RU2850277C1 - Method for forming an external reinforcing coating for a biodegradable vascular prosthesis - Google Patents

Abstract

FIELD: chemistry; medicine.

SUBSTANCE: invention relates to chemistry and medicine, namely to a method for forming an external reinforcing coating for a biodegradable vascular prosthesis. In accordance with the proposed method, an external reinforcing coating is formed on the surface of the main polymer tubular frame of a biodegradable vascular prosthesis by electrospinning from a solution containing 6.99 wt. % thermoplastic polyurethane selected from Tecoflex or Pelletane brands in trichloromethane, wherein the main polymer tubular frame is obtained by electrospinning from a polymer solution of polycaprolactone in trichloromethane.

EFFECT: to provide an external reinforcing coating on the surface of biodegradable vascular prostheses prone to aneurysm formation, and additionally prevents delamination of said prosthesis during operation due to the structural uniformity of its wall layers.

1 cl, 5 dwg, 1 ex

Description

The present invention relates to small diameter vascular grafts that can successfully reproduce natural blood flow and to a device for producing such grafts.

Today, the incidence of atherosclerosis is steadily increasing in the population, including with damage to the coronary arteries and peripheral arterial blood vessels. Consequently, the number of surgical interventions to restore effective blood flow in damaged blood vessels through grafting or bypass grafts is increasing. The best option for surgical treatment of this pathology is the use of autologous material (the patient's own blood vessels), which is currently the gold standard. However, these grafts have limited availability due to previous surgeries involving these vessels, progressive atherosclerosis, and other medical conditions. Furthermore, the harvesting process and subsequent evaluation of the graft before implantation can damage the vessel and lead to endothelial dysfunction, a proinflammatory response, and, ultimately, thrombosis and graft occlusion. High failure rates make this treatment method largely controversial, necessitating the development of artificial alternatives.

Synthetic grafts have proven effective in the replacement of large-diameter vessels. When using these grafts for medium- and small-diameter vessels, a high rate of thrombosis and neointimal hyperplasia was observed, although these grafts are resistant to aneurysm formation. Vascular grafts made of xenogeneic materials are used for the replacement of medium-diameter vessels, but despite their excellent physical and mechanical properties, they are subject to a high risk of thrombosis and aneurysm formation due to wall degeneration. Attempts to use biological grafts for the replacement of small-diameter arteries have been unsuccessful.

One of the promising modern areas involved in the development of small-diameter vascular prostheses is vascular tissue engineering, which allows the use of non-standard types of materials to create medical devices (biodegradable polymers, natural polymers, autologous biological fluids and tissues), as well as original approaches to their manufacture, ensuring the porosity of the created structures and, as a result, the effective migration of vascular cells into the wall of these structures to form new healthy tissue in situ.

Non-woven biodegradable small-diameter vascular prostheses, due to their high porosity and prolonged resorption with the involvement of cells of the monocyte-macrophage system, are capable of complete remodeling with replacement by newly formed vascular tissue, but are susceptible to the formation of aneurysms due to the possibility of desynchronization of the rate of resorption of the main framework of the prosthesis and the maturation of newly formed vascular tissue. It should be noted that the vascular tissue formed during the bioresorption of the biodegradable prosthesis framework, as a rule, lacks elastin fibers and true smooth muscle cells, which aggravates the early occurrence of aneurysms of the remodeled wall of the biodegradable prosthesis under the influence of the pulse wave of arterial blood flow [Antonova L.V., Mironov A.V., Yuzhalin A.E., Krivkina E.O., Shabaev A.R., Rezvova M.A., Tkachenko V.O., Khanova M.Y., Sergeeva T.Y., Krutitskiy S.S., Barbarash L.S. A brief report on an implantation of small-caliber biodegradable vascular grafts in a carotid artery of the sheep. Pharmaceuticals (Basel). - 2020. - V. 13. - No. 5. - P. 101. doi.org/10.3390/ph13050101].

