A strategy for mechanically integrating robust hydrogel-tissue hybrid to promote the anti-calcification and endothelialization of bioprosthetic heart valve.

Bioprosthetic heart valve (BHV) replacement has been the predominant treatment for severe heart valve diseases over decades. Most clinically available BHVs are crosslinked by glutaraldehyde (GLUT), while the high toxicity of residual GLUT could initiate calcification, severe thrombosis, and delayed endothelialization. Here, we construed a mechanically integrating robust hydrogel-tissue hybrid to improve the performance of BHVs. In particular, recombinant humanized collagen type III (rhCOLIII), which was precisely customized with anti-coagulant and pro-endothelialization bioactivity, was first incorporated into the polyvinyl alcohol (PVA)-based hydrogel via hydrogen bond interactions. Then, tannic acid was introduced to enhance the mechanical performance of PVA-based hydrogel and interfacial bonding between the hydrogel layer and bio-derived tissue due to the strong affinity for a wide range of substrates. In vitro and in vivo experimental results confirmed that the GLUT-crosslinked BHVs modified by the robust PVA-based hydrogel embedded rhCOLIII and TA possessed long-term anti-coagulant, accelerated endothelialization, mild inflammatory response and anti-calcification properties. Therefore, our mechanically integrating robust hydrogel-tissue hybrid strategy showed the potential to enhance the service function and prolong the service life of the BHVs after implantation.

A fully degradable transcatheter ventricular septal defect occluder: Towards rapid occlusion and post-regeneration absorption.

Degradable heart occluders are a promising replacement for currently clinically used non-degradable ones without concerns about the complications caused by the persistent residue of a foreign implant. However, the inherent mechanical properties of degradable occluders are poor and decline with material degradation, leading to a preference for a long degradation period upon designing a degradable heart occluder. This configuration can lower the risk of occluder dislodgement but reduce the benefits of degradable implants over their non-degradable counterparts due to a longer retention of foreign materials in the human body. Here, we fabricated a fully degradable ventricular septum defect (VSD) occluder consisting of polydioxanone (PDO) fiber and poly-L-lactic acid (PLLA) membrane featuring an auto-locking function. The degradable occluder showed an excellent shape recovery effect after transcatheter delivery and anchored securely to a heart defect as evidenced by in vitro and in vivo experiments. The degradable occluder could warrant robust fixation ability during the first 3-months of implantation within which tissue reconstruction was accomplished and be completely absorbed within 12 months. Benefitting from these merits, the degradable occluder displayed desired occlusion and no complications after being implanted in the VSD sites of canines during a 24-months follow-up. Compared with traditional non-degradable occluders, our degradable occluder could provide a potentially superior approach for rapidly repairing the congenital VSD without interfering with the normal development and physiological function of the heart.

Inflammation-triggered dual release of nitroxide radical and growth factor from heparin mimicking hydrogel-tissue composite as cardiovascular implants for anti-coagulation, endothelialization, anti-inflammation, and anti-calcification.

Cardiovascular implants made from heterogeneous tissues (HT) often clinically face premature failures such as thrombosis, inflammation, and calcification. Herein, we report a hydrogel-tissue composite exhibiting inflammation instructive release of multiple components towards preventing coagulation, promoting endothelial growth, and modulating reactive oxygen species (ROS) homeostasis. The hydrogel composed of MMP-responsive segment-crosslinked heparin mimicking polymer was loaded with a nitroxide radical via ROS cleavable boronic ester bonds and vascular endothelial growth factor (VEGF) via electrostatic attraction. Matrix metalloproteinase (MMP), which reportedly showed elevated expression in inflammation response to foreign implant degraded the hydrogel and led to the release of heparin mimicking polymer and VEGF, enhancing its anti-coagulation capacity and accelerating the growth of endothelial cells on it. In addition, the composite could sense oxidation biosignal present in the inflammation environment and subsequently release a ROS scavenger for auto-regulation of ROS balance. Subcutaneous implantation in mice suggested that the composite could steer the immune response toward an anti-inflammation state and subcutaneous implantation in rats suggested an anti-calcification effect of it. The enhanced hemocompatibility and endothelialization effects in vivo were further confirmed by the endovascular implantation of tissues via membrane-covered stent delivery. The current findings demonstrate that the incorporation of functional hydrogel into the tissue sophistically exploiting host response for controlled release of multiple active cargos is a feasible approach to boost the anticoagulant, endothelialization, anti-inflammatory, and anti-calcification functions of HT-based cardiovascular implants.

