Publications by authors named "Parag K Shah"

75 Publications

Pediatric choroidal neovascularization: Etiology and treatment outcomes with anti-vascular endothelial growth factors.

Eur J Ophthalmol 2021 Oct 7:11206721211048799. Epub 2021 Oct 7.

Department of Retina and Vitreous services, Aravind Eye Hospital, Coimbatore, India.

Purpose: To describe the etiology and treatment outcomes of choroidal neovascularization (CNV) in a pediatric population with intravitreal anti-vascular endothelial growth factors (VEGF).

Methods: Retrospective single center interventional case series. A total of 26 eyes of 23 consecutive pediatric patients with CNV of various etiologies were treated with intravitreal injection of anti-VEGF agents.

Results: There were 15 males (65.2%) and eight females (34.8%), diagnosed with CNV during the study period. The mean age at presentation with CNV was 11.7 ± 3.3 years, (range 4-16 years) and the mean follow was 28.1 ± 18 months, (range 8-72 months). Inflammatory CNV was the most common etiology. The mean best corrected visual acuity (BCVA) and mean central macular thickness (CMT) at presentation, were logMAR 0.8 ± 0.3 and 367.6 ± 134.8 µm respectively. At the final visit, CNV in all eyes remained regressed with significant improvement in mean BCVA to logMAR 0.4 ± 0.4 ( < 0.0001) and mean CMT to 242.5 ± 82.4 µm ( < 0.0001). A mean of two intravitreal injections per eye was required for CNV regression.

Conclusion: Intravitreal anti-VEGF therapy for pediatric CNV is an effective treatment in majority of affected eyes.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1177/11206721211048799DOI Listing
October 2021

International Classification of Retinopathy of Prematurity, Third Edition.

Ophthalmology 2021 10 8;128(10):e51-e68. Epub 2021 Jul 8.

Department of Pediatric Retina, Narayana Nethralaya Eye Institute, Bangalore, Karnataka, India.

Purpose: The International Classification of Retinopathy of Prematurity is a consensus statement that creates a standard nomenclature for classification of retinopathy of prematurity (ROP). It was initially published in 1984, expanded in 1987, and revisited in 2005. This article presents a third revision, the International Classification of Retinopathy of Prematurity, Third Edition (ICROP3), which is now required because of challenges such as: (1) concerns about subjectivity in critical elements of disease classification; (2) innovations in ophthalmic imaging; (3) novel pharmacologic therapies (e.g., anti-vascular endothelial growth factor agents) with unique regression and reactivation features after treatment compared with ablative therapies; and (4) recognition that patterns of ROP in some regions of the world do not fit neatly into the current classification system.

Design: Review of evidence-based literature, along with expert consensus opinion.

Participants: International ROP expert committee assembled in March 2019 representing 17 countries and comprising 14 pediatric ophthalmologists and 20 retinal specialists, as well as 12 women and 22 men.

Methods: The committee was initially divided into 3 subcommittees-acute phase, regression or reactivation, and imaging-each of which used iterative videoconferences and an online message board to identify key challenges and approaches. Subsequently, the entire committee used iterative videoconferences, 2 in-person multiday meetings, and an online message board to develop consensus on classification.

Main Outcome Measures: Consensus statement.

Results: The ICROP3 retains current definitions such as zone (location of disease), stage (appearance of disease at the avascular-vascular junction), and circumferential extent of disease. Major updates in the ICROP3 include refined classification metrics (e.g., posterior zone II, notch, subcategorization of stage 5, and recognition that a continuous spectrum of vascular abnormality exists from normal to plus disease). Updates also include the definition of aggressive ROP to replace aggressive-posterior ROP because of increasing recognition that aggressive disease may occur in larger preterm infants and beyond the posterior retina, particularly in regions of the world with limited resources. ROP regression and reactivation are described in detail, with additional description of long-term sequelae.

Conclusions: These principles may improve the quality and standardization of ROP care worldwide and may provide a foundation to improve research and clinical care.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.ophtha.2021.05.031DOI Listing
October 2021

High Refractive Index Photopolymers by Thiol-Yne "Click" Polymerization.

ACS Appl Mater Interfaces 2021 Apr 29;13(13):15647-15658. Epub 2021 Mar 29.

Department of Chemical and Biological Engineering, University of Colorado at Boulder, Boulder, Colorado 80309, United States.

