Calcium Sulphate/Hydroxyapatite Carrier for Bone Formation in the Femoral Neck of Osteoporotic Rats

Hydroxyapatite-based carriers for tumor targeting therapy

At present, targeted drug delivery is regarded as the most effective means of tumor treatment, overcoming the lack of conventional chemotherapeutics that are difficult to reach or enter into cancer cells. Hydroxyapatite (HAP) is the main component of biological hard tissue, which can be regarded as a suitable drug carrier due to its biocompatibility, nontoxicity, biodegradation, and absorbability. This review focuses on the cutting edge of HAP as a drug carrier in targeted drug delivery systems. HAP-based carriers can be obtained by doping, modification, and combination, which benefit to improve the loading efficiency of drugs and the response sensitivity of the microenvironment in the synthesis process. The drug adsorbed or in situ loaded on HAP-based carriers can achieve targeted drug delivery and precise treatment through the guidance of the in vivo microenvironment and the stimulation of the in vitro response. In addition, HAP-based drug carriers can improve the cellular uptake rate of drugs to achieve a higher treatment effect. These advantages revealed the promising potential of HAP-based carriers from the perspective of targeted drug delivery for tumor treatment.

Advances in materials-based therapeutic strategies against osteoporosis

Osteoporosis is caused by the disruption in homeostasis between bone formation and bone resorption. Conventional management of osteoporosis involves systematic drug administration and hormonal therapy. These treatment strategies have limited curative efficacy and multiple adverse effects. Biomaterials-based therapeutic strategies have recently emerged as promising alternatives for the treatment of osteoporosis. The present review summarizes the current status of biomaterials designed for managing osteoporosis. The advantages of biomaterials-based strategies over conventional systematic drug treatment are presented. Different anti-osteoporotic delivery systems are concisely addressed. These materials include injectable hydrogels and nanoparticles, as well as anti-osteoporotic bone tissue engineering materials. Fabrication techniques such as 3D printing, electrostatic spinning and artificial intelligence are appraised in the context of how the use of these adjunctive techniques may improve treatment efficacy. The limitations of existing biomaterials are critically analyzed, together with deliberation of the future directions in biomaterials-based therapies. The latter include discussion on the use of combination strategies to enhance therapeutic efficacy in the osteoporosis niche.

A bifunctional zoledronate sustained-release system in scaffold: Tumor therapy and bone repair

It is of great challenges to repair bone defect and prevent tumor recurrence in bone tumors postoperative treatment. Bone scaffolds loaded with zoledronate (ZOL) are expected to solve these issues due to its osteogenesis and anti-tumor ability. Furthermore, ZOL needs to be sustained release to meet the requirement of long-term therapy. In this study, ZOL was loaded into amination functionalized mesoporous silicon (SBA15NH₂), and then incorporated into poly (L-lactic acid) to prepare PLLA/SBA15NH₂-ZOL scaffold via selective laser sintering technology. On one hand, ZOL of local release not only can inhibit growth and proliferation of bone tumor cells but also inhibit osteoclast differentiation through competitive binding of receptor activator of nuclear factor (NF)-kB (RANK) in osteoclast precursors. On the other hand, amination function could change the surface charge of mesoporous silica to positive charge to enhance the absorption of ZOL, mesoporous structure and abundant amino groups of SBA15NH₂ play a barrier role and form hydrogen bond with phosphate groups of ZOL, respectively, thereby achieving its sustained release. The results showed that the loading amount of ZOL was 236.53 mg/g, and the scaffold could sustainedly release ZOL for more than 6 weeks. The scaffold inhibited proliferation of osteosarcoma cells through inducing apoptosis and cell cycle arrest. TRAP staining and F-actin ring formation experiment showed the scaffold inhibited differentiation and mature of osteoclast. Pit formation assay indicated that bone resorption activity was inhibited strongly.

