Effect of hyaluronic acid incorporation method on the stability and biological properties of polyurethane-hyaluronic acid biomaterials

Thrombogenicity Assessment of Perfusable Tissue-Engineered Constructs: A Systematic Review

Vascular surgery is facing a critical demand for novel vascular grafts that are biocompatible and thromboresistant. This urgency is particularly applicable to bypass operations involving small caliber vessels. In the realm of tissue engineering, the development of fully vascularized organs is promising as a solution to organ shortage for transplantation. To achieve this, it is essential to (re)construct a biocompatible and nonthrombogenic vascular network within these organs. In this systematic review, we identify, classify, and discuss basic principles and methods used to perform in vitro/ex vivo dynamic thrombogenicity testing of perfusable tissue-engineered organs and tissues. We conducted a preregistered systematic review of studies published in the last 23 years according to PRISMA-P Guidelines. This comprised a systematic data extraction, in-depth analysis, and risk of bias assessment of 116 included studies. We identified shaking (n = 28), flow loop (n = 17), ex vivo (arteriovenous shunt, n = 33), and dynamic in vitro models (n = 38) as the main approaches for thrombogenicity assessment. This comprehensive review reveals a prevalent lack of standardization and provides a valuable guide in the design of standardized experimental setups.

Tranexamic acid loaded in a physically crosslinked trilaminate dressing for local hemorrhage control: Preparation, characterization, and in-vivo assessment using two different animal models

This work aimed at formulating a trilaminate dressing loaded with tranexamic acid. It consisted of a layer of 3 % sodium hyaluronate to initiate hemostasis. It was followed by a mixed porous layer of 5 % polyvinyl alcohol and 2 % kappa-carrageenan. This layer acted as a drug reservoir that controlled its release. The third layer was 5 % ethyl cellulose backing layer for unidirectional release of tranexamic acid towards the wound. The 3 layers were physically crosslinked by hydrogen bonding as confirmed by Infrared spectroscopy. Swelling and release studies were performed, and results proposed that increasing number of layers decreased swelling properties and sustained release of tranexamic acid for 8 h. In vitro blood coagulation study was performed using human blood and showed that the dressing significantly decreased coagulation time by 70.5 % compared to the negative control. In vivo hemostatic activity was evaluated using tail amputation model in Wistar rats. Statistical analysis showed the dressing could stop bleeding in a punctured artery of the rat tail faster than the negative control by 59 %. Cranial bone defect model in New Zealand rabbits was performed to check for bone hemostasis and showed significant decrease in the hemostatic time by 80 % compared to the control.

Surface functionalization of polyurethanes: A critical review

Synthetic polymers, particularly polyurethanes (PUs), have revolutionized bioengineering and biomedical devices due to their customizable mechanical properties and long-term stability. However, the inherent hydrophobic nature of PU surfaces arises common issues such as high friction, strong protein adsorption, and thrombosis, especially in the physiological environment of blood contact. To overcome these issues, researchers have explored various modification techniques to improve the surface biofunctionality of PUs. In this review, we have systematically summarized several typical surface modification methods including surface plasma modification, surface oxidation-induced grafting polymerization, isocyanate-based chemistry coupling, UV-induced surface grafting polymerization, adhesives-assisted attachment strategy, small molecules-bridge grafting, solvent evaporation technique, and hydrogen bonding interaction. Correspondingly, the advantages, limitations, and future prospects of these surface modification methods were discussed. This review provides an important guidance or tool for developing surface functionalized PUs in the fields of bioengineering and medical devices.

Review of Polymeric Biomimetic Small-Diameter Vascular Grafts to Tackle Intimal Hyperplasia

Small-diameter artificial vascular grafts (SDAVG) are used to bypass blood flow in arterial occlusive diseases such as coronary heart or peripheral arterial disease. However, SDAVGs are plagued by restenosis after a short while due to thrombosis and the thickening of the neointimal wall known as intimal hyperplasia (IH). The specific causes of IH have not yet been deduced; however, thrombosis formation due to bioincompatibility as well as a mismatch between the biomechanical properties of the SDAVG and the native artery has been attributed to its initiation. The main challenges that have been faced in fabricating SDAVGs are facilitating rapid re-endothelialization of the luminal surface of the SDAVG and replicating the complex viscoelastic behavior of the arteries. Recent strategies to combat IH formation have been mostly based on imitating the natural structure and function of the native artery (biomimicry). Thus, most recently, developed grafts contain a multilayered structure with a designated function for each layer. This paper reviews the current polymeric, biomimetic SDAVGs in preventing the formation of IH. The materials used in fabrication, challenges, and strategies employed to tackle IH are summarized and discussed, and we focus on the multilayered structure of current SDAVGs. Additionally, the future aspects in this area are pointed out for researchers to consider in their endeavor.