A scalable synthesis of high refractive index, optically transparent photopolymers from a family of low-viscosity multifunctional thiol and alkyne monomers via thiol-yne "click" is described herein. The monomers designed to incorporate high refractive index cores consisting of aryl and sulfide groups with high intrinsic molar refraction were synthesized starting from commercially available low-cost raw materials. The low-viscosity (<500 cP) thiol-yne resins formulated with these new multifunctional monomers and a phosphine oxide photoinitiator underwent efficient thiol-yne polymerizations upon exposure to 405 nm light at 30 mW/cm. In contrast to the previously reported thiol-ene systems, the kinetic profile of these photopolymerizations showed significant dependence on the nature of the thiol and alkyne monomers. However, the ability of the thiol-yne reaction to introduce a large number of sulfide linkages compared to that of thiol-ene systems yielded cross-linked high optical quality photopolymers with a polymer refractive index that exceeds 1.68 (/20 °C). Interestingly, the photopolymer formed from the least sterically hindered alkynyl thioether monomer with flexible thioether core and the dithiol exhibited unprecedented difference in the polymer refractive index as compared to that of the resin with polymerization-induced changes reaching up to 0.08. Furthermore, the implementation of these low-viscosity thiol-yne resins was demonstrated by preparing two-stage photopolymeric holographic materials with a dynamic range of ∼0.02 and haze < 1.5% in two-dimensional high refractive index structures.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.1c00831DOI Listing
April 2021

Coincidental ocular findings during retinopathy of prematurity telescreening of 9105 neonates.

Eur J Ophthalmol 2022 Jan 15;32(1):563-574. Epub 2021 Mar 15.

Department of Paediatric Retina & Ocular Oncology, Aravind Eye Hospital & Postgraduate Institute of Ophthalmology, Coimbatore, Tamil Nadu, India.

Purpose: To describe the magnitude and spectrum of abnormal ocular findings other than retinopathy of prematurity (ROP) detected during an ROP telescreening programme.

Methods: Retrospective review of the records of all premature babies screened for ROP from August 2015 to December 2019.

Results: A total 9105 babies were screened during the study period with total 17,075 imaging sessions. Non-ROP ocular abnormalities were seen in 566 eyes of 383 babies (4.2%) including 207 male (54%) and 176 female babies (46%). Posterior segment abnormalities were seen in 88.2% babies (338/383) with haemorrhage being the most common (77%, 295/383). Anterior segment pathologies were seen in 12% babies (46/383) with congenital cataract being the most common pathology requiring surgical intervention. Other findings included globe abnormalities in 0.8% babies (3/383), adnexal disorders in 0.5% babies (2/383) and squint in 0.3% babies (1/383). Rare life-threatening conditions such as retinoblastoma and lipaemia retinalis were also detected. Eighty-seven babies (22.7%) were diagnosed with referral-warranted non-ROP pathologies, with an overall prevalence of 1% (87/9105). Prompt surgical intervention was advised for 7.3% babies (28/383), 3.4% babies (13/383) were treated medically and 4.2% babies (16/383) needed visual rehabilitation for non-amenable pathologies.

Conclusion: This is the largest study describing the magnitude and spectrum of neonatal ocular pathologies other than ROP in a cohort of premature babies. Digital imaging has a significant impact on early detection and timely intervention for various vision as well as life-threatening non-ROP pathologies, which would have been missed or delayed otherwise.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1177/11206721211001318DOI Listing
January 2022

Applications of Artificial Intelligence for Retinopathy of Prematurity Screening.

Pediatrics 2021 03;147(3)

Athinoula A. Martinos Center for Biomedical Imaging and Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts.

Objectives: Childhood blindness from retinopathy of prematurity (ROP) is increasing as a result of improvements in neonatal care worldwide. We evaluate the effectiveness of artificial intelligence (AI)-based screening in an Indian ROP telemedicine program and whether differences in ROP severity between neonatal care units (NCUs) identified by using AI are related to differences in oxygen-titrating capability.

Methods: External validation study of an existing AI-based quantitative severity scale for ROP on a data set of images from the Retinopathy of Prematurity Eradication Save Our Sight ROP telemedicine program in India. All images were assigned an ROP severity score (1-9) by using the Imaging and Informatics in Retinopathy of Prematurity Deep Learning system. We calculated the area under the receiver operating characteristic curve and sensitivity and specificity for treatment-requiring retinopathy of prematurity. Using multivariable linear regression, we evaluated the mean and median ROP severity in each NCU as a function of mean birth weight, gestational age, and the presence of oxygen blenders and pulse oxygenation monitors.

Results: The area under the receiver operating characteristic curve for detection of treatment-requiring retinopathy of prematurity was 0.98, with 100% sensitivity and 78% specificity. We found higher median (interquartile range) ROP severity in NCUs without oxygen blenders and pulse oxygenation monitors, most apparent in bigger infants (>1500 g and 31 weeks' gestation: 2.7 [2.5-3.0] vs 3.1 [2.4-3.8]; = .007, with adjustment for birth weight and gestational age).

