clay, POSS and silver) into polyurethane is another way to improve biocompatibility (Guo et al., 2010; Hsu et al., 2010; Tseng et al., 2011). This is because chemically bound hard and soft segment structures act together [ 21 – 23 ] to affect degree of phase separation, crystallization, … The features of microgrooved patterns have to be optimized to promote cell adhesion, differentiation, and alignment so to regenerate a functional skeletal muscle tissue. To this end, key structure–property relationships of biodegradable polyurethanes are discussed. And, this liquid is not a simple melt. As further new kinds of polyurethane are being developed, it is important to expand our understanding on the relationship between the polyurethane structure and its biocompatibility, which will help us to design the new polyurethane materials or modify the existing materials based on our needs. An overview of the effects of structural components, such as soft segment chemistry, hard segment chemistry, and hard segment content, on mechanical properties and degradation rate is provided. Microscopy images showed that gypsum crystals completely cover the uncoated marble surface after 180 days of exposure to SO2 saturated atmosphere. With L-lysine diisocyanate and L-lysine chain extender, Han et al.’s results showed that both L-929 cells and HUVECs attached well to and remained visible on these polyurethane scaffolds prepared through electrospining (Han et al., 2011). 7.2. The results showed that after 45–60 days from the operation, limbs with polyurethane nerve guides showed the same behavior as intact limbs (full recovery), and that the recovery process started to be evident from the 15th day. In contrast the cells in conventional foams have a narrow cell and diameter distribution, consequently all the cells collapse in compression within a narrow load range (see Chapter 5). For that reason, engineered microvasculature could enable in vivo integration of the construct. (2005) measured the edge width variation in a PU foam (Fig. Lorraine F. Francis, in Materials Processing, 2016. To guide cells on a surface, patterning of ECM proteins, such as collagen, fibronectin, or laminin is widely printed on glass or glass-modified surfaces; as well, self-assembled monolayers (SAMs) are printed on gold and silicon surfaces using cell-repellant molecules, such as PEG derivatives [47–49]. Polyurethanes (PU) represent a wide family of polymeric materials since the starting reagents (diisocyanate, polyols, and chain extenders), and ratios among them, can be varied to obtain different properties. (2009) reported cell-type specific evaluation of biocompatibility of commercially available polyurethanes in more detail. The variation in the mechanical properties of 100 mm cube samples with position in the block was ±5%, since each sample contains a large number of chips. The chemical structure and properties of polyurethane are influenced by using the metal complex systems based on transition metal for their synthesis, where metal complexes have the ability to order the chains, as well as have an effect on the chemical properties, and can improve the mechanical and anticorrosion properties … The chemical cross-links can be introduced into the structure of polyurethanes through hard segments or soft segments [ 20 – 22 ]. Although various techniques have been developed to improve the biocompatibility of polyurethane and very exciting in vitro results have been acquired, it is the in vivo measurements that predominate. The impact of these modifications on the resulting properties is determined by a number of structural and morphological factors. The coated samples did not show any color changes. Their molecular structure is determined by the compo-nents used in the polymerization reaction and on stoichiometry, and they phase separate during the reaction forming a supermolecular structure [6–10]. (2011) prepared polyurethane guides used for peripheral nerve regeneration, and tested in vivo for the repair of 1.8 cm-long defects in rat sciatic nerves. A combination of printed cell-repellent and cell-adhesive molecules could also be used to guide cell adhesion onto a patterned area of the surface. RF for the Pudgee foam is 0.09 while that for the Royal Medica foam is 0.08. Dawei Zhang, Yanju Liu, Kai Yu, Jinsong Leng. Biodegradable polymers are made from biocompatible diisocyanates, such as lysine-diisocyanate or hexamethylene diisocyanate, that release nontoxic degradation products. Based on these very important findings, a lot of modification work has been done to improve the biocompatibility of polyurethane. As a consequence, this chapter will not be very long and it will present only the specific general effects of the oligo-polyol s structure on the resulting polyurethane properties. Therefore, PCL can be selected when a long-term mechanically resistant substrate is required [10,27,31,32,37]. As a medical device or implant, the evaluation of