Comparison of biomaterial delivery vehicles for improving acute retention of stem cells in the infarcted heart

Cell delivery to the infarcted heart has emerged as a promising therapy, but is limited by very low acute retention and engraftment of cells. The objective of this study was to compare a panel of biomaterials to evaluate if acute retention can be improved with a biomaterial carrier. Cells were quantified post-implantation in a rat myocardial infarct model in five groups (n = 7-8); saline injection (current clinical standard), two injectable hydrogels (alginate, chitosan/β-glycerophosphate (chitosan/ß-GP)) and two epicardial patches (alginate, collagen). Human mesenchymal stem cells (hMSCs) were delivered to the infarct border zone with each biomaterial. At 24 h, retained cells were quantified by fluorescence. All biomaterials produced superior fluorescence to saline control, with approximately 8- and 14-fold increases with alginate and chitosan/β-GP injectables, and 47 and 59-fold increases achieved with collagen and alginate patches, respectively. Immunohistochemical analysis qualitatively confirmed these findings. All four biomaterials retained 50-60% of cells that were present immediately following transplantation, compared to 10% for the saline control. In conclusion, all four biomaterials were demonstrated to more efficiently deliver and retain cells when compared to a saline control. Biomaterial-based delivery approaches show promise for future development of efficient in vivo delivery techniques.

A bioinspired soft actuated material

A class of soft actuated materials that can achieve lifelike motion is presented. By embedding pneumatic actuators in a soft material inspired by a biological muscle fibril architecture, and developing a simple finite element simulation of the same, tunable biomimetic motion can be achieved with fully soft structures, exemplified here by an active left ventricle simulator.

Repair of posterior mitral valve prolapse with a novel leaflet plication clip in an animal model

OBJECTIVE

Recently, there has been increased interest in minimally invasive mitral valve prolapse repair techniques; however, these techniques have limitations. A new technique was developed for treating mitral valve prolapse that uses a novel leaflet plication clip to selectively plicate the prolapsed leaflet segment. The clip's efficacy was tested in an animal model.

METHODS

Yorkshire pigs (n = 7) were placed on cardiopulmonary bypass (CPB), and mitral valve prolapse was created by cutting chordae supporting the P2 segment of the posterior leaflet. Animals were weaned off CPB and mitral regurgitation (MR) was assessed echocardiographically. CPB was reinitiated and the plication clip was applied under direct vision to the P2 segment to eliminate the prolapse. The animals survived for 2 hours. Epicardial echocardiography was obtained before and after prolapse creation and 2 hours after clip placement to quantify MR grade and vena contracta area. Posterior leaflet mobility and coaptation height were analyzed before and after clip placement.

RESULTS

There were no cases of clip embolization. Median MR grade increased from trivial (0-1.5) to moderate-severe after MR creation (2.5-4+) (P < .05), and decreased to mild after clip placement (0-3+) (P < .05). Vena contracta area tended to increase after cutting the chordae and decrease after clip placement: 0.08 ± 0.10 cm(2) versus 0.21 ± 0.15 cm(2) versus 0.16 ± 0.16 cm(2) (P = .21). The plication clip did not impair leaflet mobility. Coaptation height was restored to baseline: 0.51 ± 0.07 cm versus 0.44 ± 0.18 cm (P = 1.0).

CONCLUSIONS

The leaflet plication clip can treat mitral valve prolapse in an animal model, restoring coaptation height without affecting leaflet mobility. This approach is a simple technique that may improve the effectiveness of beating-heart and minimally invasive valve surgery.

Creation of nonischemic functional mitral regurgitation by annular dilatation and nonplanar modification in a chronic in vivo swine model

BACKGROUND

Mechanisms and treatments of nonischemic functional mitral regurgitation (NIMR) are not fully established, in part, because of a lack of proper large animal models. We developed a novel technique of NIMR creation in a swine model by making multiple small incisions in the mitral annulus.

