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Coronary Arterial Drug-Eluting Stent:
From Structure to Clinical
Tim Wu and Stephen McCarthy
Biomedical Engineering and Biotechnology,
University of Massachusetts Lowell, MA,
USA
1. Introduction
1.1 Cardiovascular diseases and Percutaneous Coronary Intervention (PCI)
Coronary Artery Disease (CAD) is the chronic blocking or narrowing of the coronary arteries caused by neointimal hyperplasia of the arterial wall. It has been the number one killer in the United States since 1900 and remains a common cause of death in the Western world despite therapeutic advances. Approximately 14 million Americans have CAD, 500,000 people die from acute myocardial infarction, and one million more survive but with a 1.5 to 15 times greater risk of mortality or morbidity than the rest of the population each year. The annual health care cost of the disease is in excess of $112 billion 1. The current levels of predictors of heart disease risk, such as obesity, diabetes, and smoking, suggests that this will continue to be a significant public health problem for the foreseeable future 2.
The options for CAD treatments include medications, percutaneous coronary arterial interventions (PCI, including angioplasty and stenting), or coronary artery bypass graft surgery (CABG). In general, patients with coronary narrowing that does not limit coronary artery blood flow receive medications and lifestyle modification to help prevent progression. If a patient has coronary atherosclerosis that limits blood flow in the coronary arteries, balloon angioplasty and stenting can be offered. In patients with multiple areas of coronary artery narrowing or blockage, CABG is generally recommended.
1.1.1 Coronary Artery Bypass Graft Surgery (CABG)
Of those patients with coronary artery disease, about 10% undergo CABG surgery. Patients with severe narrowing or blockage of the left main coronary artery or those with disease involving two or three coronary arteries are generally considered for bypass surgery. In a CABG, the surgeon uses a portion of a healthy vessel (either an artery or vein) from the leg, chest, or arm to create a detour or bypass around the blocked portion of the coronary artery. Depending on how many coronary arteries (and main branches) are blocked, patients typically receive 1 to 5 bypasses. The most commonly used bypass vessels are the saphenous vein from the leg, the internal mammary artery from the chest,
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Coronary Artery Diseases and the radial artery from the arm. During a CABG, a heart-lung machine artificially maintains circulation while the surgeon operates on the heart. CABG operations require general anesthesia and typically 4 to 7 days in the hospital. It may take up to 3 months to fully recover from the surgery.
1.1.2 Percutaneous Interventions (PCIs)
Percutaneous Interventions (PCIs), which include percutaneous transluminal coronary artery angioplasty (PTCA) and coronary artery stenting (CAS) are the major therapies for CAD treatment. PTCA involves insertion of an expandable balloon catheter against a primary atherosclerotic plaque or secondary restenotic lesion to increase vessel patency and blood flow. Clinical stenting was introduced in 1986 with the Wallstent to repair abrupt closure after PTCA and has revolutionized interventional cardiology 3. In CAS, the stent (a tiny metal scaffolding) functions to brace the vessel wall and reduce the risk of restenosis following angioplasty. CAS reduces the rate of angiographic and clinical restenosis compared to PTCA alone. This results in a significant reduction in the frequency of major adverse cardiac events (MACE) after PCI driven mainly by a reduction in target vessel revascularization (TVR). CAS not only increases procedural success rates, but also increases the safety of procedures by decreasing the need for emergency CABG surgery. As a result, stents are currently utilized in over 85% of the two million PCIs in US and the total direct cost for those life-saving procedures is over $5 billion annually.
1.2 Problems in current DESs
Since the introduction of the stent, there exist two serious complications: namely, thrombosis (subacute and late-stage) and in-stent restenosis (ISR). While subacute thrombosis has been controlled with the use of dual anti-platelet therapy, late-stage thrombosis occurring in drug-eluting stents (DESs) has been a big concern recently. Restenosis remains among the most challenging problems in interventional cardiology. The recent development of DESs is a major breakthrough as a potential solution for the restenosis problem.
1.2.1 In-stent Restenosis (ISR)
Restenosis, the re-narrowing of an opened artery after stenting or PTCA procedure, is due to a proliferative response of the intima, a layer of cells that lines the lumen of the vessel composed of connective tissue and smooth muscle cells (SMC). In restenosis, vascular neointimal hyperplasia results in complete blockage of the original artery and insufficient oxygenation of cardiac tissue, leading to cardiac arrhythmia or cardiac arrest. Restenosis has been the biggest problem in PCI until the recent successful development of DESs. Initially, the restenosis rate in PTCA procedures was over 50% within six months post balloon dilation. Stenting lowers this rate to 20-30%. Both Sirolimus (Cypher?, Cordis Inc, Fla) and Paclitaxel (Taxus?, Boston Scientific Inc, Natick, MA) coated DESs can significantly reduce the rate of restenosis to <10%4-6. However, restenosis in patients with high risk such as small vessels, diabetes, and long diffusion diseased arteries still remains
Coronary Arterial Drug-Eluting Stent: From Structure to Clinical 199 unacceptably high (30%-60% in bare metal stents [BMSs] and 6%-18% in DESs)7-9 despite DES implantation.
ISR formation is a multi-factorial, sequential process. Although the detailed mechanism of the arterial tissue response to an implanted stent is still under investigation, it is generally believed that three stages are involved in the process. 1)Thrombotic Phase(day 0-3): this phase is the initial response of the artery tissue to stent implantation characterized with rapid activation, adhesion, aggregation and deposition of platelets and neutrophils to form a thrombus at the injured site. 2) Recruitment Phase:this phase occurs between days 3 to 8 and is characterized by an intensive inflammatory cell infiltration. In this phase, inflammatory cells are activated and infiltrate into the injured vessel wall. Subsequently, the recruited inflammation cells provide the key stimulus for subsequent smooth muscle cell (SMC) proliferation and migration. 3)Proliferate Phase:This phase lasts 1 to 3 months depending on the thickness of the residual thrombus and the rate of growth. At this stage, inflammation cells colonize the residual thrombus, forming a “cap” across the mural thrombus. The cells progressively proliferate, resorbing residual thrombus until all thrombus is gone and is replaced by the neointima tissue 10-12.
The process of neointimal growth, which consists of SMCs, extracellular matrix, and macrophages recruited over a period of several weeks, is similar to the process of tumor tissue growth 13. This pathologic similarity between tumor cell growth and benign neointimal formation has led to the discovery of anti-tumor drugs such as Paclitaxel as effective agents for the treatment of ISR 12, 13.
1.2.2 Stent thrombosis
In spite of restenosis remaining a clinical problem in approximately 10% of patients with DES implantation, it can often be successfully treated with repeat implantation. The greatest concern, however, has been for stent thrombosis which is associated with a high rate of myocardial infarction and death. The rate of early stent thrombosis (less than 30 days following implantation) appears similar in both BMSs and DESs (Cypher?and Taxus?) 14. However, late stent thrombosis has been increasingly reported beyond 12 months following DES implantation with the greatest risk occurring as a result of premature discontinuation of anti-platelet therapy 15-19. Although the precise mechanism of late stage stent thrombosis is unknown, it is generally believed that the combination of delayed endothelialization due to anti-proliferative therapy and persistence of the nonerodable polymer contribute to a hypersensitivity reaction, possibly with some residual active drug that may not be eluted 20, 21.
2. The structure and components of a drug eluting stent
Drug eluting stents are comprised of three major parts: 1) drug delivery platform (metal stent) to hold the drug and provide supporting forces for the collapsed artery; 2) drug coating polymer to attach the drug on the stent surface; 3) anti restenosis drugs released from the stent to inhibit restenosis formation after stent implantation. We review each component systemically in order to have an anatomic understanding of drug eluting stent.
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Coronary Artery Diseases 2.1 Stent platforms
2.1.1 Stent materials
2.1.1.1 Non degradable material
316L stainless steel: 316L stainless steel (316L SS) is the most commonly used metal material in stents due to its excellent mechanical properties and corrosion resistance and is used in the first generation DESs, Cypher (sirolimus-eluting stent, Cordis, Warren, NJ) and Taxus (paclitaxel-eluting stent, Boston Scientific, Natick, MA). However, its ferromagnetic nature and low density make it a non-MRI compatible and poorly visible fluoroscopic material. Furthermore, the release of nickel, chromate and molybdenum ions is likely to provoke immune reactions and inflammatory responses, which may result in ISR22. Therefore, a number of materials have been used as coatings to improve its visibility and biocompatibility.
Co-Cr: Co-Cr alloy exhibits superior radial strength and improved radiopacity compared to 316L SS. It allows for thinner stent struts, which is a significant advantage because the thickness of stent struts is a important factor on the reduction of restenosis in BMSs23, 24. At the same time, it reduces device profile and consequently improves its deliverability to the target lesion. Co-Cr platforms are employed in the second generation DES, Xience V (everolimus-eluting stent, Abott Vascular, CA) and Endeavor (zotarolimus-eluting stent, Medtronic Vascular, Santa Rosa, CA).
Ta: The highly stable surface oxide layer, preventing electron exchange between the metal and the absorbed biological species25, 26, make Ta an excellent corrosion resistant material. Ta has been coated on 316L SS to improve corrosion properties and biocompatibility of 316L SS27. Its high density and non-ferromagnetic properties28,29 make Ta an excellent fluoroscopically visible and MRI compatible material. However, its poor mechanical properties make Ta stents have higher rates of recoil compared to 316L SS based stents and result in enhanced neointimal formation30. Although no Ta based stents have been approved by FDA for general use to date, a bare Ta stent has been used by Cordis? (Johnson & Johnson, USA) in clinical trials and released commercially in Japan, Canada and Europe31. Ti: Although Ti has excellent biocompatibility and corrosion resistance, pure Ti is not commonly used for making stents due to its low tensile strength and ductility. However, Ti alloys might be optimum for stents. Ti-nitride-oxide coating on 316L SS was biologically inert, reducing platelet and fibrinogen deposition, and neointimal hyperplasia32. Promising results were reported in clinical trials by the Titan stent (Hexacath, France) using this coating33,34. Moreover, Ti-based Ta and niobium alloys showed excellent haemocompatibility35, indicating they have potential applications for stents. An extensively used Ti alloys in stents is Ni-Ti.
Ni-Ti:Ni-Ti alloy is also a common material for stents which has good biocompatibility, radial force and shape memory. However, the release of nickel ions and their toxic effects on tissues have been reported36, 37. In addition, it is suspected of producing mild inflammation when contacting monocytes38. In order to solve these problems, the surface of Ni-Ti is passivated to increase the Ti oxide concentration and decrease the Ni concentration39, 40, and it is coated by some materials such as polyurethane41, Ti nitride42 and polycrystalline oxides43 to improve the corrosion resistance. Another problem is that the Ni-Ti alloy does
Coronary Arterial Drug-Eluting Stent: From Structure to Clinical 201 not have adequate visibility under fluoroscopy44 though it can be visualized by MRI45. Ni-Ti is used by ACT-One TM (Progressive Angioplasty Systems, USA)46, Paragon (Progressive Angioplasty Systems, USA)47, and Radius (Scimed, USA)48 in clinical trials.
