Understanding the biodegradation of polyurethanes: from classical implants to tissue engineering materials

A functional tacrolimus-releasing nerve wrap for enhancing nerve regeneration following surgical nerve repair

JOURNAL/nrgr/04.03/01300535-202501000-00036/figure1/v/2024-05-14T021156Z/r/image-tiff Axonal regeneration following surgical nerve repair is slow and often incomplete, resulting in poor functional recovery which sometimes contributes to lifelong disability. Currently, there are no FDA-approved therapies available to promote nerve regeneration. Tacrolimus accelerates axonal regeneration, but systemic side effects presently outweigh its potential benefits for peripheral nerve surgery. The authors describe herein a biodegradable polyurethane-based drug delivery system for the sustained local release of tacrolimus at the nerve repair site, with suitable properties for scalable production and clinical application, aiming to promote nerve regeneration and functional recovery with minimal systemic drug exposure. Tacrolimus is encapsulated into co-axially electrospun polycarbonate-urethane nanofibers to generate an implantable nerve wrap that releases therapeutic doses of bioactive tacrolimus over 31 days. Size and drug loading are adjustable for applications in small and large caliber nerves, and the wrap degrades within 120 days into biocompatible byproducts. Tacrolimus released from the nerve wrap promotes axon elongation in vitro and accelerates nerve regeneration and functional recovery in preclinical nerve repair models while off-target systemic drug exposure is reduced by 80% compared with systemic delivery. Given its surgical suitability and preclinical efficacy and safety, this system may provide a readily translatable approach to support axonal regeneration and recovery in patients undergoing nerve surgery.

Nano-Micron Combined Hydrogel Microspheres: Novel Answer for Minimal Invasive Biomedical Applications

Hydrogels, key in biomedical research for their hydrophilicity and versatility, have evolved with hydrogel microspheres (HMs) of micron-scale dimensions, enhancing their role in minimally invasive therapeutic delivery, tissue repair, and regeneration. The recent emergence of nanomaterials has ushered in a revolutionary transformation in the biomedical field, which demonstrates tremendous potential in targeted therapies, biological imaging, and disease diagnostics. Consequently, the integration of advanced nanotechnology promises to trigger a new revolution in the realm of hydrogels. HMs loaded with nanomaterials combine the advantages of both hydrogels and nanomaterials, which enables multifaceted functionalities such as efficient drug delivery, sustained release, targeted therapy, biological lubrication, biochemical detection, medical imaging, biosensing monitoring, and micro-robotics. Here, this review comprehensively expounds upon commonly used nanomaterials and their classifications. Then, it provides comprehensive insights into the raw materials and preparation methods of HMs. Besides, the common strategies employed to achieve nano-micron combinations are summarized, and the latest applications of these advanced nano-micron combined HMs in the biomedical field are elucidated. Finally, valuable insights into the future design and development of nano-micron combined HMs are provided.

Materials Strategies to Overcome the Foreign Body Response

The foreign body response (FBR) is an immune-mediated reaction that can occur with most biomaterials and biomedical devices. The FBR initiates a deterioration in the performance of implantable devices, representing a longstanding challenge that consistently hampers their optimal utilization. Over the last decade, significant strides are achieved based on either hydrogel design or surface modifications to mitigate the FBR. This review delves into recent material strategies aimed at mitigating the FBR. Further, the authors look forward to future novel anti-FBR materials from the perspective of clinical translation needs. Such prospective materials hold the potential to attenuate local immune responses, thereby significantly enhancing the overall performance of implantable devices.

Simultaneous Formation of Polyhydroxyurethanes and Multicomponent Semi-IPN Hydrogels

This study introduces an efficient strategy for synthesizing polyhydroxyurethane-based multicomponent hydrogels with enhanced rheological properties. In a single-step process, 3D materials composed of Polymer 1 (PHU) and Polymer 2 (PVA or gelatin) were produced. Polymer 1, a crosslinked polyhydroxyurethane (PHU), grew within a colloidal solution of Polymer 2, forming an interconnected network. The synthesis of Polymer 1 utilized a Non-Isocyanate Polyurethane (NIPU) methodology based on the aminolysis of bis(cyclic carbonate) (bisCC) monomers derived from 1-thioglycerol and 1,2-dithioglycerol (monomers A and E, respectively). This method, applied for the first time in Semi-Interpenetrating Network (SIPN) formation, demonstrated exceptional orthogonality since the functional groups in Polymer 2 do not interfere with Polymer 1 formation. Optimizing PHU formation involved a 20-trial methodology, identifying influential variables such as polymer concentration, temperature, solvent (an aprotic and a protic solvent), and the organo-catalyst used [a thiourea derivative (TU) and 1,8-diazabicyclo [5.4.0]undec-7-ene (DBU)]. The highest molecular weights were achieved under near-bulk polymerization conditions using TU-protic and DBU-aprotic as catalyst-solvent combinations. Monomer E-based PHU exhibited higher Mw¯ than monomer A-based PHU (34.1 kDa and 16.4 kDa, respectively). Applying the enhanced methodology to prepare 10 multicomponent hydrogels using PVA or gelatin as the polymer scaffold revealed superior rheological properties in PVA-based hydrogels, exhibiting solid-like gel behavior. Incorporating monomer E enhanced mechanical properties and elasticity (with loss tangent values of 0.09 and 0.14). SEM images unveiled distinct microstructures, including a sponge-like pattern in certain PVA-based hydrogels when monomer A was chosen, indicating the formation of highly superporous interpenetrated materials. In summary, this innovative approach presents a versatile methodology for obtaining advanced hydrogel-based systems with potential applications in various biomedical fields.

