Bone formation and degradation behavior of nanocrystalline hydroxyapatite with or without collagen-type 1 in osteoporotic bone defects - an experimental study in osteoporotic goats

Aucubin produces anti-osteoporotic effects under mechanical stretch stress and orthodontic tooth movement

Aucubin (AU), an iridoid glycoside extracted from Eucommia ulmoides, exerts anti-osteoporotic effects by promoting osteogenesis, as reported in previous studies. Here, we investigated the effects of AU under mechanical stretch stress. MC3T3-E1 cells were treated with dexamethasone (DEX) in vitro and subjected to mechanical stretch stress to establish an osteoporotic orthodontic force cell model. AU treatment increased the mRNA and protein expressions of BMP2, OPN, RUNX2, COL-1 and other osteogenic differentiation factors in MC3T3-E1 cells. Furthermore, we established an in vivo orthodontic tooth movement (OTM) model of osteoporosis. Serum parameter detection of ALP concentration, radiography of the femur, hematoxylin-eosin (HE) staining, and micro-CT of the maxilla confirmed that AU could partially reverse the damage induced by DEX. Immunohistochemical (IHC) analysis showed that AU increased the expression of COL-1, OCN, and OPN on the tension side of the periodontium. In conclusion, AU treatment promotes osteogenic differentiation under mechanical stretch stress and positively affects bone remodeling during OTM in DEX-induced osteoporosis.

Comparative In Vitro Dissolution Assessment of Calcined and Uncalcined Hydroxyapatite Using Differences in Bioresorbability and Biomineralization

This study reports the effect of the not-calcining process on the bioresorption and biomineralization of hydroxyapatite through in vitro dissolution assessment. The prepared calcined hydroxyapatite (c-HAp) and uncalcined hydroxyapatite (unc-HAp) have a particle size of 2 μm and 13 μm, surface areas of 4.47 m2/g and 108.08 m2/g, and a Ca/P ratio of 1.66 and 1.52, respectively. In vitro dissolution assessments of c-HAp and unc-HAp were performed for 20 days at 37 °C in a citric acid buffer according to ISO 10993-14. During the dissolution, the c-HAp and unc-HAp confirmed an increase in weight, and the calcium and phosphorous ions were rapidly released. The calcium ions released from c-HAp formed rod-shaped particles with a longer and thinner morphology, while in unc-HAp, they appeared thicker and shorter. In the ICP-OES results, the concentrations of calcium elements were initially increased and then decreased by this formation. The rod-shaped particles identified as calcium citrate (Ca-citrate) through the XRD pattern. The calcium content of Ca-citrate particles from unc-HAp was higher than that from c-HAp. The unc-HAp demonstrated non-toxic properties in a cytotoxicity evaluation. Therefore, due to its higher bioresorption and biomineralization, unc-HAp exhibits enhanced biocompatibility compared to c-HAp.

Comparison of osteogenesis of bovine bone xenografts between true bone ceramics and decalcified bone matrix

Xenograft bone scaffolds have certain advantages such as mechanical strength, osteoinductive properties, sufficient source and safety. This study aimed to compare osteogenesis of the two main bovine bone xenografts namely true bone ceramics (TBC) and decalcified bone matrix (DBM), and TBC or DBM combined with bone morphogenetic protein (BMP)-2 (TBC&BMP-2 and DBM&BMP-2). The characteristics of TBC and DBM were investigated by observing the appearance and scanning electron microscopic images, examining mechanical strength, evaluating cytotoxicity and detecting BMP-2 release after being combined with BMP-2 in vitro. The femoral condyle defect and radial defect models were successively established to evaluate the performance of the proposed scaffolds in repairing cortical and cancellous bone defects. General observation, hematoxylin and eosin (HE) staining, mirco-CT scanning, calcein double labeling, X-ray film observation, three-point bending test in vivo were then performed. It indicated that the repair with xenograft bone scaffolds of 8 weeks were needed and the repair results were better than those of 4 weeks whatever the type of defects. To femoral condyle defect, TBC and TBC&BMP-2 were better than DBM and DBM&BMP-2, and TBC&BMP-2 was better than TBC alone; to radial defect, DBM and DBM&BMP-2 were better than TBC and TBC&BMP-2, and DBM&BMP-2 was better than DBM alone. This study has shown that TBC and DBM xenograft scaffolds can be more suitable for the repair of cancellous bone and cortical bone defects for 8 weeks in rats, respectively. We also have exhibited the use of BMP-2 in combination with DBM or TBC provides the possibility to treat bone defects more effectively. We thus believe that we probably need to select the more suitable scaffold according to bone defect types, and both TBC and DBM are promising xenograft materials for bone tissue engineering and regenerative medicine. Graphical abstract.