Conclusions: Integration of AI into ROP screening programs may lead to improved access to care for secondary prevention of ROP and may facilitate assessment of disease epidemiology and NCU resources.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1542/peds.2020-016618DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7924138PMC
March 2021

Photopolymerization shrinkage-stress reduction in polymer-based dental restoratives by surface modification of fillers.

Dent Mater 2021 04 8;37(4):578-587. Epub 2021 Feb 8.

Department of Chemical and Biological Engineering, University of Colorado Boulder, CO, United States; Department of Craniofacial Biology, School of Dental Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, United States. Electronic address:

Objectives: This research explores the use of polymer brushes for surface treatment of fillers used in polymer-based dental restoratives with focus on shrinkage stress reduction. The influence of interfacial reactive groups on shrinkage stress is explored.

Methods: Oligomers of varying lengths and with varying number of reactive groups along the length were synthesized by modifying commercial oligomers. Surface of silica fillers (OX50) was treated with methylaminopropyltrimethoxysilane and this was further reacted with the synthesized oligomers to obtain a series of polymer brushes on the surface. Fillers modified with γ-methacryloxypropyltrimethoxysilane were used as a control. Filler surface treatment was confirmed using diffuse reflectance spectroscopy and thermogravimetric analysis. Fillers were added at 30 wt % to a resin made of BisGMA/TEGDMA and polymerization kinetics, shrinkage stress, volumetric shrinkage, flexural strength and modulus, viscosity were measured.

Results: Composites with polymer brush functionalized fillers showed up to a 30 % reduction in shrinkage stress as compared to the control, with no reduction in flexural strength and modulus. Shrinkage stress reduced with increasing length of the polymer brush and increased with increase in number of reactive groups along the length of the polymer brush.

Significance: The interface between inorganic fillers and an organic polymer matrix has been utilized to reduce shrinkage stress in a composite with no compromise in mechanical properties. This study gives insights into the stress development mechanism at the interface.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.dental.2021.01.013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7996127PMC
April 2021

Laminaria-like Vitreoschisis in Persistent Fetal Vasculature.

Ophthalmol Retina 2021 01;5(1):70

Aravind Eye Hospital, Coimbatore, Tamil Nadu, India.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.oret.2020.06.009DOI Listing
January 2021

Coexistent Retinoblastoma and Retinopathy of Prematurity in a Preterm Infant.

Ophthalmic Surg Lasers Imaging Retina 2020 Dec;51(12):732

[Ophthalmic Surg Lasers Imaging Retina. 2020;51:732.].
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3928/23258160-20201202-09DOI Listing
December 2020

Type of article: Letter to editor.

Retina 2020 Dec 7. Epub 2020 Dec 7.

Pediatric Retina and Ocular Oncology Department, Aravind Eye Hospital & Postgraduate Institute of Ophthalmology, Coimbatore, Tamilnadu, India.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1097/IAE.0000000000003074DOI Listing
December 2020

Design and development of model eye for retina laser by using additive manufacturing.

Proc Inst Mech Eng H 2021 Jan 28;235(1):89-98. Epub 2020 Sep 28.

Department of Ophthalmology, Aravind Eye Hospital, Coimbatore, Tamil Nadu, India.

Surgical skill of the surgeon can be improved by surgical simulation. Especially in ophthalmology, it is impossible to use real human/non-human primate eyes for ophthalmology surgery practice. However, surgical practice is most important for ophthalmologist. The retina laser surgery is one of the ophthalmology surgeries and it requires more surgical practice for surgeons to use the laser beam precisely to coagulate and fuse small areas of tissue. Dealing with the prospect of vision reduction or vision loss presents a peculiar problem and that can be highly stressful and frustrating for both doctors and patients. In this regard, training for indirect ophthalmoscopy and retinal photocoagulation is undergone using model eyes instead of real eyes. Properties and functioning of an existing model eye are huge and they differ from real human eye such as casings are completely rigid and focusing of retinal fundus is not completely covered. Therefore, this research concentrates to develop a model eye that assimilates close to the human eye by focussing on the maximum viewing area that is not done at the moment. Finally, the design and development of re-engineered model eye for retina laser is fabricated by additive manufacturing. Compared to existing plastic model eye, viewing area and viewing angle of the re-engineered model eye is increased by 16.66% and 6.14%, respectively. Due to design modifications and elimination of the insert, it can be reduced by 18.99% and 13.95% of height and weight of the top casing respectively. Developed re-engineered model eye will improve the surgical and diagnostic skill of the surgeon and increase their confidence and proficiency. It also augments the effective use of essential ophthalmic instruments. Additionally, it can reduce the surgical error and meet the existing demand of actual eyes for surgical practices.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1177/0954411920960548DOI Listing
January 2021

Paclitaxel- and/or cyclophosphamide-induced severe ischaemic retinopathy.

