Functional Biomaterials E-Book

• Herausgeber: Wiley-VCH GmbH
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 1113

Veröffentlichungsjahr: 2023

Beschreibung

This book merges the two most important trends in biomaterials: functionalization and renewable chemistry. It covers a variety of biopolymers and various approaches for the transformation of these biopolymers into functional units.

Leseprobe

Table of Contents

Cover

Title Page

Copyright

Volume 1

Preface

1 Definitions and Types of Microbial Biopolyesters and Derived Biomaterials

1.1 Introduction

1.2 Biopolymers as Bioinspired Alternatives

1.3 Types of PHA Biopolyesters

1.4 Conclusions

References

2 Analysis of Chemical Composition of Biopolymers and Biomaterials: An XPS Study

2.1 Basics of X‐Ray Photoelectron Spectroscopy (XPS)

2.2 Chemical Derivatization

2.3 Some Further Examples of XPS Analyses of Complex Organic Systems

2.4 Charging

2.5 Background Information

2.6 Angle‐Resolved XPS (ARXPS)

2.7 Functional Coatings on Polymers

2.8 Practical Considerations

2.8 Acknowledgments

References

3 Methods for Characterization of Dielectric and Thermal Properties of Biomaterials

3.1 Introduction to Thermal Analysis Techniques

3.2 The Significance of Thermal Analysis in Biopolymers

3.3 Applications of Thermal Analysis in the Characterization of Biopolymers

3.4 Conclusions

References

4 Methods for Characterization of Surface Charge and Solid–Liquid Interaction Studies of Biomaterials

4.1 Introduction

4.2 Surface Charge Characterization of Biomaterials

4.3 Methods for Characterization of Solid–Liquid Interaction of Biomaterials

References

5 Methods for Analyzing the Biological and Biomedical Properties of Biomaterials

5.1 Introduction

5.2 Fundamentals of Cell Biology as a Base for Testing

5.3 In Vitro Methods for Analyzing Biomaterials

5.4 In Vivo Methods for Analyzing Biomaterials

5.5 Concluding Remarks and Perspectives

References

6 Polysaccharide Thin Films – Preparation and Analysis

6.1 Biopolymer Thin‐Film Preparation

6.2 Characterization of Biopolymer Thin Films

6.3 Conclusion

References

7 Biopolymer Thin Films as “Smart” Materials in Biomedical Applications

7.1 Introduction

7.2 Frequently Used Biopolymers

7.3 Stimuli‐Responsive Biopolymer Thin Films

7.4 Biomedical Applications of Biopolymers

7.5 Conclusions

Acknowledgment

References

8 Biopolymer‐Based Nanofibers – Synthesis, Characterization, and Application in Tissue Engineering and Regenerative Medicine

8.1 Introduction

8.2 Different Strategies of Nanofiber Development

8.3 Biopolymers

8.4 Characterization Techniques

8.5 Applications

8.6 Conclusions

References

9 Formation of Polysaccharide‐Based Nanoparticles and Their Biomedical Application

9.1 Introduction

9.2 Nanoparticle Formation

9.3 Interaction with Cells

9.4 Release Mechanisms

9.5 Examples in Therapeutics and Diagnostics

References

Volume 2

10 Advanced Methods for Design of Scaffolds for 3D Cell Culturing

10.1 Introduction

10.2 General Considerations in Tissue Engineering

10.3 Building Scaffolds

10.4 Computer‐Aided Design and Manufacturing

10.5 Challenges and Future Outlook

References

11 Methods and Challenges in the Fabrication of Biopolymer‐Based Scaffolds for Tissue Engineering Application

11.1 Introduction

11.2 Conventional Methods for 3D Scaffold Engineering

11.3 Advanced Fabrication Methods – Solid Freeform Fabrication

11.4 Conclusions and Future Perspectives

References

12 Solvent‐Casting Approach for Design of Polymer Scaffolds and Their Multifunctional Applications

12.1 Introduction

12.2 Solvent‐Casting Technology

12.3 Conclusions

References

13 Freeze‐Casted Biomaterials for Regenerative Medicine

13.1 Introduction

13.2 Freeze‐Casted Scaffolds for Regenerative Medicine

13.3 Summary and Outlook

References

14 Polysaccharide‐Based Stimuli‐Responsive Nanofibrous Materials for Biomedical Applications

14.1 Introduction

14.2 Stimuli Responsiveness in Polysaccharides

14.3 Nanofibrous Materials and Electrospinning

14.4 Needleless Electrospinning

14.5 Electrospinning Techniques for Preparation of Stimuli‐Responsive Nanofibers

14.6 Stimuli‐Responsive Polysaccharide‐Based Nanofibrous Materials for Wound Dressings Application

14.7 Conclusions

References

15 Cells Responses to Surface Geometries and Potential of Electrospun Fibrous Scaffolds

15.1 Introduction

15.2 Electrospinning

15.3 Surface Geometry and Typical Cell Responses

15.4 Surface Potential Importance and Typical Cell Responses

15.5 Conclusions

Acknowledgments

References

16 Biopolymer Beads for Biomedical Applications

16.1 Introduction

16.2 Agarose

16.3 Cellulose

16.4 Alginate

16.5 Chitin and Chitosan

16.6 Conclusion and Outlook

References

17 Recent Advances in 3D Printing in the Design and Application of Biopolymer‐Based Scaffolds

17.1 Introduction

17.2 Fundamental Principles of the 3D Bioprinting Process

17.3 Recent Advances in 3D Bioprinting Approaches and Their Application

17.4 Materials Used in 3D Bioprinting

17.5 Designing the Ideal Bioink

17.6 Application of 3D Bioprinting for the Fabrication of Tissues and Organs

17.7 Concluding Remarks

Acknowledgments

References

Index

End User License Agreement

List of Tables

Chapter 2

Table 2.1 Inelastic mean free paths for photoelectrons with the kinetic ene...

Table 2.2 Chemical derivatization agents that are the most often used to de...

Table 2.3 Surface composition of the defluorinated surface of PTFE when cal...

Table 2.4 Surface composition of the PE sample before and after treatment a...

Table 2.5 Surface composition of the PE sample before and after treatment a...

Table 2.6 Surface composition of the as‐deposited chestnut honey and after ...

Chapter 7

Table 7.1 Examples of biopolymers commonly used in controlled‐delivery syst...

Table 7.2 Commonly used biopolymers and their biological role in wound heal...

Chapter 8

Table 8.1 Electrospinning parameters used in different research studies.

Chapter 11

Table 11.1 Fabrication methods with their advantages, limitations, and rela...

Chapter 12

Table 12.1 Different surface modification techniques employed in solvent‐ca...

Chapter 14

Table 14.1 Polysaccharides and their responses.

Table 14.2 Effects of solution, process, and ambient parameters on nanofibe...

List of Illustrations

Chapter 1

Figure 1.1 Production and life cycle of TPS.

Figure 1.2 Production and life cycle of PLA. The * in the graphic indicates ...

