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Issue 05/2020

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Highlights: Fibres & Textiles Polyurethanes / Elastomers Basics: Resorbable Biopolymers

Basics Resorbable

Basics Resorbable biopolymers By Michael Thielen Bioresorbable polymers, such as polylactic acid (PLA), polyglycolic acid, (PGA), combinations of these in the form of a copolymer called poly(DL-lactic acid-coglycolic acid) (PLGA) [1], Poly-ε-caprolacton (PCL) [2] and others are a rapidly growing group of alternatives to traditional materials in many medical applications. Their main advantages are biocompatibility and safety. As they are degradable in the human body, they are particularly suitable for products needed only temporarily for the healing process [3]. These polyesters, which, like other thermoplastics, are suitable for processing by extrusion and injection moulding, are used mainly for wound closure products (sutures, staples, clips), fracture fixation devices (nails, screws, plates) and parenteral depot systems for the sustained release of drugs. All these products are only required to serve their purpose for a certain period of time, which can range from weeks to months. During the degradation process in the body, the resulting substances are excreted by the human metabolism [3]. PLA and PGA PLA is more hydrophobic and less crystalline than PGA and takes longer to degrade [1]. By modifying the molecular weight and polymer composition (including adjusting the stereochemistry, i.e. the sequence of right- or left-handed lactic acid chains), the degradation rate and mechanical stability can be adopted to the individual requirements of the application [4, 5]. In an aqueous environment, PLA undergoes hydrolytic scission into its lactic acid monomer. This is incorporated into the tricarboxylic acid cycle and is excreted by the lung as carbon dioxide. PGA is degraded through hydrolysis and enzymes (nonspecific esterases and caroboxy-peptidases) into its glycolic acid monomer, which enters the tricarboxylic acid cycle or is excreted in the urine. PLA and PGA degradation therefore induce acidic by-products, which may disrupt homeostasis and increase inflammation in poorly perfused tissue [1]. Semi-crystalline polymers such as homo and copolymers of L-lactide, D,L-lactide, glycolide, caprolactone, or dioxanone are typically used to produce medical devices such as orthopedic and soft tissue fixation devices. Amorphous polymers such as homo- and copolymers of D,L-lactide and glycolide are the key excipients for many sustained release drug delivery systems. They improve targeting combined with precise delivery timing – for one or even several active pharmaceutical ingredients [4]. Caprolactone The resorbable polymer Poly-ε-caprolactone (PCL) belongs to the group of aliphatic polyesters and is also hydrolytically degraded in the body. Unlike e.g. polylactides, the degradation of PCL is not accompanied by a decreasing pH value inside the component due to bulk degradation. Neither is there any damage to the surrounding tissue due to the abrupt release of the acidic degradation products as a result of implant failure, as may be the case with polylactides [2]. Processing is a challenge “Due to their toughness, PLA compounds are demanding in terms of processing and require corresponding knowhow in injection moulding,” explains Sven Kitzlinger from the medical technology applications consulting department at the German injection moulding machine manufacturer Arburg on devicemed.de [6]. “With costs of several thousand euros per kilogram, the material is quite expensive and also sensitive to high temperatures and long residence times. You shouldn’t make any mistakes in injection moulding here”. Heavy shearing during processing would also damage the material and lead to premature degradation in the body. “For gentle processing and short residence time, we therefore use a special 15 millimetre screw with widened flights and chrome nitride (CrN) coating. This prevents undesirable deposits and micro-crimping,” Sven says [6]. Another interesting field of application is the additive production of customisable implants, which, as the name suggests, can be designed to fit the patient exactly. At their Technology Days in 2016, Arburg demonstrated that medical PLA can be processed with their Freeformer. Examples were a facial bone and a skull bone (see photos). [6] Latest developments Recent developments in the field of resorbable bioplastics for medical applications were presented by Xiang Zhang, University of California, Berkeley. The presentation included topics such as new concepts of resorbable polymer hybrids or the synthesis of resorbable bio-copolymers with tailored mechanical properties and degradation rate. Such copolymers include polylactic acid, polycaprolactone and poly(ethylene glycol). Zhang is also working on the design and development of resorbable polymer hybrids consisting of organic and inorganic nano-composites [7]. References [1] Halka, A.T. et al: Bioresorbable Polymer, in: Biomaterials and Devices for the Circulatory System, Woodhead Publishing, 2010 [2] Michaelis, I.: Qualifikation des biodegradierenden Polymers Poly-ε- Caprolacton als mplantatwerkstoff, IKV (RWTH Aachen), Verlag Mainz [3] Amecke, B.; Bendix, D.; Entenmann, G.: Resorbable polyesters: Composition, properties, applications; Clinical Materials, Volume 10, Issues 1–2, 1992, Pages 47-50, Elsevier https://doi.org/10.1016/0267- 6605(92)90084-7 [4] N.N. Resomer: Empowering Innovation: Innovative biomaterials for parenteral controlled release and medical devices, Brochure EVONIK NUTRITION & CARE GmbH, 2018 [5] https://de.wikipedia.org/wiki/Kunststoff#Sonderkunststoffe [6] Schäfer K.: Resorbierbare Implantate: Eines Tages sind sie weg, Device- Med, https://www.devicemed.de/resorbierbare-implantate-eines-tagessind-sie-weg-a-552783/ [7] Zhang, X.: New concept of resorbable biopolymer hybrids for implant applications, 2nd World Congress on Biopolymers, London, UK, 2016 [8] https://commons.wikimedia.org/wiki/File:ACLI_Interference_Screws_01.jpg 52 bioplastics MAGAZINE [05/20] Vol. 15

