Thromboresistant semi-IPN hydrogel coating: Towards improvement of the hemocompatibility/biocompatibility of metallic stent implants

Hydrogel coating containing heparin and cyclodextrin/paclitaxel inclusion complex for retrievable vena cava filter towards high biocompatibility and easy removal

Aiming to improve the retrieval rate of retrievable vena cava filters (RVCF) and extend its dwelling time in vivo, a novel hydrogel coating loaded with 10 mg/mL heparin and 30 mg/mL cyclodextrin/paclitaxel (PTX) inclusion complex (IC) was prepared. The drug-release behavior in the phosphate buffer solution demonstrated both heparin and PTX could be sustainably released over approximately two weeks. Furthermore, it was shown that the hydrogel-coated RVCF (HRVCF) with 10 mg/mL heparin and 30 mg/mL PTX IC effectively extended the blood clotting time to above the detection limit and inhibited EA.hy926 and CCC-SMC-1 cells' proliferation in vitro compared to the commercially available bare RVCF. Both the HRVCF and the bare RVCF were implanted into the vena cava of sheep and retrieved at at 2nd and 4th week after implantation, revealing that the HRVCF had a significantly higher retrieval rate of 67 % than the bare RVCF (0 %) at 4th week. Comprehensive analyses, including histological, immunohistological, and immunofluorescent assessments of the explanted veins demonstrated the HRVCF exhibited anti-hyperplasia and anticoagulation properties in vivo, attributable to the hydrogel coating, thereby improving the retrieval rate in sheep. Consequently, the as-prepared HRVCF shows promising potential for clinical application to enhance the retrieval rates of RVCFs.

Citric Acid Loaded Hydrogel-Coated Stent for Dissolving Pancreatic Duct Calculi

In recent years, the incidence of chronic pancreatitis has increased significantly. Pancreatic calculi obstruct the pancreatic duct and induce abdominal pain in the patients. Pancreatic duct stenting is the major treatment option for chronic pancreatitis with calculi. In this study, a new kind of drug-eluting stent, a pancreatic stent coated by methacrylated gelatin (GelMA) hydrogel loaded with citric acid (CA), was designed for the interventional treatment of pancreatic duct calculi. The CA loading capacity reached up to 0.7 g CA/g hydrogel-coated stent. The GelMA hydrogel coating has higher mechanical strength and lower swelling performance after loading with CA. The in vitro experiments of stents exhibited good performance in CA sustained release and the calculi can be dissolved in almost 3 days. The stents also showed good blood compatibility and cell compatibility. This research has important clinical value in the treatment of chronic pancreatitis with pancreatic calculi.

Performance of a Hydrogel Coated Nitinol with Oligonucleotide-Modified Nanoparticles Within Turbulent Conditions of Blood-Contacting Devices

INTRODUCTION

Hydrogels offer a wide range of applications in the antithrombotic modification of biomedical devices. The functionalization of these hydrogels with potentially drug-laden nanoparticles in the context of deviceassociated turbulence is critically under-studied. Thus, the purpose of this study was to use a hydrogel-coating nitinol surface as a model to understand the functions of hydrogels and the capture of nanoparticles under clinically relevant flow conditions.

METHODS

Nitinol was coated by an oligonucleotide (ON) functionalized hydrogel. Nanoparticles were functionalized with complementary oligonucleotides (CONs). The capture of CONfunctionalized nanoparticles by the ON-functionalized hydrogel surfaces was studied under both static and dynamic attachment conditions. Fluorescent-labelling of nanoparticles was utilized to assess capture efficacy and resistance to removal by device-relevant flow conditions.

RESULTS

The specificity of the ON-CON bond was verified, exhibiting a dose-dependent attachment response. The hydrogel coating was resistant to stripping by flow, retaining >95% after exposure to one hour of turbulent flow. Attachment of nanoparticles to the hydrogel was higher in the static condition than under laminar flow (p < 0.01), but comparable to that of attachment under turbulent flow. Modified nitinol samples underwent one hour of flow treatment under both laminar and turbulent regimes and demonstrated decreased nanoparticle loss following static conjugation rather than turbulent conjugation (36.1% vs 53.8%, p < 0.05). There was no significant difference in nanoparticle functionalization by upstream injection between laminar and turbulent flow.

