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Additive manufacturing of dental prostheses e.g. composite materials is continuously finding broader application in dentistry. In the oral environment, the materials are subjected to hydrolysis and accelerated hydrolysis by enzymes. With the aim to compare an additively manufactured composite with a self-curing and a CAD/CAM material of the same composition, the effect of enzymatic degradation and hydrolysis on the materials were investigated. The experimental composites consisted of 50 wt. % inorganic filler and 50 wt. % monomer matrix (BisEMA, BisGMA, TEGDMA). The influence of hydrolysis via a buffer system was investigated in comparison to enzymatic degradation by cholesterol esterase over 22 days. The detection of degradation products over time was conducted by HPLC-DAD analysis. Degradation products and monomers calibrated were: TEGDMA, BisGMA, BisEMA, MA, TEGMA, Bis-HPPP and E-bis-PA. Surface roughness of polished specimens was measured by AFM and hardness with a Vickers micro hardness tester. After enzymatic degradation and hydrolysis, BisGMA was detected in the eluates of the additively manufactured composites. The samples fabricated by CAD/CAM behaved similar during hydrolysis, where additionally MA was detected. After enzymatic degradation, furthermore TEGMA and BisEMA were detected qualitatively. In contrast, the self-curing material exhibited traces of MA, TEGMA, TEGDMA and BisGMA after enzymatic degradation. Hereof detectable upon hydrolysis were MA, TEGMA and BisGMA. Surface roughness was comparable for all manufactured samples whereas the hardness was lowest of the 3D printed material. Enzymatic degradation and hydrolysis had no effect on surface roughness and hardness. The additively manufactured composite appeared to have low susceptibility to enzymatic degradation and hydrolysis. Due to the manufacturing process, the polishability and initial hardness are poorer.

The growing significance of surface properties in modern materials, particularly in medical technology, drives the need for accurate characterization techniques. Traditional contact angle measurements face challenges when applied to intricate surfaces like dental implants. Here, tensiometry applying the Wilhelmy plate method has been described in the last decade to offer one solution for the evaluation of complex surface geometries by quantifying apparent contact angles based on wetting forces. This study evaluates a simple setup employing the Wilhelmy balance concept for immersion angle determination. Instead of using a force sensor as in tensiometers, the wetting force is determined via changes in mass signal by means of an analytical balance available in standard laboratories. The force is thus recorded inverse to conventional tensiometry. The approach was validated on diverse geometries and extended to intricate structures, including plasma‐treated dental implants. Results were compared to conventional contact angle analysis systems underlining the reliability of the method in characterizing non‐planar and complex surfaces. Additionally, the method was successfully extended to the evaluation of surface energies on planar and non‐planar surfaces using various solvent sets. However, results evidenced that specimen geometry can influence the measurements to such an extent that immersion contact angles can no longer be calculated due to capillary effects. An outlook suggests further exploration with a wider range of test liquids to enhance accuracy in surface energy determination. [ABSTRACT FROM AUTHOR]

Despite the increasing importance of recycling, the medical sector is hardy engaged at this time due to regulatory issues. The aim of this study was to evaluate the influence of γ‐radiation sterilization (48–52 kGy) on the repetitive injection molding of a polypropylene copolymer for medical applications. For this purpose, the material was analyzed after injection molding and irradiation. To evaluate the irradiation and reprocessing influence, optical, rheological, and mechanical properties were investigated in addition to chromatography. The latter comprised the quantitative determination of Irgafos 168 and the qualitative comparison of volatile degradation products formed, including the radiolysis product 1,3‐di‐tert‐butylbenzene. The influence of irradiation on the content of Irgafos 168, volatile organic compounds, and 1,3‐di‐tert‐butylbenzene was greatest after the first irradiation, with a decrease of Irgafos 168 content by 40%. The yellowness index and melting enthalpy were influenced by irradiation and processing, but showed no direct relationship to the individual process steps. The zero viscosity correlated directly with gas chromatography–mass spectrometry results and decreased by 80% after the first irradiation. In addition, the elongation at break was reduced by 95% after the second irradiation. The influence of irradiation on the studied characteristics was high, whereas the influence of repetitive processing did not show any measurable differences [ABSTRACT FROM AUTHOR]

The properties of graphene (GP) filled rubber nanocomposites were investigated in functions of rubber type (unmodified natural rubber (NR) and epoxidized natural rubber with 25 mol% epoxides (ENR-25)) and filler content. The Fourier transform infrared spectroscopy (FTIR) spectrum indicated that GP surfaces contain polar hydroxyl and carbonyl functional groups. The ENR-25/GP compound exhibited higher maximum torque, torque difference, storage modulus, initial relaxation modulus, bound rubber, and degree of reinforcement with smaller GP aggregates dispersed in the rubber matrix than the NR/GP composites. Additionally, an increasing trend of tensile strength was observed in the ENR-25/GP composite, but the contrary trend was obviously seen in the NR/GP composites due to the interaction between polar functional groups in ENR-25 and GP surfaces. Furthermore, a higher Payne effect (filler-filler interaction) was found in the NR/GP composites, corresponding to larger GP agglomerates and voids dispersed in the NR matrix. Moreover, the ENR-25/GP composite had higher electrical conductivity and dielectric constant than the NR/GP composite due to the higher polarity of the ENR with the dipoles, leading to increasing orientation polarization and interfacial polarization. [ABSTRACT FROM AUTHOR]

