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A laboratory study of spontaneous combustion of coal:the influence ofinorganic matter and reactor sizeWiwik Sujanti,Dong-ke Zhang*CRC for New Technologies for Power Generation from Low-rank Coal,Department of Chemical Engineering,The University of Adelaide,Adelaide,SA5005,AustraliaReceived8May1998;received in revised form30September1998;accepted9October1998AbstractA laboratory investigation into the effect of inorganic matter on spontaneous combustion behaviour of a Victorian brown coal.Fourteen samples were prepared,namely,the raw coal,water-washed coal,acid-washed coal,and acid-washed coal doped with11additives.Each of the samples was then tested in an isothermal reactor to obtain its critical ambient temperature,above which spontaneous combustion occurs. The relative effectiveness of the additives was determined by comparing their critical ambient temperatures with those of the raw coal and the acid-washed coal.Potassium chloride,Montan powder,and sodium chloride were found to be the most effective inhibitors,followed by magnesium acetate,and calcium chloride.The presence of sodium nitrate and ammonium chloride in the coal samples did not show any significant influence on the spontaneous combustion.However,calcium carbonate,sodium acetate,potassium acetate,and pyrite promoted the spontaneous combustion.The effect of additive loading was also investigated for an inhibition agent(KCl)and a promotion agent (NaAc).It was revealed that the effectiveness of these promotion and inhibition agents was enhanced with an increase in the additive loading. Low-temperature oxidation kinetics were also estimated by an energy balance approach and compared with the self-heating potential of these samples.The effects of reactor size and reactor specific surface area on the critical ambient temperatures are also discussed.᭧1999Elsevier Science Ltd.All rights reserved.Keywords:Additives;Coal combustion;Reactivity;Inorganic matter;Self-heating;Spontaneous combustion1.IntroductionSelf-heating and spontaneous combustion of coal have long been known to pose a serious problem for coal produ-cers and users[1].This is because spontaneous combustion of coal can lead to loss of desirable coal properties and product,and raise concerns about safety,especially in coal stockpiles,transportation over long distances,and in underground mining[1–3].A number of studies were carried out to determine the best method of preventing the spontaneous combustion of coal[4–6].Compaction of coal piles and inerting the atmo-sphere were applied[4].Additives,such as carbamide, diammonium phosphate,gel solution from water glass[5], aqueous solutions of inorganic salts,and salt–clay mixtures were also examined as potential inhibition agents to spon-taneous combustion[6].Smith,et al.[4]evaluated the effec-tiveness of10additives to suppress the self-heating process and revealed that sodium nitrate,sodium chloride,and calcium carbonate inhibited the spontaneous combustion, whereas sodium formate and sodium phosphate stimulated the self-heating process.The main aim of the work described in this paper was to examine the effect of inherent inorganic matter and different additives on spontaneous combustion so as to obtain a better understanding of the role of the inorganic matter in the low-temperature oxidation processes.An isothermal reactor was used to determine the critical ambient temperature,above which spontaneous ignition(thermal runaway)occurs.The critical ambient temperatures were then used to compare the tendency of various coal samples toward spontaneous combustion.An increase in the critical ambient temperature due to the use of an additive may indicate the effectiveness of the additive to suppress the self-heating potential of the coal.The effect of additive loading on the critical ambient temperature for spontaneous combustion was investigated for typical promotion and inhibition additives.Low-temperature oxidation kinetics of these coal samples are also estimated from the temperature measurements.The effects of reactor size on the critical ambient temperaturesFuel78(1999)549–556 0016-2361/99/$-see front matter᭧1999Elsevier Science Ltd.All rights reserved. PII:S0016-2361(98)00188-4*Corresponding author.Tel.:ϩ61-8-8303-5085;fax.:ϩ61-8-8303-6081.and the estimated low-temperature oxidation kinetics are also examined.2.Experimental 2.1.Coal samplesA Victorian brown coal was selected for this study,Table 1features the proximate,ultimate and inorganic analyses of the coal.The freshly picked raw coal was crushed and sieved and the 0.25–1.00mm size fraction was retained for preparation of all other samples.Double-deionised water-washed and acid-washed samples [7,8]were prepared to investigate the effect of inherent inorganic matter on the spontaneous combustion.Double-deionised waterwashing removed the water-soluble inorganic matter and acid-washing (37%HCl acid solution)removed most of the inorganic matter from the raw coal To investigate the effect of individual inorganic compo-nents in coal on spontaneous combustion,11additives were selected and,respectively,added into the acid-washed coal.They were pyrite (FeS 2),potassium acetate (KAc),sodium acetate (NaAc),calcium carbonate (CaCO 3),sodium nitrate (NaNO 3),ammonium chloride (NH 4Cl),calcium chloride (CaCl 2),magnesium acetate [Mg(Ac)2],sodium chloride (NaCl),potassium chloride (KCl),and Montan powder [CaCl 2powder ϩ3%sodium dodecyl sulphate (SDS)].Water soluble additives [KAc,NaAc,NaNO 3,NH 4Cl,CaCl 2,Mg(Ac)2,NaCl,and KG]were dissolved in double-deionised water to form solutions with a concentration of4.76wt%.2.5l of each solution and 600g of acid-washed coal were mixed to form slurry.The mass ratio of the addi-tive in a solution to the acid-washed coal was 25%.The slurry was continuously stirred for 24h.The liquid in the slurry was then allowed to drain through a filter,and the resulting paste was dried in nitrogen at 105ЊC for 8–10h.Chemical analysis confirmed that the samples prepared in such a way contain about 5wt.%additive.Water insoluble additives (FeS 2,CaCO 3,and Montan powder)were added to the coal as solid fine powder and the mixtures were well mixed.The concentration of water insoluble additives in the coal samples was 5wt.%.All the samples were stored in tightly sealed plastic bags to avoid pre-oxidation before experimentation.2.2.Experimental proceduresA sample to be tested was loosely placed in an isothermal reactor,a stainless-steel cylindrical reactor of 8cm height and 4cm diameter.Four thermocouples were inserted inside the reactor to monitor temperatures along the reactor axis.The thermocouples had a precision of ^0.1ЊC.A gas (N 2or air)was preheated in an 18m long copper tube to the oven temperature,and then passed through the coal sample from the bottom of the reactor.The oven was first preheated to a preselected temperature.During this stage,nitrogen gas passed through the reactor at 100ml min Ϫ1(N.T.P.)to minimise any pre-oxidation.Once the desired temperature was reached,air then replaced the nitrogen at the same flow rate and was maintained through-out the experiment.A data acquisition system was activated to record the temperatures.A schematic diagram of experi-mental apparatus used in this work is shown in Fig.1.In preliminary experiments,attempts were also made to follow the gas products in the exiting gas from the reactor using a gas chromatograph.However,no detectable CO or CO 2was noticed,nor was there any depletion of oxygen at temperatures of interest.This was apparently due to the low reaction temperatures (thus slow reaction rates)and the small quantity of coal samples used.Therefore,temperature measurement was chosen as the sole technique to monitor development of spontaneous combustion in these experi-ments.It was also confirmed that the four thermocouples gave exactly the same temperature reading.The experiment was terminated either when a thermal runaway occurred or when the temperature of the sample continued to level off towards the oven temperature.Typical temperature profiles of the Mg(Ac)2-added-coal are shown in Fig.2.It can be seen that at temperatures below 155ЊC,thermal runaway did not occur,so that the experiments were terminated when the average temperature along the reactor showed a trend to level off.However,at 155ЊC,thermal runaway occurred.Experiments were repeated for different oven temperatures,at a 5ЊC interval,until the critical ambi-ent temperature,T crit ,of a sample was determined.Repeat-ability of the determined T crit values was confirmed byW.Sujanti,D.Zhang /Fuel 78(1999)549–556550Table 1Proximate and ultimate of coal used [7]Proximate analysis (wt%)Moist VM (db) F.C.