CONCLUSION

The results demonstrate promising potential of hydrogelfunctionalized nitinol for capturing nanoparticles using nucleic acid hybridization. The hydrogel structure and ONCON bond integrity both demonstrated a resistance to mechanical damage and loss of biomolecular functionalization by exposure to turbulence. Further investigation is warranted to highlight drug delivery and antithrombogenic modification applications of nanoparticle-functionalized hydrogels.

Biofunctionalization of cardiovascular stents to induce endothelialization: Implications for in- stent thrombosis in diabetes

Stent thrombosis remains one of the main causes that lead to vascular stent failure in patients undergoing percutaneous coronary intervention (PCI). Type 2 diabetes mellitus is accompanied by endothelial dysfunction and platelet hyperactivity and is associated with suboptimal outcomes following PCI, and an increase in the incidence of late stent thrombosis. Evidence suggests that late stent thrombosis is caused by the delayed and impaired endothelialization of the lumen of the stent. The endothelium has a key role in modulating inflammation and thrombosis and maintaining homeostasis, thus restoring a functional endothelial cell layer is an important target for the prevention of stent thrombosis. Modifications using specific molecules to induce endothelial cell adhesion, proliferation and function can improve stents endothelialization and prevent thrombosis. Blood endothelial progenitor cells (EPCs) represent a potential cell source for the in situ-endothelialization of vascular conduits and stents. We aim in this review to summarize the main biofunctionalization strategies to induce the in-situ endothelialization of coronary artery stents using circulating endothelial stem cells.

Phenylalanine-based poly(ester urea)s composite films with nitric oxide-releasing capability for anti-biofilm and infected wound healing applications

Infected wounds show delayed and incomplete healing processes and even render patients at a high risk of death due to the formed bacterial biofilms in the wound site, which protect bacteria against antimicrobial treatments and immune response. Nitric oxide based therapy is considered a promising strategy for eliminating biofilms and enhancing wound healing, which encounters a significant challenge of controlling the NO release behavior at the wound site. Herein, a kind of phenylalanine based poly(ester urea)s with high thermal stability are synthesized and fabricated to electrospun films as NO loading vehicle for infected wound treatment. The resultant films can continuously and stably release nitric oxide for 360 h with a total concentration of 1.15 μmol L^-1, which presents obvious advantages in killing the bacteria and removing biofilms. The results exhibit the films have no cytotoxicity and may accelerate the wound repair without causing inflammation, hemolysis, or cytotoxic reactions as well as stimulate the proliferation of fibroblasts and increase the synthesis of collagen. Therefore, the films may be a suitable NO releasing dressing for removing biofilms and repairing infected wounds.

Considerations in the Development of Small-Diameter Vascular Graft as an Alternative for Bypass and Reconstructive Surgeries: A Review

BACKGROUND

Current design strategies for small diameter vascular grafts (< 6 mm internal diameter; ID) are focused on mimicking native vascular tissue because the commercially available grafts still fail at small diameters, notably due to development of intimal hyperplasia and thrombosis. To overcome these challenges, various design approaches, material selection, and surface modification strategies have been employed to improve the patency of small-diameter grafts.

REVIEW

The purpose of this review is to outline various considerations in the development of small-diameter vascular grafts, including material choice, surface modifications to enhance biocompatibility/endothelialization, and mechanical properties of the graft, that are currently being implanted. Additionally, we have taken into account the general vascular physiology, tissue engineering approaches, and collective achievements of the authors in this area. We reviewed both commercially available synthetic grafts (e-PTFE and PET), elastic polymers such as polyurethane and biodegradable and bioresorbable materials. We included naturally occurring materials by focusing on their potential application in the development of future vascular alternatives.

