Hybrid luminescent/magnetic nanostructured porous silicon particles for biomedical applications

Manufacture of Mesoporous Silicon Microparticles (MSMPs) as Adjuvants for Vaccine Delivery

The advent of computational approaches has accelerated the identification of vaccine candidates like epitope peptides. However, epitope peptides are usually very poorly immunogenic and adequate platforms are required with adjuvant capacity to verity immunogenicity and antigenicity of vaccine subunits in vivo. Silicon microparticles are being developed as potential new adjuvants for vaccine delivery due to their physicochemical properties. This chapter explains the methodology to fabricate and functionalize mesoporous silicon microparticles (MSMPs) which can be loaded with antigens of different nature, such as viral peptides, proteins, or carbohydrates, and this strategy is particularly suitable for delivery of epitopes identified by computer.

Time-gated luminescence imaging of positively charged poly-l-lysine-coated highly microporous silicon nanoparticles in living Hydra polyp

The development of non-toxic fluorescent agents alternative to heavy metal-based semiconductor quantum dots represents a relevant topic in biomedical research and in particular in the bioimaging field. Herein, highly luminescent Si─H terminal microporous silicon nanoparticles with μs-lived photoemission are chemically modified with a two step process and successfully used as label-free probes for in vivo time-gated luminescence imaging. In this context, Hydra vulgaris is used as model organism for in vivo study and validity assessment. The application of time gating allows to pursue an effective sorting of the signals, getting rid of the most common sources of noise that are fast-decay tissue autofluorescence and excitation scattering within the tissue. Indeed, an enhancement by a factor ~ 20 in the image signal-to-noise ratio can be estimated.

Porous Si Partially Filled with Water Molecules-Crystal Structure, Energy Bands and Optical Properties from First Principles

The paper reports the results on first-principles investigation of energy band spectrum and optical properties of bulk and nanoporous silicon. We present the evolution of energy band-gap, refractive indices and extinction coefficients going from the bulk Si of cubic symmetry to porous Si with periodically ordered square-shaped pores of 7.34, 11.26 and 15.40 Å width. We consider two natural processes observed in practice, the hydroxylation of Si pores (introduction of OH groups into pores) and the penetration of water molecules into Si pores, as well as their impact on the electronic spectrum and optical properties of Si superstructures. The penetration of OH groups into the pores of the smallest 7.34 Å width causes a disintegration of hydroxyl groups and forms non-bonded protons which might be a reason for proton conductivity of porous Si. The porosity of silicon increases the extinction coefficient, k, in the visible range of the spectrum. The water structuring in pores of various diameters is analysed in detail. By using the bond valence sum approach we demonstrate that the types and geometry of most of hydrogen bonds created within the pores manifest a structural evolution from distorted hydrogen bonds inherent to small pores (∼7 Å) to typical hydrogen bonds observed by us in larger pores (∼15 Å) which are consistent with those observed in a wide database of inorganic crystals.

Nanostructured porous silicon: the winding road from photonics to cell scaffolds - a review

For over 20 years, nanostructured porous silicon (nanoPS) has found a vast number of applications in the broad fields of photonics and optoelectronics, triggered by the discovery of its photoluminescent behavior in 1990. Besides, its biocompatibility, biodegradability, and bioresorbability make porous silicon (PSi) an appealing biomaterial. These properties are largely a consequence of its particular susceptibility to oxidation, leading to the formation of silicon oxide, which is readily dissolved by body fluids. This paper reviews the evolution of the applications of PSi and nanoPS from photonics through biophotonics, to their use as cell scaffolds, whether as an implantable substitute biomaterial, mainly for bony and ophthalmological tissues, or as an in vitro cell conditioning support, especially for pluripotent cells. For any of these applications, PSi/nanoPS can be used directly after synthesis from Si wafers, upon appropriate surface modification processes, or as a composite biomaterial. Unedited studies of fluorescently active PSi structures for cell culture are brought to evidence the margin for new developments.

