The vision of gluing two bone fragments with biodegradable and biocompatible adhesives remains highly fascinating and attractive to orthopedic surgeons. Possibly shorter operation times, better stabilization, lower infection rates, and unnecessary removal make this approach very appealing. After 30 years of research in this field, the first adhesive systems are now appearing in scientific reports that may fulfill the comprehensive requirements of bioadhesives for bone. For a successful introduction into clinical application, special requirements of the musculoskeletal system, challenges in the production of a bone adhesive, as well as regulatory hurdles still need to be overcome. In this article, we will give an overview of existing synthetic polymers, biomimetic, and bio-based adhesive approaches, review the regulatory hurdles they face, and discuss perspectives of how bone adhesives could be efficiently introduced into clinical application, including legal regulations.

Implant loosening, bone healing failure, implant-associated infections, and large bony defects remain challenges in orthopedic surgery. Implant surface modifications and coatings are being developed to promote osteointegration, prevent colonization by bacteria, and release bioactive factors. The following mini-review briefly discusses the clinical problem, explains the four "osteos", presents examples of coatings used for different orthopedic indications, and finally raises awareness of the coating and translational requirements.

Artificial prostheses for joint replacement are indispensable in orthopedic surgery. Unfortunately, the implanted surface is attractive to not only host cells but also bacteria. To enable better osteointegration, a mechanically stable porous structure was created on a titanium surface using laser treatment and metallic silver particles were embedded in a hydrophilic titanium oxide layer on top. The laser structuring resulted in unique amphora-shaped pores. Due to their hydrophilic surface conditions and capillary forces, the pores can be loaded preoperative with the antibiotic of choice/need, such as gentamicin. Cytotoxicity and differentiation assays with primary human osteoblast-like cells revealed no negative effect of the surface modification with or without gentamicin loading. An in vivo biocompatibility study showed significantly enhanced osteointegration as measured by push-out testing and histomorphometry 56 days after the implantation of the K-wires into rat femora. Using a S. aureus infection model, the porous, silver-coated K-wires slightly reduced the signs of bone destruction, while the wires were still colonized after 28 days. Loading the amphora-shaped pores with gentamicin significantly reduced the histopathological signs of bone destruction and no bacteria were detected on the wires. Taken together, this novel surface modification can be applied to new or established orthopedic implants. It enables preoperative loading with the antibiotic of choice/need without further equipment or post-coating, and supports osteointegration without a negative effect of the released dug, such as gentamicin.

Salamanders have developed a wide variety of antipredator mechanisms, including tail autotomy, colour patterns, and noxious skin secretions. As an addition to these tactics, the red-legged salamander (Plethodon shermani) uses adhesive secretions as part of its defensive strategy. The high bonding strength, the fast-curing nature, and the composition of the biobased materials makes salamander adhesives interesting for practical applications in the medical sector. To understand the adhesive secretions ofP.shermani, its components were chemically analysed by energy dispersive X-ray spectroscopy (EDX), inductively coupled plasma mass spectrometry (ICP-MS), amino acid analysis, and spectroscopy (ATR-IR, Raman). In addition, proteins were separated by gel-electrophoresis and selected spots were characterised by peptide mass fingerprinting. The salamander secretion contains a high amount of water and predominantly proteins (around 77% in the dry stage). The gel-electrophoresis and peptide mass fingerprint analyses revealed ade novoset of peptides/proteins, largely with a pI between 5.0 and 8.0 and a molecular mass distribution between 10 and 170 kDa. Only low homologies with other proteins present in known databases could be identified. The results indicate that the secretions of the salamanderPlethodonclearly differ chemically from those shown for other glue-producing terrestrial or marine species and thus represent a unique glue system.

Implant-associated infections represent a serious risk in human medicine and can lead to complications, revisions and in worst cases, amputations. To target these risks, the objective was to design a hybrid implant surface that allows a local burst release of antibiotics combined with long-term antimicrobial activity based on silver. The efficacy should be generated with simultaneous in vitro cytocompatibility. The investigations were performed on titanium K-wires and plates and gentamicin was selected as an illustrative antibiotic. A gentamicin depot (max 553 µg/cm²) was created on the surface using laser structuring. The antibiotic was released within 15 min in phosphate buffered saline (PBS) or agar medium. Metallic silver particles (4 µg/cm²) in a titanium dioxide layer were deposited using plasma vapor deposition (PVD). About 16% of the silver was released within 28 days in the agar medium. The local efficacy of the incorporated silver was demonstrated in a direct contact assay with a reduction of more than 99.99% (Escherichia coli). The local efficacy of the hybrid surface was confirmed in a zone of inhibition (ZOI) assay using Staphylococcus cohnii. The biocompatibility of the hybrid surface was proven using fibroblasts and osteoblasts as cell systems. The hybrid surface design seems to be promising as treatment of implant-associated infections, considering the achieved amount and release behavior of the active ingredients (gentamicin, silver). The generated in vitro results (efficacy, biocompatibility) proofed the concept. Further in vivo studies will be necessary translate the hybrid surface towards clinical applied research.

Improved implant osteointegration offers meaningful potential for orthopedic, spinal, and dental implants. In this study, a laser treatment was used for the structuring of a titanium alloy (Ti6Al4V) surface combined with a titanium dioxide coating, whereby a porous surface was created. The objective was to characterize the pore structure shape, treatment-related metallographic changes, cytocompatibility, and attachment of osteoblast-like cells (MG-63). The treatment generated specific bottleneck pore shapes, offering the potential for the interlocking of osteoblasts within undercuts in the implant surface. The pore dimensions were a bottleneck diameter of 27 µm (SD: 4 µm), an inner pore width of 78 µm (SD: 6 µm), and a pore depth of 129 µm (SD: 8 µm). The introduced energy of the laser changed the metallic structure of the alloy within the heat-affected region (approximately 66 µm) without any indication of a micro cracking formation. The phase of the alloy (microcrystalline alpha + beta) was changed to a martensite alpha phase in the surface region and an alpha + beta phase in the transition region between the pores. The MG-63 cells adhered to the structured titanium surface within 30 min and grew with numerous filopodia over and into the pores over the following days. Cell viability was improved on the structured surface compared to pure titanium, indicating good cytocompatibility. In particular, the demonstrated affinity of MG-63 cells to grow into the pores offers the potential to provide significantly improved implant fixation in further in vivo studies.