**6. Management of patients following re-transplantation**

Many studies have highlighted the high early mortality seen after ReTx and patient factors that might be driving this observation. This may reflect the increased complexity of the surgical operation as well as medical frailty in patients undergoing ReTx, but highlights the importance of careful early management. As mentioned previously, the most important aspect of patient management is careful selection of patients who are likely to benefit from ReTx. However, once an appropriate patient has been selected, it is important to optimize the perioperative care in order to attain the best possible outcomes.

From a surgical perspective, it is important to identify the surgical technique used in the initial transplant. It may be especially pertinent to determine if the patient underwent bicaval or bi-atrial anastomosis as well as the level of anastomosis of the pulmonary artery and aorta. Dedicated thoracic imaging, either computed tomographic or magnetic resonance, may help identify anastomotic sites and areas with significant fibrotic tissue. It is not clear if it is necessary to completely excise all of the tissue from the initial cardiac transplant and no guidelines exist to advise clinical practice. Theoretically, it may help to reduce the potential for immunogenicity in those patients; however, this benefit needs to be weighed against increasing the complexity of the operation, which could potentially prolong bypass time and increase peri-operative complications. Finally, careful attention to hemostasis is important as always, but may be particularly important in ReTx patients in whom peri-operative bleeding is more frequent.

There are no clear guidelines on the post-operative care for patients undergoing ReTx. Theoretically, it may not be necessary to add induction therapy if patients have been maintained on high doses of immunosuppression, since their immune response is already significantly blunted. This is not the case for patients undergoing ReTx for refractory rejection or patients who are highly sensitized. However, most transplant centers have used similar induction and immunosuppressive regimens for their primary transplant and ReTx patients. Following induction, it may be reasonable to de-escalate immunosuppression more quickly than would be typical after initial transplantation in order to reduce the long-term risks associated with malignancy and infection.

**9. Conclusions**

**Conflict of interest**

**Author details**

**References**

Robert JH Miller\* and Kiran Khush

Palo Alto, California, United States

2017;**36**:1037-1046

The authors have no relevant conflicts of interest to declare.

\*Address all correspondence to<EMAIL_ADDRESS>
Lung Transplantation. 2016;**35**:1158-1169

ReTx represents a small proportion of heart transplant procedures today; however, survival following cardiac transplantation has improved dramatically and more patients are surviving until they develop late complications such as CAV or graft failure. ReTx is the only therapy that offers meaningful improvement in survival to these patients. Survival after ReTx seems to be reduced, but may be acceptable in appropriately chosen patients. Tailored surgical and post-operative care is critical to improving patient outcomes in those accepted for ReTx.

Cardiac Re-Transplantation: A Growing Indication with Unique Considerations

http://dx.doi.org/10.5772/intechopen.74585

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Department of Medicine, Stanford University, Division of Cardiovascular Medicine,

[1] Lund LH, Khush KK, Cherikh WS, et al. The registry of the International Society for Heart and Lung Transplantation: Thirty-fourth adult heart transplantation Report-2017; focus theme: Allograft ischemic time. The Journal of Heart and Lung Transplantation.

[2] Mehra MR. Contemporary concepts in prevention and treatment of cardiac allograft

[3] Magee JC, Barr ML, Basadonna GP, et al. Repeat organ transplantation in the United

[4] Goldraich LA, Stehlik J, Kucheryavaya AY, Edwards LB, Ross HJ. Retransplant and medical therapy for cardiac allograft vasculopathy: International Society for Heart and Lung Transplantation registry analysis. American Journal of Transplantation. 2016;**16**:301-309

[5] Lund LH, Edwards LB, Dipchand AI, et al. The registry of the International Society for Heart and Lung Transplantation: Thirty-third adult heart transplantation report-2016; Focus theme: Primary diagnostic indications for transplant. The Journal of Heart and

vasculopathy. American Journal of Transplantation. 2006;**6**:1248-1256

States, 1996-2005. American Journal of Transplantation. 2007;**7**:1424-1433


2.2.4. Real Engine Combustion System

The engine used in this study is a direct-injection type single-cylinder CI engine (Daedong Co., Model:ND10DE, Kyeongsan, Korea). Figure 6 shows the single-cylinder diesel engine system and its specifications are given in Table 5. Table 6 shows the combustion test conditions for the single-cylinder diesel engine. The emission performance of the most optimized DPI type and the conventional type was analyzed by measuring the exhaust gas through an exhaust gas measurement system (Horiba, Model:MEXA-554JKNO*x*, Kyoto, Japan). The main specifications of the exhaust gas measurement system are shown in Table 7.

