Greenhouse gas emissions causing climate change

Greenhouse gas emissions causing climate change Introduction Climate change is the consequence of any kind of adjustments in the climate system. Change in climate is caused by fluctuations in the factors that influence climatic patterns. This phenomenon has become one of the greatest environmental threats and risks that the world is facing. Persistent human activities such as driving cars, farming, deforestation, and industrialization result into production of greenhouse gases. These gases gather in the atmospheric space, and trap the heat from the sun. This is what causes climate change manifested through global warming and other processes. The effects of disruptive changes have led to catastrophic events like storms, droughts, rise in the sea levels, and floods (Kammen Casillas 2010, p. 1181). Climate change is majorly caused by greenhouse gas emissions. Most of the intervention efforts meant to mitigate the impacts of climate change thus target human activities that contribute to additional emission of greenhouse gases into the atmosphere (Letcher ScienceDirect 2009, p. 67). Therefore, renewable energy has been considered as one of the leading solutions to climate change. Provision of ‘carbon-neutral sources of power, heat, transport fuels and renewable energy options has been considered by environmental scientists as a great move in the right direction. The objective is to enact a transition from high to low carbon economy. Although the renewable energy sector is quickly changing, climate change crises dictate that the energy system be drastically transformed. This will help in combating the dangers that are associated with global warming that threatens to slump the global economy in the face of globalization and industrialization. Roggema (2009, p. 211) cited air pollution caused by transport and power sectors of the economy have been a great threat not only to the human health but have also shifted the climate systems. Prospective Interventions to Address Climate Change Crisis Climate change as an environmental problem is essentially a problem caused by the extreme utilization of fossil energy. Agriculture, changes in land use, cement production and use of chemicals all contribute to the emission of the greenhouse gases (Roggema 2009, p. 234). However, 70% of the global warming/climate change problems is caused by unsustainable use of fossil fuels. Therefore, in order to deal with the problems related to climate change, there has to be a shift from use of fossil fuels at home, in the industries, transport and generally the entire sectors of the economy (Roggema 2009, p. 203). In order to avert the challenges associated with climate change, saving of energy is essential. Electricity, automobiles and carbon emissions are the main causes of problems related to climate change. The regular incandescent light bulbs should thus be changed and replaced with the energy saving compact fluorescent bulbs which are more efficient and energy saving. The emissions that result from automobiles like motor vehicles, motorcycles should also be reduced (Letcher ScienceDirect 2009, p. 154). Climate change has been caused by human activities such as deforestation in search of more space for agricultural activities. Therefore carbon dioxide concentration in the atmosphere continues to rise. Being a greenhouse gas, carbon dioxide has contributed to the rise of global temperatures. Roggema (2009, p. 183) cited that human activities that encroach to the environment should thus be limited to prevent further crises associated with global warming. Traditional methods of conservation of forest ecosystems should be embraced to preserve the ecosystem and mitigate the effects of climate change (Tracy 2010, p.353). Therefore reforestation should be encouraged so that the greenhouse gases like carbon dioxide are reduced from the atmosphere. Farming activities that promote environmental hazards such as soil erosion should thus be limited and replaced with farming approaches that are environmentally custodial. Industrialization is the major contributor to climate change. This is because of the emission of the greenhouse gases like Nitrous Oxide and Carbon dioxide (Tracy 2010, p. 354). In order to avert climate change challenges there should be focus on change in the energy used in the industries from the dirty to clean energy. Climate change scientists have advocated for the use of renewable energy as the solution to the climate change problems that are caused by the use of environmentally hazardous fuels like coal and nuclear energy in the industries in the global economy (Tracy 2010, p. 355). Climate Change and the options for Renewable Energy Human activities and natural environmental processes are all responsible for climate change. Natural causes include volcanic eruptions, ocean currents, changes in the earths orbit and solar variations. An eruption of volcanoes throws out great volumes of sulphur dioxide, water vapor, dust, and ash into the atmosphere (Wengenmayr 2008, p. 141). The large volumes of gases and ash have the ability to influence climatic patterns by increasing the planetary reflectivity leading to atmospheric cooling. The aerosols are produced by volcanoes also affects the purity of air in the atmosphere. These contribute greatly to climate change. The oceans currents are considered a great threat to the climate stability. The currents release great amounts of heat across the planet. Besides, the interaction between the ocean and the atmosphere can produce El Nino. The oceans determine the atmospheric concentration