Implant / Implant's Designing & Manufacturing
Shima Bahramizadeh-Sajadi; Hamid Reza Katoozian; Alireza Baradaran-Rafii; Miguel-Angel Ariza-Gracia; Philippe Buchler
Volume 15, Issue 4 , March 2022, , Pages 329-339
Abstract
Keratoconus (KC) is a non-inflammatory and degenerative disease of the cornea. It is manifested by the formation of cone-shaped regions accompanying severe eyesight issues. Implantation of intrastromal corneal ring segments (ICRS) is a popular treatment to improve visual acuity. Controversies exist ...
Read More
Keratoconus (KC) is a non-inflammatory and degenerative disease of the cornea. It is manifested by the formation of cone-shaped regions accompanying severe eyesight issues. Implantation of intrastromal corneal ring segments (ICRS) is a popular treatment to improve visual acuity. Controversies exist over restoring functionality of different ICRSs. In this study, numerical models were used to quantify the mechanical and optical effects of different ICRSs on a reference cornea with central cone. Finite element (FE) simulations were used to simulate the implantation of two classes of ICRS sets common in clinical settings: a) single segment arcs of 360º (1×360), 350º (1×350), 320º (1×320), and, b) symmetric double-segment arcs of 160º each (2×160), 150º each (2×150), 120º each (2×120), and 90º each (2×90). Results showed that implantation of symmetric double-segment arcs caused the symmetric displacement and stress distribution contours on both anterior and posterior corneal surfaces. This study shows the potential impact of a detailed mechanical analysis of ICRS placement and represents a first step toward the development of an evidence-based nomogram for the different implantation techniques and the optimization of the surgical intervention based on patient-specific modeling.
Tissue Engineering
Giti Torkamaan; Ali Akbar Sharafi; Ali Fallah; Hamid Reza Katouzian; Mahmoud Mofid
Volume -1, Issue 1 , June 2004, , Pages 93-100
Abstract
Pressure ulcers are areas of tissue necrosis that tend to develop when tissue is compressed between a bony prominence and an external surface. Normal structure and physiological function of tissue viability are recognized but mechanism of tissue breakdown is unknown. In this study, an attempt has been ...
Read More
Pressure ulcers are areas of tissue necrosis that tend to develop when tissue is compressed between a bony prominence and an external surface. Normal structure and physiological function of tissue viability are recognized but mechanism of tissue breakdown is unknown. In this study, an attempt has been made to recognize the tissue mechanical changes after pressure application using 61 male albino guinea pigs, 4-6 months old, weighing 300-450 g. A computer controlled indentor system was developed to induce pressure sore. This system is capable of monitoring and adjusting the applied pressure, friction and shearing force throughout the experiment. The applied force remained within ±10g of desired target force. The applied pressures were at 291 and 387 mmHg for 1,3 or 5 hours over the trochanter region of animal hind limb. The tissue was removed and blood was taken immediately, 2 and 7 days after pressure release. Uniaxial tensile test was performed using deformation rate of 20 mm/min. In this test, the contralateral site on the experimental animal served as intra-animal control. Full- thickness biopsy was taken and stained with H & E, trichrome and orcein for histological examination. Results of tensile tests showed that the maximum tensile strength (Fmax), stress and the area under load-deformation curve (work) have decreased significantly 7 days after pressure application (P<0.05). Histological study immediately and 2 days after force release, showed an increase in cellularity and inflammatory cells infiltration. Muscle necrosis and reduction of the skin fibers density were observed 7 days after load release. Serum CPK (2 days after) was increased. The amount of lactic acid as well as phosphorus immediately and 2 days after pressure also increased (P<0.05). Finally it was distinguished that pressure changed the biomechanical properties of skin and muscle. Decrease of tissue resistance was consistent with the histological findings as well as elevation of muscle specific enzymes in blood. It was also observed that pressure resulted in the tissue ischemia and breakdown.
