Toward high-resolution 3D-printing of pharmaceutical implants - A holistic analysis of relevant material properties and process parameters.

In this work, filament-based 3D-printing, the most widely used sub-category of material extrusion additive manufacturing (MEAM), is presented as a promising manufacturing platform for the production of subcutaneous implants. Print nozzle diameters as small as 100 µm were utilized demonstrating MEAM of advanced porous internal structures at the given cylindrical implant geometry of 2 mm × 40 mm. The bottlenecks related to high-resolution MEAM of subcutaneous implants are systematically analyzed and the print process is optimized accordingly. Custom synthesized biodegradable phase-separated poly(ether ester) multiblock copolymers exhibiting appropriate melt viscosity at comparatively low printing temperatures of 135 °C and 165 °C were utilized as 3D-printing feedstock. The print process was optimized to minimize thermomechanical polymer degradation by employing print speeds of 30 mm∙s-1 in combination with a nozzle diameter of 150 µm at layer heights of 110 µm. These results portray the basis for further development of subcutaneous implantable drug delivery systems where drug release profiles can be tailored through the adaption of the internal implant structure, which cannot be achieved using existing manufacturing techniques.

Personalised urethra pessaries prepared by material extrusion-based additive manufacturing.

Material extrusion-based additive manufacturing, commonly referred to as 3D-printing, is regarded as the key technology to pave the way for personalised medical treatment. This study explores the technique's potential in customising vaginal inserts with complex structures, so-called urethra pessaries. A novel, flawlessly 3D-printable and biocompatible polyester-based thermoplastic elastomer serves as the feedstock. Next to the smart selection of the 3D-printing parameters cross-sectional diameter and infill to tailor the pessary's mechanical properties, we elaborate test methods accounting for its application-specific requirements for the first time. The key property, i.e. the force the pessary exerts on the urethra to relief symptoms of urinary incontinence, is reliably adjusted within a broad range, including that of the commercial injection-moulded silicone product. The pessaries do not change upon long-term exposure to vaginal fluid simulant and compression (in-vivo conditions), satisfying the needs of repeated pessary use. Importantly, the vast majority of the 3D-printed pessaries allows for self-insertion and self-removal without any induced pessary rupture. Summarising, 3D-printed pessaries are not only a reasonable alternative to the commercial products, but build the basis to effectively treat inhomogeneous patient groups. They make the simple but very effective pessary therapy finally accessible to every woman.

Biofunctional Glycol-Modified Polyethylene Terephthalate and Thermoplastic Polyurethane Implants by Extrusion-Based Additive Manufacturing for Medical 3D Maxillofacial Defect Reconstruction.

This work addresses the topic of extrusion-based additive manufacturing (filament-based material extrusion) of patient-specific biofunctional maxillofacial implants. The technical approach was chosen to overcome the shortcomings of medically established fabrication processes such as a limited availability of materials or long manufacturing times. The goal of the work was a successful fabrication of basic implants for defect reconstruction. The underlying vision is the implants' clinic-internal and operation-accompanying application. Following a literature search, a material selection was conducted. Digitally prepared three-dimensional (3D) models dealing with two representative mandible bone defects were printed based on the material selection. An ex-vivo model of the implant environment evaluated dimensional and fitting traits of the implants. Glycol-modified PET (PETG) and thermoplastic polyurethane (TPU) were finally selected. These plastics had high cell acceptance, good mechanical properties, and optimal printability. The subsequent fabrication process yielded two different implant strategies: the standard implant made of PETG with a build-up rate of approximately 10 g/h, and the biofunctional performance implant with a TPU shell and a PETG core with a build-up rate of approximately 4 g/h. The standard implant is meant to be intraoperatively applied, as the print time is below three hours even for larger skull defects. Standard implants proved to be well fitting, mechanically stable and cleanly printed. In addition, the hybrid implant showed particularly cell-friendly behavior due to the chemical constitution of the TPU shell and great impact stability because of the crack-absorbing TPU/PETG combination. This biofunctional constellation could be used in specific reconstructive patient cases and is suitable for pre-operative manufacturing based on radiological image scans of the defect. In summary, filament-based material extrusion has been identified as a suitable manufacturing method for personalized implants in the maxillofacial area. A further clinical and mechanical study is recommended.

Cell Morphology on Poly(methyl methacrylate) Microstructures as Function of Surface Energy.

