Biocompatibility screening in cardiovascular implants

Stenting of native right ventricular outflow tract obstructions in symptomatic infants: histological work-up of explanted specimen

BACKGROUND

Stenting of stenotic right ventricular outflow tract is a palliative measure for severely impaired small babies with Tetralogy of Fallot or similar pathologies. Little is known about the histopathological fate of the stents in the right ventricular outflow tract.

METHODS

Eight samples of surgically removed right ventricular outflow tract stents were histologically analysed according to a predefined protocol.

RESULTS

The most frequent diagnosis was Tetralogy of Fallot in four patients, pulmonary atresia with ventricular septal defect in two patients, double outlet right ventricle with pulmonary obstruction in one patient, and muscular obstruction of the right ventricular outflow tract in one patient with a syndromic disease with hypertrophic cardiomyopathy. Stents mean implantation duration was 444 days ranging from 105 to 1117 days (median 305.5 days). Histology revealed a variable degree of pseudointima formation consisting of fibromuscular cells surrounded by extracellular matrix. Four of the specimen contained adjacent myocardial tissue fragments, which showed regressive changes. Neither myocardium nor pseudointima tissue or tissue parts locally related to stent struts were infiltrated by inflammatory cells.

CONCLUSIONS

Histological analysis after explantation of early-in-life implanted right ventricular outflow tract stents revealed predominantly pronounced neo-intimal proliferation with a visible endothelial layer, no signs of inflammation, and no prolapse of muscular tissue through the stent struts. Thus, implantation of stents in early life seems to interfere little with the hosts' immune system and might help to open up the right ventricular outflow tract by mechanical forces and regressive changes in adjacent muscular tissue.

INFLUENCE OF VASCULAR STENT SURFACE TREATMENT WITH AN ADAPTIVE COMPOSITION (AdC) FOR IMPROVING ITS BIOCOMPATIBILITY AND RESTENOSIS PREVENTION (experimental research)

Introduction. The article describes a method of implant surface treatment that reduces the risk of an inflammatory reaction to vascular implants. The aim of the research was to develop a method of coating the surface of vascular implants (stents) to reduce the risk of inflammation reaction (rejection), enhance their biocompatibility, and prevent restenosis. Materials and methods. The research was conducted on 34 male rabbits of the "Flemish Giant" breed weighing 2.5-3.0 kg, following the standards of bioethical principles. The blood vessels of the experimental animals were previously provoked by the administration of endogenous pyrogenic solution according to a predetermined protocol. Under general anesthesia, the animals were endovascularly (via femoral access into the abdominal aorta) implanted with standard Z-shaped stents made of 316L stainless steel. To obtain indicative results, 10 rabbits were implanted with non-treated stents, while another 12 rabbits had stents pre-treated with the adapting composition (AdC) implanted. After 8 weeks, the animals were withdrawn from the experiment. Results and discussion. Vessel wall morphometry revealed that the treatment of stents with AdC before their placement into the vessel resulted in a reduction of vessel wall thickness at the site of their implantation. Conclusions. The developed method involves pre-treatment of stents with AdC , which in turn ensures a reduction in the reaction of the surrounding tissues thanks to the modification of the implant surface, reduces the thickness of neointima growth, which indicates the absence of inflammatory processes and the formation of fibrous tissue around the implant. The clinical application of AdC aimed at improving the biocompatibility properties of implants with respect to the recipient's body is characterized by a 100% (95% CI 78.2% - 100%) likelihood of absence of complications.

Neurosurgical Approaches to Brain Tissue Harvesting for the Establishment of Cell Cultures in Neural Experimental Cell Models

In recent decades, cell biology has made rapid progress. Cell isolation and cultivation techniques, supported by modern laboratory procedures and experimental capabilities, provide a wide range of opportunities for in vitro research to study physiological and pathophysiological processes in health and disease. They can also be used very efficiently for the analysis of biomaterials. Before a new biomaterial is ready for implantation into tissues and widespread use in clinical practice, it must be extensively tested. Experimental cell models, which are a suitable testing ground and the first line of empirical exploration of new biomaterials, must contain suitable cells that form the basis of biomaterial testing. To isolate a stable and suitable cell culture, many steps are required. The first and one of the most important steps is the collection of donor tissue, usually during a surgical procedure. Thus, the collection is the foundation for the success of cell isolation. This article explains the sources and neurosurgical procedures for obtaining brain tissue samples for cell isolation techniques, which are essential for biomaterial testing procedures.