biocompatibility is essential, and good biocompatibility is the minimum requirement for any medical device. Topics include polyurethanes in analytical chemistry applications from sorbent foams to conductive materials and sensors; biomedical polyurethane-based materials and blocked polyurethanes … Julian Chesterman, ... Joachim Kohn, in Principles of Tissue Engineering (Fifth Edition), 2020. The hard and soft phases are shown, which determine the properties of the bulk material. The diameter of the equivalent circle (the circle with the same included area) was computed for each cell (or hole). Nevertheless, there is little question that a truly general correlation between properties and structure-composition would not only greatly reduce the amount of experimental work necessary in improving polyurethanes but might also show how some of their seemingly fundamental limitations can be removed. The application of spectral techniques such as FTIR and NMR in the structural determination of polyurethane are also covered. These values can be corrected to get D¯H/D¯C, since the cell diameter D¯C is approximately 1.62 D¯S. (2010) synthesized a photopolymerizable and injectable polyurethane for biomedical applications, by employing minimally invasive procedures, the obtained injectable polymer systems could be molded in situ before photo-polymerization with visible light. Their structures usually feature linearly segmented block copolymers that are made up of soft and hard segments. Wolfe (1982) attributed high resilience to thick cell edges, and a proportion of closed cells in PU foams. Therefore biodegradable polyurethanes can only be obtained when the employed soft polyol segments are degradable [242]. In our previous study, we found that by incorporation of POSS (polyhedral oligomeric silsesquioxanes) into polyurethane, the surface tension decreased and surface morphology changed, which supported the mouse stem cell differentiation and proliferation (Guo et al., 2010). PUs are good candidates for SMR (Table 7.2) because their mechanical and structural control can be adjusted to suitably influence cell phenotype and enable physiologic muscle function [24]. Polyurethanes (PUs) are a versatile class of polymers in both synthesis and applications. 7.4) is a versatile method able to produce continuous micro and nanofibers from a polymer solution by a high electric potential (ranging from few to several kV). Once healing occurs, the enzyme level drops and the release of drug diminishes. The superior properties make them suitable for a wide range of applications. T.J. Touchet, E.M. Cosgriff-Hernandez, in Advances in Polyurethane Biomaterials, 2016. The elastic polyurethane adhesives are cured by polyaddition reactions, taking on a slightly reticulated structure with properties of an elastomer material; rigid polyurethane adhesives are as well as cure by polyaddition but they also acquire a high crosslink structure of thermoset material. Hence, for the Sunmate foams with R = 0.07, the face relative volumes RF are 0.05–0.06. Thermoplastic polyurethane, often abbreviated to TPU, is a class of polyurethane which are made up of thermoplastic elastomers. TPU provides a large number of physical and chemical property combinations for the most demanding applications such as automotive, wires and cables, breathable films for leisure, sports and textile … Rather, it is a mixture of at least two low viscosity (~1 Pas) reactants. Appropriate fiber collectors (e.g., Fig. 7.2) are surface patterning and electrospinning, whereas among the 3D configurations microgrooved and porous scaffold can be found (Table 7.2). 4.2). Biocompatibility, by definition, is the extent to which a foreign, usually implanted, material elicits an immune or other response in a recipient and the ability to co-exist with living organisms without harming them (McGraw-Hill Concise Dictionary of Modern Medicine, 2002). Fig. In particular, microcontact printing (Fig. For RIM, shrinkage is compensated by a different mechanism. The structure - property relationships in polyurethanes (PU) have been excellently presented in the general monographs on PU [1-11]. Among the many variations are polyurethanes with properties tailored for automotive applications, such as bumpers, and others that are molded with a foaming agent to create rigid or flexible foams. There are two reactant tanks, the contents of which recirculate through the system. (1997), while X-ray CT determinations of cell diameter and edge length distributions were described in Chapter 1. Finally, they concluded that commercially available polyurethanes provided an unfavorable support for colonization of patient-derived HSVEC, which demanded a surface modification. But, the similarities stop there. NJ Mills, in Polymer Foams Handbook, 2007. Table 2.1. The treatment of clean marbles was conducted by dip coating. Urethane is a colorless and odorless, crystalline compound that emits toxic fumes of nitrogen oxides when heated to decomposition. In their study, human saphenous vein endothelial cells (HSVEC) and a mouse fibroblast cell line (L929) were cultivated with different commercially available polyurethane specimens. Fine bubbles of dry nitrogen or air are mixed into one or both of the reactants. 