Amperometric bio-sensing of lactate and oxygen concurrently with local field potentials during status epilepticus

Epilepsy is a prevalent neurological disorder with a complex pathogenesis and unpredictable nature, presenting limited treatment options in >30 % of affected individuals. Neurometabolic abnormalities have been observed in epilepsy patients, suggesting a disruption in the coupling between neural activity and energy metabolism in the brain. In this study, we employed amperometric biosensors based on a modified carbon fiber microelectrode platform to directly and continuously measure lactate and oxygen dynamics in the brain extracellular space. These biosensors demonstrated high sensitivity, selectivity, and rapid response time, enabling in vivo measurements with high temporal and spatial resolution. In vivo recordings in the cortex of anaesthetized rats revealed rapid and multiphasic fluctuations in extracellular lactate and oxygen levels following neuronal stimulation with high potassium. Furthermore, real-time measurement of lactate and oxygen concentration dynamics concurrently with network electrical activity during status epilepticus induced by 4-aminopyridine (4-AP) demonstrated phasic changes in lactate levels that correlated with bursts of electrical activity, while tonic levels of lactate remained stable during seizures. This study highlights the complex interplay between lactate dynamics, electrical activity, and oxygen utilization in epileptic seizures.

Thermoplastic polyurethane/POSS nanohybrids: Synthesis, morphology, and biological properties

Recent studies show good osteoinductive properties of polyurethanes modified with polyhedral oligomeric silsesquioxanes (POSS). In this work, three types of POSS; propanediolisobutyl-POSS (PHI-POSS), disilanolisobutyl-POSS (DSI-POSS), and octahydroxybutyl-POSS (OCTA-POSS) were chemically incorporated into linear polyurethane based on an aliphatic isocyanate, hexamethylene diisocyanate (HDI), to obtain new nanohybrid PU-POSS materials. The full conversion of POSS was confirmed by Fourier transform infrared spectroscopy (FTIR-ATR) spectra of the model reactions with pure HDI. The materials obtained were investigated by FTIR, SEM-EDS, and DSC. The DSC studies showed the thermoplasticity of the obtained materials and apparently good recovery. 30-day immersion in SBF (simulated body fluid) revealed an increase in the rate of deposition of hydroxyapatite (HAp) for the highest POSS loadings, resulting in thick layers of hydroxyapatite (~60-40 μm), and the Ca/P ratio 1.67 (even 1.785). The structure and properties of the inorganic layer depend on the type of POSS, the number of hard segments, and those containing POSS, which can be tailored by changing the HDI/poly(tetramethylene glycol) (PTMG) ratio. Furthermore, the obtained composites revealed good biocompatibility, as confirmed by cytotoxicity tests conducted on two cell lines; normal human dermal fibroblasts (NHDF) and primary human osteoblasts (HOB). Adherent cells seeded on the tested materials showed viability even after a 48-h incubation. After this time, the population of viable, and proliferating cells exceeded 90%. Bioimaging studies have shown the fibroblast and osteoblast cells were well attached to the surface of the tested materials.

Tissue formation and host remodeling of an elastomeric biodegradable scaffold in an ovine pulmonary leaflet replacement model

In pursuit of a suitable scaffold material for cardiac valve tissue engineering applications, an acellular, electrospun, biodegradable polyester carbonate urethane urea (PECUU) scaffold was evaluated as a pulmonary valve leaflet replacement in vivo. In sheep (n = 8), a single pulmonary valve leaflet was replaced with a PECUU leaflet and followed for 1, 6, and 12 weeks. Implanted leaflet function was assessed in vivo by echocardiography. Explanted samples were studied for gross pathology, microscopic changes in the extracellular matrix, host cellular re-population, and immune responses, and for biomechanical properties. PECUU leaflets showed normal leaflet motion at implant, but decreased leaflet motion and dimensions at 6 weeks. The leaflets accumulated α-SMA and CD45 positive cells, with surfaces covered with endothelial cells (CD31+). New collagen formation occurred (Picrosirius Red). Accumulated tissue thickness correlated with the decrease in leaflet motion. The PECUU scaffolds had histologic evidence of scaffold degradation and an accumulation of pro-inflammatory/M1 and anti-inflammatory/M2 macrophages over time in vivo. The extent of inflammatory cell accumulation correlated with tissue formation and polymer degradation but was also associated with leaflet thickening and decreased leaflet motion. Future studies should explore pre-implant seeding of polymer scaffolds, more advanced polymer fabrication methods able to more closely approximate native tissue structure and function, and other techniques to control and balance the degradation of biomaterials and new tissue formation by modulation of the host immune response.

Nitric Oxide-Releasing Porous Coating with Antibacterial Activity and Blood Compatibility

Nitric oxide (NO)-releasing coating is promising to enhance the biocompatibility of medical devices. In this study, polyurethane (PU) and S-nitrosated keratin (KSNO) were dissolved with dimethyl sulfoxide (DMSO) and tetrahydrofuran (THF) to prepare a coating solution. This solution is facile to form a porous coating on various substrates based on solvent-evaporation-induced phase separation (SEIPS). The coating could continuously release NO up to 200 h in the presence of ascorbic acid (Asc). In addition, the coating could accelerate endothelialization by promoting the viability of human umbilical vein endothelial cells (HUVECs) while inhibiting the proliferation of human umbilical artery smooth muscle cells (HUASMCs). Furthermore, the coating had good antibacterial activity and blood compatibility. Taken together, this universal coating provides wider potential applications in the field of cardiovascular implants.

Electrospun methacrylated natural/synthetic composite membranes for gingival tissue engineering

New functional materials for engineering gingival tissue are still in the early stages of development. Materials for such applications must maintain volume and have advantageous mechanical and biological characteristics for tissue regeneration, to be an alternative to autografts, which are the current benchmark of care. In this work, methacrylated gelatin (GelMa) was photocrosslinked with synthetic immunomodulatory methacrylated divinyl urethanes and defined monomers to generate composite scaffolds. Using a factorial design, with the synthetic monomers of a degradable polar/hydrophobic/ionic polyurethane (D-PHI) and GelMa, composite materials were electrospun with polycarbonate urethane (PCNU) and light-cured in-flight. The materials had significantly different relative hydrophilicities, with unique biodegradation profiles associated with specific formulations, thereby providing good guidance to achieving desired mechanical characteristics and scaffold resorption for gingival tissue regeneration. In accelerated esterase/collagenase degradation models, the new materials exhibited an initial rapid weight loss followed by a more gradual rate of degradation. The degradation profile allowed for the early infiltration of human adipose-derived stromal/stem cells, while still enabling the graft's structural integrity to be maintained. In conclusion, the materials provide a promising candidate platform for the regeneration of oral soft tissues, addressing the requirement of viable tissue infiltration while maintaining volume and mechanical integrity. STATEMENT OF SIGNIFICANCE: There is a need for the development of more functional and efficacious materials for the treatment of gingival recession. To address significant limitations in current material formulations, we sought to investigate the development of methacrylated gelatin (GelMa) and oligo-urethane/methacrylate monomer composite materials. A factorial design was used to electrospin four new formulations containing four to five monomers. Synthetic immunomodulatory monomers were crosslinked with GelMa and electrospun with a polycarbonate urethane resulting in unique mechanical properties, and resorption rates which align with the original design criteria for gingival tissue engineering. The materials may have applications in tissue engineering and can be readily manufactured. The findings of this work may help better direct the efforts of tissue engineering and material manufacturing.

