Conference Agenda

Introduction

Synthetic models of vessels may be used for numerous applications, including the training of surgical interven-tions. Conventional manufacturing with polymers (e.g. molding) allows to use various materials to mimick the mechanical properties of a blood-vessel. However, this restricts the possible vessel geometries. Additive manu-facturing allows for greater geometric freedom, but the material choice is limited. In particular, materials that are both flexible and transparent are not very common. A combination of different fabrication methods allows to combine the individual advantages and to overcome the drawbacks.

Methods

A hollow sacrificial core of water-soluble polyvinyl alcohol (PVA) is printed using an Ultimaker 3 3D-printer (Ultimaker, Utrecht, Netherlands). The outer form is printed of a hard material using a Form 3B 3D-printer (Form-labs, Somerville, USA). The resulting mold is then filled with a two-component transparent silicone, or alterna-tively the silicone can be dyed to the specific need of the application. After the polymerisation, the core is dis-solved in water. Normally, this process is time-consuming due to a small contact surface between the water and the PVA, which is a disadvantage of the method especially for complex vessels. However, our method using a hollow core allows a much faster dissolution of the core, which significantly improves the hybrid manufacturing of complex vessels.

Results

Arterial models, which are especially relevant for neurosurgical interventions, were printed using this method, including an aortic arch, subclavian arteries and carotid arteries. The transparent silicone we used for the produc-tion allows for the visual observation of the position of a catheter inside the vessel, and thus provides an excel-lent basis for highly accurate and cost-efficient surgical training. As the vessels are waterproof, perfusion can be simulated with a blood-mimicking fluid, while in addition, the haptic feedback is much closer to human vessels than in most other training phantoms, which greatly increases the realism of the training.

Conclusion

The novel method allows for the efficient production of blood vessels, which is not necessarily limited to arter-ies. Further development of the method can address the modelling of other pathologies as well, which would wid-en the range of training scenarios to other surgical procedures.

Poly(ethylene glycol) diacrylate (PEGDA) is a common polymer in the field of biomedical engineering and can be used for the production of drug delivery systems (DDS). The main advantages of PEGDA are biocompatibility and the ability to alter the physical and chemical properties, thereby ensuring individualized drug release behaviour. The processing of PEGDA via inkjet printing is relevant for the production of DDS. This can be challenging due to the high viscosity of pure PEGDA. In this work, PEGDA, with a molecular weight of 250 g/mol (PEGDA250), was inkjet printed using a Nanoplotter 2.1 with a piezoelectric heatable NanoTip HV-J-H printhead (GeSiM mbH, Radeberg, Germany) at different voltages and temperatures. Droplet generation was analysed in terms of droplet volume and angle deviations. PEGDA250 can be inkjet printed reproducibly in a voltage range of 60 V – 80 V at room temperature (20 °C) or heated up to 38 °C. The average volume of heated (38 °C) PEGDA250 droplets was approximately 110 pl – 150 pl higher than the droplet volume of PEGDA250 in the unheated state. The average angle deviations of main and satellite droplets were mostly < 3°. Increasing voltage or excessive heating of more than 38 °C caused greater instabilities in the droplet generation as well as larger satellite droplets which can affect the accuracy negatively. The studies have shown that PEGDA250 can be processed via inkjet printing and thus can be used as a drug carrier for DDS without the need for mixing with a solvent.

Fused deposition modelling (FDM) technology allows the use of a wide range of thermally processable biocompatible or biodegradable polymers. Biomedical research is currently focusing on the development of 3D-printed stents that can be biodegradable, as well as drug-eluting. In this proof-of-concept study, a cylindrical substrate was integrated into a commercial FDM printer to establish a process for stent printing. Stents printed on a planar substrate were compared with those printed on the cylindrical substrate. The typical stepped structure along the stent struts on the planar print bed caused by layered printing is avoided with the cylindrical substrate.

