Cora rotary pump for implantable left ventricular assist device: biomaterial aspects

Design and Experimental Study of a Tetragonal Rotor Pump Based on Wankel Geometry

Wankel pump designs have not been fully established, with existing designs limited to bicornous rotor pumps and triangular rotor pumps. Here, on the basis of Wankel geometry, we present a tetragonal rotor pump with a three-lobe epicycloid and its conjugate envelope as chamber and rotor profile. First, the design method and basic working principle of the pump are introduced. Four groups of prototypes with different shape factors were manufactured, and their flow and pressure characteristics were experimentally studied. Numerical study showed that the flow rate irregularity of the pump is lower than that of existing Wankel pumps. Finally, the feasibility the pump for mixing applications was verified by a flow field observation experiment. The work in this paper provides a new type of rotary displacement pump design, representing an study of reverse application of a Wankel engine structure.

Control of Blood Coagulation by Hemocompatible Material Surfaces-A Review

Hemocompatibility of biomaterials in contact with the blood of patients is a prerequisite for the short- and long-term applications of medical devices such as cardiovascular stents, artificial heart valves, ventricular assist devices, catheters, blood linings and extracorporeal devices such as artificial kidneys (hemodialysis), extracorporeal membrane oxygenation (ECMO) and cardiopulmonary bypass. Although lower blood compatibility of materials and devices can be handled with systemic anticoagulation, its side effects, such as an increased bleeding risk, make materials that have a better hemocompatibility highly desirable, particularly in long-term applications. This review provides a short overview on the basic mechanisms of blood coagulation including plasmatic coagulation and blood platelets, as well as the activation of the complement system. Furthermore, a survey on concepts for tailoring the blood response of biomaterials to improve the hemocompatibility of medical devices is given which covers different approaches that either inhibit interaction of material surfaces with blood components completely or control the response of the coagulation system, blood platelets and leukocytes.

Atomic Absorption Spectrophotometry (AAS) for the Evaluation of Metallosis in Prostheses and Artificial Organs: A New Approach

To study the presence of metals in body fluids and tissues after implantation of metallic biomaterials and possible related diseases, a new approach in Atomic Absorption Spectrophotometry (AAS) was developed. This technique was compared to three traditional methods: mineralisation with acid digestion (method A) also known as “wet method”, dry ashing (with or without oxygen) (method B); classic Kjeldaal (method C). The new approach (method D) modifies the mineralisation phase and the instrument operating instructions. Al, Na, Cr, K, Ni, Co, Ti, Fe, Hg, Pb, V, Sb and Cu levels were tested with the four methods on bone, muscle, cartilage, skin, brain, lymph nodes, blood, urine, and hair. Test results were checked by the addition method. Results demonstrated a significantly higher percentage of Al, Cr, Ni, Ti and Hg recovery with the new approach. The advantages of method D are no residue, no redox reaction, insignificant loss of analytes and enhanced sensitivity (at ppb level vs ppm of the other methods). This approach should be considered especially when testing heavy metals and complex matrices. Its disadvantages are that it is more time consuming and requires the presence of an operator.

Evaluation of Subretinal Implants Coated with Amorphous Aluminum Oxide and Diamond-like Carbon

Retinal prostheses may be used to support patients suffering from age-related macular degeneration (AMD) or retinitis pigmentosa (RP). A hermetic encapsulation of the poly(imide) (PI)-based prosthesis is important in order to prevent the leakage of water and ions into the electric circuitry embedded in the poly(imide) matrix. The deposition of amorphous aluminum oxide (by sputtering) and diamond like carbon (by pulsed laser ablation) were made for applications in retinal prostheses. The thin films obtained were characterized for composition, thickness, adhesion and smoothness by scanning electron microscopy-energy dispersive spectroscopy, atomic force microscopy, profilometry and light microscopy. Biocompatibility was tested in vivo by implanting coated specimen subretinally in the eye of Yucatan pigs. While amorphous aluminum oxide is more readily deposited with sufficient adhesion quality, superior biocompatibility behavior was shown by diamond-like carbon. Amorphous aluminum oxide had more adverse effects and caused more severe damage to the retinal tissue.

