FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
PROVISIONAL SPECIFICATION
TITLE OF THE INVENTION
"Intraductal Patent Ductus Arteriosus Occlusion Device And A Method For Making The Same"
APPLICANTS
Indian Institute of Technology, Bombay
An Autonomous Educational Institute
having its registered address at
Powai, Mumbai 400 076
Maharashtra, India
INVENTORS
Prof. Jayesh Bellare, Dr. B ha rat Dalvi,
Mrs. Vaibhavi A Sonetha, Ms. Megha Agrawal
and Satyajeet Parakh
All are Indian Nationals of
Indian Institute of Technology, Bombay
An Autonomous Educational Institute
having its registered address at
Powai, Mumbai 400 076
Maharashtra, India
PREAMBLE TO THE DESCRIPTION The following specification describes the invention.

Field of Invention
This invention relates to an intraductal patent ductus arteriosus occlusion device and a method for making the same.
Background of Invention
Persistence of the ductus arteriosus (DA) after birth leads to the congenital heart disease known as Patent Ductus Arteriosus (PDA). Persistent PDA is the sixth most common congenital heart defect, occurring in 6% to 11% of all children with Congenital Heart Disease (CHD). The All India Institute of Medical Sciences (AIIMS) reported 8-10 incidences of CHD per 1000 live births in India. Nearly one-third to half of these CHDs are critical and require intervention in first year of life itself. In 1996, AIIMS reported 13 cases with PDA out of the 5000 cases of CHD. Symptoms are uncommon but in the first year of life include increased work of breathing, poor weight gain and cyanosis. In older children or adults PDA may lead to congestive heart failure if left uncorrected. As a large volume of turbulent blood flow at high pressure occurs at the PDA, the lining of Pulmonary Artery (PA) becomes inflamed- increasing the risk of infection inside the cardiovascular system known as "Bacterial/Infective Endarteritis".
At the beginning of the natural history, the arterial duct shunt is left-to-right. As a consequence of pulmonary hypertension, a right- to-left shunt results. This pattern causes pulmonary overflow and increase of the pulmonary artery pressure and resistances; over time, the pulmonary artery resistances become fixed and the ductal shunt reverses, thus resulting in progressive cyanosis. In other words, it allows blood to go from the systemic circulation to the pulmonary circulation. This condition is known as "Eisenmenger's Syndrome". In case of small defects the duct can be closed by the use of medicines like Indomethacin. However, surgical repair is preferred in case of larger defects. Surgical closure by ligation or division is an effective treatment but factors like post-operative recovery time, pain and discomfort, long hospital stay, residual surgical scars and psychological trauma to the patients are the disadvantages of this mode of therapy. These

factors coupled with the advancements in device design led to the development of minimally invasive surgical techniques. In the medical field, the use of an occlusion device is categorized under non-invasive forms of abnormal duct closures. In minimally invasive treatment, the principle of occlusion or closure involves introducing a physical barrier to flow of blood in the duct, which is done by implanting the device in the duct. Besides acting as a physical barrier, the device also facilitates the process of thrombogenesis. The clot, with the device in its core, acts as a natural permanent plug and effectively occludes the duct. Such transcathetral minimally invasive techniques have higher success rates, leave no scars and reduce hospital stay to three days or less.
With the increasing availability and general acceptance of the percutaneous approach, more and more patients started to undergo this minimally invasive method of PDA occlusion, either because of the high risk involved in undergoing general anesthesia or because of the patients' preference. The transcatheter ductus occluder and delivery system underwent several major changes since 1978 because of problems related to transition in production or as a result of specific complications encountered in the early clinical trials. In 1967, Porstmann reported the first transcatheter closure of PDA using an Ivalon plug but it was not widely used because of a large size arterial delivery sheath. In 1979, Rashkind reported the use of an umbrella device for closure of PDA. Following this pioneering work, Rashkind's single-disk, foam-covered umbrella with grappling hooks, and USCI Rashkind PDA occluding system consisting of a double disk, non-hooked prosthesis were developed.
However, it was not until the 1990s that transcatheter PDA occlusion was widely available and used as an alternative to surgery. Sideris introduced a self-adjustable PDA device and this was followed by its modification into a buttoned device and the Bottallo-occluder and Lock-clamshell devices. Among all the devices initially introduced, the Rashkind PDA occlude was most extensively used. This device, however, had a high incidence of residual leak with a continued risk of infective endarteritis. The residual leaks tended to close spontaneously over time in several cases, yet in a significant subset