of carbon dioxide. This implies that changes in the ocean circulation greatly affects climate and significantly contributes to the climate (Wengenmayr 2008, p. 231). Climate change has been caused by human activities. MacZulak (2010, p. 9) cited that this is majorly through the burning of fossil fuels, changes in the land use, and industrialization. With industrial revolution of the 19th century, fossil fuels have been used to support industrial processes. Fossil fuels such as oil, coal and natural gas have been great energy supplies for the industrialized economies. However, these sources of energy have contributed to great emissions of the greenhouse gases in the atmosphere. These are responsible for climate change (MacZulak 2010, p. 8). Carbon dioxide concentration in the atmosphere has increased because of human activities such as deforestation and agriculture. Methane is released through oil drilling, mining of coal, leaking gas pipelines, landfills and waste dumps (MacZulak 2010, p. 9). These greenhouse gases cause great increase in the climate change and are significantly responsible for global warming. The greatest cause of climate change and global warming however is the burning of the fossil fuels. These fuels cause emission of greenhouse gases into the earths atmosphere leading to depletion of the ozone layer and global warming (Twidell Weir 2006, p. 143). Options for Renewable Energy The term renewable energy is used in reference to the energy resources that occur naturally in the environment and can always be re-used after the initial function. Examples of this energy are the solar, wind, hydro, and geothermal energy.   Rivers, biomass and garbage are also considered as renewable energies (Abid, Crawford Davoudi 2009, p.167). Renewable energy is the future of the earths energy needs. However, in order to effectively combat climate change-related challenges, the global mean temperatures have to be kept below two degrees Celsius. This calls for prior planning and transformation of the industrial sectors use of energy. Renewable energy has the potential decreasing the use of fossil fuels that are to blame for most of the problems associated with climate change (Abid et al 2009, p. 169). Renewable energy sources such as wind energy, solar energy, and the bio-fuels are increasingly being used as energy alternatives. With the climate change and its crises, such form of energy has the advantage of energy security since the fossil fuels will be depleted as a result of climate change. Climate change is largely a consequence of anthropogenic activities such as burning of the fossil fuels, industrial processes, deforestation and the release of greenhouse gases into the atmosphere. It is estimated that the power sector by itself contributes about 40% of the total carbon emissions (Abid et al 2009, p. 297). This can only be altered by shifting to the use of renewable energy. Climatic impacts such as tsunamis, droughts, wildfires, floods, storms, heat waves and tornados are consequences of climate change (MacZulak 2010, p. 8). However, according to the climate change specialists, clean air policy that includes use of renewable energy can substantially mitigate the negative impacts of climate change caused by fossil fuels. Renewable energy technologies are considered to be the most potential mitigation for greenhouse gases. In the steadily growing awareness on the importance of environmental protection priorities, renewable energy is considered appropriate in the mitigation of climate change effects (Chiras 2007, p. 67). Renewable energy is the alternative to the climate change crises since it does not produce greenhouse gas emissions and pollute the air as is the case with the fossil fuels. Chiras (2007, p. 17) indicated that biomass energy for example, has been used as an alternative for fossil fuels so as to conserve the environment. It is considered a greenhouse gas neutral since its combustion releases no more carbon dioxide than was absorbed during growth period of the organic material. Biomass fuel also contain little sulphur and low combustion temperatures. This limits the formation of nitrogen oxide which is a greenhouse gas dangerous to the environment (Abid et al 2009, p. 269). Responding to Climate Change The transport industry is driven mostly by petrol. This causes emission of carbon dioxide into the atmosphere. The carbon dioxide combines with other greenhouse gases in the atmosphere and cause global warming. In order to deal with this menace, there is need for countries to invest in energy efficient technologies like plug-in hybrid electric vehicles and new technologies such as hydrogen cars (Abid et al 2009, p. 297). This has the potential of reducing petroleum emissions of greenhouse gases into the air. Further, there is need to shift from air and truck transports to electric rail transport that reduces emissions significantly. Industries should shift from the fossil fuels to use of bio-fuels such as ethanol and biodiesel fuels should be used in the gasoline engines in the industrial economies. Abid et al (2009, p. 169) cited that electric vehicles can contribute into reduction of dangerous gases into the atmosphere especially if the energy is produced through the renewable energy sources. In order to deal with climate change and environmental crises associated with it, elimination of waste methane is required. Methane is considered to be one of the strongest greenhouse gases that are responsible for the climate change problems. Waste methane should thus be dealt with responsibly. This is through careful handling of oil