Evaluation of an Injectable Biphasic Calcium Sulfate/Hydroxyapatite Cement for the Augmentation of Fenestrated Pedicle Screws in Osteoporotic Vertebrae: A Biomechanical Cadaver Study

Cement augmentation of pedicle screws is one of the most promising approaches to enhance the anchoring of screws in the osteoporotic spine. To date, there is no ideal cement for pedicle screw augmentation. The purpose of this study was to investigate whether an injectable, bioactive, and degradable calcium sulfate/hydroxyapatite (CaS/HA) cement could increase the maximum pull-out force of pedicle screws in osteoporotic vertebrae. Herein, 17 osteoporotic thoracic and lumbar vertebrae were obtained from a single fresh-frozen human cadaver and instrumented with fenestrated pedicle screws. The right screw in each vertebra was augmented with CaS/HA cement and the un-augmented left side served as a paired control. The cement distribution, interdigitation ability, and cement leakage were evaluated using radiographs. Furthermore, pull-out testing was used to evaluate the immediate mechanical effect of CaS/HA augmentation on the pedicle screws. The CaS/HA cement presented good distribution and interdigitation ability without leakage into the spinal canal. Augmentation significantly enhanced the maximum pull-out force of the pedicle screw in which the augmented side was 39.0% higher than the pedicle-screw-alone side. Therefore, the novel biodegradable biphasic CaS/HA cement could be a promising material for pedicle screw augmentation in the osteoporotic spine.

Triphasic calcium-based implant material resorbs and is replaced with bone in ovariectomized rats with or without bisphosphonate treatment

This study evaluated the effects of AGN1, a triphasic calcium-based material, and alendronate (A) on distal femoral defect bone repair in ovariectomized (OVX) rats. Of 106 rats, 92 were OVX'ed at 12 weeks old and underwent a 12-week induction period. Animals were randomized into five groups: OVX Control, OVX Alendronate Control, Normal Control, OVX Implantation, OVX Alendronate + Implantation. OVX Alendronate Control and OVX Alendronate + Implantation groups received alendronate injection twice weekly (0.015 mg/kg) from 6 weeks until sacrifice. Twelve weeks after OVX, 2.5 mm diameter by 4.0 mm long cylindrical, bilateral distal femoral defects were created in experimental animals. One defect was left empty, and one filled with AGN1. Dual-energy X-ray absorptiometry, microcomputed tomography, and histomorphometry were performed 0-, 6-, 12-, and 18-week postdefect/implantation surgery (N = 6-8/group). Results showed OVX induced significant and progressive bone loss which alendronate prevented. Histomorphometry demonstrated rapid AGN1 resorption: AGN1 resorbed from 95.1 ± 0.7% filling of the implant site (week 0) to 1.3 ± 1.0% (18 weeks) with no significant alendronate effect (1.6 ± 1.1%, 18 weeks). Bone formation in empty defects consisted primarily of cortical wall healing, whereas AGN1 implants demonstrated cortical wall healing with new trabecular bone filling the subcortical space. Alendronate dramatically increased bone formation in empty and AGN1 defects. We conclude AGN1 is resorbed and replaced by new cortical and trabecular bone in this OVX model, and alendronate did not compromise these effects.

Surgical Classification for Preclinical Rat Femoral Bone Defect Model: Standardization Based on Systematic Review, Anatomical Analysis and Virtual Surgery

Though surgical techniques profoundly influence in vivo experiments, significant heterogeneity exists in current surgeries for inducing rat femoral bone defects. Such variations reduce the reproducibility and comparability of preclinical studies, and are detrimental to clinical translation. The purposes of this study were: (1) to conduct a systematic review of rat femoral defect models, summarizing and analyzing the surgical techniques; (2) to analyze surgical design and potential pitfalls via 3D anatomy and virtual surgeries for fostering future precision research; and (3) to establish a surgical classification system, for improving the reproducibility and comparability among studies, avoiding unnecessary repetitive experiments. The online database PubMed was searched to identify studies from January 2000 to June 2022 using keywords, including rat, femur, bone defect. Eligible publications were included for a review of surgical methods. Anatomical analysis and virtual surgeries were conducted based on micro-CT reconstruction of the rat femur for further investigation and establishment of a classification system. A total of 545 publications were included, revealing marked heterogeneity in surgical methods. Four major surgical designs were reported for inducing defects from the proximal to distal femur: bone tunnel, cortical window, segmental defect, and wedge-shaped defect. Anatomical analysis revealed potential pitfalls hindering efficient clinical translation. A classification system was established according to the anatomical region, surgical design, and fixation devices. This systematic review in combination with 3D analysis and virtual surgery provides a general overview of current surgical approaches to inducing femoral defects in rats, and establishes a surgical classification facilitating preclinical research of quality and translational value.