Pt-Ir:The bare stents made from Pt-Ir alloy of 90% platinum and 10% iridium have been implanted in animal models, showing excellent radiopacity and a reduction in both thrombosis and neointimal proliferation with less inflammatory reactions. However, their recoiling percentage was much higher (16%) than the 316L SS stents (5%)49, 50. Though Pt-Ir alloy stents have been proved safe and effective in a human clinical trial51, the biocompatibility and haemocompatibility of Pt-Ir alloys needs be further investigated.
2.1.1.2 Biodegradable metallic materials
Besides the aforementioned non-degradable metallic stents, a new concept is biodegradable metallic stent. The recently used biodegradable metallic materials are pure Fe52 and Mg alloys53.
Pure Fe: The degradation of Fe was completed through the oxidation of Fe into ferrous and ferric irons which were dissolved into biological media54. It is reported that ferrous ions could reduce the proliferation rate of vascular smooth muscle cell in vitro by influencing growth-related gene expression and therefore may antagonize restenosis in vivo54. The pure Fe (more than 99.5%) stents with strut thickness varied from 100 to 120μm have been implanted successfully in rabbit and porcine and endothelialization was observed52, 55. However, further investigation is needed on the modification of the composition and design of the stent to expedite the degradation process55.
Mg alloys: Mg and its alloys has been used as orthopedic materials56, but it is a new principle to apply these materials to coronary stents53. Unlike pure Fe, pure Mg is not suitable for making stents due to mechanical and corrosion properties. There are two Mg alloys, AE2153 and WE4357, used for making stents. These materials are radiolucent and thus cannot be imaged by X-rays. However, they can be visualized by intravascular ultrasound and MRI58. The Lekton Magic stent (Biotronik, Switzerland) is made from WE43, which is safe and can provide sufficient support to the collapsed arteries within its degradation time (2-3 months)59,60. It has been implanted in porcine models, and the preliminary clinical data showed promising results that after one-month implantation of magic stents, 18 out of 20 patients had normal flow while 30%-40% restenosis occurred in the other 2 patients57. However, mixed results were found in a human study using a Biotronik’s Mg absorbable metal stents61,62, indicating further evaluation is needed.
2.1.2 Stent geometric design
Self-expanding vs. balloon-expandable: Basically, there are two stent types: the self-expanding and the balloon-expandable stents. The self-expanding stent is made of a coil, mesh or zigzag configuration that is constrained with an outer sheath. The stent elastically springs open to a predetermine size after the sheath is removed. The balloon-expandable stent is crimped and premounted on a balloon, and expanded by the inflation of the balloon whose diameter determines the size of expanded stent. Though the self-expanding stent will expand to a calculated size automatically, it is not recommended and seldom used at present because it continues to expand in the weeks after deployment and thus leads to the
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Coronary Artery Diseases stent migration to the adventia and the stent cross-sectional area increasing accompanied by medial compression63, 64.
Coil vs. Tube: Generally, the balloon-expandable stent is classified into two groups: the tube and the coil design. The tubular stent is cut from a steel tube or a flat sheet of metal which is then rolled and welded to form a tube. The coil design is composed of a continuously wound wire or a series of flat sheet coils, which has a greater strut width with gaps and fewer or no connections between struts compared with the tubular stent65. These characteristics make coil stents more flexible but have poor radial strength and the wide gap allows tissue prolapse66. As a result, coil design is being replaced by the tube design gradually.
Slotted tube vs. Modular: Tubular balloon-expandable stents also can be divided into two types: slotted tube and modular design. Both of them are cut from a tube of metal. A clinical study showed slotted tube stents resisted restenosis more than the modular stents (22.1% vs 25.2%)67. The slotted tube stent also has two kinds: one is closed cell design, and the other one is open cell design. The former one is loser to the original concept of slotted tubes, while the latter is more like the modular stent. In a clinical study, less platelet activation was found in the implantation of closed cell stents than the open cell stents, which may have resulted from a greater degree of tissue prolapsed with the open cell stents68.
Long vs. Short: It has been proven that stent length is associated with restenosis rate and clinical events (mainly target lesion revascularization): 20 mm length stent resulted in 22.6% angiographic restenosis rate; 27 mm length stent led to 36% angiographic restenosis rate; and 43 mm length stent produced 67.5% angiographic restenosis rate69. Similar results were found in another clinical study that showed the angiographic restenosis rates were 20.8% and 37.3%, respectively, in the implantation of 16 mm and ≥ 32 mm BMSs, and the angiographic restenosis rates were 7.2% and 10.3% for the implantation of the same length of DESs70. Therefore, stent length is still a problem in DESs. On the one hand, the DESs can reduce restesnosis in both long and short lesions compared with BMSs, but a long stent is expected to cover all the diseased area. On the other hand, a long DES may increase the occurrence of restenosis.
Wide vs. Narrow: As with stent length, the stent width is another problem in both BMSs and DESs. The same study mentioned above showed the angiographic rates were 40.8% in the 2.5 mm diameter vs. 12.9% in the 3.5 mm diameter BMSs, and 8.8% vs. 5.5% in the same diameter DESs70. Although the study suggested that the wide diameter stent is more favorable than the narrow one, the width is still a problem which has not been eliminated by DESs.
More struts vs. less: An animal study, of stainless steel stents with different configurations implanted in rabbit iliac arteries, indicated that the stents with 12 struts per cross section had 50% to 60% less mural thrombus and 2-fold less neointimal area than those of identical stents with only 8 struts per cross section71. However, another animal study showed the neointimal growth is not related to the number of struts, but associated with the stretching of arteries and the injury depth caused by the implantation of stents72. Therefore, further research is needed to evaluate the impact of the number of struts in a stent on thrombosis and restenosis.
Coronary Arterial Drug-Eluting Stent: From Structure to Clinical 203 Thick vs. thin struts: As discussed above, the injury depth and the stretching of the coronary arteries have a great impact upon neointimal growth72, and the two parameters are vary inversely with the thickness of the stent struts. Thinner struts slice into tissue more easily and hence induce more deep injury to the coronary arteries, but unlike thicker struts, they cause less angulations and stretching of the arterial wall. The effect of strut thickness on restenosis incidence was evaluated in both ISAR-STEREO and ISAR-STEREO 2 trials23, 24. In the ISAR-STEREO trial, 326 patients were implanted with thin-strut stents (strut thickness is 50 μm) while in the other 325 patients were assigned to receive thick-strut stents (strut thickness is 140 μm) randomly. The results showed the incidence of angiographic restenosis was 15.0% in the thin-strut group vs. 25.8% in the thick-strut group (P=0.003), clinical restenosis was also significantly reduced, with a reintervention rate of 8.6% among thin-strut patients vs 13.8% among thick-strut patients (relative risk, 0.62; 95% CI, 0.39 to 0.99; P=0.03), and no difference was observed in the combined 1-year rate of death and myocardial infarction (MI)23. In the ISAR-STEREO 2 trial, a total of 611 patients with symptomatic coronary artery disease were randomly assigned to receive two different kind of stents in both design and strut thickness: the thin-strut ACS RX Multilink stent with interconnected ring design (Guidant, Advanced Cardiovascular Systems, Santa Clara, California) (strut thickness 50μm) were implanted into 309 patients while the thick-strut BX Velocity stent with closed cell design (Cordis Corp., Miami, Florida) (strut thickness 140μm) were implanted into 302 patients. The results showed the incidence of angiographic restenosis was 17.9% in the thin-strut group vs. 31.4% in the thick-strut group (p < 0.001), a target-vessel revascularization (TVR) due to restenosis was required in 12.3% of the thin-strut group vs. 21.9% of the thick-strut group (p = 0.002), and no significant difference was observed in the combined incidence of death and MI at one year24. Therefore, the stents with thinner struts is preferred for the design of new stents as they can reduce angiographic and clinical restenosis more than those with thicker struts.
Square vs. round strut cross-section: Another note worthy stent geometry is the shape of the strut cross-section. An in vitro study showed the migration distance of human aortic endothelial cells along the surface of the flat pieces of 316L stainless steel with the sharpest edge angles of the bottom surfaces (35°) was significantly greater than with larger angles (70°, 90°, and 140°, P < 0.05) under static and flow conditions, indicating the edge angle of stent struts does influence the rate of endothelialization. The stents with smaller edge angles and slopes facilitate endothelialization as compared with the larger angles73. In addition, when compared to those with smaller edge angles, the stents with larger angels have sharper edges in the direction of blood flow, which may interfere with blood by slicing the blood cells. Therefore, the square strut cross-section is not recommended and the round strut cross-section without corners or sharp edges is popular at present.
Rough vs. smooth surface: The stent surface topography is thought to play an important role in stent performance. Though some studies showed a smooth, polished surface reduced thrombus adhesion and neointimal growth74, it does not mean extremely smooth surfaces are optimal for re-endothelialization. Recently, an in vitro study suggested that a stent surface with a microscopic pattern of parallel grooves disposed in the direction of blood flow leads to a faster re-endothelialization process than the stent with smooth surface75. In addition, in a recent animal study, a similar result was observed a stent with a microscopic parallel grooves accelerated the endothelialization rate significantly 1 week after implantation in porcine carotid arteries compared to smooth stents76, 77. In order to
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Coronary Artery Diseases determine the relationship between the stent surface topography and outcome in patients undergoing implantation of stents with rough and smooth surfaces, a clinical trial of 200 patients with significant stenosis in native coronary vessels were randomly assigned in a double-blind study to receive either a rough or a smooth-surface stent. The study indicated rough stent surface does not increase late lumen loss after stent implantation as compared with a conventional smooth stent surface, and the angiographic restenosis rates were 25% with rough-surface stents vs 35% with smooth surface stents (P=0.19)78. Therefore, a relatively rough surface is better for stent performance than a smooth one.
Symmetry of Deployment: Previous studies suggested that the degree of restenosis is related to the symmetry of stent expansion and increased neointimal thickening was found in the unevenly deployed stents71, 79. In the presence of calcified lesions, the stents usually were expanded asymmetrically80, 81. It is believed that the symmetry of stent deployment might be influenced by the balloon folding patterns82. Currently, trefoil or tetrafoil folding is common, which prevents excessive expansion of one side of the stent83.
2.2 Drug delivery vehicles – Coating polymer
Polymers are large molecule compounds consisting of repeating structural units typically connected by covalent chemical bonds, which can be broadly classified into nonbiodegradable and biodegradable polymers when used as drug carriers in DESs.
2.2.1 Non biodegradable polymers
Both the first and the second generation of DESs are using nonbiodegradable polymers to control the drug-elution profile. In the first generation of DES, Cypher (sirolimus-eluting stent, Cordis, Warren, NJ) used polyethylene-co-vinyl acetate (PEVA)/poly-n-butyl methacrylate (PBMA) to delivery sirolimus, while Taxus (paclitaxel-eluting stent, Boston Scientific, Natick, MA) used polystyrene-b-isobutylene-b-styrene (SIBS) to delivery paclitaxel. Both stents can reduce restenosis significantly compared to BMSs70,84-86, however, an increase in the rate of MI and mortality was reported in patients following 18 months to 3 years after the implantation of Cypher or Taxus87-90. In the second generation of DES, Xience V (everolimus-eluting stent, Abott Vascular, CA) employed a fluoropolymer to carry everolimus, while Endeavor (zotarolimus-eluting stent, Medtronic Vascular, Santa Rosa, CA) employed phosphorylcholine (PC) to carry zotarolimus. Compared with the respective BMS, the target vessel revascularization (TVR) was reduced significantly by both Endeavor and Xience V stents91,92. Xience V stents reduced angiographic late loss without an increase of stent thrombosis compared with Taxus stents in the SPIRIT III study93, whereas Endeavor stents showed a higher incidence of restenosis compared with Cypher stents in the ENDEAVOR III trial94. However, both Endeavor and Taxus stents had an equivalent target lesion revascularization rate in a later trial95. In addition, there were no cases of very late stent thrombosis in earlier ENDEAVOR trials over 4 years indicating Endeavor stents are safe in the long-term96.