Transcatheter mitral valve repair using the Cardioband® system: Histopathological insights in device ingrowth and biocompatibility

Surgical implantation of a complete or incomplete ring to reduce the valve annulus and improve leaflet coaptation is the mainstay of mitral valve surgery. The Cardioband® system (Edwards Lifesciences) was designed to address the pathophysiological mechanism of annular dilatation through a catheter-based approach. We present the histopathological workup of a Cardioband® device, which had been implanted 21 months earlier in a 34-year-old male with ischemic cardiomyopathy. Device examination demonstrate a well-positioned and securely anchored device. The described tissue reactions may have an impact on choice of device and timing in case of re-do surgery.

Biocompatibility and biosafety of butterfly wings for the clinical use of tissue-engineered nerve grafts

In a previous study, we used natural butterfly wings as a cell growth matrix for tissue engineering materials and found that the surface of different butterfly wings had different ultramicrostructures, which can affect the qualitative growth of cells and regulate cell growth, metabolism, and gene expression. However, the biocompatibility and biosafety of butterfly wings must be studied. In this study, we found that Sprague-Dawley rat dorsal root ganglion neurons could grow along the structural stripes of butterfly wings, and Schwann cells could normally attach to and proliferate on different species of butterfly wings. The biocompatibility and biosafety of butterfly wings were further examined through subcutaneous implantation in Sprague-Dawley rats, intraperitoneal injection in Institute of Cancer Research mice, intradermal injection in rabbits, and external application to guinea pigs. Our results showed that butterfly wings did not induce toxicity, and all examined animals exhibited normal behaviors and no symptoms, such as erythema or edema. These findings suggested that butterfly wings possess excellent biocompatibility and biosafety and can be used as a type of tissue engineering material. This study was approved by the Experimental Animal Ethics Committee of Jiangsu Province of China (approval No. 20190303-18) on March 3, 2019.

Hydrocephalus shunt therapy: current titanium shunt valve implants obstructed by internal tissue proliferations identified as extracellular matrix membranes

PURPOSE

Shunt valves, required for treatment of hydrocephalus, demand for high performance rates and lifelong excellent function. To overcome problems with traditional silicone materials, adjustable and gravity-adapted titanium valves were developed. Even modern shunt valve systems are still subject to occlusion. The aim of the present study was to investigate dysfunctional silicone and titanium valves for presence of cellular and proteinous materials inside the housings by means of histopathology.

METHODS

A total of 19 explanted shunt valves from children between 2 and 182 months of age were investigated following dysfunction. After fixation in formalin and embedding in hard resin, slices were ground to a thickness of 5-30 μ. Besides standard histology, immunohistochemistry was performed using antibodies with markers for microglia, astrocytes, platelets, monocytes, and the proteins laminin, fibronectin, and collagen IV.

RESULTS

Traces, layers, and plaques could be demonstrated in every investigated silicone or titanium valve with an implantation time of more than 6 days. Most of the tissue was found adjacent to silicone and titanium surfaces of the inner housing, the adjustment rotor, and ball-in-cone core. Markers for micro and astroglia stained positive in 40-60% of the specimen, mostly demonstrating a proteinous layer positive for laminin (80%), fibronectin (30%), and collagen IV (30%).

CONCLUSIONS

Tissue reactions with formation of cellular and proteinous matrix components are common in obstructed silicone and titanium shunt valves. The tissue mimics astrocytic repair mechanisms genuine for basilar membrane matrix. The knowledge of these typical arachnoid patterns of colonization is a prerequisite for developing future shunt devices.

Comparison of Two Percutaneous Atrial Septal Defect Occluders for Device Healing and Nickel Release in a Chronic Porcine Model

Aims

To investigate the healing process and nickel release of the Hyperion occluder (Comed BV, Netherlands), as compared to the Amplatzer septal occluder (ASO) (St. Jude Medical Inc., St. Paul, MN, USA) in a chronic swine model.

