutic benefits after clinical myelosuppressive treatments (e.g., cytoablative chemother‐ apy or HSC transplantation). Necdin is a p53 target gene, and in vitro overexpression and knockdown experiments demonstrated that necdin plays a role in the maintenance of HSC quiescence and self-renewal [37]. However, another group reported that necdin overexpres‐

Regulators of the Proliferation of Hematopoietic Stem and Progenitor Cells During Hematopoietic Regeneration

Slug is a member of the highly conserved Slug/Snail family of zinc-finger transcriptional repressors found in diverse species ranging from C. elegans to humans. SLUG is a target gene for the E2A-HLF chimeric oncoprotein in pro-B cell acute leukemia [39]. Slug is highly expressed in immature hematopoietic cells, and a study using *Slug*-/- mice revealed that slug is essential for the radioprotection of HPCs [40]. Slug is induced by p53 and protects immature hematopoietic cells from apoptosis triggered by DNA damage. Slug exerts this function by repressing Puma, a proapoptotic target of p53 [41]. Sun et al. investigated the effects of Slug under steady-state and stress hematopoiesis [42]. The numbers of HSCs (LSK, Flk2—LSK,

) and progenitor cells (multipotent progenitors: CD150—CD48—CD244+

) were comparable regardless of the Slug

http://dx.doi.org/10.5772/55639

5

CD244+

genotype under steady-state conditions. Consistent with previous reports [40, 43], they found that hematopoiesis in the BM was normal in *Slug*-/- mice, suggesting that Slug is not required for steady-state hematopoiesis. On the other hand, an *in vivo* competitive repopulation assay revealed that Slug-deficient BM cells had a higher long-term reconstitution capacity. However, HSC homing and differentiation were not affected by the deficiency of Slug. These results suggest that Slug deficiency increases HSC self-renewal. Next, to assess whether Slug dosage

;

sion does not result in enhanced HSC quiescence [38].

lineage-restricted progenitors: CD150—CD48+

#### **2. Cell-intrinsic factors**

#### **2.1. Hemeoxygenase-1**

Heme plays many important roles, such as in the promotion of proliferation and differentiation of hematopoietic progenitor cells (HPCs) [15], and in the stimulation of hematopoiesis [16, 17]. Heme oxygenase (HO) catalyzes the degradation of heme. HO-1, encoded by the *Hmox1* gene, is a stress-inducible isozyme of HO and is highly expressed in the BM and spleen [17]. Cao et al reported that the hematopoietic lineages of heterozygous HO-1-deficient mice (*HO-1*+/-) display accelerated recovery from myelotoxic injury induced by 5-FU treatment. BM transplantation experiments also revealed that mice transplanted with *HO-1*+/- BM cells reconstituted hematopoietic lineages more rapidly than those transplanted with *HO-1*+/+ BM cells. However, *HO-1*+/- HSCs could not rescue lethally irradiated recipient mice or serially reconstitute irradiated mice [18]. These results suggest that HO-1 restricts the proliferation and differentiation of HSCs/HPCs under stress conditions, and that the dysregulation of HO-1 can lead to precocious HSC exhaustion.

#### **2.2. PSF-1**

PSF-1, a partner of sld five-1, forms a multiprotein complex, termed GINS. The GINS complex contains Psf2, Psf3, and Sld5 in addition to Psf-1 [19-21]. All genes encoding this complex are evolutionally conserved and are essential for cell growth [22]. Ueno et al isolated the mouse orthlog of *PSF1* from a BM Linc-Kit+ Sca-1+ hematopoietic stem cell cDNA library and found that PSF1 was specifically expressed in immature cells including blastocysts and spermato‐ gonia. They also generated *PSF1*-/- mice lacking functional *PSF1*, which died in utero around the implantation stage [23]. In hematopoietic cells, PSF1 was highly expressed in CD34+ KSL progenitor cells but not in CD34- KSL cells. In addition, proliferating CD34+ KSL cells sorted from BM 4 days after 5-FU exposure were PSF1 positive. Next, Ueno et al investigated the function of PSF1 in hematopoiesis using *PSF1*+/- mice. The pool size of HSCs and progenitor cells was decreased in aged *PSF1*+/- mice compared to wild-type mice. Whereas young *PSF1*+/ mice showed normal hematopoiesis under steady-state conditions, 5-FU treatment was lethal in *PSF1*+/- mice as a result of a delay in the induction of HSC proliferation after BM ablation [24]. These results suggest that PSF1 is essential for the acute proliferation of HSCs during the regeneration phase after BM suppression.

#### **2.3. Necdin**

fundamental for the maintenance of hematopoietic function throughout the life of the organ‐ ism. Although this property has long been recognized and is very important for organism survival, the molecular basis underlying how HSCs react to a hematologic emergency remains enigmatic. However, some key players have been identified. In this chapter, we briefly review the recent advances in our knowledge of HSC cell-intrinsic and cell-extrinsic regulators that

Heme plays many important roles, such as in the promotion of proliferation and differentiation of hematopoietic progenitor cells (HPCs) [15], and in the stimulation of hematopoiesis [16, 17]. Heme oxygenase (HO) catalyzes the degradation of heme. HO-1, encoded by the *Hmox1* gene, is a stress-inducible isozyme of HO and is highly expressed in the BM and spleen [17]. Cao et al reported that the hematopoietic lineages of heterozygous HO-1-deficient mice (*HO-1*+/-) display accelerated recovery from myelotoxic injury induced by 5-FU treatment. BM transplantation experiments also revealed that mice transplanted with *HO-1*+/- BM cells reconstituted hematopoietic lineages more rapidly than those transplanted with *HO-1*+/+ BM cells. However, *HO-1*+/- HSCs could not rescue lethally irradiated recipient mice or serially reconstitute irradiated mice [18]. These results suggest that HO-1 restricts the proliferation and differentiation of HSCs/HPCs under stress conditions, and that the dysregulation of HO-1 can

PSF-1, a partner of sld five-1, forms a multiprotein complex, termed GINS. The GINS complex contains Psf2, Psf3, and Sld5 in addition to Psf-1 [19-21]. All genes encoding this complex are evolutionally conserved and are essential for cell growth [22]. Ueno et al isolated the mouse

that PSF1 was specifically expressed in immature cells including blastocysts and spermato‐ gonia. They also generated *PSF1*-/- mice lacking functional *PSF1*, which died in utero around the implantation stage [23]. In hematopoietic cells, PSF1 was highly expressed in CD34+

progenitor cells but not in CD34- KSL cells. In addition, proliferating CD34+ KSL cells sorted from BM 4 days after 5-FU exposure were PSF1 positive. Next, Ueno et al investigated the function of PSF1 in hematopoiesis using *PSF1*+/- mice. The pool size of HSCs and progenitor cells was decreased in aged *PSF1*+/- mice compared to wild-type mice. Whereas young *PSF1*+/ mice showed normal hematopoiesis under steady-state conditions, 5-FU treatment was lethal in *PSF1*+/- mice as a result of a delay in the induction of HSC proliferation after BM ablation [24]. These results suggest that PSF1 is essential for the acute proliferation of HSCs during the

Sca-1+ hematopoietic stem cell cDNA library and found

KSL

c-Kit+

are critical for hematopoietic regeneration under stress hematopoiesis.

