Rat Model of Normothermic Ex-Situ Perfused Heterotopic Heart Transplantation.

Heart transplantation is the most effective therapy for end-stage heart failure. Despite the improvements in therapeutic approaches and interventions, the number of heart failure patients waiting for transplantation is still increasing. The normothermic ex situ preservation technique has been established as a comparable method to the conventional static cold storage technique. The main advantage of this technique is that donor hearts can be preserved for up to 12 h in a physiologic condition. Moreover, this technique allows resuscitation of the donor hearts after circulatory death and applies required pharmacologic interventions to improve donor function after implantation. Numerous animal models have been established to improve normothermic ex situ preservation techniques and eliminate preservation-related complications. Although large animal models are easy to handle compared to small animal models, it is costly and challenging. We present a rat model of normothermic ex situ donor heart preservation followed by heterotopic abdominal transplantation. This model is relatively cheap and can be accomplished by a single experimenter.

Extracorporeal circulation models in small animals: beyond the limits of preclinical research.

Extracorporeal membrane oxygenation (ECMO) use has remarkably increased in recent years. Although ECMO has become essential for patients with refractory cardiac and respiratory failure, extracorporeal circulation (ECC) is associated with significant complications. Small-animal models of ECC have been developed and widely used to better understand ECC-induced pathophysiology. This review article summarizes the development of small-animal ECC models, including the animal species, circuit configuration, priming, perioperative procedures, cannulation, and future perspectives of small-animal ECMO models.

Rapid remodeling observed at mid-term in-vivo study of a smart reinforced acellular vascular graft implanted on a rat model.

BACKGROUND: The poor performance of conventional techniques used in cardiovascular disease patients requiring hemodialysis or arterial bypass grafting has prompted tissue engineers to search for clinically appropriate off-the-shelf vascular grafts. Most patients with cardiovascular disease lack suitable autologous tissue because of age or previous surgery. Commercially available vascular grafts with diameters of < 5 mm often fail because of thrombosis and intimal hyperplasia. RESULT: Here, we tested tubular biodegradable poly-e-caprolactone/polydioxanone (PCL/PDO) electrospun vascular grafts in a rat model of aortic interposition for up to 12 weeks. The grafts demonstrated excellent patency (100%) confirmed by Doppler Ultrasound, resisted aneurysmal dilation and intimal hyperplasia, and yielded neoarteries largely free of foreign materials. At 12 weeks, the grafts resembled native arteries with confluent endothelium, synchronous pulsation, a contractile smooth muscle layer, and co-expression of various extracellular matrix components (elastin, collagen, and glycosaminoglycan). CONCLUSIONS: The structural and functional properties comparable to native vessels observed in the neoartery indicate their potential application as an alternative for the replacement of damaged small-diameter grafts. This synthetic off-the-shelf device may be suitable for patients without autologous vessels. However, for clinical application of these grafts, long-term studies (> 1.5 years) in large animals with a vasculature similar to humans are needed.

A Comparative Study of an Anti-Thrombotic Small-Diameter Vascular Graft with Commercially Available e-PTFE Graft in a Porcine Carotid Model.

BACKGROUND: We have designed a reinforced drug-loaded vascular graft composed of polycaprolactone (PCL) and polydioxanone (PDO) via a combination of electrospinning/3D printing approaches. To evaluate its potential for clinical application, we compared the in vivo blood compatibility and performance of PCL/PDO + 10%DY grafts doped with an antithrombotic drug (dipyridamole) with a commercial expanded polytetrafluoroethylene (e-PTFE) graft in a porcine model. METHODS: A total of 10 pigs (weight: 25-35 kg) were used in this study. We made a new 5-mm graft with PCL/PDO composite nanofiber via the electrospinning technique. We simultaneously implanted a commercially available e-PTFE graft (n = 5) and our PCL/PDO + 10%DY graft (n = 5) into the carotid arteries of the pigs. No anticoagulant/antiplatelet agent was administered during the follow-up period, and ultrasonography was performed weekly to confirm the patency of the two grafts in vivo. Four weeks later, we explanted and compared the performance of the two grafts by histological analysis and scanning electron microscopy (SEM). RESULTS: No complications, such as sweating on the graft or significant bleeding from the needle hole site, were seen in the PCL/PDO + 10%DY graft immediately after implantation. Serial ultrasonographic examination and immunohistochemical analysis demonstrated that PCL/PDO + 10%DY grafts showed normal physiological blood flow and minimal lumen reduction, and pulsed synchronously with the native artery at 4 weeks after implantation. However, all e-PTFE grafts occluded within the study period. The luminal surface of the PCL/PDO + 10%DY graft in the transitional zone was fully covered with endothelial cells as observed by SEM. CONCLUSION: The PCL/PDO + 10%DY graft was well tolerated, and no adverse tissue reaction was observed in porcine carotid models during the short-term follow-up. Colonization of the graft by host endothelial and smooth muscle cells coupled with substantial extracellular matrix production marked the regenerative capability. Thus, this material may be an ideal substitute for vascular reconstruction and bypass surgeries. Long-term observations will be necessary to determine the anti-thrombotic and remodeling potential of this device.

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.

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.