Clin Exp Ophthalmol 2020 11 13;48(8):1113-1115. Epub 2020 Sep 13.

Department of Pediatric Retina & Ocular Oncology, Aravind Eye Hospital & Postgraduate Institute of Ophthalmology, Coimbatore, India.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/ceo.13854DOI Listing
November 2020

Ocular oncology practice guidelines during COVID-19 pandemic-An expert consensus.

Indian J Ophthalmol 2020 Jul;68(7):1281-1291

Pediatric Oncology, Cytecare Cancer Hospitals, Bangalore, India.

The outbreak of rapidly spreading COVID-19 pandemic in December 2019 has witnessed a major transformation in the health care system worldwide. This has led to the re-organization of the specialty services for the effective utilization of available resources and ensuring the safety of patients and healthcare workers. Suspension of oncology services will have major implications on cancer care due to delayed diagnosis and treatment leading to irreversible adverse consequences. Therefore various oncology organizations have called for a continuation of cancer care during this crisis with diligence. The COVID-19 pandemic has forced the clinicians to transform the components of care from screening to outpatient care and primary management. The purpose of this article is to establish guidelines and recommendations for ocular oncology in the management of ocular tumors set by a multidisciplinary team of experts including ocular, medical and radiation oncologists, and pathologists. As the pandemic is evolving fast, it will require constant updates and reformation of health strategies and guidelines for safe and quality health care.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.4103/ijo.IJO_1669_20DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7574098PMC
July 2020

Bilateral macular ischemia following oral etoposide.

Indian J Ophthalmol 2020 06;68(6):1184

Department of Pediatric Retina and Ocular Oncology, Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Coimbatore, Tamil Nadu, India.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.4103/ijo.IJO_1850_19DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7508099PMC
June 2020

Primary intraocular mesenchymal chondrosarcoma: a histopathological surprise in an enucleated eye.

Can J Ophthalmol 2020 06 23;55(3):e104-e107. Epub 2019 Dec 23.

Aravind Eye Hospital & Postgraduate Institute of Ophthalmology, Coimbatore, India.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.jcjo.2019.10.010DOI Listing
June 2020

Vinyl sulfonamide based thermosetting composites via thiol-Michael polymerization.

Dent Mater 2020 02 30;36(2):249-256. Epub 2019 Nov 30.

Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, CO, United States. Electronic address:

Objective: To assess the performance of thiol Michael photocurable composites based on ester-free thiols and vinyl sulfonamides of varying monomer structures and varied filler loadings and to contrast the properties of the prototype composites with conventional BisGMA-TEGDMA methacrylate composite.

Methods: Synthetic divinyl sulfonamides and ester-free tetrafunctional thiol monomers were utilized for thiol-Michael composite development with the incorporation of thiolated microfiller. Polymerization kinetics was investigated using FTIR spectroscopy. Resin viscosities were assessed with rheometry. Water uptake properties were assessed according to standardized methods. Thermomechanical properties were analyzed by dynamic mechanical analysis. Flexural modulus/strength and flexural toughness were measured on a universal testing machine in three-point bending testing mode.

Results: The vinyl sulfonamide-based thiol-Michael resin formulation demonstrated a wide range of viscosities with a significant increase in the functional group conversion when compared to the BisGMA-TEGDMA system. The two different types of vinyl sulfonamide under investigation demonstrated significant differences towards the water sorption. Tertiary vinyl sulfonamide did not undergo visible swelling whereas the secondary vinyl sulfonamide composite swelled extensively in water. With the introduction of rigid monomer into the polymer matrix the glass transition temperature increased and so increased the toughness. Glassy thiol-Michael composites were obtained by ambient curing.

Significance: Employing the newly developed step-growth thiol-Michael resins in dental composites will provide structural uniformity, improved stability and lower water sorption.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.dental.2019.11.012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7012731PMC
February 2020

Commentary: The challenges of treating retinoblastoma in India.

Authors:
Parag K Shah

Indian J Ophthalmol 2019 12;67(12):2004

Department of Pediatric Retina and Ocular Oncology, Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Coimbatore, Tamil Nadu, India.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.4103/ijo.IJO_1274_19DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6896528PMC
December 2019

Aggressive posterior retinopathy of prematurity in two cohorts of patients in South India: implications for primary, secondary, and tertiary prevention.

J AAPOS 2019 10 12;23(5):264.e1-264.e4. Epub 2019 Sep 12.