Whilst the significance of substrate topography as a regulator of cell function is well established, a systematic analysis of the principles underlying this is still unavailable. Here we evaluate the hypothesis that surface energy plays a decisive role in substrate-mediated modulation of cell phenotype by evaluation of cell behaviour on synthetic microstructures exhibiting pronounced differences in surface energy. These microstructures, specifically cubes and walls, were fabricated from a biocompatible base polymer, poly(methyl methacrylate), by variotherm injection molding. The dimensions of the cubes were 1 µm x 1 µm x 1 µm (height x width x length) with a periodicity of 1:1 and 1:5 and the dimensions of the walls 1 µm x 1 µm x 15 mm (height x width x length) with a periodicity of 1:1 and 1:5. Mold inserts were made by lithography and electroplating. The surface energy of the resultant microstructures was determined by static contact angle measurements. Light scanning microscopy of the morphology of NT2/D1 and MC3T3-E1 preosteoblast cells cultured on structured PMMA samples in both cases revealed a profound surface energy dependence. "Walls" appeared to promote significant cell elongation, whilst a lack of cell adhesion was observed on "cubes" with the lowest periodicity. Contact angle measurements on walls revealed enhanced surface energy anisotropy (55 mN/m max., 10 mN/m min.) causing a lengthwise spreading of the test liquid droplet, similar to cell elongation. Surface energy measurements for cubes revealed increased isotropic hydrophobicity (87° max., H2O). A critical water contact angle of ≤ 80° appears to be necessary for adequate cell adhesion. A "switch" for cell adhesion and subsequently cell growth could therefore be applied by, for example, adjusting the periodicity of hydrophobic structures. In summary cell elongation on walls and a critical surface energy level for cell adhesion could be produced for NT2/D1 and MC3T3-E1 cells by symmetrical and asymmetrical energy barrier levels. We, furthermore, propose a water-drop model providing a common physicochemical cause regarding similar cell/droplet geometries and cell adhesion on the investigated microstructures.

Differential apoptotic response of MC3T3-E1 pre-osteoblasts to biodegradable magnesium alloys in an in vitro direct culture model.

The biodegradable magnesium-based implants have been widely utilized in medical orthopedic applications in recent years. We have recently shown that direct culture on Pure Mg and Mg2Ag alloys lead to a progressive differentiation impairment of MC3T3-E1 pre-osteoblasts. In this study, we aimed to analyze the apoptotic reaction of MC3T3-E1 cells in response to the direct culture on Pure Mg, Mg2Ag and Extreme High Pure Mg (XHP Mg) alloy samples. Our results demonstrated that long-term culturing of MC3T3-E1 cells on Pure Mg and Mg2Ag alloys induce time-dependent expression of active caspase-3 (active casp-3) and cleaved PARP-1 (cl. PARP-1), the hallmark of apoptosis reactions concomitant with a significant increase in the number of dead cells. However, direct culture on XHP Mg material results in a lower number of dead cells in comparison to Pure Mg and Mg2Ag alloys. Furthermore, XHP Mg materials influence expression of apoptotic markers in a process resembles that of observed in osteogenic condition apparently indicative of MC3T3-E1 osteodifferentiation. This study indicates that Mg alloy samples mediated differential apoptotic reactions of MC3T3-E1 cells can be ascribed to factors such as distinct topography and hydrophobicity features of Mg material surfaces, contrasting nature/composition of corrosion products as well as different impurities of these materials. Therefore, initial Mg alloys surface preparation, controlling the growth and composition of corrosion products and Mg alloys purity enhancement are necessary steps towards optimizing the Mg alloys usage in medical orthopedic applications.

Effects of the polymeric niche on neural stem cell characteristics during primary culturing.

The polymeric niche encountered by cells during primary culturing can affect cell fate. However, most cell types are primarily propagated on polystyrene (PS). A cell type specific screening for optimal primary culture polymers particularly for regenerative approaches seems inevitable. The effect of physical and chemical properties of treated (corona, oxygen/nitrogen plasma) and untreated cyclic olefin polymer (COP), polymethymethacrylate (PMMA), PP, PLA, PS, PC on neuronal stem cell characteristics was analyzed. Our comprehensive approach revealed plasma treated COP and PMMA as optimal polymers for primary neuronal stem cell culturing and propagation. An increase in the number of NT2/D1 cells with pronounced adhesion, metabolic activities and augmented expression of neural precursor markers was associated to the plasma treatment of surfaces of COP and PMMA with nitrogen or oxygen, respectively. A shift towards large cell sizes at stable surface area/volume ratios that might promote the observed increase in metabolic activities and distinct modulations in F-actin arrangements seem to be primarily mediated by the plasma treatment of surfaces. These results indicate that the polymeric niche has a distinct impact on various cell characteristics. The selection of distinct polymers and the controlled design of an optimized polymer microenvironment might thereby be an effective tool to promote essential cell characteristics for subsequent approaches.