2.2.2 Biodegradable polymers
As nonbiodegradable polymers may lead to inflammatory response97, the biodegradable polymers applied for stent coatings to delivery drugs are being investigated. The most
Coronary Arterial Drug-Eluting Stent: From Structure to Clinical 205 commonly used polymers now are polylactic acid (PLA), polyglycolic acid (PGA) and their copolymer, polylactic-co-glycolic acid (PLGA)98, 99, which are fully metabolized to water and carbon dioxide and excreted via the respiratory system. Despite a series of promising preliminary data that was reported100-103, the development of biodegradable polymers in DES is still challenging. On the one hand, the degradation of polymers are affected by a variety of factors104 such as the pH, the polymer’s size, molecular weight and crystallinity, etc, making the drug release control difficult. On the other hand, the accumulated acidic products from polymer degradation may result in significant inflammatory response of the vessel wall and therefore lead to restenosis.
2.2.3 Other materials and methods
Other stents that do not use a polymer at all are still under development. For example, a titanium–nitric oxide alloy has been applied to stainless steel stents with encouraging results, including decreased platelet adhesion and neointimal hyperplasia compared with BMS34. A microporous stainless steel stent (Yukon, Translumina, Germany) allows for dose-adjustable, multiple drugs, and on-site coating105 [63]. The system is therapeutically effective with rapamycin106. A nanoporous hydroxyapetite (a biocompatible crystalline derivative of calcium phosphate) coating, which can be impregnated with anti-restenotic drugs, is currently under development107. A stainless steel stent coated with nanoporous aluminium oxide and tacrolimus showed disappointing results, however, with evidence of particle debris shed from the coating contributing to increased neointimal hyperplasia108. An interesting drug delivery system developed recently is composed of magnetic nanoparticles (MNPs) loaded with endothelial cells and a 304 grade stainless steel109. The endothelial cells were loaded on polylactide modified MNPs and then moved by a magnetic field gradient towards the stent surface after injection, which enabled artificial endothelialization and repeated dosing, showing promising future. However, further evaluation in animal studies and clinical trials is required.
2.3 Therapeutic agents
2.3.1 Sirolimus and its analogues
Sirolimus: Sirolimus (rapamycin), a macrocyclic lactone used in the Cypher stents, binds to FK-binding protein 12 and subsequently inhibits the mammalian target of rapamycin (mTOR). The mTOR prevents the degradation of p27kip1, a cyclin-depengdent kinase inhibitor, thereby inhibits the migration and proliferation of SMCs110, 111. However, the mTOR is also a downstream target of the phosphatidylinositol-3 kinase pathway, which inhibits the tissue factor in endothelial cells and monocytes112-114. Therefore, the inhibition of mTOR by sirolimus leads to increasing expression and activity of tissue factor in endothelial cells112.
Zotarolimus: The former name of zotarolimus is ABT-578, which is one of the sirolimus analogues developed by Abbott laboratories. The extremely lipophilic property and low water solubility115 make zotarolimus a better candidate for DES than sirolimus. It has been employed in Medtronic’s Endeavor stents which was approved by FDA in 2008 and showed better endothelialization than Cypher at 14 days post implantation116. It is also used in Zomaxx stents developed by Abbott laboratories117.
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Coronary Artery Diseases Everolimus: Everolimus is another sirolimus analogue, which is also used as an immunosuppressive agent 118. As with sirolimus, it inhibits smooth muscle cell proliferation and in-stent neointimal growth119, 120. However, compared to sirolimus, everolimus has a better pharmacokinetic profile and bioavailability when used in organ transplant121. When it is used in intracoronary elution, everolimus absorbs to local tissue more rapidly and has a longer celluar residence time and activity122. It has been used in another FDA approved stent, Xience V, which also showed better endothelialization than Cypher at 14 days post implantation of stents116.
Biolimus A9: Biolimus A9 has similar immunosuppressive potency to sirolimus, but it is absorbed by vessel walls more readily and enters cells more rapidly123, 124. It has been investigated in two PLA coated stainless steel stents, Biomatrix (Biosensors International, Singapore) and Nobori (Terumo, Japan) 124-126. The biolimus-eluting stent has been proven to be safe and effective in reducing neointimal proliferation when compared to BMSs and Taxus in the Nobori 1 trial126.
2.3.2 Paclitaxel and its analogues
Paclitaxel: Paclitaxel, a lipophilic diterpenoid, binds to β-subunit of the tubulin heterodimer, promoting tubulin polymerization and cell cycle arrest, thus inhibiting the migration and proliferation of SMCs127, 128. Notwithstanding, an important regulator of endothelial and monocytic tissue factor induction113, 114, c-Jun NH2-terminal kinase, is also activated by paclitaxel129, 130, and, consequently, enhances the activity of tissue factor in endothelial cells 130. Coroxane: To improve the solubility of paclitaxel and reduce non-drug-related toxicties131, a protein-engineered nanoparticle albumin bound paclitaxel (nab-paclitaxel) named Coroxane was developed by Abraxis Bioscience Inc.. The phase 1 study has been conducted showing 10-30 mg/m2 doses of the drug are safe for humans132. The phase II study is ongoing. Docetaxel: Docetaxel is a semi-synthetic analogue of paclitaxel used for the treatment of ovarian, breast and non-small cell lung cancer133. Compared to paclitaxel, docetaxel has better anti-proliferative properties134, however, it has dose-dependent cytotoxicity135.
2.3.3 Others
Tacrolimus: Tacrolimus (FK-506 or Fujimycin or Prograf), a hydrophobic macrolide immunosuppressant drug, is a T cell inhibitor resulting in cell apoptosis by holding cells in the G0 phase of the cell cycle and has a different mechanism from that of sirolimus136, 137 . Moreover, unlike the mTOR inhibitors and paclitaxel, tacrolimus does not increase expression of tissue factor since it has a preferential effect on SMCs as suppressed endothelial cells112, 130, 138, 139. Although some studies showed that tacrolimus-eluting stents can significantly reduce neointimal proliferation108, 140, a study on Janus, a new design of tacrolimus-eluting stent (Sorin Biomedica Cardio, Italy), indicated the performance of Janus was no better than a BMS141. Other tacrolimus-eluting stents and their long term outcomes are still under investigation142.
Pimecrolimus: Pimecrolimus (SDZ ASM 981), an analogue of ascomycin, has similar effects and mechanism of tacrolimus. It has received substantial interest for its significant anti-inflammatory activity, immunomodulatory capabilities and low systemic immunosuppressive potential143.
Coronary Arterial Drug-Eluting Stent: From Structure to Clinical 207 Curcumin: Curcumin, a component of turmeric, exhibits a variety of biological activities such as anti-proliferative activity, anti-inflammatory, anti-oxidant activity, wound healing ability, and anti-microbial activity144-146. Thus, curcumin is an excellent candidate in the application of coronary stents to inhibit the proliferation of SMCs and prevent inflammatory response, and hence prevent the occurrence of restenosis.
Resveratrol: Resveratrol (3, 5, 4′- trihydroxystilbene), is a phytoalexin found in various plants, such as grapes, berries, peanuts and wines, and has many biological activities including anti-fungal, anti-bacterial, anti-viral, anti-oxidant, and anti-inflammatory activity147, 148. It is most important, however, that resveratrol has the potential to be used as a therapeutic agent in DES to inhibit thrombosis and restenosis because of its ability to block the aggregation of human platelets and prevent the proliferation of vascular smooth muscle cells149-152.
CD 34 antibody: Contrary to SMC inhibition, a novel prohealing technology is used in the Genous TM stent (Orbus Neich, Fort Lauderdale, Florida), which is a stainless steel stent coated with murine monoclonal antihuman CD34 antibodies that attracts endothelial progenitor cell to enhance re-endothelialization. The reported results indicate that the Genous TM stent is effective and promising153-156.
Anti-VEGF: Another similar concept is the bevacizumab-eluting stent (Biocompatibles Ltd., London, UK)157. Bevacizumab, a specific anibody of vascular endothelial growth factor (VEGF), was coated on the surface of BiodivYsio stent to inhibit the development of the vaso vasorum and thereby promote atheromatous plaque stability. Further investigation is in progress.
Drug Combinations: Besides developing new individual drugs to inhibit thrombosis and restenosis, combining the known effective drugs together on the stents is a novel method. For example, pimecrolimus and paclitaxel were loaded together on Symbio stents; heparin and sirolimus were coated on Synchronnium stents; genistein were combined with sirolimus158.
3. Current commercially available and investigational DESs
Currently, four drug-eluting stents have been approved by the FDA for the U.S. market including: Sirolimus coated Cypher? stent (Cordis, Inc.), Paclitaxel coated Taxus? stent (Boston Scientific, Inc.), Zotarolimus coated Endeavour? stent(Medtronic, Minneapolis, MN) and Everolimus coated Xience? Stent (Abbott, Redwood city, California). Cook, MIV Therapeutics, Inc. and a few others including MicroMedical Group, Inc. have been working hard to enter the stent market as well. The table below provides a summary of currently available and investigational DESs and their status.
Among currently available nonbiodegradable DESs, both Cypher? and Taxus? stents have been well- accepted by clinical cardiologists and patients. The incidences of in-stent restenosis in both stents are effectively confined to less than 10%. However, the common problem faced with both stents is late-stage thrombosis which occurs at approximately 0.4% after one year of implantation. Endeavour? and Xience? are relatively new to the market, and therefore their long-term clinical safety and efficacy need to be further investigated. Cypher? and Taxus? stents, the first generation of DESs, are constructed from 316L stainless steel, while recently approved Endeavour? and Xience? stents are made from
208
Coronary Artery Diseases Cobalt chrome. All four approved DESs are coated with nonbiodegradable polymers. Nonbiodegradable polymers were used rather than biodegradable polymers primarily due to the bio-incompatibility issues of existing biodegradable polymers.
Table 1. The current commercially available and investigational DESs and their status
3.1 Cypher? stent
Cypher? stent has 8-33 mm in length and is offered in 2.5-3.5 mm diameters. Its coating matrix is composed of three nonbiodegradable polymers: Parylene C coated primer layer for improving adhesion of polymer to the metal surface, followed by a layer of polyethylene-co-vinyl acetate (PEVA)/poly n-butyl methacrylate (PBMA) copolymer containing the active agent of Sirolimus. The top layer is a drug-free coating of PBMA to control drug release and to prevent a burst effect. The Cypher? stent releases 50% of its Sirolimus content during the first week after implantation and 85% of the drug over 30 days. All of the Sirolimus is eluted over 90 days.
3.2 Taxus? stent
Taxus? stent comes in lengths of 8-28mm and diameters of 2.5-3.75mm. The stent is coated with non-biodegradable poly (styrene-b-isobutylene-b-styrene), known as TransLute polymer. The stent provides a burst release of Paclitaxel during the initial 48 hours followed by slow release over the next 10 days and no further release after 30 days.
