50 years of scanning electron microscopy of bone——a comprehensive overview of the important discoveries made and insights gained into bone material properties in health,disease,and taphonomy

Bone is an architecturally complex system that constantly undergoes structural and functional optimisation through renewal and repair.The scanning electron microscope (SEM) is among the most frequently used instruments for examining bone.It offers the key advantage of very high spatial resolution coupled with a large depth of field and wide field of view.Interactions between incident electrons and atoms on the sample surface generate backscattered electrons,secondary electrons,and various other signals including X-rays that relay compositional and topographical information.Through selective removal or preservation of specific tissue components (organic,inorganic,cellular,vascular),their individual contribution(s) to the overall functional competence can be elucidated.With few restrictions on sample geometry and a variety of applicable sample-processing routes,a given sample may be conveniently adapted for multiple analytical methods.While a conventional SEM operates at high vacuum conditions that demand clean,dry,and electrically conductive samples,non-conductive materials (e.g.,bone) can be imaged without significant modification from the natural state using an environmental scanning electron microscope.This review highlights important insights gained into bone microstructure and pathophysiology,bone response to implanted biomaterials,elemental analysis,SEM in paleoarchaeology,3D imaging using focused ion beam techniques,correlative microscopy and in situ experiments.The capacity to image seamlessly across multiple length scales within the meso-micro-nano-continuum,the SEM lends itself to many unique and diverse applications,which attest to the versatility and user-friendly nature of this instrument for studying bone.Significant technological developments are anticipated for analysing bone using the SEM.

Magnesium implant degradation provides immunomodulatory and proangiogenic effects and attenuates peri-implant fibrosis in soft tissues

Implants made of magnesium(Mg)are increasingly employed in patients to achieve osteosynthesis while degrading in situ.Since Mg implants and Mg^(2+)have been suggested to possess anti-inflammatory properties,the clinically observed soft tissue inflammation around Mg implants is enigmatic.Here,using a rat soft tissue model and a 1-28 d observation period,we determined the temporo-spatial cell distribution and behavior in relation to sequential changes of pure Mg implant surface properties and Mg^(2+)release.Compared to nondegradable titanium(Ti)implants,Mg degradation exacerbated initial inflammation.Release of Mg degradation products at the tissue-implant interface,culminating at 3 d,actively initiated chemotaxis and upregulated mRNA and protein immunomodulatory markers,particularly inducible nitric oxide synthase and toll-like receptor-4 up to 6 d,yet without a cytotoxic effect.Increased vascularization was demonstrated morphologically,preceded by high expression of vascular endothelial growth factor.The transition to appropriate tissue repair coincided with implant surface enrichment of Ca and P and reduced peri-implant Mg^(2+)concentration.Mg implants revealed a thinner fibrous encapsulation compared with Ti.The detailed understanding of the relationship between Mg material properties and the spatial and time-resolved cellular processes provides a basis for the interpretation of clinical observations and future tailoring of Mg implants.

Bone without borders-Monetite-based calcium phosphate guides bone formation beyond the skeletal envelope

Calcium phosphates(CaP)represent an important class of osteoconductive and osteoinductive biomaterials.As proof-of-concept,we show how a multi-component CaP formulation(monetite,beta-tricalcium phosphate,and calcium pyrophosphate)guides osteogenesis beyond the physiological envelope.In a sheep model,hollow dome-shaped constructs were placed directly over the occipital bone.At 12 months,large amounts of bone(~75%)occupy the hollow space with strong evidence of ongoing remodelling.Features of both compact bone(osteonal/osteon-like arrangements)and spongy bone(trabeculae separated by marrow cavities)reveal insights into function/need-driven microstructural adaptation.Pores within the CaP also contain both woven bone and vascularised lamellar bone.Osteoclasts actively contribute to CaP degradation/removal.Of the constituent phases,only calcium pyrophosphate persists within osseous(cutting cones)and non-osseous(macrophages)sites.From a translational perspective,this multi-component CaP opens up exciting new avenues for osteotomy-free and minimally-invasive repair of large bone defects and augmentation of the dental alveolar ridge.