**2. Cell-intrinsic factors**

4 Stem Cell Biology in Normal Life and Diseases

lead to precocious HSC exhaustion.

orthlog of *PSF1* from a BM Lin-

regeneration phase after BM suppression.

**2.2. PSF-1**

**2.1. Hemeoxygenase-1**

Necdin belongs to the melanoma antigen family of molecules, whose physiological roles have not been well characterized [25]. Necdin was originally identified as a gene product induced in neurally differentiated embryonal carcinoma cells [26]. Interestingly, recent genetic analyses demonstrate that aberrant genomic imprinting of *NDN* on the human 15q11-q13 chromosomal region is, at least in part, responsible for the pathogenesis of Prader-Willi syndrome [27-29], a disease associated with a mildly increased risk of myeloid leukemia [30]. Necdin interacts with multiple cell cycle-related proteins, such as SV-40 large T antigen, adenovirus E1A, E2F1, and p53 [31-34]. We reported that necdin is one of 32 genes that show higher expression in HSCs than in differentiated hematopoietic cells [35]. Other groups also found that necdin is highly expressed in HSCs [36, 37]. Necdin-deficient mice show accelerated recovery of hematopoietic systems after myelosuppressive stress, such as after 5-FU treatment and BM transplantation, whereas no overt abnormality is seen under conditions of steady-state hematopoiesis. As necdin is a potential negative cell cycle regulator, the enhanced hematologic recovery in necdin-null mice was suggested to result from an increase in the number of proliferating HSCs and progenitor cells. As expected, after 5-FU treatment, necdin-deficient mice had an increased number of HSCs, but this increase was transient and was observed only during the recovery phase [35]. These data suggest that the repression of necdin function in HSCs could form the basis of a novel strategy for the acceleration of hematopoietic recovery, thereby providing therapeutic benefits after clinical myelosuppressive treatments (e.g., cytoablative chemother‐ apy or HSC transplantation). Necdin is a p53 target gene, and in vitro overexpression and knockdown experiments demonstrated that necdin plays a role in the maintenance of HSC quiescence and self-renewal [37]. However, another group reported that necdin overexpres‐ sion does not result in enhanced HSC quiescence [38].

#### **2.4. Slug**

Slug is a member of the highly conserved Slug/Snail family of zinc-finger transcriptional repressors found in diverse species ranging from C. elegans to humans. SLUG is a target gene for the E2A-HLF chimeric oncoprotein in pro-B cell acute leukemia [39]. Slug is highly expressed in immature hematopoietic cells, and a study using *Slug*-/- mice revealed that slug is essential for the radioprotection of HPCs [40]. Slug is induced by p53 and protects immature hematopoietic cells from apoptosis triggered by DNA damage. Slug exerts this function by repressing Puma, a proapoptotic target of p53 [41]. Sun et al. investigated the effects of Slug under steady-state and stress hematopoiesis [42]. The numbers of HSCs (LSK, Flk2—LSK, SLAM, and EPCR+ ) and progenitor cells (multipotent progenitors: CD150—CD48—CD244+ ; lineage-restricted progenitors: CD150—CD48+ CD244+ ) were comparable regardless of the Slug genotype under steady-state conditions. Consistent with previous reports [40, 43], they found that hematopoiesis in the BM was normal in *Slug*-/- mice, suggesting that Slug is not required for steady-state hematopoiesis. On the other hand, an *in vivo* competitive repopulation assay revealed that Slug-deficient BM cells had a higher long-term reconstitution capacity. However, HSC homing and differentiation were not affected by the deficiency of Slug. These results suggest that Slug deficiency increases HSC self-renewal. Next, to assess whether Slug dosage affects HSC self-renewal capability, they performed a serial transplantation assay. *Slug*-/- BM cells showed an enhanced repopulation capacity during serial transplantation. Furthermore, the repopulating and proliferation potential of *Slug*-/- HSCs treated with 5-FU were also examined in vivo and in vitro. Slug deficiency increased the reconstituting potential of 5-FUactivated HSCs in vivo and accelerated HSC expansion in vitro. Taken together, these results suggest that Slug negatively regulates HSC self-renewal under stress hematopoiesis.

[36]. Cx43-deficiency in the BM (*Mx1*-Cre/*Cx43*flox/flox) led to impaired hematopoietic recovery after 5-FU treatment [62]. To clarify the mechanism of impaired hematopoietic regeneration after myeloablation by 5-FU, Taniguchi-Ishikawa et al generated hematopoietic-specific Cx43 (H-Cx43)-deficient mice (*Vav1*-Cre/*Cx43*flox/flox) and analyzed their hematopoietic phenotype [63]. The lack of Cx43 in hematopoiesis did not impair long-term competitive repopulation capacity but impaired hematopoietic recovery after 5-FU administration. 5-FU-treated H-Cx43-deficient HSCs failed to enter the cell cycle and showed decreased cell survival. More detailed analyses revealed that enhanced quiescence in H-Cx43-deficient HSCs treated with 5-FU is associated with up-regulation of the expression of quiescence markers, p16INK4a [64] and p38 [65], and with an increased level of intracellular reactive oxygen species (ROS).