wells, landfills, coal mines and the waste treatment plants (Chiras 2007, p. 17). This will provide a net greenhouse gas emission benefits. Biomass as a source of bio-energy can be used to capture carbon. Biomass traps carbon dioxide in the atmosphere through photosynthesis. When biomass is decomposed through combustion, carbon is released as carbon dioxide. This is the process involved in the carbon cycle. Biomass fuelled power plants result into a net-negative carbon dioxide emission. This implies that there will be less carbon in the atmosphere will be trapped through the technology and reduce greenhouse gases that are a threat to the environment (Abid et al 2009, p. 169). The adoption of renewable energy technologies is strategic in addressing the problems associated with climate change and global warming (Ehrfeld 2009, p. 113). From 1970s and 80s, development agencies have promoted small-scale renewable energy technologies. This includes the use of biogas, cooking stoves, the wind turbines and solar heaters in the industrializing countries. In the large scale developing countries have responded to climate change through the use of ethanol in the transport sector. This is especially the case in Brazil. In India, biogas is being used in households for lighting and cooking. Grid connected power in India and hydropower are being used in India and Nepal respectively as renewable sources of energy and safe energy for environmental conservation (Ehrfeld 2009, p. 119). Naturally Sustainable Renewable Energy As oil reservoirs and oil wells in the world run dry due to extensive exploitation and use in the energy sector, there is also an outcry in the environment that is caused by their consequences. Renewable energy sources include geothermal energy, solar, hydroelectric, biomass and wind energy (Chiras 2007, p. 233). These forms of energy have been considered to be the most environmental friendly because they dont produce high levels of greenhouse gases and other substances that are not environmentally friendly. The challenge that these forms of renewable energy have is sustainable use. Hydroelectric power uses the movement of falling water to run the turbines. Unlike other sources of energy, hydroelectricity does not depend on the fuels like natural gas or petrol to run the engines. This makes it more environmentally friendly. Besides, it is more sustainable with the sustainability of the environment so that water capacity of the dams is not interfered with. It uses the natural progression nature to generate electricity (Chiras 2007, p. 117). Hydroelectric power does not produce direct waste that pollutes the environment. It is thus considered to be environmentally sustainable (Ehrfeld 2009, p. 114). The carbon dioxide levels produced by hydroelectric power plants are considerably very low. This is however only produced during the construction stage of the plants and not in the operational phase of the plants making it environmentally friendly. As a renewable source of energy, hydroelectric power does not need the use of fuels to run the turbines. The use of petrol in the production of hydroelectric energy is not existent. This implies that when the price of the fossil fuels rises, the hydroelectric plants are often not affected. This makes it a sustainable and reliable source of energy when compared to other sources of energy (Ehrfeld 2009, p. 116). It also means that the consumer price of this form of renewable energy is fairly constant. In terms of sustainability, hydroelectric power stations last longer than the energy plant stations that are powered by fossil fuels. They are generally easy to maintain and pose no much threat to human life and property. Hydroelectric energy plants contribute to conservation of the environment. In the countries where great investments have been done in the hydropower such as Bhutan, environmental stewardship and custodianship is encouraged. Ehrfeld (2009, p. 119) cited that since it depends on water, a lot of forest conservation and reforestation is encouraged. This helps in the reduction of the carbon dioxide concentration in the atmosphere. The human activities that contribute environmental degradation are also reduced through investment in the hydroelectric power plants. Climate change is caused by human activities that tamper with the environment. However, when a country invests in the hydroelectric plants, environmental conservations efforts are boosted. With the conservation of the water catchment areas and the forests, hydroelectricity becomes a very sustainable and reliable source of renewable energy. As it produces clean energy through environmentally friendly approaches, it also helps in the protection of Mother Nature (Ehrfeld 2009, p.121). International Agreements and Government Interventions in Climate Change Various intervention efforts have been made at the community and individual levels to combat climate change and to reduce the negative effects of human activities on the environment. However, much is still needed to be done especially at the inter-state and governmental level. One of the efforts that the governments from the industrialized countries are making in the mitigating climate change is through the Kyoto Protocol. The focus of the protocol is in the reduction of greenhouse gas emissions especially from the industrialized countries by 2012. The developed countries have the responsibility to reduce their emission of greenhouse gases from their large industries. These gases contribute to global warming and climate change. The Kyoto Protocol intervention targets reduction of carbon in the atmosphere (Karlsson, Lund, Mathiesen 2010, p. 488). This is through emission trading, clean development mechanism and the joint implementation. These strategies target reductions of greenhouse gases in the atmosphere. The countries that are signatories are thus investing in renewable energy technology options in the industries. The UK government considers climate change as a priority. Its approaches include targeting households to help in energy saving and strengthen renewable energy adoption. Civil society, community and private organizations are also strengthened through grants to help in generation of renewable heat from the renewable sources (Ehrfeld 2009, p. 115). The industrialized countries are re-focusing investments towards generation of renewable energies that are environmentally friendly and are sustainable. There is thus need to encourage less use of fossil fuels and more investment in the bio-fuels. Improvement of energy efficiency is a good government strategy for dealing with the climate change problems. Reduced use of energy implies reduced production of carbon dioxide. Karlsson et al (2010 p. 501) cited that this calls for more efficient vehicles, motors, appliances and industrial processes. Besides, development of renewable energy sources such as solar, geothermal, hydroelectricity, and biomass should be encouraged to reduce the consequences of greenhouse gases in the atmosphere. The transport sector should reduce gasoline consumption. The trucks, cars and buses use almost half of the oil in the United States. There is therefore urgent need for investment in electric and fuel-celled vehicles so as to reduce the emission of carbon dioxide. Transport policies should also encourage less driving of single-passenger vehicles in order to reduce greenhouse emissions (Ehrfeld 2009, p. 115). Human activities that involve land use are largely to blame for destruction of the environment. Governments should focus on developing agricultural policies that discourage environmentally hazardous practices and activities such deforestation and other human activities that are dangerous to the environment. Climate change has negatively impacted on food security. In order to therefore fight poverty, climate change must be addressed through agricultural activities and policies that are environmentally friendly (Kammen Casillas 2010, p. 1181-1182). Conclusion Climate change is greatly caused by human activities more than the natural processes. Industrialization and agricultural activities are largely responsible for the production of greenhouse gases that promote global warming and other consequences. These threaten wildlife and human existence and as such should be addressed. Renewable energy is the potential rescue of the environment from the negative effects of human activities. Governments and countries thus need to use less of fossil fuels and invest more in renewable energy technology options. These include hydropower, geothermal, wind energy and other reliable sources of environmentally friendly renewable energy sources.

Purchasing and Supply Organization Department

I contacted a consultant for Mansell Ltd. and a great deal of information was gathered and analyzed. The following advice would be given for ways of improving their purchasing and supply organization. Currently, Mansell Ltd. Operates from six sites and has a central purchasing and stock control department in the North of England. Upon an analysis of the company, it has been found that orders for production materials have been placed with over 6000 different companies during the last four years. There are many benefits to be gained from buying from a smaller number of suppliers. The purchasing and supply department would be better organized and thus more efficient if less supply companies were used. Purchasing supplies from fewer companies would result in better pricing of supplies. For example, if the company purchased the same items from several different companies, it is probably getting charged more. Purchasing the same item from only one company will result in savings for the number of items bought because many companies give a discount for large quantities of items purchased. When using the same companies for purchasing, a rapport between the two is possible. When a supplier knows that his/her products will be needed by a certain company, he/she will be more likely to have those products more readily available. For example, if the seller knows that the buyer needs a thousand items each week, the seller will make sure that those items are in stock and will save them for the purchaser instead of selling them to another company. The more sellers, the more confusion there will be. Even with computer technology, having so many sellers presents a logistical problem. A purchasing and supply organization should follow certain business fundamentals. Low cost, quality, and timeless are fundamental to the business. Planning is required. Buying from fewer companies results in fewer persons to deal with. Six thousand suppliers are a large number to be dealing with. Those are far too many suppliers involved. Keeping up with that great a number of suppliers would keep several people in the purchasing department busy. In order to become more efficient and use fewer numbers of man-hours, using fewer suppliers is the answer. Diversity is good in some instances. However, the purchasing and supply organization is not one of them. In fact, diversity only caused unnecessary confusion, and too many chances for problems. Purchasing is one of the vital parts of any company. The products acquired enable the