A combined fracture and mortality risk index useful for treatment stratification in hip fragility fractures

Objectives

In this study, we aimed to assess the stratification ability of the Fracture and Mortality Risk Evaluation (FAME) index for reoperation, new fragility fracture, and mortality during one-year follow-up.

Patients and methods

Between November 2018 and July 2019, a total of 94 consecutive hip fragility fracture patients from two centers (20 males, 74 females; mean age: 79.3±8.9 years; range, 57 to 100 years) were retrospectively analyzed. The patients were classified into high, intermediate, and low fracture and mortality risk groups according to the Fracture Risk Assessment Tool (FRAX) score and Sernbo score, respectively, as well as nine combined categories according to the FAME index. Hospital records were reviewed to identify re-fractures (reoperations, implant failure, new fragility fractures on any site) and mortality at one year following the FAME index classification.

Results

Overall re-fracture and mortality rates were 20.2% and 33%, respectively. High fracture risk category (FRAX-H) was significantly associated with higher re-fracture (odds ratio [OR]: 2.9, 95% confidence interval [CI]: 1-8.2, p=0.037) and mortality rates compared to others (OR: 3.7, 95% CI: 1.5-9.3, p=0.003). The patients classified within the FRAX-H category (n=35) had different mortality rates according to their Sernbo classification; i.e., patients classified as low mortality risk (Sernbo-L) (n=17) had lower mortality rates compared to others in this group (n=18) (35.3% and 66.7%, respectively), indicating a low statistical significance (OR: 0.3, 95% CI: 0.1-1.1, p=0.063). Similarly, within patients classified in Sernbo-L category (n=64), those classified as high fracture risk (FRAX-H) (n=17) had significantly higher re-fracture rates compared to others in this group (n=47) (35.3% and 8.5%, respectively), (OR: 5.9; 95% CI: 1.4-24.5), (p=0.017). Multivariate logistic regression analyses adjusting for covariates (age, sex, length of hospital stay and BMI) yielded similar results.

Conclusion

The FAME index appears to be a useful stratification tool for allocating patients in a randomized-controlled trial for augmentation of hip fragility fractures.

An examination of two different approaches for the study of femoral neck fracture: Towards a more relevant rodent model

Femoral neck fractures are a massive personal and health programme burden. Methods to study femoral neck strength, across its combined trabecular and cortical components are therefore essential. Rodent ovariectomy-induced osteoporosis models are commonly coupled with ex vivo 3-/4-point bending methods to measure changes in femoral cortical diaphysis. The loading direction used to assess these properties are often non-physiologic and, moreover, these ovariectomy models are linked to marked weight gain that can influence the biomechanical properties. Herein, we explore whether more physiological axial ex vivo loading protocols applied to femoral neck samples of ovariectomised (OVX) rodents provide anatomically-relevant models for the assessment of strength. We examine the use of mouse and rat femurs, loaded in constrained and unconstrained configuration, respectively, and explore whether weight-correction increases their utility. Accordingly, the mid-shaft of the proximal half of femurs from OVX and sham-operated (Sham) mice was methacrylate-anchored and the head loaded parallel to the diaphysis (constrained). Alternatively, femurs from OVX and Sham rats were isolated intact and axially-loaded through hip and knee joint articular surfaces (unconstrained). Yield displacement, stiffness, maximum load and resilience were measured and fracture pattern classified; effects of body weight-correction via a linear regression method or simple division were assessed. Our data reveal significant deficiencies in biomechanical properties in OVX mouse femurs loaded in constrained configuration, only after weight-correction by linear regression. In addition, evaluation of rat femur biomechanics in unconstrained loading demonstrated greater variation and that weight-correction by simple division improved scope to reveal significant OVX impact. We conclude that greater femoral neck fracture susceptibility can indeed be measured in OVX rodents as long as multiple biomechanical parameters are reported, care is taken in choosing the method for assessing load-bearing strength and weight-correction applied. These studies advance the establishment of more relevant rodent models for the study of femoral neck fracture.