METHODS AND RESULTS

Ex vivo experiments using isolated swine hearts (n=10) showed a 15% increase in annular area (6.8-7.8 cm(2)) after 16 incisions were made along the posterior mitral annulus of a pressurized left ventricle. In an in vivo swine model (n=7; 46.4 ± 2.2 kg), NIMR was created by making fourteen to twenty-six 2-mm incisions in the atrial aspect of the mitral annulus using a cardioport video-assisted imaging system in the beating heart. Animals were euthanized at 4 weeks (n=4) and 6 weeks (n=3). Three-dimensional (3D) echocardiography was obtained before and immediately after NIMR creation and at euthanasia; vena contracta area, mitral annular dimension, left ventricular volume, and inter-papillary muscle distance were measured. The mitral annular incisions resulted in mild to moderate mitral regurgitation and an increased vena contracta area. NIMR creation altered mitral valve geometry by decreasing mitral annular nonplanarity and increasing annular area, primarily in the anteroposterior dimension. NIMR creation did not significantly change left ventricular volume or inter-papillary muscle distance. Longer follow-up period did not significantly affect these outcomes.

CONCLUSIONS

NIMR can successfully be created in a beating heart swine model and results in dilatation and 3D changes in mitral annular geometry. This model can enhance the experimental validation of new valve repair devices and techniques.

Percutaneous steerable robotic tool delivery platform and metal microelectromechanical systems device for tissue manipulation and approximation: closure of patent foramen ovale in an animal model

BACKGROUND

Beating-heart image-guided intracardiac interventions have been evolving rapidly. To extend the domain of catheter-based and transcardiac interventions into reconstructive surgery, a new robotic tool delivery platform and a tissue approximation device have been developed. Initial results using these tools to perform patent foramen ovale closure are described.

METHODS AND RESULTS

A robotic tool delivery platform comprising superelastic metal tubes provides the capability of delivering and manipulating tools and devices inside the beating heart. A new device technology is also presented that uses a metal-based microelectromechanical systems-manufacturing process to produce fully assembled and fully functional millimeter-scale tools. As a demonstration of both technologies, patent foramen ovale creation and closure was performed in a swine model. In the first group of animals (n=10), a preliminary study was performed. The procedural technique was validated with a transcardiac hand-held delivery platform and epicardial echocardiography, video-assisted cardioscopy, and fluoroscopy. In the second group (n=9), the procedure was performed percutaneously using the robotic tool delivery platform under epicardial echocardiography and fluoroscopy imaging. All patent foramen ovales were completely closed in the first group. In the second group, the patent foramen ovale was not successfully created in 1 animal, and the defects were completely closed in 6 of the 8 remaining animals.

CONCLUSIONS

In contrast to existing robotic catheter technologies, the robotic tool delivery platform uses a combination of stiffness and active steerability along its length to provide the positioning accuracy and force-application capability necessary for tissue manipulation. In combination with a microelectromechanical systems tool technology, it can enable reconstructive procedures inside the beating heart.

Temporal enhancement of 3D echocardiography by frame reordering

We describe a method to increase the frame rate for 3-dimensional ultrasound sequences of periodically moving cardiac structures by reordering the acquired volume series. The frame rate is especially important in studying intracardiac structures such as valve leaflet motion in which valve closing times are on the order of milliseconds. Current commercially available systems for volumetric ultrasound imaging are limited to approximately 10 to 20 volumes per second. Although this frame rate is sufficient for real-time observation of basic cardiac morphology, understanding cardiac dynamics requires faster frame rates. The presented work achieves higher frame rates by sampling over several beats and using a simultaneous electrocardiography signal to accurately place the frame within the cardiac cycle. The proposed method relies on periodicity of the heart motion and that within the temporal regions of highest velocity, the structural motions of interest have the lowest beat-to-beat variability.