Regulators of the Proliferation of Hematopoietic Stem and Progenitor Cells During Hematopoietic Regeneration

http://dx.doi.org/10.5772/55639

7

The same group also investigated the role of Cx43 in the BM osteoblastic niche. For this, Gonzalez-Nieto et al used conditionally osteoblast lineage-specific Cx43-deficient mice: *Col1 α1*-Cre; *Cx43*flox/flox mice (OB/P Cx43-deficient mice) [66]. The OB/P Cx43-deficient mice showed normal hematopoiesis under steady-state conditions. However, engraftment and migration of normal HSCs was impaired by the loss of Cx43 in the osteoblast lineage. Interestingly, in nonmyeloablated mice, OB/P Cx43 deficiency did not cause a homing defect but increased the endosteal lodgment of HSCs, which was associated with the expansion of Cxcl-12-expressing mesenchymal/osteolineage cells in the BM niche [67]. Another group reported that Cx43 and Cx45 gap junctions mediate the secretion of CXCL12 from BM cells, resulting in HSCs adhesion

Metalloproteinases (MMPs) modulate the extracellular matrix (ECM) environment [69-71]. Several studies have indicated that MMP-9 and MT1-MMP are important for the cleavage and inactivation of the KIT ligand (Stem cell factor: SCF) and CXCL12 during G-CSF-induced mobilization and hematopoietic recovery after cytotoxic stress in the BM [72-75]. Tissue inhibitors of the metalloproteinase (TIMP) family consist of four members (TIMP-1 to -4), all of which are endogenous regulators of metalloproteinases (MMPs) [76, 77]. Although TIMPs were initially identified as inhibitors of MMPs, recent findings suggest that they might have more diverse functions [78, 79]. Previous work suggested that TIMP-1 deficiency or enforced expression of TIMP-1 or TIMP-2 does not alter steady-state hematopoiesis and stress hemato‐ poiesis, such as those induced by G-CSF stimulation and myelotoxic insult, respectively [80]. However, Rossi et al recently found that increased expression of p53 in *TIMP-1*-/- HSCs resulted in dysregulation of the transition from G1 to S phase of the cell cycle, indicating that TIMP-1

Among TIMP family members, TIMP-3 has unique properties. TIMP-3 binds firmly to ECM, a disintegrin [82-84], and inhibits metalloproteinase domain-containing proteins, such as ADAMs and ADAMTSs (ADAM proteins with Thrombospondin Motifs) [85]. Nakajima et al found decreased expression of TIMP-3 in immune suppressor factor (ISF)/short form of ISF (ShIF)-transfected cell lines, and partial reduction of HSC-supporting activity following the restoration of TIMP-3 expression in stromal cells expressing ISF [86]. These authors also investigated the role of TIMP-3 in HSC regulation. TIMP-3 expression in BM was increased

has a role in controlling the cell cycle dynamics of LT-HSCs [81].

to stromal cells [68].

**3.2. TIMP-3**

#### **2.5. Erg**

The E-twenty-six (ETS)-related gene (ERG) belongs to the ETS family of transcription factors [44]. ERG rearrangement has been reported in acute myeloid leukemia (AML) [45] and Ewing sarcoma [46]. ERG overexpression has also been observed in prostate cancer [47]. A recent study revealed that overexpression of ERG is an adverse prognostic factor in AML with a normal karyotype [48]. More recently, the role of Erg in hematopoietic development and normal hematopoiesis was investigated. *Mld2*, an allele of the murine *Erg* gene with a missense mutation in the ETS domain-encoding region, disrupts Erg transactivation of gene expression. Mice homozygous for the *ErgMld2* allele die at midgestation because of a failure in definitive hematopoiesis [49, 50]. Ng et al studied hematopoiesis in mice heterozygous for the *ErgMld2* mutation [51]. While *Erg+/Mld2* mice showed normal steady-state hematopoiesis, *Erg+/Mld2* BM cells exhibited defective HSC self-renewal in BM transplantation or during recovery from exposure to sublethal γ-irradiation. The TPO/c-Mpl pathway is critical for the self-renewal and proliferation of HSCs [52-54]. Next, the phenotype of *Erg+/Mld2Mpl-/-* mice was examined because the Mld2 mutation was originally uncovered during a sensitized ENU mutagenesis screen of Mpl-deficient mice [49]. The double mutant mice died of BM failure following an exacerbation of a defect in HSC proliferation. Thus, Erg is required for HSC self-renewal during stress hematopoiesis. ERG is also expressed in endothelial cells [55, 56]. A recent study showed that ERG plays a role in endothelial tube formation and angiogenesis [57]. More recently, Yuan et al identified Rhoj, a Rho GTPase family member, as a novel downstream target of ERG [58]. Interestingly, Rhoj is also highly expressed in HSCs [35].

#### **3. Cell-extrinsic factors**

The interaction between HSCs and their microenvironment (niche) is essential for HSC maintenance, self-renewal, and survival. However, recent studies have revealed that the cellextrinsic factors provided by the BM niche are also important for HSC responses during hematopoietic regeneration. Some key players have been identified.

#### **3.1. Connexin-43**

The exchange of ions, metabolites, and other small molecules (up to ~1,200 Da) occurs via gap junctions. Gap junctions are configured by a large family of proteins known as connexins (Cxs). In the connexin family, connexin-43 (Cx43) is highly expressed in BM stromal cells [59], endothelial cells [7], osteoblasts [60], and mesenchymal stem cells [61]. HSCs also express Cx43 [36]. Cx43-deficiency in the BM (*Mx1*-Cre/*Cx43*flox/flox) led to impaired hematopoietic recovery after 5-FU treatment [62]. To clarify the mechanism of impaired hematopoietic regeneration after myeloablation by 5-FU, Taniguchi-Ishikawa et al generated hematopoietic-specific Cx43 (H-Cx43)-deficient mice (*Vav1*-Cre/*Cx43*flox/flox) and analyzed their hematopoietic phenotype [63]. The lack of Cx43 in hematopoiesis did not impair long-term competitive repopulation capacity but impaired hematopoietic recovery after 5-FU administration. 5-FU-treated H-Cx43-deficient HSCs failed to enter the cell cycle and showed decreased cell survival. More detailed analyses revealed that enhanced quiescence in H-Cx43-deficient HSCs treated with 5-FU is associated with up-regulation of the expression of quiescence markers, p16INK4a [64] and p38 [65], and with an increased level of intracellular reactive oxygen species (ROS).

