An Informative Guide to Soft Tissue Replacement Implants
Soft tissues play an important role in our body. They are substances that connect, support, and surround structures other than bone. These substances act as connective elements and also act as elements of transportation. Some examples are skin, fascicle, ligament, tendon, muscle, nerve, fat, and blood vessels. They are produced by the fibroblasts and contain an extracellular matrix with the following composition.
Collagen+ Elastin + Ground substance= Extra Cellular Matrix (ECM)
These structures are highly delicate and the implants used for the replacement of such soft tissues are called soft tissue replacement implants. The following are the properties needed for soft tissue implants:-
- Resemble the soft tissue to be implanted
- Biocompatible (non toxic, non-carcinogenic, non-inflammatory, non-allergic)
- Stable, easy to apply, cost-effective, patient-friendly
- must be delicate and not induce any thick encapsulation
The following are the different types of soft tissue implants covered in this blog:-
- adhesive tapes
- tissue adhesives
- percutaneous and skin implants
Sutures are nothing but a thread that is attached with a stainless steel needle. They are used to close the cut that was done surgically. The following are the properties of a good suture.
- in-vitro retention strength
- needle holding strength
- needle penetration force
- knot security
- ease of knotting
The following flowchart represents the classification of sutures.
Catgut is the first-ever known natural suture material. It is made from the submucosa of the sheep’s intestine. It generally prevents adsorption (decay) for 2 weeks and treating it with chromic salt can make it to prevent decay for 3 weeks. This suture is kept in a fluidic medium in order to maintain the necessary moisture and compliance.
Polyglycolide (PG) is the first-ever made synthetic suture material. This material has modulus and it can resist adsorption up to 4 months and this can be improved using 90/10 glycolide lactide copolymer. The tissue response for such materials are up to a week and can increase in case of contaminated materials.
These are materials that get hydrolyzed or get acted upon by proteolytic enzymes. These are used for patients who wouldn’t require suture removal or correction procedures. After some weeks, the suture will degrade completely without leaving any material behind for immune reactions. Some notable examples are catgut, PLA, PCL, and PG.
These are used in high-stress and pressure environments like the heart and bladder where adsorbable sutures fail to work. These sutures cause a less immune response, and scarring, and withstand high stress. These have to be kept permanently or have to be removed. These don’t degrade. Some examples are silk, polyester, polypropylene etc.
These are white, translucent pressure-sensitive materials that are used to hold the wound dressing. These are white due to the presence of zinc oxide, which prevents infections. They are meant to reduce necrosis, scarring, and abscess formation in host tissue. Tapes have been successfully used in assembling a scrap of tissue graft and neural correction in nerve regrowth. Misalignment in the edges, poor adhesion in wet wounds, and separation would be some considerable problems in surgical tapes.
Tissue adhesives are used for tissues that are exceptionally soft and delicate and can’t handle a suture needle due to mechanical damage and stress. The following are the properties of an ideal tissue adhesive.
- Non-interference with the normal healing process
- Easy application
- Rapid polymerization in presence of heat or moisture
- Wet nature and easy bonding
The two best examples of tissue adhesives are fibrin and cyanoacrylate. Fibrin is a natural material that is responsible for clotting blood in a human blood vessel. It is used widely in the U.K but not in the U.S due to its risk of contamination of hepatitis, since it is prevalent there. It has limited mechanical strength and is an ideal sealant for bone and skin grafts.
Cyanoacrylates are made from formaldehyde and cyanoacetate. When this compound comes in contact with moisture, a rapid polymerization occurs, hence forming a bridge between two ends of the skin. This reaction often releases heat. Dermabond is the most advanced type of cyanoacrylate. It has less toxicity and it reaches maximum bond strength in 3 minutes. The natural healing mechanism of the human body takes around 10 days to achieve the same strength. The only problem associated with tissue adhesive is the lowered mechanical strength and less predicted in vivo performance.
These are the implants inserted inside the body through a needle puncture. Classic examples are hemodialysis catheters, pacemaker chargers, and TENS. The following flowchart shows the factors to be considered for the design of such an implant.
Hydroxyapatite and laminin-5 are some promising materials for implants. All implant materials till now arent completely satisfactory, producing some errors. Hence research is going on in this field. Artificial skin is a type of percutaneous implant.
Used to adhere to large areas affected by burns and wounds to prevent loss of fluid, and electrolytes and to aid in the normal healing process. Cross-linked collagen and polysaccharide composite was used along with surgical tape for face skin grafting. Apart from those, reconstituted collagen, vinyl chloride, and acetate are used as wound dressings. Nylon mesh, alcohol sponges, silicone rubber, and woven fabric were used to reduce evaporation at the site and induce tissue growth. Implanting of allogenic fibroblast is a good solution for long-term skin replacement.
The problems that are associated with percutaneous implants are:-
- difficult maintenance of attachment over dermal surfaces
- down growth of epithelium over material leads to extrusion
- extra growth of epithelium over material leads to invagination
- the opening would be large enough for bacteria to enter and contaminate
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