| Objective:Vitreous body provides a range of functions,such as maintaining the normal anatomical position of the eye,supporting the retina location,reducing the external shocks,etc.Vitreous body works like a storage device,stored with oxygen,glucose and ascorbic acid,etc.It also supports the metabolism of the adjacent structures.Meanwhile,the water-soluble substances in the retina can get through the blood-retina barrier and reach the vitreous body,avoiding the expansion of the substances between retina and anterior segment.Vitreous body is the largest refractive material in the eye,but it is not renewable.Intraocular inflammation,ocular trauma,intraocular hemorrhage and systemic diseases such as diabetes,high blood pressure can lead to vitreous retinal lesions.And vitreous retinal diseases can get effective treatment by vitrectomy.After vitrectomy,the appropriate material is required to replace the vitreous body to maintain the volume of the eyeball and sustain the retina.Hydrogels have become a hot spot for vitreous fillers due to their high water content,optical clarity and rheological properties.In this study,we measured the optical properties,physical properties,gelation time of thermophilic hydroxylbutyl chitosan(HBC)in vitro and acute eye irritation in vivo.Compare the difference between thermosensitive hydroxybutyl chitosan and the natural characteristics of vitreous.Then fill the temperature sensitive chitosan into the vitreous of rabbit eyes to observe the safety and stability in vivo.Methods:Experiment One: Study on the related basic properties of thermosensitive hydroxybutyl chitosan as an artificial vitreous bodythermosensitive hydroxybutyl chitosan is a transparent sol at low temperature,and it can be transformed into transparent solid gel at high temperature.The gelation transparency is also related to the concentration of the material.The higher the concentration is,the lower the gelation temperature and transparency are.Which 0.8% thermosensitive hydroxybutyl chitosan can be turn into plastic in 37 ℃,in line with the normal temperature of the human body.This experiment selected 0.8% thermosensitive hydroxybutyl chitosan as an experimental material.(1)、Compared with the moisture content,transmittance,refractive index,specific gravity,pH value and storage energy,loss energy of 0.8% thermosensitive hydroxybutyl chitosan gel and natural vitreous in vitro.(2)、Repeatedly measure and record the phase transition time about sol to gel.(3)、Dropped 0.1ml and 0.3ml thermosensitive hydroxybutyl chitosan into 6 rabbit conjunctival sacs.And through the slit lamp to observe the condition of conjunctiva,cornea,iris in 72 h.2.Experiment Two: The safety of thermosensitive hydroxybutyl chitosan implanted in vitreous of rabbit eyes36 rabbits were randomly divided into three groups,and the right eye was choosen to take operation.The surgeries were performed according to the principle of sterile operation.Group A was filled with thermosensitive hydroxybutyl chitosan,group B was filled with sodium hyaluronate gel,and group C was the control group and filled with balanced salt solution after vitrectomy.On the 1st,3rd,7th,14 th,21st and 28 th day after operation,use the slit lamp and direct ophthalmoscopy to examine the condition of anterior segment(conjunctiva,cornea,anterior chamber,lens,vitreous,fundus)and the fundus of eye.And while use the tonometer to messure the intraocular pressure.At the 4th week,8 weeks and 12 weeks,the B scan ultrasound,fundus camera and retinal optical coherence tomography were performed on the rabbit eyes.And part of experimental animals were randomly selected to make pathological sections,and the ultrastructural changes were observed by optical microscopy and electron microscopy.Results:1.The moisture content of the 0.8% thermosensitive hydroxybutyl chitosan gel was 98.7%,the refractive index was 1.3321,the light transmittance was 99.95%,The specific gravity was 1.008 g/cm3.The physical properties and optical properties are close to the natural vitreous.pH value was 6.97,lower than the natural vitreous,but the difference may result from the operation error or temperature effects.The average storage modulus of thermosensitive hydroxybutyl chitosan gel is 267.08 ± 0.78 Pa,and the average energy loss is 17 ± 1.12 Pa,which belongs to elastic material.The average time of thermosensitive hydroxybutyl chitosan from low temperature solution to high temperature solid gel(4 ℃ → 37 ℃)was 59 ± 2s.The thermosensitive hydroxybutyl chitosan was dropped into the conjunctival sac of the experimental animals in 72 h,and then the conjunctiva of fornix was observed with gel residue and few secretions.There was no conjunctival hyperemia,no corneal damage.And eye pupil reflection was normal.2.After vitrectomy,three groups rabbits appeared temporary inflammation and cataract,the incidence of the three groups was not statistically significant.The intraocular pressure of A group decreased in 7th day(P <0.05).The intraocular pressure of B group decreased in 2 months(P <0.05).Vitreous of A group showing gray and white lumps of turbidity,with the lumps gradually become smaller,and eyes blurred can not be seen clearly.Group B vitreous transparency was poor,the eyes of red reflective can be seen,but the fundus blood vessels can not be seen.The fundus detail through vitreous body of Group C was clearly visible.Histopathology showed the retinal structure of group A and group C were clear without retinal detachment and hyperplasia.The ultrastructure of corneal and retinal had not been found obvious abnormalities.But the number of ganglion cells decreased in group B.Conclusion:1.The optical properties and physical and viscoelasticity of 0.8% thermosensitive hydroxybutyl chitosan gels can be simulated by natural vitreous.2.The thermosensitive hydroxybutyl chitosan gel in rabbit eyes showed good biocompatibility,but will cause vitreous opacity,is not yet as an ideal vitreous substitute.However,intravitreal hydrogel drug delivery system only holds a small portion of the vitreous cavity,and it does not necessarily require intraocular clear,so thermosensitive hydroxybutyl chitosan may be further studied in intravitreal drug delivery system. |
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