(db)Ash (db)61.348.348.7 3.0Ultimate analysis (wt%db)C H N O Organic sulfur S Total 67.4 4.70.726.90.260.26Fig.1.Schematic diagram of the experimental apparatus.repeating the experiments and essentially the same T crit value was obtained.Thus,for each sample,the critical ambient temperature was taken as the average of the lowest temperature at which the thermal runaway occurred and the highest temperature at which the thermal runaway did not occur,with an accuracy of^2.5ЊC.3.Results and discussion3.1.The effect of inherent inorganic matterThe presence of inorganic matter in coal may catalyse the oxidation of coal[7],and removing the inorganic matter may change the coal reactivity.Table2shows the inorganic analysis of raw,water-washed,and acid-washed coal.It is shown that water-washing only removes small amount of Na,Fe and K,while acid-washing removes most of this inorganic matter.Therefore,in this instance,the influence of inherent inorganic matter on the spontaneous combustion can be substantially eliminated by treating the raw coal with an acid.Table3shows that the critical ambient temperatures of the water-washed sample(145ЊC)and the acid-washed sample(147.5ЊC)are higher than that of the raw coal (142.5ЊC).The differences are small in relation to the accu-racy of determination but the increase in critical ambient temperature indicates that removing the inherent inorganic matter from coal helps reduce its self-heating potential.3.2.The effect of additivesTable3also shows that among the11additives used, FeS2,KAc,NaAc,and CaCO3promote the spontaneous combustion of the coal used as the relevant critical ambient temperatures are considerably lower than that of the acid-washed coal.NH4Cl and NaNO3are effectively neutral,but CaCl2and Mg(Ac)2increase the critical ambient tempera-ture for spontaneous combustion by5ЊC–152.5ЊC,and Montan powder,KCl,and NaCl push the critical ambient temperature to157.5ЊC,indicating that these additives inhi-bit the spontaneous combustion.For additives which show the same critical ambient temperatures of the samples,such as Montan powder,KCl,and NaCl,or CaCl2and Mg(Ac)2, their abilities to suppress the spontaneous combustion are compared,based on the rates of temperature rise at their critical ambient temperatures.It has been acknowledged[1,2,7,9]that FeS2in coal cata-lyses the oxidation reaction.In addition,in a moist air,FeS2 itself also experiences an exothermic oxidation reaction which helps accelerate the coal self-heating[1,2,7,9]. Sodium and potassium also catalyse the spontaneous combustion especially when they are present as organic salts[7,9].The results for FeS2,KAc and NaAc added samples used in the present study are in agreement with previously published work.The addition of CaCO3to the acid-washed coal decreases the critical ambient temperature of the acid-washed coal by 10ЊC to137.5ЊC,which could be due to the catalytic effectW.Sujanti,D.Zhang/Fuel78(1999)549–556551Fig.2.Temperature histories of Mg(Ac)2-added-coal sample at several oven temperatures.Table2Inorganic analyses of raw coal,water-washed coal,and acid-washed coalSamples Inorganic analysis(wt%db)Na Mg Fe Si Al K Ca Raw coal0.090.280.29Ͻ0.05Ͻ0.050.0070.62 Water-washed coal0.060.280.22Ͻ0.05Ͻ0.050.0060.62 Acid-washed coalϽ0.0010.0010.03Ͻ0.05Ͻ0.05Ͻ0.0020.004of the calcium on the spontaneous combustion.NaNO3does not show any effect,suggesting that sodium in an inorganic salt would have little catalytic effect when compared with its organic salts.However,these results do not agree with the previousfindings[4]that NaNO3and CaCO3inhibited spon-taneous combustion.NH4Cl was also found to have no significant effect on the spontaneous combustion behaviour of the coal,but this may be a consequence of the decom-position of the salt at100ЊC,which would eliminate any catalytic activity of the NHϩ4.In general,alkali and alkaline-earth metals in organic salts tend to promote the spontaneous combustion while inorganic salts would inhibit spontaneous combustion. However,Mg(Ac)2seems to be an exception,as it inhibits the spontaneous combustion.It was suggested[10,11]that Mg can enhance oxidation of carbon,probably at high temperatures.However,Mg2ϩmay have no catalytic effect or be a negative catalyst for the low-temperature(Ͻ200ЊC) oxidation reaction of coal.3.3.The effect of additive loadingTo investigate the effect of additive loading on promotion or inhibition of spontaneous combustion,samples with1,5, and10wt%of NaAc and KCl were prepared and tested. Table4presents the critical ambient temperatures of these samples.In general,the critical ambient temperature decreases with increasing NaAc loading,but increases with KAc loading,indicating that promotion and inhibition effects of these additives on spontaneous combustion depend on their loading levels.Although1%and5wt% NaAc loadings in the samples offered a similar critical ambient temperature,within the accuracy(^2.5ЊC)of the experiments,a closer examination of the temperature profiles during the self-heating revealed that for the5wt% NaAc loading a higher rate of temperature rise was experi-enced.Similarly,in the presence of1wt%KCl the sample showed the same critical ambient temperature as the acid-washed coal,but its rate of temperature rise was lower due to the inhibition effect of KCl.3.4.Estimation of low-temperature oxidation kineticsTo compare reactivities of the samples and correlate the reactivities with their self-heating behaviour observed in the experiments,low-temperature oxidation kinetics wereW.Sujanti,D.Zhang/Fuel78(1999)549–556552Table3Summary of critical ambient temperatures,heat of oxidation reaction,and apparent kinetic constants estimated for various samples Sample T crit(ЊC)Q(MJ kgϪ1)E(kJ molϪ1)A(kg m-3sϪ1PaϪ1)FeS2ϩcoal110.0^2.518.879.6 4.91×103KAcϩcoal125.0^2.521.8111.9 3.53×107NaAcϩcoal137.5^2.522.2109.5 1.79×107CaCO3ϩcoal137.5^2.521.2189.6 1.83×1017Raw coal142.5^2.522.9144.59.84×1010Water-washed coal145.0^2.523.7239.7 1.55×1022Acid-washed coal147.5^2.524.2164.4 2.43×1013NH4Clϩcoal147.5^2.522.6160.2 4.21×1012NaNO3ϩcoal147.5^2.522.3203.5 1.42×1018CaCl2ϩcoal152.5^2.520.3145.6 6.53×1010Mg(Ac)2ϩcoal152.5^2.522.6103.2 5.07×105Montan powderϩcoal157.5^2.520.4102.9 3.52×105KClϩcoal157.5^2.521.5109.1 2.00×106NaClϩcoal157.5^2.515.7219.57.35×1019Table4Summary of the critical ambient temperatures and kinetic constants estimated for samples with various additive loadings Sample T crit(ЊC)Q(MJ kgϪ1)E(kJ molϪ1)A(kg m-3sϪ1PaϪ1)Acid-washed coal137.5^2.524.2103.6 1.62×1061%NaAc-added-coal132.5^2.523.1180.18.92×10155%NaAc-added-coal132.5^2.522.2208.0 4.34×101910%NaAc-added-coal122.5^2.521.0256.5 5.78×10261%KCl-added-coal137.5^2.522.4164.09.03×10135%KCl-added-coal142.5^2.521.5179.5 5.64×101510%KCl-added-coal147.5^2.520.4179.1 2.45×1015estimated by an energy balance approach.The heat balance for a sample in an isothermal reactor at a point when the coal temperature is equal to the oven temperature(T o),under which condition there is no heat loss from the sample to the oven environment,can be written as:c sd Td t!oQA eϪE R T o P n O21where c is the specific heat capacity of coal[7](J kgϪ1KϪ1), 1550J kgϪ1KϪ1;s is the bulk density of coal(kg mϪ3), 1350kg mϪ3;T is the coal temperature(K)and t is time (s);Q is the heat of oxidation reaction(J kgϪ1)which was determined experimentally for each of the samples.A is the apparent pre-exponential,factor(kg mϪ3sϪ1PaϪ1)and E is the apparent activation energy(J molϪ1);R is the universalgas constant.P O2is the partial pressure of oxygen gas,which is21kPa in the present case.The apparent reaction order,n,is assumed to be1.According to Eq.