3.3 Endeavour? DES
Endeavour? stent is a cobalt chrome stent with strut thickness of 91 μm (originally S660 stent). The stent was coated with 4.3 μm of phosphorylcholine polymer and the immunosuppressive drug: Zotarolimusan an analog of Sirolimus.
Coronary Arterial Drug-Eluting Stent: From Structure to Clinical 209 3.4 Xience? DES
Xience? stent is the most recently FDA approved DES. The stent is made by using Abbott’s cobalt chrome Multilink? Vision stent as a platform, coated with7.6um of nonbiodegradable fluropolymer and another Sirolimus analogue drug, Everolimus.
4. Fully Biodegradable Drug Eluting Stent (BDES)
Despite a tremendous amount of capital invested in developing fully biodegradable stents to overcome the drawbacks existing in current nonbiodegradable stents, only five fully biodegradable stents have been investigated in humans so far:
1.The Igaki-Tamai bioabsorbable stent (Igaki Medical Planning Company, Kyoto, Japan)
2.Biodegradable everolimus eluting XIENCE V stent (BVS, Abbott Vascular, Santa Clara,
CA, USA).
3.Tyrosine polycarbonate biodegradable stent (Reva Medical Inc, San Diego, CA)
4.Salicylate-based polyanhydride ester biodegradable sirolimus-eluting stent (Ideal?
Bioabsorbable Therapeutics Inc., CA, USA), and
5.Biodegradable magnesium alloy stent (Biotronik AG, Berlin, German)
Table 2 below summarizes the physical, chemical and structural characteristics of these five stents (159).
4.1 The Igaki-Tamai Bioabsorbable Stent
Igaki-Tamai Bioabsorbable Stent is the first absorbable stent that was implanted in humans. It is constructed from poly-L-lactic acid (PLLA). The stent is designed in a zig-zag helical coil structure with a 170um strut thickness. The stent is delivered by a balloon-mounted self-expanding sheathed system with warmed contrast medium. As PLLA is radiolucent, gold markers at each end provide radio-opacity for stent identification. The stent does not release any antiproliferative drug. In the preliminary, first-in-man prospective, nonrandomized clinical trial that enrolled 50 patients, a 4-year follow-up of all the patients (100%) revealed a low complication rate with 1 in-hospital stent thrombosis causing a Q-wave MI, 1 non cardiac death, and 18% repeat PCI and no surgical revascularization. Although there have been no further human coronary implants and the focus is now on a peripheral application, this stent is important in the history of PCI with absorbable stents.
4.2 Biodegradable everolimus-eluting XIENCE V stent
XIENCE Stent has a backbone of circumferential hoops of crystalline PLA, with a strut thickness of 150μm, linked directly together or held by straight bridges achieving a radial strength similar to the Multi-link Vision metal stent. At both ends of the stent, two adjacent radio-opaque metal markers facilitate correct fluoroscopic positioning. The stent was coated with everolimus( 8.2 μg/mm) and amorphous PLA matrix in the ratio of 1:1. Eighty percent of the coated drug is released in 30 days, which is similar to the release patterns of the Xience V? and Cypher? DESs. The stent has been evaluated in an observational first-in-man study of 30 patients with single de novo coronary artery lesions. At the 2-year follow-up, the device has been shown to be safe with no cardiac deaths, target lesion revascularizations, nor stent thromboses and only one non-Q wave MI. In-stent late loss amounted to 0.43 ± 0.44 mm at 6 months and 0.48 ± 0.28 mm at 2 years. Binary restenosis
210
Coronary Artery Diseases was observed in 7.7% of patients (2/26) at 6 months and in 0% of patients at 2 years (0/19). One third of stent struts had resolved after 2 years as assessed by optical coherence tomography. Although these data are encouraging, the small number of patients enrolled in the trial and the simplicity of the lesions treated means that a great deal of work remains to be done before the device can be considered for routine use in clinical practice. The stent is currently commercially available in Europe.
4.3 Tyrosine polycarbonate biodegradable REVA stent
The REVA stent is made from monomeric units of the common amino acid L-tyrosine, chemically modified to incorporate iodine molecules so as to make this stent radiopaque. This polymer degrades to carbon dioxide and water in a similar fashion to PLA. The stent struts were designed with a “slide and lock’” feature that enables strut thickness to be reduced without compromising radial integrity. The RESORB first-in-man trial showed unfavorable outcomes between 4 and 6 months post-implantation with a higher-than-anticipated target lesion revascularization rate driven mainly by reduced stent diameter
4.4 Polyanhydride ester (PAE) polymeric stent
The PAE stent is made by incorporating salicylic acid into the backbone of a PAE polymer. The stent surface is coated with Sirolimus with complete elution of the drug by 30 days. The stent offers the advantages of being absorbable and providing anti-inflammatory and antiproliferative properties. In the first-in-man Whisper trial, a stent with strut thickness of 200um and a crossing profile of 2.0 mm with a stent-to-artery coverage of 65% was implanted in 8 patients. Because of the higher-than-expected intimal hyperplasia in this FIM study, a subsequent design with thinner struts, a higher dose of Sirolimus, and a lower percent wall coverage is currently under investigation.