Modulation of osteoblast behavior on TiNxOy coatings by altering the N/O stoichiometry while maintaining a high thrombogenic potential

INTRODUCTION

Titanium nitride oxide (TiNxOy) coatings are known to stimulate osteoblast proliferation and osseointegration when compared to microrough titanium implants. The objectives of the present study were to determine whether the beneficial effects of TiNxOy coatings observed with implant osseointegration are dependent on N/O stoichiometry, with the final goal of optimizing these benefits. MMS: TiNxOy coatings with various N/O compositions were deposited on microrough titanium plates (Ti-SLA, 11 × 11 mm). Human primary osteoblast (hOBs) proliferation and gene expression were analyzed for a time course of three weeks, with or without additional stimulation by 1.25 (OH)2 vitamin D3 100 nM. Platelet adhesion/activation and thrombin generation were also assessed.

RESULTS

hOBs proliferation gradually increased with the amount of oxygen contained in the coatings. The effect was observed from day 7 to reach a maximum at day 10, with a 1.8 fold increase for the best coating as compared to Ti-SLA. SEM views indicated that cells adhered, spread and elongated faster on oxygen-rich TiNxOy films, while the differentiation process as well as the thombogenic potential was not affected.

CONCLUSIONS

The effect of TiNxOy coatings on osteoblast is dependent on their chemical composition; it increases with the amount of oxygen. TiNxOy coatings may act as a catalyst for cell-adhesion and proliferation early after seeding. In contrast, thrombogenicity of Ti-SLA surface is not affected by TiNxOy application.

Loosening torque of Universal Abutment screws after cyclic loading: influence of tightening technique and screw coating

PURPOSE

The purpose of this study was to evaluate the influence of tightening technique and the screw coating on the loosening torque of screws used for Universal Abutment fixation after cyclic loading.

MATERIALS AND METHODS

Forty implants (Titamax Ti Cortical, HE, Neodent) (n=10) were submerged in acrylic resin and four tightening techniques for Universal Abutment fixation were evaluated: A - torque with 32 Ncm (control); B - torque with 32 Ncm holding the torque meter for 20 seconds; C - torque with 32 Ncm and retorque after 10 minutes; D - torque (32 Ncm) holding the torque meter for 20 seconds and retorque after 10 minutes as initially. Samples were divided into subgroups according to the screw used: conventional titanium screw or diamond like carbon-coated (DLC) screw. Metallic crowns were fabricated for each abutment. Samples were submitted to cyclic loading at 10(6) cycles and 130 N of force. Data were analyzed by two-way ANOVA and Tukey's test (5%).

RESULTS

The tightening technique did not show significant influence on the loosening torque of screws (P=.509). Conventional titanium screws showed significant higher loosening torque values than DLC (P=.000).

CONCLUSION

The use of conventional titanium screw is more important than the tightening techniques employed in this study to provide long-term stability to Universal Abutment screws.

In vivo biocompatibility evaluation of a new resilient, hard-carbon, thin-film coating for ventricular assist devices

The purpose of this study was to evaluate in vivo the biocompatibility of BioMedFlex (BMF), a new resilient, hard-carbon, thin-film coating, as a blood journal bearing material in Cleveland Heart's (Charlotte, NC, USA) continuous-flow right and left ventricular assist devices (RVADs and LVADs). BMF was applied to RVAD rotating assemblies or both rotating and stator assemblies in three chronic bovine studies. In one case, an LVAD with a BMF-coated stator was also implanted. Cases 1 and 3 were electively terminated at 18 and 29 days, respectively, with average measured pump flows of 4.9 L/min (RVAD) in Case 1 and 5.7 L/min (RVAD) plus 5.7 L/min (LVAD) in Case 3. Case 2 was terminated prematurely after 9 days because of sepsis. The sepsis, combined with running the pump at minimum speed (2000 rpm), presented a worst-case biocompatibility challenge. Postexplant evaluation of the blood-contacting journal bearing surfaces showed no biologic deposition in any of the four pumps. Thrombus inside the RVAD inlet cannula in Case 3 is believed to be the origin of a nonadherent thrombus wrapped around one of the primary impeller blades. In conclusion, we demonstrated that BMF coatings can provide good biocompatibility in the journal bearing for ventricular assist devices.