A solution to this problem may be the formation of an external reinforcing coating for biodegradable small-diameter vascular prostheses prone to aneurysm formation.

A method is known for strengthening the wall of a small diameter vascular prosthesis with a spiral located in the middle layer of the prosthesis. Patent US 20230064651 A1 United States (BIPORE MEDICAL DEVICES Inc. Small diameter vascular prosthesis. A61F 2/06. 02.03.2023. 2021-08-30 Priority to US 17/460,429. 2023-02-28 Publication of US 11589975 B1. 2041-08-30 Anticipated expiration. The small diameter vascular prosthesis consists of an outer textile graft, an intermediate self-supporting coil or stent and an inner microporous layer. The outer textile graft provides tissue ingrowth. The inner microporous layer provides impermeability to blood, without preventing the formation of blood clots in the prosthesis. The coil or stent provides resistance to kinking and the formation of aneurysms in the event of destruction of the outer textile and inner microporous layers.

The main drawback of the presented technical solution is the obvious and expected difficulties in creating anastomoses with the vessel being prosthetized, as the coil is a rigid structure, and its ends are difficult to insert into the anastomosis during its formation. Differences in compliance between the coil-reinforced prosthesis wall and the wall of the vessel being prosthetized in the anastomotic area will trigger thrombus formation.

A method for producing a three-layer artificial blood vessel is known (CN 106075596 B, A61L 27/507, China. Preparation technology of three-layer artificial blood vessel. 2016-07-21: Application filed by Nankai University; 2016-07-21: Priority for CN 201610589001.3A; 2016-11-09: Publication of CN 106075596 A; 2021-02-09: Application granted; 2021-02-09: Publication of CN 106075596 B; Status Active; 2036-07-21: Expected shelf life). The blood vessel prosthesis is manufactured in three stages. In the first stage, the inner layer of the artificial blood vessel is fabricated by inkjet printing using biodegradable macromolecules as raw materials and consists of a smooth, compact film-like layer 10-100 microns thick. In the second stage, spirally oriented fibers 5-100 microns in diameter are formed in the middle layer of the vascular prosthesis using one or more of the following technologies: electrospinning, wet spinning, melt spinning, or 3D printing. Because the middle layer of the artificial blood vessel has a structure of micron-sized fibers with a spiral orientation, this allows the artificial blood vessel to withstand blood pressure for a long time after implantation in vivo and protects against aneurysm formation. In the third stage, the outer layer of the artificial blood vessel is fabricated using melt spinning and 3D printing, and the winding of polymer fibers 50-500 microns thick. Thus, the outer layer of the artificial blood vessel is formed by spirally wound coarse polymer fibers that fit tightly to the middle layer, preventing rupture of the blood vessel prosthesis when bent.

The disadvantages of the proposed method are the production of all layers of the blood vessel prosthesis, including the middle antianeurysmal one, from biodegradable polymers (polycaprolactone (PCL), polylactide (PLA), poly (lactide-coglycolic acid) (PLGA), polyglycolic acid (PGA), polyhydroxyalkanoate (PHA), poly (lactide-caprolactone) copolymer (PLCL), poly (p-dioxanone) (PDS), etc.), and the final structural characteristics of each layer (polymer film, spirally oriented fibers produced by electrospinning; coarse spirally oriented fibers obtained by extrusion or 3-D printing), which will not allow all layers to be intimately fastened in one product, which will lead to inevitable delamination of the wall of the blood vessel prosthesis during or after its implantation into the bloodstream.

The closest to the claimed solution is patent No. 173457 "Small-diameter biological arterial prosthesis with external reinforcement" [Text] / Barbarash J.I.C. (RU), Antonova L.V. (RU), Kudryavtseva Yu.A. (RU), Federal State Budgetary Scientific Institution "Research Institute for Complex Issues of Cardiovascular Diseases" (RI CPCCZ) (RU) - 2016125920; declared 28.06.2016; registered 28.08.2017 Bulletin No. 25 - p. 3). The outer reinforcing shell for the preserved xenogeneic vascular prosthesis is formed during the electrospinning procedure or from a pre-fabricated non-woven fabric, which is subsequently intended for wrapping the vascular prosthesis from the outside.