Figure 1.3 Production and life cycle of “bio‐PE.”

Figure 1.4 Productionand life cycle of PCL.

Figure 1.5 Production and life cycle of PBAT (Ecoflex®).

Figure 1.6 Production and life cycle of PE.

Figure 1.7 Classification of diverse polymers. Polymers marked in green meet...

Figure 1.8 Organization of native PHA granules in living cells of

C. necator

Figure 1.9 Simplified illustration of the PHA metabolism starting from diver...

Figure 1.10 Composition of

scl

‐,

mcl

‐, and

lcl

‐PHA based on the general stru...

Figure 1.11 Schematic of PHA homopolyester (left polymer chain; the polyeste...

Chapter 2

Figure 2.1 The schematic principle of XPS.

Figure 2.2 An inelastic mean free path (IMFP) of photoelectrons from polysty...

Figure 2.3 An example of the XPS survey spectrum of polyethylene foil (lower...

Figure 2.4 An example of the high‐resolution carbon C1s peak: (a) comparison...

Figure 2.5 Some typical chemical shifts of C 1s in organic samples.

Figure 2.6 The high‐resolution spectrum of carbon of polyvinyl trifluoroacet...

Figure 2.7 An example of the high‐resolution carbon C1s peak of carboxymethy...

Figure 2.8 An example of the high‐resolution carbon C1s peak of heparin graf...

Figure 2.9 (a) Some typical chemical shifts of N1s in organic samples....

Figure 2.10 Chemical structure of chitosan.

Figure 2.11 A correlation between the C—C content and the O/C ratio for appr...

Figure 2.12 A correlation between the C—C content and the O/C ratio for some...

Figure 2.13 Examples of C1s spectra of the filter paper recorded at various ...

Figure 2.14 (a) A comparison of the two selected C1s spectra from Figure...

Figure 2.15 Some examples of using different types of background subtraction...

Figure 2.16 Different structure of the surface causes different background o...

Figure 2.17 Survey spectra showing a background of fluorine F1s peak of fluo...

Figure 2.18 (a) A correlation between the sampling depth and the take‐off an...

Figure 2.19 Carbon C1s spectra of fluorinated PET polymer recorded at differ...

Figure 2.20 A redistribution of functional groups from the surface toward th...

Figure 2.21 The F/C ratio of the defluorinated surface of polymer PTFE after...

Figure 2.22 The difference in the F/C ratio when computed from F1s or F2s si...

Figure 2.23 Scheme of alginic acid immobilization on the polymer surface.

Figure 2.24 XPS high‐resolution carbon spectra of (a) PE polymer substrate, ...

Figure 2.25 The scheme of chitosan immobilization on the polymer surface.

Figure 2.26 XPS survey spectra of PE polymer substrate, plasma‐activated PE ...

Figure 2.27 XPS survey spectra of PE polymer substrate, plasma‐activated PE ...

Figure 2.28 The scheme of immobilization of nanoformulation of chitosan with...

Figure 2.29 XPS survey spectra of the untreated PE foil (lower curve), after...

Figure 2.30 High‐resolution carbon spectra of: (a) the untreated PE foil, (b...

Figure 2.31 The XPS survey spectrum of chestnut honey deposited on the quart...

Figure 2.32 The XPS survey spectrum of chestnut honey after cold plasma ashi...

Chapter 3

Figure 3.1 Thermal analysis methods.

Figure 3.2 Thermogravimetric curve with a single mass loss step.

Figure 3.3 The main events that can be detected in polymers by DSC.

Figure 3.4 Assessment of glass transition by DSC.

Figure 3.5 Principles of DMA.

Figure 3.6 The variation of the dielectric constant, dielectric loss, real a...

Figure 3.7 Thermogravimetric analysis of pullulan/MWCNT hydrogels.

Figure 3.8 Chemical structure of (a) cellulose, (b) pullulan, (c) chitosan....

Figure 3.9 DMA of chitosan in the first (a) and second heating run (b).

Figure 3.10 DSC of chitosan in the second heating run.

Figure 3.11 DMA data at 0.1 Hz for cellulose (a) before treatment; (b) befor...

Figure 3.12 DMA data at 1 Hz for cellulose during consecutive heating steps....

Figure 3.13 Temperature dependences of proton conductivity for pure cell, an...

Chapter 4

Figure 4.1 A graphical representation of the solid–liquid interactions of bi...

Figure 4.2 (a) pH‐potentiometric and (b) conductometric titration curves for...

Figure 4.3 Adsorption of polyelectrolyte, as a function of equilibrium conce...

Figure 4.4 Schematic presentations of the principles of (a) electrophoretic ...

Figure 4.5 Beat signal accumulated during electrophoretic light scattering (...

Figure 4.6 Electric double‐layer model describing the charge distribution at...

Figure 4.7 (a) Dependence of zeta potential on pH of an aqueous solution for...

Figure 4.8 Monitoring the formation of a polypeptide–polysaccharide multilay...

Figure 4.9 Comparison of the pH dependence of the zeta potential for a serie...

Figure 4.10 Correlation between the isoelectric points and the composition o...

Figure 4.11 (a) A schematic representation of the QCM device and its key ele...

Figure 4.12 Schematic representation of a shear wave propagation through var...

Figure 4.13 Schematic representation of the principles of the SPR technique....

Figure 4.14 (a) Frequency (Δ

f

) and (b) dissipation (Δ...

Figure 4.15 A schematic depiction of the mechanics of adsorbed molecules and...

Figure 4.16 Frequency (Δ

f

) changes during absorption water and...

Figure 4.17 Frequency (Δ

f

) changes during adsorption of...

Figure 4.18 Frequency (Δ

f

) vs. dissipation (Δ...

Figure 4.19 (a) Experimental setup allowing simultaneous time‐resolved SPR a...

Figure 4.20 (a) QCM frequency (Δ

f

) change during adsor...

Figure 4.21 Kinetics of adsorption of a monoclonal antibody on a silicone tu...

Chapter 5

Figure 5.1 Cell–biomaterial interactions.

Figure 5.2 Different types of tests to evaluate cytotoxicity according to IS...

Figure 5.3 F‐actin staining assay of HUIEC grown on CMC‐ and PLGA‐coated pla...

Figure 5.4 Live/dead cell viability assay of Saos‐2 cells cultured on gelati...

Figure 5.5 Schematic representation of some cell viability assays.

Figure 5.6 Schematic representation of some common metabolic activity assays...

Figure 5.7 (a) 3D confocal micrograph showing the porous microstructure of C...

Figure 5.8 Use of nanoneedles for testing intracellular activities. (a) AFM ...

Figure 5.9 MEMS pressure sensor for intracellular pressure measurement. (a) ...

Figure 5.10 LEFT: 3D (upper) and 2D (lower) μCT scans for...

Chapter 6

Figure 6.1 Langmuir–Blodgett deposition technique. Monolayer formation by (a...

Figure 6.2 Schematic description of the spin coating process – (a) depositio...