a second procedure had to be performed, and for larger ducts. Similarly, the Lock-clamshell device was used for larger ducts but was withdrawn following reports of mechanical instability. The regular buttoned device and its modified versions had problems of residual shunts and subcritical aortic perforation. Likewise, problems encountered during introduction of Gianturco coils for transcatheter occlusion of the patent arterial duct.
Similarly, there were devices like the Gianturco-Grifta vascular occlusion device, the Duct-occlud and Nit-occlud but none of them proved to be the gold standard. Over the years most of these devices have become obsolete. On the other hand, the Amplatzer duct occluder (ADO) (AGA Medical Corporation, Golden Valley, MN) is a device that has gained a lot of clinical popularity over the years and is currently the occlusion device preferred by surgeons worldwide.
However, one of the major drawback associated with the ADO might be the occurrence of aortic obstruction caused by the protrusion of its retention disk into the Aorta. The device protrusion into the Aorta can lead to problems like coarctation and device misplacement. Since the device relies on thrombogenesis for occlusion there is a possibility that the clot so formed may be dislodged due to the aortic flow. According to the local Pediatrics & Cardiologists, the available commercial devices are not 100% reliable and therefore there is a need for better PDA closure devices.
The invention overcomes the drawbacks associated with currently the most popular closure device, the ADO. The intraductal patent ductus arteriosus occlusion device in accordance with this invention does not depend on a retention disk for anchorage and thus does away with the problems associated with having one.
Brief Description of the Drawings
Figure 1: Different views of the proposed intraductal design (a) Top view (b) Isometric
view

Figure 2: Dimensions of the jig (in mm) used for shaping wires. The smaller circles are
pins of diameter 1.5mm and height 3mm while the larger circles are screws for fixing the
wires.
Figure 3: The different steps for the fabrication of the device, (a) Adhering the wire
to the plate (b) Assembling the wire and closing the ends with an O ring (c) Immersion
of the assembly in a hot water bath
Figure 4: (a). The final assembly of Novel Device (b) Final assembly with Dacron fabric
suturing
Figure 5: The different materials that were subjected to biological tests (a) Thermally
treated Nitinol wire (b) Medical grade Stainless Steel wire (c) Dacron fiber 1 (d) Dacron
fiber 2.
Figure 6: Hemolysis results for thermally treated Nitinol wire and 316L Stainless Steel
wire
Figure 7: Hemolysis results for different GSM Dacron Fibers
Figure 8: SEM Micrographs of (a) Glass cover slip before platelet exposure and (b) after
platelet exposure (c) Thermally treated Nitinol before platelet exposure and (d) after
platelet exposure (e) Medical Grade Stainless Steel before platelet exposure and (f) after
exposure
Figure 9: SEM Micrographs of (a) Fiber 1 before platelet exposure and (b) after platelet
exposure (c) Fiber 2 before platelet exposure and (d) after platelet exposure
Figure 10: Schematic of the Flow dynamics setup
Description of Invention
Device Fabrication:
Different views of an intraductal patent ductus arteriosus occlusion device ND36 are shown in Fig.l. The said intraductal patent ductus arteriosus occlusion device is made of network of around 36 biocompatible super elastic wires of Nitinol, which permit slenderization and in situ extension. These wires are shaped to the requisite design specifications shown in Fig. 2, by thermal forming. Nitinol wires of diameter 0.004"