4.5 Absorbable magnesium stent
The AMS stent is composed of 93% magnesium and 7% rare-earth metals. It degrades within the body over a 2-to-3-month time frame, forming inorganic salts containing calcium, chloride, oxide, sulfates and phosphates. The AMS stent has been evaluated in an observational study (PROGRESS) of 71 patients with an angiographic and IVUS assessment at 4 months and clinical follow-up at 1 year. The relatively high in-stent late loss of 1.08 ± 0.49 mm at 4 months translated into a TLR rate of 48.4% at 1 year. The main contributors to restenosis, as detected by IVUS at 4 months, were a decrease of external elastic membrane volume and neointimal hyperplasia, but only small remnants of the stent material were observed at 4 months.
5. Future Development of DES
Ideal DES, from a clinical aspect, should possess the following characteristics: a remarkable ease of use, unparalleled efficacy, impeccable safety, and restoration of conduit vessel physiology. However, from an engineering point of view, it is impossible to incorporate all parameters to make an “apple-pie” DES. Therefore the next generation of DES will be continuously developed by optimizing these three components through a variety ways including the new material selection, new platform design, and new drug incorporation, etc.
Table 2. Comparison of the Preoterties Among 5 Absorable Stents https://www.doczj.com/doc/4610354184.html,
Coronary Artery Diseases
212 The challenges faced by emerging technologies are to reduce restenosis in high-risk lesions, without compromising healing, in order to avoid late thrombotic complications and to improve system deliverability to allow treatment of more complex patients. Currently, a number of strategies are being utilized to achieve these goals through the development of novel stent platforms, coating with biodegradable polymers or moving away from polymers, and with new generations and/or combinations of biological agents that both inhibit proliferation and promote endothelialization. With the recent positive data from Abbott’s ABSORB trial, clinical consensus is building that fully bioabsorbable stents (BDS) represent the next generation in DES. Table 3 summarizes the potential benefits for the
Faciltates noninvasive diagnosis imaging(MR/CT)Surgical option not restricted Easier repeat revascularization May limit late-stent thrombosis Allows late favorable positive remodeling May reduce long-term dual antiplatelet therapy Has Larger drug-loading capacity Addresses patient's concerns about permanent implants
Table 3. Potential Benefits of Biodegradable Stent. 6. References
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中国移动互联网发展史 赛迪研究院互联网研究所陆峰博士本世纪以来，我国移动互联网伴随着移动网络通信基础设施的升级换代快速发展，尤其是2009年国家开始大规模部署3G网络，2014年又开始大规模部署4G网络，两次移动通信基础设施的升级换代，有力地促进了中国移动互联网快速发展，服务模式和商业模式大规模创新。 一、萌芽期（2000年-2007年） 技术发展：WAP应用是移动互联网应用的主要模式。 该时期由于受限于移动2G网速和手机智能化程度，中国移动互联网发展处在一个简单WAP应用期。WAP应用把Internet网上HTML的信息转换成用WML描述的信息，显示在移动电话的显示屏上。由于WAP只要求移动电话和WAP 代理服务器的支持，而不要求现有的移动通信网络协议做任何的改动，因而被广泛地应用于GSM、CDMA、TDMA等多种网络中。在移动互联网萌芽期，利用手机自带的支持WAP协议的浏览器访问企业WAP门户网站是当时移动互联网发展的主要形式。 市场竞争：移动梦网催生了一大批SP服务商。 2000年12月中国移动正式推出了移动互联网业务品牌“移动梦网Monternet”，移动梦网就像一个大超市，囊括
了短信、彩信、手机上网（WAP），百宝箱（手机游戏）等各种多元化信息服务。在移动梦网技术支撑下，当时涌现了雷霆万钧、空中网等一大批基于梦网的SP服务提供商，用户通过短信、彩信、手机上网等模式享受移动互联网服务。但由于移动梦网服务提供商存在业务不规范、乱收费等现象，2006年4月，国家开展了移动梦网专项治理行动，明确要求扣费必须用户确认、用户登录WAP需要资费提示等相关规范，大批SP服务商因为违规运营退出了市场。 二、成长培育期（2008年-2011年） 技术发展：3G移动网络建设掀开了中国移动互联网发展新篇章 随着3G移动网络的部署和智能手机的出现，移动网速大幅提升初步破解了手机上网带宽瓶颈，简单应用软件安装功能的移动智能终端让移动上网功能得到大大增强，中国移动互联网掀开了新的发展篇章。经过3G网络一年多的试点商用，2009年1月7日工业和信息化部宣布，批准中国移动、中国电信、中国联通三大电信运营商分别增加TD-SCDMA、CDMA2000、WCMDA技术制式的第三代移动通信（3G）业务经营许可，中国3G网络大规模建设正式铺开，中国移动互联网全面进入了3G时代。 市场竞争：各大互联网公司都在探索抢占移动互联网入口
预制装配式建筑的优势及普及化难点 摘要：本文介绍了国内外预制装配式建筑发展及现状，阐述预制装配式建筑的特点及优势，结合国内农村房屋存在的问题浅谈预制装配式建筑未来在农村建筑中的应用前景及应用难度。提出了未来预制装配式建筑普及方向。 关键词：预制装配式建筑；农村房屋改进方向；建筑工厂化。正文： 0.引言 长久以来，我国建筑业主要采用的是现场施工的方法，即从搭脚手架、支模板、绑钢筋、及浇注混凝土，大部分工作都是在现场完成人工完成。这造成了巨大的劳动强度及巨大的施工风险，此外对环境的破坏较大，大量的固体建筑垃圾以及噪声影响着城市的发展及市民的生活质量，现场施工带来的工程质量与精度不高也亟待解决。 预制装配式建筑是将组成建筑的部分构件或全部的构件在工厂内加工完成，然后运输到施工现场将预制构件通过可靠的连接方式拼装就位而建成的建筑形式[1] 1.国内外预制装配式建筑的发展及现状 上世纪50年代，二战使欧洲遭受到严重的创伤，建筑尤其是住宅急需大量的重建。为了解决住房问题，欧洲采取工业化的建造方式建造了大批的房屋，并因此建成了标准的、完整的的住宅体系，并延续至今。同样在上世纪70年代能
源危机期间美国开始推行配件工厂化机械式的生产。美国的城市发展部颁布了一系列严格的行业标准规范，并且沿用至今。美国城市的建筑结构基本上是装配式混凝土结构和钢结构。其预制与预应力混凝土协会编制的《PCI设计手册》中就包括了与装配式结构相关的部分。该手册不仅仅是在美国，更是在整个国际上都具有深远的影响力！[2-3] 久远的发展历史下产业化住宅的比例在瑞典占80%，英国、美国、日本都在70%以上。[4] 与发达国家相比，我国的装配式建筑起步时间较晚。在20世纪70年代才开始出现装配化建筑的概念，期望可以发展出集高质高效高速及低成本为一体的建筑形式。80年代，已有不少工程中采用预制屋面梁、吊车梁、预制屋面板、空心楼板等构件，但是因为当时的技术水平有限，虽然预制构件得到不少应用，建成的建筑质量普遍不太高，并存在构件跨度小、承载力低、整体性延性差等的缺点。楼屋面板由于密封胶的质量问题及防水措施不完善，使用两三年后就开始出现了渗水漏水现象，保温隔热隔声的效果也不好，使消费者留下了不好的印象。90年代现浇混凝土施工技术的迅速发展，更加使得预制装配式建筑的发展一度停滞不前。[5]而到了最近十年来，随着我国经济快速的发展，人工成本又大幅度上升，预制装配式施工技术和管理水平较以往有了长足的进展，预制装配式建筑的应用重新被提及，并有了快速发展
中国互联网发展史 中国互联网的产生虽然比较晚，但是经过几十年的发展，依托于中国民经济和政府体制改革的成果，已经显露出巨大的发展潜力。中国已经成为国际互联网的一部分，并且将会成为最大的互联网用户群体。 纵观我国互联网发展的历程，我们可以将其划分为以下4个阶段： 一、从1987年9月20日钱天白教授发出第一封E-mail开始，到1994年4月20日NCFG正式连入Internet这段时间里，中国的互联网在艰苦地孕育着。它的每一步前进都留下了深深的脚印。 二、从1994-1997年11月中国互联网信息中心发布第一次《中国Internet发展状况统计报告》，互联网已经开始从少数科学家手中的科研工具，走向广大群众。人们通过各种媒体开始了解到互联网的神奇之处：通过谦价的方式方便地获取自己所需要的信息。 三、 1998-1999年中国网民开始成几何级数增长，上网从前卫变成了一种真正的需求。一场互联网的革命就这么在两年的时间里传遍了整个中华大地。对于IT业来说，这是个追梦的年代这个时候到处都充斥着美梦成真的故事。 四、对于进入2000年的中国IT业来说，梦想已不再那么浪漫了，尽管跨入新千年的天仍然是互联网的天，但这片天空中已飘起了阵阵冷雨，让为网而狂的人们分明感到了几许凉意…… "第一"的年代 正如从0开始后必然是1一样，中国网络时代自1994年从零开始以后，就不停地产生着"第一"，因为这是一个创新的年代。让我们通过这些第一记住这个时代。 1、中科院高能物理研究所的IHEPNET与互联网络的连通，迈出了中国和世界各地数百万台电脑的共享信息和软硬件的第一步。边疆也因此而成为我国第一家进入Internet的单位。 2、中国的第一批互联网使用者是全国一千多名科学家。 3、高能所提供了中国第一套万维网服务器。