Figure 6.3 Regeneration of TMSC to cellulose by exposure to HCl vapor.

Figure 6.4 Regeneration of CX to cellulose using HCl vapor.

Figure 6.5 AFM images (2 × 2 μm

2

) and the corresp...

Figure 6.6 Schematic description of the (a) contact mode and the (b) tapping...

Figure 6.7 AFM artifacts can arise when imaging small convex obstacles with ...

Figure 6.8 Calculated XRR curves for a structure containing 10 nm of a polys...

Figure 6.9 Schematic of an XPS measurement setup.

Figure 6.10 XPS spectra of cellulose surface (a) rendered with cationic cell...

Figure 6.11 Schematic representation of (a) hydrophilic and (b) hydrophobic ...

Figure 6.12 Negative‐charged surface of a particle with a positively charged...

Figure 6.13 Zeta potential of the membrane surfaces as a function of solutio...

Figure 6.14 (a) Plot of the changes of the mean correlation length

l

CH

*

...

Figure 6.15 (a) Schematic description of a SPR measurement setup in the Kret...

Figure 6.16 Comparison of the adsorption behavior of the different starches ...

Figure 6.17 Comparison of the adsorbed

fluorescein isothiocyanate

(

FITC

)‐BSA...

Chapter 7

Figure 7.1 Molecular structure of cellulose.

Figure 7.2 Structure of (a) amylose molecule, and (b) amylopectin molecule....

Figure 7.3 Structure of chitin molecule, showing two of

N

‐acetylglucosamine ...

Figure 7.4 Molecular structure of completely deacetylated chitosan.

Figure 7.5 Structure of alginic acid.

Figure 7.6 Chemical structure of poly(3‐hydroxybutyrate) (PHB), the first an...

Figure 7.7 Production scheme of poly(lactic) acid (PLA) through polycondensa...

Figure 7.8 Schematic presentation of a designed pH‐sensitive thin film for d...

Figure 7.9 Reversibly controlled cell attachment and detachment on the therm...

Figure 7.10 Ibuprofen‐loaded chitosan film for potential oral mucosal drug‐d...

Figure 7.11 The process of fabrication of (a) an electrochemical glucose bio...

Chapter 8

Figure 8.1 Schematic representation of nanofiber formation by drawing.

Figure 8.2 Schematic representation of nanofiber formation by template synth...

Figure 8.3 Schematic representation of nanofiber formation by phase separati...

Figure 8.4 Schematic representation of nanofiber formation by self‐assembly....

Figure 8.5 Schematic representation of nanofiber formation by electrospinnin...

Figure 8.6 Field emission scanning electron microscopy (FESEM) images of (a)...

Figure 8.7 Transmission electron microscopy (TEM) images of cellulose nanofi...

Figure 8.8 AFM images of the electrospun cholesteryl‐succinyl silane (CSS) n...

Figure 8.9 Representation of the healing process in a wound rat model.

Chapter 9

Figure 9.1 Schematic presentation of nanoprecipitation methods applying dial...

Figure 9.2 Plot of the reduced viscosity vs. the concentration of cellulose ...

Figure 9.3 Schematic illustration for the nanoprecipitation of cellulose ste...

Figure 9.4 Dependence of particle morphology from Δ...

Figure 9.5 SEM images of dextran furoate pyroglutamate nanospheres.

Figure 9.6 Schematic diagram of the nanoparticle formation by double‐emulsio...

Figure 9.7 FE‐SEM images of ethyl cellulose particles prepared in the presen...

Figure 9.8 Scheme for the main pathways of nanoparticle endocytosis.

Figure 9.9 (a) Structural features of amphiphilic polysaccharide derivatives...

Figure 9.10 Schematic illustration of formation and effect mechanism of mult...

Chapter 10

Figure 10.1 Classification of scaffold preparation approaches. Compared to c...

Figure 10.2 Scaffold fabrication approaches without the aid of computer‐aide...

Figure 10.3 Subtractive manufacturing approaches. (a) Shows two possible app...

Figure 10.4 General overview over common approaches to additive manufacturin...

Figure 10.5 Droplet‐based techniques. (a) 3D Silk fibroin scaffolds printed ...

Figure 10.6 Scaffolds fabricated by microextrusion bioprinting. (a) A “woodp...

Figure 10.7 Photolithographic bioprinting methods. (a) Micro‐ and nanostruct...

Figure 10.8 Laser‐assisted bioprinting techniques. (a) Basic principle (left...

Chapter 11

Figure 11.1 Schematic representation of the common techniques for scaffold f...

Chapter 12

Figure 12.1 Common scaffold fabrication techniques. (a) Porogen leaching, (b...

Figure 12.2 Schematic representation of solvent‐casting process.

Figure 12.3 The schematic diagram of solvent‐casting particulate‐leaching te...

Figure 12.4 Density of PLA scaffolds in different solvents.

Figure 12.5 Microstructure of the optimized scaffolds: PMMA‐S2 (a), PMMA‐S3 ...

Figure 12.6 Typical tensile stress–strain curves for poly(ester urethane)ure...

Figure 12.7 Hematoxylin and eosin (H&E) staining of vascular smooth muscle c...

Figure 12.8 Schematic diagram showing methodology used for the preparation o...

Figure 12.9 SEM micrographs of MG63 cell morphology: (a) after three days in...

Figure 12.10 The degradation percentage of PHB films up to six weeks.

Figure 12.11 The microbial number in soil at the buried site for different P...

Figure 12.12 Variation in degradation for solvent‐cast films of different co...

Figure 12.13 Average porosity of the film (a) and average pore diameter (b) ...

Chapter 13

Figure 13.1 Documents by (a) year, (b) type, and (c) subject area, according...

Figure 13.2 Schematic diagram of the freeze‐casting principles. (a) Suspensi...

Figure 13.3 SEM micrographs of transverse (a) and longitudinal (b) cross‐sec...

Figure 13.4 Fluorescence micrographs of the scaffolds' top (a) and bottom (b...

Figure 13.5 Color‐coded images of bacterial cellulose–gelatin membranes, emp...

Figure 13.6 SEM images of unidirectionally frozen 10% gelatin samples, with ...

Figure 13.7 Fluorescence microscopy images of cross‐sections (a) and cross‐p...

Figure 13.8 Fluorescent microscopy images depicting FITC‐labeled gelatin com...

Figure 13.9 SEM (a) and fluorescent microscopy images from cross‐sections of...

Chapter 14

Figure 14.1 Graph of the transition phenomena connecting stimulus and respon...

Figure 14.2 (a) Needle electrospinning set‐up and (b)

scanning electron micr

...

Figure 14.3 Spinning solution's path in electrospinning process.

Figure 14.4 Schematic presentation of drop formation and formation of Taylor...

Figure 14.5 Schematic presentation of polymer jet instabilities.

Figure 14.6 Effect of polymer and solvent concentration of nanofiber morphol...

Figure 14.7 Needleless electrospinning set‐up.

