Fluorescence-readout as a powerful macromolecular characterisation tool

The last few decades have witnessed significant progress in synthetic macromolecular chemistry, which can provide access to diverse macromolecules with varying structural complexities, topology and functionalities, bringing us closer to the aim of controlling soft matter material properties with molecular precision. To reach this goal, the development of advanced analytical techniques, allowing for micro-, molecular level and real-time investigation, is essential. Due to their appealing features, including high sensitivity, large contrast, fast and real-time response, as well as non-invasive characteristics, fluorescence-based techniques have emerged as a powerful tool for macromolecular characterisation to provide detailed information and give new and deep insights beyond those offered by commonly applied analytical methods. Herein, we critically examine how fluorescence phenomena, principles and techniques can be effectively exploited to characterise macromolecules and soft matter materials and to further unravel their constitution, by highlighting representative examples of recent advances across major areas of polymer and materials science, ranging from polymer molecular weight and conversion, architecture, conformation to polymer self-assembly to surfaces, gels and 3D printing. Finally, we discuss the opportunities for fluorescence-readout to further advance the development of macromolecules, leading to the design of polymers and soft matter materials with pre-determined and adaptable properties.

Thiol-Based Three-Dimensional Printing of Fully Degradable Poly(propylene fumarate) Star Polymers

Poly(propylene fumarate) star polymers photochemically 3D printed with degradable thiol cross-linkers yielded highly tunable biodegradable polymeric materials. Tailoring the alkene:thiol ratio (5:1, 10:1, 20:1 and 30:1) and thus the cross-link density within the PPF star systems yielded a wide variation of both the mechanical and degradation properties of the printed materials. Fundamental trends were established between the polymer network cross-link density, glass transition temperature, and tensile and thermomechanical properties of the materials. The tensile properties of the PPF star-based systems were compared to commercial state-of-the-art non-degradable polymer resins. The thiolene-cross-linked materials are fully degradable and possess properties over a wide range of mechanical properties relevant to regenerative medicine applications.

Methacrylated Bovine Serum Albumin and Tannic Acid Composite Materials for Three-Dimensional Printing Tough and Mechanically Functional Parts

Nature uses proteins as building blocks to create three-dimensional (3D) structural components (like spiderwebs and tissue) that are recycled within a closed loop. Furthermore, it is difficult to replicate the mechanical properties of these 3D architectures within synthetic systems. In the absence of biological machinery, protein-based materials can be difficult to process and can have a limited range of mechanical properties. Herein, we present an additive manufacturing workflow to fabricate tough, protein-based composite hydrogels and bioplastics with a range of mechanical properties. Briefly, methacrylated bovine-serum-albumin-based aqueous resins were 3D-printed using a commercial vat photopolymerization system. The printed structures were then treated with tannic acid to introduce additional non-covalent interactions and form tough hydrogels. The hydrogel material could be sutured and withstand mechanical load, even after immersion in water for 24 h. Additionally, a denaturing thermal cure could be used to virtually eliminate rehydration of the material and form a bioplastic. To highlight the functionality of this material, a bioplastic screw was 3D-printed and driven into wood without damage to the screw. Moreover, the 3D-printed constructs enzymatically degraded up to 85% after 30 days in pepsin solution. Thus, these protein-based 3D-printed constructs show great potential for biomedical devices that degrade in situ.

Next Evolution in Organ-Scale Biofabrication: Bioresin Design for Rapid High-Resolution Vat Polymerization

The field of bioprinting has made significant advancements in recent years and allowed for the precise deposition of biomaterials and cells. However, within this field lies a major challenge, which is developing high resolution constructs, with complex architectures. In an effort to overcome these challenges a biofabrication technique known as vat polymerization is being increasingly investigated due to its high fabrication accuracy and control of resolution (µm scale). Despite the progress made in developing hydrogel precursors for bioprinting techniques, such as extrusion-based bioprinting, there is a major lack in developing hydrogel precursor bioresins for vat polymerization. This is due to the specific unique properties and characteristics required for vat polymerization, from lithography to the latest volumetric printing. This is of major concern as the shortage of bioresins available has a significant impact on progressing this technology and exploring its full potential, including speed, resolution, and scale. Therefore, this review discusses the key requirements that need to be addressed in successfully developing a bioresin. The influence of monomer architecture and bioresin composition on printability is described, along with key fundamental parameters that can be altered to increase printing accuracy. Finally, recent advancements in bioresins are discussed together with future directions.

