Characterization of biodegradable polyurethane nanoparticles and thermally induced self-assembly in water dispersion

Preparation and characterization of amphiphilic, biodegradable, waterborne polyurethanes without using organic solvent and catalyst

Traditionally, waterborne polyurethanes (WPUs) are prepared using toxic organic solvents and catalysts. These WPUs are non-biodegradable and are buried or incinerated after the expiration date. This has adverse effects on the environment and human health, which limits the applications of WPUs. Herein, a special synthetic method was developed for biodegradable waterborne polyurethane (BWPU) by adding hydrophilic prepolymers into WPU prepolymers without using organic solvents and catalysts. Different proportions of polyethylene glycol (PEG) were introduced into polycaprolactone (PCL)-based BWPUs to improve the comprehensive properties. Results showed that as the PEG content was increased from 0 to 16 wt%, the solid content of BWPU increased from 34.8 wt% to 53.1 wt%, while the tensile strength and Young's modulus of BWPU films increased from 21.81 MPa to 56.83 MPa and 8.08 MPa to 19.4 MPa, respectively. However, the elongation at break did not decrease significantly, but still reached 827.17%. With an increase in PEG content, the crystallinity and phase separation decreased, while the hydrophilicity and surface energy increased for BWPU films. In addition, the prepared BWPUs had good biodegradability in PBS/lipase solution. The mass loss of BWPU without PEG reached 6.3 wt% after 4 weeks of degradation, whereas the mass losses of BWPUs with PEG reached 2.3-4.3 wt%. Obviously, the introduction of PEG did not increase biodegradability. Thus, the higher the PCL content, the faster the biodegradation rate. This work would provide an effective method for the preparation of ecofriendly biodegradable BWPU with excellent comprehensive properties.

The Multi-Step Chain Extension for Waterborne Polyurethane Binder of Para-Aramid Fabrics

The comprehensive balance of the mechanical, interfacial, and environmental requirements of waterborne polyurethane (WPU) has proved challenging, but crucial in the specific application as the binder for high-performance polymer fiber composites. In this work, a multi-step chain extension (MCE) method was demonstrated using three kinds of small extenders and one kind of macro-chain extender (CE) for different chain extension steps. One dihydroxyl blocked small molecular urea (1,3-dimethylolurea, DMU) was applied as one of the CEs and, through the hybrid macrodiol/diamine systems of polyether, polyester, and polysiloxane, the WPU was developed by the step-by-step optimization on each chain extending reaction via the characterization on the H-bonding association, microphase separation, and mechanical properties. The best performance was achieved when the ratio of polyether/polyester was controlled at 6:4, while 2% of DMU and 1% of polysiloxane diamine was incorporated in the third and fourth chain extension steps, respectively. Under the condition, the WPU exhibited not only excellent tensile strength of 30 MPa, elongation of break of about 1300%, and hydrophobicity indicated by the water contact angle of 98°, but also effective interfacial adhesion to para-aramid fabrics. The peeling strength of the joint based on the polysiloxane incorporated WPU after four steps of chain extension was 430% higher than that prepared through only two steps of chain extension. Moreover, about 44% of the peeling strength was sustained after the joint had been boiling for 40 min in water, suggesting the potential application for high-performance fabric composites.

Polyurethane-gelatin methacryloyl hybrid ink for 3D printing of biocompatible and tough vascular networks

A polyurethane-gelatin methacryloyl (PU-GelMA) hybrid ink was developed as a photo-crosslinkable elastic hydrogel. With the additional acrylic monomer, the ink can be tuned to accommodate elasticity and printability. Attributed to the shear-thinning properties of GelMA, PU-GelMA was preferable for extrusion printing. 3D-constructs were printed by direct extrusion or by using a sacrificial scaffold to resemble the vascular networks. The proliferation of endothelial cells on the PU-GelMA hydrogel indicated decent biocompatibility and potential utilization in artificial vessels.

Full-Atomistic Optimized Potentials for Liquid Simulations and Polymer Consistent Force Field Models for Biocompatible Shape-Memory Poly(ε-caprolactone)

Thermally induced shape memory poly(ε-caprolactone) (PCL)-based polymers are one of the most extensively researched families of biocompatible materials. They are degradable under physiological conditions and have high applicability in general biomedical engineering, with cross-linked PCL networks being particularly useful for tissue engineering. In this study, we used the optimized potentials for liquid simulations (OPLS) force field, which is well suited for describing intermolecular interactions in biomolecules, and the class II polymer consistent force field (PCFF) to investigate the properties of telechelic PCL with diacrylates as reactive functionalities on its end groups. PCFF has been specifically parameterized for simulating synthetic polymeric materials. We compare the findings of all-atom molecular dynamics simulations with known experimental data and theoretical assumptions to verify the applicability of both these force fields. We estimated the melt density, volume, transition temperatures, and mechanical characteristics of two-branched PCL diacrylates with a molecular weight of 2481 Da. Our findings point to the utility of the aforementioned force fields in predicting the properties of PCL-based polymers. It also opens avenues for developing PCL cross-linked polymer models and employing OPLS to investigate the interactions of synthetic polymers with biomolecules.