Department of Ophthalmology, Casey Eye Institute, Oregon Health and Science University, Portland, Oregon. Electronic address:

Background: Aggressive posterior retinopathy of prematurity (APROP), which has a poor visual prognosis, is common in low- and middle-income countries (LMICs) as a result of suboptimal oxygen monitoring (primary prevention). The purpose of this study was to compare outcomes in APROP eyes treated with laser to eyes treated with antivascular endothelial growth factor (anti-VEGF) therapy.

Methods: The medical records of a cohort of APROP eyes treated with anti-VEGF (2010-2018) and another of eyes treated with laser photocoagulation (2002-2010) at the same institution in South India were reviewed retrospectively and compared. The main outcome was the proportion of eyes developing retinal detachment during resolution of acute ROP.

Results: A total of 398 eyes of 199 preterm babies with APROP were included: 168 eyes were treated with photocoagulation; 230, with anti-VEGF. From 2002 to 2010, compared to the more recent cohort, babies diagnosed with APROP tended to be heavier (P < 0.001), older (P < 0.001), and exposed to fewer days of oxygen (P = 0.02). In the laser-treated cohort, 17 of 168 eyes (10%) developed retinal detachment (7, stage 5; 12, stage 4), compared with 3 of 230 (1%) in the anti-VEGF cohort (all stage 4 [P = 0.002]).

Conclusions: The incidence of retinal detachment was significantly lower in eyes treated with anti-VEGF compared with laser-.treated eyes In the absence of a randomized trial, these data suggest that anti-VEGF may lead to better anatomic outcomes, although questions remain concerning dosage, timing, and risks.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.jaapos.2019.05.014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7219568PMC
October 2019

Refractive, sensory, and biometric outcome among retinopathy of prematurity children with a history of laser therapy: A retrospective review from a tertiary care center in South India.

Indian J Ophthalmol 2019 06;67(6):871-876

Department of Paediatric Ophthalmology and Adult Strabismus, Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Coimbatore, Tamil Nadu, India.

Purpose: Ocular morbidities like high refractive error, strabismus, and amblyopia are common among laser-treated retinopathy of prematurity children (ROP). Long-term optical status and refractive outcomes including the sensory outcomes were less investigated in these children from this region. The purpose of our study is to evaluate the long-term outcome (refractive, biometric profile, sensory) of treatment for ROP using laser.

Methods: This study is a retrospective, cross-sectional, observational, and intervention research among 6-15-year-old children who underwent laser for ROP with a minimum of 6-year follow-up.

Results: Eighty lasered eyes of 41 children were assessed. Mean age was 9.71 years (±3.39). Seventy-three eyes (91.2%) achieved visual acuity better than 20/40. The mean visual acuity in LogMAR was 0.18 (20/30). The mean spherical equivalence was -5.29 D ± 4.9. Mean astigmatism measured was -1.53 DC (range: +0.50 DC to -4.5DC). Fifty-three eyes (66.25%) had significant astigmatism. The mean axial length was 23.5 ± 1.35 (21-26) mm. Mean lens thickness was 3.76 ± 0.30 (3.03-4.34) mm. Correlation analysis among the low and high spherical equivalent group signified that axial length (P value = 0.001), visual acuity (P value = 0.0002), and myopic shift (P value = 0.0006) were found to be statistically significant. Stereopsis better than 480 s of arc for near was observed in 41% children. Structural posterior pole sequelae developed in 3 eyes (3.75%).

Conclusion: A significant number of children with high myopia, astigmatism, and strabismus had satisfactory visual outcome observed at long-term follow-up after treatment for ROP using laser. Our study revealed that myopia was influenced by an increase in axial length than the lens thickness.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.4103/ijo.IJO_2023_18DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6552594PMC
June 2019

Dynamic Covalent Chemistry at Interfaces: Development of Tougher, Healable Composites through Stress Relaxation at the Resin-Silica Nanoparticles Interface.

Adv Mater Interfaces 2018 Sep 3;5(18). Epub 2018 Jul 3.

Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309-0596, USA.

The interfacial region in composites that incorporate filler materials of dramatically different modulus relative to the resin phase acts as a stress concentrator and becomes a primary locus for composite failure. A novel adaptive interface (AI) platform formed by coupling moieties capable of dynamic covalent chemistry (DCC) is introduced to the resin-filler interface to promote stress relaxation. Specifically, silica nanoparticles (SNP) are functionalized with a silane capable of addition fragmentation chain transfer (AFT), a process by which DCC-active bonds are reversibly exchanged upon light exposure and concomitant radical generation, and copolymerized with a thiol-ene resin. At a fixed SNP loading of 25 wt%, the toughness (2.3 MJ m) is more than doubled and polymerization shrinkage stress (0.4 MPa) is cut in half in the AI composite relative to otherwise identical composites that possess a passive interface (PI) with similar silane structure, but without the AFT moiety. In situ activation of the AI during mechanical loading results in 70% stress relaxation and three times higher fracture toughness than the PI control. When interfacial DCC was combined with resin-based DCC, the toughness was improved by 10 times relative to the composite without DCC in either the resin or at the resin-filler interface.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/admi.201800511DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6521971PMC
September 2018

Photo-responsive liposomes composed of spiropyran-containing triazole-phosphatidylcholine: investigation of merocyanine-stacking effects on liposome-fiber assembly-transition.

