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Technical Q&A

Re-Sterilisation

Can your sealed and unsealed grafts be re-sterilised?

All Vascutek Ltd Unsealed Vascular Prostheses are sterilised using Ethylene Oxide gas and are supplied sterile for single use only. 

Any attempt to re-sterilise or reprocess this device in any way, may render it unfit for its intended use and may result in risk to the patient.

Vascutek Ltd GelatinSealed Vascular Prostheses

Any attempt to resterilise or reprocess these devices in any way will render them unfit for the intended use and will result in a risk to the patient.

 

Packaging

Packaging

Why do you use an outer foil pouch for packaging your sealed grafts?

All Vascutek Ltd. sealed grafts are double blister packed and, together with a dessicant, are sealed in an outer foil pouch.

A unique feature of our gelatin sealant enables its removal by in vivo hydrolysis alone. Exposure to moisture, other than pre-soaking the graft in saline, heparin, rifampicin or any combination of these immediately prior to implantation should be avoided. The foil pouch acts as a vapour barrier, which together with the silica gel sachet prevents hydration of the sealant and maintains the graft's optimal characteristics. An illustration giving the packaging opening sequence is shown here.

Packaging opening sequence

It should be noted the foil pouch and outer blister are not sterile. Only the innermost blister may be introduced to the sterile field.


 

 

What should I do if we have opened the sealed graft pouch but do not immediately use the product?

Opening the foil pouch and subsequent exposure of the graft to moisture will cause hydrolysis.  However the graft may still be safely used providing it is implanted within 1 month of its removal from the foil pouch (Data on file, Vascutek Ltd 2005). Beyond this time period the product should be destroyed by the user and not returned to Vascutek Ltd., as it cannot be reprocessed.

The graft must not be re-sterilised as this will compromise product performance and patient care.

 

Vascutek Gelatin

Vascutek Gelatin

What is gelatin?

Gelatin is a protein that is not a naturally occurring substance but is derived from a parent protein collagen that is highly water insoluble.

The collagen fibre consists of a network of tropocollagen fibres which when exposed to heat or chemical processes is transformed into water soluble gelatin molecules.1

Collagen Fibre

The gelatin molecule may then be stabilised during the manufacturing process using a chemical cross-linking agent.

Vascutek's sealed grafts use a unique patented minimally cross-linked mammalian gelatin in order to achieve zero porosity at implantation. Post implantation this modified sealant undergoes controlled hydrolysis over a period of 14 days allowing earlier cellular ingrowth which does not significantly alter or delay normal healing, which might not be the case with sealants that are retained for a longer period (2)

References (Click to expand)

  1. Kambic H et al. 
    Biolized Surfaces as Chronic Blood Compatible Interfaces
     
    Biocompatible Polymers, Metals and Composites. Ed M Szycher, Technomic Pub Co Ltd.  pp179-198, 1983.
  2. Drury J K et al.
    Experimental and Clinical Experience with a Gelatin Impregnated Dacron® Prosthesis
    Ann Vasc Surg 1987, 542-547.

How can Vascutek modified gelatin be broken down by hydrolysis alone?

Vascutek uses a unique, patented, partially succinylated gelatin formulation where a specified proportion of amino groups have been replaced by carboxyl groups.

A controlled level of cross-linking, i.e. chemical bond formation, between the amino groups is thus achieved (1). The remaining bonds between the amino groups are susceptible to hydrolytic breakdown alone allowing the sealant to be removed in a controlled manner within 14 days (2,3).

Comparative Sealant HydrolysisComparative Sealant Hydrolysis

Unlike other sealants, no enzymatic activity is required to facilitate this process.

References (Click to expand)

  1. US Patent No. 4,747,848
  2. Data on file at Vascutek Ltd.
  3. Drury J K et al.
    Experimental and Clinical Experience with a Gelatin Impregnated Dacron® Prosthesis.
    Ann Vasc Surg 1987, 542-547.

 

Surgical Technique

Surgical Technique

Can Gelweave™ be used without a cautery?

Cauteries are commonly used to tailor grafts for specific patient needs. Due to the perpendicular arrangement of the polyester yarns within all woven products, this type of structure is more prone to fraying when cut with scissors. This characteristic may lead to reduced suture retention.

The unique twill woven structure of Gelweave™ reduces the degree of fraying, leading to improved suture retention. However, as with all woven products the use of a cautery is still recommended. In common with other textile grafts its immersion in saline immediately prior to use will prevent focal burning that may result during cauterisation.


What are the dilatation characteristics of knitted vascular grafts?

All conventional warp knitted grafts show a degree of dilatation under blood pressure due to polyester yarn re-orientation within the wall structure post implant.