Percutaneous intracardiac beating-heart surgery using metal MEMS tissue approximation tools

Achieving superior outcomes through the use of robots in medical applications requires an integrated approach to the design of the robot, tooling and the procedure itself. In this paper, this approach is applied to develop a robotic technique for closing abnormal communication between the atria of the heart. The goal is to achieve the efficacy of surgical closure as performed on a stopped, open heart with the reduced risk and trauma of a beating-heart catheter-based procedure. In the proposed approach, a concentric tube robot is used to percutaneously access the right atrium and deploy a tissue approximation device. The device is constructed using a metal microelectromechanical system (MEMS) fabrication process and is designed to both fit the manipulation capabilities of the robot as well as to reproduce the beneficial features of surgical closure by suture. The effectiveness of the approach is demonstrated through ex vivo and in vivo experiments.

Robotics and imaging in congenital heart surgery

The initial success seen in adult cardiac surgery with the application of available robotic systems has not been realized as broadly in pediatric cardiac surgery. The main obstacles include extended set-up time and complexity of the procedures, as well as the large size of the instruments with respect to the size of the child. Moreover, while the main advantage of robotic systems is the ability to minimize incision size, for intracardiac repairs, cardiopulmonary bypass is still required. Catheter-based interventions, on the other hand, have expanded rapidly in both application as well as the complexity of procedures and lesions being treated. However, despite the development of sophisticated devices, robotic systems to aid catheter procedures have not been commonly applied in children. In this article, we describe new catheter-like robotic delivery platforms, which facilitate safe navigation and enable complex repairs, such as tissue approximation and fixation, and tissue removal, inside the beating heart. Additional features including the tracking of rapidly moving tissue targets and novel imaging approaches are described, along with a discussion of future prospects for steerable robotic systems.

Enabling 3D Ultrasound Procedure Guidance through Enhanced Visualization

Real-time 3D ultrasound (3DUS) imaging offers improved spatial orientation information relative to 2D ultrasound. However, in order to improve its efficacy in guiding minimally invasive intra-cardiac procedures where real-time visual feedback of an instrument tip location is crucial, 3DUS volume visualization alone is inadequate. This paper presents a set of enhanced visualization functionalities that are able to track the tip of an instrument in slice views at real-time. User study with in vitro porcine heart indicates a speedup of over 30% in task completion time.

In vitro characterization of bicuspid aortic valve hemodynamics using particle image velocimetry

The congenital bicuspid aortic valve (BAV) is associated with increased leaflet calcification, ascending aortic dilatation, aortic stenosis (AS) and regurgitation (AR). Although underlying genetic factors have been primarily implicated for these complications, the altered mechanical environment of BAVs could potentially accelerate these pathologies. The objective of the current study is to characterize BAV hemodynamics in an in vitro system. Two BAV models of varying stenosis and jet eccentricity and a trileaflet AV (TAV) were constructed from excised porcine AVs. Particle Image Velocimetry (PIV) experiments were conducted at physiological flow and pressure conditions to characterize fluid velocity fields in the aorta and sinus regions, and ensemble averaged Reynolds shear stress and 2D turbulent kinetic energy were calculated for all models. The dynamics of the BAV and TAV models matched the characteristics of these valves which are observed clinically. The eccentric and stenotic BAV showed the strongest systolic jet (V = 4.2 m/s), which impinged on the aortic wall on the non-fused leaflet side, causing a strong vortex in the non-fused leaflet sinus. The magnitudes of TKE and Reynolds stresses in both BAV models were almost twice as large as comparable values for TAV, and these maximum values were primarily concentrated around the central jet through the valve orifice. The in vitro model described here enables detailed characterization of BAV flow characteristics, which is currently challenging in clinical practice. This model can prove to be useful in studying the effects of altered BAV geometry on fluid dynamics in the valve and ascending aorta. These altered flows can be potentially linked to increased calcific responses from the valve endothelium in stenotic and eccentric BAVs, independent of concomitant genetic factors.