(1),from a linear plot of ln[d T/d t]o versus1/T o the apparent kinetic constants,A and E,can be determined.Fig.3shows typical plots of ln[d T/d t]o versus1/ T o for the raw and acid-washed coal samples.Since it is evident that a linear relation between ln[d T/d t]o versus1/ T o does exist,and that the temperature inside the reactor is noticed to be uniform,Eq.(1)can be used as a technique for estimation of apparent kinetics of coal in such spontaneous combustion tests.Fig.4compares the Arrhenius plots of several samples in the presence of promotion agents,raw coal,water-washed, and acid-washed coal.The presence of FeS2in the coal results in the highest reactivity which corresponds to the lowest critical ambient temperature observed.The reactivity of the samples with the presence of KAc and NaAc are lower than that of the sample with FeS2,but higher than those of raw coal,water-washed,and acid-washed coal samples.However,the reactivity of the water-washed coal is higher than that of the raw coal,which is not in agreementW.Sujanti,D.Zhang/Fuel78(1999)549–556553Fig.3.Typical linear plots of ln[d T/d t]versus1/T o for the raw and acid-washed coal samples for estimation of apparent oxidation kinetics ofcoal.parison of reaction rates for various samples in temperature range of110ЊC–150ЊC,assuming an oxygen partial pressure of21kPa.with their critical ambient temperature data.To further clar-ify this,the reaction rates estimated using the calculated kinetics are plotted against the critical ambient temperatures for all samples studied in Fig.5.In general,Fig.5shows an overall trend that the lower the critical ambient temperature of a sample,the higher its oxidation reactivity.However,the data are more scattered for those samples containing the inhibition agents.The reactivities of samples with the inhi-bition agents do not show a clear trend with their critical ambient temperatures.It is possible that the assumed sample densities and specific heat capacities of the samples used in Eq.(1)may have contributed to the inconsistency in the reactivity–critical ambient temperature correlation.The varying packing density of the samples in the reactors could also have contributed to this inconsistency.However,reproducible critical ambient temperature measurements reject this argument,although the effect of packing density is of interest on its own,which will be further investigated in future studies.Further,the coal treatments,i.e.washing and additive loading,may have changed the coal structure,and thus the coal reactivity.Fig.6compares the Arrhenius plots of several samples with the presence of NaAc and KCl in various loadings.Fig.6shows that 10wt%of NaAc in the coal sample leads to the highest reactivity of the NaAc loaded samples,which corre-sponds to the critical ambient temperatures observed.Fig.6also shows that although,within the experimental accuracy,both 1and 5wt%NaAc-added-coal samples have the same critical ambient temperature,the 5wt%NaAc-added-coal sample is more reactive.The reactivities of the samples with KCl in them show the opposite trend;the higher KCl load-ing,the lower its reactivity.W.Sujanti,D.Zhang /Fuel 78(1999)549–556554Fig.5.Low-temperature oxidation rates versus the critical temperature for various samples in air at 140ЊC.Fig.6.The effect of additive loading on the estimated oxidation rates for NaAc and KCl added coal samples.4.The effect of reactor sizesTo examine the effect of reactor size on the self-heating process,three larger isothermal reactors were constructed,with 27,15and 12cm height and 9.8,8and 6cm diameter,respectively.The four isothermal reactors,R-1,R-2,R-3,and R-4,respectively,were filled with 1000,350,140and 30g of coal,and the critical ambient temperature of each reactor was determined.In general,it was observed that the critical ambient temperatures decreased with increasing coal mass.However,the correlation between the critical ambient temperatures and the coal mass is not rectilinear.Whether a spontaneous combustion occurs or not is deter-mined by two competing processes:the rate of heat genera-tion due to oxidation,and the rate of heat loss to the surroundings which depends on the external surface area.Thus,Fig.7shows that the critical ambient temperature increases linearly with specific external surface area.This suggests that for a given coal,the spontaneous combustion behaviour depends on the external heat transfer environ-ment.The apparent kinetic parameters,E and A ,from these four reactors (R-1,R-2,R-3and R-4)were also determined.It was found that the values of E obtained from these reactors are similar,i.e.106.16,105.49,107.37and 107.10kJ mol Ϫ1,respectively.However,the values of A are significantly different,i.e. 2.99×108,1.97×108,1.09×108and 1.60×107kg m Ϫ3s Ϫ1Pa Ϫ1,respectively.Fig.8shows that the smaller the reactor,thus the larger the specific exter-nal surface area,the lower the reactivities.As summarised by Chen [12]the value of A varies with temperature,and extent of reaction.It was observed during the experiments that the smaller the reactor,the higher the critical ambient temperature required for the thermal runaway to occur,and thus the more rapid the oxidation of the coal.The pre-oxidation before the thermal runaway is detected,could have caused a loss of the reactivity for smaller reactors.W.Sujanti,D.Zhang /Fuel 78(1999)549–556555Fig.7.A plot of critical temperature versus reactor specific external surfacearea.Fig.8.The effect of reactor size on the estimated reactivity of coal oxidation in air between 70ЊC and 140ЊC.5.ConclusionsWater-washing only removes a small amount of inherent inorganic matter,while acid-washing removes most of the inorganic matter in this coal.The critical ambient tempera-ture of acid-washed coal is higher than those of raw and water-washed coals,indicating the catalytic effect of inher-ent inorganic matter in the coal.Of the eleven additives applied to the acid-washed coal,FeS2,KAc,NaAc and CaCO3were found to promote the spontaneous combustion, while Montan powder,KCl,NaCl,CaCl2,and Mg(Ac)2 inhibit the spontaneous combustion.NaNO3and NH4Cl, have very little effect.The low-temperature oxidation kinetics of the samples were also estimated,and whilst the reactivities show a general trend of lower critical ambient temperature,the higher the reactivity of the sample,further investigation is required in order to improve the accuracy of the kinetic estimation.The promotion and inhibition effects of NaAc and KCl,respectively,on spontaneous combustion are enhanced with an increase in their loadings.The critical ambient temperatures were also determined for various reactor sizes.The critical ambient temperature showed a linear correlation with the reactor specific external surface area,indicating the important role of external heat transfer in the spontaneous combustion process. AcknowledgementsThe authors gratefully acknowledge thefinancial and other support received for this research from the Coopera-tive Research Centre(CRC)for New Technologies for Power Generation from Low-rank Coal,which is estab-lished and supported under the Australian Government’s Cooperative Research Centres program.Sujanti would also like to thank the CRC for a postgraduate scholarship. The authors also wish to thank Prof.Chuguang Zheng of Huazhong University of Science and Technology,China, for measurements of the heating values of the coal samples. References[1]Carras JN,Young BC.Prog Energy Combust Sci1994;20:1.