ABSTRACT
New laser methods have introduced new possibilities and partly replaced traditional methods in corneal surgery. Femtosecond lasers have traditionally been used to replace the surgeons' knife in corneal refractive surgery and corneal transplantation. Excimer laser has been used from the beginning of 1990 for the reshaping of cornea. With the development of excimer laser, traditional photorefractive corneal surgery has improved and new methods have been found such as PRK, PTK, epi-LASIK, and LASEK. Today LASIK, the most commonly used refractive surgery, uses both femtosecond and excimer lasers. SMILE, the most recent method in corneal refractive surgery, is solely based on the use of femtosecond laser.
Subject(s)
Corneal Surgery, Laser/methods , Corneal Surgery, Laser/instrumentation , HumansABSTRACT
Surface-eroding biodegradable polymers can provide many advantages in drug delivery, such as controllable and zero-order drug release. Photocrosslinkable poly(ester anhydride)s are a recently developed family of surface-eroding polymers with readily modifiable oligomer chemistry allowing tailoring of polymer properties. For example, in vivo release rate of peptide from photocrosslinked poly(ester anhydride)s can be controlled by oligomer hydrophobicity. In this study, X-ray microtomography (micro-CT) was used to gain a deeper understanding on internal structure, polymer erosion and drug release mechanisms of photocrosslinked poly(ester anhydride)s. Micro-CT is non-destructive and able to provide quantitative and qualitative information on the 3D structure of the sample in micrometer resolution. Photocrosslinked poly(ester anhydride) samples with varying drug loading degrees (propranolol HCl 0%, 10% and 60% w/w) and hydrophobicity (with and without 12-carbon alkenyl chain) were prepared. The samples, both freshly prepared and exposed to buffer solution for varying durations were characterized by micro-CT. The results showed that drug release from photocrosslinked poly(ester anhydride)s was primarily controlled by the surface erosion. However, drug diffusion had also a significant role in drug release from less hydrophobic samples with very high (60% w/w) drug loading degrees. In conclusion, micro-CT is a valuable tool in the characterization of surface-eroding polymers.
Subject(s)
Anhydrides/chemistry , Polyesters/chemistry , Polymers/chemistry , X-Ray Microtomography/methods , Buffers , Drug Delivery Systems/methods , Hydrophobic and Hydrophilic Interactions , Particle Size , Peptides/chemistry , Propranolol/chemistry , Solutions/chemistryABSTRACT
Ridge waveguide 1.3 mum GaInNAs lasers were fabricated from high quality double quantum well material grown by molecular beam epitaxy. Short cavity (250 mum) lasers have low threshold currents and small temperature dependencies of threshold current and slope efficiency, with a characteristic temperature of the threshold current as high as 200 K. The temperature stability allows for uncooled 2.5 Gb/s operation up to temperatures as high as 110 degrees C with a constant modulation voltage and only the bias current adjusted for constant average output power. Under these conditions, an extinction ratio larger than 6 dB and a spectral rms-width smaller than 2 nm are obtained.
