Artificial cornea is a special device made of foreign body molding materials. In 1817, Weber implanted crystals into the cornea of patients for the first time, creating the history of artificial cornea transplantation.
However, the development of artificial cornea is not smooth sailing, and its development process can be roughly divided into the following four stages
❶ exploration period (early 18th century ~ early 20th century)
❷ stagnation period (early 20th century to 1930s)
❸ recovery period (1930s-1960s)
❹ development period (after 1960s)
During this period, the design and materials of artificial cornea were also "updated".
There are many types of artificial cornea design, but the most commonly used one is composed of a transparent lens column and a peripheral support of a fixed lens column. Most of the mirror columns are made of PMMA materials, while the supports are made of various materials, including PMMA, titanium metal, nylon, polyester, polytetrafluoroethylene, and self teeth. Michal artificial cornea is composed of PMMA optical lens column and titanium stent.
So, what are the materials for making the artificial corneal scaffold and lens column? What are the advantages of the two materials used in the Michaelis artificial cornea? Look down.
Optical mirror column material
The material requires good optical performance, light transmittance greater than 90%, and high refractive index.
○ hydrogel
Polyhydroxyethyl methacrylate (pHEMA) hydrogel has a water content of 20% ~ 70%, has certain permeability to electrolyte, gas and glucose, and has good transmittance and diopter. However, long-term fixation and surface epithelial activation still need to be solved. Later, it was found that there was calcium deposition on the surface of pHEMA, indicating that the surface calcification was obvious.
○ polymethylmethacrylate (PMMA)
In the field of Ophthalmology, PMMA is a commonly used material for corneal contact lens, artificial lens and artificial eye piece. It has the advantages of stable property, high transmittance (92%), large refractive index, no degradation by biological oxidation reaction of the body, light biological reaction to the body, and convenient processing. It is an ideal optical material, and has been proved to have good biocompatibility in clinic.
After the successful application of PMMA intraocular lens in the clinic in 1949, stone first used this material for the production of artificial cornea, which greatly promoted the progress of artificial cornea research.
○ silicon gel
The main component is dimethylvinyl siloxane (methylvinyl silicone oil for short) with dimethylvinyl siloxane as the end group. In 2000, some scholars implanted artificial cornea made of domestic g1n515 transparent silicon gel into 26 patients, and followed up for 3 years. Most of the results were good.
○ glass
It is the first corneal material used in clinic. Due to its heavy weight, easy to break and difficult to process, it has not been greatly developed. From the current trend, it has been replaced by the new material PMMA.
Support material
The scaffold material is the part of the optical lens that directly contacts the maternal corneal tissue. It requires good biocompatibility, reasonable shape and sufficient strength to support the whole corneal tissue.
The scaffold plays a bridge role in structure. In function, on the one hand, it must have good biocompatibility and be fused with corneal tissue, and at the same time, it must not be biodegraded and retained for a long time; On the other hand, it must have a corresponding strength so that the optical mirror column can be fixed and tightly combined without leakage.
○ fluorocarbon polymer
Expanded polytetrafluoroethylene (PTFE) is mostly used. In the early 1990s, some scholars found that expanded polytetrafluoroethylene can adapt to normal rabbit corneal tissue and improve the stability of implants after implantation into human corneal tissue.
○ titanium: titanium is widely used in biomedical fields, especially in orthopedics, Stomatology, plastic surgery and other clinical fields. Titanium has excellent biocompatibility, mechanical properties and corrosion resistance.
As the main component of implanted cornea, the biocompatibility of titanium scaffolds is an important factor for the stability of artificial cornea.
○ hydroxyapatite (HA)
It is made of natural coral reef after chemical treatment. The main chemical component is Cai (PO) (OH). It is light in weight and porous structure, which is favorable for fusion with epithelial cells. It is a common material for making cornea.
○ biomaterials
In order to reduce the immune rejection of the immune system to foreign bodies, many scientists began to use autologous tissues as corneal scaffolds. At present, teeth, periosteum and cartilage have better effects. Other biological materials, such as Bioglass.