Figure 14.8 Formation of Taylor cones and polymer jets on a rotating electro...

Figure 14.9 Schematic presentation of core–shell electrospinning.

Figure 14.10 Schematic presentation of emulsion electrospinning.

Figure 14.11 Loading and release of drugs from electrospun nanofibers: (a) d...

Figure 14.12

In vitro

release profile of KET upon different environment temp...

Figure 14.13 PNIPAAm/gelatin nanofibers with loaded DOX and their release pr...

Figure 14.14 (a) SEM images of prepared CA/RC nanofibers, regenerated CA/RC ...

Figure 14.15 Scheme of PEO/CS/GO/DOX nanofiber preparation and release profi...

Figure 14.16 Prepared CA nanofibers and their release profile combined with ...

Chapter 15

Figure 15.1 Schematic of electrospinning process with the examples of random...

Figure 15.2 SEM micrographs showing cell attachment to a different type of s...

Figure 15.3 SEM micrographs focused on cell–fiber attachment after the third...

Figure 15.4 KPFM results showing (a–e) surface topography, (f–j) map of the ...

Figure 15.5 SEM micrographs of cells growing on smooth, porous PCL fibers an...

Figure 15.6 3D reconstructions from FIB‐SEM tomography of cell interaction w...

Chapter 16

Figure 16.1 General method of making porous agarose beads via emulsification...

Figure 16.2 (a) Pictorial presentation of equipment for premix membrane emul...

Figure 16.3 Pictorial representation of spray‐gelation technique to design a...

Figure 16.4 (a) Molecular structure of cellulose showing hydroxyl groups ava...

Figure 16.5 Schematic presentation of scalable alginate beads design system....

Figure 16.6 Different stages of the preparation of alginate beads by emulsif...

Figure 16.7 A pictorial representation of chitin and chitosan chemical struc...

Chapter 17

Figure 17.1 A typical bioprinting process consisting of three steps: (i) pre...

Figure 17.2 Examples of cell‐laden scaffolds produced with various biop...

Figure 17.3 Extrusion‐based 3D bioprinting of tubular structures. (a) ...

Figure 17.4 4D bioprinting. (a) Alignment of collagen fibers in printable bi...

Figure 17.5 Materials used in 3D bioprinting . (a) 3D‐printed functional part...

Figure 17.6 3D bioprinting of biomimetic scaffolds . (a) A continuous multima...

Figure 17.7 3D bioprinting of skin tissue constructs. (A) Microscopic cross‐...

Figure 17.8 3D bioprinting of cardiac tissue. (a) Bioprinting of cardiac tis...

Figure 17.9 3D bioprinting of bone tissue. (A) Sketch of the process for 3D ...

Figure 17.10 3D bioprinting of cartilage tissue . (a) Design and melt electro...

Guide

Cover

Table of Contents

Title Page

Copyright

Preface

Begin Reading

Index

WILEY END USER LICENSE AGREEMENT

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Functional Biomaterials

Design and Development for Biotechnology, Pharmacology, and Biomedicine

Volume 1

Edited by Tamilselvan Mohan and Karin Stana Kleinschek

Functional Biomaterials

Design and Development for Biotechnology, Pharmacology, and Biomedicine

Volume 2

Edited by Tamilselvan Mohan and Karin Stana Kleinschek

The Editors

Prof. Tamilselvan Mohan

Graz University of Technology

Institute for Chemistry and Technology of Bio‐Based Systems (IBioSys)

Stremayrgasse 9

8010 Graz

Austria

and

University of Maribor

Faculty of Mechanical Engineering

Laboratory for Characterization and Processing of Polymers

Smetanova Ulica 17

2000 Maribor

Slovenia

Prof. Karin Stana Kleinschek

Graz University of Technology

Institute for Chemistry and Technology of Bio‐Based Systems (IBioSys)

Stremayrgasse 9

8010 Graz

Austria

Cover Image: © Pixabay

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All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law.

Print ISBN: 978‐3‐527‐35157‐2

ePDF ISBN: 978‐3‐527‐82764‐0

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The Editors

Prof. Tamilselvan Mohan

Graz University of Technology

Institute for Chemistry and Technology of Bio‐Based Systems (IBioSys)

Stremayrgasse 9

8010 Graz

Austria

and

University of Maribor

Faculty of Mechanical Engineering

Laboratory for Characterization and Processing of Polymers

Smetanova Ulica 17

2000 Maribor

Slovenia

Prof. Karin Stana Kleinschek

Graz University of Technology

Institute for Chemistry and Technology of Bio‐Based Systems (IBioSys)

Stremayrgasse 9

8010 Graz

Austria

Cover Image: © Pixabay

All books published by WILEY‐VCH GmbH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.

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A catalogue record for this book is available from the British Library.

Bibliographic information published by the Deutsche Nationalbibliothek

The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at <http://dnb.d-nb.de>.

© 2023 WILEY‐VCH GmbH, Boschstraße 12, 69469 Weinheim, Germany

All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law.

Print ISBN: 978‐3‐527‐35158‐9

ePDF ISBN: 978‐3‐527‐82764‐0

ePub ISBN: 978‐3‐527‐82766‐4

oBook ISBN: 978‐3‐527‐82765‐7

Preface

Broadening the spectrum of biopolymers, their classification, chemical nature, isolation, and characterization is very important for better understanding the usability of biopolymers in new applications. It is also important for the development of completely new materials based on the special properties of polysaccharides (cellulose‐based and others) compared to the biomaterials currently used in various high‐tech applications (e.g. inorganic materials and non‐degradable synthetic polymers). In this context, this book focuses largely on the fundamental knowledge of biopolymers (natural: cellulose and its derivatives; other polysaccharides such as chitosan, glycosaminoglycans (GAG's), etc.; and synthetic ones such as polyethylene terephthalate and others), their origin, classifications, chemical nature, and isolation methods. This book also covers various classical and modern approaches to the transformation of these biopolymers into different forms, from thin films (model surfaces), nanoparticles, nanofibers, to 3D scaffolds. The application of these biopolymer‐based multifunctional materials (e.g. 2D thin films to 3D scaffolds) in applications such as biosensors (e.g. for detection of DNA, antibodies, affibodies, and moisture sensors), antifouling surfaces, drug delivery systems, microfluidic devices, microarrays, two‐photon absorption lithography, enzymatic digestion systems, wound models, to name a few important areas are also discussed in detail. A library of analytical methods used for the analysis of morphology, structure, shape, thermal, electrical, and surface properties, as well as for the study of solid–liquid interaction of biomaterials, is also covered in detail in this book.