4D bioprintable self-healing hydrogel with shape memory and cryopreserving properties

Four-dimensional (4D) bioprinting is an emerging biofabrication technology that integrates time as a fourth dimension with three-dimensional (3D) bioprinting for fabricating customizable tissue-engineered implants. 4D bioprinted implants are expected to possess self-healing and shape memory properties for new application opportunities, for instance, fabrication of devices with good shape integrity for minimally invasive surgery. Herein, we developed a self-healing hydrogel composed of biodegradable polyurethane (PU) nanoparticles and photo-/thermo-responsive gelatin-based biomaterials. The self-healing property of hydrogel may be associated with the formation of reversible ionomeric interaction between the COO^-group of PU nanoparticles and NH₃⁺group on the gelatin chains. The self-healing hydrogel demonstrated excellent 3D printability and filament resolution. The UV-crosslinked printed hydrogel showed good stackability (>80 layers), structural stability, elasticity, and tunable modulus (1-60 kPa). The shape-memorizable 4D printed constructs revealed good shape fixity (∼95%) and shape recovery (∼98%) through the elasticity as well as forming and collapsing of water lattice in the hydrogel. The hydrogel and the printing process supported the continuous proliferation of neural stem cells (NSCs) (∼3.7-fold after 14 days). Moreover, the individually bioprinted NSCs and mesenchymal stem cells in the adjacent, self-healed filaments showed mutual migration and such interaction promoted the cell differentiation behavior. The cryopreserved (-20 °C or -80 °C) 4D bioprinted hydrogel after awakening and shape recovery at 37 °C demonstrated cell proliferation similar to that of the non-cryopreserved control. This 4D bioprintable, self-healable hydrogel with shape memory and cryopreserving properties may be employed for customized biofabrication.

Recent trends in gelatin methacryloyl nanocomposite hydrogels for tissue engineering

Gelatin methacryloyl (GelMA), a photocrosslinkable gelatin-based hydrogel, has been immensely used for diverse applications in tissue engineering and drug delivery. Apart from its excellent functionality and versatile mechanical properties, it is also suitable for a wide range of fabrication methodologies to generate tissue constructs of desired shapes and sizes. Despite its exceptional characteristics, it is predominantly limited by its weak mechanical strength, as some tissue types naturally possess high mechanical stiffness. The use of high GelMA concentrations yields high mechanical strength, but not without the compromise in its porosity, degradability, and three-dimensional (3D) cell attachment. Recently, GelMA has been blended with various natural and synthetic biomaterials to reinforce its physical properties to match with the tissue to be engineered. Among these, nanomaterials have been extensively used to form a composite with GelMA, as they increase its biological and physicochemical properties without affecting the unique characteristics of GelMA and also introduce electrical and magnetic properties. This review article presents the recent advances in the formation of hybrid GelMA nanocomposites using a variety of nanomaterials (carbon, metal, polymer, and mineral-based). We give an overview of each nanomaterial's characteristics followed by a discussion of the enhancement in GelMA's physical properties after its incorporation. Finally, we also highlight the use of each GelMA nanocomposite for different applications, such as cardiac, bone, and neural regeneration.

Polyurethane-functionalized starch nanocrystals as anti-tuberculosis drug carrier

Studies related to loading ability and delivery of clinically used first-line anti-tuberculosis drugs (ATDs) such as isoniazid, rifampicin, pyrazinamide and streptomycin on the surface of starch-derived bulk and nanopolyurethanes (SBPUs and SNPUs) as drug delivery systems (DDS) have been focused to minimise or remove the drug-associated adverse effects. The efficiencies of nanopolyurethanes obtained from the differently substituted cyclic aliphatic and aromatic isocyanates have been studied for drug loading and release purposes. Different advanced instrumental techniques analysed the structural and morphological properties, thermal stability and crystallinity of the starch nanopolyurethans. Average particle sizes ranging from 27.35–42.38 nm to 126.89–218.60 nm for starch nanopolyurethans, SNPU3i and SNPU4i, respectively, were determined by high-resolution transmission electron microscopy. Similarly, the loading efficiency of ATDs to the surfaces of SNPUs and SBPUs was observed in the range of 60–97% while ATDs-loaded SNPUs showed a sustainable release profile for all ATDs except for streptomycin. However, most SBPUs provided burst-release for all the above-mentioned ATDs in pH-dependent studies. The anti-tuberculosis assay against the Mycobacterium tuberculosis H37Rv strain revealed that streptomycin-loaded SNPU4i and isoniazid-loaded SNPU7i are approximately 42 and 7 times more active than the native streptomycin and isoniazid, respectively.

Cellulose and Graphene Based Polyurethane Nanocomposites for FDM 3D Printing: Filament Properties and Printability

3D printing has exponentially grown in popularity due to the personalization of each printed part it offers, making it extremely beneficial for the very demanding biomedical industry. This technique has been extensively developed and optimized and the advances that now reside in the development of new materials suitable for 3D printing, which may open the door to new applications. Fused deposition modeling (FDM) is the most commonly used 3D printing technique. However, filaments suitable for FDM must meet certain criteria for a successful printing process and thus the optimization of their properties in often necessary. The aim of this work was to prepare a flexible and printable polyurethane filament parting from a biocompatible waterborne polyurethane, which shows potential for biomedical applications. In order to improve filament properties and printability, cellulose nanofibers and graphene were employed to prepare polyurethane based nanocomposites. Prepared nanocomposite filaments showed altered properties which directly impacted their printability. Graphene containing nanocomposites presented sound enough thermal and mechanical properties for a good printing process. Moreover, these filaments were employed in FDM to obtained 3D printed parts, which showed good shape fidelity. Properties exhibited by polyurethane and graphene filaments show potential to be used in biomedical applications.