Long-Term Response to a Bioactive Biphasic Biomaterial in the Femoral Neck of Osteoporotic Rats

Osteoporosis often leads to fragility fractures of the hip, resulting in impaired quality of life and increased mortality. Augmenting the proximal femur could be an attractive option for prevention of fracture or fixation device failure. We describe a tissue engineering based strategy to enhance long-term bone formation in the femoral neck of osteoporotic rats by locally delivering bioactive molecules; recombinant human bone morphogenic protein-2 (rhBMP-2), and zoledronic acid (ZA) by using a calcium sulfate/hydroxyapatite (CaS/HA) biomaterial. A defect was created by reaming the femoral neck canal of osteoporotic (OVX) rats and they were treated as follows: G1. Empty, G2. CaS/HA, G3. CaS/HA+Systemic ZA, G4. CaS/HA+Local ZA, and G5. CaS/HA+Local ZA+rhBMP-2. Bone formation was evaluated 6 months after treatment. Further, radioactively labeled 14C-ZA was used to study the bioavailability of ZA at the defect location, which was determined by using scintillation counting. Micro-CT indicated significantly higher bone volume in groups G4 and G5 compared with the other treatment groups. This was confirmed qualitatively by histological assessment. Addition of rhBMP-2 gave no additional benefit in this model. Local delivery of ZA performed better than systemic administration of ZA. Mechanical testing showed no differences between the groups, likely reflecting that the addition of bioactive molecules had limited effect on cortical bone or the choice of mechanical testing setup was not optimal. Scintillation counting revealed higher amounts of 14C-ZA present in the treated leg of G4 compared with its contralateral control and compared with G3, indicating that local ZA delivery can be used to achieve high local concentrations without causing a systemic effect. This long-term study shows that local delivery of ZA using a CaS/HA carrier can regenerate cancellous bone in the femoral neck canal and has clear implications for enhancing implant integration and fixation in fragile bone.

Bone mineral as a drug-seeking moiety and a waste dump

Bone is a dynamic tissue with a quarter of the trabecular and a fifth of the cortical bone being replaced continuously each year in a complex process that continues throughout an individual's lifetime. Bone has an important role in homeostasis of minerals with non-stoichiometric hydroxyapatite bone mineral forming the inorganic phase of bone. Due to its crystal structure and chemistry, hydroxyapatite (HA) and related apatites have a remarkable ability to bind molecules. This review article describes the accretion of trace elements in bone mineral giving a historical perspective. Implanted HA particles of synthetic origin have proved to be an efficient recruiting moiety for systemically circulating drugs which can locally biomodulate the material and lead to a therapeutic effect. Bone mineral and apatite however also act as a waste dump for trace elements and drugs, which significantly affects the environment and human health. Cite this article: Bone Joint Res 2020;9(10):709-718.

A biphasic nanohydroxyapatite/calcium sulphate carrier containing Rifampicin and Isoniazid for local delivery gives sustained and effective antibiotic release and prevents biofilm formation

Long term multiple systemic antibiotics form the cornerstone in the treatment of bone and joint tuberculosis, often combined with local surgical eradication. Implanted carriers for local drug delivery have recently been introduced to overcome some of the limitations associated with conventional treatment strategies. In this study, we used a calcium sulphate hemihydrate (CSH)/nanohydroxyapatite (nHAP) based nanocement (NC) biomaterial as a void filler as well as a local delivery carrier of two standard of care tuberculosis drugs, Rifampicin (RFP) and Isoniazid (INH). We observed that the antibiotics showed different release patterns where INH showed a burst release of 67% and 100% release alone and in combination within one week, respectively whereas RFP showed sustained release of 42% and 49% release alone and in combination over a period of 12 weeks, respectively indicating different possible interactions of antibiotics with nHAP. The interactions were studied using computational methodology, which showed that the binding energy of nHAP with RFP was 148 kcal/mol and INH was 11 kcal/mol, thus varying substantially resulting in RFP being retained in the nHAP matrix. Our findings suggest that a biphasic ceramic based drug delivery system could be a promising treatment alternative to bone and joint TB.