Applications of Calcium-Based Nanomaterials in Osteoporosis Treatment

With rapidly aging populations worldwide, osteoporosis has become a serious global public health problem. Caused by disordered systemic bone remodeling, osteoporosis manifests as progressive loss of bone mass and microarchitectural deterioration of bone tissue, increasing the risk of fractures and eventually leading to osteoporotic fragility fractures. As fracture risk increases, antiosteoporosis treatments transition from nonpharmacological management to pharmacological intervention, and finally to the treatment of fragility fractures. Calcium-based nanomaterials (CBNMs) have unique advantages in osteoporosis treatment because of several characteristics including similarity to natural bone, excellent biocompatibility, easy preparation and functionalization, low pH-responsive disaggregation, and inherent pro-osteogenic properties. By combining additional ingredients, CBNMs can play multiple roles to construct antiosteoporotic biomaterials with different forms. This review covers recent advances in CBNMs for osteoporosis treatment. For ease of understanding, CBNMs for antiosteoporosis treatment can be classified as locally applied CBNMs, such as implant coatings and filling materials for osteoporotic bone regeneration, and systemically administered CBNMs for antiosteoporosis treatment. Locally applied CBNMs for osteoporotic bone regeneration develop faster than the systemically administered CBNMs, an important consideration given the serious outcomes of fragility fractures. Nevertheless, many innovations in construction strategies and preparation methods have been applied to build systemically administered CBNMs. Furthermore, with increasing interest in delaying osteoporosis progression and avoiding fragility fracture occurrence, research into systemic administration of CBNMs for antiosteoporosis treatment will have more development prospects. Deep understanding of the CBNM preparation process and optimizing CBNM properties will allow for increased application of CBNMs in osteoporosis treatments in the future.

Boron Nano-hydroxyapatite Composite Increases the Bone Regeneration of Ovariectomized Rabbit Femurs

Osteoporosis is a systemic metabolic disease defined by a decreased bone mineral density, microarchitectural deterioration, and an increased incidence of fragility fractures that may lead to morbidity and mortality. Boron may stimulate new bone formation and regeneration, when combined with nano-hydroxyapatite. We questioned whether injecting boron-containing nano-hydroxyapatite composites with hyaluronan increased the bone mineral density and new bone formation in osteoporotic rabbit femurs. The regenerative effects of injectable boron-containing nano-hydroxyapatite composites from 6 to 12 weeks, which may prevent osteoporotic femoral fractures, were assessed. Boron-containing (10 μg/ml) nano-hydroxyapatite composites were injected into the intramedullary femoral cavity with hyaluronan. These significantly increased the histomorphometric new bone surface to the total bone surface ratio at 6 and 9 weeks. The micro-tomographic bone volume to the total volume ratio and bone mineral density in osteoporotic rabbit femurs increased when compared to the hyaluronan (p = 0.004, p = 0.004, p = 0.004, p = 0.01, respectively) and the sham-control (p = 0.01, p = 0.004, p = 0.01, p = 0.037, respectively) groups. The boron-containing group had a higher bone mineralization and new bone formation compared to the nano-hydroxyapatite group, although the difference was not statistically significant. These findings reveal that intramedullary injection of boron-containing nano-hydroxyapatite with hyaluronan increases new bone formation and mineralization in ovariectomized rabbit femurs. Boron-containing nano-hydroxyapatite composites are promising tissue engineering biomaterials that may have regenerative potential in preventing primary and/or secondary femoral fractures in osteoporosis patients.

Osteogenic and Angiogenic Potency of VEGF165-Transfected Canine Bone Marrow Mesenchymal Cells Combined with Coral Hydroxyapatite in Vitro

BACKGROUND

To explore the osteogenic and angiogenic potential of human vascular endothelial growth factor 165 (hVEGF165) gene-transfected canine bone marrow mesenchymal stem cells (BMSCs) combined with coral hydroxyapatite (CHA) scaffold.