Waterborne Polyurethane Dispersions and Thin Films: Biodegradation and Antimicrobial Behaviors

Biodegradable and antimicrobial waterborne polyurethane dispersions (PUDs) and their casted solid films have recently emerged as important alternatives to their solvent-based and non-biodegradable counterparts for various applications due to their versatility, health, and environmental friendliness. The nanoscale morphology of the PUDs, dispersion stability, and the thermomechanical properties of the solid films obtained from the solvent cast process are strongly dependent on several important parameters, such as the preparation method, polyols, diisocyanates, solid content, chain extension, and temperature. The biodegradability, biocompatibility, antimicrobial properties and biomedical applications can be tailored based on the nature of the polyols, polarity, as well as structure and concentration of the internal surfactants (anionic or cationic). This review article provides an important quantitative experimental basis and structure evolution for the development and synthesis of biodegradable waterborne PUDs and their solid films, with prescribed macromolecular properties and new functions, with the aim of understanding the relationships between polymer structure, properties, and performance. The review article will also summarize the important variables that control the thermomechanical properties and biodegradation kinetics, as well as antimicrobial and biocompatibility behaviors of aqueous PUDs and their films, for certain industrial and biomedical applications.

Thermoresponsive and Conductive Chitosan-Polyurethane Biocompatible Thin Films with Potential Coating Application

Conductive thin films have great potential for application in the biomedical field. Herein, we designed thermoresponsive and conductive thin films with hydrophilicity, strain sensing, and biocompatibility. The crosslinked dense thin films were synthesized and prepared through a Schiff base reaction and ionic interaction from dialdehyde polyurethane, N-carboxyethyl chitosan, and double-bonded chitosan grafted polypyrrole. The thin films were air-dried under room temperature. These thin films showed hydrophilicity and conductivity (above 2.50 mS/cm) as well as responsiveness to the deformation. The tensile break strength (9.72 MPa to 15.07 MPa) and tensile elongation (5.76% to 12.77%) of conductive thin films were enhanced by heating them from 25 °C to 50 °C. In addition, neural stem cells cultured on the conductive thin films showed cell clustering, proliferation, and differentiation. The application of the materials as a conductive surface coating was verified by different coating strategies. The conductive thin films are potential candidates for surface modification and biocompatible polymer coating.

Mechanism and control of "coffee-ring erosion" phenomena in structurally colored ionomer films

Ionomer polyesters have polymer backbones functionalized with charged groups that make them water-dispersible. Despite the widespread use of ionomer polymers in environmentally friendly coatings without volatile organic solvents, the fundamental understanding of their film formation properties is still limited. In the study, we deposited polyester nanofilms of brilliant structural colors and correlated the macroscale optical properties to the microscale thickness of the thin films. We found that sessile water droplets deposited on these films drive the formation of a rich variety of structures by an evaporation-induced effect of "coffee-ring erosion". The ionomers spontaneously get partially re-dispersed in the form of nanoparticles in the sessile droplets and driven by convective evaporation flows, become redistributed in multiple colorful ring patterns. By using the structural colors as means to follow the polymer redistribution, we characterized further the coffee-ring patterns and found that the generated patterns are dictated by polymer composition but are mostly independent on molecular weight. As expected by colloidal theory, this phenomenon was suppressed in presence of electrolytes. Furthermore, we show that the integrity of these thin polyester films can be significantly improved by thermal densification without any further chemical curing.

Self-Healing Hydrogels and Cryogels from Biodegradable Polyurethane Nanoparticle Crosslinked Chitosan

Hydrogels are widely used in tissue engineering owing to their high water retention and soft characteristics. It remains a challenge to develop hydrogels with tunable degradation rates, proper environmental responsiveness, and injectability. In this study, biodegradable difunctional polyurethane (DFPU) nanoparticle dispersions are synthesized from an eco-friendly waterborne process involving the use of glyoxal. Such DFPU is used to crosslink chitosan (CS). Schiff base linkages between DFPU and CS successfully produce self-healing hydrogels at room temperature. Moreover, cryogels are generated after being frozen at -20 °C. These gels are found to be sensitive to low pH and amine-containing molecules owing to the property of Schiff bases. Furthermore, the degradation rates can be adjusted by the type of the component oligodiols in DFPU. Rheological evaluation verifies the excellent self-healing properties (≈100% recovery after damage). Both the self-healing gels and cryogels are injectable (through 26-gauge and 18-gauge needles, respectively) and biocompatible. Rat implantation at 14 d shows the low immune responses of cryogels. The functionalized biodegradable polyurethane nanoparticles represent a new platform of crosslinkers for biomacromolecules such as chitosan through the dynamic Schiff reaction that may give rise to a wide variety of self-healing gels and cryogels for biomedical applications.