CONCLUSION

Until now, there are few comprehensive reviews regarding considerations in the design of small-diameter vascular grafts in the literature. Here-in, we have discussed in-depth the various strategies employed to generate engineered vascular graft due to their high demand for vascular surgeries. While some TEVG design strategies have shown greater potential in contrast to autologous or synthetic ePTFE conduits, many are still hindered by high production cost which prevents their widespread adoption. Nonetheless, as tissue engineers continue to develop on their strategies and procedures for improved TEVGs, soon, a reliable engineered graft will be available in the market. Hence, we anticipate a viable TEVG with resorbable property, fabricated via electrospinning approach to hold a greater potential that can overcome the challenges observed in both autologous and allogenic grafts. This is because they can be mechanically tuned, incorporated/surface-functionalized with bioactive molecules and mass-manufactured in a reproducible manner. It is also found that most of the success in engineered vascular graft approaching commercialization is for large vessels rather than small-diameter grafts used as cardiovascular bypass grafts. Consequently, the field of vascular engineering is still available for future innovators that can take up the challenge to create a functional arterial substitute.

Merging 3D printing with electrospun biodegradable small-caliber vascular grafts immobilized with VEGF

The major challenge of commercially available vascular substitutes comes from their limitations in terms of hydrophobic surface, which is hostile to cell growth. To date, tissue-engineered and synthetic grafts have not translated well to clinical trials when looking at small diameters. We conceptualized a cell-free structurally reinforced biodegradable vascular graft recapitulating the anisotropic feature of a native blood vessel. The nanofibrous scaffold is designed in such a way that it will gradually degrade systematically to yield a neo-vessel, facilitated by an immobilized bioactive molecule-vascular endothelial growth factor (VEGF). The nano-topographic cue of the device is capable of direct host cell infiltration. We evaluated the burst pressure, histology, hemocompatibility, compression test, and mechanical analysis of the new graft. The graft implanted into the carotid artery of a porcine model demonstrated a good patency rate as early as two week post-implantation. This graft reinforced design approach when employed in vascular tissue engineering might strongly influencing regenerative medicine.

Hydrogel membranes: A review

Hydrogel membranes (HMs) are defined and applied as hydrated porous media constructed of hydrophilic polymers for a broad range of applications. Fascinating physiochemical properties, unique porous architecture, water-swollen features, biocompatibility, and special water content dependent transport phenomena in semi-permeable HMs make them appealing constructs for various applications from wastewater treatment to biomedical fields. Water absorption, mechanical properties, and viscoelastic features of three-dimensional (3D) HM networks evoke the extracellular matrix (ECM). On the other hand, the porous structure with controlled/uniform pore-size distribution, permeability/selectivity features, and structural/chemical tunability of HMs recall membrane separation processes such as desalination, wastewater treatment, and gas separation. Furthermore, supreme physiochemical stability and high ion conductivity make them promising to be utilised in the structure of accumulators such as batteries and supercapacitors. In this review, after summarising the general concepts and production processes for HMs, a comprehensive overview of their applications in medicine, environmental engineering, sensing usage, and energy storage/conservation is well-featured. The present review concludes with existing restrictions, possible potentials, and future directions of HMs.

Incorporation of dumbbell-shaped and Y-shaped cross-linkers in adjustable pullulan/polydopamine hydrogels for selective adsorption of cationic dyes

Hydrogel adsorbents have attracted considerable attention due to their sludge minimization, good water permeability and renewable performance. Here, a promising strategy for the one-step preparation of pullulan/polydopamine hybird hydrogels (PPGels) was presented. Dumbbell-shaped cross-linker neopentyl glycol diglycidyl ether (NGDE, 2 arms) and Y-shaped cross-linker trimethylolpropane triglycidyl ether (TTE, 3 arms) were selected to study the relationship between cross-linker structure and hydrogel performances. The NGDE possessing less molecular repulsive force and higher reactivity demonstrated more effective cross-linking with the pullulan, which leaded to a decrease in pore size of the hydrogel. Meanwhile, the introduction of polydopamine significantly enhanced the adsorption ability and gave the resulting hybrid gel the specific selectivity toward cationic dyes (96 mg/g for crystal violet, 25.8 mg/g for methylene blue and barely not adsorption for azophloxine). Our data suggested that the electrostatic interaction played a vital role in the dye adsorption process, and the adsorption data could be explained by pseudo-second-order model and Langmuir isotherm model. Furthermore, the obtained PPGel could be easily separated after adsorption. This study describes the relationship between cross-linker structure and properties of pullulan/polydopamine hybrid gels, which provides a new strategy to create polysaccharide-based adsorbents for wastewater remediation.