about 12cm in length are shaped on a pin jig as shown in Fig. 2. An extra length on one side for subsequent assembly and for attachment of a weight is provided. The weight is applied to maintain tension in the wire to ensure that the wire remains parallel to the surface of the jig. Screws are used to fasten the tensioned wire to the jig. After proper fixing by tightening the screws, the weights are removed and the jig with wires fixed on it is placed in a muffle furnace at 550°C for 30 minutes. The jig with the wire is then quenched with cold water and the screws loosened to unfasten the wire. The obtained wires are then checked for planarity.
The 36 individual planar shaped wires (which are much less than the material required for the ADO cutting down on the raw material costs) are assembled into a device by using an assembly jig having plates with a plate holder. The wires are stuck on to the plates, using a water soluble adhesive, as shown in Fig. 3(a). The plates are shaped so as to fit in slots, radial on a plate with a 10° equal angular separation as shown in Fig. 3(b). The wire ends, which protrude out on the outer sides of the plate are bunched together using a string atid an O ring of medical grade syringe is inserted and fixed with a water insoluble adhesive. The needle is also clipped using a pair of pliers to fix the position of the wires. The entire assembly is then placed in a hot- water bath (Fig. 3 (c)) to dissolve the water soluble adhesive thus removing the plates from the wires. An O-ring is then passed through the other end and stuck similarly fixing the position of wires from both ends. The final device assembly is shown in Fig. 4.
Suturing the FabHc
A hollow metal punch of inner diameter 10mm is heated and then placed on the stretched fabric of non-woven dacron fibers for shaping the fabric. The fibers in contact with the punch edges are melted and neat, edge-sealed circular discs of diameter 10mm are obtained. This prevents disintegration of the fiber from the sides, which is usually seen when the disc is simply cut out from the fiber stretch. These circular discs are th^n sutured to the 36 "wire framework assembly using polypropylene monofilament surgical suture under a stereomicroscope. Fig. 4(b) shows the image of the final sutured device.

Experiments
Hemolysis Tests
Hemolysis tests were carried out on the thermally treated Nitinol wires using medical grade stainless steel wire as a control (Fig. 5). The medical grade stainless steel wire (Cr 17.43%, Ni 17.35%, and Mo 2.75%) was purchased from Sushrut Surgicals Pvt Ltd. The medical implant diamond drawn wire was 0.8mm in diameter. For any other controls as required by the tests, separate controls were used to capture the variations that could be introduced because of difference in the tests. Tests were also carried out on two Dacron fibers of different thicknesses and area densities (listed in Table 1) to choose the optimum dimensions for the suturing fabric (Fig. 5).
The hemocompatibility of the substrates were evaluated using a method reported in literature [8].The human blood, used for the hemolysis experiments and the platelet adhesion studies, was drawn from the antecubital area of the arm of a healthy donor after informed consent using a standard 22g size needle. While doing so, a tourniquet was tied on the arm, about 3-5 inches above the potential venipuncture site. EDTA or Ethylenediaminetetraacetic acid, to be used as an anticoagulant, was obtained from LOBA Chemie Pvt. Ltd., Mumbai and was used without any further purification. Sodium Chloride (NaCl) (GR Grade), to prepare normal saline (0.9%NaCl) was obtained from LOBA Chemie Pvt. Ltd., Mumbai and was used without any further purification.
12ml of whole blood was collected from a healthy individual in standard vials containing EDTA (91.8mg/ml) which acts as an anticoagulant. The blood was immediately centrifuged at lOOOg for 20 minutes in a REMI R4C centrifuge at room temperature (RT: 25±2°C). The buffy coat was removed and the packed cells were washed thrice with normal saline (0.9% NaCl). Normal saline was added to the cells to get 50% hematocrit. The cell solution so obtained was then divided equally (about 1ml) in test tubes containing the materials to be tested for hemolysis and one test tube which served as a control; one without any material. These samples were incubated at 37°C for lhour in a

water bath. After 1 hour, 50ul of cells from each sample containing the materials as well as from control were added to 1.95ml of normal saline respectively. Three replicates were taken from each sample as well as control. For a sample showing 100% hemolysis 50|il of cells was added to 1.95ml of de-ionized water. These samples were again incubated for 1 hour at 37°C in a water bath. After incubation, the samples were centrifuged at lOOOg for 20 minutes in a REMI R4C centrifuge. The absorbance of the supernatant was measured at 540nm. Percentage Hemolysis was then calculated as