Development of Innovative Biomaterials and Devices for the Treatment of Cardiovascular Diseases.

Cardiovascular diseases have become the leading cause of death worldwide. The increasing burden of cardiovascular diseases has become a major public health problem and how to carry out efficient and reliable treatment of cardiovascular diseases has become an urgent global problem to be solved. Recently, implantable biomaterials and devices, especially minimally invasive interventional ones, such as vascular stents, artificial heart valves, bioprosthetic cardiac occluders, artificial graft cardiac patches, atrial shunts, and injectable hydrogels against heart failure, have become the most effective means in the treatment of cardiovascular diseases. Herein, an overview of the challenges and research frontier of innovative biomaterials and devices for the treatment of cardiovascular diseases is provided, and their future development directions are discussed.

Visible light-induced cross-linking of porcine pericardium for the improvement of endothelialization, anti-tearing, and anticalcification properties.

Population aging and the development of transcatheter aortic valve replacement boost the implantation of bioprosthetic heart valves (BHVs) in patients worldwide. However, the traditional glutaraldehyde cross-linked BHVs fail within 12-15 years mainly due to leaflet tear and calcification defects. In this study, a novel visible light-induced cross-linking of the porcine pericardium (PP) was realized by the photo-oxidation of the furfuryl-modified PP in the presence of Rose Bengal. The resulting material showed comparable collagen stability with the glutaraldehyde cross-linked PP and appropriate biomechanical properties such as tensile strength, modulus, and elongation, suggesting that this material could meet the general requirement for BHVs. Besides, this cross-linked PP showed significantly improved cytocompatibility compared with the Glut-cross-linked PP, with no cytotoxicity to L929 cells and the ability to support HUVECgrowth. Meanwhile, this material showed superior anti-tearing performance and much less calcification than the Glut-cross-linked PP in hope of reducing the risk of BHV failure. Considering these results, the visible light-induced cross-linking method proposed in this study could provide a promising way to construct a biocompatible and robust biomaterial for the fabrication of the BHV.

Adaptive neural network projection analytical fault-tolerant control of underwater salvage robot with event trigger.

Introduction: To solve the problem of control failure caused by system failure of deep-water salvage equipment under severe sea conditions, an event-triggered fault-tolerant control method (PEFC) based on proportional logarithmic projection analysis is proposed innovatively. Methods: First, taking the claw-type underwater salvage robot as the research object, amore universal thruster fault model was established to describe the fault state of equipment failure, interruption, stuck, and poor contact. Second, the controller was designed by the proportional logarithmic projection analytical method. The system input signal was amplified and projected as a virtual input, which replaces the original input to isolate and learn the fault factor online by the analytical algorithm. The terminal sliding mode observer was used to compensate for the external disturbance of the system, and the adaptive neural network was used to fit the dynamic uncertainty of the system. The system input was introduced into the event-triggered mechanism to reduce the output regulation frequency of the fault thruster. Results: Finally, the simulation results showed that the method adopted in this study reduced the power output by 28.95% and the update frequency of power output by 75% compared with the traditional adaptive overdrive fault-tolerant control (AOFC) method and realized accurate pose tracking under external disturbance and system dynamic uncertain disturbance. Discussion: It has been proven that the algorithm used in this research can still reasonably allocate power to reduce the load of a fault thruster and complete the tracking task under fault conditions.

An ultralow dose paclitaxel coated drug balloon with an outer protective sheath for peripheral arterial disease treatment.

Use of a drug-eluting coated balloon (DCB) represents a promising therapeutic method for peripheral arterial disease (PAD) due to its advantages such as no implant permanently retained in the patient and no inflammatory reaction and endothelialization barrier caused by a permanent stent. However, there is still a huge challenge of controlling the release of drugs from the DCB into vessel tissue. The uncontrolled release of drugs and high drug loading amounts could potentially lead to distal embolization and mortality events. In our study, an ultralow dose paclitaxel (PTX) coated DCB appended with an outer protective sheath was designed to treat peripheral vessel stenosis. An in vitro study demonstrated that the sheath could significantly reduce the drug loss during the delivery process and the meglumine matrix could effectively promote the transfer of PTX into vessel tissue. The pharmacokinetics study in the swine model also demonstrated that the PTX amount remaining in the vessel after being treated by our DCB was comparable to similar products on market although only less than a third of the PTX was used. The safety study indicated that the DCB treatment did not have any adverse impact on the physiological function of the vessel. Therefore, our ultralow dose PTX coated DCB could provide an effective and safe treatment for PAD.