Surface coatings for ventricular assist devices

This article focuses on the surface engineering of ventricular assist devices (VADs) for the treatment of heart failure patients, which involves the modification of surfaces contacting blood in order to improve the blood compatibility (hemocompatibility) of the VADs. Following an introduction to the categorization and the complications of VADs, this article pays attention on the hemocompatibility, applications and limitations of six types of surface coatings for VADs: titanium nitride coatings, diamond-like carbon coatings, 2-methacryloyloxyethyl phosphorylcholine polymer coatings, heparin coatings, textured surfaces and endothelial cell linings. In particular, diamond-like coatings and heparin coatings are the most commonly used for VADs owing to their excellent hemocompatibility, durability and technical maturity. For high performance and a long lifetime of VADs, surface modification with coatings to ensure hemocompatibility is as important as the mechanical design of the device.

Mechanical and biological properties of nanoporous carbon membranes

Implantable blood glucose sensors have inadequate membrane-tissue interfaces for long term use. Biofouling and inflammation processes restrict biosensor membrane stability. An ideal biosensor membrane material must prevent protein adsorption and exhibit cell compatibility. In addition, a membrane must exhibit high porosity and low thickness in order to allow the biosensor to respond to analyte fluctuations. In this study, the structural, mechanical and biological properties of nanoporous alumina membranes coated with diamond-like carbon thin films were examined using scanning probe microscopy, nanoindentation and MTT viability assay. We anticipate that this novel membrane material could find use in immunoisolation devices, kidney dialysis membranes and other medical devices encountering biocompatibility issues that limit in vivo function.

Hemolysis Resulting From Surface Roughness Under Shear Flow Conditions Using a Rotational Shear Stressor

The degree of hemolysis as a function of surface roughness value and roughened area under shear flow conditions was investigated using a rotational shear stressor. The shearing portion of the stressor is cone shaped in its upper and lower positions, with a cylindrical central section. Surface roughness was applied to the cylindrical section. Bovine blood was sheared for 30 min over a set of roughened surfaces of between arithmetic mean roughness (Ra) 0.1 and 0.8 mm covering 10% of the surface area of the cylindrical section (equivalent to 1.8% of the whole blood contact area) at a shear rate of 3750/s. The threshold value thus obtained for rapid increase in hemolysis was between Ra 0.6 and 0.8 mm. When sheared with a roughened surface of Ra 0.8 mm applied to the cylindrical surface at areas between 0 and 100% (equivalent to between 0 and 18% of the whole blood-contacting area), the hemolysis level did not increase from 10 to 100%, but a significant difference was obtained between 0 and 10%. This suggests that red blood cells were destroyed not by fatigue failure caused by rolling on the roughened surface, but due to the high shear stress generated by surface roughness. Moreover, it appears that the shear stress was generated over the entire cylindrical section, regardless of the area of surface roughness.

Hemolysis caused by surface roughness under shear flow

In this study, the relationship between the degree of roughness of blood contact surfaces under laminar shear flow conditions and the level of hemolysis resulting from this roughness was investigated using a rotational shear stressor. Unlike previous in vitro experiments that used a pumped circuit, the level of hemolysis was directly evaluated under a constant shear flow. In total, 1.8% of the blood contact area was roughened to an arithmetic mean roughness (Ra) value of between 0.4 and 9.2 microm by machine processing and a shear load was applied for 30 min at a shear flow rate of 3750 s(-1). As a result, the threshold Ra value for the induction of hemolysis was found to be between 0.4 and 0.8 microm. In addition, the results of this experiment suggested that the high shear stress resulting from surface roughness plays a major role in determining the level of hemolysis caused by surface roughness.