Advancements in modification of membrane materials over membrane separation for biomedical applications-Review

A comprehensive overview of various modifications carried out on polymeric membranes for biomedical applications has been presented in this review paper. In particular, different methods of carrying out these modifications have been discussed. The uniqueness of the review lies in the sense that it discusses the surface modification techniques traversing the timeline from traditionally well-established technologies to emerging new techniques, thus giving an intuitive understanding of the evolution of surface modification techniques over time. A critical comparison of the advantages and pitfalls of commonly used traditional and emerging surface modification techniques have been discussed. The paper also highlights the tuning of specific properties of polymeric membranes that are critical for their increased applications in the biomedical industry specifically in drug delivery, along with current challenges faced and where the future potential of research in the field of surface modification of membranes.

Endothelium-Mimicking Surface Combats Thrombosis and Biofouling via Synergistic Long- and Short-Distance Defense Strategy

Thrombosis and infections are the main causes of implant failures (e.g., extracorporeal circuits and indwelling medical devices), which induce significant morbidity and mortality. In this work, an endothelium-mimicking surface is engineered, which combines the nitric oxide (NO)-generating property and anti-fouling function of a healthy endothelium. The released gas signal molecules NO and the glycocalyx matrix macromolecules hyaluronic acid (HA) jointly combine long- and short-distance defense actions against thrombogenicity and biofouling. The biomimetic surface is efficiently fabricated by cografting a NO-generating species (i.e., Tri-tert-butyl 1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetraacetate-chelated Cu²⁺ , DTris@Cu) and the macromolecular HA on an aminated tube surface through one-pot amide condensation chemistry. The active attack (i.e., NO release) and zone defense (i.e., HA tethering) system endow the tubing surface with significant inhibition of platelets, fibrinogen, and bacteria adhesion, finally leading to long-term anti-thrombogenic and anti-fouling properties over 1 month. It is envisioned that this endothelium-mimicking surface engineering strategy will provide a promising solution to address the clinical issues of long-term blood-contacting devices associated with thrombosis and infection.

Fouling in ocular devices: implications for drug delivery, bioactive surface immobilization, and biomaterial design

The last 30 years has seen a proliferation of research on protein-resistant biomaterials targeted at designing bio-inert surfaces, which are prerequisite for optimal performance of implantable devices that contact biological fluids and tissues. These efforts have only been able to yield minimal results, and hence, the ideal anti-fouling biomaterial has remained elusive. Some studies have yielded biomaterials with a reduced fouling index among which high molecular weight polyethylene glycols have remained dominant. Interestingly, the field of implantable ocular devices has not experienced an outflow of research in this area, possibly due to the assumption that biomaterials tested in other body fluids can be translated for application in the ocular space. Unfortunately, progression in the molecular understanding of many ocular conditions has brought to the fore the need for treatment options that necessitates the use of anti-fouling biomaterials. From the earliest implanted horsehair and silk seton for glaucoma drainage to the recent mini telescopes for sight recovery, this review provides a concise incursion into the gradual evolution of biomaterials for the design of implantable ocular devices as well as approaches used to overcome the challenges with fouling. The implication of fouling for drug delivery, the design of immune-responsive biomaterials, as well as advanced surface immobilization approaches to support the overall performance of implantable ocular devices are also reviewed.

A scope at antifouling strategies to prevent catheter-associated infections

The use of invasive medical devices is becoming more common nowadays, with catheters representing one of the most used medical devices. However, there is a risk of infection associated with the use of these devices, since they are made of materials that are prone to bacterial adhesion with biofilm formation, often requiring catheter removal as the only therapeutic option. Catheter-related urinary tract infections (CAUTIs) and central line-associated bloodstream infections (CLABSIs) are among the most common causes of healthcare-associated infections (HAIs) worldwide while endotracheal intubation is responsible for ventilator-associated pneumonia (VAP). Therefore, to avoid the use of biocides due to the potential risk of bacterial resistance development, antifouling strategies aiming at the prevention of bacterial adherence and colonization of catheter surfaces represent important alternative measures. This review is focused on the main strategies that are able to modify the physical or chemical properties of biomaterials, leading to the creation of antiadhesive surfaces. The most promising approaches include coating the surfaces with hydrophilic polymers, such as poly(ethylene glycol) (PEG), poly(acrylamide) and poly(acrylates), betaine-based zwitterionic polymers and amphiphilic polymers or the use of bulk-modified poly(urethanes). Natural polysaccharides and its modifications with heparin, have also been used to improve hemocompatibility. Recently developed bioinspired techniques yielding very promising results in the prevention of bacterial adhesion and colonization of surfaces include slippery liquid-infused porous surfaces (SLIPS) based on the superhydrophilic rim of the pitcher plant and the Sharklet topography inspired by the shark skin, which are potential candidates as surface-modifying approaches for biomedical devices. Concerning the potential application of most of these strategies in catheters, more in vivo studies and clinical trials are needed to assure their efficacy and safety for possible future use.