Platelet Adhesion Tests
The following chemicals were purchased for the platelet adhesion studies and used without any further purification. Tri - Sodium Citrate (AR Grade) to be used as an anticoagulant and Ethanol (99.9% Omnis) to be used as a dehydrator were obtained from s. d. fine - CHEM LTD., Mumbai. Glutaraldehyde (25% aqueous solution for synthesis) to be used for fixation of platelets was obtained from LOBA Chemie Pvt. Ltd., Mumbai.
Platelet rich plasma (PRP) was prepared following the method by Gutensohn and group. The blood after being drawn was introduced in a test tube containing 3.8% sodium citrate solution such that the volumetric ratio of blood to sodium citrate solution was 9:1. The blood solution was thoroughly but gently mixed. The solution was then centrifuged at 500g for 20 minutes at room temperature (RT: 25±2°C) in a REMI R4C centrifuge. The upper plasma layer was analyzed in a Hemocytometer to know the concentration of platelets and RBC. Platelet concentration was on an average recorded at 200-300><106 ul"1 while RBC concentration was on an average recorded at 0.01-0.02><106 uT1. The plasma was used for the platelet adhesion studies.
The platelet adhesion test procedure followed was on the lines of that followed by Yuan and group. Blood platelet attachment in vitro was evaluated using SEM (JSM Model

6400 Scanning electronic microscopy, JEOL, Japan). The materials, thermally treated Nitinol wire, medical grade stainless steel wire and glass cover slip, were equilibrated with Phosphate Buffered Saline (PBS) for 120 minutes. Freshly prepared PRP of human blood was added to the materials after removing the PBS solution. After 120 minutes incubation at 37°C, samples were rinsed three times with PBS by mild shaking to remove non-adherent platelets. Adhered platelets were fixed with 2.5% Glutaraldehyde for 30 min at room temperature. After thorough washing with PBS, the platelets adhering to the materials were dehydrated in an ethanol-graded series [50, 60, 70, 80, 90, 95, 100% (v/v)] for 30 min each and allowed to evaporate and dry at room temperature in desiccators. The platelet attached materials were gold deposited in vacuum and examined by SEM. The glass cover slip was used as a positive control; one which has guaranteed platelet adhesion. The medical grade stainless steel wire served as a standard for medical grade materials. Separate experiments were conducted for Dacron fibers in a similar manner with glass cover slip as reference.
Flow Dynamics Testing
A flow simulation circuit is built to resemble the flow path in-vitro similar to that present in the body. The Aorta and PA ducts were modeled by using Poly Vinyl Chloride (PVC) pipes of lengths 30 mm and 25 mm respectively. A 9mm length, 4mm diameter rubber tube, represented the PDA, connected to the pipes using a sealant. Sphygmomanometer gauges were attached to the pipes on one side of the duct connection (Fig. 10). Hose couplers were attached on the ends of the pipes to enable connection of 15mm diameter delivery pipes. To measure the flow rates 4 inline rotameters, with a range of 0 - 101pm and working viscosity of lcp were purchased from Asian Engineering Ltd., Mumbai. Two rotameters were connected on the input side and two were connected on the output side of the duct assembly. The working fluid used for the experiment was water under steady flow conditions. As the heart is a continuously working pump, a motor pump (94W, 2780 rpm) was used for facilitating the water flow

The required pressure values in Aortic and PA pipes were adjusted through the three gate valve connections as shown in the schematic in Fig. 10. The physiological pressure ratio for Aorta to PA is approximately 4:1. We applied similar pressure ratio values on the pipes. The pressures on Aorta and PA were measured with the pressure gauges initially, while keeping the duct closed. The PDA duct was then connected simulating the in-vivo PDA condition. In PDA, there is an increased load on lungs and subsequent decrease in the amount of oxygenated blood pumped by the heart indicated by an increased blood pressure on the PA and decreased pressure on the Aorta. A similar condition is observed and is recorded as the output pressure without the device in the table 2. The output pressure values after putting the device ND36 at PDA site are recorded and tabulated. The experiment was carried out for both ND36 and ADO under similar conditions to carry out a comparative analysis.
Results
The results of the hemolysis tests were plotted on bar graphs reporting the % hemolysis. Two sets of results were obtained- one for the wire and the other for the Dacron fibers. In the first set of results the % hemolysis values recorded were near 0 shown by normal saline (Fig. 6). In the test on Dacron fibers, fibers 1 and 2 showed hemolysis comparable to 0% hemolysis (Fig. 7).
Figure 8 shows (a) glass cover slip before platelet exposure and (b) after platelet exposure; (c) thermally treated Nitinol before platelet exposure and (d) after platelet exposure; (e) medical grade stainless steel before platelet exposure and (f) after exposure.
Figure 9 shows the SEM micrographs from the platelet adhesion studies for the selection of the requisite fiber from the range of available fibers. Both fibers showed adhesion, however the adhesion was low in case of fiber 1 (Figure 9(a) fiber 1 before platelet exposure and 9(b) after platelet exposure) and many platelets were seen in an inactivated state. Fiber 2 (Figure 9(c) fiber 2 before platelet exposure and 9(d) after platelet exposure) showed extensive platelet adhesion.