An abutment screw loosening study of a Diamond Like Carbon-coated CP titanium implant

The aim of this study was to quantify the extent of abutment screw loosening and thus understand the role of frictional and wear factors in abutment screw loosening by using a cyclic loading device to compare Diamond Like Carbon (DLC)-coated and non-coated implants. The properties of DLC films, including hardness, wear resistance, chemical stability, and biocompatibility, are similar to those of real diamond materials. In this study, a 1-mum thick DLC film served to protect and lubricate a layer of commercially-pure titanium affixed to the top of a dental implant (external hexagon-shaped implant). A cyclic loading force was then applied to the top of the prosthetic portion of the implants in order to determine the difference in looseness of the titanium abutment screw between ten DLC-coated implants and ten non-coated implants. The abutment screw loosening tests were performed with 100 N of force at a frequency of 20 Hz. Data indicate that implants with a DLC coating are more resistant to an applied force (P = 0.002) than are those without the coating. We hope these results will be useful for preventing implant abutment screw loosening.

Material-specific thrombin generation following contact between metal surfaces and whole blood

Little is known about the blood compatibility of metals used in various medical devices. We have previously shown that titanium and derivatives thereof are among the most thrombogenic materials which may explain its outstanding osteointegrating properties. The aim of the present study was to characterize the thrombogenic and complement-activating properties of various metals used today in medical applications. Polyester chips were coated with 50- to 100-nm thick layers of aluminium, iridium, indium, nickel, tantalum, tin, titanium, or zirconium using magnetron sputtering. The metal-coated chips were then incubated in direct contact with whole blood in an in vitro chamber model, and the blood was then analyzed for platelet counts, thrombin-antithrombin (AT), fXIIa-AT, fXIa-AT and fXIIa-C1INH complexes and the complement parameters C3a and sC5b-9. Titanium, tantalum and indium were found to exhibit pronounced thrombogenic properties, whereas aluminium, nickel and, in particular, iridium were essentially non-thrombogenic. Tin and zirconium were intermediate activators. All metals activated complement to a similar degree, with the exception of aluminium, which had more pronounced activating properties. This study clearly indicates that metals indeed have varying thrombogenic and complement activating properties. These studies have implications for the selection of metals intended for medical applications.

In vivo evaluation of a MPC polymer coated continuous flow left ventricular assist system

The aim of this study was the evaluation of the thrombogenicity and the biocompatibility of the SunMedical EVAHEART left ventricular assist system (LVAS) coated with 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer compared to a diamond-like carbon (DLC) coating. Four calves were implanted with the MPC polymer-coated LVAS. Eight calves were implanted with DLC coated LVAS. The thrombogenicity and biocompatibility of the pumps were evaluated. At explant, 60.0 +/- 37.2% (5-85%) of the pump surface area was still coated with MPC polymer after the duration of 45.0 +/- 32.0 days. In 1 out of 4 MPC and 2 out of 8 DLC coated pumps, there was a very small amount of thrombus around the seal ring; otherwise the blood contacting surfaces were free of thrombus. Major organs were normal except for a few lesions in kidneys from both groups. The MPC polymer coated EVAHEART LVAS seems to have low thrombogenicity and high biocompatibility similar to the DLC coated system. The current study demonstrated that the MPC polymer coating shows great promise for being used as an antithrombogenic substrate for the LVAS due to its ease of application, significant cost benefit, and reduction in anticoagulation therapy in acute postoperative period.