Basics Materials Erdöl ist knapp und wird immer teurer. Die Verbrennung von Erdölprodukten (auch Kunststoffen) hat einen Einfluss auf den Klimawandel. Biokunststoffe können hier eine Alternative darstellen. Biokunststoffe sind zum einen biobasierte Kunststoffe (aus nachwachsenden Rohstoffen) und zum anderen biologisch abbaubare (oder bioabbaubare) Kunststoffe. Viele Biokunststoffe sind beides. Erdöl ist knapp und wird immer teurer. Die Verbrennung von Erdöl- Aber nicht alle — und so ist es ein weit verbreitetes Missverständnis, biobasierte Kunststoffe seien automatisch biologisch abbaubar produkten (auch Kunststoffen) hat einen Einfluss auf den Klimawandel. Biokunststoffe können hier eine Alternative darstellen. und umgekehrt. Biokunststoffe sind zum einen biobasierte Kunststoffe (aus nachwachsenden Rohstoffen) und zum anderen biologisch abbaubare Dieses Buch gibt eine kurze Einführung in Kunststoffe und Biokunststoffe, erläutert aus welchen nachwachsenden Rohstoffen (oder bioabbaubare) Kunststoffe. Viele Biokunststoffe sind beides. Biokunststoffe hergestellt werden können und welche Typen von Aber nicht alle — und so ist es ein weit verbreitetes Missverständnis, biobasierte Kunststoffe seien automatisch biologisch abbaubar Biokunststoffen es grundsätzlich — und welche es bereits am Markt gibt. und umgekehrt. Dieses Buch gibt eine kurze Einführung in Kunststoffe Kapitel und zu Biokunststoffe, erläutert aus welchen nachwachsenden Anwendungen, Markt, End-of-Life Szenarien, politischen Rahmenbedingungen Rohstoffen und Zukunftsaussichten runden das Werk ab. Biokunststoffe hergestellt werden können und welche Das Buch Typen ist von bewusst knapp gehalten und möchte dennoch einen Biokunststoffen es grundsätzlich — und welche es umfassenden bereits am Einstieg in die Thematik der Biokunststoffe ermöglichen. Eine Vielzahl von Literaturangaben und Internetadressen Markt gibt. Kapitel zu Anwendungen, Markt, End-of-Life Szenarien, erleichtert politischen es dem Leser sich mit einzelnen Aspekten ausführlicher Rahmenbedingungen und Zukunftsaussichten runden zu beschäftigen. das Werk ab. Das Buch ist bewusst knapp gehalten und möchte dennoch einen umfassenden Einstieg in die Thematik der Biokunststoffe ermöglichen. Eine Vielzahl von Literaturangaben und Internetadressen erleichtert es dem Leser sich mit einzelnen Aspekten DER ausführlicher AUTOR DR. MICHAEL THIELEN zu beschäftigen. ... ist der Gründer und Herausgeber der Fachzeitschrift bioplastics MAGAZINE. Der Maschinenbau- Ingenieur hat an der RWTH Aachen die Fachrichtung Kunststofftechnik studiert und dort auch promoviert. Er hat mehrere Bücher zur Blasformtechnik DER AUTOR DR. MICHAEL THIELEN geschrieben und in zahlreichen Vorträgen, Gastvor- und Lehraufträgen an Fachhochschulen ... ist der Gründer und Herausgeber der Fachzeit-lesungeschrift bioplastics MAGAZINE. Der Maschinenbau- im In- und Ausland kunststofftechnisches Wissen Ingenieur hat an der RWTH Aachen die Fachrichtung vermittelt. Kunststofftechnik studiert und dort auch promoviert. Er hat