Nanostructured copper/porous silicon hybrid systems as efficient sound-emitting devices

In the present work, the photo-acoustic emission from nanostructured copper/porous silicon hybrid systems was studied. Copper nanoparticles were grown by photo-assisted electroless deposition on crystalline silicon and nanostructured porous silicon (nanoPS). Both the optical and photo-acoustic responses from these systems were determined. The experimental results show a remarkable increase in the photo-acoustic intensity when copper nanoparticles are incorporated to the porous structure. The results thus suggest that the Cu/nanoPS hybrid systems are suitable candidates for several applications in the field of thermoplasmonics, including the development of sound-emitting devices of great efficiency.

Soft Hybrid Nanoparticles: from Preparation to Biomedical Applications

Hybrid particles are a class of materials that include both organic and inorganic moieties at the same time and possess interesting magnetic, optical and mechanical properties. Extensive research is being carried out to develop soft hybrid nanoparticles utilizing their superparamagnetic, biodegradable and fluorescence properties and to explore their biomedical applications. This chapter discusses the important methods for the development of different types of soft hybrid nanoparticles, including polymer immobilization on preformed particles, adsorption of polymers on colloidal particles, adsorption of polymers via layer-by-layer self-assembly, adsorption of nanoparticles on colloidal particles, chemical grafting of preformed polymers, polymerization from and on to colloidal particles, click chemistry, atom-transfer radical polymerization (ATRP), reversible addition–fragmentation chain-transfer radical (RAFT) polymerization, nitroxide-mediated polymerization (NMP) and conventional seed radical polymerization. With current rapid advances in nanomedicine, colloidally engineered hybrid particles are gaining immense importance in fields such as cancer therapy, gene therapy, disease diagnosis and bioimaging. The applications of soft hybrid nanoparticles with respect to diagnosis are discussed briefly and a comprehensive account of their applications in the capture and extraction of nucleic acids, proteins and viruses is presented in this chapter.

Design and characterization of biofunctional magnetic porous silicon flakes

Magnetic porous silicon flakes (MPSF) were obtained from mesoporous silicon layers formed by multi-step anodization and subsequent composite formation with Fe oxide nanoparticles by thermal annealing. The magnetic nanoparticles adhered to the surface and penetrated inside the pores. Their structure evolved as a result of the annealing treatments derived from X-ray diffraction and X-ray absorption analyses. Moreover, by tailoring the magnetic load, the dynamic and hydrodynamic properties of the particles were controlled, as observed by the pressure displayed against a sensor probe. Preliminary functionality experiments were performed using an eye model, seeking potential use of MPSF as reinforcement for restored detached retina. It was observed that optimal flake immobilization is obtained when the MPSF reach values of magnetic saturation >10(-4)Am(2)g(-1). Furthermore, the MPSF were demonstrated to be preliminarily biocompatible in vitro. Moreover, New Zealand rabbit in vivo models demonstrated their short-term histocompatibility and their magnetic functionality as retina pressure actuators.

Engineering of silicon surfaces at the micro- and nanoscales for cell adhesion and migration control

The engineering of surface patterns is a powerful tool for analyzing cellular communication factors involved in the processes of adhesion, migration, and expansion, which can have a notable impact on therapeutic applications including tissue engineering. In this regard, the main objective of this research was to fabricate patterned and textured surfaces at micron- and nanoscale levels, respectively, with very different chemical and topographic characteristics to control cell–substrate interactions. For this task, one-dimensional (1-D) and two-dimensional (2-D) patterns combining silicon and nanostructured porous silicon were engineered by ion beam irradiation and subsequent electrochemical etch. The experimental results show that under the influence of chemical and morphological stimuli, human mesenchymal stem cells polarize and move directionally toward or away from the particular stimulus. Furthermore, a computational model was developed aiming at understanding cell behavior by reproducing the surface distribution and migration of human mesenchymal stem cells observed experimentally.

High surface water interaction in superhydrophobic nanostructured silicon surfaces: convergence between nanoscopic and macroscopic scale phenomena

In the present work, we investigate wetting phenomena on freshly prepared nanostructured porous silicon (nPS) with tunable properties. Surface roughness and porosity of nPS can be tailored by controlling fabrication current density in the range 40-120 mA/cm(2). The length scale of the characteristic surface structures that compose nPS allows the application of thermodynamic wettability approaches. The high interaction energy between water and surface is determined by measuring water contact angle (WCA) hysteresis, which reveals Wenzel wetting regime. Moreover, the morphological analysis of the surfaces by atomic force microscopy allows predicting WCA from a semiempiric model adapted to this material.