Medical Adhesives and Sealants

1. Medical Adhesives and Sealants

2. Adhesion Definition: The state at which two surfaces are held together by interfacial forces, which may consist of all known chemical attractive forces, as well as mechanical interlocking action or both.

3. Adhesive • A substance capable of holding materials together in a functional manner by surface attachment (performance). A general term that includes cement, glue, mucilage and paste.

4. Sealant • A material applied to a joint in paste or liquid form that hardens or cures in place, forming a barrier against gas or liquid entry.

5. Adhesives and Sealants-Biomaterials? • Join components of medical devices-Mechanical fastening; • Prevent corrosion; • Resist fatigue; • Fill space – smooth contours-joining prosthesis to bone; • Wound sealing & closure

6. Adhesive Materials can be classified in a number of ways: • Natural or synthetic polymer base; • Thermoplastic or thermosets; • Physical form (one or multiple component, films, etc) • Functional type (structural, hot melt, pressure sensitive; • Chemical families (epoxy, silicone, etc.)

7. General Considerations in the Application of Adhesive Bonding • When applied adhesives have to 'wet' the surface; • They need to be mobile and flow into all the tiny nooks and crannies of the substrate; • If the adhesive does not wet the substrate well, poor adhesion is likely to be a result; • Once good wetting takes place, an adhesive needs to become solid and not flow at all. This is called setting or curing (polymerization); and, • Positional indication (imaging).

8. Adhesive Joint Breaking strength is determined by: • Mechanical properties of the materials of the joint; • The extent of the interfacial contact (number, extent, type and distribution of voids); • Presence of internal stresses; • The joint geometry; and, • The details of mechanical loading.

9. Adhesives are Polymers • Thermoplastics • Thermosets • Available as solids, liquids and pastes and most can be supported by films of various thickness.

10. Adhesives • Acrylics • Epoxies • Polyurethanes • Silicones

11. Bonding Mechanisms • Mechanical Interlocking; • Formation of covalent bonds across the interface; • Electrostatic Attraction-dominant • Forces are not significant beyond 0.5 nm-therefore contact is necessary

12. Surface Treatment • No treatment (low cost poor reproducibility); • Solvent wiping; • Vapor degreasing; • Mechanical abrasion; • Plasma treatment; • Etching; • Chemical deposition-primers, organosilanes

13. Modes of Failure A uniform stress pattern in an adhesive joint is seldom produced by the application of external force. • Structural failure • Adhesive failure • Cohesive failure

14. Urethanes • Urethane polymerization-diisocyanate and a diol or diamine • Two part system- mix, spread and cure; • Flexible joint and sealing agent.

15. Poly (methyl methacrylate) PMMA R-Group Bone Cement

16. Selection of the starting monomers • C4-C12-alkyl acrylates supply the initial adhesion owing to the low glass transition temperature (Tg).

17. Cure Profile of Condensation versus Addition Polymerization Addition polymer Condensation polymer Degree of Cure -----> Time

18. Cyanoacrylates • In 1959, a variety of cyanoacrylate adhesives were developed, some types of which are now used for surgical purposes in US, Canada, and Europe. These glues polymerize on contact with basic substances such as water or blood to form a strong bond. • The first glue developed was methyl cyanoacrylate, which was studied extensively for medical applications and was rejected due to its potential tissue toxicity such as inflammation or local foreign body reactions. Methyl alcohol has a short molecular chain which contributes to these complications. • By changing the type of alcohol in the compound to one with a longer molecular chain, the tissue toxicity is much reduced. All the medical grade tissue adhesives currently available for human use contain butyl-esters.

19. Cyanoacrylate adhesives were first used on wounded soldiers in Vietnam: a quick spray over the wounds stopped bleeding and bought time until conventional surgery could be performed. • Midwives found cyanoacrylate glue and medical cyanoacrylate glues useful as the tissue adhesives. Some even used Super Glue successfully in lieu of suture to close the perineum. • Surgeons have used household cyanoacrylate adhesive to apply sutureless pericardial patches that stopped bleeding in critically injured patients with torn or ruptured myocardium. Cyanoacrylates are also used in repairing corneas and retinas and as synthetic skin in treating severe burns.

20. Methyl 2- cyanopropanoate R-Group Methyl -cyanoacrylate monomer polymerizes in the presence of trace amounts of almost any electron-donor compound (the initiator) by anionic vinyl polymerization, examples include water, alcohols, amines, carboxylate ions, and electron rich olefins.