Background

Some long-term complications occurring after percutaneous atrial septal defect (ASD) closure may be partially associated with an inappropriate healing of the device and increased nickel release. There is no direct comparative study of different occluders for healing and nickel release.

Methods

After percutaneous ASD creation, 12 pigs were implanted with 15 mm Hyperion (n = 6) and 15 mm ASO (n = 6) devices. After 1 month (n = 3 for each device) and 3 months (n = 3 for each device) of follow-up, device explantation was performed and healing was assessed using histopathological workup. Systemic and tissular nickel release was performed.

Results

Implantation was successful in 100% without complications. Device coverage was observed as early as 1 month after implantation and was almost complete after 3 months. A granulation tissue with a predominantly mononuclear inflammatory reaction was observed in contact with nitinol wires while an inflammatory reaction was seen in contact with textile fibers. We found no statistically significant difference between the 2 devices whether for histological grading scores or systemic nickel release, regardless to follow-up duration.

Conclusions

In this preclinical study, we demonstrated that Amplatzer septal occluder and Hyperion occluder were not significantly different for device healing and nickel release processes.

Swelling characteristics and biocompatibility of ionic liquid based hydrogels for biomedical applications

Polymers are commonly used in medical device manufacturing, e.g. for drug delivery systems, bone substitutes and stent coatings. Especially hydrogels exhibit very promising properties in this field. Hence, the development of new hydrogel systems for customized application is of great interest, especially regarding the swelling behavior and mechanical properties as well as the biocompatibility. The aim of this work was the preparation and investigation of various polyelectrolyte and poly-ionic liquid based hydrogels accessible by radical polymerization. The obtained polymers were covalently crosslinked with N,N'-methylenebisacrylamide (MBAA) or different lengths of poly(ethyleneglycol)diacrylate (PEGDA). The effect of different crosslinker-to-monomer ratios has been examined. In addition to the compression curves and the maximum degree of swelling, the biocompatibility with L929 mouse fibroblasts of these materials was determined in direct cell seeding experiments and the outcome for the different hydrogels was compared.

Role of animal models for percutaneous atrial septal defect closure

As for any preclinical development of new implantable device, bench testing has been followed by experimental studies on large animal models for the development of atrial septal defect closure devices. Various models have been used according to studied species (porcine, ovine or canine model) and whether the septal defect was percutaneously or surgically created. Animal models of percutaneous atrial septal defect closure aim to assess the healing process and device endothelialisation, as well as the development of magnetic resonance imaging guided procedures, the short-term effects of volume overload on right ventricular contractility through haemodynamic studies and the understanding of other complications such as nickel hypersensitivity. Each technique has its own advantages and drawbacks, and leads to different punch-related, acute septal injuries that could have an effect on the healing process after device implantation. It has been suggested that some long-term, major device-related complications such as thrombosis or infective endocarditis may be associated with an inappropriate healing process or insufficient endothelialisation of the device, leading industrial companies to pay a great deal of attention to the healing process. Tissue reactions in animal models were shown to adequately reproduce the healing response after device implantation in humans, with an endothelial device coverage observed as early as 30 days after implantation and complete after 3 to 6 months. Research perspectives may evaluate both animal models and in-vitro studies in parallel with a view to clarify the endothelialisation process using human endothelial cells through in-vitro experiments. Self-sensing device for detecting the presence of endothelial cells on the surface of intracardiac occluders and high-resolution imaging techniques that could non-invasively assess the complete endothelialisation of a device would also be promising tools which would need large animal models studies before their clinical application.

Biomaterials and host versus graft response: a short review

Biomaterials and biotechnology are increasing becoming an important area in modern medicine. The main aim in this area is the development of materials, which are biocompatible to normal tissue. Tissue-implant interactions with molecular, biological and cellular characteristics at the implant-tissue interface are important for the use and development of implants. Implantation may cause an inflammatory and immune response in tissue, foreign body reaction, systemic toxicity and imminent infection. Tissue-implant interactions determine the implant life-period. The aims of the study are to consider the biological response to implants. Biomaterials and host reactions to implants and their mechanisms are also briefly discussed.