Gradient versus End-Capped Degradable Polymer Sequence Variations Result in Stiff to Elastic Photochemically 3D-Printed Substrates

Additive manufacturing affords the construction of complex scaffolds for tissue engineering, yet the limitation in material choice remains a barrier to clinical translation. Herein, a series of poly(propylene fumarate-co-propylene succinate) were synthesized using both one-pot and sequential ring-opening copolymerization reactions. Continuous liquid interface production-based photochemical 3D printing utilizing thiol-ene chemistry was used to fabricate precise structures with improved build time over the traditional poly(propylene fumarate)/diethyl fumarate 3D printing processes. Significantly, the materials do not exhibit a yield point under tension and Young's modulus of the 3D printed products can be tuned by more than 2 orders of magnitude (0.6-110 MPa) using polymer composition and the degree of polymerization. Printed constructs degrade fully under hydrolytic conditions and degradation rates can be tailored using polymer composition, polymer sequence, and resin formulation.

Biodegradable and Crosslinkable Poly(propylene fumarate) Liquid Crystal Polymers

In recent years, liquid crystal polymers (LCPs) have attracted extensive attention due to their widespread applications in artificial muscles, engineering plastics and high-modulus fibers, etc. However, the design and fabrication...

3D Printed Elastomers with Sylgard‐184‐like Mechanical Properties and Tuneable Degradability

The 3D printing of biodegradable elastomers with high mechanical strength is of great interest for personalized medicine, but rather challenging. In this study, we propose a dual-polymer resin formulation for digital light processing of biodegradable elastomers with tailorable mechanical properties comparable to those of Sylgard-184.

Digital light 3D printing of biodegradable elastomers with mechanical properties comparable to the ones of Sylgard-184 via dual-polymer resins.

Biodegradable macromers for implant bulk and surface engineering

Macromers, polymeric molecules with at least two functional groups for cross-polymerization, are interesting materials to tailor mechanical, biochemical and degradative bulk and surface properties of implants for tissue regeneration. In this review we focus on macromers with at least one biodegradable building block. Manifold design options, such as choice of polymeric block(s), optional core molecule and reactive groups, as well as cross-co-polymerization with suitable anchor or linker molecules, allow the adaptation of macromer-based biomaterials towards specific application requirements in both hard and soft tissue regeneration. Implants can be manufactured from macromers using additive manufacturing as well as molding and templating approaches. This review summarizes and discusses the overall concept of biodegradable macromers and recent approaches for macromer processing into implants as well as techniques for surface modification directed towards bone regeneration. These aspects are reviewed including a focus on the authors' contributions to the field through research within the collaborative research project Transregio 67.

Fabrication of Biomedical Scaffolds Using Biodegradable Polymers

Degradable polymers are used widely in tissue engineering and regenerative medicine. Maturing capabilities in additive manufacturing coupled with advances in orthogonal chemical functionalization methodologies have enabled a rapid evolution of defect-specific form factors and strategies for designing and creating bioactive scaffolds. However, these defect-specific scaffolds, especially when utilizing degradable polymers as the base material, present processing challenges that are distinct and unique from other classes of materials. The goal of this review is to provide a guide for the fabrication of biodegradable polymer-based scaffolds that includes the complete pathway starting from selecting materials, choosing the correct fabrication method, and considering the requirements for tissue specific applications of the scaffold.

Three-Dimensional Printing of Hydroxyapatite Composites for Biomedical Application

Hydroxyapatite (HA) and HA-based nanocomposites have been recognized as ideal biomaterials in hard tissue engineering because of their compositional similarity to bioapatite. However, the traditional HA-based nanocomposites fabrication techniques still limit the utilization of HA in bone, cartilage, dental, applications, and other fields. In recent years, three-dimensional (3D) printing has been shown to provide a fast, precise, controllable, and scalable fabrication approach for the synthesis of HA-based scaffolds. This review therefore explores available 3D printing technologies for the preparation of porous HA-based nanocomposites. In the present review, different 3D printed HA-based scaffolds composited with natural polymers and/or synthetic polymers are discussed. Furthermore, the desired properties of HA-based composites via 3D printing such as porosity, mechanical properties, biodegradability, and antibacterial properties are extensively explored. Lastly, the applications and the next generation of HA-based nanocomposites for tissue engineering are discussed.

Digital light 3D printing of customized bioresorbable airway stents with elastomeric properties

Central airway obstruction is a life-threatening disorder causing a high physical and psychological burden to patients. Standard-of-care airway stents are silicone tubes, which provide immediate relief but are prone to migration. Thus, they require additional surgeries to be removed, which may cause tissue damage. Customized bioresorbable airway stents produced by 3D printing would be highly needed in the management of this disorder. However, biocompatible and biodegradable materials for 3D printing of elastic medical implants are still lacking. Here, we report dual-polymer photoinks for digital light 3D printing of customized and bioresorbable airway stents. These stents exhibit tunable elastomeric properties with suitable biodegradability. In vivo study in healthy rabbits confirmed biocompatibility and showed that the stents stayed in place for 7 weeks after which they became radiographically invisible. This work opens promising perspectives for the rapid manufacturing of the customized medical devices for which high precision, elasticity, and degradability are sought.

Synthesis of core-crosslinked star polymers via organocatalyzed living radical polymerization

Core-crosslinked star polymers synthesized via a grafting-through approach using RCMP.