Biocompatibility of polyurethane-coated breast implants: A histological comparison of implant capsules

BACKGROUND

Biocompatibility describes the influence of materials on their biological environment. Implant material in the human body can cause a foreign body reaction and the formation of a capsule around the foreign material. Since capsular formation is the most frequent issue after breast-implant insertion, knowledge and awareness of biocompatibility is crucial, especially since worldwide, breast augmentation continues to be the most popular plastic surgery, with over 1.6 million procedures performed in 2020, according to surveys by the International Society of Aesthetic Plastic Surgery (ISAPS).

MATERIAL AND METHODS

This study includes 80 capsular samples of female patients who underwent revision surgery after breast-implant insertion at the University Hospital Regensburg. Capsules of breast implants with different surface structures (smooth, textured and polyurethane-coated) and shapes (round-shaped, anatomically-shaped) were analyzed histologically after hematoxylin-eosin-staining in respect to capsular thickness and layer formation.

RESULTS

Capsular thickness and layering showed a statistically significant difference between polyurethane-coated and smooth as well as polyurethane-coated and textured implants. Capsules around polyurethane-coated implants presented greater thickness. However, the difference between smooth and textured implants was not statistically significant. Furthermore, the shape of the implants also indicated a statistically significant difference in capsular thickness. Implants of anatomical shape resulted in a thinner capsule than round-shaped breast-implants.

CONCLUSION

In conclusion, this study demonstrated a thicker capsule around polyurethane-coated breast implants and no difference in capsular thickness between smooth and textured breast implants. Anatomically shaped breast-implants presented a thinner capsule than round shaped breast-implants.

Bioadhesive Technology Platforms

Bioadhesives have emerged as transformative and versatile tools in healthcare, offering the ability to attach tissues with ease and minimal damage. These materials present numerous opportunities for tissue repair and biomedical device integration, creating a broad landscape of applications that have captivated clinical and scientific interest alike. However, fully unlocking their potential requires multifaceted design strategies involving optimal adhesion, suitable biological interactions, and efficient signal communication. In this Review, we delve into these pivotal aspects of bioadhesive design, highlight the latest advances in their biomedical applications, and identify potential opportunities that lie ahead for bioadhesives as multifunctional technology platforms.

Injectable smart stimuli-responsive hydrogels: pioneering advancements in biomedical applications

Hydrogels have established their significance as prominent biomaterials within the realm of biomedical research. However, injectable hydrogels have garnered greater attention compared with their conventional counterparts due to their excellent minimally invasive nature and adaptive behavior post-injection. With the rapid advancement of emerging chemistry and deepened understanding of biological processes, contemporary injectable hydrogels have been endowed with an "intelligent" capacity to respond to various endogenous/exogenous stimuli (such as temperature, pH, light and magnetic field). This innovation has spearheaded revolutionary transformations across fields such as tissue engineering repair, controlled drug delivery, disease-responsive therapies, and beyond. In this review, we comprehensively expound upon the raw materials (including natural and synthetic materials) and injectable principles of these advanced hydrogels, concurrently providing a detailed discussion of the prevalent strategies for conferring stimulus responsiveness. Finally, we elucidate the latest applications of these injectable "smart" stimuli-responsive hydrogels in the biomedical domain, offering insights into their prospects.

A Temperature and pH Dual-Sensitive Multifunctional Polyurethane with Bacteria-Triggered Antibacterial Activity

An effective and practical antibacterial strategy is to design multifunctional and stimuli-responsive materials that exhibit antibacterial activity in response to bacterial triggers. In this study, because the metabolism of Staphylococcus aureus (S. aureus) can acidify the surrounding environment and pH level can affect the lower critical solution temperature of temperature/pH dual-sensitive polymers, a monomer containing a temperature-sensitive N-isopropyl amide derivative and pH-sensitive tertiary amine groups is first synthesized. Then, the monomer is copolymerized with a polyurethane chain, and partial tertiary amine groups are quaternized to obtain bactericidal activity. The modified polyurethane exhibits temperature/pH sensitivity, antibacterial adhesion activity, bactericidal activity, and good cytocompatibility. An in situ investigation of bacterial behavior and pH changes in the bacterial suspension during the process confirms that the temperature/pH dual-sensitive polyurethane successfully achieves antibacterial activity though the metabolic activity of S. aureus without external intervention. This design concept provides a new perspective for antibacterial material design.

An overview of polyurethane biomaterials and their use in drug delivery

Polyurethanes are a versatile and highly tunable class of materials that possess unique properties including high tensile strength, abrasion and fatigue resistance, and flexibility at low temperatures. The tunability of polyurethane properties has allowed this class of polymers to become ubiquitous in our daily lives in fields as diverse as apparel, appliances, construction, and the automotive industry. Additionally, polyurethanes with excellent biocompatibility and hemocompatibility can be synthesized, enabling their use as biomaterials in the medical field. The tunable nature of polyurethane biomaterials also makes them excellent candidates as drug delivery vehicles, which is the focus of this review. The fundamental idea we aim to highlight in this article is the structure-property-function relationships found in polyurethane systems. Specifically, the chemical structure of the polymer determines its macroscopic properties and dictates the functions for which it will perform well. By exploring the structure-property-function relationships for polyurethanes, we aim to elucidate the fundamental properties that can be tailored to achieve controlled drug release and empower researchers to design new polyurethane systems for future drug delivery applications.