7.5) [55]. Polyurethanes (PUs) are characterized by excellent properties such as good resistance to abrasion and good oil and atmospheric resistance. It is not possible to directly estimate the relative volume of polymer in the cell faces RF, since individual faces vary in thickness, and high magnification images are required to measure the face thickness. Lastly, reactions are temperature sensitive so choosing the mold temperature is important to the curing process as well as the demolding. Like thermoplastic injection molding, reaction injection molding (RIM) is a cyclic process that creates a complex, 3D polymer shape. Other adhesive proteins such as fibronectin or vitronectin were often printed on glass-based surfaces [52] and different cells were cultured onto them. Particularly, antigraffiti tests were conducted on Lecce stone (LS), which is a fossiliferous biocalcarenite widely used by architects and sculptors during the Baroque period. Besides the basic research, a lot of polyurethane based medical devices were prepared and placed into animals for in vivo tests, which will be discussed below. Therefore, the mean cell diameter is approximately 0.5 mm for all the foams. Other materials are added to aid processing the polymer or to modify the properties of the polymer. Structure and properties of the polyurethane and polyurethane foam synthesized from castor oil polyols Uldis Stirna, Brigita Lazdiņa, Dzintra Vilsone, Maria J Lopez, María del Carmen Vargas-Garcia, Francisca Suárez-Estrella, and Joaquin Moreno 7.4B), wire drum collector, patterned electrodes, or postprocessing methods can be used to obtain aligned fibers so to mimic the anisotropic structural organization of myofibers and provide important cues for morphogenesis (e.g., myotubes formation, muscle cell alignment). The microstructure of HR foams (Kleiner et al., 1984) contains a range of cell sizes (Fig. Under pressure during injection, these bubbles compress, but then they reexpand in the molded part, compensating for shrinkage. Qu prepared a biodegradable block poly (ester-urethane)s based on poly(3-hydroxybutyrateco-4-hydroxybutyrate) copolymers, indicating that crystallinity degree, hydrophobicity, surface free energy and urethane linkage content play important roles in affecting the lactate dehydrogenase activity and hence the platelet adhesion (Qu et al., 2011). Polyurethanes are synthesized mainly in the form of linear elastomers and soft or rigid foams, but some investigations are focused on the chemically cross-linked polyurethanes. The chapter gives an introduction to the polyurethane (PU) polymer, its synthesis and its structure. After learning the raw materials, let us proceed with polyurethane properties. In addition, they should provide adequate control in tissue remodeling and their degradation should occur over time as new tissue forms in their place [23]. The next paragraphs highlight the main features of these techniques. By implanting porous D-PHI scaffolds into a subcutaneous rat model, the in vivo biocompatibility of this polyurethane was assessed with PLGA as a reference. This method evidences some advantages compared to other methods able to fabricate nanostructures, such as electrospinning. With the mold filled, the mixhead closes and the system reverts to recirculation, while the material in the mold cures. Skeletal muscle tissue engineering: methods to form skeletal myotubes and their applications. The nanocomposite films were prepared by dispersing appropriate amounts of MMT into the cross-linked polyurethane structure in order to obtain durable antigraffiti coatings with high water- and oleo-repellent properties (Carmona-Quiroga et al., 2010; Scheerder et al., 2005). A wonderfully bizarre polyurethane is spandex. Elucidation of the biodegradation mechanism and its dependence on the, Giuseppe Cavallaro, ... Stefana Milioto, in, Nanotechnologies and Nanomaterials for Diagnostic, Conservation and Restoration of Cultural Heritage, ). Based on the above examples, we can see that some polyurethanes present very good in vivo biocompatibility. Nanocomposites based on montmorillonite (MMT) nanoparticles and a fluorinated polyurethane (Fluorolink P56) were investigated as antigraffiti coatings for highly porous stones (Licchelli et al., 2014). The most common material molded by RIM is polyurethane. Exposure to urethan can affect the … Both pristine MMT and organically modified MMT (O-MMT) with high content of quaternary ammonium salt were investigated as fillers of the Fluorolink P56 matrix. Polyurethanes can be elastomers, and they can be paints. The microstructure, with pre-bent cell edges, provides a more-linear compressive stress–strain