The same group also investigated the role of Cx43 in the BM osteoblastic niche. For this, Gonzalez-Nieto et al used conditionally osteoblast lineage-specific Cx43-deficient mice: *Col1 α1*-Cre; *Cx43*flox/flox mice (OB/P Cx43-deficient mice) [66]. The OB/P Cx43-deficient mice showed normal hematopoiesis under steady-state conditions. However, engraftment and migration of normal HSCs was impaired by the loss of Cx43 in the osteoblast lineage. Interestingly, in nonmyeloablated mice, OB/P Cx43 deficiency did not cause a homing defect but increased the endosteal lodgment of HSCs, which was associated with the expansion of Cxcl-12-expressing mesenchymal/osteolineage cells in the BM niche [67]. Another group reported that Cx43 and Cx45 gap junctions mediate the secretion of CXCL12 from BM cells, resulting in HSCs adhesion to stromal cells [68].

#### **3.2. TIMP-3**

affects HSC self-renewal capability, they performed a serial transplantation assay. *Slug*-/- BM cells showed an enhanced repopulation capacity during serial transplantation. Furthermore, the repopulating and proliferation potential of *Slug*-/- HSCs treated with 5-FU were also examined in vivo and in vitro. Slug deficiency increased the reconstituting potential of 5-FUactivated HSCs in vivo and accelerated HSC expansion in vitro. Taken together, these results

The E-twenty-six (ETS)-related gene (ERG) belongs to the ETS family of transcription factors [44]. ERG rearrangement has been reported in acute myeloid leukemia (AML) [45] and Ewing sarcoma [46]. ERG overexpression has also been observed in prostate cancer [47]. A recent study revealed that overexpression of ERG is an adverse prognostic factor in AML with a normal karyotype [48]. More recently, the role of Erg in hematopoietic development and normal hematopoiesis was investigated. *Mld2*, an allele of the murine *Erg* gene with a missense mutation in the ETS domain-encoding region, disrupts Erg transactivation of gene expression. Mice homozygous for the *ErgMld2* allele die at midgestation because of a failure in definitive hematopoiesis [49, 50]. Ng et al studied hematopoiesis in mice heterozygous for the *ErgMld2* mutation [51]. While *Erg+/Mld2* mice showed normal steady-state hematopoiesis, *Erg+/Mld2* BM cells exhibited defective HSC self-renewal in BM transplantation or during recovery from exposure to sublethal γ-irradiation. The TPO/c-Mpl pathway is critical for the self-renewal and proliferation of HSCs [52-54]. Next, the phenotype of *Erg+/Mld2Mpl-/-* mice was examined because the Mld2 mutation was originally uncovered during a sensitized ENU mutagenesis screen of Mpl-deficient mice [49]. The double mutant mice died of BM failure following an exacerbation of a defect in HSC proliferation. Thus, Erg is required for HSC self-renewal during stress hematopoiesis. ERG is also expressed in endothelial cells [55, 56]. A recent study showed that ERG plays a role in endothelial tube formation and angiogenesis [57]. More recently, Yuan et al identified Rhoj, a Rho GTPase family member, as a novel downstream target of ERG [58].

The interaction between HSCs and their microenvironment (niche) is essential for HSC maintenance, self-renewal, and survival. However, recent studies have revealed that the cellextrinsic factors provided by the BM niche are also important for HSC responses during

The exchange of ions, metabolites, and other small molecules (up to ~1,200 Da) occurs via gap junctions. Gap junctions are configured by a large family of proteins known as connexins (Cxs). In the connexin family, connexin-43 (Cx43) is highly expressed in BM stromal cells [59], endothelial cells [7], osteoblasts [60], and mesenchymal stem cells [61]. HSCs also express Cx43

suggest that Slug negatively regulates HSC self-renewal under stress hematopoiesis.

Interestingly, Rhoj is also highly expressed in HSCs [35].

hematopoietic regeneration. Some key players have been identified.

**3. Cell-extrinsic factors**

**3.1. Connexin-43**

**2.5. Erg**

6 Stem Cell Biology in Normal Life and Diseases

Metalloproteinases (MMPs) modulate the extracellular matrix (ECM) environment [69-71]. Several studies have indicated that MMP-9 and MT1-MMP are important for the cleavage and inactivation of the KIT ligand (Stem cell factor: SCF) and CXCL12 during G-CSF-induced mobilization and hematopoietic recovery after cytotoxic stress in the BM [72-75]. Tissue inhibitors of the metalloproteinase (TIMP) family consist of four members (TIMP-1 to -4), all of which are endogenous regulators of metalloproteinases (MMPs) [76, 77]. Although TIMPs were initially identified as inhibitors of MMPs, recent findings suggest that they might have more diverse functions [78, 79]. Previous work suggested that TIMP-1 deficiency or enforced expression of TIMP-1 or TIMP-2 does not alter steady-state hematopoiesis and stress hemato‐ poiesis, such as those induced by G-CSF stimulation and myelotoxic insult, respectively [80]. However, Rossi et al recently found that increased expression of p53 in *TIMP-1*-/- HSCs resulted in dysregulation of the transition from G1 to S phase of the cell cycle, indicating that TIMP-1 has a role in controlling the cell cycle dynamics of LT-HSCs [81].

Among TIMP family members, TIMP-3 has unique properties. TIMP-3 binds firmly to ECM, a disintegrin [82-84], and inhibits metalloproteinase domain-containing proteins, such as ADAMs and ADAMTSs (ADAM proteins with Thrombospondin Motifs) [85]. Nakajima et al found decreased expression of TIMP-3 in immune suppressor factor (ISF)/short form of ISF (ShIF)-transfected cell lines, and partial reduction of HSC-supporting activity following the restoration of TIMP-3 expression in stromal cells expressing ISF [86]. These authors also investigated the role of TIMP-3 in HSC regulation. TIMP-3 expression in BM was increased after 5-FU injection, and addition or overexpression of TIMP-3 resulted in enhanced prolifer‐ ation of HSCs in vitro. BM regeneration after myelotoxic stress was impaired in TIMP-3 deficient mice, but was accelerated by enforced expression of TIMP-3 in vivo [87]. Another group also studied the role of TIMP-3 in hematopoiesis. They found that TIMP-3 was highly expressed in the endosteal region of the BM, the HSC niche, whereas its expression was low in HSCs and progenitor cells. They also examined the effect of human TIMP-3 (huTIMP-3) overexpression in HSCs in vivo. TIMP-3 overexpression resulted in increased myelopoiesis and decreased lymphopoiesis. Consistent with the study of Nakajima et al [87], HSC prolifer‐ ation was increased by huTIMP-3 overexpression in vitro and in vivo [88]. These results suggest that TIMP-3 is important for the cellular response to myelosuppression.