4D Printing of Biocompatible Scaffolds via In Situ Photo-crosslinking from Shape Memory Copolyesters

The complexity of surgical treatments for large-area soft tissue injuries makes placing large implants into injury sites challenging. Aliphatic polyesters are often used for scaffold preparation in tissue engineering owing to their excellent biodegradability and biocompatibility. Scaffolds with shape-memory effect (SME) can also avoid large-volume trauma during the implantation. However, the complexity and diversity of diseases require more adaptable and precise processing methods. Four-dimensional (4D) printing, a booming smart material additive manufacturing technology, provides a new opportunity for developing shape memory scaffolds. With the aim of personalized or patient-adaptable soft tissues such as blood vessels, we developed a feasible strategy for fabricating scaffolds with fine architectures using 4D printing crosslinkable shape memory linear copolyesters using fused deposition modeling (FDM). To overcome the weak bonding strength of each printed layer during FDM, a catalyst-free photo-crosslinkable functional group derived from biocompatible cinnamic acid was embedded into the linear copolyesters as in situ crosslinking points during FDM printing. Under ultraviolet-assisted irradiation, the resulting 4D scaffold models demonstrated excellent SME, desirable mechanical performance, and good stability in a water environment owing to the chemical bonding between each layer. Moreover, the excellent biocompatibility of the scaffold was evaluated in vitro and in vivo. The developed composite scaffolds could be used for minimally invasive soft tissue repair.

Arrhenius-model-based degradable oligourethane hydrogels for controlled growth factor release

Biodegradable hydrogels are growing in demand to enable the delivery of biomolecules (e.g. growth factors) for regenerative medicine. This research investigated the resorption of an oligourethane/polyacrylic acid hydrogel, a biodegradable hydrogel which supports tissue regeneration. The Arrhenius model was used to characterize the resorption of the polymeric gels in relevant in vitro conditions, and the Flory-Rehner equation was used to correlate the volumetric swelling ratio with the extent of degradation. The study found that the swelling rate of the hydrogel follows the Arrhenius model at elevated temperatures, estimating degradation time in saline solution at 37°C to be between 5 and 13 months, serving as a preliminary approximation of degradation in vivo. The degradation products had low cytotoxicity towards endothelial cells, and the hydrogel supported stromal cell proliferation. Additionally, the hydrogels were able to release growth factors and maintain the biomolecules' bioactivity towards cell proliferation. The study of the vascular endothelial growth factor (VEGF) release from the hydrogel used a diffusion process model, showing that the electrostatic attraction between VEGF and the anionic hydrogel allowed for controlled and sustained VEGF release over three weeks. In a rat subcutaneous implant model, a selected hydrogel with desired degradation rates exhibited minimal foreign body response and supported M2a macrophage phenotype, and vascularization. The low M1 and high M2a macrophage phenotypes within the implants were associated with tissue integration. This research supports the use of oligourethane/polyacrylic acid hydrogels as a promising material for delivering growth factors and supporting tissue regeneration. STATEMENT OF SIGNIFICANCE: There is a need for degradable elastomeric hydrogels that can support the formation of soft tissues and minimize long-term foreign body responses. An Arrhenius model was used to estimate the relative breakdown of hydrogels, in-vitro. The results demonstrate that hydrogels made from a combination of poly(acrylic acid) and oligo-urethane diacrylates can be designed to resorb over defined periods ranging from months to years depending on the chemical formulation prescribed by the model. The hydrogel formulations also provided for different release profiles of growth factors, relevant to tissue regeneration. In-vivo, these hydrogels had minimal inflammatory effects and showed evidence of integration into the surrounding tissue. The hydrogel approach can help the field design a broader range of biomaterials for tissue regeneration.

Long-Term Degradation Assessment of a Polyurethane-Based Surgical Adhesive-Assessment and Critical Consideration of Preclinical In Vitro and In Vivo Testing

Tissue adhesives constitute a great possibility to improve conventional wound closure. In contrast to sutures, they enable nearly immediate hemostasis and can prevent fluid or air leaks. In the present study, a poly(ester)urethane-based adhesive was investigated which already proved to be suitable for different indications, such as reinforcing vascular anastomosis and sealing liver tissue. Using in vitro and in vivo setups, the degradation of the adhesives was monitored over a period of up to 2 years, to evaluate long-term biocompatibility and determine degradation kinetics. For the first time, the complete degradation of the adhesive was documented. In subcutaneous locations, tissue residues were found after 12 months and in intramuscular locations, tissue degradation was complete after about 6 months. A detailed histological evaluation of the local tissue reaction revealed good biocompatibility throughout the different degradation stages. After full degradation, complete remodeling to physiological tissue was observed at the implant locations. In addition, this study critically discusses common issues related to the assessment of biomaterial degradation kinetics in the context of medical device certification. This work highlighted the importance and encouraged the implementation of biologically relevant in vitro degradation models to replace animal studies or at least reduce the number of animals in preclinical testing prior to clinical studies. Moreover, the suitability of frequently used implantation studies based on ISO 10993-6 at standard locations was critically discussed, especially in light of the associated lack of reliable predictions for degradation kinetics at the clinically relevant site of implantation.

Surface decoration with leucine tetrapeptide: An antibacterial strategy against Gram-negative bacteria

Surface-associated microbe contamination by Gram-negative bacteria poses a serious problem in medical care. Cationic peptides or polymers are the main materials used for antibacterial surface coating, but the positive charge may lead to blood coagulation. Therefore, exploiting surface coating which is free of positive charge and is effective for Gram-negative bacteria inactivation is in urgent need. In this study, inspired by the affinity between lipopolysaccharides of Gram-negative bacteria and Toll-like receptors of immune cells, we develop a leucine-based tetrapeptide coating strategy for combating Gram-negative bacteria. The obtained surface has excellent bactericidal activity against Gram-negative bacteria like Pseudomonas aeruginosa and Escherichia coli. A 1 mm² coated glass surface could kill > 9.9 × 10⁴ CFU bacteria in 1 h and has nearly no damage to mammal cells. Moreover, this surface coating strategy could be applied on various surfaces like glass slices, glass capillary cavity and thermoplastic polyurethane slices. And the coated surface could largely mitigate the microbe contamination in an in vivo subcutaneous implantation. This work paves a new way for antibacterial surface-coating which is behaving no positive charge and is of great importance for biomedical devices.