Effective naked plasmid DNA delivery into stem cells by microextrusion-based transient-transfection system for in situ cardiac repair

BACKGROUND AIMS

Combining the use of transfection reagents and physical methods can markedly improve the efficiency of gene delivery; however, such methods often cause cell damage. Additionally, naked plasmids without any vector or physical stimulation are difficult to deliver into stem cells. In this study, we demonstrate a simple and rapid method to simultaneously facilitate efficient in situ naked gene delivery and form a bioactive hydrogel scaffold.

METHODS

Transfecting naked GATA binding protein 4 (GATA4) plasmids into human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) by co-extruding naked plasmids and hUC-MSCs with a biomimetic and negatively charged water-based biodegradable thermo-responsive polyurethane (PU) hydrogel through a microextrusion-based transient-transfection system can upregulate the other cardiac marker genes.

RESULTS

The PU hydrogels with optimized physicochemical properties (such as hard-soft segment composition, size, hardness and thermal gelation) induced GATA4-transfected hUC-MSCs to express the cardiac marker proteins and then differentiated into cardiomyocyte-like cells in 15 days. We further demonstrated that GATA4-transfected hUC-MSCs in PU hydrogel were capable of in situ revival of heart function in zebrafish in 30 days.

CONCLUSIONS

Our results suggest that hUC-MSCs and naked plasmids encapsulated in PU hydrogels might represent a new strategy for in situ tissue therapy using the microextrusion-based transient-transfection system described here. This transfection system is simple, effective and safer than conventional technologies.

Smart polymers for cell therapy and precision medicine

Soft materials have been developed very rapidly in the biomedical field over the past 10 years because of advances in medical devices, cell therapy, and 3D printing for precision medicine. Smart polymers are one category of soft materials that respond to environmental changes. One typical example is the thermally-responsive polymers, which are widely used as cell carriers and in 3D printing. Self-healing polymers are one type of smart polymers that have the capacity to recover the structure after repeated damages and are often injectable through needles. Shape memory polymers are another type with the ability to memorize their original shape. These smart polymers can be used as cell/drug/protein carriers. Their injectability and shape memory performance allow them to be applied in bioprinting, minimally invasive surgery, and precision medicine. This review will describe the general materials design, characterization, as well as the current progresses and challenges of these smart polymers.

Double-Network Polyurethane-Gelatin Hydrogel with Tunable Modulus for High-Resolution 3D Bioprinting

Three-dimensional (3D) bioprinting is a technology to print materials (bioink) with cells into customized tissues for regeneration or organoids for drug screening applications. Herein, a series of biodegradable polyurethane (PU)-gelatin hydrogel with tunable mechanical properties and degradation rates were developed as the bioink. The PU-gelatin hydrogel demonstrated good printability in 24-31 °C and could print a complicated structure such as the nose-shaped construct. Due to the excellent shear thinning and fast strain recovery properties, the PU-gelatin hydrogel also had long working windows for bioprinting (over 24 h), stacking ability (up to 80 layers), and feasibility for high-resolution printing (through an 80 μm nozzle). The structure stability of the PU-gelatin hydrogel was maintained by two-stage double-network formation through Ca²⁺ chelation and thermal gelation at 37 °C without any toxic cross-linking reagent. The compressive modulus of printed PU-gelatin hydrogel constructs increased in about 3-fold by the treatment of CaCl₂ solution for 15 min and enhanced further after incubation because of the thermal sensitivity of PU at 37 °C. Mesenchymal stem cells (MSCs) printed with the PU-gelatin hydrogel through the 80 μm nozzle showed good viability, high mobility, and ∼200% proliferation ratio (or an ∼300% proliferation ratio through a 200 μm nozzle) in 10 days. Furthermore, the MSC-laden PU-gelatin constructs containing small molecular drug Y27632 underwent chondrogenesis in 10 days. The novel series of PU-gelatin hydrogels with tunable modulus, long working window, convenient bioprinting process, and high-resolution printing possibilities may serve as new bioink for 3D bioprinting of various tissues.

A glimpse of biodegradable polymers and their biomedical applications

Over the past two decades, biodegradable polymers (BPs) have been widely used in biomedical applications such as drug carrier, gene delivery, tissue engineering, diagnosis, medical devices, and antibacterial/antifouling biomaterials. This can be attributed to numerous factors such as chemical, mechanical and physiochemical properties of BPs, their improved processibility, functionality and sensitivity towards stimuli. The present review intended to highlight main results of research on advances and improvements in terms of synthesis, physical properties, stimuli response, and/or applicability of biodegradable plastics (BPs) during last two decades, and its biomedical applications. Recent literature relevant to this study has been cited and their developing trends and challenges of BPs have also been discussed.