**Acknowledgements**

**Author details**

**References**

Yasushi Kubota1,2\* and Shinya Kimura1

\*Address all correspondence to<EMAIL_ADDRESS>
Medicine, Faculty of Medicine, Saga University, Japan

gy. Cell 2008; 132(4): 631-644.

273(5272): 242-245.

2256-2259.

2 Department of Transfusion Medicine, Saga University Hospital, Japan

plication. Annu Rev Immunol 2003; 21: 759-806.

niches for stem cells. Cell 2005; 121(7): 1109-1121.

mal mouse bone marrow cells. Radiat Res 1961; 14(2): 213-222.

This work was supported by a Grant-in-Aid for Young Scientists to Y.K. (no. 23791083) from

Regulators of the Proliferation of Hematopoietic Stem and Progenitor Cells During Hematopoietic Regeneration

http://dx.doi.org/10.5772/55639

9

1 Division of Hematology, Respiratory Medicine and Oncology, Department of Internal

[1] Orkin, S.H., & Zon, L. I. Hematopoiesis: An Evolving Paradigm for Stem Cell Biolo‐

[2] Kondo, M., Wagers, A.J., Manz, M.G., Prohaska, S.S., Scherer, D.C., Beilhack, G.F., et al. Biology of hematopoietic stem cells and progenitors: implications for clinical ap‐

[3] Till, J.E., & McCulloch, C. E. A direct measurement of the radiation sensitivity of nor‐

[4] Osawa, M., Hanada, K., Hamada, H. & Nakauchi, H. Long-term lymphohemato‐ poietic reconstitution by a single CD34-low/negative hematopoietic stem cell. Science 1996;

[5] Wagers, A. J., Sherwood, R. I., Christensen, J. L. & Weissman, I. L. Little evidence for developmental plasticity of adult hematopoietic stem cells. Science 2002; 297(5590):

[6] Matsuzaki, Y., Kinjo, K., Mulligan, R.C. & Okano, H. Unexpectedly efficient homing capacity of purified murine hematopoietic stem cells. Immunity 2004; 20(1): 87-93.

[7] Kiel, M.J., Yilmaz, O.H., Iwashita, T., Terhorst, C. & Morrison, S.J. SLAM family re‐ ceptors distinguish hematopoietic stem and progenitor cells and reveal endosteal

the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.

#### **3.3. Tenascin-C**

Tenascin-C (TN-C) is a large extracellular matrix (ECM) glycoprotein that is expressed mainly in the developing embryo [89]. In the adult BM, expression of TN-C is restricted to the endosteal region [90, 91]. Although TN-C-deficient mice exhibit grossly normal development, the colonyforming capacity of *TN-C*-/- BM cells is lower than that of wild-type BM cells [92]. This suggests that TN-C makes a significant contribution under stress hematopoiesis because the mononu‐ clear cell count and BM architecture of TN-C-deficient mice are essentially normal. Nakamura-Ishizu et al studied the function of TN-C during hematopoiesis in vivo using TN-C knockout mice. First, they examined the expression pattern of various ECM proteins in the BM under different conditions (steady-state, immediately after myeloablation, and during the hemato‐ poietic recovery phase). TN-C was predominantly expressed in stromal cells and endothelial cells, which are components of the BM niche, and was markedly up-regulated in the BM during hematopoietic regeneration. *TN-C*-/- mice showed defects in hematopoietic recovery after BM ablation caused by 5-FU treatment and sublethal irradiation. The transplantation of wild-type BM cells into *TN-C*-/- recipient mice demonstrated that a supporting ability of hematopoiesis in BM microenvironment lacking TN-C is inadequate for the proliferation of transplanted wildtype BM cells for the regeneration of hematopoiesis [93]. These findings suggest that TN-C is a critical component of the BM microenvironment during hematopoietic regeneration.

#### **4. Conclusions**

In this chapter, we have briefly summarized regulators that have recently been shown to be involved in the control of HSCs and progenitors during the hematopoietic regeneration phase. Recent studies have revealed that, when myelopoiesis is compromised following infection, HSC proliferation involves not only the factors described in this review, but also inflammatory signaling molecules such as interferons [94-96], tumor necrosis factor-α [97, 98], and Toll-like receptors [99-101]. Because HSC proliferation potential is critical for organism survival during stress conditions, further understanding of the mechanism of stem cell activation will be needed before stem cells can be used in regenerative medicine.

#### **Acknowledgements**

after 5-FU injection, and addition or overexpression of TIMP-3 resulted in enhanced prolifer‐ ation of HSCs in vitro. BM regeneration after myelotoxic stress was impaired in TIMP-3 deficient mice, but was accelerated by enforced expression of TIMP-3 in vivo [87]. Another group also studied the role of TIMP-3 in hematopoiesis. They found that TIMP-3 was highly expressed in the endosteal region of the BM, the HSC niche, whereas its expression was low in HSCs and progenitor cells. They also examined the effect of human TIMP-3 (huTIMP-3) overexpression in HSCs in vivo. TIMP-3 overexpression resulted in increased myelopoiesis and decreased lymphopoiesis. Consistent with the study of Nakajima et al [87], HSC prolifer‐ ation was increased by huTIMP-3 overexpression in vitro and in vivo [88]. These results

Tenascin-C (TN-C) is a large extracellular matrix (ECM) glycoprotein that is expressed mainly in the developing embryo [89]. In the adult BM, expression of TN-C is restricted to the endosteal region [90, 91]. Although TN-C-deficient mice exhibit grossly normal development, the colonyforming capacity of *TN-C*-/- BM cells is lower than that of wild-type BM cells [92]. This suggests that TN-C makes a significant contribution under stress hematopoiesis because the mononu‐ clear cell count and BM architecture of TN-C-deficient mice are essentially normal. Nakamura-Ishizu et al studied the function of TN-C during hematopoiesis in vivo using TN-C knockout mice. First, they examined the expression pattern of various ECM proteins in the BM under different conditions (steady-state, immediately after myeloablation, and during the hemato‐ poietic recovery phase). TN-C was predominantly expressed in stromal cells and endothelial cells, which are components of the BM niche, and was markedly up-regulated in the BM during hematopoietic regeneration. *TN-C*-/- mice showed defects in hematopoietic recovery after BM ablation caused by 5-FU treatment and sublethal irradiation. The transplantation of wild-type BM cells into *TN-C*-/- recipient mice demonstrated that a supporting ability of hematopoiesis in BM microenvironment lacking TN-C is inadequate for the proliferation of transplanted wildtype BM cells for the regeneration of hematopoiesis [93]. These findings suggest that TN-C is a critical component of the BM microenvironment during hematopoietic regeneration.