Soft Matter 2019 May;15(18):3740-3750

Department of Chemical and Biological Engineering, University of Colorado Boulder, UCB 596, Colorado 80309, USA.

A spiropyran-containing triazole-phosphatidylcholine (SPTPC) was synthesized through a copper-catalyzed azide alkyne cyclo-addition (CuAAC) reaction. In water, SPTPCs self-assembled and a spontaneous spiropyran-to-merocyanine (SP-to-MC) isomerization occurred, resulting in coexistence of liposomes and fibers, and switching from the spiropyran (SP) to the merocyanine (MC) isomeric structure induced a reversible transition between these molecular assemblies. Study of the self-assembly of SPTPCs and photo-induced liposome-fiber assembly-transition revealed that the presence of MC enabled additional inter-membrane interaction during self-assembly and that the MC-stacking effect was the driving force for the assembly-transition. Exposure to UV light induced switching from SP to MC, where the planar structure of MC and the confinement of MC led to enhanced MC-stacking. The effect of MC-stacking was both advantageous and disadvantageous: MC-stacking perturbed the hydrophobic phase in the bilayer membrane and facilitated the liposome-to-fiber transition, otherwise the MC-stacking retarded switching of MC to SP, and caused an incomplete recovery of MC to SP during fiber-to-liposome recovery, thus a fatigue of SP was induced by MC-stacking during the liposome-to-fiber transition cycle. To decrease the intermolecular interactions and suppress MC-stacking, photo-inert triazole-phosphatidylcholine (TPC) was incorporated to prepare two-component TPC/SPTPC-liposomes, which exhibited better recovery kinetics. The photo-adaptive behavior of TPC/SPTPC-liposomes confirmed the disturbance of bilayer membranes by inter-membrane MC-stacking and the formation of MCTPC-enriched phases in the bilayer membrane.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c8sm02181cDOI Listing
May 2019

Modification of filler surface treatment of composite resins using alternative silanes and functional nanogels.

Dent Mater 2019 06 16;35(6):928-936. Epub 2019 Apr 16.

Craniofacial Biology Department, University of Colorado, Aurora, CO, United States; Chemical and Biological Engineering, University of Colorado, Boulder, CO, United States. Electronic address:

Objectives: This study probes how modifiedapproaches for filler surface treatment in dental composites based on alternative silanes and functional nanogel additives affects physicochemical properties of these materials with a focus on polymerization stress development.

Methods: Nanogels were synthesized from isobornyl methacrylate, ethoxylated bisphenol-A dimethacrylate and isocyanatoethyl methacrylate followed by partial further reaction with 2-hydroxyethyl methacrylate to provide both isocyanate and methacrylate functionalization. A barium glass filler (˜1 μm particle size) was treated with either γ-methacryloxypropyltrimethoxysilane (MPS), N-methylaminopropyltrimethoxy (MAP) or N-allylaminopropyltrimethoxy (AAP) silanes. The reactive nanogels were then covalently attached to the aminosilane-treated fillers. Surface treatment was characterized by thermogravimetric analysis (TGA) and diffuse reflectance infrared spectroscopy (DR-IR). Composites were formulated with 60 wt% of the various functionalized fillers and the materials were evaluated for polymerization kinetics, polymerization stress (PS), volumetric shrinkage, mechanical properties and photorheology. Data were evaluated by one-way ANOVA and Tukey's test at 5% significance level.

Results: Filler surface treatments were confirmed by TGA and DR-IR analyses. Nanogel-functionalized fillers significantly reduced PS up to 20%, while the degree of conversion and elastic modulus were not compromised. Similar storage modulus development during polymerization was observed among materials by photorheology although the rate of polymerization was significantly increased for nanogel-based treatments. A significant decrease in flexural strength was observed for amino functional silane groups; however, there was no statistical difference in strength for the MPS control group compared with the nanogel-modified composites.

Significance: Filler surface treatment modified with a reactive nanogel enables significant PS reduction, without compromise to degree of conversion or mechanical properties of dental composites.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.dental.2019.03.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6530473PMC
June 2019

Curious case of retrolental mass: An unusual tele-screening artifact.

Indian J Ophthalmol 2019 Mar;67(3):415-416

Department of Paediatric Retina and Ocular Oncology, Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Coimbatore, Tamil Nadu, India.