The technique of 3D-printed micro-optics has experienced significant advancements over the last few years. This progressive evolution has been marked by remarkable strides in precision and miniaturization, making it particularly attractive to applications in the field of medical endoscopy. One noteworthy application entails the fabrication of micro-lenses directly on optical fibers, thereby creating endoscopic devices with unparalleled capabilities. A significant at-tribute of these micro-optical systems lies in their capability for precise imaging and their adept navigation through exceptionally narrow biological structures. For instance, the application of the 3D-printed endoscopy technology has facilitated insertion into the aorta of mice, as well as severely diseased human carotid arteries. This unprecedented level of accessibility and adaptability holds immense promise for diagnostic and therapeutic interventions in the realm of cardiovascular medicine and beyond. In the future, it may also be conceivable for micro-lenses to serve not only as imaging tools, but also as integral components of 3D-printing processes aimed at repairing damaged human tissue with bio-materials.

Performance quality is invariably necessary after lens production. With confocal surface profiling, only the surface shape information of micro-optics can be obtained. However, not only the shape of 3D-printed optics is relevant for its quality, but also its refractive index distribution is crucial when determining its overall optical performance. Therefore, the measurement of the wavefront is decisive in evaluating lens performance. Lateral shear interferometry presents it-self as a compact and precise method for wavefront measurements. The only essential component required in the set-up is a pair of glass plates with high surface quality. Consequently, the entire setup can be notably streamlined, as there is no requirement to construct an interferometer reference arm. This advantage facilitates the development of a notably compact setup, making lateral shear interferometry particularly advantageous for integration with microscope and 3D-printer, despite the requirement for more complex algorithms in analyzing lateral shear interferograms.

In this paper, simulation of shear interferogram fringes corresponding to wavefronts exhibiting varying aberrations are presented. Additionally, we discuss measurement and analysis of shear interferograms obtained from wavefronts transmitted through different 3D-printed lenses with deliberately added third order aberrations. Compared to the mathematical model and the simulation program illustrating the intensity map of two overlapping beams with specific aberration parameters, the experimental interferograms exhibit similar fringe patterns. Moreover, as aberration increases, the fringe patterns demonstrate analogous trends of change.

Grayscale lithography of a Nanoscribe Quantum X printer is used and the printing accuracy is evaluated, demonstrating λ/100 RMS wavefront error for 3D-printed aspheric singlet lenses with d = 140 µm and f = 570 µm, which represents states-of-art and diffraction-limited performance.

Shear interferometry provides a direct, rapid, and dependable method for measuring wavefronts on 3D-printed micro-optics. Its compact design facilitates easy integration into microscope setups. Furthermore, there are prospective plans to integrating the shear plate interferometer directly into the 3D printer. This integration aims to enable real-time optimization of optics printing alongside the printing process itself.

Introduction

Conventional surgery typically inflicts considerable tissue damage. Endoscopy based keyhole interventions helped to reduce side effects, however, surgical tools continue to operate in primarily subtractive fashion and our ability to directly regenerate tissue in situ remains limited. To overcome this, we propose a highly miniaturized bio-3D-printer at the tip of an endoscope to additively fabricate tissue on site.

Methods

To facilitate two-photon 3D printing of organotypic bio-inks with sub-cellular resolution at the tip of an optical fibre, we use a 780 nm femtosecond laser combined with an anomalous dispersive pulse compression to compensate propagation through a 2.5 m long singlemode optical fiber. A custom high-NA immersion objective lens at the tip of the fibre tightly focuses the delivered femtosecond laser pulses to pattern commercial photoresist as well as custom protein based bio-ink recipes. Printed scaffolds are analysed using electron microscopy, in biocompatibility assays and for their micro-mechanical profiles.

Results

At the tip of the fibre, we reach up to 40-fold pulse length compression leading to pulse lengths down to 110 fs or peak powers up to 1900 W. We successfully seal our 3D-printed endoscopic writing objective against photoresist intrusion and demonstrate diffraction limited focal spots at an NA of 0.625. In our experimental setup we show endoscopic 3D printing of microstructures with lateral dimensions of ~ 1 µm and axial dimensions of ~ 5 µm with commercial plastic resin as well as custom hydrogel photoresists which demonstrates a plausible path towards endoscopic 3D printing of tissue scaffolds.