The main drawback of this approach is its use to prevent aneurysm formation in biological prostheses, as it is impossible to achieve intimate adhesion of the reinforcing anti-aneurysmal layer to the biological prosthesis wall, which in turn prevents a high-quality anastomosis with the vessel being prosthetized. Uneven distribution of the reinforcing layer due to the variable topography of the biological prosthesis, especially when the prosthesis is wrapped in prefabricated nonwoven fabric using electrospinning, can lead to uneven stress distribution within the system and reduced structural stability. Furthermore, there is no evidence that storing a biological prosthesis with external reinforcement made of synthetic or biodegradable polymers in a preservative solution is feasible, which is essential for biological prostheses to prevent desiccation and infection.

The technical result of the proposed invention is a method for forming an external reinforcing coating for biodegradable vascular prostheses prone to aneurysm formation. The technical result is achieved by combining the following parameters:

1. The external reinforcing anti-aneurysmal coating of the biodegradable vascular graft will be an outer layer made by electrospinning from thermoplastic polyurethane (PU) such as Tecoflex™ or Pelletane™. Polyurethane is a synthetic elastomer polymer with high biocompatibility and excellent mechanical properties. It is characterized by increased stability in biological systems and is used in the biomedical industry. Manufacturing the external reinforcing coating from polyurethane will preserve the physical and mechanical properties of the grafts similar to those of the native artery, will not add weight to the structure, and will ensure the graft walls are resistant to aneurysm formation due to the extremely low rate of hydrolytic degradation of polyurethane.

2. The production of the main frame of the prosthesis and the outer reinforcing layer from polyurethane will be carried out using a single method - electrospinning, which will prevent delamination of the prosthesis during its use due to the structural uniformity of the layers of the prosthesis wall.

The method for forming an external reinforcing coating of a biodegradable vascular prosthesis prone to aneurysm formation is carried out as follows.

Stage 1. Manufacturing of the main polymer tubular frame of the vascular prosthesis from the biodegradable polymer polycaprolactone (PCL) using electrospinning.

To produce the main polymer tubular framework of the prosthesis, a solution of polycaprolactone in trichloromethane with a mass percentage of polycaprolactone of 8.27% is prepared. For this, 0.6 g of PCL is dissolved in 5.0 ml of trichloromethane, mixing using a magnetic stirrer or ultrasonic bath until a homogeneous polymer solution is formed.

Electrospinning of the polymer solution is performed on the surface of a rotating metal pin with a diameter of 1.5-6 mm at a solution flow rate of 0.2-1 ml/h, an applied voltage of 20-25 kV, a distance of 10-15 cm from the polymer thread exit to the collector, and a collector rotation speed of 200-1000 rpm. The electrospinning process continues until a layer 250-1000 μm thick is formed. The wall thickness of the vascular graft is 250-1000 μm, depending on its diameter.

Stage 2. Formation of the external reinforcing coating of the biodegradable vascular prosthesis.

To create the outer reinforcing coating of the main polymer tubular frame of the prosthesis, a polyurethane solution in trichloromethane with a polyurethane content of 6.99% by weight is prepared. For this, 0.3 g of PU is dissolved in 3.0 ml of trichloromethane, mixing using a magnetic stirrer or ultrasonic bath until a homogeneous polymer solution is formed.

Electrospinning of the polymer solution is carried out on the surface of the manufactured main polymer framework, without removing it from a metal pin of the selected diameter, at a solution flow rate of 0.2-1 ml/h, an applied voltage of 20-25 kV, a distance of 10-15 cm from the polymer thread exit to the collector, and a collector rotation speed of 200-1000 rpm. The electrospinning process is continued until a layer 150-250 µm thick is formed.

The essence of the invention is explained by illustrations.