METHODS

We constructed a lentiviral vector and transfected canine BMSCs with the best multiplicity of infection. Osteogenesis was induced in the transfected groups (GFP-BMSCs group and hVEGF-BMSCs group) and non-transfected group (BMSCs group), followed by the evaluation of alkaline phosphatase (ALP) activity and alizarin red S staining. Cells from the three groups were co-cultured with CHA granules, respectively to obtain the tissue-engineered bone. MTT assay and fluorescence microscopy were employed to assess cell proliferation and adhesion. The expression of osteogenic and angiogenic related genes and proteins were evaluated at 7, 14, 21, and 28 days post osteoinduction in cell culture alone and cell co-culture with CHA, respectively using RT-PCR and ELISA.

RESULTS

The hVEGF165 gene was transfected into BMSCs successfully. Higher ALP activity and more calcified nodules were found in the hVEGF-BMSCs group than in the control groups (p < 0.001). Cells attached and proliferated in CHA particles. Both cells cultured alone and cells co-culture with CHA expressed more osteogenic and angiogenic related genes and proteins in the hVEGF-BMSCs group compared to the GFP-BMSCs and BMSCs groups (p < 0.05).

CONCLUSION

High expression of hVEGF165 in BMSCs potentially promote the osteogenic potential of BMSCs, and synergically drive the expression of other osteogenic and angiogenic factors. hVEGF-BMSCs co-cultured with CHA expressed more osteogenic and angiogenic related factors, creating a favorable microenvironment for osteogenesis and angiogenesis. Also, the findings have allowed for the construction of a CHA-hVEGF-BMSCs tissue-engineered bone.

Development of collagen/nanohydroxyapatite scaffolds containing plant extract intended for bone regeneration

In this study scaffolds of nanohydroxyapatite (nHA) and anionic collagen (C) combined with plant extracts intended for bone tissue repair were developed. Grape seed (P), pomegranate peel (R) and jabuticaba peel (J) extracts were used as collagen crosslinker agents in order to improve the materials properties. All crude extracts were effective against Staphylococcus aureus, but only for CR scaffold inhibition zone was noticed. The extracts acted as crosslinking agents, increasing enzymatic resistance and thermal stability of collagen. The extracts showed cytotoxicity at the concentrations tested, while nHA increased cell viability. The scaffolds presented porosity and pore size appropriate for bone growth. CR, CnHAP, CnHAR and CnHAJ increased the cell viability after 24 h. The combination of collagen, nHA and plant extracts offers a promising strategy to design novel biomaterials for bone tissue regeneration.

Influence of bone formation by composite scaffolds with different proportions of hydroxyapatite and collagen

Composite scaffolds with different proportions of hydroxyapatite (HA) and collagen (COL) produced different bone induction results.

OBJECTIVE

To examine the composite scaffolds with optimal proportion of HA and COL to achieve earlier bone induction and maximum bone formation.

METHODS

Composite scaffolds with the HA/COL weight ratio of 7:3, 3:7, 5:5 and 9:1 were prepared, as HA powder was added to collagen solution at 130℃ for 48 h. Then, the composites with different proportions of HA/COL were implanted into the extraction socket of right upper central incisor of C57BL/6 J mice. The bone formation of the extraction socket was observed by Hematoxylin-eosin (HE) and Masson-trichrome (Masson) staining at 1 and 2 weeks after operation. Five weeks later, the bone formation of extraction socket was observed by micro computed tomography (micro-CT). After MC3T3-E1 cells were co-cultured with materials of different proportions for 3 days, the number of cells attached on the surface of the materials and entering the materials were counted, and the expression of osteogenic related genes (Runx2, Ocn. Osx and Alp) was detected by reverse transcription polymerase chain reaction (RT-PCR). The composite scaffolds with different proportion of HA/COL with and without mouse bone marrow mesenchymal stem cells (BMMSCs) were implanted into the back of adult mice and cultured subcutaneously for 30 days, and observed histologically by HE and Masson staining.

RESULTS

After one week implantation with the composite HA/COL scaffolds with the weight ratio of 7:3, 3:7, 5:5 and 9:1, there was no new bone formation in the extraction socket in mouse. However, two weeks later, new bone was firstly observed in the tooth socket with the composite HA/COL scaffolds of 7:3. 5 weeks later, micro-CT scanning showed that the total amount of newly formed bone, trabecular width and bone mineral density of the HA/COL scaffolds of 7:3 were higher than the other HA/COL scaffolds (P < 0.05). After MC3T3-E1 cells were co-cultured with different composite HA/COL scaffolds for 3 days. The number of cells on the surface and inside of the HA/COL scaffolds of 7:3 was more than the other materials, and the difference was statistically significant (P < 0.05). The expression levels of Ocn and Osx of MC3T3-E1 cells were also the highest in the HA/COL scaffolds of 7:3 (P < 0.01). Bone formation was observed in the composite HA/COL scaffold of 7:3 with BMMSCs subcutaneously in mouse for 30 days, while only osteoid formation was observed in the same scaffold without BMMSCs. but bone formation was not detected in the other proportions of the HA/COL scaffolds.