It also provides a comprehensive overview of the latest developments in the applicability of biopolymers, especially polysaccharides, for the production of sustainable biomaterials used in medicine, focusing on potential applications and future developments. Therefore, it is unique and of interest not only to students and scientists but also to industry as well as stakeholders and policy makers. This coincides with recent trends to replace fossil materials with indigenous materials. In addition, readers will get an overview of the specific and very special properties of biopolymers that can be used for the production of sustainable but high‐quality functional biomaterials. Overall, this book will contribute to a better understanding of the physicochemical properties of biopolymers and their use in the preparation of completely new materials for various advanced biomedical applications. In summary, there are no books to date that deal exclusively with the classification, isolation, preparation, and characterization of biopolymers and the design of new functional biomaterials, with a particular emphasis on the application of biomaterials in various advanced technological applications.

The content of the book is formulated to serve as a reference for the fundamental understanding of biopolymers/biomaterials and can be used by academicians, industrialists, researchers, graduate, and undergraduate students.

Graz/Austria, April 2022

Tamilselvan Mohan

Karin Stana Kleinschek

1Definitions and Types of Microbial Biopolyesters and Derived Biomaterials

Martin Koller1,2

1University of Graz, Institute of Chemistry, NAWI Graz, Heinrichstrasse 28/VI, 8010 Graz, Austria

2ARENA – Association for Resource Efficient and Sustainable Technologies, Inffeldgasse 21b, 8010 Graz, Austria

1.1 Introduction

The increasing quantities of petrol‐based plastics used for numerous applications in our daily life are among the most prevailing ecological threats of our days. In this regard, we are steadily confronted with phrases currently circulating in the media such as “plastic contamination of marine ecosystems,” “microplastic,” “growing garbage dumps,” and “bans on everyday plastic materials” such as traditional “plastic shopping bags” or, more recently, cotton swabs with plastic rods or plastic drinking straws. Indeed, the currently produced plastics amount to more than 400 megatons (Mt) annually; their production exploits limited fossil resources, and, after their life span, these plastics need to be disposed of due to their lacking biodegradability [1–3]. In the beginning of 2020, approximately 150 Mt of plastics have already accumulated in the world's oceans alone, estimated to cause perishing of 100 000 marine mammals and about ten times as many birds year by year [4]. Just the other day, the dramatic death of a sperm whale carrying an unbelievable number of around eighty plastic bags in its, making it impossible for the animal to take organic food, and shocked the general public [5]. Only recently, Zheng et al. reported an estimate that, by 2050, the global production of plastics will quadruple, which will be connected with a doubling of plastic waste [6].

In fact, significantly less than one third of plastic waste is recycled in Europe, the rest ends up in landfills or in the environment, or is simply burned [7]. In this context, the increased release of microplastics from recycled food containers, especially from plastic bottles (“Re‐PET”), into food, been described [8]. Moreover, it should be noted that recycling of plastic delays, rather than prevents, its final disposal in landfills [9]. Landfilled plastic waste, in turn, returns to the sea via detours, such as wind or river systems, and finally enters the food chain as microplastic and eventually into the human metabolism. This cycle applies to about 500 000 t of plastic waste per year in the EU alone. It is self‐explanatory that this represents enormous risks for the biosphere and the health of the entire world population. But from the resource‐technological perspective as well, our today's dependence on plastic is inadequate, unsustainable, and short sighted not only because current plastics production depends on exploiting limited fossil resources, but also because most plastic products are per definitionem designed as disposable products for single use only. This circumstance is a major environmental “fire accelerator”; as typical “end‐of‐the‐pipe” product, plastics donate high short‐term benefits through their favorable nature and, at the same time, are available at the discount price.

In particular, microplastics directly endanger food security and human health; starting from their consumption by plankton, such microplastics, which per definitionem have particle sizes ranging from 0.1 to 5.000 μm, easily climb up the entire trophic chain, until they finally get accumulated in its top, namely the human metabolism. Only during the last few years, concrete understanding of the detritus mechanisms of microplastic on the ecosystem and the metabolism of animals and humans is developing. In addition to microplastic uptake via the trophic chain, diverse techniques during food production using equipment with plastic parts, in addition to food storage in plastic containers like bottles, are also direct source of microplastic contamination of food, mainly by abrasion and by the currently fashionable use of recycled poly(ethylene terephthalate) (PET) bottles [8]. The documentation and quantification of possible diverse effects of microplastics on human health is currently only in its infancy. In 2018, microparticles in the size of 50–500 μm of a total of nine different petrochemical plastics, predominately poly(propylene) (PP) and PET, were for the first time clearly identified by an Austrian research team in the human intestine [10]. Considering the fact that the deterioration of intestine cells (villi) by microplastics was already demonstrated for fish and nematodes [11], it has to be expected that such microplastic particles also cause negative reactions in the human intestine, such as inflammation or even cancer. Moreover, by intestinal uptake, microplastics could potentially be transported to the blood and lymph system and to various organs.

To change this situation, a reasonable and fair pricing of plastics is required, reflecting not only its benefits but also the damage caused by the high environmental footprint of this end‐of‐pipe technology. In this way, plastics would no longer be disposed of in bulk; even more important, a fair pricing would, wherever possible, foster the production and implementation of alternative materials like bioinspired alternatives in order to finally find the way out of the “plastic predicament” [4].

1.2 Biopolymers as Bioinspired Alternatives

1.2.1 Defining “Bioplastics” Is No Trivial Task!

Looking back to the very beginnings of the “plastic age,” we remember that the first plastic‐like polymer indeed was biobased, namely natural cis‐1,4‐poly(isoprene) rubber obtained from the rubber tree Hevea brasiliensis (reviewed by Wycherley [12]). However, especially the decades between 1940 and the turn of the millennium were dominated by synthetic, not biodegradable, polymers of petrochemical origin. As a real alternative to many of the currently used plastics, one can switch to bio‐inspired alternatives [13]. In this context, we have to be careful when talking about “bioplastics,” which is a scientifically ambiguous expression. It is of major importance to differentiate different groups of “bioplastics”:

Plastics that are biobased (originating from renewable resources) and, at the same time, biosynthesized (monomers converted to polymers by the action of living organisms), and biodegradable/compostable. Prime examples: microbial

polyhydroxyalkanoate

s (

PHA

life cycle). As additional characteristic, PHAs are also biocompatible; hence, they do not exert any negative effect on the biosphere surrounding them (e.g. living organisms, cell lines, ecosystems) according to the standardized ISO 10993 norm. Other natural polymers, which can be processed to generate materials with plastic‐like properties (e.g. processing starch to

thermoplastic starch

[14]

–

TPS

life cycle; see

Figure 1.1

), or others, e.g. proteins gelatin

[15]

, whey proteins

[16]

, etc., chitin

[17]

, or cellulose

[18]

, which are compatible with PHA and other polymers, also belong to the group of biopolymers

sensu stricto

.

Plastics that are biobased and biodegradable/compostable, but not biosynthesized (monomers converted to polymers by classical chemical methods, often demanding toxic catalysts). Prime example:

poly(lactic acid)

(

PLA

), which currently is considered a competitor of PET or

poly(styrene)

(

PS

); for the life cycle of PLA, please refer to

Figure 1.2

. Here, one has to consider high recalcitrance of highly crystalline PLA toward biodegradation and restrictions regarding its

in vivo

biocompatibility

[19]

.