business to create or generate its product. There are a diverse number of potential suppliers, as evidenced by the 6,000 suppliers that have been utilized in the past. This number makes purchasing a chore instead of an easy adventure. The purchasing department needs as few challenges as possible. Eliminating a number of suppliers cuts down on the challenge they pose. With insight into the management of the purchasing and supply department's inner workings, many of the sellers can be eliminated. It would not be prudent to reduce the number to a handful of suppliers, what with the market what it is, but there is certainly no need for a great number of suppliers. Purchasers and buyers have a specific function. â€Å"Purchasers and buyers seek to obtain the highest quality merchandise at the lowest possible purchase cost for their employers. (In general, purchasers buy goods and services for the use of their company or organization whereas buyers buy items for resale.) They determine which commodities or services are best, choose the suppliers of the product or service, negotiate the lowest price, and award contracts that ensure the correct amount of the product or service is received at the appropriate time. In order to accomplish these tasks successfully, purchasers and buyers study sales records and inventory levels of current stock, identify foreign and domestic suppliers, and keep abreast of changes affecting both the supply of and demand for products and materials for which they are responsible† (Anonymous, 1998, PG). The way to reduce the number of suppliers would be as follows. An analysis of past purchases is required. Decide which companies have the best products for the lowest price. This is not the only factor to consider, however. Other issues, such as ability to get the product to Mansell Ltd. in a timely fashion is also important. Lower prices do not matter if the product does not get there when it is According to Steele and Court (1996), the understanding of purchasing is critical to a company's long-term ability to profit, and its survival as a company. Understanding of purchasing includes the knowledge of how best to buy resources. This includes the sellers from whom the product is purchased as well as the amount of supplies that are purchased and when they are purchased (Steele & Court, 1996). Check out the competition. Ask for samples. Make sure that the seller can deliver when he/she says he/she will, the amount of product that was agreed upon, and at or below the agreed upon cost. Proper training for the purchasing staff is vital. Regular meetings must be held. All purchasers must know the guidelines of the company. Training programs that teach the purchasers about the best manner in which to perform their jobs is important. A typical training program should include instruction by trained personnel that covers specified goals and only lasts for a day or two. Not a great deal of time should be taken up with training, but the training is vital. The proper changes must be implemented as soon as it is possible. Negotiation with potential suppliers is important. Having a good rapport between the buyer and the seller is also important. The buyer should travel to the prospective seller's company and see what the company has to offer. One-on-one meetings are still important. By getting out there and getting to know the seller, the buyer will become more than a faceless person in the North of England. He/she becomes a ‘real' person. Making acquaintances is important for business. A bond should be created between the buyer and the seller. Together the two can have a working relationship that is beneficial to the both of them. According to Killen and Kamauff (1995), purchasing is a planning process. The purchaser should determine both short and long-term needs for business operation. The purchasing function must be controlled. By doing this, its conformance to expectation levels can be ensured. Evaluations are important on a cyclic basis (Killen; Kamauff, 1995). The buyer should be able to negotiate with the seller. Prospective sellers should be able to give better prices for larger quantities. This allows the purchaser to make better decisions. The seller should be able to meet the needs of the buyer. If he/she does not, then that is not the company to deal with. The buyer does not need added stress; he/she needs products as they are required. When a seller is given the lion's share of purchases, he/she can more readily fill the orders. A purchaser must have certain tactics. Those tactics include such items as vulnerability management, supply positioning, and suppliers' preferences. He/she must be able to work with others. Communication is vital for the purchaser. Teamwork is a necessary element of purchasing. Constant reevaluation is necessary (Steele & Court, 1996). According to Malley (1998), the Internet is a viable tool for purchasing departments. Barbara Chilson is the vice president and general manager of Internet commerce for her company, which is W. W. Grainger. In Chilson's opinion, â€Å"the advent of purchasing supplies electronically, increasingly referred to as paperless purchasing, can be attributed to a variety of factors and emerging technology† (Malley, 1998). Purchasing is vital to Mansell Ltd. The purchasing department must streamline and make changes in order to make Mansell Ltd. be as profitable as possible. Having too many suppliers results in chaos. This can be resolved by reducing the number of suppliers. Technology is another important consideration. Purchasing of some items can be done online, which saves time and money.