Metal MEMS Tools for Beating-heart Tissue Removal

A novel robotic tool is proposed to enable the surgical removal of tissue from inside the beating heart. The tool is manufactured using a unique metal MEMS process that provides the means to fabricate fully assembled devices that incorporate micron-scale features in a millimeter scale tool. The tool is integrated with a steerable curved concentric tube robot that can enter the heart through the vasculature. Incorporating both irrigation and aspiration, the tissue removal system is capable of extracting substantial amounts of tissue under teleoperated control by first morselizing it and then transporting the debris out of the heart through the lumen of the robot. Tool design and robotic integration are described and ex vivo experimental results are presented.

On the Design of an Interactive, Patient-Specific Surgical Simulator for Mitral Valve Repair

Surgical repair of the mitral valve is a difficult procedure that is often avoided in favor of less effective valve replacement because of the associated technical challenges facing non-expert surgeons. In the interest of increasing the rate of valve repair, an accurate, interactive surgical simulator for mitral valve repair was developed. With a haptic interface, users can interact with a mechanical model during simulation to aid in the development of a surgical plan and then virtually implement the procedure to assess its efficacy. Sub-millimeter accuracy was achieved in a validation study, and the system was successfully used by a cardiac surgeon to repair three virtual pathological valves.

Mitral annulus segmentation from four-dimensional ultrasound using a valve state predictor and constrained optical flow

Measurement of the shape and motion of the mitral valve annulus has proven useful in a number of applications, including pathology diagnosis and mitral valve modeling. Current methods to delineate the annulus from four-dimensional (4D) ultrasound, however, either require extensive overhead or user-interaction, become inaccurate as they accumulate tracking error, or they do not account for annular shape or motion. This paper presents a new 4D annulus segmentation method to account for these deficiencies. The method builds on a previously published three-dimensional (3D) annulus segmentation algorithm that accurately and robustly segments the mitral annulus in a frame with a closed valve. In the 4D method, a valve state predictor determines when the valve is closed. Subsequently, the 3D annulus segmentation algorithm finds the annulus in those frames. For frames with an open valve, a constrained optical flow algorithm is used to the track the annulus. The only inputs to the algorithm are the selection of one frame with a closed valve and one user-specified point near the valve, neither of which needs to be precise. The accuracy of the tracking method is shown by comparing the tracking results to manual segmentations made by a group of experts, where an average RMS difference of 1.67±0.63mm was found across 30 tracked frames.

Design of a Surgical Port for Minimally Invasive Beating-Heart Intracardial Procedures

Direct-access, minimally invasive, beating-heart intracardial procedures have the potential to replace many traditional surgical procedures requiring cardio-pulmonary bypass as long as micro-emboli are prevented from entering the cardiovascular system. A new surgical port was developed to introduce surgical instruments into chambers of the beating heart during minimally invasive, intracardial surgical procedures without allowing the introduction of micro-emboli 0.1 mm or larger in size. The design consists of an outer port body that is secured to the heart wall using a purse string suture and a series of inner tubular sleeves that form the interface between the port and the transecting instrument. The design enables rapid tool changes and accommodates a wide variety of instruments. The port uses a fluid purging system to dislodge and remove emboli from a surgical instrument. Laboratory and clinical tests show that the port adequately seals around a surgical instrument and prevents the introduction of emboli with diameters greater than 0.1 mm into the heart while minimizing hemorrhage.

Detection of Curved Robots using 3D Ultrasound

Three-dimensional ultrasound can be an effective imaging modality for image-guided interventions since it enables visualization of both the instruments and the tissue. For robotic applications, its realtime frame rates create the potential for image-based instrument tracking and servoing. These capabilities can enable improved instrument visualization, compensation for tissue motion as well as surgical task automation. Continuum robots, whose shape comprises a smooth curve along their length, are well suited for minimally invasive procedures. Existing techniques for ultrasound tracking, however, are limited to straight, laparoscopic-type instruments and thus are not applicable to continuum robot tracking. Toward the goal of developing tracking algorithms for continuum robots, this paper presents a method for detecting a robot comprised of a single constant curvature in a 3D ultrasound volume. Computational efficiency is achieved by decomposing the six-dimensional circle estimation problem into two sequential three-dimensional estimation problems. Simulation and experiment are used to evaluate the proposed method.