The phenomenon of knitted graft dilatation is not new.  Nunn et al have reported a series with up to 138 months follow-up in 1979 (1). Subsequent research by a number of authors confirmed this observation (2,3,4). In one of these earlier studies, no association between dilatation and graft complications was found (3).

Conversely woven products exhibit significantly less dilatation since the yarns are arranged perpendicular to one another thus allowing minimal re-orientation and resultant dilatation.

Vascutek has developed a unique patented Köper knitted product, Gelsoft™ Plus, a new generation of vascular graft that minimises the level of dilatation while retaining the excellent handling associated with conventional knitted grafts. This is achieved by the yarns being arranged perpendicular to one another on the internal graft surface i.e. more typical of a woven structure.

ConventionalConventional

 

KöperKöper

Comparative SEM's of Knitted Graft Structures

This significant development can be illustrated using a pulsed pressure model in vitro5.

Comparative Graft Dilation

Comparative Graft Dilatation
Pulsed Pressure Testing 80-120mmHg over 30 days.

Animal studies confirm the excellent radial stability of Gelsoft™ Plus over the long-term6. Clinical data from a prospective, multicentre, randomized trial with 6 months follow-up showed Gelsoft™ Plus dilated significantly less than the conventionally knitted Hemashield Microvel®, i.e. up to a mean of 18 v 33% respectively7.

Whilst the long-term clinical significance of knitted graft dilatation is not known, it is however, clearly desirable to minimise this phenomenon. This has been achieved with the development of Gelsoft™ Plus.

References (Click to expand)

  1. Nunn DB et al. 
    Postoperative alterations in size of Dacron® Aortic Grafts.
     
    Ann Vasc. Surg (1979); 189: 741-744.
  2. Cavallaro A et al. 
    In vivo
     study of Dacron® Aortic Grafts through B-Mode Ultrasonography. 
    J Ultrasound Med, 4: 235-238, May 1985.
  3. Blumenberg RM et al. 
    Clinical Significance of Aortic Graft Dilation.
     
    J Vasc Surg 1991; 14: 175-180.
  4. Nunn DB et al. 
    Dilative Characteristics of Microvel® and Vasculour™ II Aortic Bifurcation Grafts.
     
    J Biomed Mat Res Vol. 30, 41-46, 1996.
  5. Walker D et al. 
    Novel Structure for a Polyester Vascular Prosthesis with Improved Mechanical Properties.
     
    Society for Biomaterials. March 1995.
  6. Guidoin R et al. 
    In Vitro
     and In Vivo Studies of a Polyester Arterial Prosthesis with a Warp-Knitted Sharkskin Structure. 
    Journal of Biomedical Materials Research (1997) 35, 459-472.
  7. Goëau-Brissonnière, Olivier et al. 
    Can Knitting Structure Affect Dilation of Bifurcated Polyester Prostheses? A Randomized Study with the Use of Helical Tomographic Scanning.
    J Vasc Surg 2000; 31: 157-163.

Can I remove the support on Vascutek externally reinforced grafts?

The support may be peeled where it extends to the ends of the prosthesis, in order to facilitate the fashioning of the anastomosis.  ePTFE grafts with central support and polyester Equi-Flo™ (Axillo-bifemoral) and femoro-femoral grafts are designed so that the external support does not need to be removed.

To remove the spiral support, gently lift the end of the support with gloved hands or atraumatic instruments.  Unwind the support by peeling at a right angle to the graft (Figure A).  Rapid unwinding and/or removal of the support parallel to the axis of the graft may damage the product (Figure B).  In addition, the use of surgical blades or sharp instruments to remove the support may damage the graft.

Figure AFigure A

Figure BFigure B

What types of sutures are recommended for use with our polyester prostheses?

Round body taper point needles should be used in order to minimise fibre damage.

The use of cutting needles is contraindicated as this may compromise graft integrity and suture retention.

Can thrombolytic agents be safely used with sealed grafts?

It is difficult to predict the effect of thrombolytic agents on any sealed polyester graft.

Thrombolytic agents are unlikely to affect sealants, however, opinions vary regarding their safe use in association with polyester grafts.

In normal circumstances haemostasis would be maintained by fibrin deposition. Thrombolytic agents could lyse this fibrin leading to transgraft bleeding. In a clinical setting this may occur even after a long implant duration1.

In contrast to these clinical findings an animal model showed no problem2.

The reason for the unpredictability of thrombolytic agents on polyester grafts is unclear and as a manufacturer it is inappropriate to give instructions on clinical practice.

An excellent review on the general use of thrombolytic therapy written by Belkin et al is worthy of note3.