Plastics that are biobased, but neither biosynthesized nor biodegradable/compostable. Prime example: biobased

poly(ethylene)

(bio‐

PE

), which resorts to chemical conversion of saccharose to ethylene via ethanol and chemical polymerization of ethylene to PE (life cycle; see

Figure 1.3

). Such “bio‐PE” is currently strongly emerging regarding its market volume, which is expected to amount to estimated 300 000 t per year in 2022. In 2018, even the company LEGO™ switched to bio‐PE to manufacture their globally famous toy bricks; however, bio‐PE is not biodegradable, and its production exploits food resources

[20]

. Partly, this group also encompasses the “green bottle” commercialized by The Coca Cola™ company, which consists of so‐called “biobased PET”; however, this material has a biobased carbon content stemming from renewable resources (the ethylene part) of only 30%, and is not biodegradable/compos

table [21]

.

Other plastics are not biobased and not biosynthesized, but still biodegradable/compostable; they have a petrochemical origin. Prime examples are

poly(ε‐caprolactone)

(

[22]

life cycle: see

Figure 1.4

), or the random copolyester

poly(butylene adipate terephthalate)

(

PBAT

), which is used for materials commercialized by, e.g. the company BASF SE under the trade name Ecoflex® and follow‐up products (

[23]

life cycle: see

Figure 1.5

). These materials enter the natural cycle of carbon after being biodegraded; hence, they do not need to be incinerated or landfilled, but their production still exploits fossil resources (cyclohexanone made of cyclohexane in the case of PCL, or adipic acid, 1,4‐butanediol, and terephthalic acid in the case of PBAT, respectively)

[22]

.

Figure 1.1 Production and life cycle of TPS.

Source: Christian Gahle/Wikimedia Commons/CC BY‐SA 3.0; atoss/Adobe Stock; Robin/Pixabay.

Figure 1.2 Production and life cycle of PLA. The * in the graphic indicates chiral centers.

Source: epitavi/Adobe Stock.

Figure 1.3 Production and life cycle of “bio‐PE.”

Source: lzf/Adobe Stock.

Figure 1.4 Productionand life cycle of PCL.

Source: epitavi/Adobe Stock.

Figure 1.5 Production and life cycle of PBAT (Ecoflex®).

Figure 1.6 Production and life cycle of PE.

Classical synthetic thermoplastic and elastomeric resins, among them PE (life cycle: see

Figure 1.6

), PP (these two account for more than half of all plastics currently produced!), PS,

poly(vinyl chloride)

(

PVC

),

poly(urethane)

(

PU

),

poly(vinyl alcohol)

(

PVA

), PET, or silicone rubbers are extensively used, and omnipresent in our today's world. Yes, they brought progress to numerous goods and services, but they are not accessible toward biodegradation/composting within a manageable time frame. Here, some data for moderate biological degradation of hydrolyzable petrochemical plastics like PET or PU are available for laboratory‐scale enzymatic experiments, while full‐carbon backbone polymers, making up more than 80% of all plastics, can only undergo degradation after prior oxidation, which makes them highly recalcitrant

[24]

. In any case, they all entirely resort to fossil resources.

1.2.2 Biodegradability of PHA and Other Biopolymers

In the context of integration of PHA into nature's closed carbon cycle, it should be reminded that “biodegradability” is not equal to “compostability.” Both characteristics are defined via norms and assessed by certificates. Here, the norm EN‐13432 addressing biodegradation and composting of polymeric packaging materials claims that a material is “biodegradable,” if 90% of its carbon is metabolized within 180 days. In contrast, the same norm postulates that a material is “compostable” when leftovers in a sieve of 2 mm pore size after 180 days of composting do not exceed 10% of the material (reviewed by Koller et al. [25]). Generally, aerobic degradation of PHA by microorganisms like fungi or bacteria generates CO2 and water, while anaerobic PHA consumption by living organisms, e.g. in biogas plants, results in the formation of methane in addition to water and CO2[26]. Factors influencing biodegradability of PHA, such as shape and thickness of polymer specimens, crystallinity, composition, environmental factors (pH value, temperature, humidity, UV exposure), and surrounding microflora, were comprehensively summarized before [27].

Most importantly, plastic‐like biopolymers like PLA, TPS, or, as the subject of the chapter at hand, microbial PHAs, are based on renewable resources; hence, they do not deplete limited fossil resources. Beyond that, these biomaterials are integrated into the closed carbon cycle on our planet; this means that their biodegradation does not further increase the concentration of CO2 in the atmosphere. This can simply be understood by considering that raw materials typically implemented for the production of PHA and other “bioplastics” are renewable resources (prime examples: carbohydrates, alcohols, or lipids), hence, products of the natural metabolism of plants and microorganisms, which were not entrapped inside our planet since millions of years. This is a pivotal difference to crude oil, the raw material for the production of established plastics [4]. After their life span as bioplastic items, aerobic biodegradation of PHA and other biopolymers generates biomass and CO2, which again becomes part of the natural carbon cycle, by getting fixed by green plants or phototrophic microbes; the generation of renewable feedstocks for biopolymer synthesis can start de novo. This is a fundamental difference to the degradation of petrochemistry‐derived plastics by incineration; here, carbon that had been deprived of its natural cycle by fossil fuel fixation for millions of years is suddenly released into the atmosphere as additional CO2[3].

In this context, extracellular enzymes like PHA depolymerases and biocatalysts of lower specificity are excreted by various microbes and degrade PHA into microbially convertible substrates, namely small oligomers and monomers [28]. PHAs are typically degraded in vivo by microbial depolymerases and other hydrolytic effects during a 52‐week period [29]. Moreover, several studies have compared biodegradability of PHA with (semi)synthetic polymers. In this context, Gil‐Castell et al. compared the durability of poly(lactic‐co‐glycolic acid) (PLGA), polydioxanone (PDO), poly(ε‐caprolactone) (PCL), and the PHA homopolyester poly(3‐hydroxybutyrate) (PHB) when used as scaffolds. It was shown that PCL and PHB were more appropriate materials when used for long‐term applications compared to PLGA and PDO, which should rather be used for short‐term applications [30]. Concerning PHB biodegradability under not biocatalytic conditions in water or phosphate buffer saline at 37 °C, a progressive decrease of molecular mass was described; after 650 days of immersion, molecular mass was reduced by almost 50%. Importantly, biodegradability of PHA depends on various factors such as the composition of the biopolyesters on the monomeric level (homopolyesters typically degraded faster than copolyesters), the stereoregularity, crystallinity (higher degradability at lower crystallinity), molecular mass (biopolymers of lower molecular mass are typically biodegraded faster than their counterparts of higher molecular mass), and environmental conditions (temperature, pH value, humidity, and availability of nutrients) [27]. Figure 1.7 illustrates the categorization of PHA biopolyesters, among other heavily used plastic‐like polymers, based on the categories “biobased,” “biodegradable/compostable,” and “biosynthesized.”