Biodegradable, anti-adhesive and tough polyurethane hydrogels crosslinked by triol crosslinkers

The mechanical and biodegradable properties of hydrogels are two essential properties for practical biomaterial applications. In this work, a series of biodegradable polyurethane (PU) hydrogels were successfully synthesized using two kinds of triol crosslinkers with different chain structures. One crosslinker is normal glycerol (GC) with short chain length, and the other is biodegradable poly (ε-caprolactone)-triol (CAPA) with long chain length. All PU hydrogels showed considerable water uptake around ~60%, excellent strength (above 3 MPa), advisable modulus (0.9~1.7 MPa), high elasticity (above 700%), as well as good biodegradability and biocompatibility. Hydrogen bonds served as reversible sacrificial bonds in the PU hydrogels endow them good toughness with partial hysteresis during deformation. The biodegradable long chain crosslinker CAPA can certainly accelerate the degradation of PU hydrogels compared with the GC crosslinked hydrogels. The degradation of these hydrogels was a process of continuous erosion from the surface to interior, which contributes to the high remain of mechanical properties after 30 days-degradation. Besides, the hydrogels also show excellent antifouling ability of protein and anti-adhesion of cells. Therefore, these hydrogels suggest great potential used as biological anti-adhesive membranes or catheters.

Facile preparation of biodegradable dual stimuli-responsive micelles from waterborne polyurethane for efficient intracellular drug delivery

A novel waterborne polyurethane based on main chain degradation under acidic and reductive conditions of tumors was synthesized.

Chemical insights into bioinks for 3D printing

Dedicated chemical strategies are required to form hydrogel networks from bioink components, allowing cell survival during 3D bioprinting processes.

Molecular Structures and Mechanisms of Waterborne Biodegradable Polyurethane Nanoparticles

Biodegradable hydrogels have become promising materials for many biological applications in the past years. Recently, novel waterborne biodegradable polyurethane (WDPU) nanoparticles have been synthesized by a green water-based process, and serve as fundamental building blocks to form materials with great biocompatibility, biodegradability, and mechanical properties. However, the molecular structures and mechanisms of the WDPU nanoparticles and the relationship between the chemical compositions of the polymer segments and the material properties of the biodegradable hydrogels at macro-scale are still not well understood. In this study, we explore the fundamental mechanisms of WDPU nanoparticles through a full atomistic simulation approach to understand how the chemical compositions at the molecular level affect the molecular structures and material properties of WDPU nanoparticles. Specifically, we compare two WDPUs, i.e. PCL75LL25 and PCL75DL25, of the same hard segment composition and very similar soft segment composition [75% poly(e-caprolatone) and 25% polylactide], except the lactide in the former is L-form and in the latter is D,L-form. Our results show that the material properties of the biodegradable hydrogel can be designed by tuning the chemical compositions of the polymer segments. We find that the PCL75DL25 and PCL75LL25 have distinct molecular structures and physical crosslinks within the nanoparticles. The molecular structure of WDPU with PDLLA as soft segments is more extended, leading to more physical crosslinks between PCL segments. This study provide fundamental insights into the molecular structures and mechanisms of WDPU nanoparticles and help enabling the design of material properties of biocompatible hydrogel.

Intra-articular injection of kartogenin-conjugated polyurethane nanoparticles attenuates the progression of osteoarthritis

Osteoarthritis (OA) is the most common form of joint disease and a leading cause of physical disability, there is an urgent need to attenuate the progression of OA. Intra-articular (IA) injection is an effective treatment for joints diseases, however, the therapeutic effects mostly depend on the efficacy of drug duration in joints. Drug delivery system can provide drug-controlled release and reduce the number of IA injection. In this study, amphiphilic polyurethanes with pendant amino group were synthesized and amide bonds were formed between the amine group of polyurethane and the carboxyl group of kartogenin (KGN), a small molecular reported to show both regenerative and protective effects on cartilage. Our results showed that KGN-conjugated polyurethane nanoparticles (PN-KGN) were spherical and regular in shape with an average size of 25 nm and could sustained and controlled release of KGN in vitro. PN-KGN showed no cytotoxicity and pro-inflammatory effects on chondrocytes. The therapeutic effects in OA model showed that IA injection of KGN could attenuate the progress of OA, however, the cartilage degeneration became obviously at 12 weeks with matrix loss and vertical fissures. By contrast, IA injection of PN-KGN showed less cartilage degeneration with significant lower OARSI scores even at 12 weeks, indicating PN-KGN could further arrest the development of OA. Immunohistochemistry also validated that IA injection of PN-KGN retained the normal compositions of cartilage matrix, with much stronger Col II staining and less Col I staining. In conclusion, IA injection of PN-KGN is a better potential strategy to treat OA, with long-time cartilage protection and less IA injections.

Polyurethane Nanoparticle-Loaded Fenofibrate Exerts Inhibitory Effects on Nonalcoholic Fatty Liver Disease in Mice

Polyurethane (PU) nanoparticles are potential drug carriers. We aimed to study the in vitro and in vivo efficacy of biodegradable PU nanoparticles loaded with fenofibrate (FNB-PU) on nonalcoholic fatty liver disease (NAFLD). FNB-PU was prepared by a green process, and its preventive effects on NAFLD were investigated on HepG2 cells and mice. FNB-PU showed sustained in vitro FNB release profile. Compared to FNB crude drug, FNB-PU significantly decreased triglyceride content in HepG2 cells incubated with oleic acid and in livers of mice with NAFLD induced by a methionine choline deficient diet, and increased plasma FNB concentration of the mice. FNB-PU increased absorption of FNB and therefore enhanced the inhibitory effects of FNB on NAFLD.