A Polypyrrole-Polycarbonate Polyurethane Elastomer Alleviates Cardiac Arrhythmias via Improving Bio-Conductivity

Myocardial fibrosis, resulting from myocardial infarction (MI), significantly alters cardiac electrophysiological properties. As fibrotic scar tissue forms, its resistance to incoming action potentials increases, leading to cardiac arrhythmia, and eventually sudden cardiac death or heart failure. Biomaterials are gaining increasing attention as an approach for addressing post-MI arrhythmias. The current study investigates the hypothesis that a bio-conductive epicardial patch can electrically synchronize isolated cardiomyocytes in vitro and rescue arrhythmic hearts in vivo. A new conceived biocompatible, conductive, and elastic polyurethane composite bio-membrane, referred to as polypyrrole-polycarbonate polyurethane (PPy-PCNU), is developed, in which solid-state conductive PPy nanoparticles are distributed throughout an electrospun aliphatic PCNU nanofiber patch in a controlled manner. Compared to PCNU alone, the resulting biocompatible patch demonstrates up to six times less impedance, with no conductivity loss over time, as well as being able to influence cellular alignment. Furthermore, PPy-PCNU promotes synchronous contraction of isolated neonatal rat cardiomyocytes and alleviates atrial fibrillation in rat hearts upon epicardial implantation. Taken together, epicardially-implanted PPy-PCNU could potentially serve as a novel alternative approach for the treatment of cardiac arrhythmias.

Study on the blood flow characteristics of venous needle retention with different super-hydrophobic surface structures

A venous retention needle, as an implanted device, is very likely to cause thrombosis. In view of the thrombosis phenomenon caused by retention needles, this paper compares the influence of different superhydrophobic surface retentions on blood flow. Compared with other superhydrophobic bulges, the fluid velocity of the four-prism bulge is the highest (0.08 m/s), and the vorticity and shear force of the hemispherical bulge are higher. A large number of vortices can inhibit thrombosis better. The tire vortices generated in the superhydrophobic convex grooves are important vortices to inhibit thrombosis. The enhancement and development of the tire vortex weakens the resistance near the wall of the needle and reduces the probability of platelet aggregation. The superhydrophobic surface structure studied in this paper can not only provide guidance for the design of venous retention needles with better performance but also provide corresponding technical support for the development of human implantation devices.

Novel Tumor-Targeted Self-Nanostructured and Compartmentalized Water-in-Oil-in-Water Polyurethane-Polyurea Nanocapsules for Cancer Theragnosis

Encapsulation of water-soluble bioactive compounds for enabling specific accumulation in tumor locations, while avoiding premature clearance and/or degradation in the bloodstream, is one of the main hallmarks in nanomedicine, especially that of NIR fluorescent probes for cancer theragnosis. The herein reported technology furnishes water-dispersible double-walled polyurethane-polyurea hybrid nanocapsules (NCs) loaded with indocyanine green (ICG-NCs), using a versatile and highly efficient one-pot and industrially scalable synthetic process based on the use of two different prepolymers to set up the NCs walls. Flow cytometry and confocal microscopy confirmed that both ICG-loaded NCs internalized in monocyte-derived dendritic cells (moDCs). The in vivo analysis of xenograft A375 mouse melanoma model revealed that amphoteric functionalization of NCs' surface promotes the selective accumulation of ICG-NCs in tumor tissues, making them promising agents for a less-invasive theragnosis of cancer.

Precision medicine strategies for spinal degenerative diseases: Injectable biomaterials with in situ repair and regeneration

As the population ages, spinal degeneration seriously affects quality of life in middle-aged and elderly patients, and prevention and treatment remain challenging for clinical surgeons. In recent years, biomaterials-based injectable therapeutics have attracted much attention for spinal degeneration treatment due to their minimally invasive features and ability to perform precise repair of irregular defects. However, the precise design and functional control of bioactive injectable biomaterials for efficient spinal degeneration treatment remains a challenge. Although many injectable biomaterials have been reported for the treatment of spinal degeneration, there are few reviews on the advances and effects of injectable biomaterials for spinal degeneration treatment. This work reviews the current status of the design and fabrication of injectable biomaterials, including hydrogels, bone cements and scaffolds, microspheres and nanomaterials, and the current progress in applications for treating spinal degeneration. Additionally, registered clinical trials were also summarized and key challenges and clinical translational prospects for injectable materials for the treatment of spinal degenerative diseases are discussed.

Green Chemistry for Biomimetic Materials: Synthesis and Electrospinning of High-Molecular-Weight Polycarbonate-Based Nonisocyanate Polyurethanes

Conventional synthesis routes for thermoplastic polyurethanes (TPUs) still require the use of isocyanates and tin-based catalysts, which pose considerable safety and environmental hazards. To reduce both the ecological footprint and human health dangers for nonwoven TPU scaffolds, it is key to establish a green synthesis route, which eliminates the use of these toxic compounds and results in biocompatible TPUs with facile processability. In this study, we developed high-molecular-weight nonisocyanate polyurethanes (NIPUs) through transurethanization of 1,6-hexanedicarbamate with polycarbonate diols (PCDLs). Various molecular weights of PCDL were employed to maximize the molecular weight of NIPUs and consequently facilitate their electrospinnability. The synthesized NIPUs were characterized by nuclear magnetic resonance, Fourier-transform infrared spectroscopy, gel permeation chromatography, and differential scanning calorimetry. The highest achieved molecular weight (M _w) was 58,600 g/mol. The NIPUs were consecutively electrospun into fibrous scaffolds with fiber diameters in the submicron range, as shown by scanning electron microscopy (SEM). To assess the suitability of electrospun NIPU mats as a possible biomimetic load-bearing pericardial substitute in cardiac tissue engineering, their cytotoxicity was investigated in vitro using primary human fibroblasts and a human epithelial cell line. The bare NIPU mats did not need further biofunctionalization to enhance cell adhesion, as it was not outperformed by collagen-functionalized NIPU mats and hence showed that the NIPU mats possess a great potential for use in biomimetic scaffolds.