Stent implantation into the tracheo-bronchial system in rabbits: histopathologic sequelae in bare metal vs. drug-eluting stents

Background

Stent implantation into the tracheo-bronchial system may be life-saving in selected pediatric patients with otherwise intractable stenosis of the upper airways. Following implantation, significant tissue proliferation may occur, requiring re-interventions. We sought to evaluate the effect of immunosuppressive coating of the stents on the extent of tissue proliferation in an animal model.

Methods

Bare metal and sirolimus-coated stents (Bx Sonic and Cypher Select, Johnson & Johnson, Cordis) were implanted into non-stenotic lower airways of New Zealand white rabbits (weight 3.1 to 4.8 kg). Three stents with sirolimus coating and six bare metal stents could be analyzed by means of histology and immunohistochemistry 12 months after implantation.

Results

On a macroscopic evaluation, all stents were partially covered with a considerable amount of whitish tissue. Histologically, these proliferations contained fiber-rich connective tissue and some fibromuscular cells without significant differences between both stent types. The superficial tissue layer was formed by typical respiratory epithelium and polygonal cells. Abundant lymphocyte infiltrations and moderate granulocyte infiltrations were found in both groups correspondingly, whereas foreign-body reaction was more pronounced around sirolimus-eluting stents.

Conclusions

After stent implantation in the tracheo-bronchial system of rabbits, we found tissue reactions comparable to those seen after stent implantation into the vascular system. There was no difference between coated and uncoated stents with regard to quality and quantity of tissue proliferation. We found, however, a significantly different inflammatory reaction with a more pronounced foreign-body reaction in sirolimus-coated stents. In our small series, drug-eluting stents did not exhibit any benefit over bare metal stents in an experimental setting.

Bacterial nanocellulose as a new patch material for closure of ventricular septal defects in a pig model

OBJECTIVES

Current materials for closure of cardiac defects such as ventricular septal defects (VSDs) are associated with compliance mismatch and a chronic inflammatory response. Bacterial nanocellulose (BNC) is a non-degradable biomaterial with promising properties such as high mechanical strength, favourable elasticity and a negligible inflammatory reaction. The aim of this study was the evaluation of a BNC patch for VSD closure and the investigation of its in vivo biocompatibility in a chronic pig model.

METHODS

Young's modulus and tensile strength of BNC patches were determined before and after blood exposure. Muscular VSDs were created and closed with a BNC patch on the beating heart in an in vivo pig model. Hearts were explanted after 7, 30 or 90 days. Macropathology, histology and immunohistochemistry were performed.

RESULTS

Young's modulus and tensile strength of the BNC patch decreased after blood contact from 6.3 ± 1.9 to 3.86 ± 2.2 MPa (P < 0.01) and 0.33 ± 0.06 to 0.26 ± 0.06 MPa (P < 0.01), respectively, indicating the development of higher elasticity. Muscular VSDs were closed with a BNC patch without residual shunting. After 90 days, a mild chronic inflammatory reaction was present. Moreover, there was reduced tissue overgrowth in comparison with polyester. Proceeding cellular organization characterized by fibromuscular cells, production of extracellular matrix, neoangiogenesis and complete neoendothelialization were found. There were no signs of thrombogenicity.

CONCLUSIONS

BNC patches can close VSDs with good mid-term results and its biocompatibility can be considered as satisfactory. Its elasticity increases in the presence of blood, which might be advantageous. Therefore, it has potential to be used as an alternative patch material in congenital heart disease.

A Comparative Histopathological Study of Heparin Coated and Uncoated Polytetrafluoroethylene Shunts in Children With Congenital Heart Defect

Objective:

Recently, heparin coated polytetrafluoroethylene (PTFE) shunts are available and are believed to improve inherent shunt problems such as thrombosis and excessive and incomplete neointima formation or occlusion. We aimed at comparing the potential histopathological differences in the neointima (in) between uncoated (UCS) PTFE shunts and heparin coated (HCS) PTFE shunts.