Synthesis and Characterization of Dual Stimuli-Sensitive Biodegradable Polyurethane Soft Hydrogels for 3D Cell-Laden Bioprinting

Three-dimensional bioprinting serves as an attractive platform to fabricate customized tissue-engineered substitutes from biomaterials and cells for the repair or replacement of injured tissues and organs. A common challenge for 3D bioprinting materials is that the structures printed from the biodegradable polymer hydrogels tend to collapse because of the poor mechanical stability. In this study, dual stimuli-responsive biodegradable polyurethane (PU) dispersions (PUA2 and PUA3) were synthesized from an eco-friendly waterborne process. Acrylate group was introduced in the PU chain end to serve as a photosensitive moiety for UV-induced cross-linking and improvement of the printability, while mixed oligodiols in the soft segment remained to be the thermosensitive moiety. The photo/thermal-induced morphological changes of PU nanoparticles were verified by dynamic light scattering, small-angle X-ray scattering, and rheological measurement of the dispersions. It was observed that these PU nanoparticles became more rod-like in shape after UV treatment and formed compact packing structures upon further heating. With the thermosensitive properties, these UV-cured PU dispersions underwent rapid thermal gelation with gel moduli in the range 0.5-2 kPa near body temperature. The rheological properties of the PU hydrogels including dynamic viscoelasticity, creep recovery, and shear thinning behavior at 37 °C were favorable for processing by microextrusion-based 3D printing and could be easily mixed with cells before printing to produce cell-laden constructs. The dual-responsive hydrogel constructs demonstrated higher resolution and shape fidelity as well as better cell viability and proliferation than the thermoresponsive control. Moreover, the softer hydrogel (PUA3) with a low modulus (<1 kPa) could offer neural stem cells a tofu-like, stable, and inductive 3D microenvironment to proliferate and differentiate. We expect that the photo/thermoresponsive biodegradable polyurethane ink may offer unique rheological properties to contribute toward the custom-made bioprinting of soft tissues.

Cell reprogramming by 3D bioprinting of human fibroblasts in polyurethane hydrogel for fabrication of neural-like constructs

3D bioprinting is a technique which enables the direct printing of biodegradable materials with cells into 3D tissue. So far there is no cell reprogramming in situ performed with the 3D bioprinting process. Forkhead box D3 (FoxD3) is a transcription factor and neural crest marker, which was reported to reprogram human fibroblasts into neural crest stem-like cells. In this study, we synthesized a new biodegradable thermo-responsive waterborne polyurethane (PU) gel as a bioink. FoxD3 plasmids and human fibroblasts were co-extruded with the PU hydrogel through the syringe needle tip for cell reprogramming. The rheological properties of the PU hydrogel including the modulus, gelation time, and shear thinning were optimized for the transfection effect of FoxD3 in situ. The corresponding shear rate and shear stress were examined. Results showed that human fibroblasts could be reprogrammed into neural crest stem-like cells with high cell viability during the extrusion process under an average shear stress ∼190 Pa. We further translated the method to the extrusion-based 3D bioprinting, and demonstrated that human fibroblasts co-printed with FoxD3 in the thermo-responsive PU hydrogel could be reprogrammed and differentiated into a neural-tissue like construct at 14 days after induction. The neural-like tissue construct produced by 3D bioprinting from human fibroblasts may be applied to personalized drug screening or neuroregeneration.

STATEMENT OF SIGNIFICANCE

There is no study so far on cell reprogramming in situ with 3D bioprinting. In this manuscript, a new thermoresponsive polyurethane bioink was developed and employed to deliver FoxD3 plasmid into human fibroblasts by the extrusion-based bioprinting. When the polyurethane gel was extruded through the syringe tip, the shear stress generated may have caused the transient membrane permeability for transfection. The shear stress was optimized for transfection in situ by 3D bioprinting. We demonstrated that human fibroblasts could be reprogrammed into neural crest-like stem cells by 3D bioprinting with the gel, and the reprogrammed cells underwent neural differentiation in the printed structure after induction. The neural-like tissue engineering constructs fabricated by 3D bioprinting from human fibroblasts may be applied for neuroregeneration or further developed as mini-brain for basic research and drug screening.

Polymer-Based Nanomaterials and Applications for Vaccines and Drugs

Nanotechnology plays a significant role in drug development. As carriers, polymeric nanoparticles can deliver vaccine antigens, proteins, and drugs to the desired site of action. Polymeric nanoparticles with lower cytotoxicity can protect the delivered antigens or drugs from degradation under unfavorable conditions via a mucosal administration route; further, the uptake of nanoparticles by antigen-presenting cells can increase and induce potent immune responses. Additionally, nanomaterials are widely used in vaccine delivery systems because nanomaterials can make the vaccine antigen long-acting. This review focuses on some biodegradable polymer materials such as natural polymeric nanomaterials, chemically synthesized polymer materials, and biosynthesized polymeric materials, and points out the advantages and the direction of research on degradable polymeric materials. The application and future perspectives of polymeric materials as delivery carriers and vaccine adjuvants in the field of drugs and vaccines are presented. With the increase of knowledge and fundamental understandings of polymer-based nanomaterials, means of integrating some other attractive properties, such as slow release, target delivery, and alternative administration methods and delivery pathways are feasible. Polymer-based nanomaterials have great potential for the development of novel vaccines and drug systems for certain needs, including single-dose and needle-free deliveries of vaccine antigens and drugs in the future.