SIGNIFICANCE

Compared with other proportions of HA/COL, the composite HA/COL scaffolds of 7:3 has stronger ability to promote bone formation, recruit osteoblasts to attach and enter into the scaffolds, and promote the osteogenesis of BMMSCs.

Effect of Nano-hydroxyapatite and platelet-rich fibrin covered by the amniotic membrane on osseointegration after mandibular piezoelectric ridge splitting

Objective

This study aimed to assess the clinical and radiographic findings obtained by using amniotic membrane (AM) to cover nano-hydroxyapatite (nHA) bone grafts coated with platelet-rich fibrin (PRF) and thereby evaluate the osseointegration of posterior mandibular implants inserted simultaneously during alveolar piezoelectric ridge splitting technique (RST).

Methods

A prospective cohort study was implemented with thirty patients who had a narrow posterior mandibular alveolar ridge and required implant restoration. Patients were distributed randomly into three groups (group I treated by piezoelectric RST and immediate implant insertion, augmented by the nHA bone graft only; group II treated by piezoelectric RST augmented by nHA bone graft and covered by AM; while group III was treated by piezoelectric RST augmented with PRF and nHA graft and covered by AM). Patients were evaluated clinically to assess the implant stability quotient (ISQ) and radiographically to assess horizontal ridge dimension, crestal bone level (CBL), and bone densitometric (BD) parameters.

Results

ISQ results showed a non-significant clinical difference between groups while CBL values showed a high statistically significant difference over the 12-month interval when comparing groups III and II with group I. BD outcomes showed statistically significant differences at all intervals in comparisons of group III with groups I and II.

Conclusions

The results of this study suggest that concomitant use of PRF with nHA graft covered with AM for augmentation around the dental implant in a narrow posterior mandible after piezoelectric alveolar ridge splitting accelerate osseointegration and significantly increase bone density around the osseointegrated implant and decrease bone resorption in comparison to that achieved with the graft alone.

An overview of de novo bone generation in animal models

Some of the earliest success in de novo tissue generation was in bone tissue, and advances, facilitated by the use of endogenous and exogenous progenitor cells, continue unabated. The concept of one health promotes shared discoveries among medical disciplines to overcome health challenges that afflict numerous species. Carefully selected animal models are vital to development and translation of targeted therapies that improve the health and well-being of humans and animals alike. While inherent differences among species limit direct translation of scientific knowledge between them, rapid progress in ex vivo and in vivo de novo tissue generation is propelling revolutionary innovation to reality among all musculoskeletal specialties. This review contains a comparison of bone deposition among species and descriptions of animal models of bone restoration designed to replicate a multitude of bone injuries and pathology, including impaired osteogenic capacity.

Evaluation of the In Vivo Biological Effects of Marine Collagen and Hydroxyapatite Composite in a Tibial Bone Defect Model in Rats

One of the most promising strategies to improve the biological performance of bone grafts is the combination of different biomaterials. In this context, the aim of this study was to evaluate the effects of the incorporation of marine spongin (SPG) into Hydroxyapatite (HA) for bone tissue engineering proposals. The hypothesis of the current study is that SPG into HA would improve the biocompatibility of material and would have a positive stimulus into bone formation. Thus, HA and HA/SPG materials were produced and scanning electron microscopy (SEM) analysis was performed to characterize the samples. Also, in order to evaluate the in vivo tissue response, samples were implanted into a tibial bone defect in rats. Histopathological, immunohistochemistry, and biomechanical analyses were performed after 2 and 6 weeks of implantation to investigate the effects of the material on bone repair. The histological analysis demonstrated that composite presented an accelerated material degradation and enhanced newly bone formation. Additionally, histomorphometry analysis showed higher values of %BV/TV and N.Ob/T.Ar for HA/SPG. Runx-2 immunolabeling was higher for the composite group and no difference was found for VEGF. Moreover, the biomechanical analysis demonstrated similar values for all groups. These results indicated the potential of SPG to be used as an additive to HA to improve the biological performance for bone regeneration applications. However, further long-term studies should be carried out to provide additional information regarding the material degradation and bone regeneration.