In Vitro and In Vivo Cell-Interactions with Electrospun Poly (Lactic-Co-Glycolic Acid) (PLGA): Morphological and Immune Response Analysis

Random electrospun three-dimensional fiber membranes mimic the extracellular matrix and the interfibrillar spaces promotes the flow of nutrients for cells. Electrospun PLGA membranes were analyzed in vitro and in vivo after being sterilized with gamma radiation and bioactivated with fibronectin or collagen. Madin-Darby Canine Kidney (MDCK) epithelial cells and primary fibroblast-like cells from hamster’s cheek paunch proliferated over time on these membranes, evidencing their good biocompatibility. Cell-free irradiated PLGA membranes implanted on the back of hamsters resulted in a chronic granulomatous inflammatory response, observed after 7, 15, 30 and 90 days. Morphological analysis of implanted PLGA using light microscopy revealed epithelioid cells, Langhans type of multinucleate giant cells (LCs) and multinucleated giant cells (MNGCs) with internalized biomaterial. Lymphocytes increased along time due to undegraded polymer fragments, inducing the accumulation of cells of the phagocytic lineage, and decreased after 90 days post implantation. Myeloperoxidase⁺ cells increased after 15 days and decreased after 90 days. LCs, MNGCs and capillaries decreased after 90 days. Analysis of implanted PLGA after 7, 15, 30 and 90 days using transmission electron microscope (TEM) showed cells exhibiting internalized PLGA fragments and filopodia surrounding PLGA fragments. Over time, TEM analysis showed less PLGA fragments surrounded by cells without fibrous tissue formation. Accordingly, MNGC constituted a granulomatous reaction around the polymer, which resolves with time, probably preventing a fibrous capsule formation. Finally, this study confirms the biocompatibility of electrospun PLGA membranes and their potential to accelerate the healing process of oral ulcerations in hamsters’ model in association with autologous cells.

Biocompatible Nanocapsules for Self-Healing Dental Resins and Bone Cements

Bone cements and dental resins are methacrylate-based materials that have been in use for many years, but their failure rates are quite high with essentially all dental resins failing within 10 years and 25% of all prosthetic implants will undergo aseptic loosening. There are significant healthcare costs and impacts on quality of life of patients. Self-healing bone cements and resins could improve the lifespan of these systems, reduce costs, and improve patient outcomes, but they have been limited by efficacy and toxicity of the components. To address these issues, we developed a self-healing system based on a dual nanocapsule system. Two nanocapsules were synthesized, one containing an initiator and one encapsulating a monomer, both in polyurethane shells. The monomer used was triethylene glycol dimethacrylate. The initiator capsules synthesized contained benzoyl peroxide and butylated hydroxytoluene. Resins containing the nanocapsules were tested in tension until failure, and the fractured surfaces were placed together. 33% of the samples showed self-healing behaviors to the point where they could be reloaded and tested in tension. Furthermore, the capsules and their components showed good biocompatibility with Caco-2 cells, a human epithelial cell line suggesting that they would be well tolerated in vivo.

Hemocompatibile Thin Films Assessed under Blood Flow Shear Forces

The aim of this study was to minimize the risk of life-threatening thromboembolism in the ventricle through the use of a new biomimetic heart valve based on metal-polymer composites. Finite volume element simulations of blood adhesion to the material were carried out, encompassing radial flow and the cone and plane test together with determination of the effect of boundary conditions. Both tilt-disc and bicuspid valves do not have optimized blood flow due to their design based on rigid valve materials (leaflet made of pyrolytic carbon). The main objective was the development of materials with specific properties dedicated to contact with blood. Materials were evaluated by dynamic tests using blood, concentrates, and whole human blood. Hemostability tests under hydrodynamic conditions were related to the mechanical properties of thin-film materials obtained from tribological tests. The quality of the coatings was high enough to avoid damage to the coating even as they were exposed up to maximum loading. Analysis towards blood concentrates of the hydrogenated carbon sample and the nitrogen-doped hydrogenated carbon sample revealed that the interaction of the coating with erythrocytes was the strongest. Hemocompatibility evaluation under hydrodynamic conditions confirmed very good properties of the developed coatings.

Cytotoxicity of nanomixture: Combined action of silver and plastic nanoparticles on immortalized human lymphocytes

BACKGROUND

Silver nanoparticles (AgNP) are one of the most commercialized types of nanomaterials, with a wide range of applications owing to their antimicrobial activity. They are particularly important in hospitals and other healthcare settings, where they are used to maintain sterility of surfaces, textiles, catheters, medical implants, and more. However, AgNP can not only harm bacteria, but also damage mammalian cells and tissue. While the potential toxicity of AgNP is an understood risk, there is a lack of data on their toxicity in combination with polymeric materials, especially plastic nanoparticles such as polystyrene nanoparticles (PSNP) that can be released from surfaces of polystyrene devices during their medical use.

AIM

This study aimed to investigate combined effect of AgNP and nanoplastics on human immune response.

METHODS

Cells were treated with a range of PSNP and AgNP concentrations, either applied alone or in combination. Cytotoxicity, induction of apoptosis, generation of oxidative stress, uptake efficiency, intracellular localization and nanomechanical cell properties were selected as exposure biomarkers.

RESULTS

Collected experimental data showed that nanomixture induced oxidative stress, apoptosis and mortality of Jurkat cells stronger than its individual components. Cell treatment with AgNP/PSNP mixture also significantly changed cell mechanical properties, evidenced by reduction of cells' Young Modulus.

CONCLUSION

AgNP and PSNP showed additive toxic effects on immortalized human lymphocytes, evidenced by increase in cellular oxidative stress, induction of apoptosis, and reduction of cell stiffness. These results have important implications for using AgNP and PSNP in medical contexts, particularly for long-term medical implants.