国内外装配式建筑技术现状及发展趋势研究 [摘要]2016年3月份的两会，李克强总理在《政府工作报告》中进一步强调，大力发展钢结构和装配式建筑，加 快标准化建设，提高建筑技术水平和工程质量。党中央、国 务院高度重视装配式建筑的发展，印发了《中共中央国务院 关于进一步加强城市规划建设管理工作的若干意见》（中发[1016]6号）提出，要发展新型建造方式，大力推广装配式建筑，力争用10年左右时间，使装配式建筑占新建建筑面积 的比例达到30%。2016年9月27日，国务院办公厅印发了 《关于大力发展装配式建筑的指导意见》（国办发（2016]7l 号），提出以京津冀、长三角、珠三角三大城市群为重点推 进地区，常住人口超过300万的其他城市为积极推进地区， 其余城市为鼓励推进地区。因地制宜发展装配式混凝土结构、 钢结构和现代木结构建筑。 [关键词]建筑工业化装配式建筑技术现状 我国的装配式建筑在上世纪八十年代后期突然停滞并 很快走向消亡，PC技术沉寂了三十多年之后又重新在我国兴起，这是一个令人鼓舞和值得期待的事件。时隔30年的断 档期，无论是技术还是人员都非常匮乏，短期之内无法从根 本上解决人员、技术、管理、工程经验等软件方面的问题。 从市场占有率来说，我国装配式建筑市场尚处于初级阶段，
全国各地基本上集中在住宅工业化领域，尤其是保障性住房 这一狭小地带，前期投入较大，生产规模很小，且短期之内 还无法和传统现浇结构市场竞争。但随着国家和行业陆续出 台相关发展目标和方针政策的指导，面对全国各地向建筑产 业现代化发展转型升级的迫切需求，我国各地20多个省市 陆续出台扶持相关建筑产业发展政策，推进产业化基地和试 点示范工程建设。相信随着技术的提高，管理水平的进步， 装配式建筑将有广阔的市场与空间。 美国装配式住宅盛行于20世纪70年代。1976年，美国国会通过了国家工业化住宅建造及安全法案，同年出台一系 列严格的行业规范标准，一直沿用至今。除注重质量，现在 的装配式住宅更加注重美观、舒适性及个性化。在美国，大 城市住宅的结构类型以混凝土装配式和钢结构装配式住宅 为主，美国住宅用构件和部品的标准化、系列化、专业化、 商品化、社会化程度很高，几乎达到100%。用户可通过产 品目录，买到所需的产品。这些构件结构性能好，有很大通 用性，也易于机械化生产。 德国的装配式住宅主要采取叠合板、混凝土、剪力墙结构体系，采用构件装配式与混凝土结构，耐久性较好。德国 是世界上建筑能耗降低幅度最快的国家，近几年更是提出发 展零能耗的被动式建筑。从大幅度的节能到被动式建筑，德 国都采取了装配式住宅来实施，装配式住宅与节能标准相互
装配式建筑的内涵国内外装配式建筑的发展历 程与趋势 Document serial number【LGGKGB-LGG98YT-LGGT8CB-LGUT-
装配式建筑的内涵、国内外装配式建筑的发展历程与趋势 （1）内涵 装配式建筑是指用预制的构件在现场装配而成的建筑 从结构形式来说，装配式混凝土结构、钢结构、木结构都可以称为装配式建筑，是工业化建筑的重要组成部分。 这种建筑的优点是建造速度快，受气候条件制约小，既可节约劳动力又可提高建筑质量，用通俗的话形容，就是像造汽车那样造房子。
装配式建筑是转变城市建设模式、有降低建筑能耗、推进工业化的重要载体。 联合国经济委员会对工业化的定义 ■生产过程的连续性。 房屋建造的全过程联结为完整的一体化产业链。 ■生产物的标准化。 设计的标准化，建筑部品、构配件的通用化和系列化。 ■生产过程的集成化。 是指建筑技术、部品与建造工艺、工法的系统集成。 ■工程高度组织化。 科学管理方法把建造全过程组织起来 ■生产的机械化。 是指减少现场人工作业，实现构件生产工厂化、施工建造机械化。 《工业化建筑评价标准》：2016年1月1日实施 采用以标准化设计、工厂化生产、装配化施工、一体化装修和信息化管理等为主要特征的工业化生产方式建造的建筑。 （基本条件）。 为什么要编制这个标准 1.国务院、住建部对推动建筑产业现代化提出了一系列明确要求。 2.全国30多个省、自治区、市纷纷出台了指导意见和鼓励措施。 3.设计、构件生产、施工、装备制造和房地产开发企业积极响应，建设了一大批装
配式建筑试点，初步形成了“政府推动、企业参与、产业化蓬勃发展”的良好态势。 迫切需要建立一套适合我国国情的工业化建筑评价体系，制订并实施统一、规范的评价标准。
中国互联网发展史情况介 绍 Ting Bao was revised on January 6, 20021
中国互联网发展史情况介绍 （开场白）概况：本次关于中国互联网发展史的情况介绍由本团队担任，介绍分为4个板块，了解什么是互联网，互联网是怎么诞生、发展的。了解中国互联网的发展。了解互联网在美国发达国家的发展及应用。今天的我们是怎么利用互联网互联网给我们的生活带来了怎样的改变。分别有组员依次介绍。让我们穿越一下，回到19世纪50年代，看看那时的人们是怎么创造出互联网并应用互联网。 了解什么是互联网，互联网是怎么诞生、发展的。 了解中国互联网的发展。 了解互联网在美国发达国家的发展及应用。 今天的我们是怎么利用互联网互联网给我们的生活带来了怎样的改变。
什么是互联网 打个比方，互联网就是高速公路，网站就是连接各高速公路的城区，电脑就是汽车，人就是司机，信息就是南来北往的货物。 互联网，即广域网、局域网及单机按照一定的通讯协议组成的国际计算机网络。是全球最大的、开放的、由众多网络和计算机通过电话线、卫星及其他远程通信系统互连而成的超大型计算机网络，也称为国际互联网，英语为internet，中文译名为“因特网”。 互联网的起源：商务概论第19页。 互联网的发展 阿帕网（APPANet）------以太网（Ethernet）-------TCP/IP协议--------“word wide web”万维网 互联网的诞生在1950年代，通信研究者认识到需要允许在不同计算机用户和通信网络之间进行常规的通信。这促使了分散网络、排队论和封包交换的研究。 而美国为了能在爆发核战争时保障通信联络，所以建立了阿帕网。 1960年美国国防部国防前沿研究项目署（ARPA）建立的ARPA网引发了技术进步并使其成为互联网发展的中心。 插入人物介绍：利奥纳德·科仑洛克他在其博士论文中最早用排队论证明分组交换网络的优越性（1961）。并在1969年12月，参与了美国四所大学使用接口消息处理器（IMP）建立起阿帕网。 . 以太网（Ethernet）在1980年在全世界开始普及，也是目前因特网中数量最多的局域网络。 曾在施乐公司工作的迈特考夫博士（DR·METCALFE）于1973年发明了与传统的计算机网络实现方法完全不同的局域网络——以太网（Ethernet）1970年末，APPA开始了一个称为Internet的研究计划，主要研究如何将各种局域网（LAN）和广域网（WAN）互联起来，这个研究项目的成果就是 TCP/IP协议。1973年ARPA网扩展成互联网，第一批接入的有英国和挪威计算机。
(1) 原始住居与建筑雏形的形成 早在五十万年前的旧石器时代，中国原始人就已经知道利用天然的洞穴作为栖身之所，北京、辽宁、贵州、广东、湖北、浙江等地均发现有原始人居住过的崖洞。到了新石器时代，黄河中游的氏族部落，利用黄土层为墙壁，用木构架、草泥建造半穴居住所，进而发展为地面上的建筑，并形成聚落。长江流域，因潮湿多雨，常有水患兽害，因而发展为杆栏式建筑。对此，古代文献中也多有「构木为巢，以避群害」、「上者为巢，下者营窟」的记载。据考古发掘，约在距今六、七千年前，中国古代人已知使用榫卯构筑木架房屋（如浙江余姚河姆渡遗址），黄河流域也发现有不少原始聚落（如西安半坡遗址、临潼姜寨遗址）。这些聚落，居住区、墓葬区、制陶场，分区明确，布局有致。木构架的形制已经出现，房屋平面形式也因造做与功用不同而有圆形、方形、吕字形等。这是中国古建筑的草创阶段。 西元前二十一世纪夏朝建立，标志着原始社会结束，经过夏、商、周三代，而春秋、战国，在中国的大地上先后营建了许多都邑，夯土技术已广泛使用于筑墙造台。如河南偃师二里头早商都城遗址，有长、宽均为百米的夯土台，台上建有八开间的殿堂，周围以廊。此时木构技术较之原始社会已有很大提高，已有斧、刀、锯、凿、钻、铲等加工木构件的专用工具。木构架和夯土技术均已经形成，并取得了一定的进步。西周兴建了丰京、镐京和洛阳的王城、成周；春秋、战国的各诸侯国均各自营造了以宫室为中心的都城。这些都城均为夯土版筑，墙外周以城濠，辟有高大的城门。宫殿布置在城内，建在夯土台之上，木构架已成为主要的结构方式，屋顶已开始使用陶瓦，而且木构架上饰用彩绘。这标志着中国古代建筑已经具备了雏形，不论夯土技术、木构技术还是建筑的立面造型、平面布局，以及建筑材料的制造与运用，色彩、装饰的使用，都达到了雏形阶段。这是中国古代建筑以后历代发展的基础。 (2) 中国古代建筑发展史上的第一个高潮 西元前221年，秦始皇吞并了韩、赵、魏、楚、燕、齐六国之后，建立起中央集权的大帝国，并且动用全国的人力、物力在咸阳修筑都城、宫殿、陵墓。今人从阿房宫遗址和始皇陵东侧大规模的兵马俑列队埋坑，可以想见当时建筑之宏大雄伟。此外，又修筑通达全国的驰道，筑长城以防匈奴南下，凿灵渠以通水运。这些巨大工程，动辄调用民力几十万，几乎都是同时并进，秦帝国终以奢欲过甚，穷用民力，二世而亡。 汉代继秦，经过约半个多世纪的休养生息之后，又进入大规模营造建筑时期。汉武帝刘彻先后五次大规模修筑长城，开拓通往西亚的丝绸之路；又兴建长安城内的桂宫、光明宫和西南郊的建章宫、上林苑。西汉末年还在长安南郊建造明堂、辟雍。东汉光武帝刘秀依东周都城故址营建了洛阳城及其宫殿。 总秦、汉五百年间，由于国家统一，国力富强，中国古建筑在自己的历史上出现了第一次发展高潮。其结构主体的木构架已趋于成熟，重要建筑物上普遍使用斗栱。屋顶形式多样化，庑殿、歇山、悬山、攒尖、囤顶均已出现，有的被广泛采用。制砖及砖石结构和拱券结构有了新的发展。 (3) 传统建筑持续发展和佛教建筑传入 两晋、南北朝是中国历史上一次民族大融合时期，此期间，传统建筑持续发展，并有佛教建筑传入。西晋统一中国不久，就爆发了「八王之乱」，处于西北
中国网络发展史 中国互联网的产生虽然比较晚，但是经过几十年的发展，依托于中国民经济和政府体制改革的成果，已经显露出巨大的发展潜力。中国已经成为国际互联网的一部分，并且将会成为最大的互联网用户群体。 纵观我国互联网发展的历程，我们可以将其划分为以下4个阶段： 一、从1987年9月20日钱天白教授发出第一封E-mail开始，到1994年4月20日NCFG 正式连入Internet这段时间里，中国的互联网在艰苦地孕育着。它的每一步前进都留下了深深的脚印。 二、从1994-1997年11月中国互联网信息中心发布第一次《中国Internet发展状况统计报告》，互联网已经开始从少数科学家手中的科研工具，走向广大群众。人们通过各种媒体开始了解到互联网的神奇之处：通过谦价的方式方便地获取自己所需要的信息。 三、 1998-1999年中国网民开始成几何级数增长，上网从前卫变成了一种真正的需求。一场互联网的革命就这么在两年的时间里传遍了整个中华大地。对于IT业来说，这是个追梦的年代这个时候到处都充斥着美梦成真的故事。 四、对于进入2000年的中国IT业来说，梦想已不再那么浪漫了，尽管跨入新千年的天仍然是互联网的天，但这片天空中已飘起了阵阵冷雨，让为网而狂的人们分明感到了几许凉意…… "第一"的年代 正如从0开始后必然是1一样，中国网络时代自1994年从零开始以后，就不停地产生着"第一"，因为这是一个创新的年代。让我们通过这些第一记住这个时代。 1、中科院高能物理研究所的IHEPNET与互联网络的连通，迈出了中国和世界各地数百万台电脑的共享信息和软硬件的第一步。边疆也因此而成为我国第一家进入Internet的单位。 2、中国的第一批互联网使用者是全国一千多名科学家。 3、高能所提供了中国第一套万维网服务器。 4、 1994年5月15日，中国科学院高能物理研究所设立了国内第一个WEB服务器，推出中国第一套网页，内容除介绍我国高科技发展外，还有一个栏目叫"Tour in China"。此后，该栏目开始提供包括新闻，经济，文化，商贸等更为广泛的图文并茂的信息并改名为《中国之窗》。 5、 1994年，由NCFC生理委员会主办，中国科学院，北京大学，清华大学协办的APNG（亚太地区网络工作组）年会在清华大学召开。这是国际Internet界在中国召开的第一次亚太地区年会。 6、 NCFC是我国最早的Internet网。