The present study reports on the long‐term drug release and mechanical properties of bioactive dental filling materials based on chlorhexidine diacetate (CHX) or octinidine (di)hydrochloride (ODH) incorporated in a composite based on dimethacrylates or an ormocer. CHX or ODH were added to a nano‐hybrid ormocer (O) and a nano‐hybrid composite (C) with the amount of 2 wt% to achieve four matrix‐drug combinations: O‐CHX, O‐ODH, C‐CHX, and C‐ODH. Drug extraction and release were measured using high‐performance liquid chromatography with diode‐array detection (HPLC‐DAD), while drug distribution was assessed by using energy dispersive X‐ray spectroscopy (EDX). Drug release in water at 37°C was observed over 87 d. To determine the material properties, the water absorption, water solubility, flexural strength and hardness were measured and compared to the reference materials. Persistent drug release over 87 d was observed for both ODH‐based systems and both ormocer‐systems, with the longest duration of activity seen for the O‐ODH combination. Persistent drug release was achieved via the loosening of the polymer network indicated via decreasing polymerization enthalpies, enhanced water absorption, and water solubility. As a consequence, the flexural strengths of the materials were reduced. However, surface hardness was hardly reduced. ODH seems to be more adequate than CHX for the design of bioactive dental filling materials based on nano‐hybrid ormocer and composites. [ABSTRACT FROM AUTHOR]

With the aim to design bioactive dental restorative material, the present study investigated the influence of the antimicrobial agents chlorhexidine diacetate (CHX) and octinidine (di)hydrochloride (ODH) when incorporated in two different materials. Selected parameters were polymerization enthalpy, short‐term drug release, and the effect on Streptococcus mutans as well as human gingival fibroblasts. Samples were made by mixing a nano‐hybrid ormocer (O) and a methacrylate‐based nano‐hybrid composite (C), each with a mass fraction of 2% CHX or ODH. Release profiles and concentrations of active agents from the resins were assessed, and the cell proliferation of human gingival fibroblasts as well as Streptococcus mutans cultured with the eluates were evaluated. The influence on polymerization was assessed by means of differential scanning calorimetry. Both drugs, especially ODH, showed a decreasing effect on polymerization enthalpies associated with a lowered crosslinking degree. At the same time ODH appeared to be released more persistently than CHX. Moreover, ODH was more efficient with regard to bacteria growth inhibition but also more cytotoxic in terms of reduction of cell viability. ODH is deemed more appropriate for application in a dental resin‐based drug delivery system, because of the more persistent drug release than seen for CHX. [ABSTRACT FROM AUTHOR]

Abstract Background Bio-conjugated nanoparticles are important analytical tools with emerging biological and medical applications. In this context, in situ conjugation of nanoparticles with biomolecules via laser ablation in an aqueous media is a highly promising one-step method for the production of functional nanoparticles resulting in highly efficient conjugation. Increased yields are required, particularly considering the conjugation of cost-intensive biomolecules like RNA aptamers. Results Using a DNA aptamer directed against streptavidin, in situ conjugation results in nanoparticles with diameters of approximately 9 nm exhibiting a high aptamer surface density (98 aptamers per nanoparticle) and a maximal conjugation efficiency of 40.3%. We have demonstrated the functionality of the aptamer-conjugated nanoparticles using three independent analytical methods, including an agglomeration-based colorimetric assay, and solid-phase assays proving high aptamer activity. To demonstrate the general applicability of the in situ conjugation of gold nanoparticles with aptamers, we have transferred the method to an RNA aptamer directed against prostate-specific membrane antigen (PSMA). Successful detection of PSMA in human prostate cancer tissue was achieved utilizing tissue microarrays. Conclusions In comparison to the conventional generation of bio-conjugated gold nanoparticles using chemical synthesis and subsequent bio-functionalization, the laser-ablation-based in situ conjugation is a rapid, one-step production method. Due to high conjugation efficiency and productivity, in situ conjugation can be easily used for high throughput generation of gold nanoparticles conjugated with valuable biomolecules like aptamers.

Abstract Ultrashort pulsed laser ablation in liquids represents a powerful tool for the generation of pure gold nanoparticles (AuNPs) avoiding chemical precursors and thereby making them especially interesting for biomedical applications. However, because of their electron accepting properties, laser-generated AuNPs might affect biochemical properties of biomolecules, which often adsorb onto the nanoparticles. We investigated possible effects of such laser-generated AuNPs on biological functionality of DNA molecules. We tested four differently sized and positively charged AuNPs by incubating them with recombinant eGFP-C1-HMGB1 DNA expression plasmids that code for eGFP fusion proteins and contain the canine architectural transcription factor HMGB1. We were able to show that successfully transfected mammalian cells are still able to synthesize and process the fusion proteins. Our observations revealed that incubation of AuNP with the plasmid DNA encoding the recombinant canine HMGB1 neither prevented the mediated uptake of the vector through the plasma membrane in presence of a transfection reagent nor had any effect on the transport of the synthesized fusion proteins to the nuclei. Biological activity of the recombinant GFP-HMGB1 fusion protein appears to have not been affected either, as a strong characteristic protein accumulation in the nucleus could be observed. We also discovered that transfection efficiencies depend on the size of AuNP. In conclusion, our data indicate that laser-generated AuNPs present a good alternative to chemically synthesized nanoparticles for use in biomedical applications.