**Figure 6.** Experiment system of single-cylinder diesel engine.

**Table 6.** Engine combustion test conditions.

**Table 7.** Specifications of the exhaust gas measuring device.


**6.1 Extrusion**

Extrusion is a high volume manufacturing process for fabricating parts from thermoplastic elastomers. This processing technique is essential in the melting of raw materials and shaping them into different continuous profiles. The most common extrusion methods are film and sheet extrusion, blow film extrusion, cast film extrusion, coextrusion, tubing extrusion and extrusion coating. The end products made by extrusion are pipe/tubing, wire insulation, film, sheets, adhesive tapes and window frames.

Basically, the extrusion process involves heating a thermoplastic above its melting temperature and forcing it through the die. The extruder is a heating and pressurizing device involves one or more screws operating in a heated barrel. The key determinant of an extruder's performance is the screw. It has three main functions to perform: feeding and conveying the raw material feed; melting, compressing and homogenizing the material; and metering and pumping it through the extrusion die at a constant rate. Raw thermoplastic elastomer material is fed into the barrel of the extruder and comes into contact with the screw. As a melt delivery device, the rotating screw forces the polymer forward into barrel which is heated at a desired temperature. After leaving the screw, the molten travels through a screen pack/plate breaker, where the contaminants in the melt are removed. Breaker plate also creates back pressure in the barrel which is needed for uniform melting and proper mixing of polymer. After that, the molten enters the die, where the cross section of the extruded product is determined.

## **6.2 Injection molding**

Injection molding is by far the most used processing technique of producing parts from thermoplastic elastomers due to its high productivity. Injection molding machines and molds are very expensive because of the high pressures required and complexity of the process control. However, the shortcoming of this technique is balanced by its ability to produce a complex finished part in a single and rapid operation.

The principle of injection molding is very simple. The plastic material is fed into the injection barrel by gravity through hopper. Upon entrance into the barrel, the polymer is heated to the melting temperature. It is then forced into a closed mold that defined the shape of the article to be produced. The mold is cooled constantly to a temperature that allows the molten to solidify and the mold is opened, the finished product is ejected and the process continues.

The injection molding process is capable in producing a variety of parts, from the smallest components to entire body panels of car in a single molding operation. Other part designs

by thermoplastics. A disadvantage is that TPE have an operating temperature below that at

Several factors need to be taken into account during the processing of TPEs, including viscosity or rheology of the two-phase polymer, temperature at which the hard phase can be processed, thermal stability since the complex structures will potential have several weak chemical links, thermal conductivity since the hard phase is surrounded by soft phase, crystallinity in the hard phase that must be melted with excess enthalpy, and moisture that

Extrusion is a high volume manufacturing process for fabricating parts from thermoplastic elastomers. This processing technique is essential in the melting of raw materials and shaping them into different continuous profiles. The most common extrusion methods are film and sheet extrusion, blow film extrusion, cast film extrusion, coextrusion, tubing extrusion and extrusion coating. The end products made by extrusion are pipe/tubing, wire

Basically, the extrusion process involves heating a thermoplastic above its melting temperature and forcing it through the die. The extruder is a heating and pressurizing device involves one or more screws operating in a heated barrel. The key determinant of an extruder's performance is the screw. It has three main functions to perform: feeding and conveying the raw material feed; melting, compressing and homogenizing the material; and metering and pumping it through the extrusion die at a constant rate. Raw thermoplastic elastomer material is fed into the barrel of the extruder and comes into contact with the screw. As a melt delivery device, the rotating screw forces the polymer forward into barrel which is heated at a desired temperature. After leaving the screw, the molten travels through a screen pack/plate breaker, where the contaminants in the melt are removed. Breaker plate also creates back pressure in the barrel which is needed for uniform melting and proper mixing of polymer. After that, the molten enters the die, where the cross section

Injection molding is by far the most used processing technique of producing parts from thermoplastic elastomers due to its high productivity. Injection molding machines and molds are very expensive because of the high pressures required and complexity of the process control. However, the shortcoming of this technique is balanced by its ability to

The principle of injection molding is very simple. The plastic material is fed into the injection barrel by gravity through hopper. Upon entrance into the barrel, the polymer is heated to the melting temperature. It is then forced into a closed mold that defined the shape of the article to be produced. The mold is cooled constantly to a temperature that allows the molten to solidify

The injection molding process is capable in producing a variety of parts, from the smallest components to entire body panels of car in a single molding operation. Other part designs

and the mold is opened, the finished product is ejected and the process continues.

which the hard phase becomes dimensionally unstable.

may cause hydrolysis at processing temperatures.

insulation, film, sheets, adhesive tapes and window frames.

produce a complex finished part in a single and rapid operation.

of the extruded product is determined.

**6.2 Injection molding**

**6.1 Extrusion**

obtained from injection molding include threads, springs, storage containers, mechanical parts and automotive dashboards.