Crosslinking porcine aortic valve by radical polymerization for the preparation of BHVs with improved cytocompatibility, mild immune response, and reduced calcification.

Over one million artificial heart valve transplantations are performed each year due to valvular stenosis or regurgitation. Among them, bioprosthetic heart valves (BHVs) are increasingly being used because of the absence of the need for lifelong anticoagulation. Almost all of the commercial BHVs are treated with Glutaraldehyde (GLUT). As GLUT-treated BHVs are prone to calcification and structural degradation, their durability is greatly reduced with a service life of only 12-15 years. The physiological structure and mechanical properties of the porcine aortic valve (PAV) are closer to that of a human heart valve, so in this study, PAV is used as the model to explore the comprehensive properties of the prepared BHVs by radical polymerization crosslinking method. We found that PAV treated by radical polymerization crosslinking method showed similar ECM stability and biaxial mechanical properties with GLUT-treated PAV. However, radical polymerization crosslinked PAV exhibited better cytocompatibility and endothelialization potential in vitro cell experiment as better anticalcification potential and reduced immune response than GLUT-treated PAV through subcutaneous animal experiments in rats. To conclude, a novel crosslinking method of non-glutaraldehyde fixation of xenogeneic tissues for the preparation of BHVs is expected.

Inorganic-polymerization crosslinked tissue-siloxane hybrid as potential biomaterial for bioprosthetic heart valves.

Bioprosthetic heart valve (BHV) replacement is increasingly used for treating valve-related diseases worldwide but the current commercially used BHVs treated with glutaraldehyde (Glut) often failed within 12-15 years due to degradation, thrombosis, inferior biocompatibility, and calcification. Herein, 3-glycidyloxypropyl trimethoxysilane (GPTMS) was used to crosslink porcine pericardium (PP) at the concentration (vol/vol) of 0.25%, 1%, 2%, and 4% and their performance for potential application in BHVs was evaluated. The crosslinking mechanism mainly involved the ring-opening of epoxide by amine attack and silanol poly-condensation. The stability of collagen in higher concentration (1%, 2%, and 4%) GPTMS crosslinked PPs (GPTMS-PPs) was clearly increased. GPTMS-PPs showed no cytotoxicity and supported the growth of endothelial cells while Glut-PP did not. GPTMS-PPs were less prothrombotic than Glut-PP. GPTMS-PP crosslinked at 1% concentration showed comparable mechanical properties to Glut-PP while had better anti-tearing performance. The subcutaneous implantation in rat for 30 days showed that GPTMS crosslinking was able to effectively inhibit the calcification of BHV.

A method for simultaneously crosslinking and functionalizing extracellular matrix-based biomaterials as bioprosthetic heart valves with enhanced endothelialization and reduced inflammation.

With the coming of an aging society and the emergence of transcatheter valve technology, the implantation of bioprosthetic heart valves (BHVs) in patients with valvular disease has significantly increased worldwide. Currently, most clinically available BHVs are crosslinked with glutaraldehyde (GLUT). However, the GLUT treated BHV is less durable due to the combined effect of multiple factors such as cytotoxicity, immune responses, and calcification. In this study, the in-situ polymerization of sulfonic monomers with a decellularized extracellular matrix (ECM) was performed to simultaneously achieve the crosslinking and functionalization of ECM. Subsequently, the feasibility of the hybrid ECM used as leaflet material of BHV was evaluated. In in-vitro tests, the results indicated that the hybrid ECM fixed collagen efficiently and the introduction of sulfonic polymer promoted the proliferation and migration of human umbilical vein endothelial cells (HUVECs). In in-vivo tests, after being implanted in SD rats and mice, the hybrid ECM significantly inhibited immune response and calcification compared with the non-hybrid counterpart and GLUT crosslinked tissue. These results indicated that the hybrid ECM exhibited more competitive stability and better biocompatibility compared to these features in GLUT-crosslinked valve. Therefore, the sulfonic polymer hybrid ECM provides a potential material for more durable BHV and the in-situ polymerization strategy can serve as a general treatment method for tissue crosslinking as well as tailoring the biophysical properties of ECM.

Tough pNAGA hydrogel hybridized porcine pericardium for the pre-mounted TAVI valve with improved anti-tearing properties and hemocompatibility.