Fig. 1. Stereomicroscopy of a polycaprolactone vascular prosthesis with an external reinforcing polyurethane coating, magnification x10.

Fig. 2. SEM of a cross-section of a polycaprolactone vascular prosthesis with an external reinforcing polyurethane coating, magnification x100.

Fig. 3. A vascular prosthesis made of polycaprolactone with an external reinforcing polyurethane coating, implanted in the carotid artery of a sheep: A - view of the prosthesis; B - prosthesis with a ruler (length measurement)

Fig. 4. Results of histological examination of a polycaprolactone vascular prosthesis with an external reinforcing polyurethane coating after 12 months of implantation into the carotid artery of a sheep: A - hematoxylin and eosin staining, light microscopy; van Gieson staining, light microscopy; B - alizarin red C staining, fluorescence microscopy; G - orcein staining, light microscopy. Magnification x100.

Fig. 5. Scanning electron microscopy of a polycaprolactone vascular prosthesis with an external reinforcing polyurethane coating after 12 months of implantation into the carotid artery of a sheep: A - cross-section of the wall, magnification x100; B - cross-section of the wall, magnification x200; C - cross-section of the wall, magnification x1000; neoadventitia with vasa vasorum, magnification x200.

An example of implementing the proposed method.

Formation of an external reinforcing polyurethane coating on the surface of a polycaprolactone vascular prosthesis.

Fabrication of a polymer tubular framework for a vascular prosthesis: 0.6 g of PCL with an average molecular weight of 80,000 was added to 5.0 ml of trichloromethane and stirred with a magnetic stirrer at 25°C until a homogeneous polymer solution was formed. Electrospinning was performed using a blunted 22G needle at a voltage of 23 kV, a solution feed rate of 0.5 ml/h, a collector rotation speed of 200 rpm, a distance from the needle to the winding collector of 150 mm, and a needle cleaning time of 30 sec. A stainless steel pin with a diameter of 4.0 mm was used as the collector. The fabrication time for one prosthesis was 4 hours.

Fabrication of the external polyurethane reinforcing coating: 0.3 g of PU was dissolved in 3.0 ml of trichloromethane and stirred magnetically at 25°C until a homogeneous polymer solution was formed. Electrospinning was continued on a pin with a freshly fabricated polyurethane tubular frame using a blunt 22G needle at a voltage of 23 kV, a solution feed rate of 0.5 ml/h, a collector rotation speed of 200 rpm, a distance from the needle to the winding collector of 150 mm, and a needle cleaning time of 30 sec. The reinforcing coating fabrication time was 2 hours.

Evaluation of the effectiveness of the developed technology.

The surface structure of a biodegradable vascular prosthesis with an external reinforcing coating was assessed before and after implantation into the carotid artery of a sheep using an S-3400N scanning electron microscope (Hitachi, Japan) under high vacuum conditions at an accelerating voltage of 10 kV.

The effectiveness of an external reinforcing coating in preventing aneurysm formation in the wall of a biodegradable vascular graft was assessed by implanting 4.0 mm diameter grafts with a reinforcing coating into the carotid artery of sheep (n=5) for 12 months. The morphological characteristics of the explanted vascular grafts were then examined using histological examination and scanning electron microscopy. No signs of aneurysm formation were detected in any case.

Thus, the proposed method for forming an external reinforcing coating of a biodegradable vascular prosthesis prone to aneurysm formation made it possible to achieve 100% efficiency in terms of preventing aneurysm formation of biodegradable prostheses under conditions of long-term implantation into the arterial bed.

Claims (1)

A method for forming an external reinforcing coating of a biodegradable vascular prosthesis, characterized in that an external reinforcing coating is formed on the surface of the main polymer tubular framework of the biodegradable vascular prosthesis by electrospinning from a solution containing 6.99 wt.% of thermoplastic polyurethane selected from the Tecoflex or Pelletane brands in trichloromethane, wherein said main polymer tubular framework is obtained by electrospinning from a polymer solution of polycaprolactone in trichloromethane.