Charles Of The I Vs. Charles The II - 1255 Words

Judmir Bullari Brit.Lit Research Paper 3/23/15 Charles the I vs. Charles the II England has gone through many kings and leaders, some better than others obviously, for example when you compare Charles the first to his son who succeeded him years after his rule Charles the second. One key difference between the two is that Charles reign ended due to his execution, and his son was able to rule till he saw his deathbed, the reasons why are quite simple. The Stuart monarchs of England restored peace and order to England after the civil wars that led to the execution of King Charles 1 in 1649, wars that continued even after the king was dead. The people of England were done with war, worried of revolutionaries and radicals, were ready to settle down, make money, and enjoy life. In 1660, the people brought back the son of King Charles the first from his exile in France, crowned him King Charles the II, and hailed him as their savior. To warn angry revolutionaries they dug up the corpse of Oliver Cromwell and cut his head off, he had ruled England between Charles 1 and Charles II. The Monarchy was restored without shedding a drop of blood in warfare. Charles was the second son of King James the VI of Scotland. After his father inherited the English throne, Charles moved to England and spent most of the rest of his life there. He became heir to English, Irish, and also the Scottish thrones after the death of his older brother Henry Frederick. Charles was laterShow MoreRelatedOrgan Transplantation : Medical Advancements1104 Words   |  5 Pagesconsists of, I will now go into the different ways organs are distributed and then different methods of how to increase organ donations. 1. Organ distribution a. How to fairly divide limited resources is the issue b. 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Stem Cell Delivery in Regenerative Engineering and Medicine - Free Essay Example

Sample details Pages: 7 Words: 2046 Downloads: 6 Date added: 2019/06/19 Category Biology Essay Level High school Tags: Stem Cell Essay Did you like this example? Regenerate the Vascular Tissue Blood vessels composed of endothelial cells and mural cells play key roles in tissue regeneration and repair by serving as conduits to deliver oxygen and nutrients to injured and newly-formed tissues.[88] Many CVDs such as coronary artery disease (CAD) and peripheral vascular disease (PAD) are resulted from the loss of vascular supply leading to organ failure. Regeneration of blood vessels can be generally divided into two major aspects: the neovascularization in ischemic tissues, and repairing of injured blood vessels.[89] Insufficient neovascularization is the essential hurdle for treatment of ischemic diseases, especially coronary artery diseases (CADs), by regeneration of thick tissues (200 m) that cannot survival under nutrients diffusion supply alone. Delivery of endothelial cells (ECs) or related progenitor cells together with stem cells can effectively improve the neovascularization, which consequentially enhance the efficacy of stem cell therapy. For instance, a recent research reported by Zhang group encapsulated a combination of hiPSC-CMs, hiPSC-ECs, and hiPSC-derived smooth muscle cells (hiPSC-SMCs) in fibrinogen gel at ratio of 2:1:1 to fabricated human cardiac muscle patches (hCMPs) for MI treatment. Co-delivery of the hiPSC-ECs and hiPSC-SMCs with fibrinogen gel into the porcine model of MI leaded to angiogenesis factor-enriched exosome secretion that significantly improved CMs survival and maturation, and contributed to the engraftment and angiogenesis at periscar border zone, which impr oved functional recovery of myocardium as a consequence. Besides the co-delivery strategy, direct encapsulation of pro-survival peptides in biomaterials was also proved to improve angiogenesis (Figure 5).[90] Wu group conjugated bone morphogenetic protein-2 peptide analogue (BMP2), erythropoietin peptide analogue (EPO), and fibroblast growth factor-2 peptide analogue (FGF2) with collagen fibers (Col?— D?— Pep) via dendrimer linker to realize the slow release of the pro-survival factors to delivered BMMNCs. The peptide had similar biological effects as the full-length protein, but with improved stability, fewer side effects and better delivery. Due to the chemical conjugation, the pro-survival factors can be slowly released by degradation of the collagen hydrogel. The hydrogel delivery system improved the cell survival and retention. In vivo delivery of the BMMNCs with the Col?— D?— Pep hydrogel improved the blood perfusion in ischemic limb of both severe combined immune-deficient mice and immunocompetent mice. Don’t waste time! Our writers will create an original "Stem Cell Delivery in Regenerative Engineering and Medicine" essay for you Create order Besides the paracrine effect, ECs derived from human pluripotent stem cells (hPSC, including ESCs and iPSCs) were reported to integrate with host tissue to from vascular structures.[91] The researchers from Yoon Group delivered the hPSC-ECs using a self-assembled peptide amphiphile conjugated with RGDS (PA-RGDS) nanomatrix gel into ischemic limb to reconstruct the vascular structure for CVDs treatment. The PA-RGDS molecule was consisted of a hydrophobic alkyl tail, and hydrophilic domain of cell adhesive ligand RGDS and biodegradable sequence of metalloprotease-2 (MMP-2). The RGD ligand promoted the adhesion and avoided anoikis of encapsulated hPSC-ECs in nanomatrix gel which is critical for cell survival during engraftment, while the MMP-2 site provided a controlled degradation of the gel which played key roles in cell integration with the host tissue.