[2]Glasser D,Bradshaw S.Advances in reactor design and combustionscience.In:Handbook of heat and mass transfer,vol.4.1990.p.1071.[3]Kim AG,Chaiken RF.Fire in abandoned coal mines and waste banks.Information Circular,USA Bureau of Mines,1993.[4]Smith AC,Miron Y,Lazzara CP.Inhibition of spontaneous combus-tion of coal.Report of Investigation—USA Bureau of Mines,RI 9196,1988.[5]Evseev V.Twenty-first International Conference of Safety in MinesResearch Institute,Sydney,1985.p.481.[6]Chamberlain EAC.Colliery Guardian1974;March:79.[7]Durie RA.The science of Victorian brown coal:structure,propertiesand consequences for utilisation.Oxford:Butterworth-Heinemann, 1991.p.267.[8]Ye DP.Gasification of South Australian Lignite.PhD thesis,TheUniversity of Adelaide,Adelaide,1994.p.82.[9]Banerjee SC.Spontaneous combustion of coal and minefires.Rotter-dam:A.A.Balkema,1985.p.7.[10]Jackson PJ.In:Lahaye J,Prado G,editors.Fundamentals of thephysical-chemistry of pulverised coal combustion.Dordrecht:Marti-nus Nijhoff,1987.p.273.[11]Emeleus HL,Sharpe AG.Advances in inorganic chemistry and radio-chemistry,vol.1.New York:Academic Press,1959.p.180. [12]Chen XD.Twenty-fourth Australian and New Zealand ChemicalEngineering Conference and Exhibition,vol.6.Sydney,1996.p.109.W.Sujanti,D.Zhang/Fuel78(1999)549–556 556。

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实验动物学的英文名词解释

实验动物学的英文名词解释

实验动物学的英文名词解释Experimental Animal Science: An Explanation of the English TerminologyIntroductionExperimental animal science is a branch of scientific study that focuses on the use of animals in laboratory experiments for the advancement of knowledge and the development of medical treatments. In this article, we will explore and demystify the English terminologies frequently used in this field, shedding light on their meanings and significance.1. Animal ModelsAnimal models refer to living organisms that are used to study and understand biological processes or to test experimental treatments. By replicating certain characteristics or diseases prevalent in humans, animal models allow scientists to observe, manipulate, and analyze various factors in a controlled environment. Animal models provide insights into the workings of complex biological systems, facilitating the discovery of potential therapies and advancements in medical research.2. In VivoIn vivo, a Latin term, translates to "within the living." In experimental animal science, it is used to describe research conducted within a living organism, such as an animal model. In vivo studies involve observing and analyzing the effects of interventions, substances, or phenomena directly in intact organisms, providing a more holistic understanding of biological mechanisms and physiological responses.3. In VitroIn vitro, also derived from Latin, translates to "within the glass." It refers to experiments conducted outside a living organism, typically in a controlled laboratory setting using isolated cells, tissues, or organs. In vitro studies allow scientists to observecellular or molecular processes under controlled conditions, providing initial insights into the potential effects of substances and interventions before proceeding to in vivo research.4. Animal WelfareAnimal welfare pertains to the well-being of animals used in research. It encompasses the ethical responsibilities and standards that researchers must adhere to ensure animals are treated with care, respect, and minimized suffering. Animal welfare includes considerations such as providing appropriate housing, nutrition, veterinary care, and minimizing pain and distress during experimental procedures. Adhering to high standards of animal welfare is essential to ethical research and promoting public confidence in scientific advancements.5. Ethical ReviewEthical review is the process in which research involving animals is evaluated by an ethics committee or an institutional review board. The review ensures that the proposed study adheres to ethical standards, takes into account the potential impact on animal welfare, and justifies the necessity of using animals. Ethical review boards aim to strike a balance between scientific progress and animal well-being, ensuring that research involving animals is conducted responsibly, with oversight and consideration for ethical concerns.6. Animal AlternativesAnimal alternatives refer to methods or technologies that aim to replace, reduce, or refine the use of animals in research. With advancements in science and technology, researchers increasingly explore alternative testing methods such as in silico modeling, computer simulations, and in vitro techniques. Animal alternatives not only minimize animal usage but also offer the potential for more accurate, reliable, and ethically acceptable research outcomes.ConclusionExperimental animal science involves extensive research using animal models to advance scientific knowledge and medical treatments. Understanding the terminology used in this field is crucial for effective communication and ensuring ethical practices. From animal models and in vivo studies to animal welfare and ethical reviews, each term provides insight into the complex nature of experimental animal science. Incorporating animal alternatives also serves as a progressive approach, minimizing animal usage while enhancing research outcomes. By expanding our understanding of these terms, we can foster meaningful discussions, promote ethical considerations, and drive advancements in experimental animal science.。

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Scientists embark on hunt for vaccines and medicines科学家们开始寻找疫苗和药物Parti：高级实词分类记名词类：boratory 实验室12.sample样品2.outbreak 爆发13.皿配套元件，工具3. effst努力14.genome dgLiwum 基因组4.vaccine 疫苗15. academy 9 k«hmi 学院5. vims病毒16. engineering 工程6. prevention J5 防17. availability D. veil。

bibti 可利用•性7. strain；毒株3拉紧18. emergency紧急情况8. director 主任19.priority prai9. laboratory 实验室20. approval扌滩。

10.qualification 资格21. treatment 治疗11. sputum spjuiom 痰礎词9. novel新颖的；n小说1.aimed针对的动词2. provmcial 省的 1.join加入3. microbiological微生物学的 2.isolate 隔离4. ami. virus反病毒的 3. obtain获得5. clinical临床的 4. undertake 承担6. viral病毒的 5. confirm 确认7. complex复杂的 6 announce 宣布8. innovative 创新的7. comprise 包含Pa&高级词汇拓展1.aimed 针对的vtaim2.provincial 省的n province3. viral 病毒的n virus4. complex 复杂的n complexityacademic adv academicallyavailability 可利用性 adj available adv availablyPart3：高级短语荟萃 1. join efforts 共同努力2.a vaccine against the novel corona\inis 新型冠状病毒疫苗3. manage to 设;去4. isolate strains of the virus 分高病毒株5. pave the way for work on a vaccine 为研制疫苗铺平道路6.developmem of anti-virus medicines 抗病舂药物的发展7. work on genome 基因组研究 8. be developed as 发展为 9.clinical trials 临床试验10. priority approval 优先权批准 11. set up a special team 成立专门小组 12. comprise of senior experts 由资深专家组成from home and abroad 来自国内外organize research on the new vims 组织研究新鬲毒6.innovative 创新的 v innovate prevention 预防 vt prevent qualification 资格vt qualifyacademy 学院 adj 9. 