Frictional insertion kinetics of bone biopsy needles

Patients undergoing a percutaneous bone biopsy often complain of pain during needle insertion, despite local anesthesia. Bone biopsy needles are typically inserted with combined axial and twisting motions. These motions could cause pain through frictional heating or direct mechanical irritation. The hypothesis of this study is that the insertion energy of bone biopsy needles can be reduced by modifying the insertion kinetics or by adding a friction-lowering coating to the needles. Jamshidi bone biopsy needles were driven into a bone analog model by an MTS materials testing machine operating under axial and rotational displacement control. The load/torque recordings showed that, to significantly decrease insertion energy and peak resistance to needle insertion, axial velocity and angular frequency had to be decreased to one quarter of the baseline, typical-usage parameters. However the increased insertion time may not be acceptable clinically. The majority of the insertion energy was associated with the needle axial thrust rather than with needle twisting. Overcoming friction against the side of the needle consumed much more of the insertion energy than did the process of cutting per se. None of five needle coatings tested succeeded in appreciably lowering the insertion energy, and none achieved a substantial decrease in peak resisting force.

Protein adsorption and platelet attachment and activation, on TiN, TiC, and DLC coatings on titanium for cardiovascular applications

The hemocompatibility of a TiN/TiC/diamond-like carbon (DLC) multilayer structure, deposited on titanium substrates for use as coatings for a heart valve prosthesis, has been studied through the adsorption of blood proteins and the adhesion and attachment of blood platelets. All of the surfaces were characterized by stylus profilometry and water contact angles. The adsorption of albumin and fibrinogen to the surfaces was assessed using the Amido Black assay, whereas platelet attachment was studied by scanning electron microscopy and quantified using stereological techniques. The degree of platelet spreading on the surfaces was seen to correlate with differences in surface energy, indicated from contact angle measurements. The greatest spreading was seen on the more hydrophilic surfaces. When studying protein adsorption to the surfaces, no correlation could be determined between contact angle results and levels of adsorption, although the most hydrophilic surfaces did appear to promote greater amounts of fibrinogen adsorption. Thrombus formation was observed to some degree on all of the surfaces, with the exception of the DLC coating. This coating also promoted less spreading of platelets than the other surfaces. The good hemocompatibility of the DLC coating is attributed to its hydrophobicity and smooth surface, resulting in a higher ratio of albumin to fibrinogen than any of the other surfaces.

Assessing acute platelet adhesion on opaque metallic and polymeric biomaterials with fiber optic microscopy

The degree of platelet adhesion and subsequent thrombus formation is an important measure of biocompatibility for cardiovascular biomaterials. Traditional methods of quantifying platelet adhesion often are limited by the need for direct optical access, limited spatial resolution, or the lack of temporal resolution. We have developed a new imaging system that utilizes fiber optics and fluorescence microscopy for the quantification of platelet adhesion. This fiber optic remote microscope is capable of imaging individual fluorescently labeled platelets in whole blood on opaque surfaces. Using this method, platelet adhesion was quantified on a series of metallic [low-temperature isotropic carbon (LTIC); titanium alloy (Ti); diamond-like carbon (DLC); oxidized titanium alloy (TiO); and polycrystalline diamond (PCD)] and polymeric [woven Dacron (WD)] collagen-impregnated Dacron (HEM), expanded polytetrafluoroethylene (ePTFE), and denucleated ePTFE (dePTFE)] biomaterials designed for use in cardiovascular applications. These materials were perfused with heparinized whole human blood in an in vitro parallel plate flow chamber. Platelet adhesion after 5 min of perfusion ranged from 3.7 +/- 1.0 (dePTFE) to 16.8 +/- 1.5 (WD) platelets/1000 micrometer. The temporal information revealed by these studies provides a comparative measure of the acute thrombogenicity of these materials as well as some insight into their long-term hemocompatibilities. Also studied here were the effects of wall shear rate and axial position on platelet adhesion. A predicted increase in platelet adhesion with increased wall shear rate and a trend toward a decrease in platelet adhesion with increased axial distance was observed with the fiber optic microscope. Future applications for this imaging technique may include the long-term evaluation of thrombosis in blood-contacting devices in vitro and, in animal models, in vivo.