Does early post-operative exercise influence bone healing kinetics? Preclinical evaluation of non-critical sized femur defect healing.

Physical exercise is a well-known modality for maintaining healthy locomotor mechanism. A detailed preclinical research on physical exercise effect on bone healing kinetics could help to improve the rehabilitation process after fracture treatment and bone remodeling. Our aim was to evaluate the effect of early post-operative exercise effect on bone microstructural changes in a rat model. Twenty Sprague Dawley male rats underwent bi-cortical 1.6 mm hole drilling in both femur diaphysis, after which (n = 10) underwent continuous treadmill training (TR) over two weeks, while the other group of rats (n = 10) was assigned to non-training (NT) control group. New bone formation labeling was performed by subcutaneous fluorochrome injections at day 5, 14 and 31. In vivo micro-computed tomography (µCT) scans were performed once a week during the 6-week post-operative period. Ten animals (five from each group) were euthanized at 3rd week while remaining animals were euthanized at 6th week. Femur samples were extracted and underwent ex vivo µCT and histological evaluation, while serum was used for evaluating alkaline phosphatase (ALP). µCT data demonstrated increased volume and surface of newly formed bone in defect area of TR group. Bone volume/Tissue volume (BV/TV) ratio and number of osteocytes showed an increase in TR group after 3-week period. Fluorochrome distances were increased between day 5 and 14 within the training group. Serum ALP level increased in both groups over 3- and 6-weeks. Post-operative exercise increases the bone healing kinetics and stimulates the new bone formation during and after the training protocol has ended.

The combined effect of zinc and calcium on the biodegradation of ultrahigh-purity magnesium implants.

Magnesium (Mg)-based implants are promising candidates for orthopedic interventions, because of their biocompatibility, good mechanical features, and ability to degrade completely in the body, eliminating the need for an additional removal surgery. In the present study, we synthesized and investigated two Mg-based materials, ultrahigh-purity ZX00 (Mg-Zn-Ca; <0.5 wt% Zn and <0.5 wt% Ca, in wt%; Fe-content <1 ppm) and ultrahigh-purity Mg (XHP-Mg, >99.999 wt% Mg; Fe-content <1 ppm), in vitro and in vivo in juvenile healthy rats to clarify the effect of the alloying elements Zn and Ca on mechanical properties, microstructure, cytocompatibility and degradation rate. Potential differences in bone formation and bone in-growth were also assessed and compared with state-of-the-art non-degradable titanium (Ti)-implanted, sham-operated, and control (non-intervention) groups, using micro-computed tomography, histology and scanning electron microscopy. At 6 and 24 weeks after implantation, serum alkaline phosphatase (ALP), calcium (Ca), and Mg level were measured and bone marrow stromal cells (BMSCs) were isolated for real-time PCR analysis. Results show that ZX00 implants have smaller grain size and superior mechanical properties than XHP-Mg, and that both reveal good biocompatibility in cytocompatibilty tests. ZX00 homogenously degraded with an increased gas accumulation 12 and 24 weeks after implantation, whereas XHP-Mg exhibited higher gas accumulation already at 2 weeks. Serum ALP, Ca, and Mg levels were comparable among all groups and both Mg-based implants led to similar relative expression levels of Alp, Runx2, and Bmp-2 genes at weeks 6 and 24. Histologically, Mg-based implants are superior for new bone tissue formation and bone in-growth compared to Ti implants. Furthermore, by tracking the sequence of multicolor fluorochrome labels, we observed higher mineral apposition rate at week 2 in both Mg-based implants compared to the control groups. Our findings suggest that (i) ZX00 and XHP-Mg support bone formation and remodeling, (ii) both Mg-based implants are superior to Ti implants in terms of new bone tissue formation and osseointegration, and (iii) ZX00 is more favorable due to its lower degradation rate and moderate gas accumulation.

Implant degradation of low-alloyed Mg-Zn-Ca in osteoporotic, old and juvenile rats.

Implant removal is unnecessary for biodegradable magnesium (Mg)-based implants and, therefore, the related risk for implant-induced fractures is limited. Aging, on the other hand, is associated with low bone-turnover and decreased bone mass and density, and thus increased fracture risk. Osteoporosis is accompanied by Mg deficiency, therefore, we hypothesized that Mg-based implants may support bone formation by Mg2+ ion release in an ovariectomy-induced osteoporotic rat model. Hence, we investigated osseointegration and implant degradation of a low-alloyed, degrading Mg-Zn-Ca implant (ZX00) in ovariectomy-induced osteoporotic (Osteo), old healthy (OH), and juvenile healthy (JH) groups of female Sprague Dawley rats via in vivo micro-computed tomography (µCT). For the Osteo rats, we demonstrate diminished trabecular bone already after 8 weeks upon ovariectomy and significantly enhanced implant volume loss, with correspondingly pronounced gas formation, compared to the OH and JH groups. Sclerotic rim development was observed in about half of the osteoporotic rats, suggesting a prevention from foreign-body and osteonecrosis development. Synchrotron radiation-based µCT confirmed lower bone volume fractions in the Osteo group compared to the OH and JH groups. Qualitative histological analysis additionally visualized the enhanced implant degradation in the Osteo group. To date, ZX00 provides an interesting implant material for young and older healthy patients, but it may not be of advantage in pharmacologically untreated osteoporotic conditions. STATEMENT OF SIGNIFICANCE: Magnesium-based implants are promising candidates for treatment of osteoporotic fractures because of their biodegradable, biomechanical, anti-bacterial and bone regenerative properties. Here we investigate magnesium‒zinc‒calcium implant materials in a rat model with ovariectomy-induced osteoporosis (Osteo group) and compare the related osseointegration and implant degradation with the results obtained for old healthy (OH) and juvenile healthy (JH) rats. The work applied an appropriate disease model for osteoporosis and focused in particular on long-term implant degradation for different bone conditions. Enhanced implant degradation and sclerotic rim formation was observed in osteoporotic rats, which illustrates that the setting of different bone models generates significantly modified clinical outcome. It further illustrated that these differences must be taken into account in future biodegradable implant development.

Bioresorbable Magnesium-Based Alloys as Novel Biomaterials in Oral Bone Regeneration: General Review and Clinical Perspectives.

Bone preservation and primary regeneration is a daily challenge in the field of dental medicine. In recent years, bioresorbable metals based on magnesium (Mg) have been widely investigated due to their bone-like modulus of elasticity, their high biocompatibility, antimicrobial, and osteoconductive properties. Synthetic Mg-based biomaterials are promising candidates for bone regeneration in comparison with other currently available pure synthetic materials. Different alloys based on Mg were developed to fit clinical requirements. In parallel, advances in additive manufacturing offer the possibility to fabricate experimentally bioresorbable metallic porous scaffolds. This review describes the promising clinical results of resorbable Mg-based biomaterials for bone repair in osteosynthetic application and discusses the perspectives of use in oral bone regeneration.