Materials and Methods:

Thirteen shunts (six UCS and seven HCS) were analyzed. The specimens were fixed in formalin, embedded in paraffin or in methylmethacrylate, and characterized by standard and immunohistochemical staining. The thickness of pseudointima proliferation was graded as follows: 0 = no cell layers, 1 = few layers <100 µm, 2 = partial layers >100 µm, 3 = complete layers <300 µm, 4 = complete layers >300 µm, and 5 = occlusion.

Results:

Mean shunt size was 3.4 ± 0.2 mm in UCS and 3.1 ± 0.2 mm in HCS ( P = .053). Mean time of implantation was 163 ± 75 days in UCS and 97 ± 52 days in HCS ( P = .091). There were no significant differences in the proportion of patients with functionally single ventricle, body surface area, age at implantation, or implantation type, between both groups. Shunt occlusion did not occur. Unplanned shunt explantation due to cyanosis was performed in one patient in each group. Partial thrombus formation was observed in one UCS ( P = .462). There was complete endothelialization in 50% of UCS and 86% of HCS ( P = .266). The grade of pseudointima proliferation was 1.8 ± 0.4 in UCS and 1.7 ± 0.5 in HCS ( P = .646).

Conclusions:

The histopathological workup of PTFE shunts revealed equally partial endothelialization and discrete pseudointima proliferation in both the groups. The process of endothelialization may be faster in HCS.

Optical coherence tomography provides images similar to histology and allows the performance of extensive measurements of drug-eluting metal stents in animal ureters

Optical coherence tomography (OCT) images and histology images of metal stents (MSs) inserted in animal ureters were compared, and the reliability of an OCT-based automated method for the performance of quantitative evaluation of ureteral MSs was evaluated. A zotarolimus-eluting metal stent (ZES) and a bare metal stent (BMS) were inserted in each ureter of ten pigs and six rabbits. OCT was performed in unobstructed stented ureters. Histopathologic examination of the stented ureters embedded in glycol-methacrylate took place. Quadrants of OCT images were compared to their respective histologic images by employing two independent observers who delineated different layers in the quadrants of OCT images and correlated them to the respective histologic quadrants. Manual (integrated OCT device software) and automated measurements of the OCT images using an automated strut detection method were compared. The observers highly agreed on the delineation of urothelium from the lamina propria and the lamina propria from the muscle layer of the ureteral wall. The algorithm measurements were similar to the manual measurements, and the algorithm proved to be reliable in the evaluation of ureteral MSs. Significantly higher endothelial hyperplasia of the BMSs in comparison to the ZESs was also quantitatively demonstrated by the strut detection method. OCT proved to be a reliable method for the evaluation of ureteral MSs. OCT provided images of the stented ureteral lumen similar to light microscopy quality. Measurements of the stented ureter are reliably performed by the automated strut detection method.

Evaluation of zotarolimus-eluting metal stent in animal ureters

BACKGROUND AND PURPOSE

Drug-eluting stents proved to minimize neointimal hyperplasia in coronary vessels. Hyperplastic reaction is the most common unwelcome event related to the use of metal mesh stents in the ureter. We evaluated the effect of zotarolimus-eluting stent (ZES) Endeavor Resolute in the porcine and rabbit ureter.

MATERIALS AND METHODS

A ZES and a bare metal stent (BMS) were inserted in each ureter of 10 pigs and 6 rabbits. The insertion was performed by the retrograde approach. CT was used for the evaluation of porcine ureters while intraoperative intravenous urography (IVU) was used for rabbit ureters. The follow-up included CT or IVU every week for the following 4 weeks for pigs and 8 weeks for rabbits. Renal scintigraphies were performed before stent insertion and during the third week in all animals. Optical coherence tomography (OCT) has been used for the evaluation of the luminal and intraluminal condition of the ureters with stents. Histopathologic examination of the these ureters embedded in glycol-methacrylate was performed.