References (Click to expand)

  1. Rabe FE, Becker GJ, Richmond BD, Yune HY, Holden RW, Dilley RS and Klatte EC. 
    Contrast Extravasation Through Dacron Grafts: A Sequella of Low-Dose Streptokinase Therapy.
     
    AJR 1982; 138: p917-920.
  2. Trudell LA, Whittmore-Brigham AD. 
    Performance of Sealed Dacron Vascular Grafts in Intra-Arterial Thrombolytic Therapy.
     
    J of American Society for Artifical Internal Organs. Supp Jan-Mar 1995. Vol 41, pp 107.
  3. Belkin M. 
    Thrombolytic Therapy for Arterial Disease.
     
    Advances in Vascular Surgery. Whittemore et al Eds. Vol 1, 1993; p191-211.

Can vascular grafts be damaged if exposed to x-rays?

No, vascular grafts cannot be damaged if exposed to x-rays.

The largest routine dose of x-ray radiation comes from a chest/abdominal CT Scan which is commonly used for post-operative graft monitoring. This is equivalent to around 400 chest x-rays.

Polyester (PET) Grafts are routinely sterilised by gamma radiation with a dose that exceeds the x-ray dose by a factor of more than 3 x 10^6.

Polytetrafluoroethylene (PTFE) is more radiation sensitive than PET. The literature2 quotes a dose range of 0.01 Mrad to 0.1 Mrad as the minimum to affect the physical properties. 0.01 Mrad exceeds the maximum x-ray dose by a factor of greater than 1.2 x 10^4

Therefore, it is clear that neither PTFE nor PET grafts are likely to be affected by the levels of radiation used in diagnostic x-ray procedures.

References (Click to expand)

  1. Making the best use of a Department of Clinical Radiology:Guidelines for Doctors: 
    4th Edition 1998; p 13. ISBN 1-872599-37-0.
  2. The Effects of Sterilization Methods on Plastics and Elastomers.
    Gamma Radiation Resistance; 1994 Edition; p 74-75.  ISBN 1-884207-10-3.

 

Products

Products

What is the Equi-Flo™ graft and can you explain the benefits it offers?

Equi-Flo* is an externally reinforced graft unique to Vascutek Ltd. It represents a novel concept in bifurcated axillo-bifemoral product design compared to traditional 90° angle configurations.

Equi-Flo's symmetrical bifurcated "flowsplitter" at the junction of the proximal and 2 distal graft limbs provides superior haemodynamic flow characteristics over the bifurcation area1. Significantly improved patency rates have been shown for Equi-Flo v 90° angled products ie. 84% v 38% respectively after 2 years follow-up2.

Available as Gelsoft™, Gelsoft Plus™ and Gelseal™ materials in a variety of configurations to cover the full range of physiological requirements.

References (Click to expand)

  1. How T V et al. 
    Assessment of pressure drop flow rate relationship of axillo-bifemoral bypass grafts.
     
    Proc. Instn Mech Engrs Vol. 205: 243-249; 1992.
  2. Wittens C H A et al. 
    European Prospective Randomised Multi-Centre Axillo-bifemoral Trial
     
    Eur J Vasc Surg 6, 115-123 (1992).

What is Fluoropassiv™?

Fluoropassiv™ is the first macroporous fluoropolymer coated, gelatin sealed, knitted vascular biomaterial. It combines the strength and supple handling of polyester with the inertness and low thrombogenicity of a fluoropolymer. These factors make it ideally suited for carotid patching and peripheral medium bore graft applications*

Fluoropassivation is the coating process by which the fluoropolymer is incorporated into the graft matrix. Unlike other coating techniques, liquid phase technology is used ensuring complete penetration of the structure. Fluoropolymer molecules bond with the polyester forming an "Interpenetrating Molecular Network" at the interface between the two polymers.

image013Interpenetrating Molecular Network

The fluoropolymer is fully integrated into the polyester matrix completely covering each polyester fibre with an extremely thin layer ie. 10 nanometres thick. Zero-loss Energy Filtered Transmission Electron Microscopy (TEM) at 275,000 x magnification of a single fluoropassivated polyester fibre surface identifies 3 discreet layers1.

image014Surface Transverse Cross-section of a single fluoropassivated polyester fibre

The fluoropolymer coating durability has been confirmed using fluoropolymer chemical assays under accelerated simulated use as well as stress and adhesion tests2,3.