[92] Although the mechanism was not shown, the PA-RGDS nanomatrix preserved the cell viability from oxidative stress which is importa nt cytoprotection as discussed. Meanwhile, the nanomatrix gel could enhance the retention of delivered cells that were still detectable up to 21 weeks. After 10 months, the transplanted ECs integrated into host tissues which contribute to the neovascularization in ischemic areas. Additionally, providing the structural guidance such as micro-channels would further accelerate the neovascularization process.[80b, 93] Dysfunction of the narrowed arteries results in reduced blood supply to organs that will cause ischemic disease such as CAD, stroke and periphery artery disease (PAD). Current repairing strategy is bypass surgery using autologous grafts (e.g. patient vein) or synthetic polymer graft (e.g. Teflon). However, the availability of autologous grafts is patient-limited availability and the harvest process is invasive.[94] However, the usage of synthetic graft usually resulted in repeated revascularization procedures due to the acute and chronic occlusion caused by graft infection and other complication.[95] Recent development in biomaterials and cell therapy could shed light on the possible solution. For instance, Woo group manufactured the engineered vascular conduits (EVCs) using cell sheets from patient-derived smooth muscle cells (SMCs) and fibroblasts.[96] The EVCs was further perfused with human umbilical vein endothelial cells (HUVECs) for maturation. The artificial mature EVCs showe d native artery comparable structure and mechanical strength, which leaded to completely recovery of blood perfusion in ligated hindlimb of rats. Besides the cannular vascular grafts, stem cell patch was also shown to be useful in repairing of ateries. Mayer group fabricated a hybrid scaffold using an elastomeric polymer of poly-4-hydroxybutyrate (P4HB) and methacrylated gelatin (GelMa) hydrogel (Figure 6).[97] A fibrous elastic scaffold was firstly prepared with dry spinning of P4HB in random and aligned manner which had uniform and anisotropic mechanical properties, respectively. Then GelMa was introduced into the fibrous P4HB scaffold to provide a hospitable environment for cell growth. Cells encapsulated in the hybrid scaffold showed more uniform distribution compared to the cells directly seeded onto P4HB scaffold. In vivo delivery of MSCs and endothelial progenitor cells (EPCs) using the hybrid scaffold on sheep pulmonary artery enabled the tissue formation throughout the scaf fold and prevented the surface thrombosis. This was attributed to the compatible environment provided by the GelMa hydrogel encapsulation, as well as the mechanical support by P4HB fibrous scaffold under physiological pressure in vivo. Other potential strategies via decellularized vascular structures without pre-seeding of stem cells are also proved to be efficient to induce vascularization which is beyond the scope of this review.[98] Despite the achievements in preclinical studies, few clinical trials were carried involving biomaterials delivery system for stem cells therapy (Table 2).[99] Therefore, more work is required to further evaluate and translate the developed functional biomaterials to provide new options for cardiovascular regeneration to fulfill the bench-to-bedside approach. Biomaterials for Stem Cell Delivery in Neruoregeneration Damages to the brain, the spinal cord and the peripheral nerves due to traumatic injuries, stroke, tumor, infection or neurodegenerative diseases are often permanent and incapacitating, presenting tremendous burden on the patients, their families and society. The adult nervous system, especially the central nervous system (CNS), has limited capability to regenerate to establish the correct axonal and dendritic connections.[100] Instead, a cascade of events happen as a consequence of damages, including the production of glial scar, which represents a molecular and physical barrier to regeneration, leading to neuronal degeneration and cell death.[101] Current clinical treatments are designed to pharmacologically improve the disease symptoms in combination with rehabilitation activities to restore physical function to some extent; however, no therapies are yet available to fully restore lost functions or slow ongoing neurodegeneration following the injury or disease.[102] It has been re cognized that the failure of neurons to regenerate was not an intrinsic deficit of the neuron, but rather a characteristic feature of the damaged environment that either did not support or prevented regeneration.[101] Therefore, strategies aim to fully regenerate the damaged nerves should not only focus on supplying the cells lost due to injury or disease to re-establish the connections, but also improving the local environment to support regeneration and prevent further degeneration. Stem cells have great promise as a source for introducing new neurons or glial cells to the damaged nervous system. For instance, neural stem/progenitor cells (NS/PCs) can be isolated from the mammalian neonatal CNS,[103] or derived from pluripotent stem cells such as ESCs and iPSCs,[104] which can in turn be differentiated into neurons and glia cells of the nervous system when delivered to the damaged regions. In addition, NS/PCs can also modulate immune and inflammatory responses, leading to neuroprotective effect to the surrounding tissues.