We are presenting a case of premature baby born at 32 weeks of gestation who was under regular follow-up with our retinopathy of prematurity (ROP) tele-screening team. During final follow-up at 41 weeks of postconceptional age, anterior segment image captured with RetCam showed a retrolental mass lesion in right eye resembling retinoblastoma or medulloepithelioma. The baby was referred to our base hospital for further evaluation, where a detailed examination showed no retrolental lesion or intraocular mass. This is the first case where imaging artifact, despite use of high-quality imaging system by well-trained staff, during ROP tele-screening appeared like a retrolental mass lesion and resulted in false-positive referral.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.4103/ijo.IJO_1318_18DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6407378PMC
March 2019

Step-growth Production of Nanogels for Use as Macromers with Dimethacrylate Monomers.

React Funct Polym 2019 Jan 10;134:85-92. Epub 2018 Nov 10.

Materials Science and Engineering Program, University of Colorado, Boulder, Colorado 80309 -0596, USA.

A series of functional nanogels were synthesized by a step-growth mechanism that involved diisocyanate addition to a modest stoichiometric excess of multi-thiols. Nanogels with sizes less than 10 nm were obtained as room temperature liquids with residual thiol groups used to attach methacrylate functionality. Depending on nanogel structure, bulk nanogel properties varied widely, as did the properties of the nanogel-derived and nanogel-modified polymers. Photopolymerization of the reactive nanogels in combination with a dimethacrylate monomer showed dramatically enhanced reaction rate and conversion compared with the dimethacrylate homopolymer. Polymerization shrinkage/ stress as well as mechanical properties of the polymer networks were controlled by changing the ratio of nanogels and dimethacrylate monomers used in formulations. Thus, this study shows the potential of step-growth nanogels for beneficial changes in resin reactivity and application-based performance.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.reactfunctpolym.2018.11.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6327966PMC
January 2019

Evolution of ROP screening at Aravind Eye Hospital, Coimbatore - Lessons learnt and the way ahead.

Community Eye Health 2018 ;31(101):S23-S24

Senior Medical Officer: Department of Pediatric Retina & Ocular Oncology, Aravind Eye Hospital & Post Graduate Institute of Ophthalmology, Coimbatore, India.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6157806PMC
January 2018

Outcomes of transconjuctival sutureless 27-gauge vitrectomy for stage 4 retinopathy of prematurity.

World J Clin Pediatr 2018 Feb 8;7(1):62-66. Epub 2018 Feb 8.

Department of Pediatric Retina and Ocular Oncology, Aravind Eye Hospital, Coimbatore, Tamil Nadu 641014, India.

Aim: To report our initial experience with lens-sparing vitrectomy for stage 4 retinopathy of prematurity using the 27-gauge (G) system.

Methods: This retrospective case series involved nine eyes of five babies with active stage 4 ROP, who underwent 27-G lens-sparing vitrectomy. Surgery was done using 27-G valved cannulas and sclerotomies were made 1.5 mm from the limbus. Bilateral sequential vitrectomy was done in eight eyes.

Results: At one-year follow-up, anatomical outcome was favourable in all nine (100%) eyes. High-speed cutting and smaller sclerotomies were helpful in reducing the intra and post-operative complications.

Conclusion: 27-G vitrectomy is well suited for stage 4 ROP surgeries.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.5409/wjcp.v7.i1.62DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5803567PMC
February 2018

Telemedicine for ROP.

Asia Pac J Ophthalmol (Phila) 2018 Jan-Feb;7(1):52-55. Epub 2017 Jan 26.

Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Coimbatore, Tamil Nadu, India.

With the increasing survival of preterm babies in the Asia-Pacific region, there has been an increase in the incidence of retinopathy of prematurity (ROP). There is also a lack of trained ophthalmologists to screen for this disease. New strategies for screening of ROP are required, wherein the load on the ophthalmologist can be reduced. Telemedicine is an excellent tool to address this need. This paper reviews the initial studies comparing digital imaging with indirect ophthalmoscopy, the current active ROP telescreening programs in the world, and ends with studies dealing with automated diagnosis of ROP.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.22608/APO.2017478DOI Listing
March 2018

Fully recoverable rigid shape memory foam based on copper-catalyzed azide-alkyne cycloaddition (CuAAC) using a salt leaching technique.

Polym Chem 2018 Jan 29;9(1):121-130. Epub 2017 Nov 29.

Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, CO.