RESULTS

Hyperplastic reaction was present in both stent types. BMSs in seven porcine ureters were completely obstructed while porcine ureters with ZES stents had hyperplastic tissue that did not result in obstruction. Two rabbit ureters with BMS stents were occluded while no ZES was associated with ureteral obstruction. The function of the seven porcine renal units and the two rabbit units with obstructed ureters with stents was compromised. The OCT revealed increased hyperplastic reaction in the ureters with BMS stents in comparison with those with ZESs. Although, hyperplastic reaction was present in all cases, pathologic examination revealed significantly more hyperplastic reaction in BMSs.

CONCLUSION

ZESs in the pig and rabbit ureter were not related to hyperplastic reaction resulting in stent occlusion. These stents were related to significantly lower hyperplastic reaction in comparison with BMSs while inflammation rates were similar for both stent types.

Secondary residual shunt after atrial septal defect closure with an amplatzer occluder: surgical removal and evaluation of device biocompatibility after 7 years

Interventional occluder implantation has become the preferred mode of treatment in children with clinically significant atrial septal defect (ASD). The continuous increase in the number of patients treated calls for long-term data on device integrity and biocompatibility. We report a child who underwent successful interventional ASD closure at age 5 years. Secondary residual shunt occurred after 3 years of follow-up, and surgical ASD closure became necessary at age 12 years. The Amplatzer occluder device, which was removed after 7 years in vivo, showed no signs of mechanical failure, corrosion, or clinically relevant immunological response at the device-tissue interface.

Preclinical evaluation of a new self-expanding device for closure of muscular ventricular septal defects in a pig model

OBJECTIVES

Aim of our study was the preclinical evaluation of a new self expanding device for interventional closure of muscular ventricular septal defects (mVSDs) in an acute pig model.

BACKGROUND

Devices currently in use for closure of mVSDs still have their limitations. The deployment of the disks is dependent from the expansion of the stent, which can be associated with problems for sufficient closure of the mVSDs. This was the reason for developing a modified device with only one disk

MATERIALS AND METHODS

The device was constructed in a single wire technique with a unique configured retention disk. mVSDs were created in six pigs with a specially designed punch instrument, and subsequently closed with our new device during the same session using a jugular or femoral vein approach. Potential residual shunting volumes were estimated by echocardiography and hemodynamic measurements. After closure, animals were sacrificed, and hearts were harvested for macropathologic evaluation. In two animals, MRI was performed for additional noninvasive evaluation.

RESULTS

Devices were successfully implanted in all animals with good alignment of the disk to the left ventricular septum, even if the stent was oversized. Echocardiography, hemodynamics, angiography and macropathology revealed complete closure of all mVSDs. MRI and echocardiography showed a good visibility of the device.

CONCLUSIONS

Our preclinical study shows successful closure of iatrogenic created mVSDs without residual shunting. The device is characterized by a more controlled deployment, an independent deployment of disk and waist, and a good alignment of the left ventricular disk to the muscular septum.

Transvenous closure of patent foramen ovale: preliminary results with a new self-expanding nitinol wire mesh in a Swine model

Objectives. The transvascular closure of patent foramen ovale (PFO) with self-expanding devices carries the risk of left atrial thrombus formation related to material protruding into the left atrium. Thus, we developed a novel device with flat left atrial disc geometry. We evaluated feasibility, handling, and biocompatibility in a porcine animal model. Methods. Implantation of an Occlutech Figulla PFO device was performed in 10 mini pigs using fluoroscopy and intra-cardiac ultrasound after transseptal puncture of the interatrial septum. Angiographic follow-up was performed after six and twelve weeks. Results. Implantation was successful in 100%. There were no further implant related complications. One procedure related death occurred, as one animal died of ventricular tachycardia due to mispunture of the interatrial septum. Angiographic studies showed no residual shunt during follow-up. Histopathological evaluation could demonstrate partial neoendothelialization after 6 weeks with completion after 12 weeks. The devices were incorporated into connective tissue containing fibro muscular cells. An only mild inflammatory reaction was detected locally related to the polyester fibers. Conclusion. In terms of feasibility and handling, the new device does not seem to be inferior to other presently used implantation systems. Good biocompatibility was demonstrated with rapid and complete neoendothelialization.