装配式建筑的内涵、国内外装配式建筑的发展历程与趋势（1）内涵 装配式建筑是指用预制的构件在现场装配而成的建筑 从结构形式来说，装配式混凝土结构、钢结构、木结构都可以称为装配式建筑，是工业化建筑的重要组成部分。 这种建筑的优点是建造速度快，受气候条件制约小，既可节约劳动力又可提高建筑质量，用通俗的话形容，就是像造汽车那样造房子。 装配式建筑是转变城市建设模式、有降低建筑能耗、推进工业化的重要载体。 联合国经济委员会对工业化的定义 ■生产过程的连续性。 房屋建造的全过程联结为完整的一体化产业链。 ■生产物的标准化。 设计的标准化，建筑部品、构配件的通用化和系列化。 ■生产过程的集成化。 是指建筑技术、部品与建造工艺、工法的系统集成。
■工程高度组织化。 科学管理方法把建造全过程组织起来 ■生产的机械化。 是指减少现场人工作业，实现构件生产工厂化、施工建造机械化。 《工业化建筑评价标准》：2016年1月1日实施 采用以标准化设计、工厂化生产、装配化施工、一体化装修和信息化管理等为主要特征的工业化生产方式建造的建筑。 （基本条件）。 为什么要编制这个标准 1.国务院、住建部对推动建筑产业现代化提出了一系列明确要求。 2.全国30多个省、自治区、市纷纷出台了指导意见和鼓励措施。 3.设计、构件生产、施工、装备制造和房地产开发企业积极响应，建设了一大批装配式建筑试点，初步形成了“政府推动、企业参与、产业化蓬勃发展”的良好态势。 迫切需要建立一套适合我国国情的工业化建筑评价体系，制订并实施统一、规范的评价标准。
首次明确了“预制率”和“装配率”的定义。 预制率：工业化建筑室外地坪以上的主体结构和围护结构中，预制构件部分的混凝土用量占对应构件混凝土总用量的体积比。 预制率是衡量主体结构和外围护结构采用预制构件的比率, 经测算，如果低于20%的预制率，基本上与传统现浇结构的生产方式没有区别，也不可能成为工业化建筑。 预制构件类型包括：外承重墙、内承重墙、柱、梁、楼板、外挂墙板、楼梯、空调板、阳台、女儿墙等结构构件。 装配率：工业化建筑中预制构件、建筑部品的数量（或面积）占同类构件或部品总数量（或面积）的比率。 预制率不应低于20%、装配率不应低于50%的基本要求 装配率是衡量工业化建筑所采用工厂生产的建筑部品的装配化程度。 工业化建筑采用的各类建筑部品的装配率不应低于50%。 建筑部品类型包括：非承重内隔墙、集成式厨房、集成式卫生间、预制管道井、预制排烟道、护栏等。 （2）历程 1）北美（美国、加拿大） 美国：装配式住宅起源于20世纪30年代， 盛行于20世纪70年代。 1976年，美国国会通过了国家工业化住宅建造及安全法案，同年出台一系列严格的行业规范标准。
中国互联网发展现状分析 据CNNIC的最新估算，截至2002年10月31日，我国上网用户人数达到5800万，上网计算机数升至2300万，短短的四个月间分别增加了1220万和687万；与此同时，国内三大门户网站在第三季度财务报告中也分别交出了令人满意的业绩答卷。这预示着我国互联网在经历一个时期的发展低潮之后，正在开始回暖。自1994年我国正式接入互联网以来，短短的几年时间，互联网在我国得到了飞速的发展。这不仅表现在我国互联网的基础设施方面，也表现在互联网的用户人数、互联网在各行各业的广泛应用等各个方面。虽然自2000年互联网泡沫破灭后，网络业的发展遭遇了一段时期的低潮，但从近期的种种迹象来看，中国互联网业正在走向复苏，开始迎来它发展的第二个春天。 三大门户网站业绩优良 近日，国内三大门户网站新浪、搜狐和网易分别公布了第三季度财务报告。10月22日搜狐公布的季报显示，它提前实现了按照美国通用会计准则的全面盈利，盈利额度达到11.2万美元。11月5日，新浪发布的财务报告称，上季度新浪的净营业收入达到1030万美元，较去年同期增加71％，达历史最高值；按试算额计算，新浪在历史上首次实现盈利24.1万美元，而去年同期的数字为亏损290万美元。11月6日，网易公布的季报显示，今年第三季度网易收入总额达到7440万元人民币（900万美元），较上一季度增长93.3％，营业利润达310万美元，毛利率达67.6％，创历史最高。业内人士认为，与以往网站大面积亏损相比，如此良好的业绩说明互联网正在回暖。 由于业绩的大幅上升，作为中国概念股在纳斯达克的标志性代表，新浪、搜狐、
网易的股票一片飘红，大幅上涨。与一年前一些公司在纳斯达克面临摘牌的尴尬处境相比，今日的风光实在不可同日而语。国内门户网站的股票在纳斯达克受到追捧，说明了国内互联业的发展得到了投资者的认可，它们已经从过去纳股中的边缘状态、边缘待遇变成比较中心的状态了。 互联网得到广泛应用 今年以来，在国家的大力倡导下，电子政务、电子商务、企业信息化等信息化应用进展迅猛，互联网开始在各个行业、各个部门进行广泛的、实质性的渗透。政府信息化、行业信息化、企业信息化和家庭信息化的推进，使原来“不食人间烟火”的互联网与传统行业、实体经济进一步结合，也使互联网找到了广阔的应用空间，焕发了应有的生机与活力。对此，中科院互联网发展研究中心主任吕本富认为，目前中国互联网产业开始了全面复苏。 他认为，之所以说现在的复苏不是一些企业的复苏，而是全面的复苏，是因为过去中国的企业在IT方面的投入本来就不多，有一个对历史欠账回补的过程。在企业层面，网络经济高潮到来时，启发了企业对信息化的应用，让他们认识到了网络经济的重要。互联网泡沫破灭以后，整个IT产业，包括互联网业，都回到了基本面，回归到了一个在正常经济活动下的一个正常产业。 据估计，全球500强等世界大公司在IT方面的投入提前支出了1000亿美元，现在还处于消化投资阶段。相比较之下，中国的互联网业由于本身发展水平所限，非理性成分和泡沫成分都不是那么大，或者根本就没有产生太大的泡沫。而在这个时候，政府加快推进了电子政务，企业开始重视内部信息化建设，这两股力量反而成为比较强劲的推动互联网复苏的力量。目前，中国市场已经成为全球最亮丽的IT市场之一。
论述装配式建筑的发展趋势 发表时间：2017-11-22T14:36:54.110Z 来源：《建筑学研究前沿》2017年第17期作者：谭海明邓铭熙[导读] 本文先介绍了装配式建筑的国内外发展状况，然后介绍了装配式建筑的特点，最后对装配式建筑在我国的发展进行了展望。筑博设计股份有限公司佛山分公司 528000 摘要：装配式建筑是指由工厂进行预制并现场实现装配的建筑，该建筑当中的各个部分运用的都是最先进的冷压轻钢结构和轻型的材料，会使该建筑具有很多的功能。在我国，装配式建筑有很多缺点，但国外能够有效实现建筑的工业化，因此，对装配式建筑的一定普及有着很强的现实意义。 关键词：装配式建筑；发展趋势 引言： 国内建筑一般都采用现场制作的方式，而装配式建筑作为一种新型房屋建筑，与传统建造相比具有缩短工程工期、确保工程质量、节能减排等优势。本文先介绍了装配式建筑的国内外发展状况，然后介绍了装配式建筑的特点，最后对装配式建筑在我国的发展进行了展望。 一、装配式建筑的国内外发展状况 1.1 国外发展状况 欧洲是最早应用装配式建筑的国家，开发新大陆时期，17世纪欧洲向美国移民时，在移民过程中，所用木架来拼装房屋，这就属于一种最简单的装配式建筑。欧洲以法国为代表，经过30多年，法国的装配式建筑正在不断地发展完善。 美国和加拿大地区，装配式建筑被广泛推广，以致在这两个国家装配式建筑被普遍应用。北美的预制建筑主要由两部分组成，分别是预制外墙和结构预制构件，预制构件具有相同的特点，其特点是大型化可以结合预应力，可以使结构配筋及连接构造有所优化，使装配式建筑的工业化、标准化和技术经济性的特征有所体现。 瑞典研究装配式建筑较早，其装配式建筑的发展较快，在60年代，瑞典就基本上实现了有关部件规格方面的建筑工业化标准。同时，瑞典政府也制定了一些相关规范制度。目前瑞典已有80%的住宅采用装配式建筑，并将其工业化生产的模式传播予其他国家。 1.2 国内发展状况 20世纪70年代装配式建筑在我国开始慢慢流传，装配式建筑的观念也在慢慢传播；80年代，预制屋面梁、预制屋面板等构件在一些工程中也开始使用，由于当时没有很高的技术水平，所以也不能拥有很高的建筑质量。到了90年代，施工技术得到一定的改善，管理水平也有了长足进展，预制装配式建筑被提及，并得到了进一步的发展。现如今，装配式建筑在我国许多城市都得到广泛使用。比如，北京、上海地区，许多相关政策被建立，配套装置也相当齐全，装配式剪力墙技术也有所提高并逐渐成熟。北京颁布了关于混凝土结构产业化住宅的设计、质量验收等方面的标准及文件。上海出台了5项同时正在编制4项地方标准和技术管理文件。深圳是发展装配式建筑较早的城市，所以工程实践项目相对其他城市较多，并且构件质量也比较高，对产业化住宅方面编制了与此相关的11项标准和规范。随着装配式建筑的管理技术水平不断完善，会逐渐在我国的大多数城市，甚至每个城市中使用。 二、装配式建筑的特点 2.1设计多样化 目前所设计的住宅楼并不能满足人们对于住宅楼所需求的，大多数住宅楼的承重墙较多，以致分隔较多，开间较小，房内空间不能被有效分隔。而装配式建筑，可以灵活随意进行分割，满足住户的需要，根据他们的要求来进行分割。配套的轻质隔墙，可以使住宅采用灵活大空间，而轻质隔墙的材料一般都使用钢龙骨配以石膏板，或使用一些轻板。 2.2功能科技化 ①节能效果良好：由于外墙设置了保温层，冬天可以降低对暖气能源的消耗，夏天可以降低对空调能源的消耗。 ②隔声效果好：墙体设置了保温层，保温材料具有较好的吸声功能，墙体与门窗之间空隙较小，可以减少外界带来的噪音，为室内提供一个安静的环境。 ③防火：材料最大的作用就是不燃或难燃，所以火灾发生的概率会有所降低。 ④抗震：材料的轻质性可以降低建筑物的重量，这样有利于装配式建筑的充分连接，抗震效果好。 ⑤外观不奢：外观立面比较清晰，不会轻易变形、裂缝及褪色。 2.3施工装配化 在生产厂生产好各种相应的构件，然后再运输到施工现场，专业人员在现场进行安装和拼接。装配式建筑施工比传统建造施工有很多优势：施工速度快，可以缩短工期；施工现场建筑工人减少，施工作业更加方便有序，工人的劳动强度降低；施工现场废物、废水、噪声减少，减少环境污染，节能减排；进行每道工序时都可以安装设备一样，要求精度，保证质量；还可以降低施工成本。 2.4生产工厂化 装配式建筑中的外墙板在生产厂通过模具进行生产，通过为外墙板进行喷涂、烘烤可以使外墙板美观，不褪色。塑钢门窗逐渐代替了传统建造中的木窗、钢门窗，在生产厂具有很先进的生产工艺，都是通过机械生产出各种金属及连接件。石膏板、涂料等一些室内材料都可以在生产流水线制造出来。在生产过程中，可以随时调控材料的防火性、保温性、隔声等性能。 三、装配式建筑的分类 3.1砌块建筑 砌块建筑是在生产厂提前预制好块状材料，用块状材料来砌成墙体的建筑，这种建筑适用于3至5层的房屋建筑。砌块建筑有很多优势，比如，生产工艺不复杂；施工也相对比较简便；造价成本较低。按砌块的大小可以分为小型砌块、中型砌块、大型砌块。由于小型砌块较小，可以直接通过人工进行搬运和砌筑，比较灵活而且也比较方便，具有较广的适用范围；对于中型砌块采用小型机械来进行吊装，可以减少劳动力，降低劳动成本；大型砌块已不被使用，由大型板材所代替。
装配式建筑的内涵、国内外装配式建筑的发展历程与趋势 （1）内涵 装配式建筑是指用预制的构件在现场装配而成的建筑 从结构形式来说，装配式混凝土结构、钢结构、木结构都可以称为装配式建筑，是工业化建筑的重要组成部分。 这种建筑的优点是建造速度快，受气候条件制约小，既可节约劳动力又可提高建 筑质量，用通俗的话形容，就是像造汽车那样造房子。 装配式建筑是转变城市建设模式、有降低建筑能耗、推进工业化的重要载体。 联合国经济委员会对工业化的定义 ■ 生产过程的连续性。 房屋建造的全过程联结为完整的一体化产业链。 ■ 生产物的标准化。 设计的标准化，建筑部品、构配件的通用化和系列化。 ■ 生产过程的集成化。 是指建筑技术、部品与建造工艺、工法的系统集成。
■ 工程高度组织化。 科学管理方法把建造全过程组织起来 ■ 生产的机械化。 是指减少现场人工作业，实现构件生产工厂化、施工建造机械化。 《工业化建筑评价标准》：2016年 1月 1日实施 采用以标准化设计、工厂化生产、装配化施工、一体化装修和信息化管理等为主 要特征的工业化生产方式建造的建筑。 （基本条件）。 为什么要编制这个标准 1.国务院、住建部对推动建筑产业现代化提出了一系列明确要求。 2.全国 30 多个省、自治区、市纷纷出台了指导意见和鼓励措施。 3.设计、构件生产、施工、装备制造和房地产开发企业积极响应，建设了一大 批装配式建筑试点，初步形成了“政府推动、企业参与、产业化蓬勃发展”的良好态 势。 迫切需要建立一套适合我国国情的工业化建筑评价体系，制订并实施统一、规范的评价标准。
