Objectives: Implantation of a foreign body is often associated with restoration of natural body functions to prolong life expectancy and improve quality of life. However, the procedure involves considerable risk for bacterial infections. Device-related infections account for a large proportion of hospital-acquired infections, and the ability of bacteria to form a biofilm as a protective shield usually makes treatment impossible without removal of the implant. Recently, there have been several approaches to prevent bacterial attachment and biofilm formation. In particular, topographic surfaces have attracted considerable attention in studies seeking antibacterial properties without additional antimicrobial reagents.

Methods: Several surfaces with microcylinders in three different dimensions (1, 3 and 9 µm) were fabricated with a nanoprinter using two-photon lithography and evaluated for their antibacterial activity in terms of biofilm formers. The microstructured surfaces were cultured for 24 hours with different strains of Pseudomonas aeruginosa and Staphylococcus aureus to study bacterial attachment to the patterned surfaces. In addition, surface wettability was measured by contact angle measurement.

Results: The contact angles increased with the size of the cylinders, indicating that the hydrophobic properties of the surface were favored. Since previous studies have proven that bacterial attachment is usually affected by surface wettability, a difference in bacterial adhesion should be observed. However, the results demonstrated that S. aureus was not affected by the microstructures, while for P. aeruginosa the bacterial amount increased with the size of the cylinders, and compared to a flat surface, a reduction of bacteria was observed only for one strain on the smallest cylinders.

Conclusions: This study indicates that microstructures from 1 to 9 μm have little to no antibacterial properties and that a change in wettability due to surface structures has no effect on bacterial adhesion.

Recently, chitosan (CS) based composite coatings have been devoted considerable attention in the biomaterials field, but their mechanical properties need to be addressed. In this study, therefore, we aim to mimic the brick and mortar microstructure of nacre, retaining superior durability by its intricate and hierarchical stacking, and we design nacre-like CS-hydroxyapatite (HA) coatings by electrophoretic deposition (EPD). For this purpose, we synthesized the building blocks, HA particles, with plate-like morphology ahead of preparing a suspension for coating containing CS molecules with HA particles. We then successfully fabricated the hybrid layers by the EPD, harnessing the particles towards the counter electrode under an electric field, and optimized the microstructure of the coating by tuning the process parameters (voltage, electrode distance, etc.). The microstructure images taken by the scanning electron microscope (SEM) proved the layered hierarchical coatings. Consequently, we hypothesized that the electrical force turns HA particles' plate surface parallel to the substrate and moves them towards the substrate with chitosan molecules. This study highlights that EPD is a practicable procedure for producing advanced hierarchical composite coatings for biomedical applications and could be used to surge conventional hybrid coatings' mechanical properties.

Keywords: electrophoretic deposition, nacre-like coating, chitosan, hydroxyapatite

Vat Photopolymerization as Ceramic Additive Manufacturing method (CerAM VPP) and Freeze Foaming have been used for developing individualized jawbone replacement material.

CerAM VPP was used for fabricating individualized and biomechanically designed load-bearing support structures made of hydroxyapatite (HAp) and zirconia. For enabling an ingrowth of bone tissue and a vascularization of bone-mimicking components those hollow structures were filled with a so-called Freeze Foam made of hydroxyapatite. Freeze Foaming is a direct foaming technique which allows the production of an open-cell foam structure with adjustable porosity.

In a two-step approach, firstly the CerAM VPP supporting component was additively manufactured, debindered and pre-sintered. The pre-sintered parts where then filled with an aqueous hydroxyapatite paste and enclosed in a mold corresponding to a certain part of a jawbone. Those parts were transferred into the chamber of a freeze drier. By reducing the ambient pressure, the HAp paste gets inflated to a stable foam thereby filling the individualized support structure completely. The dried Freeze Foam consists of large cells resulting from the expansion of vapor and entrapped air in the paste whereas the struts show a microporosity resulting from ice crystal growth.

Both, the additively manufactured support structure and the Freeze Foam were then treated by a co-sintering step, which requires a very exact adjustment of the shrinking behavior of both structures. Thereby, the initially used bioactive HAp is transformed to biodegradable tricalcium phosphate (TCP).

Those novel individualized bone graft substitutes had been successfully tested in-vitro and in-vivo by ingrowth tests in the jaws of minipigs proven on their degradability and new bone formation.

The contribution documents a longer development period of these hybrid bone replacement structures and shows the research results from several already completed and still ongoing projects on this topic.

Hardness, high mechanical strength, wear and corrosion resistance or even heat resistance, for instance, are the most important properties of silicon nitride, which make the material interesting for various applications. This includes cutting tools, crucibles for molten metals, bearings or prostheses in medical technology. Up to now, the demands on the geometry of silicon nitride-based components could largely be met by using conventional shaping methods such as pressing and green machining or injection moulding. However, requirements in terms of complexity and function are constantly increasing. By using additive manufacturing (AM) technologies for ceramic materials, the complexity of components can be significantly increased and additional functions such as bioinspired structures with a defined porosity as well as modified surfaces, for instance, can be integrated. High-resolution AM processes such as stereolithography enable the production of very accurate and complex ceramic components. Unfortunately, for silicon nitride the state of development in lithography-based AM processes is limited and commercial systems or service providers are rare. Therefore, the authors would like to give an insight into the development status of silicon nitride at the Fraunhofer IKTS for the so-called CerAM VPP technology (Lithoz LCM process) by showing results of the "Fingerkit" project, which deals with the development of novel finger implants with integrated bioinspired structures.

Mesenchymal stem cells (MSCs) have the potential to repair and regenerate damaged tissues in response to injury, such as fracture or other tissue injury. Bone marrow and adipose tissue are the major sources of MSCs. Previous studies suggested that the regenerative activity of stem cells can be enhanced by exposure to tissue microenvironments. The aim of our project was to investigate whether extracellular matrix (ECM) engineered from human induced pluripotent stem cells-derived mesenchymal-like progenitors (hiPSCs-MPs) can enhance the regenerative potential of human bone marrow mesenchymal stromal cells (hBMSCs).

ECM was engineered from hiPSC-MPs. ECM structure and composition were characterized before and after decellularization using immunofluorescence and biochemical assays. hBMSCs were cultured on the engineered ECM, and differentiated into osteogenic, chondrogenic and adipogenic lineages. Growth and differentiation responses were compared to tissue culture plastic controls.

Decellularization of ECM resulted in efficient cell elimination, as observed in our previous studies. Cultivation hBMSCs on the ECM in osteogenic medium significantly increased hBMSC growth, collagen deposition and alkaline phosphatase activity. Furthermore, expression of osteogenic genes and matrix mineralization were significantly higher compared to plastic controls. Chondrogenic micromass culture on the ECM significantly increased cell growth and expression of chondrogenic markers, including glycosaminoglycans and collagen type II. Adipogenic differentiation of hBMSCs on the ECM resulted in significantly increased hBMSC growth, but significantly reduced lipid vacuole deposition compared to plastic controls. Together, our studies suggest that BMSCs differentiation into osteogenic and chondrogenic lineages can be enhanced, whereas adipogenic activity is decreased by the culture on engineered ECM. Contribution of specific matrix components and underlying mechanisms need to be further elucidated.

Our studies suggest that the three-lineage differentiation of aged BMSCs can be modulated by culture on hiPSC-engineered ECM. Further studies are aimed at scaling-up to three-dimensional ECM constructs for osteochondral tissue regeneration.