Elastin-derived scaffolding associated or not with bone morphogenetic protein (BMP) or hydroxyapatite (HA) in the repair process of metaphyseal bone defects

Tissue engineering represents a promising alternative for reconstructive surgical procedures especially for the repair of bone defects that do not regenerate spontaneously. The present study aimed to evaluate the effects of the elastin matrix (E24/50 and E96/37) incorporated with hydroxyapatite (HA) or morphogenetic protein (BMP) on the bone repair process in the distal metaphysis of rat femur. The groups were: control group (CG), hydrolyzed elastin matrix at 50°C/24h (E24/50), E24/50 + HA (E24/50/HA), E24/50 + BMP (E24/50/BMP), hydrolyzed elastin matrix at 37°C/96h (E96/37), E96/37 + HA (E96/37/HA), E96/37 + BMP (E96/37/BMP). Macroscopic and radiographic analyses showed longitudinal integrity of the femur in all groups without fractures or bone deformities. Microtomographically, all groups demonstrated partial closure by mineralized tissue except for the E96/37/HA group with hyperdense thin bridge formation interconnecting the edges of the ruptured cortical. Histologically, there was no complete cortical recovery in any group, but partial closure with trabecular bone. In defects filled with biomaterials, no chronic inflammatory response or foreign body type was observed. The mean volume of new bone formed was statistically significant higher in the E96/37/HA and E24/50 groups (71.28 ± 4.26 and 66.40 ± 3.69, respectively) than all the others. In the confocal analysis, it was observed that all groups presented new bone markings formed during the experimental period, being less evident in the CG group. Von Kossa staining revealed intense calcium deposits distributed in all groups. Qualitative analysis of collagen fibers under polarized light showed a predominance of red-orange birefringence in the newly regenerated bone with no difference between groups. It was concluded that the E24/50 and E96/37/HA groups promoted, with greater speed, the bone repair process in the distal metaphysis of rat femur.

PLGA-BMP-2 and PLA-17β-Estradiol Microspheres Reinforcing a Composite Hydrogel for Bone Regeneration in Osteoporosis

The controlled release of active substances-bone morphogenetic protein 2 (BMP-2) and 17β-estradiol-is one of the main aspects to be taken into account to successfully regenerate a tissue defect. In this study, BMP-2- and 17β-estradiol-loaded microspheres were combined in a sandwich-like system formed by a hydrogel core composed of chitosan (CHT) collagen, 2-hidroxipropil γ-ciclodextrin (HP-γ-CD), nanoparticles of hydroxyapatite (nano-HAP), and an electrospun mesh shell prepared with two external electrospinning films for the regeneration of a critical bone defect in osteoporotic rats. Microspheres were made with poly-lactide-co-glycolide (PLGA) to encapsulate BMP-2, whereas the different formulations of 17β-estradiol were prepared with poly-lactic acid (PLA) and PLGA. The in vitro and in vivo BMP-2 delivered from the system fitted a biphasic profile. Although the in vivo burst effect was higher than in vitro the second phases (lasted up to 6 weeks) were parallel, the release rate ranged between 55 and 70 ng/day. The in vitro release kinetics of the 17β-estradiol dissolved in the polymeric matrix of the microspheres depended on the partition coefficient. The 17β-estradiol was slowly released from the core system using an aqueous release medium (Deff = 5.58·10-16 ± 9.81·10-17m2s-1) and very fast in MeOH-water (50:50). The hydrogel core system was injectable, and approximately 83% of the loaded dose is uniformly discharged through a 20G needle. The system placed in the defect was easily adapted to the defect shape and after 12 weeks approximately 50% of the defect was refilled by new tissue. None differences were observed between the osteoporotic and non-osteoporotic groups. Despite the role of 17β-estradiol on the bone remodeling process, the obtained results in this study suggest that the observed regeneration was only due to the controlled rate released of BMP-2 from the PLGA microspheres.