3D Printed Bioinspired Stents with Photothermal Effects for Malignant Colorectal Obstruction

Stent placement is an effective palliation therapy for malignant colorectal obstruction. However, recurrent obstruction is a common severe complication caused by tumor ingrowth into the stent lumen. Conventional covered stents play a part in preventing the tumor from growing inward but at the expense of significantly increasing the risk of stent migration. Therefore, there is an urgent demand to develop stents with sustained antitumor and antimigration abilities. Herein, we propose a facile method for fabricating multifunctional bioinspired colorectal stents using 3D printing technology. Inspired by high-adhesion biological structures (gecko feet, tree frog toe pads, and octopus suckers) in nature, different types of bioinspired colorectal stents are designed to reduce migration. After functionalization with graphene oxide (GO), bioinspired colorectal stents show excellent and controllable photothermal performance, which is validated by effective ablation of colon cancer cells in vitro and tumors in vivo. Besides, the bioinspired colorectal stents demonstrate the feasibility of transanal placement and opening of the obstructed colon. More importantly, the facile manufacturing process of multifunctional bioinspired colorectal stents is appealing for mass production. Hence, the developed multifunctional bioinspired colorectal stents exhibit a highly promising potential in clinical applications.

Effects of low-intensity pulsed ultrasound stimulation on cell seeded 3D hybrid scaffold as a novel strategy for meniscus regeneration: An in vitro study

Menisci are fibrocartilaginous structures in the knee joint with an inadequate regenerative capacity, which causes low healing potential and further leads to osteoarthritis. Recently, three-dimensional (3D) printing techniques and ultrasound treatment have gained plenty of attention for meniscus tissue engineering. The present study investigates the effectiveness of low-intensity pulsed ultrasound stimulations (LIPUS) on the proliferation, viability, morphology, and gene expression of the chondrocytes seeded on 3D printed polyurethane scaffolds dip-coated with gellan gum, hyaluronic acid, and glucosamine. LIPUS stimulation was performed at 100, 200, and 300 mW/cm² intensities for 20 min/day. A faster gap closure (78.08 ± 2.56%) in the migration scratch assay was observed in the 200 mW/cm² group after 24 h. Also, inverted microscopic and scanning electron microscopic images showed no cell morphology changes during LIPUS exposure at different intensities. The 3D cultured chondrocytes under LIPUS treatment revealed a promotion in cell proliferation rate and viability as the intensity doses increased. Additionally, LIPUS could stimulate chondrocytes to overexpress the aggrecan and collagen II genes and improve their chondrogenic phenotype. This study recommends that the combination of LIPUS treatment and 3D hybrid scaffolds can be considered as a valuable treatment for meniscus regeneration based on our in vitro data.

XPS and ToF-SIMS Characterization of New Biodegradable Poly(Peptide-Urethane-Urea) Block Copolymers

New, linear, segmented poly(peptide-urethane-urea) (PPUU) block copolymers are synthesized and their surface compositions are characterized with angle dependent X-ray photoelectron spectroscopy (ADXPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). These new PPUU block copolymers contain three types of segments. The soft segment (SS) is poly(caprolactone diol) (PCL). The hard segment is lysine diisocyanate with a hydrazine chain extender. The oligopeptide segment (OPS) contains three types of amino acids (proline, hydroxyproline, and glycine). Incorporation of the OPS into the polyurethane backbone is done to provide a synthetic polymer material with controllable biodegradation properties. As biodegradation processes normally are initiated at the interface between the biomaterial and the living tissue, it is important to characterize the surface composition of biomaterials. ADXPS and ToF-SIMS results show that the surfaces of all four polymers are enriched with the PCL SS, the most hydrophobic component of the three polymer segments.

Biodegradable polyurethane scaffolds in regenerative medicine: Clinical translation review

Early explorations of tissue engineering and regenerative medicine concepts commonly utilized simple polyesters such as polyglycolide, polylactide, and their copolymers as scaffolds. These biomaterials were deemed clinically acceptable, readily accessible, and provided processability and a generally known biological response. With experience and refinement of approaches, greater control of material properties and integrated bioactivity has received emphasis and a broadened palette of synthetic biomaterials has been employed. Biodegradable polyurethanes (PUs) have emerged as an attractive option for synthetic scaffolds in a variety of tissue applications because of their flexibility in molecular design and ability to fulfill mechanical property objectives, particularly in soft tissue applications. Biodegradable PUs are highly customizable based on their composition and processability to impart tailored mechanical and degradation behavior. Additionally, bioactive agents can be readily incorporated into these scaffolds to drive a desired biological response. Enthusiasm for biodegradable PU scaffolds has soared in recent years, leading to rapid growth in the literature documenting novel PU chemistries, scaffold designs, mechanical properties, and aspects of biocompatibility. Despite the enthusiasm in the field, there are still few examples of biodegradable PU scaffolds that have achieved regulatory approval and routine clinical use. However, there is a growing literature where biodegradable PU scaffolds are being specifically developed for a wide range of pathologies and where relevant pre-clinical models are being employed. The purpose of this review is first to highlight examples of clinically used biodegradable PU scaffolds, and then to summarize the growing body of reports on pre-clinical applications of biodegradable PU scaffolds.

Silver Nanoparticle-Loaded Gelatin-Based Nanocomposite Films toward Enhanced Mechanical Properties and Antibacterial Activity

Gelatin (GH) is a natural polymer material with unique physical, chemical, and biological properties that render it a good base material for biomedical material production. Herein, Ag nanoparticles (NPs) were loaded onto a waterborne polyurethane-GH composite (WPU-g-GH) to prepare a GH-based nanocomposite (AgNP/WPU-g-GH) films). The prepared nanocomposite films were characterized using several analyses including Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, X-ray diffraction, transmission emission microscopy, mechanical strength tests, and other analyses. The results demonstrated that the nanocomposite films had high mechanical strength, good thermal stability, and controllable biodegradability. In particular, when the AgNP loading content was 0.03%, the tensile strength, elongation at break, and average particle size of the nanocomposite film reached 45.13 MPa, 476.04%, and 13.02978 ± 1.64406 nm, respectively. Disk diffusion and cytotoxicity analyses revealed that the nanocomposite films exhibited significant antibacterial activity against Gram-negative and Gram-positive bacteria without affecting the cell viability of fibroblasts. These findings indicate that the nanocomposite films with high mechanical strength and antibacterial activity could be used for wound management, tissue adhesion, and biomaterial surface coating.