Morphology-dependent pH-responsive release of hydrophilic payloads using biodegradable nanocarriers

The development of functional nanocarriers with stimuli-responsive properties has advanced tremendously to serve biomedical applications such as drug delivery and regenerative medicine. However, the development of biodegradable nanocarriers that can be loaded with hydrophilic compounds and ensure its controlled release in response to changes in the surrounding environment still remains very challenging. Herein, we achieved such demands via the preparation of aqueous core nanocapsules using a base-catalyzed interfacial reaction employing a diisocyanate monomer and functional monomers/polymers containing thiol and hydroxyl functionalities at the droplet interface. pH-responsive poly(thiourethane–urethane) nanocarriers with ester linkages were synthesized by incorporating polycaprolactone diol, which is susceptible to hydrolytic degradation via ester linkages, as a functional monomer in the reaction formulation. We could demonstrate that by systematically varying the number of biodegradable segments, the morphology of the nanocarriers can be tuned without imparting the efficient encapsulation of hydrophilic payload (>85% encapsulation efficiency) and its transfer from organic to aqueous phase. The developed nanocarriers allow for a fast release of hydrophilic payload that depends on pH, the number of biodegradable segments and nanocarrier morphology. Succinctly put, this study provides important information to develop pH-responsive nanocarriers with tunable morphology, using interfacial reactions in the inverse miniemulsion process, by controlling the number of degradable segments to adjust the release profile depending on the type of application envisaged.

The morphology and release properties of aqueous core nanocapsules for the pH-responsive release of hydrophilic payload was investigated by systematically varying the number of biodegradable segments.

A facile method to prepare superparamagnetic iron oxide and hydrophobic drug-encapsulated biodegradable polyurethane nanoparticles

Superparamagnetic iron oxide nanoparticles (SPIO NPs) have a wide range of biomedical applications such as in magnetic resonance imaging, targeting, and hyperthermia therapy. Aggregation of SPIO NPs can occur because of the hydrophobic surface and high surface energy of SPIO NPs. Here, we developed a facile method to encapsulate SPIO NPs in amphiphilic biodegradable polymer. Anionic biodegradable polyurethane nanoparticles (PU NPs) with ~35 nm size and different chemistry were prepared by waterborne processes. SPIO NPs were synthesized by chemical co-precipitation. SPIO NPs were then added to the aqueous dispersion of PU NPs, followed by application of high-frequency (~20 kHz) ultrasonic vibration for 3 min. This method rendered SPIO-PU hybrid NPs (size ~110 nm) suspended in water. SPIO-PU hybrid NPs contained ~50-60 wt% SPIO and retained the superparamagnetic property (evaluated by a magnetometer) as well as high contrast in magnetic resonance imaging. SPIO-PU NPs also showed the ability to provide cell hyperthermic treatment. Using the same ultrasonic method, hydrophobic drug (Vitamin K3 [VK3]) or (9-(methylaminomethyl) anthracene [MAMA]) could also be encapsulated in PU NPs. The VK3-PU or MAMA-PU hybrid NPs had ~35 nm size and different release profiles for PUs with different chemistry. The encapsulation efficiency for VK3 and MAMA was high (~95%) without burst release. The encapsulation mechanism may be attributed to the low glass transition temperature (Tg) and good mechanical compliance of PU NPs. The new encapsulation method involving waterborne biodegradable PU NPs is simple, rapid, and effective to produce multimodular NP carriers.

Preparation, Characterization, and Mechanism for Biodegradable and Biocompatible Polyurethane Shape Memory Elastomers

Thermally induced shape memory is an attractive feature of certain functional materials. Among the shape memory polymers, shape memory elastomers (SMEs) especially those with biodegradability have great potential in the biomedical field. In this study, we prepared waterborne biodegradable polyurethane SME based on poly(ε-caprolactone) (PCL) oligodiol and poly(l-lactic acid) (PLLA) oligodiol as the mixed soft segments. The ratio of the soft segments in polyurethanes was optimized for shape memory behavior. The thermally induced shape memory mechanism of the series of polyurethanes was clarified using differential scanning calorimeter (DSC), X-ray diffraction (XRD), and small-angle X-ray scattering (SAXS). In particular, the in situ SAXS measurements combined with shape deformation processes were employed to examine the stretch-induced (oriented) crystalline structure of the polyurethanes and to elucidate the unique mechanism for shape memory properties. The polyurethane with optimized PLLA crystalline segments showed a diamond-shape two-dimensional SAXS pattern after being stretched, which gave rise to better shape fixing and shape recovery. The shape memory behavior was further tested in 37 °C water. The biodegradable polyurethane comprising 38 wt % PCL segments and 25 wt % PLLA segments and synthesized at a relatively lower temperature by the waterborne procedure showed ∼100% shape recovery in 37 °C water. The biodegradable polyurethane SME also demonstrated good endothelial cell viability as well as low platelet adhesion/activation. We conclude that the waterborne biodegradable polyurethane SME possesses a unique thermally induced shape memory mechanism and may have potential applications in making shape memory biodegradable stents or scaffolds.