Strontium-substituted calcium sulfate hemihydrate/hydroxyapatite scaffold enhances bone regeneration by recruiting bone mesenchymal stromal cells

Fabrication of osteoconductive scaffold with osteoinductive capability and appropriate resorption rate is of great significance for treating bone defects. To achieve this aim, strontium-substituted calcium sulfate hemihydrate (Sr-CSH) and hydroxyapatite (HA) were mixed to develop a novel composite. Sr-CSH containing 5% and 10% strontium was mixed with HA at the weight ratio of 6:4, respectively. Female Sprague-Dawley rats underwent bone defect surgery in left tibia were randomly assigned to three different treatment groups filled with CSH/HA, 5% and 10% Sr-CSH/HA. Micro-CT analysis showed increased new bone formation in 10% Sr-CSH/HA group compared to CSH/HA group. In addition, histological analysis showed large amounts of chondrocytes and osteoblasts within the pores of Sr-CSH/HA composites as a result of the CSH resorption. Further, CFU-F assay demonstrated the increased amount of bone marrow mesenchymal stromal cells (BMSCs) colonies in 10% Sr-CSH/HA group. In primary BMSCs, extraction from Sr-CSH/HA composite significantly increased the migration of cells, up-regulated the expression of osteoblastic marker genes, and increased the area of mineralized nodules. Together, Sr-CSH/HA may promote bone formation by recruiting and stimulating osteogenic differentiation of BMSCs. Therefore, this composite may be proposed as an ideal substitute to repair bone defects.

Combined fracture and mortality risk evaluation for stratifying treatment in hip fracture patients: A feasibility study

OBJECTIVES

This study aims to test the feasibility of the Fracture and Mortality Risk Evaluation (FAME) Index.

PATIENTS AND METHODS

Two academic centers in Lithuania and Turkey participated in this retrospective study conducted between November 2018 and July 2019. A total of 100 consecutive patients (22 males, 78 females; mean age 78.9 years; range, 45 to 100 years) with low energy proximal femur fractures admitted for surgery were included in the study. Fracture Risk Assessment tool (FRAX) and the Sernbo scores were calculated and patients were classified into one of the nine subcategories of the FAME Index.

RESULTS

Demographics and FAME Index classifications were similar between centers. Patients with high risk of fracture and low risk of mortality accounted for 18% of all patients, which is the FAME Index subcategory to theoretically benefit from cancellous bone augmentation during internal fixation of a fragility hip fracture the most.

CONCLUSION

The FAME Index was successfully applied in clinical emergency setting utilizing a simple form, and demonstrated promising potential in stratification of hip fractures most suitable for screw and device augmentation. Larger studies with at least one-year of follow-up are warranted to verify the validity of FAME Index.

Effects of collagen/β-tricalcium phosphate bone graft to regenerate bone in critically sized rabbit calvarial defects

Bone defects remain a significant health issue and a major cause of morbidity in elderly patients. Composites based on collagen/calcium phosphate have been widely used for bone repair in clinical applications, owing to their comparability to bone extracellular matrix. This study aimed to evaluate the effects of a scaffold of collagen/calcium phosphate (COL/β-TCP) on bone formation to assess its potential use as a bone substitute to repair bone defects. Bilateral full-thickness critically sized calvarial defects (8 mm in diameter) were created in New Zealand white rabbits and treated with COL/β-TCP or COL scaffolds. One defect was also left unfilled as a control. Bone regeneration was assessed through histological evaluation using hematoxylin and eosin and Masson's trichrome staining after 4 and 8 weeks. Alizarin Red staining was also utilized to observe the mineralization process. Our findings indicated that COL/β-TCP implantation could better enhance bone regeneration than COL and exhibited both new bone growth and scaffold material degradation.