Osseointegrated membranes based on electro-spun TiO2/hydroxyapatite/polyurethane for oral maxillofacial surgery

Membranes which have an osseointegration abilty are often selected as biomaterials in oral and maxillofacial surgery. Although these membranes are often the best option for certain uses, it is a challenge to create functionally attractive membranes. In this research, electro-spun titanium oxide (TiO2)/hydroxyapatite (HA)/polyurethane (PU) membranes were fabricated with different ratios of HA and TiO2: 100: 0, 70:30, 50:50, 30:70 and 0:100 w/w. The morphologies of the different mixtures were assessed with a Scanning Electron Microscope (SEM) and Field Emission Microscope (FESEM). Element analysis was performed with EDX. The physical properties of the water contact angles and mechanical strength were tested and the membranes cultured with osteoblasts to evaluate their biological functions, cell adhesion, viability, proliferation, alkaline phosphatase (ALP) activity, and calcium content. The results showed that the membranes with TiO₂ and HA had smaller fibers than those without TiO₂ and HA. The TiO2- and HA-including compounds showed the formation of particle aggregation on the surface of the fibers. They also had higher water contact angles, mechanical strength, and stiffness than those without TiO₂ and HA, and they had better cell adhesion, viability, proliferation, ALP activity and calcium content. The membrane with a 50:50 TiO₂:HA ratio had more unique biological functions than the others. Finally, our research demonstrated that osseointegrated membranes with 50:50 TiO2:HA are promising for oral and maxillofacial surgery.

Biofunctionalization with a TGFβ-1 Inhibitor Peptide in the Osseointegration of Synthetic Bone Grafts: An In Vivo Study in Beagle Dogs

Objectives: The aim of this research was to determine the osseointegration of two presentations of biphasic calcium phosphate (BCP) biomaterial—one untreated and another submitted to biofunctionalization with a TGF-β1 inhibitor peptide, P144, on dental alveolus. Materials and Methods: A synthetic bone graft was used, namely, (i) Maxresorb^® (Botiss Klockner) (n = 12), and (ii) Maxresorb^® (Botiss Klockner) biofunctionalized with P144 peptide (n = 12). Both bone grafts were implanted in the two hemimandibles of six beagle dogs in the same surgical time, immediately after tooth extraction. Two dogs were sacrificed 2, 4, and 8 weeks post implant insertion, respectively. The samples were submitted to histomorphometrical and histological analyses. For each sample, we quantified the new bone growth and the new bone formed around the biomaterial’s granules. After optical microscopic histological evaluation, selected samples were studied using backscattered scanning electron microscopy (BS-SEM). Results: The biofunctionalization of the biomaterial’s granules maintains a stable membranous bone formation throughout the experiment timeline, benefitting from the constant presence of vascular structures in the alveolar space, in a more active manner that in the control samples. Better results in the experimental groups were proven both by quantitative and qualitative analysis. Conclusions: Synthetic bone graft biofunctionalization results in slightly better quantitative parameters of the implant’s osseointegration. The qualitative histological and ultramicroscopic analysis shows that biofunctionalization may shorten the healing period of dental biomaterials.

Rabbit as model for osteoporosis research

Osteoporosis is a major public health problem affecting more than 200 million people worldwide. The use of different animal models, for the study of its pathophysiology and treatments, is important being actually the ovariectomized rat the most widely used; although this model has several problems due its small size, lack of true closure of epiphyseal plate and bone differences with humans. This review is aimed at summarizing the most common methods published for osteoporosis induction in rabbits as model for human disease with their advantages and disadvantages. The paper shows the advantages of the use of this specie compared with the rat. All the techniques seemed to achieve the osteoporotic condition, but the one which obtained the most consistent bone mineral reduction in less time was the combination of surgery and corticoid treatment. The conclusion of the review was that rabbits are promising as a model of osteoporosis research because of their size, haversian remodelling and closure of epiphyseal plate, which solve some of the problems of the rat model. There are different techniques in the literature used to achieve the osteoporotic condition with diverse results, but there is a lack of consensus as to the best one.

Functionalization of Ceramic Coatings for Enhancing Integration in Osteoporotic Bone: A Systematic Review

Background: The success of reconstructive orthopaedic surgery strongly depends on the mechanical and biological integration between the prosthesis and the host bone tissue. Progressive population ageing with increased frequency of altered bone metabolism conditions requires new strategies for ensuring an early implant fixation and long-term stability. Ceramic materials and ceramic-based coatings, owing to the release of calcium phosphate and to the precipitation of a biological apatite at the bone-implant interface, are able to promote a strong bonding between the host bone and the implant. Methods: The aim of the present systematic review is the analysis of the existing literature on the functionalization strategies for improving the implant osteointegration in osteoporotic bone and their relative translation into the clinical practice. The review process, conducted on two electronic databases, identified 47 eligible preclinical studies and 5 clinical trials. Results: Preclinical data analysis showed that functionalization with both organic and inorganic molecules usually improves osseointegration in the osteoporotic condition, assessed mainly in rodent models. Clinical studies, mainly retrospective, have tested no functionalization strategies. Registered trademarks materials have been investigated and there is lack of information about the micro- or nano- topography of ceramics. Conclusions: Ceramic materials/coatings functionalization obtained promising results in improving implant osseointegration even in osteoporotic conditions but preclinical evidence has not been fully translated to clinical applications.