Conclusion

We propose endoscopic biofabrication as a novel approach to minimal invasive micro-surgery by building a two-photon bio-3D-printer at the tip of an endoscope. In a first proof of concept, femtosecond 3D printing through a singlemode fiber is successfully demonstrated by combination of pulse compression, a 3D-printed high NA immersion objective, and bio-ink engineering. These results could be the seed for an edoscopic biofabrication platform addressing a broad interdisciplinary spectrum of topics from physics, optical engineering, bio-/chemical engineering, microfluidics, and medical engineering.

Introduction

Point-of-care testing (POCT) is becoming increasingly important in clinical settings to directly diagnose pathogens. Clostridioides difficile (C. difficile), for example, it is the most common cause of diarrhoea and an important noso-comial problem in hospital hygiene. The emergence of hypervirulent strains and the ability to form endospores makes rapid detection essential, as an early targeted antibiotic therapy prevent severe cases and spread.

Methods

A reaction chamber was developed that was manufactured in an additive process with photopolymer resins using digi-tal light processing (DLP) and tested for biocompatibility, microfluidic effects and other optical factors (e.g. transparen-cy, autofluorescence). An isothermal recombinase polymerase amplification (RPA) assay, alternatively to classical qPCR, was established for the detection of C. difficile toxin genes tcdA and tcdB. The real-time assay was tested in the 3D printed micro reaction chamber in terms of sensitivity and specificity.

Results

The monolithically 3D-printed micro reaction chamber showed no RPA inhibition and was analysed and optimised for fluorescence readout and microfluidic mixing structures. A duplex RPA assay has been developed that allows simulta-neous toxin gene detection at 39 °C in the 3D-printed micro reaction chamber. Qualitative results are possible within 15 minutes. The RPA systems are highly sensitive (LODs ≤ 688 DNA target copies) and specific.

Conclusion

The development of rapid and robust test systems for pathogen detection is of great importance to improve medical decisions. The established duplex RPA assay was demonstrated in combination with a 3D-printed micro reaction chamber as an isothermal on-chip amplification system. It is ideally as a module for potential point-of-care applica-tions, combining rapid prototyping with rapid pathogen detection. The study has shown that the microfluidic reaction chamber can be expanded into a lab-on-a-chip system.

Ultrashort laser pulses are often used in medical applications, for instance for soft-tissue

surgeries or biomedical imaging. However, the progress on using such laser pulses for tis-

sue structuring is rather marginal so far. Therefore, we aim to realize an endoscopic fiber-

based femtosecond 3D printer to minimally invasively surgically repair organ damage on a

micrometer scale. For this, high-power femtosecond laser pulses are required, in order to

3D print desired geometries with a microfluidic bio-ink using two-photon-lithography.

We utilize a grating compressor consisting of ruled reflective diffraction gratings to pre-

chirp laser pulses by introducing anomalous dispersion, compensating the normal disper-

sion in optical fibers broadening these femtosecond laser pulses. We analyze our measure-

ments of the output pulse autocorrelation and spectrum of single mode fibers as well as

multicore fibers as a function of pulse duration, spectrum, compression, and nonlinear ef-

fects.

By optimizing the grating position peak powers are achieved that enable two-photon poly-

merization to 3D print arbitrary structures using photosensitive resins. We report on a mul-

titude of arbitrary 3D printed microstructures up to several tens of microns based on con-

ventional photoresists (IP-S and IP-Dip, Nanoscribe GmbH) using an optical single-mode

fiber and a 3D printed immersion doublet on the fiber tip.

We report on dose tests as well as on extensive investigations on optimization of print-

ing speed, laser power, pulse compression ratio and pulse duration, as well as slicing and

hatching variation. We demonstrate solid cubes as well as connected lines, leading to 3D

woodpile structures that represent scaffolds which ultimatively could be colonized by living

cells.