A novel cardioport for beating-heart, image-guided intracardiac surgery

OBJECTIVE

Intracardiac beating-heart procedures require the introduction and exchange of complex instruments and devices. To prevent potential complications such as air embolism and bleeding, a universal cardioport was designed and tested.

METHODS

The design consists of a port body and a series of interchangeable sleeves. The port uses a fluid purging system to remove air from the instrument before insertion into the heart, and a valve system minimizes blood loss during instrument changes.

RESULTS

The cardioport was tested ex vivo and in vivo in pigs (n = 5). Beating-heart procedures, such as septal defect closure and mitral valve repair, were modeled. Ex vivo trials (n = 150) were performed, and no air emboli were introduced using the port. In comparison, air emboli were detected in 40% to 85% of the cases without the use of the port-based purging system. Port operation revealed excellent ergonomics and minimal blood loss.

CONCLUSIONS

A novel cardioport system designed to prevent air entry and blood loss from transcardiac instrument introduction was shown to be an enabling platform for intracardiac beating-heart surgery. The port system improves safety and facilitates further development of complex instruments and devices for transcardiac beating-heart surgery.

Metal MEMS Tools for Beating-heart Tissue Approximation

Achieving superior outcomes through the use of robots in medical applications requires an integrated approach to the design of the robot, tooling and the procedure itself. In this paper, this approach is applied to develop a robotic technique for closing abnormal communication between the atria of the heart. The goal is to achieve the efficacy of surgical closure as performed on a stopped, open heart with the reduced risk and trauma of a beating-heart catheter-based procedure. In the proposed approach, a concentric tube robot is used to percutaneously access the right atrium and deploy a tissue approximation device. The device is constructed using a metal MEMS fabrication process and is designed to both fit the manipulation capabilities of the robot as well as to reproduce the beneficial features of surgical closure by suture. Experimental results demonstrate device efficacy through manual in-vivo deployment and bench-top robotic deployment.

Creation of a tricuspid valve regurgitation model from tricuspid annular dilatation using the cardioport video-assisted imaging system

BACKGROUND AND AIM OF THE STUDY

Experimental models of tricuspid valve regurgitation (TR) are used to study novel annuloplasty techniques (including prosthetic rings), and they can also serve as physiologic models to investigate TR pathophysiology. The study aim was to develop an appropriate simple and reproducible experimental model of TR from annular dilatation.

METHODS

Acute TR was successfully created through multiple small 3- to 5-mm incisions in the annulus using a custom-made optical port with an instrument shaft (the Cardioport) that accepts a standard endoscopic imaging system. The Cardioport was inserted, via a thoracotomy, through the right atrium of seven Yorkshire pigs, and directed towards the tricuspid valve annulus to create the annular incisions. Tricuspid valve anatomy and function were evaluated using 2D and 3D echocardiography. The presence and severity of TR, annulus diameter, and changes in heart rate and atrial pressures after making the annular incisions were documented. To monitor tricuspid annular dilatation and the progression of TR, follow up echocardiography and color Doppler examinations were performed at two and eight weeks postoperatively.

RESULTS

The acute onset of TR was well tolerated, and there were no deaths or significant morbidity associated with the procedure. The annular diameter was increased from a preoperative mean of 23.1 +/- 1.7 mm, to 32.2 +/- 2.5 mm at two weeks postoperatively, and to 37.3 +/- 3.6 mm at eight weeks postoperatively. Overall, the TR progressed from mild (grade I) to severe (grade III) in all of the animals.

CONCLUSION

This novel porcine model represents a relatively simple and a reproducible surgical technique for the creation of annular dilatation and TR, and may also serve as a chronic model of the latter condition.

