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Recent interest in photolithographic processes employing single and two-photon absorption processes have afforded advanced opportunities to fabricate both planar and three-dimensional microstructures. The fabrication of such structures is dependent on the local polymerization of the organic moieties using photoinitiating molecules, and a key parameter to consider is the dependency of the photoreactivity of these initiators on the matrices in which they are dispersed. To our knowledge, there has been no comprehensive investigation reported on the photoreactivity dependency of commercially available photoinitiators inserted within hybrid sol–gel materials. The aim of this paper is to highlight and explain the influence of the composition of hybrid organic–inorganic sol–gel materials on the photoreactivity of UV-sensitive initiators. Of particular interest is the understanding of the interactions between photoinitiating molecules and the sol– gel matrix. It is shown that both the nature of the chelating agent as well as the degree of chelation of the inorganic part of the hybrid sol–gel material significantly influence the spectral absorption of the photoinitiator. It is demonstrated that metal–ligand charge transfer processes are the main phenomena responsible for the red shift of the absorption of the amino-functionalized photoinitiators, which is strongly dependent on the condensation of the materials.

In this work, we have synthesized and characterized a novel, titanium-containing hybrid material that can be structured three-dimensionally using two-photon polymerization. We investigate the effect on the structurability of the increase of titanium isopropoxide and methacrylic acid in this photosensitive composite. We show that while it is possible to make transparent thin films with a titanium isopropoxide molar content as high as 90%, three-dimensional structures can be made only when the titanium isopropoxide molar content is less than 50%. We measure the refractive index of films with different titanium isopropoxide: methacrylic acid concentrations and we show that while the refractive index increases linearly with the titanium isopropoxide, the increase of the methacrylic acid content does not affect the refractive index of the material.

Direct laser writing by two-photon polymerization of photosensitive materials has emerged as a very promising technique for rapid and flexible fabrication of photonic crystals. In this work, a photosensitive silica sol-gel containing the nonlinear optical chromophore Disperse Red 1 is synthesized, and the two-photon polymerization technique is employed to fabricate three-dimensional photonic crystals with stop-gaps in the near-infrared. The composite material exhibits minimal shrinkage during photopolymerization, eliminating the need for shrinkage compensation or the fabrication of support structures.

Over the past twenty years, the use of rapid prototyping techniques for processing of medical devices has seen rapid growth. A number of rapid prototyping techniques currently exist for producing a broad range of medical devices using metals, ceramics, polymers, and composite materials. One promising rapid prototyping technology for creating medical devices with small scale features is two photon polymerization; this scalable photopolymerization technique enables processing of photosensitive materials such as organically-modified ceramic materials. In this study, two photon polymerization was used to produce microneedles that mimic the anatomy of the mosquito fascicle. The labrum of the mosquito was replicated in the mosquito-like microneedle. On the other hand, the maxillae of the mosquito were not replicated in the mosquito-like microneedle; the absence of these features was attributed to inadequate mechanical support of the maxillae. This study suggests that two photon polymerization and other rapid prototyping technologies may be used to produce biomimetic drug delivery devices that imitate the intricate structures found in nature.

Two-photon polymerization (2PP) is a novel technology for the fabrication of complex three-dimensional (3D) microstructures. The number of applications employing this technology is rapidly increasing, and includes the fabrication of three-dimensional photonic crystals [1-4], medical devices, and scaffolds for tissue engineering [5, 6]. We have used 2PP to fabricate microneedle arrays with various geometries. These devices provide a unique approach for transdermal delivery of nucleic acid- and protein-based pharmacologic agents. Many of issues associated with conventional intravenous drug administration, including pain to the patient, trauma at the injection site, and difficulty in providing sustained release of a pharmacological agent, may be eliminated by applying the microneedles. The effect of microneedle geometry (e.g., tip sharpness and aspect ratio) on skin penetration was examined. Our results indicate that microneedles created using 2PP technique are suitable for in vivo use, and integration with next generation MEMS- and NEMS-based drug delivery devices.

A fresh approach with a novel process and a hybrid material is explored for developing designer 3-dimensional functional tissue scaffolds. The process of two photon-induced polymerization generally used for electronic and optical materials is introduced for developing biological scaffolds. Hybrid materials containing organic-inorganic units, ORMOCERs, fabricated with this process are tested for biocompatibility using various cell-types and compared with known standards such as polystyrene and ECM (Extracellular Matrix). Results show good adherence of different cells to these materials, and a growth rate comparable to bioactive materials. Structures with various surface topologies are developed and tested for preferential growth. The study is a first step towards developing bioactive and bioresorbable heterogeneous three-dimensional scaffolds.

Our recent progress in the direct-write femtosecond laser material processing technologies, nanostructuring, and fabrication of photonic devices is reviewed. Special attention is given to the sub-wavelength microstructuring of metals and two-photon polymerization (2PP) technique. Formation of microbumps and nanojets on thin metal films under single pulse laser irradiation is discussed. Microstructuring of different photosensitive materials by 2PP technique is demonstrated. Numerous applications of this technology for the fabrication of 3d structures, waveguides, photonic crystals, etc. are studied.