Ulrich P. Froriep

Conventional push-out tests detect bone–implant failure only at the point of macroscopic instability, leaving earlier damage stages unresolved. Here we present a proof-of-concept for a push-out test stand combined with acoustic emission (AE) monitoring, aimed at capturing crack initiation before the macroscopic load drop. To provide a controlled failure process, samples were fabricated from SLA resin with defined breaking points, serving as mechanical surrogates rather than biological models. Four sample types with varying strut number and thickness were tested while recording AE, and post-processing was applied to remove friction and noise signals. A four-stage fracture model—initial, pre-fracture, fracture, and post-fracture—was defined, with the pre-fracture stage showing AE activity prior to any macroscopic load response. Increasing strut thickness and contact area raised maximum load resistance and AE activity, and Principal Component Analysis confirmed a progressive, intensity-driven separation of stages. The results demonstrate that AE monitoring resolves a pre-fracture regime inaccessible to conventional load measurement, establishing a methodological basis for future application to bone–implant samples.

Conventional push-out tests detect bone–implant failure only at the point of macroscopic instability, leaving earlier damage stages unresolved. Here we present a proof-of-concept for a push-out test stand combined with acoustic emission (AE) monitoring, aimed at cap-turing crack initiation before macroscopic load drop. To provide a controlled failure pro-cess, samples were fabricated from SLA resin with defined breaking points, serving as mechanical surrogates rather than biological models. Four sample types with varying strut number and thickness were tested while recording AE, and post-processing was applied to remove friction and noise signals. A four-stage fracture model, plastic, pre-fracture, fracture, and post-fracture, was defined, with the pre-fracture stage showing AE activity prior to any macroscopic load response. Increasing strut thickness and contact area raised maximum load resistance and AE activity, and Principal Component Analysis confirmed a progressive, intensity-driven separation of stages. The results demonstrate that AE mon-itoring resolves a pre-fracture regime inaccessible to conventional load measurement, es-tablishing a methodological basis for future application to bone-implant samples.

A major disadvantage of inhalation therapy with continuous drug delivery is the loss of medication during expiration. Developing a breath-triggered drug release system can highly decrease this loss. However, there is currently no breath-triggered drug release directly inside the patient interface (nasal prong) for preterm neonates available due to their high breathing frequency, short inspiration time and low tidal volume. Therefore, a nasal prong with an integrated valve releasing aerosol directly inside the patient interface increasing inhaled aerosol efficiency is desirable. We integrated a miniaturized aerosol valve into a nasal prong, controlled by a double-stroke cylinder. Breathing was simulated using a test lung for preterm neonates on CPAP respiratory support. The inhalation flow served as a trigger signal for the valve, releasing humidified surfactant. Particle detection was performed gravimetrically (filter) and optically (light extinction). The integrated miniaturized aerosol valve enabled breath-triggered drug release inside the patient interface with an aerosol valve response time of 4 compared to non-triggered release. This novel nasal prong with integrated valve allows breath-triggered drug release directly inside the nasal prong with short response time.

Current developments of electrodes for neural recordings address the need of biomedical research and applications for high spatial acuity in electrophysiological recordings. One approach is the usage of novel materials to overcome electrochemical constraints of state-of-the-art metal contacts. Promising materials are carbon nanotubes (CNTs), as they are well suited for neural interfacing. The CNTs increase the effective contact surface area to decrease high impedances while keeping minimal contact diameters. However, to prevent toxic dissolving of CNTs, an appropriate surface coating is required. In this study, we tested flexible surface electrocorticographic (ECoG) electrodes, coated with a CNT-silicone rubber composite. First, we describe the outcome of surface etching, which exposes the contact nanostructure while anchoring the CNTs. Subsequently, the ECoG electrodes were used for acute in vivo recordings of auditory evoked potentials from the guinea pig auditory cortex. Both the impedances and the signal-to-noise ratios of coated contacts were similar to uncoated gold contacts. This novel approach for a safe application of CNTs, embedded in a surface etched silicone rubber, showed promising results but did not lead to improvements during acute recordings.

Current personalized treatment of neurological diseases is limited by availability of appropriate manufacturing methods suitable for long term sensors for neural electrical activities in the brain. An additive manufacturing process for polymer-based biocompatible neural sensors for chronic application towards individualized implants is here presented. To process thermal crosslinking polymers, the developed extrusion process enables, in combination with an infrared (IR)-Laser, accelerated curing directly after passing the outlet of the nozzle. As a result, no additional curing steps are necessary during the build-up. Furthermore, the minimal structure size can be achieved using the laser and, in combination with the extrusion parameters, provide structural resolutions desired. Active implant components fabricated using biocompatible materials for both conductive pathways and insulating cladding keep their biocompatible properties even after the additive manufacturing process. In addition, first characterization of the electric properties in terms of impedance towards application in neural tissues are shown. The printing toolkit developed enables processing of low-viscous, flexible polymeric thermal curing materials for fabrication of individualized neural implants.