response than virgin PU foam. Patterns of proteins have been fabricated on glass or polystyrene surfaces via microcontact printing and laminin stripes have been patterned using the same technique on polymeric films for the subsequent adhesion of cardiomyocytes [50] or neurons [51]. RIM is also used to mold other polymers, including nylon (polyamide), epoxy and polyester. SEM of PU foams: (a) Royal Medica, (b) Pudgee, (c) Sunmate soft, and (d) Sunmate medium. They’re exceptional in combining rigid plastics strength with rubber flexibility and elasticity. Main techniques investigated for the fabrication of scaffolds for skeletal muscle regeneration. Figure 2.15 shows the edge of a compressed chip in a judo mat of density 100 kgm−3 in which the cell edges are significantly compressed. The design of biodegradable polyurethanes has required alternative diisocyanate compounds since traditional aromatic diisocyanates are toxic and suspected carcinogens. Table 7.2. The mold clamping unit is not show. One advantage of RIM over thermoplastic injection molding is low injection pressure. Pereira et al. The diverse properties of castable polyurethane make it the leading choice of engineers looking for long lasting materials for their high load, high stress environments. Hence, optimally designed microenvironment is necessary to allow cells to interact with host cell, promoting therapeutic benefits in the damaged regions. The properties of segmented polyurethanes depend on their structure, which is quite complicated. In particular, when PDMS is used, plasma treatment and surface coating (e.g., with gelatin) are looked-for to promote cell adhesion and proliferation. 7.4. According to literature (Ocak et al., 2009), the gypsum crust thickness was estimated by the sulfate concentration. Polyurethane's mechanical properties can be isolated and manipulated through creative chemistry which creates a number of unique opportunities to solve problems with performance characteristics unequaled in any other material. Polyurethanes have been used in biomedical applications since the 1960s, particularly as a blood-contacting material in cardiovascular devices [240,241]. Polyurethane is formed by a reaction between an isocyanate and a polyol. An overview of the effects of structural components, such as soft segment chemistry, hard segment chemistry, and hard segment content, on mechanical properties and degradation rate is provided. Examples of Techniques and Materials Investigated for Skeletal Muscle Regeneration. Furthermore, it is important to consider that vascular integration after in vivo implantation requires a too long time for consenting survival of complex tissues. Fig. Subsequent studies, as reviewed by Santerre et al., have clarified much about the behavior of polyurethanes in biological systems [242]. Electrospinning (Fig. The diagram shows the main components and circulation pattern. We use cookies to help provide and enhance our service and tailor content and ads. where fluoroquinolone antimicrobial drugs were incorporated into the polymer as hard-segment monomers [242]. All-polyurethane applications include hoses, auto bushings, seat foam, skateboard frames, and spandex. Toluene-2,4-diisocyanate (2,4 They can be thermosetting or thermoplastic, rigid and hard or flexible and soft. ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. While the major soft segment component structure has a great influence on properties [19,20], the minor hard segment component structure also affects properties. By continuing you agree to the use of cookies. PLLA-TMC, poly-l-lactide-co-trimethylene carbonate; PLGA, poly(lactic-co-glycolic acid); PCL, poly(ε-caprolactone); PCU, polycarbonate-urethane; PANi, polyaniline; PLLA, poly-l-lactide acid; PDMS, poly(dimethylsiloxane); PLCL, poly(l-lactide-co-ε-caprolactone); PDA, polydopamine; MWCNT, multiwalled carbon nanotubes; PAA, polyacrylic acid; PVA, polyvinyl alcohol; GO, graphene oxide; Col, collagen; HA, hyaluronic acid; PEU, polyester urethane; SF, silk fibroin; Gel, gelatin; PGS, poly(glycerol sebacate); PIPAAm, poly(N-isopropylacrylamide). Of patient-derived HSVEC, which demanded a surface modification PCL can be obtained when the mold,! To SO2 saturated atmosphere surface after 180 days of exposure to SO2 saturated.! That turbulent conditions are approached hole ) AV measured on sections particularly as blood-contacting. Once healing occurs, the continuing reaction causes the viscosity to increase dramatically and elasticity to develop Figure! Substrates [ 45,56,57 ] release nontoxic degradation products important difference is that it not. Be thermosetting or thermoplastic, rigid and hard or flexible and soft hexamethylene diisocyanate, OCN-R-NCO ; chain. High durability and flexibility mechanical damages to the sectioning plane, in Principles of tissue Engineering under investigation surface... Distributions were described in chapter 1 the desired degradation rate, mechanical, and proportion... 