首次明确了“预制率”和“装配率”的定义。 预制率：工业化建筑室外地坪以上的主体结构和围护结构中，预制构件部分的混凝土用量占对应构件混凝土总用量的体积比。 预制率是衡量主体结构和外围护结构采用预制构件的比率, 经测算，如果 低于 20%的预制率，基本上 与传统现浇结构的生产方式没有区别，也不可能成为工业化建筑。 预制构件类型包括：外承重墙、内承重墙、柱、梁、楼板、外挂墙板、楼梯、空 调板、阳台、女儿墙等结构构件。 装配率：工业化建筑中预制构件、建筑部品的数量（或面积）占同类构件或部品 总数量（或面积）的比率。 预制率不应低于20%、装配率不应低于50%的基本要求 装配率是衡量工业化建筑所采用工厂生产的建筑部品的装配化程度。 工业化建筑采用的各类建筑部品的装配率不应低于50%。 建筑部品类型包括：非承重内隔墙、集成式厨房、集成式卫生间、预制管道井、预制排烟道、护栏等。 （2）历程 1）北美（美国、加拿大） 美国：装配式住宅起源于20 世纪 30 年代， 盛行于 20 世纪 70 年代。 1976 年，美国国会通过了国家工业化住宅建造及安全法案，同年出台一系列严格的行业规范标准。
国内外装配式建筑发展现状 国内外装配式建筑发展现状 3.1 美国装配式建筑 美国在上世纪 70 年代能源危机期间开始实施配件化施工和机械化生产。美国 城市发展部出台了一系列严格的行业标准规范，一直沿用至今，并与后来的美国建 筑体系逐步融合。美国城市住宅结构基本上以工厂化、混凝土装配式和钢结构装配 式为主，降低了建设成本，提高了工厂通用性，增加了施工的可操作性。总部位于 美国的预制与预应力混凝土协会 PCI 编制的《PCI 设计手册》，其中就包括了装 式结构相关的部分。该手册不仅在美国，而且整个国际上也是具有非常广泛的影响 力的。从 1971 年的第一版开始，PCI 手册已经编制到了第 7 版，该版手册与 IBC 2006、ACI 318-05、ASCE 7-05等标准协调。除了 PCI 手册外，PCI 还编制 了一系列的技术文件，包括设计方法、施工技术和施工质量控制等方面。 3.2 欧洲装配式建筑 法国 1891 年就已实施了装配式混凝土的构建，迄今已有 130 年的历史。法 国建筑工业化以混凝土体系为主，钢、木结构体系为辅，多采用框架或板柱体系， 并逐步向大跨度发展。近年来，法国建筑工业化呈现的特点是: (1) 焊接连接等干法作业流行 ; (2) 结构构件与设备、装修工程分开，减少预埋，使得生产和施工质量提高 ; (3) 主要采用预应力混凝土装配式框架结构体系，装配 率达到 80%，脚手架用量减少 50%，节能可达到 70%。德国的装配式住宅主 要采取叠合板、混凝土、剪力墙结构体系，剪力墙板、梁、柱、楼板、内隔墙板、 外挂板、阳台板等构件采用构件装配式与混凝土结构，耐久性较好。
中国建筑发展史 施红雅 （09给水排水1班0938220012） 摘要：按中国的年表一一介绍中国建筑的发展史，从三个大的方面讲，其中又分小的方面，具体到朝代，让大家对中国的建筑有一个系统的了解。了解了中国建筑的发展史，也就知道了中国的历史发展。 关键词：中国古代建筑发展史，中国近代建筑发展史，中国现代建筑发展史。 建筑是历史和文化的浓缩，从建筑的发展史中能看出历史和文化的发展，也能反映一个朝代的兴与衰，而建筑也见证了一个个朝代的兴衰。 何为建筑？建筑是人们用土、石、木、钢、玻璃、芦苇、塑料、冰块等一切可以利用的材料，建造的构筑物。 1；中国古代建筑发展史 了解了什么是建筑，我们就可以来谈谈中国建筑的发展史了。 1.1原始社会时期的建筑 “中国建筑之原始，究起自何时，殆将永远笼罩于史前之玄秘中”。［1］ 在新石器时代的后期，人类从栖息于巢与穴，进步到有意识地建造房屋。出现了干阑式与木骨泥墙的房屋。姜寨有五座“大房子”共同面向一个广场，每座“大房子”周围环绕着若干或圆或方的小房子，其布局反映了母系氏族社会聚落的特色。龙山文化时期的居住遗址以西安客省庄的一座吕字形平面的房屋为例，房屋面积比仰韶时期的变小，室内有供存贮的窖穴，表现了父系氏族社会私有财产的出现。 1.2奴隶社会时期的建筑 1.2.1商 商代是我国奴隶社会大发展的时期，建筑技术明显提高，安阳殷墟是最早发掘的商代城市，经过数十年断断续续的工作，殷墟大致的面目，已约略可知。［2］宫殿建筑,建筑上已大量应用夯土技术,殿顶应是最为尊贵的重檐,庑殿顶由殿堂、庭院、廊庑和大门组成的宫殿建筑格局达到了一定的水平,对后世很有影响。 1.2.2西周 西周最具代表性的建筑遗址是陕西岐山风雏村的“中国第一四合院”，是一处二进院的宗庙建筑。［3］这种四合院式的建筑形式，规整对称,中轴线上的主体建筑具有统率全局的作用,使全体具有明显的有机整体性,体现一种庄重严谨的性格。院落又给人以安定平和的感受；这种把不大的木结构建筑单体组合成大小不同的群体的布局，是中国古代建筑最重要的群体构图方式,得到长久的继承。 1.2.3春秋 春秋时期宫殿建筑的特色是“高台榭、美宫室”。这一方面是高台建筑有利于防刺客、防洪水、可供帝王享受登临之乐，另一方面也是由于建筑技术的原因，当时要修建高大的建筑，要依傍土台才能建造成功。 1.3封建社会初期的建筑
我国预制装配式混凝土建筑与住宅产业化发展前景 张慧华河南建科软件技术有限公司 一、概述 在过去的几十年时间里，我国建筑行业蓬勃发展，极大地促进了国民经济的增长。面对我国现今土地出让费用的增加、劳动人工价格的不断上升、人们对节能环保要求意识的逐步提高，建筑行业所面临的国际竞争压力越来越大。为提高核心竞争力，新的行业产业模式——预制装配式建筑应运而生。 首先了解三个定义： (一)装配式混凝土结构，是指由预制混凝土构件通过可靠的连接方式装配而成的混凝土结构，包括装配整体式混凝土结构、全装配混凝土结构等。在建筑工程中，简称装配式建筑;在结构工程中，简称装配式结构。 (二)预制装配率，是指装配式建筑中，符合《装配式混凝土结构技术规程》(JGJ1-2014)适宜采用预制构件的部分，使用的预制构件混凝土体积所占适宜部分内全部构件混凝土体积的比例。预制装配率=预制构件混凝土体积÷全部构件混凝土体积。 (三)预制构件，是指在工厂或现场预先制作的混凝土构件，如梁、板、墙、柱、阳台、楼梯、雨棚等。 传统的住房建造技术生产效率低、施工速度慢、建设周期长、材料消耗多且工人劳动强度大，这一系列状况已不能适应现代社会对住宅的刚性需求。而装配式建筑具有以下特点：①设计多样化，可以根据住房要求进行设计；②功能现代化，可以采用多种节能环保等新型材料；③制造工厂化，可以使得建筑构配件统一工厂化生产，一气呵成；④施工装配化，可以大大减少劳动力，减少材料浪费；⑤时间最优化，使施工周期明显加快。因此，面对我国越来越大的住房需求，尽快优化建筑产业模式已势在必行。 装配式建筑注重对环境、资源的保护，其施工过程中有效减少了建筑污水、有害气体、粉尘的排放和建筑噪音的污染，降低了建筑施工对周边环境的各种影响，有利于提高建筑的劳动生产率，促进设计、建筑的精细化，提升建筑的整体质量和节能减排水率，促进了我国建筑业健康可持续发展，符合国家经济发展的需求。 上海市政府相关文件要求，采用装配式整体式混凝土结构体系的住宅和商业、办公建筑总体预制装配率不低于15%，外环线以内地区不低于25%；在每年
中国互联网发展史和几大网站的发展史 今天又把咱们国家的互联网历史翻出来研究了，每一次看都有不少发现，干脆复制这里来，下次不需要搜了 一、中国互联网产生 1987年9月20日，钱天白教授发出我国第一封电子邮件“越过长城，通向世界”，揭开了中国人使用Internet的序幕。 1990年10月，钱天白教授代表中国正式在国际互联网络信息中心的前身DDN-NIC（相当于现在的INTERNIC）注册登记了我国的顶级域名CN，并且从此开通了使用中国顶级域名CN的国际电子邮件服务。由于当时中国尚未正式连入Internet，所以委托德国卡尔斯鲁厄大学运行CN域名服务器。 二、互联网泡沫 泡沫的幽灵很早就在地球上游荡。用他的魔力导演着“一夜成乞丐，一夜成富翁的”的人间悲喜剧。 1993年，在斯坦福大学读博士学位的杨致远创建雅虎搜索网站，1998年总收入达到2.03亿美元，利润总额2500万美元。进入1999年后，Yahoo的股票市值已经接近380亿美元，超过波音公司。1994年，31岁的贝索斯决定在互联网上销售产品，亚马逊网站诞生。到1999年，亚马逊网上书店成为全球第三大图书销售商，拥有450万长期顾客。截止到1999年10月，收入达到3.56亿美元，自1997年公开上市到1998年底，其股票价格飙升了2300%。而网景，一个从成立到上市不到两年，没有挣过一分钱的公司，居然站到巨人微软的对面！一些人在比较雅虎和波音之后，甚至下了这样的定义：网络经济3年等于工业经济70年！ 网络就这样让人美梦成真。互联网制造的“暴富速成”神话，吸引了千千万万的后来者追随。而网民队伍的日渐扩大，决定了其后续发展空间永远无限。 这种泡沫示范作用迅速蔓延到中国，尽管中国的网民当时也不过600万左右。1998年，被称为中国网络三雄(搜狐、新浪、网易)之一的搜狐盈利40万美元的消息，居然被各家媒体抢发。据调查，迄今还没有几家网络公司站出来，声称自己投资网络有了盈利。 随着2000年以科技股为代表的纳斯达克股市的崩盘和“网络泡沫”的破灭，全球互联网产业进入了“严冬”，“多米诺骨牌”效应带动IT产业整体下滑，市场一片低迷。根据Webmergers统计，自2000年泡沫破灭以来，全球至少有4854家互联网公司被并购或者关门。2001年3日19日的一篇报道称：裁员像一场瘟疫，正在美国高科技企业中蔓延。裁员的问题已经从高科技“食物链”的底层辐射到顶层，这正是前几年股市过热和高科技公司盲目追求发展速度的结果。直到2002年10月互联网业追踪公司公布的调查报告显示：第三季度申请破产保护或倒闭的网络公司，已较上年同期和前季大幅减少，互联网泡沫的破灭才接近尾声。
国内装配式建筑主要技术领域发展趋势及技术水平 1 国外的技术发展趋势与水平 （1）国外住宅产业化发展趋势 美日等发达国家住宅产业化发展历程，大致经历了四个阶段： 1）第一阶段是产业化形成的初期，重点是建立工业化生产体系。 上世纪五十年代初期，由于战乱及自然灾害等原因，日本及欧洲一些国家大批房屋遭到战争破坏，同时处于城市化发展高峰期，城市人口剧增，为解决房荒问题，他们采取了象生产其他工业品一样的方式组织住宅建设。建造了大量住宅，形成了一批完整的标准化、系列化的住宅建筑体系。 2）第二阶段是推进产业化的发展期，重点是提高住宅的质量和性能价格比。 上世纪六十年代至八十年代，住宅工业化建设从数量的发展向质量提高方向过渡，由于钢结构装配简单，抗震性能好，对大自然破坏程度小等优越性能，加上钢铁业中冷轧薄钢板的生产而导致轻质型钢的制造成为可能，这在技术上为钢结构工业化住宅的发展奠定了原料供应的基础。所以钢结构住宅，特别是符合国外人住居习惯的低层独立式钢结构住宅发展很快。 3）第三阶段是产业化发展的成熟期，重点是降低住宅的物耗及对自然环境的负荷，发展资源循环型住宅。 上世纪九十年代至今，全球化变暖问题成为世人举世瞩目的焦点。人们开始研究既追求舒适与效益，又节制地消耗地球资源的可持续发展理论，建筑节能在住宅产业化中地位不断提高。
4）第四阶段即今后发展趋势是住宅大规模定制和技术集成。 A、大规模定制 这是住宅开发企业面对住宅市场激烈竞争和需求细分化的必然选择。将制造业大规模定制(Mass Customization)引入住宅的生产，把大规模生产和定制生产，这两种生产模式的优势有机结合起来—就是个性化定制产品和服务的大规模生产。在不牺牲经济效益的前提下，满足单个客户的需求。通过供应链的灵活和快速响应来实现多样化、定制化以适应市场需求。 B、技术集成 随着消费者生活水平的提高，人们对住宅的品质要求也越来越高。住宅的设计内容也随之复杂化，技术的纷杂和层出不穷，促使许多技术成为独立的专业，专业化的细分反映出住宅“精密程度”的提高，是现代设计突出的表现。也就是说，把所有的专业集成到一个住宅中来才能组合成一个好的产品，住宅的品质最终取决于先进技术的集成程度。 （2）国外住宅产业化技术水平 二十一世纪，发达国家在住宅产业化方面都取得了长足的进步：日本目前90%的建筑采用工业化方式建设。其特点是建筑物结构施工与精装修同步进行，建筑结构构件在构件厂预制，统一模数化、标准化，现场进行精细化的安装施工。 美国与加拿大住宅建筑市场发育完善，住宅用构件和部品的标准化、系列化、专业化、商品化、社会化程度很高，几乎达到100%。 澳洲在住宅施工技术上的一项重大突破是“速成墙（Rapid