A graphene–polyurethane composite hydrogel as a potential bioink for 3D bioprinting and differentiation of neural stem cells

The composite hydrogel ink containing a small amount of graphene (25 ppm) was printed with neural stem cells (NSCs) into 3D cell-laden tissue constructs, expressing neural-associated proteins after culture for only seven days without induction.

Biodegradable polymer scaffolds

Tissue engineering aims to repair the damaged tissue by transplantation of cells or introducing bioactive factors in a biocompatible scaffold. In recent years, biodegradable polymer scaffolds mimicking the extracellular matrix have been developed to promote the cell proliferation and extracellular matrix deposition. The biodegradable polymer scaffolds thus act as templates for tissue repair and regeneration. This article reviews the updated information regarding various types of natural and synthetic biodegradable polymers as well as their functions, physico-chemical properties, and degradation mechanisms in the development of biodegradable scaffolds for tissue engineering applications, including their combination with 3D printing.

Fully glutathione degradable waterborne polyurethane nanocarriers: Preparation, redox-sensitivity, and triggered intracellular drug release

Polyurethanes are important class of biomaterials that are extensively used in medical devices. In spite of their easy synthesis, polyurethanes that are fully degradable in response to the intracellular reducing environment are less explored for controlled drug delivery. Herein, a novel glutathione degradable waterborne polyurethane (WPU) nanocarrier for redox triggered intracellular delivery of a model lipophilic anticancer drug, doxorubicin (DOX) is reported. The WPU was prepared from polyaddition reaction of isophorone diisocyanate (IPDI) and a novel linear polyester polyol involving disulfide linkage, disulfide labeled chain extender, dimethylolpropionic acid (DMPA) using dibutyltin dilaurate (DBTDL) as a catalyst. The resulting polyurethane self-assembles into nanocarrier in water. The dynamic light scattering (DLS) measurements and scanning electron microscope (SEM) revealed fast swelling and disruption of nanocarriers under an intracellular reduction-mimicking environment. The in vitro release studies showed that DOX was released in a controlled and redox-dependent manner. MTT assays showed that DOX-loaded WPU had a high in vitro antitumor activity in both HDF noncancer cells and MCF- 7 cancer cells. In addition, it is found that the blank WPU nanocarriers are nontoxic to HDF and MCF-7 cells even at a high concentration of 2mg/mL. Hence, nanocarriers based on disulfide labeled WPU have appeared as a new class of biocompatible and redox-degradable nanovehicle for efficient intracellular drug delivery.

Click Cross-Linking-Improved Waterborne Polymers for Environment-Friendly Coatings and Adhesives

Waterborne polymers, including waterborne polyurethanes (WPU), polyester dispersions (PED), and polyacrylate emulsions (PAE), are employed as environmentally friendly water-based coatings and adhesives. An efficient, fast, stable, and safe cross-linking strategy is always desirable to impart waterborne polymers with improved mechanical properties and water/solvent/thermal and abrasion resistance. For the first time, click chemistry was introduced into waterborne polymer systems as a cross-linking strategy. Click cross-linking rendered waterborne polymer films with significantly improved tensile strength, hardness, adhesion strength, and water/solvent resistance compared to traditional waterborne polymer films. For example, click cross-linked WPU (WPU-click) has dramatically improved the mechanical strength (tensile strength increased from 0.43 to 6.47 MPa, and Young's modulus increased from 3 to 40 MPa), hardness (increased from 59 to 73.1 MPa), and water resistance (water absorption percentage dropped from 200% to less than 20%); click cross-linked PED (PED-click) film also possessed more than 3 times higher tensile strength (∼28 MPa) than that of normal PED (∼8 MPa). The adhesion strength of click cross-linked PAE (PAE-click) to polypropylene (PP) was also improved (from 3 to 5.5 MPa). In addition, extra click groups can be preserved after click cross-linking for further functionalization of the waterborne polymeric coatings/adhesives. In this work, we have demonstrated that click modification could serve as a convenient and powerful approach to significantly improve the performance of a variety of traditional coatings and adhesives.

Thermo-Responsive Polyurethane Hydrogels Based on Poly(ε-caprolactone) Diol and Amphiphilic Polylactide-Poly(Ethylene Glycol) Block Copolymers

Waterborne polyurethane (PU) based on poly(ε-caprolactone) (PCL) diol and an amphiphilic polylactide-poly(ethylene glycol) (PLA-PEG) diblock copolymer was synthesized. The molar ratio of PCL/PLA-PEG was 9:1 with different PLA chain lengths. The PU nanoparticles were characterized by dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and rheological analysis. The water contact angle measurement, infrared spectroscopy, wide angle X-ray scattering (WAXS), thermal and mechanical analyses were conducted on PU films. Significant changes in physio-chemical properties were observed for PUs containing 10 mol % of amphiphilic blocks. The water contact angle was reduced to 12°⁻13°, and the degree of crystallinity was 5%⁻10%. The PU dispersions underwent sol-gel transition upon the temperature rise to 37 °C. The gelation time increased as the PLA chain length increased. In addition, the fractal dimension of each gel was close to that of a percolation cluster. Moreover, PU4 with a solid content of 26% could support the proliferation of human mesenchymal stem cells (hMSCs). Therefore, thermo-responsive hydrogels with tunable properties are promising injectable materials for cell or drug delivery.