10. approval 批准⑥ V approve 11. treatment 冶疗 vt treat12. isolate 隔离 n isolation adj isolated13. confirm 确认 n confirmation adj confirmative 14. announce 宣布n announcementPart4：原汁文章思维能力提升训练双语樹读The Zhejiang Provincial Center for Disease Control and Prevention said on Monday it will soon start research and development of a vaccine against the novel coronavinis aftermanaging to isolate strains of the virus on Friday.Zhang Yanjun, director of the center s microbiological laboratory, said it obtained thequalification to undertake such research on Jan 22, and isolated the first strain from the sputum samples of a confirmed patient last week, pavmg the way for work on a vaccine and the development of anti・vuus medicines and zapid test kits.Zhang said his laboraton* was working on genome testing of the virus, but it might Take some time before the new vaccine is developed as "more clinical trials are needed”.Li Lanjuan. a member of the Chinese Academy of Engineering, said it will take at least a month to develop a vaccine for the novel corona\mis, the news website reported.At the Chinese Center fbr Disease Control and Prn ention in Beijing, researchers have startedto develop a vaccine for the novel coronavirus, the center said on Sunday.Saentists from the center have isolated ±e \inis f and are working to select the proper strainfor vaccine production, Xu Wenbo, head of the center's viral disease control and prevention institute, said.Research and development of a vaccine was complex work, he said, usually requiring between two and three years before availability fbr use. while adding it could be possible to develop a new vaccine m a feu* months in emergency conditions with priority approval.The Chinese Academy of Medical Sciences also announced on Monday that it has set up a special team comprised of senior experts from home and abroad to organize research on the new virus, including researching and developing innovative drugs and treatment.1.What is a significant step to work on a vaccine and the development of anti・virus medicinesand rapid test kits?Scientists isolating the first strain from the sputum samples of a confirmed patient paves theway for work on a vacane and the development of anti-Mius medicines and rapid test kits.2.Doest it take long to make a vaccine for the corononrus9 And why?Zhang said his laboratory was working on genome testing of the virus, but it might take some lime before the new vaccine is developed as ”more clinical trials are needed”. Research and development of a vaccine was complex work, he said, usually requiring between two and three years before availability for use.3.What is the mission of the newly・made g)«nal team according to the Chinese Academy of MedicalSciences?It has set up a special team comprised of senior experts from home and abroad to organizeresearch on the new virus, including researching and developing innovative drugs andHilltreatmentP1H5:报刊复杂切S剖析。

低氧微环境促进人嗅黏膜间充质干细胞增殖研究学习课件

低氧微环境促进人嗅黏膜间充质干细胞增殖研究学习课件


OM-MSCs可表达间充质干细胞的标记物，同时也具有自己的特点
Lindsay, S.L., Johnstone, S.A., Mountford, J.C., Sheikh, S., Allan,D.B., Clark, L., and Barnett, S.C. (2013). Human mesenchymal stem cells isolated from olfactory biopsies but not bone enhance CNS myelination in vitro. Glia 61, 368–382.
背景—干细胞春天
背景—间充质干细胞
干细胞移植治疗神 经损伤及修复一直是神 经学科界研究的热点。 目前，有研究证实胚胎 干细胞、神经干细胞、 多能干细胞等均对神经 修复治疗有效，而这些 细胞仍然存在着一些如 ：伦理、免疫排异及细 胞来源不足等问题。
间充质干细胞（MSCs）
种子细胞 Seed
背景—OM-MSCs
背景—低氧微环境
通常将小于10%的氧气浓度称为低氧，但此浓度仍比人体 正常组织及组织间隙的氧气浓度要高，人体正常组织及组织间 隙中的氧气浓度约为3%-9%，血液中氧浓度约为1%-13%，而 骨髓腔内氧气浓度仅1%-7%， 所以本实验我们选取3%O2的 微环境来培养OM-MSCs， 同时观察研究低氧对其细胞 增殖能力及细胞活性的影响。
背景—OM-MSCs安全性
通过慢病毒转染绿色荧光蛋白，转染后>98%细胞转染绿色荧光蛋白。 体内和体外致瘤的实验，在体外的软琼脂。OM-MSCs不会在软琼脂增 殖，而MKN45肿瘤细胞系会出现典型的细胞克隆球。在体外注射OMMSCs和MKN45肿瘤细胞系到免疫缺陷的小鼠上，MKN45细胞可出现 明显的肿瘤发生，而OM-MSCs注射部位未见明显肿瘤发生。
The Hidden Treasure in Apical Papilla_ The Potential Role

The Hidden Treasure in Apical Papilla_ The Potential Role

The Hidden Treasure in Apical Papilla:The Potential Role in Pulp/Dentin Regeneration and BioRoot EngineeringGeorge T.-J.Huang,DDS,MSD,DSc,*Wataru Sonoyama,DDS,PhD,§Yi Liu,DDS,PhD,‡He Liu,DDS,PhD,ʈSonglin Wang,DDS,PhD,‡and Songtao Shi,DDS,PhD†AbstractSome clinical case reports have shown that immature permanent teeth with periradicular periodontitis or ab-scess can undergo apexogenesis after conservative endodontic treatment.A call for a paradigm shift and new protocol for the clinical management of these cases has been brought to attention.Concomitantly,a new population of mesenchymal stem cells residing in the apical papilla of permanent immature teeth recently has been discovered and was termed stem cells from the apical papilla(SCAP).These stem cells appear to be the source of odontoblasts that are responsible for the formation of root dentin.Conservation of these stem cells when treating immature teeth may allow contin-uous formation of the root to completion.This article reviews current findings on the isolation and charac-terization of these stem cells.The potential role of these stem cells in the following respects will be discussed: (1)their contribution in continued root maturation in endodontically treated immature teeth with periradicu-lar periodontitis or abscess and(2)their potential uti-lization for pulp/dentin regeneration and bioroot engineering.(J Endod2008;34:645–651)Key WordsApexogenesis,apical papilla,bioroot engineering,den-tal pulp stem cells,immature teeth,periodontal liga-ment stem cells,pulp regeneration,stem cells from human exfoliated deciduous teeth,stem cells from the apical papilla A number of recent clinical case reports have revealed the possibilities that manyteeth that traditionally would receive apexification may be treated for apexogenesis.A call for a paradigm shift and new protocol for the clinical management of these cases has been made by the authors(1–3).A recent scientific finding,which may explain in part why apexogenesis can occur in these infected immature permanent teeth,is the discovery and isolation of a new population of mesenchymal stem cells(MSCs)residing in the apical papilla of incompletely developed teeth(4,5).These cells are termed stem cells from the apical papilla(SCAP),and they differentiate into odontoblast-like cells forming dentin when implanted into the subcutaneous space of immunocompromised mice using hydroxyapatite/tricalcium phosphate(HA/TCP)as a carrier vehicle(4). Although SCAP show similar characteristics to dental pulp stem cells(DPSCs)that were discovered earlier(6),they also behave differently in a number of aspects that were assessed by histologic,immunohistochemical,cellular,and molecular analyses.Evi-dence is accumulating to support the hypothesis that SCAP appear to be the source of primary odontoblasts that are responsible for the formation of root dentin,whereas DPSCs are likely the source of replacement odontoblasts.Conservation of these stem cells when treating immature teeth may allow continuous formation of the root to its completion.The goal of this review is to introduce the background of these recently described stem cells,their isolation,and characterization.The potential role of these stem cells in the contribution of the continued root maturation in endodontically treated immature teeth with periradicular periodontitis or abscess and in autotransplanted teeth are discussed.The possibility of using SCAP and other types of pulp stem cells for pulp/dentin regeneration and the combination of SCAP and periodontal ligament stem cells(PDLSCs)for bioroot engineering shown by Sonoyama et al.