This study is the first to employ the use of the copper-catalyzed azide-alkyne cycloaddition (CuAAC) polymerization to form a tough and stiff, porous material from a well-defined network possessing a high glass transition temperature. The effect of the network linkages formed as a product of the CuAAC reaction, i.e., the triazoles, on the mechanical behavior at high strain was evaluated by comparing the CuAAC foam to an epoxy-amine-based foam, which consisted of monomers with similar backbone structures and mechanical properties (i.e., T of 115 °C and a rubbery modulus of 1.0 MPa for the CuAAC foam, T of 125 °C and a rubbery modulus of 1.2 MPa for the epoxy-amine foam). When each foam was compressed uniformly to 80% strain at ambient temperature, the epoxy-amine foam was severely damaged after only reaching 70% strain in the first compression cycle with a toughness of 300 MJ/m. In contrast, the CuAAC foam exhibited pronounced ductile behavior in the glassy state with three times higher toughness of 850 MJ/m after the first cycle of compression to 80% strain. Additionally, when the CuAAC foam was heated above T after each of five compression cycles to 80% strain at ambient temperature, the foam completely recovered its original shape while exhibiting a gradual decrease in mechanical performance over the multiple compression cycles. The foam demonstrated almost complete shape fixity and recovery ratios even through five successive cycles, indicative of "reversible plasticity", making it highly desirable as a glassy shape memory foams.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c7py01121kDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5736377PMC
January 2018

Pigmented ciliary body medulloepithelioma in a newborn infant.

Oman J Ophthalmol 2017 Sep-Dec;10(3):257-258

Department of Pediatric Retina and Ocular Oncology, Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Coimbatore, Tamil Nadu, India.

Ciliary body medulloepithelioma is a nonpigmented tumor which presents during the first decade of life. It is rarely seen in newborn infants. We report a pigmented medulloepithelioma in a newborn infant, which showed a rapid growth. Ciliary body medulloepithelioma should be considered in the differential diagnosis in a newborn infant presenting with leukocoria.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.4103/ojo.OJO_1_2017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5657178PMC
November 2017

Application of an Addition-Fragmentation-Chain Transfer Monomer in Di(meth)acrylate Network Formation to Reduce Polymerization Shrinkage Stress.

Polym Chem 2017 Aug 21;8(30):4339-4351. Epub 2017 Jun 21.

Department of Chemical and Biological Engineering, University of Colorado Boulder.

A new addition-fragmentation chain transfer (AFT) capable moiety was incorporated into a dimethacrylate monomer that participated readily in network formation by copolymerizing with multifunctional methacrylates or acrylates. The process of AFT occurred simultaneously with photopolymerization of the AFT monomer (AFM) and other (meth)acrylate monomers leading to polymer stress relaxation via network reconfiguration. At low loading levels of the AFM, a significant reduction in shrinkage stress, especially for acrylate monomers, was observed with nominal effects on conversion. At higher loading levels of the AFM, the photopolymerization reaction kinetics and final double bond conversion were significantly lowered along with a delay in the gel-point conversion. Electron paramagnetic resonance studies during polymerization revealed the presence of a distinct radical species that was present in proportional quantities to the AFM content in the system. The lifetime and the character of the persistent radicals were altered due to the presence of the distinctive radical, in turn affecting the polymerization kinetics. With polymerization conducted at higher irradiance, the differential conversion between the control resin and samples with moderate AFM content was minimal, especially for the methacrylate-based formulations.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/C7PY00702GDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5665588PMC
August 2017

Accuracy of crescent sign on ocular ultrasound in diagnosing papilledema.

World J Methodol 2017 Sep 26;7(3):108-111. Epub 2017 Sep 26.

Department of Retina and Vitreous, Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Coimbatore 641014, Tamil Nadu, India.

Aim: To study the usefulness of orbital ultrasonography in the diagnosis of papilledema.

Methods: Fifty patients who were referred to the neurophthalmology clinic and clinically suspected to have papilledema were selected. Thorough, clinical examination with slitlamp biomicroscopy and visual acuity assessment was done. These patients underwent ultrasonography to demonstrate the crescent sign. The patients were further evaluated with the neurologist and magnetic resonance imaging (MRI) thus confirming the diagnosis of papilledema. The results of our ultrasonographic evaluation were correlated with final diagnosis after thorough clinical evaluation, imaging and the neurologist's opinion.

Results: Out of 50 patients diagnosed having papilledema on MRI, 46 (92%) showed crescent sign on B scan ultrasonography. Headache was most common presenting complaint in 47 (94%) and idiopathic intracranial hypertension was most common underlying cause of papilledema in 30 (60%) cases.

Conclusion: "Crescent sign" seen on ultrasonography is a sensitive tool for diagnosis of papilledema. It is cost effective, less cumbersome and effective tool to differentiate between papilledema and pseudo papilledema before subjecting the patients to costly investigations like MRI. A positive crescent sign should always be followed by MRI to find out the cause of papilledema.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.5662/wjm.v7.i3.108DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5618144PMC
September 2017
-->