[105] Clinical trials of allogenic NS/PCs transplantation to patients with ALS,[106] stroke,[107] and Pelizaeus-Merzbacher disease (PMD)[108] have found consistently favorable safety profile during early phase trials. Other cell types, such as mesenchymal stem cells (MSCs) and adipose-derived stem cells (ASCs) are also investigated by researchers preclinically[109] and clinically[110] for their ability to facilitate neuroregeneration via paracr ine actions of neural protection, plasticity, antiinflammation, and angiogenesis, rather than direct transdifferentiating into neural cells.[111] Advanced biomaterials can provide a structural platform to bridge the gap of damaged neural tissue, deliver stem cells to the site of injury, enable and augment the targeted delivery of therapeutic molecules, and help rebuild damaged circuits and repair damaged neuronal pathways.[102b, 112] In a 2016 meta-analysis of preclinical studies using NSPC transplantation for spinal cord injury treatment, it was found that scaffold use in NSPC transplantation effectively raise functional recovery comparing to scaffold-free cell suspension.[113] The ideal materials for neural regeneration should be biocompatible with low immunogenicity, mechano-compatible to provide structural support to the surrounding neural tissue, and encouraging stem cell survival, differentiation and integration.[102b, 114] In this section, we highlight some of our colleagues recent work of neuroregeneration in the brain, the spinal cord and the peripheral nerves (Table 3) that utilized advanced biomaterial-assisted ste m cell delivery strategies to regenerate neural tissues. Regenerate the Brain Tissues Stem or progenitor cell transplantation after brain damage due to ischemic stroke or traumatic injury was shown to promote neuro-regeneration in pre-clinical models.[115] Early-phase clinical studies to evaluate the intracerebral transplantation of allogenic human neural stem cells (NSCs)[107] and MSCs[116] have also demonstrated promising safety profiles in stroke patients. However, these studies are limited by poor survival of the transplant when administered as a suspended form into the damaged brain, most likely due to the ischemic and pro-inflammatory environment, the immunological attack and the abrupt withdrawal of growth factor and adhesive support.[114] To solve this problem, biomaterial scaffolds can serve as delivery vehicles for transplanted cells, facilitating neuronal outgrowth and connectivity between grafted and host cells. Moreover, the scaffolds can be modified to provide local and sustained delivery of proteins, and the surface can be topographically altered to for m alignment, coated with ligands or modified to possess a surface charge to promote attachment, growth and differentiation of neural stem cells.[102b] Some earlier works used porous biodegradable polymers such as polyglycolic acid (PGA) as cell-seeding scaffolds, which supported new brain tissue regeneration around the degenerating scaffold and formed a network of neurites with axonal regeneration.[117] However, the transplantation of cell seeded polymer scaffold requires invasive surgical procedures, which may cause further damage to the vulnerable brain tissue. Alternatively, hydrogels containing ECM proteins such as collagen, laminin and fibronectin could be injected with stem cells to allow minimally invasive cell delivery.[118] The ECM-based scaffolds were found to significantly improve cell survival rate comparing to cells in suspension by many groups.[119] However, the xenogeneic nature of ECM-based scaffolds and the potential immune response to the antigenic components of xenogeneic materials represent a critical barrier to the use of xenogeneic scaffolds in translational applications.[120] Synthetic ECM-derived peptides, s uch as laminin-derived IKVAV and fibronectin-derived RGD could be used to form ECM-memetic hydrogels by self-assembly[121] or incorporation with other biopolymer materials (e.g. hyaluronic acid[122] and alginate[123]) to allow effective delivery and differentiation of stem cells to the brain, without the use of xenogeneic materials. Engineering strategies can further encourage the migration, survival and differentiation of NS/PCs by promoting a stem cell niche-like environment that helps rebuild a functional neuronal network. As an example, the Segura group has engineered a series of hyaluronic acid (HA) based hydrogels with various peptide modifications.[122, 124] Their initial delivery of iPS-NPCs to the stroke cavity within the HA based matrix modified with RGD and MMP sensitive peptide promoted the differentiation of transplanted cells; however, the material did not significantly promote stem cell survival.[122a] To improve stem cell survival, the group utilized the Design of Experiments (DOE) methodology to optimize the concentrations of three ECM ligands (RGD, YIGSR, IKVAV) in vitro for the survival and differentiation of NPCs by determining the individual and combinatorial effects of each factor on cell activity.[124] Further DOE optimization and modification was carried out combining mechanical, biochemi cal and trophic factors, and a later animal study using the systematically optimized HA hydrogel resulted in selective control of human neural stem cell survival and differentiation after transplantation in the stroke brain[122b] (Figure 7A). Moreover, the HA hydrogel can be tracked in vivo with MRI, enabling non-invasive tracking for material distribution and degradation. Recent work from the same group also focuses on cell-free approach of brain tissue regeneration after stroke by promoting vascularization and reducing inflammation, which is beyond the scope of this review.[125]