*Grafts not approved by the FDA for use in the USA and is subject to local regulatory approval in all other countries

References (Click to expand)

  1. Dr L Tetley 
    Zero-loss Energy Filtered TEM
     
    Institute of Biomedical and Life Sciences, University of Glasgow, Scotland.
  2. Altec Laboratory Services (Scotland) Ltd 1994.
  3. Data on File at Vascutek Ltd.

Can Fluoropassiv™ Thin Wall Carotid Patches be used for Peripheral Angioplasties?

Yes, due to the Fluoropassiv™ biomaterial's low thrombogenicity1,2,3, superb handling characteristics, conformability and strength4, these patches are ideally suited for peripheral angioplasty procedures.

References (Click to expand)

  1. Ashton T et al. 
    Platelet Thrombogenic Response to Polyester can be Passivated by Fluoropolymer Surface Treatment.
     
    European Society for Biomaterials (1995).
  2. Rhee R et al. 
    Experimental Evaluation of Bleeding Complications, Thrombogenicity, and Neointimal Characteristics of Prosthetic Patch Materials used for Carotid Angioplasty.
     
    Cardiovascular Surgery (1996). Vol 4, No. 6, pp 746-752.
  3. Chinn J A et al. 
    Blood & Tissue Compatibility of Modified Polyester: Thrombosis, Inflammation and Healing.
     
    J Biomed. Mat. Res (1998), Vol.39, 130-140.
  4. Data on File at Vascutek Ltd.

Why does Vascutek Ltd. not have a Fluoropassiv™ Bifurcate product?

Fluoropassiv™ technology was specifically developed for peripheral/medium bore applications where there is reduced flow and the low thrombogenicity of biomaterials is paramount in achieving good patency1.

References (Click to expand)

  1. Reid DB et al. 
    A Postoperative Study of 100 Gelatin-Sealed Aortic Grafts. 
    Ann Vasc Surg 1991, 5 : 320-324.

How does the patency rate of Fluoropassiv™ compare to other materials?

Fluoropassivation is a unique and patented surface modification technique allowing fluoropolymer molecules to bond with and completely cover the surface of each fibre within the graft polyester matrix. This produces a new biomaterial, Fluoropassiv™, the first macroporous fluoropolymer.

Historically, polyester, and ePTFE have been shown to exhibit equivalent patency in above knee peripheral procedures1,2,3,4.

ePTFE vs Polyester

Comparative ePTFE V Polyester Primary Patency
Performance in Peripheral Procedures

Fluoropassiv™ in vitro & in vivo exhibits significantly reduced thrombogenicity compared to polyester5,7, and comparative thrombogenicity to that of ePTFE has also been demonstrated in vivo6.

Gloviczki's Group

 

Hansons Group

Gloviczki's Group
Mayo Clinic,Rochester, USA.
Dog model6
  Hanson's Group
Emory School of Medicine, Atlanta, USA
Baboon arteriovenous shunt model7

Platelet deposition comparison

References (Click to expand)

  1. Rosenthal R et al. 
    Prosthetic Above-knee Femoropopliteal Bypass for Intermittent Claudication.
     
    J.Cardiovasc Surg, (1990) 31, 462-468.
  2. Abbott W M et al. 
    Prospective Above-knee Femoropopliteal Bypass Grafting : Results of a Multicenter Randomized Prospective Trial.
     
    J Vasc Surg (1997); 25, 19-28.
  3. Robinson B I et al. 
    A prospective randomized multicentre comparison of expanded polytetrafluoroethylene and gelatin-sealed knited Dacron grafts for femoropopliteal bypass.
     
    Cardiovascular Surgery (1999), Vol 7, No 2; 214-218.
  4. Van Det et al. 
    PTFE or Dacron for Femoropopliteal Above-knee Bypass : A Multicentre Randomized Prospective Trial.
     
    Abstract, European Society for Vascular Surgery (1998) October, Paris, 140.
  5. Ashton T et al. 
    Platelet Thrombogenic Response to Polyester can be Passivated by Fluoropolymer Surface Treatment.
     
    European Society for Biomaterials (1995).
  6. Rhee R et al. 
    Experimental Evaluation of Bleeding Complications, Thrombogenicity, and Neointimal Characteristics of Prosthetic Patch Materials used for Carotid Angioplasty.
     
    Cardiovascular Surgery (1996). Vol 4, No. 6, pp 746-752.
  7. Chinn J A et al. 
    Blood & Tissue Compatibility of Modified Polyester: Thrombosis, Inflammation and Healing. J Biomed.
     
    Mat. Res - (1998), Vol 39, 130-140.

 

Contact Vascutek

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Registered Office:
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Inchinnan
Renfrewshire PA4 9RR
Scotland UK

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Tel: 00 44 141 812 5555
Fax: 00 44 141 812 7170


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