In prosthetic joint surgery, Ag coating of implant areas in direct contact with bone has been met with hesitation for fear of compromising osseointegration. The physicochemical, antibacterial and osteoconductive properties of three different Ti samples were studied: Ti6Al4V alloy that was grit-blasted (GB), Ti6Al4V alloy with an experimental Ti-Ag-nitride layer (SN) applied by physical vapour deposition (PVD) and commercially available PVD-coated Ti6Al4V alloy with a base Ag layer and a surface Ti-Ag-nitride layer (SSN, clinically known as PorAg (R)). Ag content on the surface of experimental SN and SSN discs was 27.7 %wt and 68.5 % wt, respectively. At 28 d, Ag release was 4 ppm from SN and 26.9 ppm from SSN substrates. Colonisation of discs by Staphylococcus aureus was the highest on GB [944 (+/- 91) x 10(4) CFU/mL], distinctly lower on experimental SN discs [414 (+/- 117) x 10(4) CFU/mL] and the lowest on SSN discs [307 (+/- 126) x 10(4) CFU/mL]. Primary human osteoblasts were abundant 28 d after seeding on GB discs but their adhesion and differentiation, measured by alkaline-phosphatase production, was suppressed by 73 % on SN and by 96 % on SSN discs, in comparison to GB discs. Thus, the PVD-applied Ag coatings differed considerably in their antibacterial effects and osteoconductivity. The experimental SN coating had similar antibacterial effects to the commercially available SSN coating while providing slightly improved osteoconductivity. Balancing the Ag content of Ti implants will be vital for future developments of implants designed for cementless fixation into bone.

Silver (Ag) possesses potent antimicrobial properties and is used as a coating for medical devices. The impact of silver ions released from orthopedic implants on the differentiation and osteoid formation of different osteogenic cells has yet to be systematically studied. In the present study, human mesenchymal stem cells (hMSCs) and primary human osteoblasts (hOBs) were exposed to different static Ag⁺ concentrations (0, 0.5, 1.0 or 1.5 ppm) or dynamic Ag⁺ concentrations (range 0 to 0.7 ppm) that simulated the temporal release pattern from a Ag‑nitrate coating of trabecular titanium (TLSN). Cell morphology was investigated by phase contrast and fluorescence microscopy. The activities of alkaline phosphatase (ALP) and lactate dehydrogenase, osteogenic gene expression (COL1A1, COL1A2 and ALPL), and osteoid deposition were examined for up to 4 weeks. DAPI and carboxyfluorescein diacetate staining revealed changes in the morphology of hOBs treated with ≥0.5 ppm Ag⁺, while osteocalcin‑positive cells were observed primarily in the untreated group. Elevated Ag+ concentrations did not impact the production of ALP by either hMSCs or hOBs. Treatment with 1.5 ppm Ag⁺ or TLSN Ag⁺ led to a modest reduction in COL1A2 and ALPL levels in hMSCs at 2 weeks but not at 4 weeks nor in hOBs. In hMSC cultures, mineralization decreased at ≥1 ppm Ag⁺, whereas the same concentration range significantly reduced mineralization in hOB cultures. In conclusion, Ag⁺ concentrations ranging from 1.0 to 1.5 ppm may interfere with osteogenic differentiation, possibly by altering gene expression, thereby affecting mineralization. Only Ag+ concentrations up to 0.5 ppm allowed undisturbed osteogenic differentiation and mineralization. These findings pertain to creating Ag coatings of titanium intended for cementless fixation into host bone.

Background: Technological constraints limit 3D printing of collagen structures with complex trabecular shapes. However, the Freeform Reversible Embedding of Suspended Hydrogels (FRESH) method may allow for precise 3D printing of porous collagen scaffolds that carry the potential for repairing critical size bone defects.

Methods: Collagen type I scaffolds mimicking trabecular bone were fabricated through FRESH 3D printing and compared either with 2D collagen coatings or with 3D-printed polyethylene glycol diacrylate (PEGDA) scaffolds. The porosity of the printed scaffolds was visualized by confocal microscopy, the surface geometry of the scaffolds was investigated by scanning electron microscopy (SEM), and their mechanical properties were assessed with a rheometer. The osteoconductive properties of the different scaffolds were evaluated for up to four weeks by seeding and propagation of primary human osteoblasts (hOBs) or SaOS-2 cells. Intracellular alkaline phosphatase (ALP) and lactate dehydrogenase (LDH) activities were measured, and cells colonizing scaffolds were stained for osteocalcin (OCN).

Results: The FRESH technique enables printing of constructs at the millimetre scale using highly concentrated collagen, and the creation of stable trabecular structures that can support the growth osteogenic cells. FRESH-printed collagen scaffolds displayed an intricate and fibrous 3D network, as visualized by SEM, whereas the PEGDA scaffolds had a smooth surface. Amplitude sweep analyses revealed that the collagen scaffolds exhibited predominantly elastic behaviour, as indicated by higher storage modulus values relative to loss modulus values, while the degradation rate of collagen scaffolds was greater than PEGDA. The osteoconductive properties of collagen scaffolds were similar to those of PEGDA scaffolds but superior to 2D collagen, as verified by cell culture followed by analysis of ALP/LDH activity and OCN immunostaining.

Conclusions: Our findings suggest that FRESH-printed collagen scaffolds exhibit favourable mechanical, degradation and osteoconductive properties, potentially outperforming synthetic polymers such as PEGDA in bone tissue engineering applications.

In this study, we investigated the mechanical and osteoconductive properties of a novel cross-linked collagen-hydroxyapatite (Coll-HA-XL) biomaterial ink for 3D-printed scaffolds in bone tissue engineering. The biomaterial ink was developed through three stages: initially as a hydrogel, then molded and freeze-dried into disk-shaped forms, and finally as 3D-printed scaffolds subjected to freeze-drying. To optimize the ink, we systematically varied the hydroxyapatite (HA) proportions and the sequence of HA incorporation and collagen cross-linking. The introduction of HA and subsequent collagen cross-linking significantly increased the storage modulus of the hydrogels and enhanced the compressive strength and thermal stability of the freeze-dried 3D-printed scaffolds. These improved mechanical properties enabled the fabrication of osteoconductive scaffolds via direct ink writing. To evaluate biological performance, the 3D-printed Coll-HA-XL scaffolds were seeded with primary human osteoblasts (hOBs). After four weeks of culture, hOBs demonstrated high alkaline phosphatase (ALP) activity and positive osteocalcin (OCN) staining, indicating robust osteoblastic differentiation. These findings highlight the potential of the Coll-HA-XL ink for creating 3D-printed scaffolds tailored for bone tissue engineering applications.