1.2.3 PHA as Versatile Microbial Biopolyesters – Fields of Actual and Potential Applications

PHAs, as a versatile class of microbial‐produced biopolyesters, are currently in the scientific focus of material scientists, process engineers, microbiologists, and, more and more, of systems‐ and synthetic biologists. This interest originates from PHA's versatile material characteristics, making it attractive to be used in numerous areas of the plastics market, which is currently dominated by diverse technomers and plastomers of petrochemical origin [31, 32].

Figure 1.7 Classification of diverse polymers. Polymers marked in green meet the criteria “biobased,” “biosynthesized,” or “biodegradable/compostable.” PHA: polyhydroxyalkanoates; PLA: poly(lactic acid); Bio‐PE: biobased poly(ethylene); Bio‐PP: biobased poly(propylene); PCL: poly(ε‐caprolactone); PU: poly(urethane); PVC: poly(vinyl chloride); PVA: poly(vinyl alcohol); PS: poly(styrene); CA: cellulose acetate; PTFE: poly(tetrafluoroethylene) (Teflon®); PDO: poly(dioxanone); PTT: poly(trimethylene terephthalate); PBAT: poly(butylene adipate terephthalate) (Ecoflex®); PET: poly(ethylene terephthalate); PBS: poly(butylene succinate); PGLA: poly(glycolic‐co‐lactic acid). Nota bene: PHA is the only group marked in green in all categories which displays plastic‐like properties without the need for special processing techniques and/or additives.

PHA was for the first time detected by light microscopy more than 90 years ago, when Maurice Lemoigne described light‐refractive inclusions in cells of the Gram‐positive bacterium Bacillus megaterium (reviewed by Jendrossek et al. [33]). Most importantly, PHAs display all features characterizing “green plastics”; they are biobased, biosynthesized, biodegradable, compostable, and biocompatible. Hence, they can be considered the only group of real “green plastics” sensu stricto, as described earlier. Regarding the major material properties, PHAs are water insoluble, heat resistant (at least the highly crystalline representatives) and have attractive surface structure. Importantly, PHA pellets can be processed on standard machines used for processing of petrochemistry‐derived plastics. PHA melt behaves like liquid crystalline polymers, which allows molding thin‐walled or complex structures, which is of significance to produce scaffolds for biomedical use, even on small machines [34].

1.2.3.1 PHA as Packaging Materials

Among the most prominent fields of application, PHA‐based biodegradable packaging materials come in first. This is of high significance especially in the field of food packaging, where it is often desired to have compostable, transparent packaging with high barrier for oxygen, CO2, and moisture [35]. These barrier properties can be further fine‐tuned by developing PHA‐based nanocomposite materials, which contain nanosized organic (e.g. cellulose nanowhiskers) or inorganic particles (e.g. nanoclay, nanoglass, etc.); for details of PHA‐based nanocomposites, see 1.2.3.6. Considering the expedient compostability of PHA, it appears definitely reasonable to pack perishable food in such materials; after unpacking, the PHA‐based packaging material, which is contaminated with food remains, can be easily disposed of as organic waste. Particularly, the high oxygen permeation barrier of PHA's attracts huge interest for the development of packaging materials, preventing oxidative spoilage of wrapped goods. In direct comparison to the long‐established petrochemical packaging plastic high‐density PE (HDPE), it was demonstrated that preservation of quality of food packed in PHA‐based packaging materials is at least as good. In 1996, the PHA copolyester poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBHV), which can be processed to plastic films and containers for food packaging, was EU approved for food contact application [36]. While food packaging based on PHA might have a bright future, the switch to PHA‐based shopping bags for single use still appears doubtful due to cost reasons; despite the fact that PHA can be processed, especially after addition of plasticizers, to biodegradable films, this is for sure not the method of choice for economic reasons; here, TPS seems to be the better, already broadly implemented solution to globally downsize the mountain of noncompostable shopping bags.

Paper coating with biopolymers like PHA presents a stimulating route to develop the packaging materials of the future. In this context, a study by Sängerlaub et al. demonstrates the coating of a paper substrate with PHBHV by an extrusion technique. The effect of adding up to 15% of the plasticizers triethyl citrate (TEC) or polyethylene glycol (PEG) on the processability (film thickness, melting point) and resulting characteristics (elongation at break, crystallinity) of the biopolyesters were studied. Processing, structural properties (melting and crystallization temperature and surface structure), mechanical properties (adhesion, elasticity modulus, elongation at break, tensile strength), and barrier properties of the blends and their coating performance (film thickness on paper) were assessed for different extrusion temperatures. The melting temperature (Tm) and elasticity modulus of PHBHV were reduced by both plasticizers, while the elongation at break slightly increased. Owing to PHBHV's low melt strength, the lowest obtained polymer film thickness on paper amounted to 30 μm. Moreover, the grease barrier was low due to cracks and voids in the biopolymer layers and, similar to mechanical properties and bond strength, correlated with the extrusion temperature. Extrusion coating of paper with PHBHV was successfully demonstrated, but, according to the authors, the minimum possible poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) film thickness has to be further reduced to become cost effective. Further, higher flexibility is needed in order to avoid the formation of cracks, which reduce the barrier properties of films [37].

1.2.3.2 PHA as Implant Materials

The convenient biocompatibility of PHB and PHBHV, the precondition to use these materials as implants, was confirmed in diverse animal‐model experiments. In this context, rodents were implanted with PHA sutures, and investigated the physiological and metabolic reactions in long‐term test series. Monitoring the animals during one year showed good health and normal activity; hence, implanted PHA sutures did not negatively affect the homeostasis of tested animals [38, 39].

Mechanical properties such as elasticity modulus, tensile strain, and tensile strength of PHA like PHB and its composite materials are in a similar range to that reported for bones; thus, these biomaterials hold promise for application as implant materials, e.g. for femoral fractures. In comparison to surgically used polymers such as PLA, poly(glycolate) (PGA), or PLGA, implants based on PHA have the added advantage of not reducing the local pH value during in vivo degradation; this lack of acidogenesis makes PHA well accepted by cells and the immune system. As drawbacks, the low in vivo degradation rate of PHA‐based implants and the high crystallinity, especially of PHB, complicate the enzymatic degradation of the implants, as shown by the remarkable recalcitrance of tiny bar‐shaped PHB‐based femoral implants against in vivo degradation in living rats [40].

In the context of biomaterials used for implants, modern implantation surgery often faces the problem of biomaterial‐associated microbial infections, which calls for the improvement of implant surfaces to prevent bacterial adhesion at the start of biofilm formation. To overcome this issue, a recent study developed drug‐delivery systems consisting of antibiotic‐embedding PHB and PHBHV for coating titanium implants. A simple multilayer dip‐coating technique was used for optimal coating of the implants. Drug delivery, antibacterial effect, toxicity, and cell adhesion were studied for individual coated implants. Both antibiotic‐loaded PHA coatings resulted in protection against microbial adhesion, and PHBHV coatings displayed a better drug‐release profile by faster degradation compared to coatings with the homopolyester PHB. When coatings with different antibiotic concentration per layer were used, a better controlled and more homogenous release was noticed. Because the PHA coatings degrade with time under physiological conditions, these new drug‐delivery systems performed expediently not only by preventing the initial bacterial adhesion, but also by inhibiting the subsequent bacterial reproduction and biofilm formation, which serves for a prolonged drug release [41, 42].