The test was conducted for a preliminary assessment of the stability of the device under the flow conditions characterized by pressure values. The pressure values in the pipes representing the Aorta and PA, both with and without the device in the duct, were recorded and tabulated in Table 2.
The results of the hemolysis test show that the thermally treated Nitinol wires will not induce hemolysis and thus confirm their hemocompatibilty and thereby suitability as the material for the framework of the device.
In the results of the platelet adhesion tests the favorability of Nitinol as a biomaterial was evident as no platelet adhesion was seen as was the case with medical grade stainless steel.
Dacron fibers were selected as clot-inducing agents and the suitable dimensions for the Dacron fibers to be sutured onto the Nitinol framework were determined by combining the results of the hemolysis and the platelet adhesion tests.
The platelet adhesion tests showed that out of the two fibers, fiber 1 showed low platelet adhesion as compared to fiber 2. Fiber 1 was thus rejected as it did not satisfactorily fulfill its primary function of initiating clot formation and fiber 2 with a thickness of 0.2mm was selected to be sutured on to the Nitinol wire framework.
The test was conducted for a preliminary assessment of the stability of the device under the flow conditions characterized by pressure values. Even though a non-clotting fluid has been used the motive was to carry out a comparative analysis between the two devices under similar conditions. As seen from table 2, application of the device at the PDA site reversed back the pressure values to nearly their initial values. This validates that the intraductal patent ductus arteriosus occlusion device is also able to successfully occlude the ductus and thereby prevent the shunted flow. The continued output pressure difference signifies the stability of the device in the dynamic conditions. The test symbolizes the minimum expected requirement of a device to be placed in a duct of

intense hemodynamics. As a matter of fact, in the presence of a higher viscous fluid like blood, occlusion would be easier with the presence of thrombogenic fibers with very small pore size. This would cause physical obstruction to the flow and the fibers would also serve as a host to platelets thereby initiating the process of thrombogenesis and endothilialization.
Conclusions
Due to the non-universality of the duct, existing designs of medical occlusion devices for PDA closure rely on anchorage on duct ends via retention discs thereby being obtrusive to the blood vessels. Here, a new and innovative intraductal design has been proposed. Based on the design, materials were conceptualized, selected and treated to suit the design. The materials were checked for hemocompatibility and platelet adhesion to ascertain their bi©compatibility. Thermally treated Nitinol was found to be hemocompatible as well as unsuitable for platelet adhesion, characteristic of a medical grade material. The biological tests enabled selection of the requisite fiber for the device, one with minimal hemolytic tendency and sufficient platelet adhesion potential. The device was fully assembled and the design tested for its mechanical characteristics and stability in the dynamic conditions encountered in the duct. Comparisons of the results of the ND36 with the commercially used PDA occluder were made. From pressure and flow measurements, it was concluded that the ND36 had comparable occluding capabilities as that of the ADO under the given conditions. The results of the tests were found to be comparable with the commercially used PDA occluder device in all respects. Hence we propose that, after in-vivo studies, ND36 could efficiently serve as a simplistic and cost effective alternative for PDA occlusion.
The intraductal patent ductus arteriosus occlusion device also serves as a host to form a clot which effectively seals the passage through the duct. This places another precondition on any medical device to be implanted in this region: Thrombogenic potential or clotting potential. The device should thus serve as a host to accumulate the platelets in the blood which is a starting step in clotting.

Tables
Table 1: Area densities and thicknesses of different Dacron fibers

Fibers Area Density in GSM Thickness in mm
Fiber 1 27 0.1
Fiber 2 77 0.2
Table 2: Results of the flow analysis conducted in without device and with device conditions

Pipe initial
Pressure(mm
Hg) Output Pressure (mm Hg)

Without device With device (ADO) With device (Novel Design)
Aorta 240 176 234 240
Pulmonary Artery 60 106 60 60
Aorta 120 108 118 116
Pulmonary Artery 30 38 30 34