mehrere Bücher zur Blasformtechnik geschrieben und in zahlreichen Vorträgen, Gastvorlesungen und Lehraufträgen an Fachhochschulen ISBN 978-3-9814981-0-3 im In- und Ausland kunststofftechnisches Wissen vermittelt. polymedia publisher www.polymedia-publisher.com BIOKUNSTSTOFFE GRUNDLAGEN. ANWENDUNGEN. MÄRKTE. BIOKUNSTSTOFFE GRUNDLAGEN. ANWENDUNGEN. MÄRKTE. ISBN 978-3-9814981-0-3 polymedia publisher www.polymedia-publisher.com MICHAEL THIELEN BIOKUNSTSTOFFE GRUNDLAGEN. ANWENDUNGEN. MÄRKTE. MICHAEL THIELEN MICHAEL THIELEN BIOPLASTICS BASICS. APPLICATIONS. MARKETS. BIOKUNSTSTOFFE GRUNDLAGEN. ANWENDUNGEN. MÄRKTE. NEW EDITION 2020 MICHAEL THIELEN BIOKUNSTSTOFFE GRUNDLAGEN. ANWENDUNGEN. MÄRKTE. 120 pages full color, paperback ISBN 978-3- 9814981-4-1: Bioplastics 3rd updated edition 2020 ISBN 978-3- 9814981-3-4: Biokunststoffe 3. überarbeitete Auflage 2020 Appearance of the BioCryl® screws (left, courtesy of DePuy Mitek), and their positioning (right).(CC BY-SA 2.0) [8] From a medical PLA granulate, a freeformer produces an individually adapted implant for cranial bone. (Photo: Arburg) Implant skull bone, designed as an implant that can be customised to fit the patient exactly (Photo: Arburg). ‘Basics‘ book on bioplastics This book, created and published by Polymedia Publisher, maker of bioplastics MAGAZINE is available in English and German language (Coming this fall in the third, revised edition). The book is intended to offer a rapid and uncomplicated introduction into the subject of bioplastics, and is aimed at all interested readers, in particular those who have not yet had the opportunity to dig deeply into the subject, such as students or those just joining this industry, and lay readers. It gives an introduction to plastics and bioplastics, explains which renewable resources can be used to produce bioplastics, what types of bioplastic exist, and which ones are already on the market. Further aspects, such as market development, the agricultural land required, and waste disposal, are also examined. An extensive index allows the reader to find specific aspects quickly, and is complemented by a comprehensive literature list and a guide to sources of additional information on the Internet. The author Michael Thielen is editor and publisher bioplastics MAGAZINE. He is a qualified machinery design engineer with a degree in plastics technology from the RWTH University in Aachen. He has written several books on the subject of blow-moulding technology and disseminated his knowledge of plastics in numerous presentations, seminars, guest lectures and teaching assignments. New (3 rd , updated) edition is being printed now € 20.00 coming this fall Pre-order now for € 20.00 (+ VAT where applicable, plus shipping and handling, ask for details) order at www.bioplasticsmagazine.de/books, by phone +49 2161 6884463 or by e-mail books@bioplasticsmagazine.com Or subscribe and get it as a free gift (see page 61 for details) bioplastics MAGAZINE [05/20] Vol. 15 53

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