Multipronged Approach to Combat Catheter-Associated Infections and Thrombosis by Combining Nitric Oxide and a Polyzwitterion: a 7 Day In Vivo Study in a Rabbit Model

The development of nonfouling and antimicrobial materials has shown great promise for reducing thrombosis and infection associated with medical devices with aims of improving device safety and decreasing the frequency of antibiotic administration. Here, the design of an antimicrobial, anti-inflammatory, and antithrombotic vascular catheter is assessed in vivo over 7 d in a rabbit model. Antimicrobial and antithrombotic activity is achieved through the integration of a nitric oxide donor, while the nonfouling surface is achieved using a covalently bound phosphorylcholine-based polyzwitterionic copolymer topcoat. The effect of sterilization on the nonfouling nature and nitric oxide release is presented. The catheters reduced viability of Staphylococcus aureus in long-term studies (7 d in a CDC bioreactor) and inflammation in the 7 d rabbit model. Overall, this approach provides a robust method for decreasing thrombosis, inflammation, and infections associated with vascular catheters.

Calcium Phosphate Nanocluster-Loaded Injectable Hydrogel for Bone Regeneration

Bone is a hierarchical tissue in which the extracellular matrix consists of hydroxyapatite (HAP) crystals embedded in the collagen matrix. Artificial bone regeneration remains a great challenge due to the difficulty of balancing the chemical composition, biological compatibility, and mechanical performance of the implant. Biomineralization starts from the formation of a hydrogel-like biomacromolecule matrix in many cases, while the mineralization of HAP often builds from amorphous calcium phosphate (ACP) nanoclusters. Inspired by these discoveries, here we use a hydrogel loaded with ∼1 nm sized polymer-stabilized ACP nanoclusters (cluster-loaded hydrogel) as an injectable bone regeneration material. The hydrogel is biocompatible and stabilizes the ACP clusters such that they could efficiently infiltrate into collagen fibrils leading to intrafibrillar mineralization of HAP nanocrystals. Ex vivo results reveal that the cluster-loaded hydrogel has an excellent bone affinity as well as provides a suitable environment for the proliferation and differentiation of bone cells. In vivo experiments with rat bone show that the cluster-loaded hydrogel can generate HAP-based fillings within bone defects with perfect bonding to the surrounding tissue and a mechanical performance comparable with native bone. The fluidity of the hydrogel is further beneficial by providing a feasible minimally invasive bone healing procedure via syringe injection. The discovery and utilization of the cluster-loaded hydrogel described here provide a promising bioinspired approach for bone tissue regeneration.

Osteoporotic Bone Recovery by a Highly Bone-Inductive Calcium Phosphate Polymer-Induced Liquid-Precursor

Osteoporosis is an incurable chronic disease characterized by a lack of mineral mass in the bones. Here, the full recovery of osteoporotic bone is achieved by using a calcium phosphate polymer-induced liquid-precursor (CaP-PILP). This free-flowing CaP-PILP material displays excellent bone inductivity and is able to readily penetrate into collagen fibrils and form intrafibrillar hydroxyapatite crystals oriented along the c-axis. This ability is attributed to the microstructure of the material, which consists of homogeneously distributed ultrasmall (≈1 nm) amorphous calcium phosphate clusters. In vitro study shows the strong affinity of CaP-PILP to osteoporotic bone, which can be uniformly distributed throughout the bone tissue to significantly increase the bone density. In vivo experiments show that the repaired bones exhibit satisfactory mechanical performance comparable with normal ones, following a promising treatment of osteoporosis by using CaP-PILP. The discovery provides insight into the structure and property of biological nanocluster materials and their potential for hard tissue repair.