The rate of adoption of transcatheter aortic valve implantation (TAVI) is increasing rapidly, due to the procedure being less invasive. However, TAVI still faces problems relating to durability, the potential incidence of thrombosis, and the inconvenience of storage in glutaraldehyde (Glut) solution. In this work, a tough hydrogel poly(N-acryloyl glycinamide) (pNAGA) is hybridized with Glut-crosslinked porcine pericardium (Glut-PP) via in situ polymerization and glycerolization, so as to obtain dry leafet material for the fabrication of a pre-mounted bioprosthetic heart valve (BHV). The tensile strength, anti-shearing, and anti-tearing properties of the valve are significantly improved by the process of hydrogel hybridization. Following a period of dry-state compression as a simulation for the crimping process of pre-mounted TAV, pNAGA/Glut-PP showed full recovery without structural damage when fully rehydrated. The introduction of pNAGA also improved the blood compatibility of the tissue, with less clot formation and fewer blood cells adhering to the surface of pNAGA/Glut-PP than is found with Glut-PP. Subcutaneous implantation in rats showed that pNAGA/Glut-PP induced a decreased inflammatory response compared with Glut-PP. These results indicate that the strategy for hybridization with hydrogel could be a potential method for preparing pre-mounted TAVs with an improved performance.

Riboflavin photo-cross-linking method for improving elastin stability and reducing calcification in bioprosthetic heart valves.

BACKGROUND: Glutaraldehyde cross-linked bioprosthetic heart valves might fail due to progressive degradation and calcification. METHODS: In this study, we developed a new BHVs preparation strategy named as "HPA/TRA/FMN" that utilized 3,4-hydroxyphenylpropionic acid (HPA)/tyramine (TRA) conjugated pericardium and riboflavin 5'-monophosphate (FMN) initiated photo-cross-linking method. HPA/TRA-pericardium conjugation would provide extra phenol groups for FMN initiated photo-cross-linking. RESULTS: The feeding ratio of riboflavin 5'-monophosphate was optimized. The collagenase and elastase enzymatic degradation in vitro, biomechanics, calcification, elastin stability in vivo, and macrophage marker CD68 were characterized. We demonstrated that riboflavin photo-cross-linked pericardiums had great collagen and elastin stability, improved mechanical properties, better resistance for calcification, and less CD68 positive macrophages in rat subdermal implantation study. CONCLUSIONS: This new riboflavin photo-cross-linking strategy would be a promising method to make BHVs which have better elastin stability, less calcification, and reduced inflammatory response.

EGCG and enzymatic cross-linking combined treatments for improving elastin stability and reducing calcification in bioprosthetic heart valves.

The failures of glutaraldehyde (GLUT) cross-linked bioprosthetic heart valves (BHVs) are mainly due to degeneration and calcification. In this study, we developed a new preparation strategy for BHVs named as "HPA/EDC/EGCG" that utilized 3,4-hydroxyphenylpropionic acid (HPA)-conjugated pericardium, epigallocatechin gallate (EGCG), and horseradish peroxidase (HRP)/hydrogen peroxide (H2 O2 ) enzymatic cross-linking. HPA-pericardium conjugation was done by carbodiimide coupling reaction using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS). Then HPA-conjugated pericardium was cross-linked by HRP/H2 O2 enzyme-catalyzed oxidation. The feeding ratios of HPA and EGCG were optimized. The consumption of amino groups, collagenase and elastase degradation in vitro, biomechanics, extracellular matrix stability, and calcification of HPA-/EDC-/EGCG-treated pericardiums were characterized. We demonstrated that HPA-/EDC-/EGCG-treated pericardiums had better elastin stabilization and less calcification. EGCG and enzymatic cross-linking treated pericardiums showed improved mechanical properties. This new EGCG and enzymatic cross-linking strategy would be a promising method to make BHVs with better elastin stability and anti-calcification property. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1551-1559, 2019.

Cross-Linking Methacrylated Porcine Pericardium by Radical Polymerization Confers Enhanced Extracellular Matrix Stability, Reduced Calcification, and Mitigated Immune Response to Bioprosthetic Heart Valves.