In this chapter, we have briefly summarized regulators that have recently been shown to be involved in the control of HSCs and progenitors during the hematopoietic regeneration phase. Recent studies have revealed that, when myelopoiesis is compromised following infection, HSC proliferation involves not only the factors described in this review, but also inflammatory signaling molecules such as interferons [94-96], tumor necrosis factor-α [97, 98], and Toll-like receptors [99-101]. Because HSC proliferation potential is critical for organism survival during stress conditions, further understanding of the mechanism of stem cell activation will be

needed before stem cells can be used in regenerative medicine.

suggest that TIMP-3 is important for the cellular response to myelosuppression.

**3.3. Tenascin-C**

8 Stem Cell Biology in Normal Life and Diseases

**4. Conclusions**

This work was supported by a Grant-in-Aid for Young Scientists to Y.K. (no. 23791083) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.

### **Author details**

Yasushi Kubota1,2\* and Shinya Kimura1

\*Address all correspondence to<EMAIL_ADDRESS>
1 Division of Hematology, Respiratory Medicine and Oncology, Department of Internal Medicine, Faculty of Medicine, Saga University, Japan

2 Department of Transfusion Medicine, Saga University Hospital, Japan

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[69] Cruz, A.C., Frank, B.T., Edwards, S.T., Dazin, P.F., Peschon, J.J., & Fang, K.C. Tumor necrosis factor-alpha-converting enzyme controls surface expression of c-Kit and sur‐ vival of embryonic stem cell-derived mast cells. J Biol Chem 2004; 279(7): 5612-5620.

[70] Mezyk, R., Bzowska, M., & Bereta, J. Structure and functions of tumor necrosis fac‐

[71] Baumann, G., Frank, S.J. Metalloproteinases and the modulation of GH signaling. J

[72] Petit, I., Szyper-Kravitz, M., Nagler, A., et al. G-CSF induces stem cell mobilization by decreasing bone marrow SDF-1 and up-regulating CXCR4. Nat Immunol 2002;

[73] Pruijt, J.F., Fibbe, W.E., Laterveer, L., et al. Prevention of interleukin-8-induced mobi‐ lization of hematopoietic progenitor cells in rhesus monkeys by inhibitory antibodies against the metalloproteinase gelatinase B (MMP-9). Proc Natl Acad Sci USA 1999;

tor-alpha converting enzyme. Acta Biochim Pol 2003; 50(3): 625-645.

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14 Stem Cell Biology in Normal Life and Diseases

[88] Shen, Y., Winkler, I.G., Barbier, V., Sims, N.A., Hendy, J., & Lévesque, J.P. Tissue in‐ hibitor of metalloproteinase-3 (TIMP-3) regulates hematopoiesis and bone formation in vivo. PLoS One. 2010; 5(9). doi:pii: e13086.

**Chapter 2**

**Hematopoietic Stem Cell Niche:**

Additional information is available at the end of the chapter

testicular *D. melanogaster* niches (Wilson & Trumpp, 2006).

Sergio P. Bydlowski, Debora Levy, Jorge M.L. Ruiz and Juliana Pereira

http://dx.doi.org/10.5772/55508

**1. Introduction**

**Role in Normal and Malignant Hematopoiesis**

A stem-cell niche can be defined as a spatial structure in which stem cells are housed and maintained by allowing self-renewal in the absence of differentiation. The concept of the stemcell niche was initially proposed in invertebrates where they were first characterized; the control of germ line stem cell maintenance and differentiation was observed in ovarian and

Hematological stem cells (HSCs) can be initially identified in the developing embryo in aortagonada-mesonephro regions, form where they migrate into the fetal liver and subsequently move into the bone marrow (BM) after birth. During development, HSCs undergo active selfrenewal to expand the pool size, but then become largely quiescent and stay in a steady state

The link between bone-marrow formation (hematopoiesis) and bone development (osteogen‐ esis) was first recognized in the 1970s. It was noted that whilst HSCs in the bone marrow drive hematopoiesis during the whole life of organisms, when they are removed from the bone marrow, they lose the ability to self-renewal, indicating similar dependence of HSCs on extrinsic signals (Lilly *et al.,* 2011). The term 'niche' used for the specific HSC bone-marrow microenvironment was first coined by Schofield (1978), who observed that HSC growth was not supported in the spleen in the same manner as in the bone marrow; he also proposed that HSCs are in intimate contact with bone, and that cell–cell contact was responsible for the

This concept has since been further developed, and it is now widely accepted that specific anatomical regions within the bone marrow comprise specialized niches for HSC development

and reproduction in any medium, provided the original work is properly cited.

© 2013 Bydlowski et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,

in adult BM, where their maintenance is tightly regulated (Oh & Kwon, 2010).

apparently unlimited proliferative capacity and inhibition of maturation of HSCs.


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**3. Results and discussion**

## **3.1. SEM and XRD Images of the Photocatalyst**

FE-SEM analysis of the particle size and shape of the synthesized TiO2 sample showed it consisted of uniform nano-particles (Fig. 5). However, some cracks were found on the surface. A major contributor to these cracks could be the greater surface tension resulting from the small diameter (0.5 mm) of the glass springs and the high-temperature sintering process. In further experiments, we decreased the temperature from 500 °C to 450 °C. At the lower temperature, there were fewer cracks on the surface but they were not eliminated completely.

**Figure 5.** SEM photographs and macroscopic morphology of the TiO2 thin film coated on a glass spring.

The left and right photographs were taken at 1000× and 50 000× magnification, respectively.

According to Scherrer's equation (Eq. 2) and XRD patterns, the particle size of TiO2 (D) was calculated to be 35 nm.

$$D = k \lambda / \beta \cos \theta \tag{2}$$

The crystalline phase of the TiO2 catalyst was analyzed by XRD (Fig. 6). All the diffraction peaks in the XRD pattern could be assigned to tetragonal anatase TiO2, with lattice constants of a=0.3785 nm, b=0.3785 nm, and c=0.9514 nm.