(4)in a swine model as a potential future clinical approach to replace dental implants will be thoroughly described and analyzed.Dental Papilla,Apical Papilla,and Pulp in Developing TeethIt is well known that dental papilla is derived from the ectomesenchyme induced by the overlaying dental lamina during tooth development(7,8).This developing organ evolves into dental pulp after being encased by the dentin tissue produced by odonto-blasts that come from this organ.The apical portion of the dental papilla during the stage of root development has not been described much in the literature.Most infor-mation regarding tooth development comes from studies using animal models.Re-cently,we described the physical and histologic characteristics of the dental papilla located at the apex of developing human permanent teeth and termed this tissue apical papilla(5).The tissue is loosely attached to the apex of the developing root and can be easily detached with a pair of tweezers(Fig.1).Apical papilla is apical to the epithelial diaphragm,and there is an apical cell-rich zone lying between the apical papilla and the pulp.Importantly,there are stem/progenitor cells located in both dental pulp and the apical papilla,but they have somewhat different characteristics(4,5).Because of the apical location of the apical papilla,this tissue may be benefited by its collateral circulation,which enables it to survive during the process of pulp necrosis.The Discovery of Multipotent SCAPStem-cell biology has become an important field for the understanding of tissue regeneration.In general,stem cells are defined by having two major properties.First, they are capable of self-renewal.Second,when they divide,some daughter cells give riseFrom the*University of Maryland,College of Dental Sur-gery,Dental School,Department of Endodontics,Prosthodon-tics and Operative Dentistry,Baltimore,Maryland;†Center forCraniofacial Molecular Biology,University of Southern Califor-nia School of Dentistry,Los Angeles,California;‡SalivaryGland Disease Center and the Molecular Laboratory for GeneTherapy,Capital Medical University School of Stomatology,Beijing,China;§Department of Oral and Maxillofacial Reha-bilitation,Okayama University Graduate School of Medicine,Dentistry and Pharmaceutical Sciences,Okayama,Japan;andʈPeking University School of Stomatology,Beijing,China.Address requests for reprints to Dr George T.-J.Huang,University of Maryland,College of Dental Surgery,DentalSchool,Department of Endodontics,Prosthodontics and Op-erative Dentistry,650West Baltimore St,Baltimore,MD21201. E-mail address: ghuang@.0099-2399/$0-see front matterCopyright©2008by the American Association ofEndodontists.doi:10.1016/j.joen.2008.03.001Review Articleto cells that either maintain stem cell character or give rise to differen-tiated cells.Mesenchymal stem cells (MSCs)have been identified in many tissues and are capable of differentiating into many lineages of cells when grown in defined conditions including osteogenic,chondro-genic,adipogenic,myogenic,and neurogenic lineages (9–11).MSCs were initially described as “fibroblast-like”in vitro as early as in the 1860s (12).Friedenstein et al.(13)in 1976further identified MSCs as colony-forming unit fibroblasts (CFU-Fs),which were able to commit into osteogenic differentiation.Caplan (14)and Pittenger et al.(15)showed that MSCs underwent osteogenic,chondrogenic,and adipo-genic differentiation in response to different biochemical signals.Bone marrow–derived mesenchymal stem cells (BMMSCs)are multipotent stem cells and have been the most studied MSCs.They undergo osteo-genic differentiation when stimulated by osteogenic reagents in vitro such as dexamethasone,␤-glycerophosphate,and bone morphogenetic proteins.More interestingly,when transplanted into immunocompro-mised mice,they are capable of forming bone and inducing recipient hematopoietic marrow components (6).So far there has been no evi-dence that BMMSCs have the capacity to undergo dentinogenic differ-entiation.The first type of human dental stem cells was isolated from dental pulp tissue of extracted third molars and characterized in com-parison with BMMSCs (6).These dental pulp–derived cells were named DPSCs for their clonogenic properties (ie,exhibiting CFU-Fs in cultures)and,more importantly,their ability to differentiate into odon-toblast-like cells and form dentin/pulp-like complex when implanted into the subcutaneous space of immunocompromised mice (6).Sub-sequently,a variety of dental MSCs have been isolated including stem cells from human exfoliated deciduous teeth (SHED)(16),periodontal ligament stem cells (PDLSCs)(17),and SCAP (4).An MSC surface marker STRO-1was found to be positive in apical papilla cells (4),which is the first piece of evidence suggesting the existence of stem cells in this ing collagenase/dispase diges-tion of detached apical papilla tissue,adherent clonogenic cell clusters (ie,CFU-Fs)are formed,similar to that observed for different MSC populations.Approximately 50single colonies can be generated from 105single cells cultured at low density (4).This colony-forming cell population showed a high uptake rate for bromodeoxyuridine (an in-dication of cell proliferation)and exhibited over 70population dou-blings in vitro.Ex vivo–expanded SCAP were also found to express the cell-surface molecule STRO-1(4).Isolated SCAP grown in cultures can undergo dentinogenic differ-entiation when stimulated with dexamethasone supplemented with L-ascorbate-2-phosphate and inorganic phosphate.Alizarin Red (a dye that binds calcium salts)–positive nodules form in the SCAP cultures after 4weeks of induction,indicating a significant calcium accumula-tion in vitro.Furthermore,cultured SCAP were found to express denti-nogenic markers dentin sialophosphoprotein and CBFA1/Runx2(4).In addition to their dentinogenic potential,SCAP also exhibit adipogenic and neurogenic differentiation capabilities when treated with respective stimuli (4,5).Human SCAP were also independently isolated andchar-Figure 1.Apical papilla.(A )An extracted human third molar depicting three immature roots with two pieces of apical papilla being removed from their apices (arrow heads)and one piece of apical papilla being peeled away from the root end but not completely detached (arrow ).(B )A developing root tip with attached apical papilla was cultured in vitro for 3days before being processed for hematoxylin and eosin (H&E)staining.Odontoblasts (black arrows ),apical cell-rich zone (open arrowheads),and apical papilla tissue are indicated.(C )Magnified view of the area indicated by the yellow rectangle.Review Articleacterized by Abe et al.(18)who found similar properties of these cells to those observed in our studies.SCAP Are a Unique Population of Postnatal Stem CellsThe capacity of SCAP to differentiate into functional dentinogenic cells in vivo has been verified using an implantation technique in animal models (4).Ex vivo–expanded SCAP were transplanted into immuno-compromised mice using particles of HA/TCP as a carrier.A typical dentin structure was generated in which a layer of dentin tissue was formed on the surface of the HA/TCP along with connective tissue (4).Cells that are responsible for the dentin formation stained positively with a human-specific antimitochondria antibody (4).In order to examine whether SCAP are distinct from DPSCs,SCAP and DPSCs from the same tooth were isolated and grown in cultures under the same conditions.It was found that SCAP showed a significantly greater bromodeoxyuridine uptake rate,number of population doublings,tissue regeneration ca-pacity,and number of STRO-1–positive cells when compared with DPSCs (4).In addition,SCAP express a higher level of survivin (anti-apoptotic protein)than DPSCs and are positive for hTERT (human telomerase reverse transcriptase that maintains the telomere length)activity (4),which is usually negative in MSCs.These lines of evidence suggest that SCAP derived from a developing tissue may represent a population of early stem/progenitor cells,which may be a superior cell source for tissue regeneration.Additionally,these cells also highlight an important fact that developing tissues may contain stem cells distinctive from that of mature tissues.Despite SCAP expressing many dentinogenic markers after ex vivo expansion,they express lower levels of dentin sialophosphoprotein,matrix extracellular phosphoglycoprotein,transforming growth factor (TGF)␤RII,FGFR3,Flt-1(vascular endothelial growth factor [VEGF]receptor 1),Flg (FGFR1),and MUC18(melanoma-associated glyco-protein)than do DPSCs (5).SCAP,as all ex