The aging population and the development of transcatheter aortic valve replacement (TAVR) technology largely expand the usage of bioprosthetic heart valves (BHVs) in patients. Almost all of the commercial BHVs are treated with glutaraldehyde (GA). However, the GA-treated BHVs display the drawbacks such as extracellular matrix (ECM) degradation, cytotoxicity, immune response, and calcification. In this study, radical polymerization reaction, a powerful tool commonly used in preparing polymers and hydrogels, has been developed to fix decellularized ECM instead of GA treatment. Porcine pericardium (PP) is taken as an example of ECM for BHVs fabrication to investigate the impact of radical polymerization on the tissue properties. The radical polymerization method better stabilizes collagen and elastin of PP than GA treatment and produces a soft biomaterial more like the native heart valve. Furthermore, radical polymerization cross-linked PP exhibits excellent cytocompatibility. After implanted subcutaneously in rats for 30 days, radical polymerization cross-linked PP shows better elastin stability, mitigated immune response, and reduced calcification than GA-PP. All these results suggest that radical polymerization is an ideal cross-linking method for BHVs or tissue engineering heart valve scaffolds and it also has the potential for creating a variety of ECM-polymer hybrid biomaterials in the future.

Hydrogel hybrid porcine pericardium for the fabrication of a pre-mounted TAVI valve with improved biocompatibility.

Transcatheter aortic valve implantation (TAVI) has been developed years ago for patients who cannot undergo a surgical aortic valve replacement (SAVR). Although TAVI possesses the advantages of lower trauma and simpler manipulation compared to SAVR, the need for storage in glutaraldehyde (GLU) and a tedious intraoperative assembly process have caused great inconvenience for its further application. A pre-mounted TAVI valve assembled by mounting a dry valve frame to a delivery system is expected to address these problems. However, the currently used GLU treated leaflet cannot unfold normally after being crimped for a long-term and loses its function when the BHV is assembled to the catheter. Besides, its cytotoxicity and immune response after implantation are still problems to be solved. In the present study, a hydrogel hybrid porcine pericardium (HHPP) approach was developed to endow the BHVs with a favorable unfolding property and good biocompatibility. Three monomers with different charge characteristics (sodium acrylate, 2-methacryloyloxyethyl phosphorylcholine, and acryloyloxyethyltrimethyl ammonium chloride) were complexed with GLU treated PP (GLU-PP) to form three kinds of HHPPs (SAAH-PP, MPCH-PP, and DACH-PP). The results of the crimping simulation experiment showed that all HHPPs could quickly recover in PBS after being folded for 10 days, while the traditional BHVs (GLU-PP) could not recover under the same conditions. Bovine serum albumin adsorption and platelet adhesion test showed that SAAH-PP and MPCH-PP had good anti-adhesion abilities. A cell culture study indicated that all the three HHPPs promoted HUVEC growth and proliferation. In vivo biocompatibility studies showed that the immune response induced by MPCH-PP was reduced compared to that by GLU-PP. These studies demonstrated that the strategy of MPC hydrogel hybridization may be an effective approach to prepare a pre-mounted TAVI valve with improved biocompatibility.

Radical polymerization-crosslinking method for improving extracellular matrix stability in bioprosthetic heart valves with reduced potential for calcification and inflammatory response.

In recent years, the number of heart valve replacements has multiplied with valve diseases because of aging populations and the surge in rheumatic heart disease in young people. Among them, bioprosthetic heart valves (BHVs) have become increasingly popular. Transcatheter aortic valve implantation (TAVI) valve as an emerging BHV has been increasingly applied to patients. However, the current commercially used BHVs treated with glutaraldehyde (Glut) still face the problem of durability. BHVs derived from Glut-treated xenogenetic tissues would undergo structural degeneration and calcification sometimes even as short as less than 10 years. This issue has already become a big challenge considering more and more young patients at the age of 50-60 s are receiving the BHV replacement. In our study, an approach that is totally different from the previous techniques named by us as the radical polymerization-crosslinking (RPC) method was developed to improve extracellular matrix stability, prevent calcification, and reduce inflammatory response in BHVs. The porcine pericardium (PP) tissue was decellularized, functionalized with methacryloyl groups, and subsequently crosslinked by radical polymerization. We found that high-density RPC treatment remarkably improved the stability of collagen and elastin of PP, enhanced its endothelialization potential, and provided reliable biomechanical performance as compared to Glut treatment. The in vivo rat model also confirmed the increased componential stability and the reduced inflammatory response of RPC-treated PP. Moreover, the RPC-treated PP showed better in vivo anticalcification potential than Glut-treated PP. STATEMENT OF SIGNIFICANCE: Bioprosthetic heart valves (BHVs) manufactured from glutaraldehyde (Glut)-treated xenogeneic tissues have been used to treat valve-related diseases for several decades. However, the durability of BHVs remains unresolved and becomes more pronounced particularly in younger patients. Although a number of new alternative methods for Glut crosslinking have been proposed, their overall performance is still far from ready to use in humans. In this study, radical polymerization was investigated for crosslinking the porcine pericardium (PP). This treatment was found to have advantages compared to Glut-treated PP in terms of stability, biocompatibility, and anticalcification potential with the hope of addressing the needs of more robust biomaterials for the fabrication of BHVs.

