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Abstract-The nonlinear effects in optical fiber occur either due to intensity dependence of refractive index of the medium or due to inelastic-scattering phenomenon. This paper describes various types of nonlinear effects based on first effect such as self-phase modulation, cross-phase modulation and four-wave mixing. Their thresholds, managements and applications are also discussed; and comparative study of these effects is presented.

We report the design of an injectable synthetic and biodegradable polymeric biomaterial comprised of polyethylene glycol and a polycarbonate of dihydroxyacetone (MPEG-pDHA). MPEG-pDHA is a thixotropic physically cross-linked hydrogel, displays rapid chain relaxation, is easily extruded through narrow-gauge needles, biodegrades into inert products, and is well tolerated by soft tissues. We demonstrate the clinical utility of MPEG-pDHA in the prevention of seroma, a common postoperative complication following ablative and reconstructive surgeries, in an animal model of radical breast mastectomy. This polymer holds significant promise for clinical applicability in a host of surgical procedures ranging from cosmetic surgery to cancer resection.hydrogel | seroma prevention | dihydroxyacetone | surgical biomaterial P olymeric biomaterials have contributed significantly to the advancement of medical and surgical practice over the past few decades. Their macromolecular structure can be tailored to provide the appropriate combination of chemical, physical, and biological properties necessary for a range of medical and surgical applications. The rational design of polymeric biomaterials has impacted many fields, including drug and gene delivery, orthopedics, tissue engineering, ophthalmology, and general surgery (1-3). The work reported herein focuses on the development of an injectable surgical biomaterial. Its potential impact is demonstrated in the prevention of postoperative seroma.A seroma is an abnormal collection of serous fluid within the tissues of the body, akin to an internal blister. Seroma formation is a common postoperative complication particularly following ablative and reconstructive surgeries. Surgeries that require extensive tissue dissection and create large empty spaces can disrupt normal lymphatic flow. Subsequently, transduate fluid collects in these poorly drained "dead spaces," resulting in formation of a seroma (4, 5). Seromas can lead to significant patient morbidity, such as infection, decreased limb mobility, and reoperation (4, 6, 7). Seroma formation rates range from 9.1% to 81%, depending on the nature of the surgical procedure (6,(8)(9)(10)(11)(12)(13). Notably, modified radical mastectomies lead to seroma formation rates ranging from 15% to 38.6%, and radical mastectomies report a rate as high as 52% (7,(14)(15)(16)(17). In current clinical practice, silicone surgical drains are placed in the wound bed through separate stab incisions to collect transudate fluid, but they can be a significant source of pain and discomfort to patients, especially upon their removal up to several weeks after the initial surgical procedure. Furthermore, they can increase the risk of infection at the surgical site.Several approaches to reduce seroma formation have been investigated. Surgical techniques, such as collapsing the seroma cavity with sutures, do not consistently and adequately eliminate seroma formation (16,18,19). Other methods, such as sclerotherapy (20, 21), compression dressings (22), and biolog...

The dynamical deformation of ultrasoft colloids as well as their dynamic frictional forces are numerically investigated, when one colloid is dragged past another at constant velocity. Hydrodynamic interactions are captured by a particle-based mesoscopic simulation method. At vanishing relative velocity, the equilibrium repulsive force-distance curve is obtained. At large drag velocities, in contrast, we find an apparent attractive force for departing colloids along the dragging direction. The deformation, in the close encounter of colloids, and the energy dissipation are examined as a function of the drag velocity and their separation.

We study semidilute star-polymer solutions under shear flow by hybrid mesoscale simulations. Hydrodynamic interactions are modeled by two particle-based simulation techniques, multiparticle collision dynamics (MPC) and dissipative particle dynamics (DPD). Star polymers are considered as a paradigmatic model for ultra-soft colloids with variable softness. The influence of concentration and shear rate on their structural and rheological properties is investigated. Under flow, a star polymer elongates and displays a well-defined alignment angle with respect to the flow direction. Moreover, the structural and rheological properties exhibit a universal behavior as a function of a concentrationdependent Weissenberg number for various concentrations at a given arm length. The rheological properties are characterized by the shear viscosity and the normal-stress coefficients. In dilute solution, the zero-shear viscosity follows the Einstein relation with an effective radius given by the hydrodynamic radius of a star polymer. At high shear rates, the solutions exhibit shear-thinning behavior, where the viscosity decreases faster with increasing shear rate at higher concentrations. We demonstrate that the results obtained from MPC and DPD agree in all scaling properties, with minor quantitative deviations in the numerical values.

The dynamical and rheological properties of ultrasoft colloids and star polymers are investigated in dilute and semidilute solutions under linear shear flow. We apply a hybrid mesoscale hydrodynamics simulation approach, which combines molecular dynamics simulations for the solute with the multiparticle collision dynamics approach for the solvent. We investigate the effect of concentration on relaxation, diffusion, and the rheological properties of the star polymers. We find that the relaxation time of a star-polymer arm is a universal function of a concentration-dependent Weissenberg number. The center-of-mass mean square displacements of the star polymers are anisotropic under shear flow. At high shear rate, we find shear-induced enhanced center-of-mass displacements along the vorticity and gradient directions. Moreover, we determine the shear viscosity and normal stress coefficients as a function of concentration. The shear viscosity exhibits shear thinning with a weak functionality dependence.

We investigate structural and dynamical properties of ultra-soft colloids in dilute and semi-dilute solutions by hybrid mesoscale simulations under linear shear flow. In particular, the influence of functionality on these properties is addressed. Our study combines molecular dynamics simulations for the solute with the multiparticle collision dynamics approach for the coarse-grained solvent. The star polymers exhibit large conformational and orientational changes in shear flow, which we characterize by the radius of gyration tensor and the alignment angle. These quantities show a universal dependence on a concentration- and functionality-dependent Weissenberg number with slight deviations at high shear rates. Moreover, the star polymers display a rotational dynamics with a shear-rate- and concentration-dependent rotation frequency. We attribute the concentration dependence to the screening of hydrodynamic interactions in semi-dilute star-polymer solutions.

We investigate structural and dynamical properties of a self-propelled filament using coarsegrained Brownian dynamics simulations. A self-propulsion force is applied along the bond vectors, i.e., tangent to the filament and their locations are considered in two different manners. In the case one, force is applied to all beads of the filament, which is termed as homogeneous self-propulsion. Here, we obtain a monotonic decrease in the flexibility of the filament with Péclet number. Hence, radius of gyration also displays the same trend. Moreover, the radius of gyration of the filament shows universal dependence for various bending rigidities with flexure number. The effective diffusivity of the filament shows enhancement with the active force and it increases linearly with force and bending rigidity. In the case two, self-propulsion force is applied only to few bond vectors. The location of active forces is chosen in a periodic manner starting from the tail of the filament and leaving the front end without force. In this case, filament acquires various structures such as rodlike, helical, circular, and folded states. The transition from several states is understood in terms of tangent-tangent correlation, bending energy and torsional order parameter. The helical state is identified through a crossover from exponential to oscillatory behavior of the tangent-tangent correlation. A sudden increase in the bending energy separates a helical to a folded states of the filament.