21. Medical grade products currently available contain either butyl, isobutyl or octyl esters. They are bacteriostatic and painless to apply, break down harmlessly in tissue by hydrolysis and are essentially inert once dry. • Butyl products are rigid when dry, but provide a strong bond; octyl products are more flexible when dry, but produce a weaker bond. • Histoacryl Blue (n-butyl cyanoacrylate) has been used extensively for a variety of surgical applications including middle ear surgery, bone and cartilage grafts, repair of cerebrospinal fluid leaks, and skin closure -- adhesives appear are basically safe. • DMSO (dimethyl sulfoxide) or acetone serve as removers.

22. The Market • The global medical and surgical sealant market is $542 million (2001) and growing rapidly (19% annually), driven particularly in the U.S. • Adhesives and sealants are a critical component of medical devices. • Seven and a half million people receive medical device implants annually. • As medical devices become smaller and more complex, greater demands are being made on the materials and components used in them. • Medical devices are being exported from the U.S. to foreign countries at an increasing rate. • Devices intended for the growing markets of South America and the Pacific Rim must be engineered to be cheaper and more rugged than in the US.

23. Considerations • One mitigating factor when it comes to the advancement of new technologies in the adhesives market is the speed with which the adhesive can be applied on the production line and how long it takes before the finished product can be placed on the market. • This is an area where UV-curable adhesives have made the strongest technological advances of any of the newer technologies currently on the market.

24. Light Cure Systems • Designed for high speed cure on demand medical product assembly. • Solvent free • Wide range of viscosities designed for automated dispensing

25. Light Cure Adhesives • consist essentially of low or medium molecular weight resins (called oligomers), monofunctional or multifunctional monomers, photoinitiators and/or photosensitisers; • wavelengths of 365-250nm. • typically 5-15 seconds at 80-100 mW/cm2 is sufficient for curing adhesive • visible light curing materials (e.g. resins used in dental restoration or for bonding and sealing photo-optic devices) can be cured with blue light (wavelength = 470nm).

26. Typical Applications • Bonding latex balloon onto PVC lumen in catheters. • Bonding high pressure latex balloons onto urethane lumens in high pressure catheters. • Bonding balloon to multi-lumen tubes in angioplasty, thermo dilution, foley and high pressure catheters. • Bond needle to tubing in winged infusion sets.

27. Flexible Adhesive Applications • Bonding/sealing tracheal tubes made of silicone rubber. • Bonding/sealing extruded silicone parts, colostomy, ileostomy, urostomy bags and appliances. • Bonding/sealing the balloon to the tracheal tube. • Bonding/sealing the cuff and tube assemblies in endotracheal, tracheotomy, gastrostomy devices, foley catheters and other fabricated silicone parts. • Sealing of inflators.

28. Pressure-Sensitive Adhesives • Arcylics on PET • Labels-many medical devices require a label that can be printed after the adhesive has been applied and/or can be written on after application to the device. • Adhesive tapes for attaching equipment drapes in sterile environment applications. • Lidding-effective protective barrier against contamination for storage or shipping; • EKG electrode bonding;

29. Surgical Drapes

30. Chemistry Benefits Limitations Typical Applications Cyanoacrylate Substrate versatilityRapid cureAdhesion topolyolefins withprimers Thermoplastic resinwhen curedPoor peel strength,rigidRefrigerationrequired Catheter componentsTube-set bondingPolyolefin bonding Light-CurableAcrylic Substrate versatilityGood resistancepropertiesCure on demand Capital expenditurefor light-cureequipment Needle assemblyAnesthesia masksHeat exchangersOxygenatorsTube-set bonding Epoxy Substrate versatilitySuperior thermaland chemicalresistanceLow shrinkageHigh gap filling Poor peel strength,rigidExothermic reactionTwo-part systemsrequire mixing Needle assemblyDeep section potting Polyurethane Substrate versatilityHigh peelGood resistanceproperties Moisture sensitivityPrimers required forsome substratesTwo-part systemsrequire mixing Deep section pottingBonding of tips ontovarious components

31. Benefits of Adhesives • Joins dissimilar materials • Even stress distribution • Fills large gaps • Seals and bonds • Easily automated • Aesthetically acceptable

32. Limitations of Adhesives • Requires cure • Requires fixture time • Can be messy • Requires chemicals in plant