Elastin Stabilization Through Polyphenol and Ferric Chloride Combined Treatment for the Enhancement of Bioprosthetic Heart Valve Anticalcification.

The lifetime of bioprosthetic heart valves (BHVs) is limited by the mechanical damage and calcification. The major components of BHVs are collagen and elastin. Collagen could be well protected by glutaraldehyde (GLUT) crosslinking, while elastin is not stabilized and has a high risk of degradation, which could lead to the calcification of BHVs. We aimed to develop methods for stabilizing elastin and decreasing calcification. We investigated the combined tannic acid (TA) or epigallocatechin gallate (EGCG) with ferric chloride to stabilize elastin and prevent calcification. We found that the amount of TA/EGCG bound to elastin was in a time-dependent pattern and this reaction showed better efficiency in acidic condition and ethanol-water mixed solvents. Moreover, Fe3+ could compete with Ca2+ to bind to polyphenol, which could reduce the calcium deposition on BHVs. Cytotoxicity test showed that all extracts from different treatments had similar cell viabilities (85-100%). Through the combined treatments of polyphenol and ferric chloride, the pericardium had a better resistance to elastase degradation and more excellent anticalcification performance.

Disassembly of micelle-like polyethylenimine nanocomplexes for siRNA delivery: High transfection efficiency and reduced toxicity achieved by simple reducible lipid modification.

Amphiphilic compounds consisting of polycations and lipid segments are well established as building blocks for the construction of siRNA carriers. They are capable of forming nanoparticles with high-affinity positive charges for siRNA in aqueous media due to their intra- and/or intermolecular hydrophobic and electrostatic interactions. Unfortunately, safety and efficiency of lipid-modified polycations as the two great challenges to the clinical application need to be improved. Beyond that, the role of the hydrophobic segment in the process of siRNA delivery is elusive. Herein, in this study, branched polyethylenimine with a molecular weight of 600 (bPEI600) was grafted with reducible lipids via Michael addition reaction between amines and alkyl acrylates. Reducible amphiphilic polyethylenimines (PEIs) were able to condense siRNA into nanoparticles and disassemble under the reductive environment. Investigations with these materials in vitro revealed that the polymers with higher grafting degree provided high luciferase knockdown efficacies even at lower N/P ratios and the polymers with longer lipid chain displayed greater cellular uptake rate. Interestingly, the polymers with lower grafting degree had efficient cellular uptake than native bPEI600, although their in luciferase knockdown assays were most likely inefficient. The inconsistency between the cellular uptake profile and silencing efficacy proved that the intracellular trafficking of siRNA was a bottleneck for siRNA delivery with some polymers prepared in this study. As expected, reducible lipid-modified PEIs were equally efficient and much less toxic compared to non-reducible counterparts and might provide broader therapeutic windows. These findings showed the feasibility of reducible lipid-modified PEIs as carriers for therapeutic siRNA.

Alkane-modified low-molecular-weight polyethylenimine with enhanced gene silencing for siRNA delivery.

Small interfering RNA (siRNA) has tremendous potential as a therapeutic agent for diverse diseases; however, due to its susceptibility to degradation and poor cellular uptake, the low efficiency of administration has been the most important limiting factor for clinical applications of siRNA. Herein, we synthesized alkyl chain modified low-molecular-weight polyethylenimines (LMW PEIs) and found that hydrophobically modified PEIs displayed enhanced efficiency in siRNA-mediated knockdown of target genes. To elucidate the mechanism for increased delivery, we characterized the polymers' physicochemical properties and bioactivity via nuclear magnetic resonance (NMR), gel retardation assay, dynamic laser scattering (DLS) analysis, confocal laser scanning microscopy and flow cytometry. The hydrophobic modification reduced siRNA binding affinity but facilitated the formation of nanoparticles in contrast to the original PEI. The PEIs with eight and thirteen alkyl tails were able to self-assemble into nanoparticles and yielded higher cellular uptake, which leaded to even similar efficiencies of 80-90% knockdown as Lipofectamine™ 2000 control. These results suggested that the status of polymers in aqueous solution, which depended on the degree of hydrophobic modification, played an important role in the uptake of siRNA. Therefore, we provided new information on the role of hydrophobic content in the enhanced gene silencing activity.