The Effect of Starch and Magnetite on the Physicochemical Properties of Polyurethane Composites for Hyperthermia Treatment

In this study, modified polyurethanes (PUs) with starch and magnetite were synthesized in the form of scaffolds for potential applications in orthopedics. Polyurethanes were synthesized using a one-step method. PU synthesis was carried out using poly(ε-caprolactone) 2000 as soft segments and 4,4 ${}^{\prime }$ -methylenediphenyl diisocyanate (MDI). Various molar ratios of starch and 1,5-pentanediol (PDO) as crosslinker/chain extender were applied, and the effects of incorporating different amounts of magnetite, as well as the role of PDO to starch ratio, were studied. The use of the additive in the form of magnetic particles was to feature the polyurethane materials for use in hyperthermia. The prepared polyurethanes were investigated using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetry (TG), and dynamic mechanical analysis (DMA) methods. Scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDX) analysis and preliminary bioactivity assessment were also performed. The addition of magnetic particles did not cause significant changes in the properties of the obtained materials compared to starch. The tested materials have the potential to be used to fill or replace bone defects in orthopedics, where they can undergo hyperthermia treatment.

Fabrication and assessment of a novel hybrid scaffold consisted of polyurethane-gellan gum-hyaluronic acid-glucosamine for meniscus tissue engineering

The meniscus has inadequate intrinsic regenerative capacity and its damage can lead to degeneration of articular cartilage. Meniscus tissue engineering aims to restore an injured meniscus followed by returning its normal function through bioengineered scaffolds. In the present study, the structural and biological properties of 3D-printed polyurethane (PU) scaffolds dip-coated with gellan gum (GG), hyaluronic acid (HA), and glucosamine (GA) were investigated. The optimum concentration of GG was 3% (w/v) with maintaining porosity at 88.1%. The surface coating of GG-HA-GA onto the PU scaffolds increased the compression modulus from 30.30 kPa to 59.10 kPa, the water uptake ratio from 27.33% to 60.80%, degradation rate from 5.18% to 8.84%, whereas the contact angle was reduced from 104.8° to 59.3°. MTT assay, acridine orange/ethidium bromide (AO/EB) fluorescent staining, and SEM were adopted to assess the behavior of the seeded chondrocytes on scaffolds, and it was found that the ternary surface coating stimulated the cell proliferation, viability, and adhesion. Moreover, the coated scaffolds showed higher expression levels of collagen II and aggrecan genes at day 7 compared to the control groups. Therefore, the fabricated PU-3% (w/v) GG-HA-GA scaffold can be considered as a promising scaffold for meniscus tissue engineering.

A critical review of fibrous polyurethane-based vascular tissue engineering scaffolds

Certain polymeric materials such as polyurethanes (PUs) are the most prevalent class of used biomaterials in regenerative medicine and have been widely explored as vascular substitutes in several animal models. It is thought that PU-based biomaterials possess suitable hemo-compatibility with comparable performance related to the normal blood vessels. Despite these advantages, the possibility of thrombus formation and restenosis limits their application as artificial functional vessels. In this regard, various surface modification approaches have been developed to enhance both hemo-compatibility and prolong patency. While critically reviewing the recent advances in vascular tissue engineering, mainly PU grafts, this paper summarizes the application of preferred cell sources to vascular regeneration, physicochemical properties, and some possible degradation mechanisms of PU to provide a more extensive perspective for future research.

Shape Memory Behavior of Biocompatible Polyurethane Stereoelastomers Synthesized via Thiol-Yne Michael Addition

Biodegradable shape memory elastomers have the potential for use in soft tissue engineering, drug delivery, and device fabrication applications. Unfortunately, few materials are able to meet the targeted degradation and mechanical properties needed for long-term implantable devices. In order to overcome these limitations, we have designed and synthesized a series of unsaturated polyurethanes that are elastic, degradable, and nontoxic to cells in vitro. The polymerization included a nucleophilic thiol-yne Michael addition between a urethane-based dipropiolate and a dithiol to yield an α,β-unsaturated carbonyl moiety along the polymer backbone. The alkene stereochemistry of the materials was tuned between 32 and 82% cis content using a combination of an organic base and solvent polarity, which collectively direct the nucleophilic addition. The bulk properties such as tensile strength, modulus, and glass transition temperature can also be tuned broadly, and the hydrogen bonding imparted by the urethane moiety allows for these materials to elicit cyclic shape memory behavior. We also demonstrated that the in vitro degradation properties are highly dependent on the alkene stereochemistry.

Tailor-made compostable polyurethanes

Designed polyurethanes with degradable ester units all throughout the polymer backbone and quaternized ammonium units in the hard segment (tensile strength ∼30 MPa, elongation at break ∼1400%) show degradation in 35 days in industrial compost.

Self-Assembled Oligo-Urethane Nanoparticles: Their Characterization and Use for the Delivery of Active Biomolecules into Mammalian Cells

Developing safe and effective strategies to deliver biomolecules such as oligonucleotides and proteins into cells has grown in importance over recent years, with an increasing demand for non-viral methods that enable clinical translation. Here, we investigate uniquely configured oligo-urethane nanoparticles based on synthetic chemistries that minimize the release of pro-inflammatory biomarkers from immune cells, show low cytotoxicity in a broad range of cells, and efficiently deliver oligonucleotides and proteins into mammalian cells. The mechanism of cell uptake for the self-assembled oligo-urethane nanoparticles was shown to be directed by caveolae-dependent endocytosis in murine myoblasts (C₂C₁₂) cells. Inhibiting caveolae functions with genistein and methyl-β-cyclodextrin limited nanoparticle internalization. The nanoparticles showed a very high delivery efficiency for the genetic material (a 47-base oligonucleotide) (∼80% incorporation into cells) as well as the purified protein (full length firefly luciferase, 67 kDa) into human embryonic kidney (HEK293T) cells. Luciferase enzyme activity in HEK293T cells demonstrated that intact and functional proteins could be delivered and showed a significant extension of activity retention up to 24 h, well beyond the 2 h half-life of the free enzyme. This study introduces a novel self-assembled oligo-urethane nanoparticle delivery platform with very low associated production costs, enabled by their scalable chemistry (the benchwork cost is $ 0.152/mg vs $ 974.6/mg for typical lipid carriers) that has potential to deliver both oligonucleotides and proteins for biomedical purposes.