#### **6.3 Compression molding**

Compression molding was among the first method of molding to be used to produce plastic parts. However, it is by far less used than injection molding. Generally, this method involves four steps. First of all, the raw polymer materials in pellets or powder form are placed in a heated and open mold cavity. The mold is closed with another half of the mold and at the same time, pressure is applied to force the materials into contact with all mold areas. The materials soften under high pressure and temperature, flowing to fill the mold. The part is hardened under pressure by cooling the mold before removal so the part maintains its shape.

There are six important considerations that should be bear in mind, they are the proper amount of material, the minimum energy required to heat the material, the minimum time required to heat the material, the proper heating technique, the force needed to ensure that shots attains the proper shape, the design of the mold for rapid cooling. Compression molding of TPEs usually requires longer heating and cooling time due to their high melting points. Separate platens can be used to solve this problem where one is hot press that is electrically heated and another one is cold press that is water cooled. The part is hot pressed under pressure and then transferred immediately to the cold press to chill it under pressure. The hot press is usually preheated to reduce the total cycle time.

#### **6.4 Transfer molding**

Transfer molding is a process which the polymer is melted in a separate chamber known as pot then forced into a preheated mold through a sprue, taking a shape of the mold cavity. The mold is cooled down before opening. Thermoplastic elastomers usually have high viscosity and longer transfer time is needed. The temperature of the mold should be maintained at above melting temperature of the polymer to avoid premature cooling or freezing before the completion of transfer. The important variables during the process of transfer molding are the type of polymer, melting point of the polymer, pot hold time, transfer pressure, transfer rate and the mold cooling time.

#### **6.5 Blow molding**

Blow molding is a manufacturing process that is used to produce hollow plastic parts. There is a wide variety of materials can be used in this process, including but not limited to high density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP), Poly(vinyl chloride) (PVC) and Poly(ethylene terephtalate) (PET). The basic process begins with the melting of thermoplastic and extruding it through a die head to form a hollow tube called a parison. The parison is then clamped between two mold halves, which close around it and the parsion is inflated by pressurized air until it conforms to the inner shape of the mold cavity. Lastly, the molds open and the finished part is removed.

Basically, there are three types of blow molding used to form the parison.  Injection blow molding is part injection molding and part

plasticised by choice of monomer combination. For polyolefin elastomers, it is important to identify plasticisers which have low glass transition temperature and high boiling temperature and which are compatible over a broad temperature range with both rubber

Common additives in TPEs include those materials added during or after polymerization to prevent their degradation, during monomer recovery, drying and compounding, and also

Among the additives, antioxidants are used to prevent oxidation and degradation. Primary or free radical scavenging antioxidants, which have reactive hydroxyl and amine groups, inhibit oxidation via chain terminating reactions. Secondary antioxidants inhibit oxidation

Nucleating agents are generally used to enhance the formation of nuclei for the growth of crystal in the polymer melt. A higher degree of crystallinity and a more uniform crystalline structure in the hard phase can be obtained by adding a nucleating agent in the polymer. Nucleating agents can be classified as inorganic additives (talc, silica), organic compounds (salts of mono- or polycarboxylic acids) and polymer. Nucleating agents may be used to

Colorants are often referred to as dyes and pigments. Generally, dyes are soluble in water while pigments are not. The colours from dyes are produced from the light absorption and they are transparent. Pigments produce colours from the dispersion of fine particles throughout the resin. Inorganic pigments are thermally stable than organic pigments. They are less transparent and resistant to migration, chemicals and fading. Some examples of inorganic pigments are oxides, sulfides, hydroxides, and other complexes based on metal.

Most thermoplastics are flammable, burning easily when heated to high temperature. Flame retardants are added to polymer to delay the ignition and burning of polymer. Char-formers form a foamy porous protective barrier on the polymeric material to shield it for further combustion. Flame retardants acting in the condensed phase deposit a layer on the surface of polymer to prevent it from the heat source while flame retardants acting in gas phase

Various fillers and reinforcements have been introduced into thermoplastic elastomers to enhance their processability and mechanical properties, as well as to reduce material costs.

and polyolefin plastic components.

of polymers by decomposing hydroperoxides.

enhance crystallinity of a hard phase segment.

interrupt the combustion chemistry of the fire.

**8. Additives**

**8.1 Antioxidants**

**8.2 Nucleating agents**

**8.3 Colorants**

**8.4 Flame retardants**

**9. Composites**

storage.

blow molding where the molten plastic is injection molded around the core pin and then the core pin is transferred to a blow molding station to be inflated. There are two stretch molding techniques. In one-stage process, the preform is injection molded which is then transferred to the blow mold where it is blown and ejected from the machine. In the twostage process, preform is injection-molded, stored for a short period of time, and blown into container using a reheat blow machine.


**Author details**

Bei Zhang1 \* and Varna Taranikanti2

1 University of Vermont, Burlington, The United States of America

2 Oakland University, The United States of America

\*Address all correspondence to<EMAIL_ADDRESS>
© 2024 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.