Mika Koskinen

Heat curing of UTMA-based hybrid resin : effects on the degree of conversion and cytotoxicity

This study was designed to determine the effects of the heat curing time on a urethane tetramethacrylate (UTMA)-based hybrid resin and specifically on the degree of conversion (DC) and cytotoxicity. The materials used in this study were Estenia, a new-generation hybrid resin, and an experimental fiber reinforcement, Br-100. The DC values of the hybrid resin samples were measured using a Fourier transform infrared (FTIR) spectrophotometer after 180 s of light curing followed by heat curing (0, 15, 30, and 60 min). A method comparing intensities of C = C and N—H vibrations of the sample was used to calculate the final DC values. FTIR spectra were measured both inside and on the surface of the sample. The calculated DC values increased by increasing the heat curing times. After light curing only and after 15-min heat curing, the DC values inside the samples were smaller than the corresponding DC values at the surfaces of the samples. After 60 min of heat curing, the samples achieved homogeneous polymerization (DC% = 65). The cytotoxicity of the material was studied from the glass fiber-reinforced hybrid resin samples, which were first light cured and then heat cured (15, 30, and 60 min). Cytotoxicity was tested using both direct contact and extract methods. For the extract tests, the test specimens were incubated in a cell culture media at 37°, 54°, or 72°C for 24 h. The heat curing times used had no effect on cytotoxicity. The incubation temperature, however, did have a significant effect. The extract obtained from 72°C incubation showed a cytotoxic effect whereas the others did not. The direct contact test did not show cytotoxicity.

Extended release of adenovirus from silica implants in vitro and in vivo

Despite promising preclinical results, the clinical benefits of cancer gene therapy have been modest heretofore. The main obstacle continues to be the level and persistence of gene delivery to sufficiently large areas of the tumor. One approach for overcoming this might entail extended local virus release. We studied the utility of silica gel monoliths for delivery of adenovirus to advanced orthotopic gastric and pancreatic cancer tumors. Initially, the biochemical properties of the silica-virus matrix were studied and nearly linear release as a function of time was detected. Virus stayed infective for weeks at +37 °C and months at +4 °C, which may facilitate storage and distribution. In vivo, extended release of functional replication deficient and also replication-competent, capsid-modified oncolytic viruses was seen. Treatment of mice with pancreatic cancer doubled their survival (P<0.001). Also, silica gel-based delivery slowed the development of antiadenovirus antibodies.

Effects of capsid-modified oncolytic adenoviruses and their combinations with gemcitabine or silica gel on pancreatic cancer.

Conventional cancer treatments often have little impact on the course of advanced pancreatic cancer. Although cancer gene therapy with adenoviruses is a promising developmental approach, the primary receptor is poorly expressed in pancreatic cancers which might compromise efficacy and thus targeting to other receptors could be beneficial. Extended stealth delivery, combination with standard chemotherapy or circumvention of host antiadenoviral immune response might improve efficacy further. In this work, capsid‐modified adenoviruses were studied for transduction of cell lines and clinical normal and tumor tissue samples. The respective oncolytic viruses were tested for oncolytic activity in vitro and in vivo. Survival was studied in a peritoneally disseminated pancreas cancer model, with or without concurrent gemcitabine while silica implants were utilized for extended intraperitoneal virus delivery. Immunocompetent mice and Syrian hamsters were used to study the effect of silica mediated delivery on antiviral immune responses and subsequent in vivo gene delivery. Capsid modifications selectively enhanced gene transfer to malignant pancreatic cancer cell lines and clinical samples. The respective oncolytic viruses resulted in increased cell killing in vitro, which translated into a survival benefit in mice. Early proinfammatory cytokine responses and formation of antiviral neutralizing antibodies was partially avoided with silica implants. The implant also shielded the virus from pre‐existing neutralizing antibodies, while increasing the pancreas/liver gene delivery ratio six‐fold. In conclusion, capsid modified adenoviruses would be useful for testing in pancreatic cancer trials. Silica implants might increase the safety and efficacy of the approach.

Rationale of Using Conventional Sol-Gel Derived SiO2 for Delivery of Biologically Active Agents

Progress in the research of mesoporous materials, hierarchical pore structures, chemical modification of surfaces, nanoparticle processing and hybrid materials is important and it provides new and interesting functional properties for silica structures. However, this has also left the conventional, alkoxy-based sol-gel derived silica in the shadow, although it has a lot of non-utilized potential, especially in the delivery and/or encapsulation of sensitive biologically active agents like viral vectors, proteins, nucleic acids and cells. The potential lies in the versatile possibilities to adjust the structure by using alkoxides as precursors and in the proper use of water in different steps of the processing. The conventional, alkoxy-based sol-gel silica structure can be processed so that it results in largely variable biodegradation rates, biodegradation-controlled release of encapsulated agents and beneficial environment even for highly sensitive agents. These kinds of silica structures contain more or less water and hence, they are more or less labile from the traditional viewpoint of materials science. In extreme case they could be called “unfinished silica”. The aim of this paper is to discuss how the biodegradation rate of these kinds of silica materials can be adjusted on a large scale and how this is related to a rather narrow scale adjustment of in vitro dissolution rate of silica, how the unfinished silica structures can be controlled and their properties adjusted, how they can be utilized in the delivery of biologically active agents, and what the potential problems to be solved are.

About Interactions Between Sol-Gel Derived Silica, Titania and Living Organisms

Sol-gel derived silica and titania have a specific interaction with many biological molecules, microbes, algae, cells and living tissue. The specific interactions mean that they differ from common reactions between non-viable materials and biomolecules or living tissues and the interactions are mostly beneficial from the viewpoint of biotechnical applications. Pepetides and proteins may preserve their activity and bacteria, algae and cells may preserve their viability and viruses their infectivity as encapsulated in sol-gel derived silica. Silica and titania are known to form a direct bond with living tissue which can be utilized in the biomaterial applications. Other application areas of silica and titania are in biosensing, tissue engineering, gene therapy, controlled delivery of therapeutic agents and environmental protection.

An in Vitro Study of Heparin-Immobilized Poly(Ethylene-Graft-Vinylacetate) and Poly(Ethylene-Graft-Vinylpyridine)

Polyethylene (PE) was modified by radiation-induced grafting of vinyl acetate (VAc) and vinyl pyridine (VP), followed by heparinization of the surface. The unmodified, the grafted, and the heparin-immobilized samples were studied with X-ray photoelectron spectroscopy. The heparinized samples were also studied by Laser Scanning Confocal Microscopy and by the toluidine blue method. The biological activity of heparin against thrombin formation was evaluated by the chromogenic method. The graft-copolymerization of PE with VAc or VP, as well as the heparin immobilization were successfully carried out. The heparin was strongly attached to the VP-grafter PE, but underwent slow release when immobilized on the hydrolyzed VAc-grafter PE. The grafted and heparinized materials showed no toxicity when examined by in vitro cell studies, and the immobilized heparin retained its biological activity.