vivo–expanded MSCs,are a heterogeneous population of cells.Subpopulations of STRO-1–positive SCAP are coexpressed with a variety of dentinogenic markers (5).In addition,SCAP show a positive staining for several neural markers in-cluding ␤III tubulin,glutamic acid decarboxylase,NeuN (neuronal nu-clear antigen),nestin,neurofilament M,neuron-specific enolase,and CNPase (glial marker,2=,3=-cyclic nucleotide 3=-phosphodiesterase)by immunocytochemical staining (5).The neurogenic potential of SCAPcould be because of the fact that SCAP are derived from neural crest cells or at least associated with neural crest cells analogous to other dental stem cells such as DPSCs and SHED that have been shown previously to possess a neurogenic potential (16,19).Whether the neurogenicity of dental stem cells is more potent than that of BMMSCs has not been investigated.Evidence has shown that BMMSCs have the potential for neuronal differentiation but at a much lower scale compared with stem cells derived from neural tissues (20,21).If dental stem cells are more capable of neurogenic differentiation than BMMSCs,they may present an appropriate cell source for neural tissue regeneration.The Potential Role of SCAP in Continued RootFormationThe role of apical papilla in root formation may be observed in clinical cases.A human immature incisor was injured and the crown fractured with pulp exposure.During the treatment,the apical papilla was retained while the pulp was extirpated.Continued root-tip forma-tion was observed after root canal treatment (Fig.2).Further investiga-tion is needed to verify whether the radiographic evidence of continued apical development is because of dentin formation from the apical pa-pilla or if it is merely cementum formation (3).Using minipigs as a model,a pilot experiment was conducted.Surgically removing the api-cal papilla at an early stage of the root development halted the root development despite the pulp tissue being intact.In contrast,other roots of the tooth containing apical papilla showed normal growth and devel-opment (Fig.2E ).Although the finding suggests that root apical papilla is likely to play a pivotal role in root formation,further research is needed to verify that this halted root development in the minipig was not due to damage of Hertwig’s epithelial root sheath (HERS)during the removal of the apical papilla of that particular root apex.The Potential Role of SCAP in Pulp Healing andRegenerationImmature Teeth with Periradicular Periodontitis or Abscess Uudergo ApexogenesisThere have been sporadic case reports in the literature showing the potential of root maturation even with the presence of periradicular pathoses of endodontic origin (22–27).More recently,severalclinicalFigure 2.The potential role of apical papilla in root maturation in human and minpig.(A )Human incisor crown fracture (arrows)occurred before the completion of root development.(B )Immediate root canal treatment was performed on the fractured tooth.Pulp tissue was completely removed and root canal was sealed with filling material.(C )Three months after endodontic treatment,the root tip continued to develop.(D )Seven months after treatment,a significant amount of root tip was formed.(E )When distal buccal root apical papilla of the lower first molar was surgically removed from a 9-month-old minipig,the distal buccal root stopped developing at the 3-month follow-up (black arrows ),but other roots show a normal growth and development (red arrows ).Review Articlereports with careful documentation and follow-ups have further shown that immature permanent teeth diagnosed with nonvital pulp and periradicular periodontitis or abscess can undergo apexogenesis(1–3).These recent reports challenge the traditional approach in manag-ing immature teeth by applying apexification treatment,where there is little to no expectation of continued root development.Instead,it is possible that alternative biologically based treatments may promote apexogenesis/maturogenesis.A common aspect of many of these re-ported cases is the preoperative presentation of apical periodontitis with sinus tract formation,a condition normally associated with total pulpal necrosis and infection that requires apexification.Although Iwaya et al.(1)and Banchs and Trope(2)applied the term“revascu-larization”to describe this phenomenon,what actually occurred was physiological tissue formation and regeneration.The clinical presentation of a negative response to pulpal testing with the presence of apical periodontitis is generally interpreted to indicate pulpal necrosis and infection.Lin et al.(28,29),however, found that vital tissues can even be present in pulp chambers in mature permanent teeth associated with periapical radiolucencies.The size of the lesions varies,and some may be described as moderately extensive. In the case of immature teeth,this situation could be more common, although there is a lack of histologic studies.The recent case reports of immature teeth that presented with radiolucent lesions and underwent remarkable apexogenesis after conservative treatment suggest that vital pulp tissue must have remained in the canals(1–3).Iwaya et al.(1) reported that during the treatment of an immature second mandibular premolar with a periradicular abscess,the patient felt the insertion of a smooth broach into the canal before reaching the apex suggesting a partial remaining vitality of the pulpal tissue.Thirty-five months after the treatment,the root formation was complete and the tooth responded to an electrical pulp test(1).Similarly,Chueh and Huang(3)reported four cases of immature teeth with periradicular lesions or abscess.In some of these cases,the patients either felt the entry of instruments intothe pulp chamber or there was vital pulp tissue and hemorrhage ob-served.The open apex provided a good communication from the pulp space to the periapical tissues;therefore,it may be possible for peria-pical disease to occur while the pulp is only partially necrotic and infected.Along the same line of reasoning,stem cells in pulp tissue and in apical papilla may also have survived the infection and allowed re-generation of pulp and root maturation to occur.The infection could have spread through survived pulp tissue reaching the periapex(Fig.3). Another possibility is that the bone resorption is the result of the re-leased proinflammtory cytokines from the inflamed pulp.However,this situation is less likely to cause the formation of sinus tracts,an indica-tion of abscess from severe infection.It should be noted that prolonged infection may eventually lead to a total necrosis of the pulp and apical papilla;under these conditions,apexogenesis or maturogenesis,a term that encompasses not just the completion of root-tip formation but also the dentin of the root(30),would then be unlikely.The Potential Role of SCAP in Replantation and TransplantationThe fate of human pulp space after dental trauma has been ob-served in clinical radiographs.Andreasen et al.(31,32)and Kling et al.(33)showed excellent radiographic images of the ingrowth of bone and periodontal ligament(PDL)(next to the inner dentinal wall)into the canal space with arrested root formation after the replantation of avulsed maxillary incisors,suggesting a complete loss of the viability of pulp,apical papilla,and/or HERS.Some cases showed partial formation of the root accompanied with ingrowth of bone and PDL into the canal space,and in some cases the teeth continued to develop roots to their completion,suggesting that there was partial or total pulp survival after the replantation.It is noted,however,that a pronounced narrowing of canal space is usually associated with a surviving pulp.Skoglund et al.