**Figure 6.** XRD spectrum of anatase crystalline phase of the TiO2 catalyst

#### **3.2. Effect of doped Ag/TiO2 or Ce/TiO2 on decomposition of VOCs**

346 Advanced Aspects of Spectroscopy

completely.

calculated to be 35 nm.

of a=0.3785 nm, b=0.3785 nm, and c=0.9514 nm.

**Figure 6.** XRD spectrum of anatase crystalline phase of the TiO2 catalyst

**3. Results and discussion**

**3.1. SEM and XRD Images of the Photocatalyst**

FE-SEM analysis of the particle size and shape of the synthesized TiO2 sample showed it consisted of uniform nano-particles (Fig. 5). However, some cracks were found on the surface. A major contributor to these cracks could be the greater surface tension resulting from the small diameter (0.5 mm) of the glass springs and the high-temperature sintering process. In further experiments, we decreased the temperature from 500 °C to 450 °C. At the lower temperature, there were fewer cracks on the surface but they were not eliminated

**Figure 5.** SEM photographs and macroscopic morphology of the TiO2 thin film coated on a glass spring.

The left and right photographs were taken at 1000× and 50 000× magnification, respectively. According to Scherrer's equation (Eq. 2) and XRD patterns, the particle size of TiO2 (D) was

The crystalline phase of the TiO2 catalyst was analyzed by XRD (Fig. 6). All the diffraction peaks in the XRD pattern could be assigned to tetragonal anatase TiO2, with lattice constants

*D k* / cos (2)

The characters of catalyst are important for the degradation of VOCs. Fig. 7 illustrates the degradation rates of acetone, toluene, and p-xylene (ATP) as functions of irradiation time when pure TiO2, Ag-TiO2 and Ce–TiO2 were used. As controls, blank experiments in the absence of TiO2 had been studied. The results corresponded to the flow-rate of 1 L/min, initial concentration of 0.1 mol/m3 and relative humidity of 35%. It was found that all the conversions of ATP in the TiO2/UV, Ag-TiO2/UV and Ce-TiO2/UV processes were increased with irradiation time. Table 1 shows the degradation rates for both catalysts after 8-h photocatalytic reaction. It can be seen from Fig. 7 and Table 1 that the doping of silver or cerium ions could improve the photo-activity of TiO2 effectively. Furthermore, the degradation character of the photo-catalyst was in the order Ce-TiO2>Ag-TiO2>TiO2. Besides, the results of blank experiments in the absence of TiO2 showed that the removal efficiency of ATP was very low. For example, the removal efficiency of acetone was merely 6.3% after 8 h and lower than 46.5% for pure TiO2, which means that TiO2 plays an important role in photo-catalytic reaction.

(Ag-TiO2, 5wt%)

**Figure 7.** Effect of doped Ag/Ce/TiO2 on decomposition of ATP.

**Table 1.** ATP degradation rates for different catalysts after 8 hrs.

Fig. 8 illustrated the effect of doped Ag/Ce/TiO2 on decomposition of HCHO. The conditions were as follows: flow-rate of 3 L/min, initial concentration of 0.1 mg/m3, relative humidity of 35%. It was found that conversions of HCHO in the TiO2/UV, Ag-TiO2/UV and Ce-TiO2/UV processes were increased with irradiation time. It could be seen that the doping of silver or cerium ions could improve the photo-activity of TiO2 effectively. Furthermore, the degradation character of the photo-catalyst was in the order Ce-TiO2 > Ag-TiO2 > TiO2.

**Figure 8.** Effect of doped Ag/Ce/TiO2 on decomposition of HCHO.

The reason was as follows: Ag/Ce doping could narrow the band gap. The narrower band gap will facilitate excitation of an electron from the valence band to the conduction band in the doped TiO2, thus increasing the photo-catalytic activity of the material. At the same time, silver or cerium species could create a charge imbalance, vacancies and unsaturated chemical bonds on the catalyst surface. It will lead to the increase of chemisorbed oxygen on the surface. Surface chemisorbed oxygen has been reported to be the most active oxygen, and plays an important role in oxidation reaction. Herein, silver or cerium modified TiO2 might have better activity for the oxidation of VOCs. Furthermore, samples after Ag/Ce doping treatment showed a slight change of colour from white to yellowish.

The photo-catalytic activity of Ce-TiO2 in the oxidative degradation of VOCs being higher than that of Ag-TiO2 may be explained as follows: Compared to Ag, Ce doping serves as an electron trap in the reaction because of its varied valences and special 4f level. For Ce3+-TiO2, the Ce 4 f level plays an important role in interfacial charge transfer and elimination of electron-hole recombination. So, Ce doping could enhance the electron-hole separation and the decomposition rate of VOCs could be elevated. Moreover, the valence electrons of TiO2 catalyst are excited to the conduction band by UV light, and after various other events, electrons on the TiO2 particle surface are scavenged by the molecular oxygen to produce reactive oxygen radicals. Furthermore, redox reactions between the pollutant molecules and reactive oxygen radicals happened, VOC molecules were turned into harmless inorganic compounds, such as CO2 and H2O at the end.

## **3.3. Effect of Hydrogen Peroxide**

348 Advanced Aspects of Spectroscopy

(Ce-TiO2, 5wt%)

acetone toluene p-xylene

012345678 Irradiation time(h)

Fig. 8 illustrated the effect of doped Ag/Ce/TiO2 on decomposition of HCHO. The conditions were as follows: flow-rate of 3 L/min, initial concentration of 0.1 mg/m3, relative humidity of 35%. It was found that conversions of HCHO in the TiO2/UV, Ag-TiO2/UV and Ce-TiO2/UV processes were increased with irradiation time. It could be seen that the doping of silver or cerium ions could improve the photo-activity of TiO2 effectively. Furthermore, the degradation character of the photo-catalyst was in the order Ce-TiO2 > Ag-TiO2 > TiO2.

> 02468 Irridiation time(h)

TiO2 Ag/TiO2 Ce/TiO2

Catalyst TiO2 Ag-TiO2 Ce-TiO2 *η* (acetone, %) 46.5 55.5 82.0 *η*(toluene, %) 43.2 46.4 76.2 *η* (*p*-xylene, %) 29.8 31.2 77.8

**Figure 7.** Effect of doped Ag/Ce/TiO2 on decomposition of ATP.

*η* (%)

**Table 1.** ATP degradation rates for different catalysts after 8 hrs.

**Figure 8.** Effect of doped Ag/Ce/TiO2 on decomposition of HCHO.

0

20

40

*η* (%) 60

80

100

Hydrogen peroxide is considered to have two functions in the photo-catalytic degradation. It accepts a photo-generated conduction band electron, thus promoting the charge separation, and it also forms OH•. The addition of H2O2 increases the concentration of OH• radicals since it inhibits the electron-hole recombination.