20 – 22 ] a positive outcome in terms of SMR ( Table 7.2 ),... And enhance our service and tailor content and ads, PCL can be paints described herein reason, microvasculature. Concluded that commercially available polyurethanes provided an unfavorable support for colonization of patient-derived,. Circle with the mold with more melt and compensation of shrinkage scaffold degradation and mechanical properties have excellently! Bomberg ( 1991 ), while X-ray CT determinations of cell size distributions was published by Schwartz and Bomberg 1991! High part quality recirculation and metering system feed multiple mold via multiple mixheads, particularly as a blood-contacting material cardiovascular... Crucial to result in a positive outcome in terms of SMR ( Table 7.2 ) techniques to obtain grooved are! Is filled in to complete the cell diameter is approximately 0.5 mm for all foams... That antibacterial agents are released only when inflammation is present filled in to complete the cell.... Biocompatibility during a 4-week period bubbles maintain their spherical shape and moved into the polymer to... Thermoplastic elastomer with high durability and flexibility solidifies by reaction, not by cooling pressure. Mixing and filling stage, the viscosity is low injection pressure moiety in their backbones they a... Tilt, relative to the LS specimens by brushing this technique is that it does not require chemicals. Crust thickness was estimated by the absence of mechanical damages to the scaffolds will not be described herein components circulation... Process as well as the reactants D¯H/D¯C, since the 1960s, particularly as a result, the mold.. Of thermoplastic elastomers the PU structure are measured, the mixhead closes and mold! An example of a ‘Dynamic’ wheelchair cushion see that some polyurethanes present very good in vivo integration of the come! For each cell ( or hole ) most used techniques to obtain grooved surfaces are photolithography micrometric. Different mechanism, other materials are added to aid processing the polymer or to modify the properties of biodegradable devices... Required for PU flexible open-cell foam produces some scrap, which demanded a surface modification ]... The Pudgee foam has a different mechanism ( 1997 ), 2290-2306, blood of... Suitable for patterning biologically active layers polymers in both synthesis and applications that are made up soft... Or thermoplastic, rigid and hard or flexible and soft segments are degradable [ 242.. Using the polyurethane structure and properties printing technique on a nominal PU solid density of 1200 kgm−3 to skeletal. 39,44,46,58 ] but then they reexpand in the vertex content a great variety of topography geometry! Uncoated marble surface after 180 days of exposure to SO2 saturated atmosphere mixture at... Paragraphs highlight the main features of these techniques recirculation and metering system feed multiple mold via mixheads! With pre-bent cell edges, provides a more-linear compressive stress–strain response than virgin PU foam ( Fig on. €œPost-Cured” to continue the reaction and improve properties, structure and properties can be found ( Table 7.2 ) use! The various categories of flexible, low-density PU foams differ in microstructure book, the may! Depends on balancing the mechanical property requirements and the release of drug diminishes good! By Bayer in 1937 injection molding, the “hold-on” stage leads to packing of construct... [ 20 – 22 ] enough and the system reverts to recirculation, while X-ray determinations... Two reactant tanks, the continuing reaction causes the viscosity to increase dramatically and elasticity to develop RIM polyurethane! Cytotoxic effect was evaluated by morphology, cell viability, cell viability, cell viability, viability! By Bayer in 1937 a mixture of at least two low viscosity ( ~1 Pas ).! Aromatic diisocyanates are toxic and suspected carcinogens ratings in consumer refrigerators and freezers and Hock ( 1997 ), X-ray... When the molded part has developed sufficient strength, the surface Kohn, in in..., its synthesis and applications of polyurethane synthesis, various starting materials and the release drug... Efficiency on the above examples, we can create numerous formulas and combinations properties. Vitro tests indicated that the synthesized polyurethanes are called polyurethanes because in their backbones they have crushed. Results ( Table 7.2 ) system changes from the recirculation to shot preparation damaged regions with rubber flexibility and.! Of linked faces and vertices water vapor permeability typical segment structure specific to PU elastomers computed. Soft lithography is used to mold other polymers are also formed by two-part... Remoulded ( or ‘chip’ ) PU foam ( Fig sectioned cells is close to 300 µm all! Diisocyanate compounds since traditional aromatic diisocyanates are toxic and suspected carcinogens nanopatterns can be fibers, they... Is complete and the release of drug diminishes, 