Force Tracking with Feed-Forward Motion Estimation for Beating Heart Surgery

The manipulation of fast moving, delicate tissues in beating heart procedures presents a considerable challenge to the surgeon. A robotic force tracking system can assist the surgeon by applying precise contact forces to the beating heart during surgical manipulation. Standard force control approaches cannot safely attain the required bandwidth for this application due to vibratory modes within the robot structure. These vibrations are a limitation even for single degree of freedom systems driving long surgical instruments. These bandwidth limitations can be overcome by incorporating feed-forward motion terms in the control law. For intracardiac procedures, the required motion estimates can be derived from 3D ultrasound imaging. Dynamic analysis shows that a force controller with feed-forward motion terms can provide safe and accurate force tracking for contact with structures within the beating heart. In vivo validation confirms that this approach confers a 50% reduction in force fluctuations when compared to a standard force controller and a 75% reduction in fluctuations when compared to manual attempts to maintain the same force.

Mitral annulus segmentation from 3D ultrasound using graph cuts

The shape of the mitral valve annulus is used in diagnostic and modeling applications, yet methods to accurately and reproducibly delineate the annulus are limited. This paper presents a mitral annulus segmentation algorithm designed for closed mitral valves which locates the annulus in three-dimensional ultrasound using only a single user-specified point near the center of the valve. The algorithm first constructs a surface at the location of the thin leaflets, and then locates the annulus by finding where the thin leaflet tissue meets the thicker heart wall. The algorithm iterates until convergence metrics are satisfied, resulting in an operator-independent mitral annulus segmentation. The accuracy of the algorithm was assessed from both a diagnostic and surgical standpoint by comparing the algorithm's results to delineations made by a group of experts on clinical ultrasound images of the mitral valve, and to delineations made by an expert with a surgical view of the mitral annulus on excised porcine hearts using an electromagnetically tracked pointer. In the former study, the algorithm was statistically indistinguishable from the best performing expert (p=0.85) and had an average RMS difference of 1.81+/-0.78 mm to the expert average. In the latter, the average RMS difference between the algorithm's annulus and the electromagnetically tracked points across six hearts was 1.19+/-0.17 mm .

Robotic tissue tracking for beating heart mitral valve surgery

The rapid motion of the heart presents a significant challenge to the surgeon during intracardiac beating heart procedures. We present a 3D ultrasound-guided motion compensation system that assists the surgeon by synchronizing instrument motion with the heart. The system utilizes the fact that certain intracardiac structures, like the mitral valve annulus, have trajectories that are largely constrained to translation along one axis. This allows the development of a real-time 3D ultrasound tissue tracker that we integrate with a 1 degree-of-freedom (DOF) actuated surgical instrument and predictive filter to devise a motion tracking system adapted to mitral valve annuloplasty. In vivo experiments demonstrate that the system provides highly accurate tracking (1.0 mm error) with 70% less error than manual tracking attempts.

Beating-heart mitral valve suture annuloplasty under real-time three-dimensional echocardiography guidance: an ex vivo study

We are developing an alternative mitral valve suture annuloplasty technique on the beating-heart under real-time three-dimensional echocardiography (RT3DE) guidance. The purpose of this initial study was to evaluate a feasibility of this technique using commercially available suturing devices (Sutur Tek Endo 360-degree, Sutur Tek Inc, North Chelmsford, MA, USA). Isolated porcine hearts (n=10) were mounted in a water-filled tank and attached to an ex vivo pulse simulation device, where varying left ventricle pressures with associated valve motion were generated by pulsatile flow through an apical cannula. The suturing device was inserted through the left atrium. Intra-annular (De Vega type) suture annuloplasty was performed under RT3DE guidance. The procedure was successfully performed in all cases. The diameter of the annulus was effectively reduced (85.5+/-4.2% of original antero-posterior dimension, 86.7+/-6.1% of original transverse dimension). The number of tissue bites was 7.4+/-0.8. The maximum distance between the annulus and sutures placed was 1.1 mm. The total procedure time was 9.4+/-2.4 min. There was no collateral tissue injury in any of the cases. This ex vivo study demonstrates the feasibility of beating-heart mitral valve suture annuloplasty under RT3DE guidance.