Zwitterion-Catalyzed Isomerization of Maleic to Fumaric Acid Diesters

Fumaric acid diesters are important building blocks for organic synthesis. A class of zwitterionic organocatalysts based on an amide anion/iminium cation charge pair were found to be effective in catalyzing the isomerization of maleic acid diesters to give fumaric acid diesters. Comparison of the performance of different zwitterionic organocatalysts toward the reaction revealed that nonclassical hydrogen bonding was involved in the stabilization of the Michael adduct intermediate.

Advancing Toward 3D Printing of Bioresorbable Shape Memory Polymer Stents

Stents have evolved significantly since their introduction to the medical field in the early 1980s, becoming widely used in percutaneous coronary interventions and following nephrological procedures. However, the current commercially available stents do not degrade and remain in the body forever, leading to problems like restenosis in cardiovascular applications or requiring removal procedures in ureteral applications. Efforts to replace metal with resorbable materials have largely been halted after the commercial failure of and safety concerns elicited by Abbott's Absorb stent in 2017. Industry continues to use common polymers such as poly(l-lactide) (PLLA) and polycaprolactone (PCL) for biomedical products, but due to the weak mechanical properties of these bioresorbable materials in comparison to metals, these devices have struggled to accomplish the goals set, increasing risk of thrombosis. 3D printing stents using bioresorbable and shape memory materials could provide a method of patient-personalized production, remove the need for balloon expansion, and limit stent migration, thus bringing a new age of stent technology. The investigation of a range of 3D-printable and bioresorbable shape-memory polymers can provide solutions to the shortcomings of previously explored bioresorbable stents and revitalize the medical device industry efforts into advancing stent technology.

4D Printing of Resorbable Complex Shape-Memory Poly(propylene fumarate) Star Scaffolds

3D/4D printing is enabling transformative advances in device manufacturing and medicine but remains limited by the lack of printable resorbable materials with advanced properties and functions. Herein, we report the rapid and precise 4D printing of shape-memory scaffolds based on poly(propylene fumarate) (PPF) star polymers. Scaffolds with tunable and distinguishable properties can be produced with identical polymer formulation and stoichiometry. The resulting scaffold glass transition temperatures and Young's moduli increase with the postcuring time. Significantly, both the extent and rate of shape recovery following compression can be tuned by varying the strut design, the postcuring step duration, and/or the temperature applied for the recovery step. Finally, accelerated degradation studies confirmed the resorbability of the PPF star polymer gyroid scaffolds.

100th Anniversary of Macromolecular Science Viewpoint: Macromolecular Materials for Additive Manufacturing

Additive manufacturing (AM) has drawn tremendous attention as a versatile platform for the on-demand fabrication of objects with excellent spatial control of chemical compositions and complex architectures. The development of materials that are specifically designed for AM is highly desirable for a variety of applications ranging from personal healthcare, tissue engineering, biomedical devices, self-folding origami structures, and soft robotics. Polymeric macromolecules have received increasing attention due to a wide variety of materials, the versatility for novel chemistries, and the ability to tune chemical composition and architecture. This Viewpoint highlights the development of polymeric materials for direct-ink writing and vat photopolymerization for 3D printing applications. Recent chemical innovations and polymer architectures are overviewed, which also includes recent developments in responsive and adaptive objects from AM. Polymers for biological interface and sustainability in AM are also discussed.

Alternating ring-opening copolymerization of epoxides with saturated and unsaturated cyclic anhydrides: reduced viscosity poly(propylene fumarate) oligomers for use in cDLP 3D printing

A ring-opening copolymerization of propylene oxide with saturated and unsaturated anhydrides using Mg(BHT)₂(THF)₂ catalyst followed by an isomerization yields poly(propylene fumarate) (PPF) oligomers with improved properties for 3D printing.

Selective Reactivity of Myrcene for Vat Photopolymerization 3D Printing and Postfabrication Surface Modification

Biosourced materials are gaining interest industrially, but there are still limitations on the library of available materials suitable for advanced manufacturing, especially using photopolymerization-based processing techniques. Terpenes, such as myrcene, are naturally produced materials possessing structural features, specifically alkenes, that avail themselves for such techniques. Free-radical and anionic polymerization techniques were used to explore molecular architecture, such as branching, as well as molecular weight and dispersity on physical properties prior to the production of 3D printing photopolymer resins. The polymyrcene resins were printed into dogbones and mold templates for soft materials. Model reactions with monofunctional thiols were used to demonstrate the potential for postpolymerization and fabrication functionalization, accompanying a physical demonstration where the surface hydrophobicity of polymyrcene could be tuned from superhydrophobic when using an alkyl chain monothiol (greater than 100° water contact angle) to a hydrophilic surface displaying a water contact angle of less than 45° compared with that of the unmodified surface (∼60°). Tunable bulk and surface properties are a unique feature for 3D printing materials and demonstrate the potential of polymyrcene and other biosourced photopolymers to a wide range of research applications.