(34)observed revascularization of the pulp of replanted and autotrans-planted teeth with incomplete root development in dogs.Ingrowth of new vessels occurs during the first few postoperative days.After10days, new vessels are formed in the apical half of the pulp and,after30days, in the whole pulp.In some instances,anastomoses seemed to form with preexisting vessels in the pulp.Although revascularization occurs,the pulp space is eventually filled with hard tissue.Other animal studies focusing on the changes in pulp tissue after replantation showed that various hard tissues including dentin,cemen-tum,and bone may form in the pulp space depending on the level of pulp recovery.If pulp and apical papilla are totally lost,then the root canal space may be occupied by cementum,PDL,and bone(35–40). By tracing the migration of periodontal cells after pulpectomy in imma-ture teeth,Vojinovic and Vojinovic(41)found that periodontal cells migrate into the apical pulp space during the repair process.Therefore, one may assume that when there is a total loss of pulp tissue but the canal space remains in a sterile condition,the outcome is the ingrowth of periodontal tissues.One of the clinical treatment options for missing teeth is autotrans-plantation.The process often involves extraction of a supernumerary tooth or third molar and implantation into a recipient site.With regard to the status of pulp survival and root formation of the transplanted immature teeth,the clinical observations nicely shown by Tsukiboshi (42,43)have been that(1)if the transplanted tooth has minimal root formation,there will be minimal,if any,further root development after transplantation;(2)if there is some root formation,it will continue to develop to some extent or to completion after transplantation;and(3) Figure3.The hypothetical pathway of infection of immature permanent teeth. The infection may pass through the survived pulp and apical papilla reaching the periradicular tissues and causing extensive bone resorption.Review Articlepulp tissue will be eventually replaced by hard tissue.It has been con-sidered that as long as the HERS remains viable,it stimulates the undif-ferentiated mesenchymal cells in periradicular tissues to differentiate into odontoblasts that contribute to the formation of new dentin and root maturation.However,the current understanding is that pulp cells are different from periodontal cells.Based on current available infor-mation,it is likely that odontoblast lineages are derived from stem cells in pulp tissue or apical papilla.Both SCAP and HERS appear to be important for the continued root development after transplantation. SCAP are also highly probable to survive after transplantation because minimal vascularity is found in apical papilla based on preliminary findings(5).The reason that transplanting a tooth with little or no root formation results in almost no further root development is unclear.One may speculate that the integrity of the entire tooth organ at that stage is critical for the root development to continue.During the transplanta-tion,any disruption of the structure such as the follicle,HERS,and apical papilla will prevent further root development.Stem Cells for Pulp/Dentin Tissue Engineering and RegenerationDental pulp tissue engineering was first tested by Mooney’s groups (44).Bohl et al.(45)reported that culturing pulp cells grown on polyglycolic acid(PGA)in vitro resulted in high cell density tissue sim-ilar to the native pulp.Buurma et al.(46)found that pulp cells seeded in PGA and implanted into the subcutaneous space of immunocompro-mised mice produced extracellular matrix.New blood vessels also pen-etrated the cells/PGA implants in vivo3weeks after the implantation. Since the isolation and characterization of DPSCs and SHED(6,16), using these stem cells for dentin/pulp tissue regeneration has drawn great interest(47–49).Reparative dentin-like structure is deposited on the dentin surface if DPSCs are seeded onto a human dentin surface and implanted into immunocompromised mice,suggesting the possibility of forming addi-tional new dentin on existing dentin(50).Nör has shown that by seeding SHED onto synthetic scaffolds seated in pulp chamber of a thin tooth slice,odontoblast-like cells can rise from the stem cells and localize against existing dentin surface after implanting the tooth slice construct into immunocompromised mice(49).These findings provide new lighton the possibility of generating pulp and dentin in pulpless canals. However,when implanting cells/scaffolds into root canals that have blood supply only from the apical end,enhanced vascularization is needed in order to support the vitality of the implanted cells in the scaffolds.Recent efforts in developing scaffold systems for tissue engi-neering have been focusing on creating a system that promotes angiogenesis for the formation of a vascular network(51–56).These scaffolds are impregnated with growth factors such as VEGF and/or platelet-derived growth factor or,further,with the addition of endothe-lial cells.These approaches are particularly important for pulp tissue engineering for the aforementioned reason that blood supply is only from the apical end.Collagen has been considered as a convenient pulp cell carrier and could conveniently be injected into canal space to regenerate pulp clin-ically,yet collagen as the matrix has been found to contract significantly when carrying pulp cells(47,57),which may considerably affect pulp tissue regeneration.Our in vivo experiments using mouse as a study model showed that when pulp cells were cast into collagen gel and placed into a canal space,the contraction interfered in the pulp regen-eration.This observation was also noted in vitro,where cells/collagen gel filled the entire canal space right after casting but underwent con-traction over time.Contraction-resistant scaffolds such as PLG(D,L-lactide and glycolide)appear to be a more suitable carrier for pulp cells.Seven weeks after seeding the DPSCs onto PLG scaffolds,no ob-servable contraction was noted in vitro,and the cells attached well onto the scaffold surface(Fig.4).Whether SCAP are a more suitable stem-cell source for pulp gen-eration than DPSCs and SHED because of their natural role as a source for primary odontoblasts than the replacement odontoblasts requires further investigation(5).The utilization of stem cells and an optimal scaffold system may one day be used clinically as depicted in Figure5in which engineered constructs may be inserted into canals of immature teeth to allow regeneration of pulp and dentin.The assumption for the multistep engineered tissue installments is based on the concern that blood vessel ingrowth can only occur from the apical end.A single installment,although it is more ideal and will avoid chances of intro-ducing infection,may lead to the cell death in the coronal third region because of a lack of nutrients.Whether impregnation of VEGF and other angiogenic factors would make single installment a possibility awaits experimentation.If the proposed clinical approach can be successful,it implies a fundamental breakthrough in clinical endodontic treatments using cell and tissue engineering therapy.SCAP for Bioroot EngineeringDental implants have recently gained momentum as a preferred option for replacing missing teeth instead of bridges or removable den-tures.However,although dental implants have had greatimprovements Figure4.DPSCs grown in PLG in vitro.DPSCs were seeded onto PLG scaffolds cylindrical shape,5(diameter)ϫ2(height)mm with pore diameters between 250and425␮m kindly provided by Dr L.D.Shea(Northwestern University, Evanston,IL)and cultured in vitro for7weeks.Cells attached onto the inner surfaces of the scaffold(H&E).The scaffolds without cells(control,not shown) were also processed for H&E,and no visible staining was observed(original magnification:A,ϫ100;B,ϫ400).Review Article。