Polymer Basics for Polyamides

Chemists and life scientists define polyamides as polymers whose repeating molecular units are chained together with amide links. These materials integrate hardness, durability, flexibility, and resistance. Their applications cover many fields, but their use in medical device and biotech areas is becoming much more prevalent. 

Characteristics and Properties of Polyamides

These multiple-unit molecules include proteins and peptides, natural polymers that consist of amino-acid repeating units. Silk and wool are examples of naturally occurring polyamides.

Other forms of polyamides are synthetic polymers, including flexible fibers such as nylon. Manufacturers use this material in both industrial and medical applications. Specific classifications for nylons depend on the number of carbon atoms the molecule the material contains. Researchers generally classify those that have 85 percent or more joined together by phenyl rings as aramids. They classify polyamides whose rate falls below that as nylons. Kevlar is a synthetic aramid fiber that is five times stronger than steel.


Production Methods

The production of polyamides involves polymerization chemistry, which requires the joining of two groups with amide links. All amides have the basic chemical formula CO-NH.

There are several methods to produce polyamides. The first involves the condensation reaction model. In living organisms, enzymes condense amino acids with one another to form amide linkages called peptides. These reactions result in polyamides called polypeptides. The amino acids are single aliphatic monomers that react with identical molecules to form a polyamide, which focuses on the amine (NH2) and carboxyl (CO2H) acid groups.

In laboratories, chemists use an artificial condensation reaction to produce nylon polymers, which must contain a straight aliphatic monomer. Scientists use an amine group (known as an amino group) and a carboxylic acid group to produce the amide links. 

The second production method relies on the polymerization of amino acids and amino acid derivatives to produce aromatic polyamides. Producers use the reactive acyl chloride as a monomer to produce polyamides and aramids (used in Kevlar material).

The chemical process eliminates hydrogen chloride using an amine group. Individuals may also use an acid chloride synthesis to avoid heating and obtain an instant result.

Aromatic moiety doesn't participate in an elimination reaction, but it does boost the material's resulting rigidity, strength, and durability.                   


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Common Uses in Medical Devices and Life Sciences

Clothing manufacturers regularly incorporate nylon into fashion apparel since consumers can easily maintain this material. Manufacturers also use nylon in several industrial applications, including seat belts, nets, airbags, ropes, tarpaulins, thread, and fishnets.

Today, nylon has applications beyond the fashion industry. Medical device manufacturers have also found uses for this material in the following areas:

  • Monofilament sutures – Surgeons use these sutures during microsurgery. Since they are monofilaments, they don't have interstices that can augment bacterial growth. They also don't adhere to tissue, so they cause minimal irritation. Trauma patients tolerate these sutures better than other types.
  • Nylon-coated medical instruments – These products use a thermoplastic powder resistant to abrasions and chemical wear (such as hydrocarbons). They are also able to withstand sterilization and cleaning processes.
  • Catheters – This lightweight nylon equipment is excellent in balloon applications that require more compliance than PET balloons. They are better for catheters that require stability and high precision tolerance at all atmospheric moisture content levels. It also resists crushes, cracking, tears, and punctures.

Other medical uses include:

  • Artificial hearts
  • Surgical drains
  • Feeding tubes
  • Dialysis devices
  • Hypoallergenic gloves
  • Hospital bedding
  • Compression stockings
  • Instrument cables
  • Wound dressings

Best Sterilization Methods for Polyamides

Suitable forms of sterilization include Ethylene Oxide gas (EtO) and electron beam (E-beam). EtO can sterilize materials that are too sensitive for heat or radiation sterilization, and most polyamides fall into this category. This poisonous, flammable gas requires careful handling, and although the process is complex, EtO is suitable for large-volume sterilizations.

Gamma irradiation and electron beam (E-Beam) sterilization are other potential methods to cleanse polyamides. E-beam irradiation is a more suitable sterilization method than gamma due to its lower penetrating power, resulting in less chemical degradation.

Scientists discourage two forms of sterilization for polyamides, steam (autoclave) and dry-heat, for polyamides. Heat during the autoclaving process can degrade these fibers, and dry heat is not suitable due to the low thermal conductivity of plastics.


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