An Insight into the Structural Diversity and Clinical Applicability of Polyurethanes in Biomedicine

Due to their mechanical properties, ranging from flexible to hard materials, polyurethanes (PUs) have been widely used in many industrial and biomedical applications. PUs' characteristics, along with their biocompatibility, make them successful biomaterials for short and medium-duration applications. The morphology of PUs includes two structural phases: hard and soft segments. Their high mechanical resistance featuresare determined by the hard segment, while the elastomeric behaviour is established by the soft segment. The most important biomedical applications of PUs include antibacterial surfaces and catheters, blood oxygenators, dialysis devices, stents, cardiac valves, vascular prostheses, bioadhesives/surgical dressings/pressure-sensitive adhesives, drug delivery systems, tissue engineering scaffolds and electrospinning, nerve generation, pacemaker lead insulation and coatings for breast implants. The diversity of polyurethane properties, due to the ease of bulk and surface modification, plays a vital role in their applications.

Novel microgel-based scaffolds to study the effect of degradability on human dermal fibroblasts

For improved cell integration, tissue engineering scaffolds must be designed to degrade over time. Typically, the chemistry of scaffolds is modified to alter the degradation profile by using different hydrolytic or enzymatic sites within a material. It is more challenging, however, to fabricate self-assembling, injectable scaffolds that provide tunable degradation. Our laboratory has developed microgel-based scaffolds, where individual micron-sized hydrogels are crosslinked to make larger bulk scaffolds. The size of the individual microgels permits injection, and the microgels then self-assemble into a bulk structure and crosslink. We hypothesized that the microgel-based scaffolds can be used to tune degradability by mixing degradable and non-degradable microgels at various ratios within a self-assembling scaffold. Therefore, two types of microgels were fabricated, those composed of polyethylene glycol (PEG) and those composed of a PEG-lactic acid. Importantly, the microgels were similar in size and swelling and had a low polydispersity index due to their method of fabrication. Microgels were then mixed in four ratios to fabricate scaffolds and study how changes in scaffold composition altered the 3D proliferation and morphology of human dermal fibroblasts. Microgel-based scaffolds formed with 100% degradable microgels lost >60% of their mass over the 14 days of the study. Human dermal fibroblasts were mixed within the 3D scaffolds at the time of assembly and all scaffolds had cells with high viability and typical morphology. The scaffolds that had 25%-50% degradable microgels showed statistically increased proliferation of fibroblasts after 1 and 2 weeks over non-degradable scaffolds and those scaffolds with 75% or 100% degradable microgels. Overall, this work demonstrates the development and use of a tunable, self-assembled, microgel-based scaffold to investigate the effects of degradability on cellular response.

Octadecyl Chains Immobilized onto Hyaluronic Acid Coatings by Thiol-ene "Click Chemistry" Increase the Surface Antimicrobial Properties and Prevent Platelet Adhesion and Activation to Polyurethane

Infection and thrombus formation are still the biggest challenges for the success of blood contact medical devices. This work aims the development of an antimicrobial and hemocompatible biomaterial coating through which selective binding of albumin (passivant protein) from the bloodstream is promoted and, thus, adsorption of other proteins responsible for bacterial adhesion and thrombus formation can be prevented. Polyurethane (PU) films were coated with hyaluronic acid, an antifouling agent, that was previously modified with thiol groups (HA-SH), using polydopamine as the binding agent. Octadecyl acrylate (C18) was used to attract albumin since it resembles the circulating free fatty acids and albumin is a fatty acid transporter. Thiol-ene "click chemistry" was explored for C18 immobilization on HA-SH through a covalent bond between the thiol groups from the HA and the alkene groups from the C18 chains. Surfaces were prepared with different C18 concentrations (0, 5, 10, and 20%) and successful immobilization was demonstrated by scanning electron microscopy (SEM), water contact angle determinations, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The ability of surfaces to bind albumin selectively was determined by quartz crystal microbalance with dissipation (QCM-D). Albumin adsorption increased in response to the hydrophobic nature of the surfaces, which augmented with C18 saturation. HA-SH coating reduced albumin adsorption to PU. C18 immobilized onto HA-SH at 5% promoted selective binding of albumin, decreased Staphylococcus aureus adhesion and prevented platelet adhesion and activation to PU in the presence of human plasma. C18/HA-SH coating was established as an innovative and promising strategy to improve the antimicrobial properties and hemocompatibility of any blood contact medical device.