Rapid prototyping (RP) is a common name for several techniques, which read in data from computer-aided design (CAD) drawings and manufacture automatically three-dimensional objects layer-by-layer according to the virtual design. The utilization of RP in tissue engineering enables the production of three-dimensional scaffolds with complex geometries and very fine structures. Adding micro- and nanometer details into the scaffolds improves the mechanical properties of the scaffold and ensures better cell adhesion to the scaffold surface. Thus, tissue engineering constructs can be customized according to the data acquired from the medical scans to match the each patient's individual needs. In addition RP enables the control of the scaffold porosity making it possible to fabricate applications with desired structural integrity. Unfortunately, every RP process has its own unique disadvantages in building tissue engineering scaffolds. Hence, the future research should be focused on the development of RP machines designed specifically for fabrication of tissue engineering scaffolds, although RP methods already can serve as a link between tissue and engineering.

The infection of biomaterials is determined by an interplay of adhesion and surface growth of the infecting organisms. In this study, the antimicrobial effects on adhering bacteria of a positively charged poly(methacrylate) surface (xi potential +12 mV) were compared with those of negatively charged poly(methyl methacrylate) (-12 mV) and a highly negatively charged poly(methacrylate) (-18 mV) surface. Initial adhesion of Staphylococcus aureus ATCC 12600, Staphylococcus epidermidis HBH(2) 102, Escherichia coli O2K2 and Pseudomonas aeruginosa AK1 to these surfaces was measured in a parallel plate flow chamber in phosphate-buffered saline. Adhering bacteria were allowed to multiply by perfusing the flow chamber with growth medium. All bacteria adhered most rapidly to the positively charged surface, but there was no subsequent surface growth of the Gram-negative strains. On the negatively charged surfaces, despite a slower initial adhesion, surface growth of the adhering bacteria was exponential for both Gram-positive and Gram-negative strains. These results suggest that positively charged biomaterial surfaces exert an antimicrobial effect on adhering Gram-negative bacteria, but not on Gram-positive ones.

The kinetics of the L-lactide bulk polymerization was studied using tin(II) bis(2-ethylhexanoate) and zinc bis(2,2-dimethyl-3,5-heptanedionato-0,0'). Up to 80% conversion, the rate of polymerization using tin(II) bis(2-ethylhexanoate) is higher than that with the zinc-containing catalyst, while at conversions beyond 80%, the latter catalyst has the higher rate of polymerization. Crystallization of the newly formed polymer has an accelerating effect on the polymerization. The difference in the rate of polymerization at high conversions for the two catalysts is caused by a difference in crystallinity of the newly formed polymer. Contaminants in the catalyst and monomer are the true initiators in these L-lactide polymerizations. Initiation as well as polymerization proceeds through a Lewis acid catalyzed transesterification reaction between an activated lactone and a hydroxyl group.

Signals from the microenvironment around a cell are known to influence cell behavior. Material properties, such as biochemical composition and substrate stiffness, are today accepted as significant regulators of stem cell fate. The knowledge of how cell behavior is influenced by 3D geometric cues is, however, strongly limited despite its potential relevance for the understanding of tissue regenerative processes and the design of biomaterials. Here, the role of surface curvature on the migratory and differentiation behavior of human mesenchymal stem cells (hMSCs) has been investigated on 3D surfaces with well‐defined geometric features produced by stereolithography. Time lapse microscopy reveals a significant increase of cell migration speed on concave spherical compared to convex spherical structures and flat surfaces resulting from an upward‐lift of the cell body due to cytoskeletal forces. On convex surfaces, cytoskeletal forces lead to substantial nuclear deformation, increase lamin‐A levels and promote osteogenic differentiation. The findings of this study demonstrate a so far missing link between 3D surface curvature and hMSC behavior. This will not only help to better understand the role of extracellular matrix architecture in health and disease but also give new insights in how 3D geometries can be used as a cell‐instructive material parameter in the field of biomaterial‐guided tissue regeneration.

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Designed three-dimensional biodegradable poly(ethylene glycol)/poly(D,L-lactide) hydrogel structures were prepared for the first time by stereolithography at high resolutions. A photo-polymerisable aqueous resin comprising PDLLA-PEG-PDLLA-based macromer, visible light photo-initiator, dye and inhibitor in DMSO/water was used to build the structures. Porous and non-porous hydrogels with well-defined architectures and good mechanical properties were prepared. Porous hydrogel structures with a gyroid pore network architecture showed narrow pore size distributions, excellent pore interconnectivity and good mechanical properties. The structures showed good cell seeding characteristics, and human mesenchymal stem cells adhered and proliferated well on these materials.

Extrusion-based three-dimensional bioprinting relies on bioinks engineered to combine viscoelastic properties for extrusion and shape retention, and biological properties for cytocompatibility and tissue regeneration. To satisfy these conflicting requirements, bioinks often utilize either complex mixtures or complex modifications of biopolymers. In this paper we introduce and characterize a bioink exploiting a dual crosslinking mechanism, where an enzymatic reaction forms a soft gel suitable for cell encapsulation and extrusion, while a visible light photo-crosslinking allows shape retention of the printed construct. The influence of cell density and cell type on the rheological and printability properties was assessed correlating the printing outcomes with the damping factor, a rheological characteristic independent of the printing system. Stem cells, chondrocytes and fibroblasts were encapsulated, and their viability was assessed up to 14 days with live/dead, alamar blue and trypan blue assays. Additionally, the impact of the printing parameters on cell viability was investigated. Owing to its straightforward preparation, low modification, presence of two independent crosslinking mechanisms for tuning shear-thinning independently of the final shape fixation, the use of visible green instead of UV light, the possibility of encapsulating and sustaining the viability of different cell types, the hyaluronan bioink here presented is a valid biofabrication tool for producing 3D printed tissue-engineered constructs.