1.2.3.3 PHA for Tissue Engineering

“Tissue engineering” deals with the generation of vital tissues (either hard‐tissue‐like bone and cartilage or soft‐tissue‐like skin and vascular grafts) to repair damaged or dead tissues and organs; this can be accomplished by combining biomaterials, cells, and bioactive compounds [43]. To perform as suitable tissue repairer, a biomaterial needs two central characteristics: appropriate mechanical properties to support organs during generation of new tissue and a surface topography allowing adhesion and growth of cells. Here, “engineered scaffolds” support cell growth and differentiation by mimicking the topography, spatial distribution, and chemical environment of the natural extracellular matrix of the target tissue [44]. Because of the high versatility of their mechanical properties, combined with excellent biocompatibility and in vivo degradability, PHA biopolyesters are among the most auspicious biomaterials for tissue engineering, and have been used to replace and heal different types of hard or soft tissue [34]; PHA‐based tissue engineering is described for restoring cartilage, skin, cardiovascular tissues, bone marrow, and nerve conduits (for recent reviews, see references [34, 45–48]).

Laser‐perforated biodegradable scaffold films of solvent‐casted PHBHV were prepared by Ellis et al. and studied for tissue repair performance. Generated pore sizes were in the μm range, which allowed human keratinocyte cells to attach and proliferate on the film surface; moreover, cells were able to penetrate pores and reach the injured tissue. This advanced cell adhesion and expedient cell growth and migration, as anticipated in regenerative medicine, were mechanistically explained by the authors by a considerably reduced crystallinity at the perforation edges [49].

In bone tissue regeneration, bioactive glass nanoparticles were embedded in PHA microspheres by Francis et al.; it was shown that the surface topography of the microspheres was beneficial for cell attachment and growth, and enhanced hydroxyapatite growth rate if compared with not‐PHA‐coated bioactive glass nanoparticles, which favors bone tissue repair. Moreover, these microspheres were loaded with the antibiotic gentamycin, which was slowly released during tissue growth [50]. These authors also demonstrated the positive effect of nanosized bioactive glass particles embedded in PHA microspheres pressed to films; these composites were used for wound healing. This is based on the hemostatic effect of bioactive glass by releasing Ca2+ ions, which supports blood clotting. The authors reported that these novel PHA composite microsphere films containing nanosized bioactive glass particles hold great promise for wound healing including protective, blood clotting, and tissue regeneration properties; importantly, surface nanotopography of the composite microsphere films has to be optimized [51].

Computer‐aided wet spinning is a hybrid additive‐manufacturing technique to process polymers dissolved in organic solvents; it enables preparing scaffolds of predefined geometry and custom‐made internal architecture. This technique was used by Puppi et al. to develop biodegradable stents consisting of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (PHBHHx)/PCL blends, which could be used to heal small blood vessels. Morphological characteristics like pore size, stent wall thickness, and others were adjusted during stent manufacturing by fine‐tuning the process parameters. While pure PHBHHx stents displayed excellent radial elasticity, PCL stents revealed higher axial and radial mechanical strength. Continued proliferation of human umbilical vein endothelial cells was demonstrated by in vitro cultivations; moreover, when in contact with human blood, exceptional resistance of the stents against blood clotting was shown [52].

Engineering of cartilage tissue by the aid of biopolymers like PHA was already extensively investigated [53]. In this context, Deng et al. seeded rabbit articular cartilage chondrocytes on scaffolds consisting of PHB, PHBHHx, or blends thereof. After four weeks of incubation, chondrocytes preserved their phenotype and proliferated well on all tested biopolymer scaffolds, with superior results for the blends [54]. As shown by Zhao et al., particularly a PHBHHx content of 60 wt% in such blends enhances mechanical properties compared to the pure biopolyesters; again, this study confirmed enhanced growth and physiological function of chondrocytes when using polymer blends [55].

Lizarraga‐Valderrama et al. prepared blends of PHB/poly(3‐hydroxyoctanoate) (PHO) blends to investigate their appropriateness as base materials for nerve tissue engineering. Chemical, mechanical, and biological properties of PHB/PHO blends were compared with neat PHB and PHO homopolyesters. As shown by using NG108‐15 neuronal cells, all tested blends were biocompatible; the blend containing 25% PHO turned out as the best support material for cell growth and differentiation, and revealed mechanical properties appropriate for its use as base material for manufacture of nerve guidance conduits [56].

1.2.3.4 PHA as Drug Carrier Materials

The biodegradability of PHA under diverse environmental conditions makes this biopolymer family expedient candidates for drug carriers. In this context, extracellular enzymes like PHA depolymerases and not‐that‐specific biocatalysts are excreted by various microbes, and degrade PHA into microbially convertible substrates, namely small oligomers and monomers [28, 57, 58]. The drug‐retarding properties of PHA‐based systems can be controlled primarily by their composition on the monomeric level and their molecular mass. Additionally, PHAs have already proved to have a substantial impact on the bioavailability of bioactive compounds, enhanced drug encapsulation, and reduced toxicity in comparison to other biodegradable polymers, as recently reviewed [34].

By an emulsification and solvent evaporation approach, Masood et al. prepared randomly distributed PHBHV nanoparticles containing different 3HV fractions of 200–300 nm size and coated them with PVA. Here, Gram‐positive Bacillus cereus was used as production strain because this organism generates endotoxin‐free PHBHV biopolyesters. Importantly, these nanoparticles contained the antineoplastic drug Ellipticine, which is used in cancer therapy. The high biocompatibility of PHBHV nanoparticles not loaded with Ellipticine was demonstrated by in vitro cytotoxicity tests; here, the “placebo” nanoparticles did not affect survival of cancer cells, while Ellipticine‐loaded PHBHV nanoparticles considerably inhibited their growth. Remarkably, growth inhibition was even more pronounced than when using the free (not encapsulated) drug; the authors proposed that supplying Ellipticine embedded in nanoparticles increases its bioavailability, which in turn enhances the drug's cytotoxic effect [59].

As another example for use of PHA in drug delivery, Rhodamine‐B‐loaded nanoparticles of random distributed PHBHHx copolyesters of a mean size of about 150 nm were prepared by Wu et al. These nanoparticles were coated with subcytotoxic concentrations of poly(ethylene imine) to assist attachment to and uptake by different cell types. Cell response to this nanoparticle system was studied in vitro and ex vivo. It was shown that the nanoparticles were transported along endolysosomal cell compartments, the endoplasmic reticulum, and the Golgi complex, without negatively affecting cell morphology or respiration [60].