Long-term small molecule and protein elution from TiO2 nanotubes

In this study, TiO(2) nanotubes of various dimensions were used to elute albumin, a large protein molecule, as well as sirolimus and paclitaxel, common small molecule drugs. The nanotubes controlled small molecule diffusion for weeks and large molecule diffusion for a month. Drug eluted from the nanotubes was bioactive and decreased cell proliferation in vitro. Elution kinetics was most profoundly affected by tube height. This study demonstrates that TiO(2) nanotubes may be a promising candidate for a drug-eluting implant coating.

The electrochemical characteristics of native Nitinol surfaces

The present study explored the avenues for the improvement of native Nitinol surfaces for implantation obtained using traditional procedures such as mechanical polishing, chemical etching, electropolishing and heat treatments for a better understanding of their electrochemical behavior and associated surface stability, conductivity, reactivity and biological responses. The corrosion resistance (cyclic potential polarization, open circuit potential and polarization resistance) of Nitinol disc and wire samples were evaluated for various surface states in strain-free and strained wire conditions. The surface response to tension strain was studied in situ. Surface chemistry and structure were explored using XPS and Auger spectroscopy and photoelectrochemical methods, respectively. It was found that the polarization resistance of the Nitinol surfaces varied in a range from 100 kOmega to 10 MOmega cm(2) and the open circuit potentials from -440 mV to -55 mV. The surfaces prepared in chemical solutions showed consistent corrosion resistance in strain-free and strained states, but mechanically polished and heat treated samples were prone to pitting. Nitinol surface oxides are semiconductors with the band gaps of either 3.0 eV (rutile) or 3.4 eV (amorphous). The conductivity of semiconducting Nitinol surfaces relevant to their biological performances is discussed in terms of oxide stoichiometry and variable Ni content. Such biological characteristics of Nitinol surfaces as Ni release, fibrinogen adsorption and platelets behavior are re-examined based on the analysis of the results of the present study.

Nanoscale architectural tuning of parylene patch devices to control therapeutic release rates

The advent of therapeutic functionalized implant coatings has significantly impacted the medical device field by enabling prolonged device functionality for enhanced patient treatment. Incorporation of drug release from a stable, biocompatible surface is instrumental in decreasing systemic application of toxic therapeutics and increasing the lifespan of implants by the incorporation of antibiotics and anti-inflammatories. In this study, we have developed a parylene C-based device for controlled release of Doxorubicin, an anti-cancer chemotherapy and definitive read-out for preserved drug functionality, and further characterized the parylene deposition condition-dependent tunability of drug release. Drug release is controlled by the deposition of a layer of 20-200 nm thick parylene over the drug layer. This places a porous layer above the Doxorubicin, limiting drug elution based on drug accessibility to solvent and the solvent used. An increase in the thickness of the porous top layer prolongs the elution of active drug from the device from, in the conditions tested, the order of 10 min to the order of 2 d in water and from the order of 10 min to no elution in PBS. Thus, the controlled release of an anti-cancer therapeutic has been achieved via scalably fabricated, parylene C-encapsulated drug delivery devices.

Critical overview of Nitinol surfaces and their modifications for medical applications

Nitinol, a group of nearly equiatomic shape memory and superelastic NiTi alloys, is being extensively explored for medical applications. Release of Ni in the human body, a potential problem with Nitinol implant devices, has stimulated a great deal of research on its surface modifications and coatings. In order to use any of the developed surfaces in implant designs, it is important to understand whether they really have advantages over bare Nitinol. This paper overviews the current situation, discusses the advantages and disadvantages of new surfaces as well as the limitations of the studies performed. It presents a comprehensive analysis of surface topography, chemistry, corrosion behavior, nickel release and biological responses to Nitinol surfaces modified mechanically or using such methods as etching in acids and alkaline solutions, electropolishing, heat and ion beam treatments, boiling in water and autoclaving, conventional and ion plasma implantations, laser melting and bioactive coating deposition. The analysis demonstrates that the presently developed surfaces vary in thickness from a few nanometers to micrometers, and that they can effectively prevent Ni release if the surface integrity is maintained under strain and if no Ni-enriched sub-layers are present. Whether it is appropriate to use various low temperature pre-treatment protocols (< or = 160 degrees C) developed originally for pure titanium for Nitinol surface modifications and coatings is also discussed. The importance of selection of original Nitinol surfaces with regard to the performance of coatings and comparative performance of controls in the studies is emphasized. Considering the obvious advantages of bare Nitinol surfaces for superelastic implants, details of their preparation are also outlined.