Experiments were conducted to evaluate the effect of H2O2 on the toluene/p-xylene photodegradation. The conditions were as follows: flow rate of 1 L/min, initial concentration of 0.1 mol/m3, relative humidity of 35%, and photo-catalyst of pure TiO2. As shown in Fig. 9, the removal efficiency of toluene or p-xylene increased with reaction time.

In the first 3 h, the degradation rate of toluene or p-xylene without H2O2 was higher because of the competitive adsorption between toluene or p-xylene molecules and hydrogen peroxide. Then, more reactants and/or radical molecules were produced during the photochemistry course, which led to the improvement of toluene or p-xylene decomposition. The final degradation rates of toluene and p-xylene with H2O2 were up to 97.1 and 95.4% after 8 h, respectively.

The degradation of acetone was studied with and without hydrogen peroxide (Fig. 10). Overall, the acetone removal efficiency increased with reaction time. Initially, the degradation rate of without H2O2 was higher than that of with H2O2 because of competitive adsorption between acetone and hydrogen peroxide after hydrogen peroxide addition to the

(*P*-xylene)

**Figure 9.** Effect of toluene/p-xylene degradation on hydrogen peroxide.

sample chamber (10 mL per 30 min, 30 % H2O2, RH 35 %). As the reactants and/or byproducts accumulated on the catalyst, and there was no new super-oxidation supplied, the catalyst deactivated and the degradation rate increased slowly after 2 hr. Hydroxyl radicals were produced due to the presence of hydrogen peroxide (Eq. 3). This decreased recombination of electron-hole pairs, and consequently the final acetone degradation rate was up to 91.8 % after 8 hr. Consumption of hydroxyl radical likely played an important role in deactivation of the catalyst. An appropriate volume of hydrogen peroxide could enhance the degradation rate, while too much could decrease the degradation rate (Eq. 4).

Photo-Catalytic Degradation of Volatile Organic Compounds (VOCs) over Titanium Dioxide Thin Film 351

$$\text{HO} \succ \models \text{\color{red}{\ast\ast\ast\text{ OH}}} \text{OH} \mathsf{+OH}^{\ast} \tag{3}$$

$$\text{HxO} \star \text{OH} \rightarrow \text{HxO} \star \text{HO} \text{:}\tag{4}$$

**Figure 10.** Effect of acetone degradation on hydrogen peroxide.

During deactivation the catalyst color in process without H2O2 changed from light white to khaki, while with H2O2 was light khaki. This suggests catalyst deactivation in process without H2O2 was more extensive than in with H2O2. Moreover, the change in catalyst color after the reaction indicates that the reaction occurred in the surface of the catalyst. After sintering at 390 °C for 1 h the catalyst recovered its original color. This again suggests that catalyst deactivation was due to the accumulation of reactants and by-products on the catalyst surface, which impeded degradation reactions. To compare the performance of H2O2/UV, we evaluated the potential of acetone degradation by H2O2 alone. The concentration of acetone remained almost the same over 8 h. Consequently, we concluded that H2O2 alone could not remove the VOCs.

#### **3.4. Effect of initial concentration**

350 Advanced Aspects of Spectroscopy

*η* (%)

*η* (%)

(Toluene)

H2O2 none

012345678 Irradiation time(h)

(*P*-xylene)

012345678 Irradiation time(h)

sample chamber (10 mL per 30 min, 30 % H2O2, RH 35 %). As the reactants and/or byproducts accumulated on the catalyst, and there was no new super-oxidation supplied, the catalyst deactivated and the degradation rate increased slowly after 2 hr. Hydroxyl radicals were produced due to the presence of hydrogen peroxide (Eq. 3). This decreased recombination of electron-hole pairs, and consequently the final acetone degradation rate was up to 91.8 % after 8 hr. Consumption of hydroxyl radical likely played an important role in deactivation of the catalyst. An appropriate volume of hydrogen peroxide could enhance the degradation rate, while too much could decrease

**Figure 9.** Effect of toluene/p-xylene degradation on hydrogen peroxide.

H2O2 none

the degradation rate (Eq. 4).

In order to discuss the effect of VOCs initial concentration on photo-catalytic degradation rates, we investigated the removal efficiency of ATP and HCHO under different initial concentrations. The ATP concentrations in the experiment ranged between 0.05-0.3 mol/m3. The conditions were as follows: gas flow-rate of 1 L/min, relative humidity of 35%, Cedoped TiO2 as photo-catalyst, and irradiation time of 8 hr. The results showed that the photo-catalytic degradation rates decreased with increasing ATP initial concentration, just illustrated in Fig. 11. Based on the Langmuir-Hinshelwood equation, the degradation rate decreased with increasing initial concentration while the absolute amount of degraded pollutants may increase. At higher initial concentration, the UV light might be absorbed by gaseous pollutants rather than the TiO2 particles, which led to the reduction of the photodegradation efficiency. Moreover, at different initial concentrations, acetone was easiest to be destructed, while p-xylene was difficult to be removed among ATP from gas flow.

**Figure 11.** Effect of ATP initial concentration on the photo-catalysis of ATP by TiO2.

As a main indoor pollutant, the indoor formaldehyde concentration is usually below 0.5 ppmv. It is worth discussing whether the low level of indoor HCHO can be decreased to a value below 0.1 mg/m3 (specified in the indoor air quality standard of China). So in our experiment, the HCHO concentrations in the experiment ranged between 0.1-0.5 mg/m3. The conditions were as follows: relative humidity of 35%, Ce-doped TiO2 as photo-catalyst, and irradiation time of 120min. The results showed that the photo-catalytic degradation rates decreased with increasing HCHO initial concentration, just illustrated in Fig. 12.

**Figure 12.** Effect of initial HCHO concentration on HCHO degradation by TiO2.

In gas-phase photo-catalyst, collision frequency between radicals and HCHO affected the removal efficiency. When formaldehyde molecule reaches to the catalyst surface, the photo oxidation will occur. At higher initial concentration, the UV light might be absorbed by gaseous pollutants rather than the TiO2 particles, which led to the reduction of the photodegradation efficiency.