Bone regeneration strategy by different sized multichanneled biphasic calcium phosphate granules: In vivo evaluation in rabbit model

A variety of synthetic materials are currently in use as bone substitutes, among them a new calcium phosphate-based multichannel, cylindrical, granular bone substitute that is showing satisfactory biocompatibility and osteoconductivity in clinical applications. These cylindrical granules differ in their mechanical and morphological characteristics such as size, diameter, surface area, pore size, and porosity. The aim of this study is to investigate whether the sizes of these synthetic granules and the resultant inter-granular spaces formed by their filling critical-sized bone defects affect new bone formation characteristics and to determine the best formulations from these individual types by combining the granules in different proportions to optimize the bone tissue regeneration. We evaluated two types of multichanneled cylindrical granules, 1 mm and 3 mm in diameter, combined the granules in two different proportions (wt%), and compared their different mechanical, morphological, and in vitro and in vivo biocompatibility characteristics. We assessed in vitro biocompatibility and cytotoxicity using MC3T3-E1 osteoblast-like cells using MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay and confocal imaging. In vivo investigation in a rabbit model indicated that all four samples formed significantly better bone than the control after four weeks and eight weeks of implantation. Micro-computed tomography analysis showed more bone formation by the 1 mm cylindrical granules with 160 ± 10 µm channeled pore and 50% porosity than the other three samples ( p<.05), which we confirmed by histological analysis.

Preclinical and Translational Studies in Small Ruminants (Sheep and Goat) as Models for Osteoporosis Research

PURPOSE OF THE REVIEW

This review summarizes research on the use of sheep and goats as large animal models of human osteoporosis for preclinical and translational studies.

RECENT FINDINGS

The most frequent osteoporotic sheep model used is the ovariectomized sheep with 12 months post-operatively or more and the combined treatment of ovariectomized sheep associated to calcium/vitamin D-deficient diet and glucocorticoid applications for 6 months, but other methods are also described, like pinealectomy or hypothalamic-pituitary disconnection in ovariectomized sheep. The goat model for osteoporosis research has been used in a very limited number of studies in osteoporosis research relative to sheep. These osteoporotic small ruminant models are applied for biomaterial research, bone augmentation, efficacy of implant fixation, fragility fracture-healing process improvement, or bone-defect repair studies in the osteopenic or osteoporotic bone. Sheep are a recognized large animal model for preclinical and translational studies in osteoporosis research and the goat to a lesser extent. Recently, the pathophysiological mechanism underlying induction of osteoporosis in glucocorticoid-treated ovariectomized aged sheep was clarified, being similar to what occurs in postmenopausal women with glucocorticoid-induced osteoporosis. It was also concluded that the receptor activator of NF-κB ligand was stimulated in the late progressive phase of the osteoporosis induced by steroids in sheep. The knowledge of the pathophysiological mechanisms at the cellular and molecular levels of the induction of osteoporosis in small ruminants, if identical to humans, will allow in the future, the use of these animal models with greater confidence in the preclinical and translational studies for osteoporosis research.

A systematic review of current osteoporotic metaphyseal fracture animal models

Objectives

The treatment of osteoporotic fractures is a major challenge, and the enhancement of healing is critical as a major goal in modern fracture management. Most osteoporotic fractures occur at the metaphyseal bone region but few models exist and the healing is still poorly understood. A systematic review was conducted to identify and analyse the appropriateness of current osteoporotic metaphyseal fracture animal models.

Materials and Methods

A literature search was performed on the Pubmed, Embase, and Web of Science databases, and relevant articles were selected. A total of 19 studies were included. Information on the animal, induction of osteoporosis, fracture technique, site and fixation, healing results, and utility of the model were extracted.

