Gelatin methacryloyl as environment for chondrocytes and cell delivery to superficial cartilage defects.

Cartilage damage typically starts at its surface, either due to wear or trauma. Treatment of these superficial defects is important in preventing degradation and osteoarthritis. Biomaterials currently used for deep cartilage defects lack appropriate properties for this application. Therefore, we investigated photo-crosslinked gelatin methacryloyl (gelMA) as a candidate for treatment of surface defects. It allows for liquid application, filling of surface defects and forming a protective layer after UV-crosslinking, thereby keeping therapeutic cells in place. gelMA and photo-initiator lithium phenyl-2,4,6-trimethyl-benzoylphosphinate (Li-TPO) concentration were optimized for application as a carrier to create a favorable environment for human articular chondrocytes (hAC). Primary hAC were used in passages 3 and 5, encapsulated into two different gelMA concentrations (7.5 wt% (soft) and 10 wt% (stiff)) and cultivated for 3 weeks with TGF-ß3 (0, 1 and 10 ng/mL). Higher TGF-ß3 concentrations induced spherical cell morphology independent of gelMA stiffness, while low TGF-ß3 concentrations only induced rounded morphology in stiff gelMA. Gene expression did not vary across gel stiffnesses. As a functional model gelMA was loaded with two different cell types (hAC and/or human adipose-derived stem cells [ASC/TERT1]) and applied to human osteochondral osteoarthritic plugs. GelMA attached to the cartilage, smoothened the surface and retained cells in place. Resistance against shear forces was tested using a tribometer, simulating normal human gait and revealing maintained cell viability. In conclusion gelMA is a versatile, biocompatible material with good bonding capabilities to cartilage matrix, allowing sealing and smoothening of superficial cartilage defects while simultaneously delivering therapeutic cells for tissue regeneration.

Surface analysis of different boundary layers on steel discs formed in a lubricated tribocontact during laboratory test compared with field application.

The aim of this study was to gain knowledge of tribological layers on a steel disc. This steel disc has been used in a transmission system in the field. ATF-oil (automatic transmission fluid), which contains different surface-adhering additives, serves as a lubricant and as a cooling fluid in the tribological system. Over time, the tribological characteristics of the system changed. Special interest in this study lies in the modifications of the steel surface. The field-used disc was therefore compared with model tested discs. In a disc-on-disc tribometer, all samples are tested for a short period of time to evaluate the actual condition of the system regarding friction behaviour. Analysis and characterisation of surfaces and layer formation were carried out with, among other techniques, 3D topography, SEM / EDX, AFM, XPS, and ToF-SIMS. Results indicate that in some regions a complex composed tribological layer is formed. Differences were detected between the steel discs used in the field and the model discs. This indicates the problem of evaluation of long-term behaviour exclusively by use of short or accelerated model experiments. A combination of carefully selected and sophisticated analytical methods is necessary to trace small changes of the system.