Drug release and kinetic models of anticancer drug (BTZ) from a pH-responsive alginate polydopamine hydrogel: Towards cancer chemotherapy.

A pH-sensitive polymeric carrier was developed in this study for local delivery of anticancer drug bortezomib (BTZ) to cancer cells. Our strategy is based on the conjugation of BTZ to polymeric carriers containing catechol groups, which are considered to release BTZ selectively in cancer cells. In this study we used alginate-conjugated polydopamine as a building block polymer. The catechol moiety of polydopamine binds to the boronic acid group of BTZ drug and release the drug molecules in a pH-dependent method. Cancer tissue has acidic environment where BTZ dissociate from the catechol group of polydopamine to control the release of the free drug. Mathematical equation models were used to clarify the mechanism of drug release. The release profile fitted first order with correlation coefficient (R2 = 0.98), the release mechanism was studied using Korsmeyer-Peppas, Higuchi, Hixson-Crowell, and Kopcha models. We revealed the release mechanism follows non-fickian and diffusion was the dominant mechanism while small portion contributed to erosion. The pH-sensitive mechanism controls the release of BTZ in targeted cancer cells, hence developing a novel idea that is applicable in future towards other boronic acid-containing drugs to treat various kinds of health challenges.

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

Here we developed a semi-interpenetrating network (IPN) hydrogel obtained by free radical polymerization to fabricate a coated stent with the aim of incorporating a natural topography present in the human body to improve biological activity. The method involves sandwiching a bare metal stent in the semi-IPN hydrogel via solution cast molding. The bio-functionality of the membrane could be tuned by incorporating Polydopamine into the matrix, and also the mechanical property was optimized by choosing an adequate concentration of acrylamide. The coating containing polydopamine hydrogel showed good mechanical stability under continuous flow condition, as demonstrated by crimping and deployment into a catheter without damage. Stent polymer bonding was enhanced via polydopamine incorporation in the matrix. The non-thrombogenicity of the coating containing hydrogel was confirmed through dynamic hemocompatibility studies in vitro. Vascular simulations, including other biomechanical performance, like durability testing, radial strength, and recoil, were demonstrated. The dopamine containing hydrogel membrane (DCHM) was found to promote cell material interaction due to the ability of the catechol to bind protein and induce HUVECs cytoplasmic spreading, proliferation, and migration, with reduced smooth muscle cell (SMCs) activity. SMCs inhibition correlated well with the amount of incorporated catechol in the matrix. Our results show that this material used as coated stent could be more effective in suppressing platelet aggregation with improved haemocompatibility/biocompatibility for faster re-endothelialization than bare metal stent (BMS).

Short duration cancer treatment: inspired by a fast bio-resorbable smart nano-fiber device containing NIR lethal polydopamine nanospheres for effective chemo-photothermal cancer therapy.

BACKGROUND: The objective of this study was to evaluate the efficacy of a combination of Photothermal therapy (PTT) and chemotherapy in a single nano-fiber platform containing lethal polydopamine nanopheres (PD NPs) for annihilation of CT 26 cancer cells. METHOD: Polydioxanone (PDO) nanofiber containing PD and bortezomib (BTZ) was fabricated via electrospinning method. The content of BTZ and PD after optimization was 7% and 2.5% respectively with respect to PDO weight. PD NPs have absorption band in near-infrared (NIR) with resultant rapid heating capable of inducing cancer cell death. The samples was divided into three groups - PDO, PDO+PD, and PDO+PD-BTZ for analysis. RESULTS: In combined treatment, PDO nanofiber alone could not inhibit cancer cell growth as it neither contain PD or BTZ. However, PDO+PD fiber showed a cell viability of approximately 20% after 72 hr of treatment indicating minimal killing via hyperthermia. In the case of PDO composite fiber containing BTZ, the effect of NIR irradiation reduced the viability of cancer cells down to around 5% after 72 h showing the efficiency of combination therapy on cancer cells elimination. However, due to higher photothermal conversion that may negatively affect normal cells above 46°C, we have employed 1 s "OFF" and 2 s "ON" after initial 9 s continuous irradiation to maintain the temperature between 42 and 46°C over 3 mins of treatment using 2 W/cm2; 808 nm laser which resulted to similar cell death. CONCLUSION: In this study, combination of PTT and chemotherapy treatment on CT 26 colon cancer cells within 3 min resulted in effective cell death in contrast to single treatment of either PTT and chemotherapy alone. Our results suggest that this nanofiber device with efficient heating and remote control drug delivery system can be useful and convenient in the future clinical application for localized cancer therapy.

A mussel inspired self-expandable tubular hydrogel with shape memory under NIR for potential biomedical applications.

We engineered a novel shape memory polymer (SMP), a nanocomposite hydrogel containing polydopamine nanospheres (PDNs) as a self-expandable tubular hydrogel under near-infrared (NIR) irradiation. When NIR is applied to the nanocomposite hydrogel, the PDN nanoparticles absorb light, which is locally dissipated as heat to become the driving force for shape transition behavior. Since the fabricated PDN material has good mechanical properties, including rapid self-expandability and good biocompatibility, when developed with good heating properties under (NIR) irradiation, it might be useful for many biomedical applications such as the treatment of coronary artery disease.