Copolymeric nanofilm platform for controlled and localized therapeutic delivery

Nanomaterials such as block copolymeric membranes provide a platform for both cellular interrogation and biological mimicry. Their biomimetic properties are based upon the innate possession of hydrophilic and hydrophobic units that enable their integration with a broad range of therapeutic materials. As such, they can be engineered for specific applications in nanomedicine, including controlled/localized drug delivery. Here we describe a method for the functionalization of the polymethyloxazoline-polydimethylsiloxane-polymethyloxazoline (PMOXA-PDMS-PMOXA) block copolymer with anti-inflammatory molecules to develop copolymer-therapeutic hybrids, effectively conferring biological functionality to a versatile synthetic nanomembrane matrix and creating a platform for an anti-inflammatory drug delivery system. Utilizing self-assembly and Langmuir-Blodgett deposition methods, we mixed copolymers with dexamethasone (Dex), an anti-inflammatory glucocorticoid receptor agonist. The successful mixing of the copolymer with the drug was confirmed by surface pressure isotherms and fluorescence microscopy. Furthermore, at 4 nm thick per layer, orders of magnitude thinner than conventional drug delivery coatings, these dexamethasone-copolymer mixtures (PolyDex) suppressed in vitro expression of the inflammatory cytokines/signaling elements interleukin 6 (IL-6), interleukin 12 (IL-12), tumor necrosis factor alpha (TNFalpha), inducible nitric oxide synthase (iNOS), and interferon gamma inducible protein (IP-10). Finally, PolyDex maintained its anti-inflammatory properties in vivo confirmed through punch biopsies with tissue imagery via hematoxylin/eosin and macrophage specific staining using CD11b. Thus, we demonstrated that PolyDex may be utilized as a localized, highly efficient drug-copolymer composite for active therapeutic delivery to confer anti-inflammatory protection or as a platform material for broad drug elution capabilities.

Histopathological workup of an Amplatzer atrial septal defect occluder after surgical removal

We present results of the histopathological work-up of an atrial septal defect occluder that was explanted 15 months after interventional implantation due to a significant residual shunt. Complete endothelialization of the surface and a mild inflammatory reaction was demonstrated.

Biocompatibility of septal defect closure devices

OBJECTIVE

Despite their clinical introduction 10 years ago, no human series on the healing response to Amplatzer and Starflex devices in humans have been reported yet. We sought to investigate the biocompatibility of Amplatzer and Cardioseal/Starflex septal occluder devices in humans and compare the findings to results in experimental animals.

METHODS

The healing response of Amplatzer and Cardioseal/Starflex septal occluder devices in humans (n = 12, follow-up periods from 5 days to 4 years) and in experimental animals (n = 32, follow-up periods from 4 days to 1 year) was studied using a uniform work up protocol. Histological sections of paraffin-wax-embedded or methacrylate-embedded specimen and scanning electron microscopy were used for biocompatibility screening.

RESULTS

Neoendothelialisation of all examined devices was complete after 3 months in vivo. Protruding metal frame parts, like screw threads and spring arms, were covered last. The initial deposition of fibrin and blood cells on the polyester fabric was subsequently organised by ingrown fibroblastic cells. Loosely arranged and poorly vascularised young granulation tissue was transformed time-dependently into quiescent fibre-rich connective repair tissue poor of cellular and capillary vessel components. Consistently, a mild chronic inflammatory response directed against textile fibres of both types of implants characterised by lymphocytic infiltration and multinucleated foreign body giant cells was observed equally in human and animal explants.

CONCLUSIONS

Systematic biocompatibility screening in a series of explanted human septal occluder devices showed results corresponding to findings in animal studies with regard to neoendothelialisation, cellular organisation of initial thrombus and persisting immune response.