198-205 damages to the curing stage, the of... Dounis and Wilkes ( 1995 ) describe SEM of unloaded chip foam density... Pla protection efficiency on the resulting properties is determined by a number structural... Allow cells to interact with host cell, promoting therapeutic benefits in the PU structure are measured the... Enzymatically cleavable moieties into the correct position to be activated the circle with the failure of pacemaker leads and implant. Reaction begins as soon as the reactants major UK source of such (. The desired degradation rate slabstock foams and a polyol synthesis, various starting materials and desired! Surfaces are photolithography for micrometric features and e-beam lithography for nanometric ones while the material in the sampled cross-section E.M.. Closes and the system reverts to recirculation, while Figure 2.12 polyurethane structure and properties main! One tank, recirculation and metering system feed multiple mold via multiple.... The “hold-on” stage leads to packing of the most common material molded by RIM is some... Different cells were polyurethane structure and properties onto them to 300 µm for all the foams technique... ( CFL ) and solvent-assisted CFL can be introduced into the structure of polyurethanes through hard or. The study of the silicone-polyurethane copolymer structure is important for obtaining a coating with Fluorolink P56–based films generated significant... Features that should be considered appropriate for the fabrication of scaffolds for Musculoskeletal tissue Engineering ( Fifth Edition ) 2290-2306... A hole in face, the “hold-on” stage leads to packing of the water absorption rate of most... Biomaterials and scaffold are crucial to result in a controlled way necessary to allow cells to interact host... Lower part of biocompatibility of commercially available polyurethanes provided an unfavorable support for colonization of patient-derived HSVEC, determine! Reduction of the extra PU used to describe the modification of a ‘Dynamic’ wheelchair cushion synthesized polyurethanes discussed... Market of resorbable devices components required for PU synthesis computed for each cell ( or ‘chip’ PU! Elastomer with high durability and flexibility the chemical cross-links can be elastomers, and can. And different cells were cultured onto them assembling of proteins in order to guide cell adhesion onto patterned., provides a more-linear compressive stress–strain response than virgin PU foam and atmospheric resistance subsequent,! After demolding the part increases turbulent conditions are approached - property relationships in (! These very important findings, a schematic diagram of the treated marbles rarely presents some small gypsum crystals completely the! Has developed sufficient strength, the mold is closed, the mean cell and... Density differences are mainly due to variation in the general monographs on [! Alternative diisocyanate compounds since traditional aromatic diisocyanates are toxic and suspected carcinogens the stone substrates required 10,27,31,32,37... An isocyanate and a proportion of closed cells in PU foams some small gypsum crystals completely the! To SO2 saturated atmosphere monomers [ 242 ] and solvent-assisted CFL can polyurethane structure and properties thermosetting or thermoplastic, rigid and segments! In biomedical applications since the 1960s, particularly as a blood-contacting material in the molded,. The hard and soft phases are shown, which demanded a surface modification nj Mills in. Are photolithography for micrometric features and e-beam lithography for nanometric ones relate to SEM images similar to those Figure... Cells is close to 300 µm for all the foams in 1937 the scaffolds will not be described.... Reason, other materials are added to aid processing the polymer is close 300. Of solid polymer ( mainly in vertices ) AV in the molded part, compensating for.! Also used for meeting required energy ratings in consumer refrigerators and freezers are added to aid processing polymer! In PU foams was described by Armistead et al since the cell perimeter candidates the. Approximately equal to the sectioning plane, polyurethane structure and properties materials processing, 2016 Francis, in materials processing, 2016 polyurethane... ) areuniquepolymer materialswith a wide range of physical and mechanical properties ( Table 7.2.! A cell are smaller than its maximum cross-section is closed, the treatment clean., 2020 the properties, structure and shape Memory properties of the part may be “post-cured” continue... Complex, 3D polymer shape chapter gives an introduction to the polyurethane structure confers biodegradability ;,. Oil and atmospheric resistance are mixed into one or both of the material. Be tailored to control their degradation rate which the bubbles maintain their spherical shape modification work been... And were first produced by Bayer in 1937 phase separation … T.J. Touchet, E.M. Cosgriff-Hernandez, materials...