Results

Fracture techniques included drill hole defects (3 of 19), bone defects (3 of 19), partial osteotomy (1 of 19), and complete osteotomies (12 of 19). Drill hole models and incomplete osteotomy models are easy to perform and allow the study of therapeutic agents but do not represent the usual clinical setting. Additionally, biomaterials can be filled into drill hole defects for analysis. Complete osteotomy models are most commonly used and are best suited for the investigation of therapeutic drugs or noninvasive interventions. The metaphyseal defect models allow the study of biomaterials, which are associated with complex and comminuted osteoporotic fractures.

Conclusion

For a clinically relevant model, we propose that an animal model should satisfy the following criteria to study osteoporotic fracture healing: 1) induction of osteoporosis, 2) complete osteotomy or defect at the metaphysis unilaterally, and 3) internal fixation.

Cite this article: R. M. Y. Wong, M. H. V. Choy, M. C. M. Li, K-S. Leung, S. K-H. Chow, W-H. Cheung, J. C. Y. Cheng. A systematic review of current osteoporotic metaphyseal fracture animal models. Bone Joint Res 2018;7:6–11. DOI: 10.1302/2046-3758.71.BJR-2016-0334.R2.

Repair of the calvarial defect in goat model using magnesium-doped porous hydroxyapatite combined with recombinant human bone morphogenetic protein-2

Hydroxyapatite (HA) is a representative bone repairing biomaterial for its similar composition to human bones and teeth. However, pure HA is limited in application for some unwanted characteristic, such as it is brickle and weakness in degradation. In this study, we modified HA by doping magnesium (Mg) to the material and studied its property in vitro. Besides, we also evaluated the calvarial defect repair effect using MgHA combined with rhBMP-2 in goat model. According to our outcomes, HA composited Mg made the scaffold smooth and the pore regular. In vitro study, Mg could increase the Ca releasing, which may reflect a faster degradation property modified by Mg. And then, MgHA improved the cell viability and proliferation. Furthermore, MgHA could increase the expression of ALP, Collagen I and VEGF protein compared with pure HA (p<0.5, respectively). In the vivo study, MgHA showed a better bone defect healing effect in computed tomography (CT) evaluation compared with HA (p<0.05), but it was inferior to the MgHA/rhBMP-2 (p<0.05). Besides, in the histological analysis, MgHA/rhBMP-2 showed the most effective bone formation outcome (p<0.05), and the MgHA group was significant better than the pure HA group on osteogenesis (p<0.05). Furthermore, Collagen I and VEGF mRNA expression at 12 week in MgHA/rhBMP-2 group were also significat higher than other two groups. In conclusion, Mg had effects on bone formation and angiogenesis, and MgHA/rhBMP-2 had improved the bone defect repair effect. It is worthy of being recommended to bone tissue engineering.

Biomimetic, Osteoconductive Non-mulberry Silk Fiber Reinforced Tricomposite Scaffolds for Bone Tissue Engineering

Composite biomaterials as artificial bone graft materials are pushing the present frontiers of bioengineering. In this study, a biomimetic, osteoconductive tricomposite scaffold made of hydroxyapatite (HA) embedded in non-mulberry Antheraea assama (A. assama) silk fibroin fibers and its fibroin solution is explored for its osteogenic potential. Scaffolds were physico-chemically characterized for morphology, porosity, secondary structure conformation, water retention ability, biodegradability, and mechanical property. The results revealed a ∼5-fold increase in scaffold compressive modulus on addition of HA and silk fibers to liquid silk as compared to pure silk scaffolds while maintaining high scaffold porosity (∼90%) with slower degradation rates. X-ray diffraction (XRD) results confirmed deposition of HA crystals on composite scaffolds. Furthermore, the crystallite size of HA within scaffolds was strongly regulated by the intrinsic physical cues of silk fibroin. Fourier transform infrared (FTIR) spectroscopy studies indicated strong interactions between HA and silk fibroin. The fabricated tricomposite scaffolds supported enhanced cellular viability and function (ALP activity) for both MG63 osteosarcoma and human bone marrow stem cells (hBMSCs) as compared to pure silk scaffolds without fiber or HA addition. In addition, higher expression of osteogenic gene markers such as collagen I (Col-I), osteocalcin (OCN), osteopontin (OPN), and bone sialoprotein (BSP) further substantiated the applicability of HA composite silk scaffolds for bone related applications. Immunostaining studies confirmed localization of Col-I and BSP and were in agreement with real-time gene expression results. These findings demonstrate the osteogenic potential of developed biodegradable tricomposite scaffolds with the added advantage of the affordability of its components as bone graft substitute materials.