Restoration of segmental defects in long bones remains a challenging task in orthopedic surgery. Although autologous bone is still the ‘Gold Standard’ because of its high biocompatibility, it has nevertheless been associated with several disadvantages. Consequently, artificial materials, such as calcium phosphate and titanium, have been considered for the treatment of bone defects. In the present study, the mechanical properties of three different scaffold designs were investigated. The scaffolds were made of titanium alloy (Ti6Al4V), fabricated by means of an additive manufacturing process with defined pore geometry and porosities of approximately 70%. Two scaffolds exhibited rectangular struts, orientated in the direction of loading. The struts for the third scaffold were orientated diagonal to the load direction, and featured a circular cross-section. Material properties were calculated from stress-strain relationships under axial compression testing. In vitro cell testing was undertaken with human osteoblasts on scaffolds fabricated using the same manufacturing process. Although the scaffolds exhibited different strut geometry, the mechanical properties of ultimate compressive strength were similar (145–164 MPa) and in the range of human cortical bone. Test results for elastic modulus revealed values between 3.7 and 6.7 GPa. In vitro testing demonstrated proliferation and spreading of bone cells on the scaffold surface.

Healing capacity of cartilage is low. Thus, cartilage defects do not regenerate as hyaline but mostly as fibrous cartilage which is a major drawback since this tissue is not well adapted to the mechanical loading within the joint. During in vitro cultivation in monolayers, chondrocytes proliferate and de-differentiate to fibroblasts. In three-dimensional cell cultures, de-differentiated chondrocytes could re-differentiate toward the chondrogenic lineage and re-express the chondrogenic phenotype. The objective of this study was to characterize the mesenchymal stem cell (MSC) potential of human chondrocytes isolated from articular cartilage. Furthermore, the differentiation capacity of human chondrocytes in three-dimensional cell cultures was analyzed to target differentiation direction into hyaline cartilage. After isolation and cultivation of chondrogenic cells, the expression of the MSC-associated markers: cluster of differentiation (CD)166, CD44, CD105, and CD29 was performed by flow cytometry. The differentiation capacity of human chondrocytes was analyzed in alginate matrix cultured in Dulbecco?s modified eagle medium with (chondrogenic stimulation) and without (control) chondrogenic growth factors. Additionally, the expression of collagen type II, aggrecan, and glycosaminoglycans was determined. Cultivated chondrocytes showed an enhanced expression of the MSC-associated markers with increasing passages. After chondrogenic stimulation in alginate matrix, the chondrocytes revealed a significant increase of cell number compared with unstimulated cells. Further, a higher synthesis rate of glycosaminoglycans and a positive collagen type II and aggrecan immunostaining was detected in stimulated alginate beads. Human chondrocytes showed plasticity whilst cells were encapsulated in alginate and stimulated by growth factors. Stimulated cells demonstrated characteristics of chondrogenic re-differentiation due to collagen type II and aggrecan synthesis.

To prevent de-differentiation of chondrocytes in vitro, the 3D environment, growth factors and different oxygen concentrations were considered. In this in vitro study, we quantified the influence of insulin-like growth factor (IGF)-1 and/or transforming growth factor (TGF)-β1 under differing oxygen (5/21% O(2)) levels on the proliferation and synthesis rates of hyaline extracellular matrix (ECM) components in chondrogenic pellet cultures. Human chondrocytes isolated from articular cartilage were transferred into conical tubes to form pellets. Pellets were stimulated with TGF-β1 and/or IGF-1. After 2 and 5 weeks of cultivation the DNA concentration and expression of pro-collagen type 1, type 2 and aggrecan were analysed. Under hypoxia the DNA content remained stable. In contrast, under normoxia, cells showed an increase of DNA concentration after stimulation with TGF-β1/IGF-1 and TGF-β1. Nevertheless, DNA contents under normoxia did not reach the values of hypoxic-cultivated cells. Under both culture conditions a reduced synthesis of pro-collagen type 1 could be determined. Although the expression of pro-collagen type 2 was significantly higher under normoxia, a decrease in the case of TGF-β1/IGF-1- and IGF-1-stimulated cells was observed. Under hypoxia pro-collagen type 2 contents remained stable or increased for TGF-β1/IGF-1-stimulated cells. Furthermore, incubation with growth factors resulted in aggrecan accumulation under hypoxia, while a reduced expression under normoxia could be determined for TGF-β1/IGF-1- and IGF-1-stimulated cells. Our results demonstrate that the treatment with growth factors causes differences in the expression of ECM compounds within pellet cultures. While under normoxia TGF-β1 alone leads to a positive effect of the expression of hyaline cartilage-specific ECM components, an additive effect of both growth factors was only determined under hypoxia.

In total hip arthroplasty, wear particles generated at articulating surfaces and interfaces between bone, cement and implants have a negative impact on osteoblasts, leading to osteolysis and implant loosening. The aim of this experimental study was to determine the effects of particulate wear debris generated at the interface between straight stainless steel hip stems (Exeter(®)) and three different bone cements (Palacos(®) R, Simplex™ P and Cemex(®) Genta) on cell viability, collagen synthesis and cytokine expression in human osteoblasts. Primary osteoblasts were treated with various concentrations of wear particles. The synthesis of procollagen type I and different cytokines was analysed, and markers for apoptosis and necrosis were also detected. The cytokine synthesis rates in the osteoblasts were initially increased and varied, depending on incubation time and particle concentration. Specific differences in the synthesis rates of interleukin (IL)‑6, IL-8, vascular endothelial growth factor (VEGF) and monocyte chemotactic protein-1 (MCP-1) were observed with the different bone cements examined. The negative effect of the particles on the synthesis of procollagen type I and increased rates of cell apoptosis and necrosis were observed with all three cements analysed. Our present data suggest that wear particles from the interface between the total hip stem and bone cement have a significant effect on viability, cytokine expression and collagen synthesis in human osteoblasts, depending on the bone cement used.

A major clinical problem within synthetic, large-scaled scaffolds is the insufficient nutrient supply resulting in inhomogeneous cell proliferation and differentiation. The aim of this study was to analyse pH value, oxygen consumption and migration of human osteoblasts within a 3D tantalum scaffold, clinically used for larger bone defects. After 24 h the oxygen concentration within the scaffold decreased significantly and remained low during incubation. Monitoring of the pH value inside the tantalum scaffold showed a slightly acidification under static culture conditions. However, cell migration within the 3D scaffold was detected. Hence, in clinical application it can be assumed that porous tantalum scaffolds can be settled by osteoblasts under critical oxygen and nutrient supply. In general, monitoring of cell migration, oxygen consumption and acidification can be a suitable instrument for creating advanced 3D bone scaffolds.