Anti-VEGFs hinder bone healing and implant osseointegration in rat tibiae

Dental implant considerations in patients with systemic diseases: An updated comprehensive review

BACKGROUND

Various medical conditions and the drugs used to treat them have been shown to impede or complicate dental implant surgery. It is crucial to carefully monitor the medical status and potential post-operative complications of patients with systemic diseases, particularly elderly patients, to minimize the risk of health complications that may arise.

AIM

The purpose of this study was to review the existing evidence on the viability of dental implants in patients with systemic diseases and to provide practical recommendations to achieve the best possible results in the corresponding patient population.

METHODS

The information for our study was compiled using data from PubMed, Scopus, Web of Science and Google Scholar databases and searched separately for each systemic disease included in our work until October 2023. An additional manual search was also performed to increase the search sensitivity. Only English-language publications were included and assessed according to titles, abstracts and full texts.

RESULTS

In total, 6784 studies were found. After checking for duplicates and full-text availability, screening for the inclusion criteria and manually searching reference lists, 570 articles remained to be considered in this study.

CONCLUSION

In treating patients with systemic conditions, the cost-benefit analysis should consider the patient's quality of life and expected lifespan. The success of dental implants depends heavily on ensuring appropriate maintenance therapy, ideal oral hygiene standards, no smoking and avoiding other risk factors. Indications and contraindications for dental implants in cases of systemic diseases are yet to be more understood; broader and hardcore research needs to be done for a guideline foundation.

Bevacizumab, a vascular endothelial growth factor inhibitor, promotes orthodontic tooth movement in an experimental rat model

Objective

This study aimed to evaluate the impact of bevacizumab on orthodontic tooth movement (OTM) in Wistar rats.

Materials and methods

The OTM model was constructed by placing an orthodontic coil spring between the maxillary first molar and anterior tooth. Bevacizumab (Avastin®; 10 mg/kg twice per week) was started one week before the OTM and continued for 3 weeks. After 1 and 2 weeks, OTM distance and anterior tooth mobility were measured. Thereafter, the maxilla was dissected for micro-CT microarchitectural analysis, followed by histological analysis, and tartrate-resistant acid phosphatase (TRAP) staining. Moreover, the distributions of collagen fibers type-I and -III (Col-I and Col-III) were evaluated using Picro-Sirius red staining.

Results

Orthodontic force prompted bone resorption and formation on the pressure and tension sides, respectively. Bevacizumab therapy resulted in a 42% increase of OTM, particularly after 2 weeks. Furthermore, bevacizumab disturbed the morphometric structure at both pressure and tension sites. The histological evaluation indicated about 35-44% fewer osteoblasts in the bevacizumab group, especially at the tension side, whereas the proportion of TRAP-positive osteoclasts at the pressure side was 34-37% higher than the control. The mature Col-I was reduced at the tension site by 33%, whereas the Col-III/Col-I ratio was enhanced by 20-44% at pressure and tension sites, after 2 weeks, in the bevacizumab group.

Conclusion

Anti-vascular bevacizumab therapy accentuates OTM in rat model, possibly through the enhancement of bone resorption, at the pressure side, and the reduction of bone formation, at the tension side as well as dysregulation of collagen fibers distribution.

The Role of Surface Chemistry in the Osseointegration of PEEK Implants

Poly(etheretherketone) (PEEK) implants suffer from poor osseointegration because of chronic inflammation. In this study, we hypothesized that adding NH₂ and COOH groups to the surface of PEEK could modulate macrophage responses by altering protein adsorption and improve its osseointegration. NH₂ and COOH-functionalized PEEK surfaces induced pro- and anti-inflammatory macrophage responses, respectively, and differences in protein adsorption patterns on these surfaces were related to the varied inflammatory responses. The macrophage responses to NH₂ surfaces significantly reduced the osteogenic differentiation of mesenchymal stem cells (MSCs). MSCs cultured on NH₂ surfaces differentiated less than those on COOH surfaces even though NH₂ surfaces promoted the most mineralization in simulated body fluid solutions. After 14 days in rat tibia unicortical defects, the bone around NH₂ surfaces had thinner trabeculae and higher specific bone surface than the bone around unmodified implants; surprisingly, the NH₂ implants significantly increased bone-binding over the unmodified implants, while COOH implants only showed a trend for increasing bone-binding. Taken together, these results suggest that both mineral-binding and immune responses play a role in osseointegration, and PEEK implant integration may be improved with mixtures of these two functional groups to harness the ability to reduce inflammation and bind bone strongly.

Histological assessment of mandibular bone tissue after guided bone regeneration with customized computer-aided design/computer-assisted manufacture titanium mesh in humans: A cohort study

BACKGROUND

Innovative customized computer-aided design/computer-assisted manufacture (CAD-CAM) titanium meshes have been proposed for guided alveolar bone regeneration. Histological confirmation on the quality of the regenerated bone is needed. Purpose of the study is to assess the integration capabilities of these innovative meshes and to evaluate the histological features of the regenerated alveolar bone.

MATERIALS AND METHODS

Twenty partially edentulous patients, with severe posterior mandibular atrophy, underwent a guided bone regeneration technique by means of customized CAD-CAM titanium mesh in association with a mixture of autologous bone in chips and deproteinized bovine bone (1:1). At 9 months of healing, titanium meshes and bone samples were collected and histomorphometrically analyzed.

RESULTS

In all patients, implants were placed according to the original plan. At histologic analysis, mesh appeared well osseointegrated, except that in sites where membrane exposure occurred. In all sites, newly formed tissue resulted highly mineralized, well-organized, and formed by 35.88% of new lamellar bone, 16.42% of woven bone, 10.88% of osteoid matrix, 14.10% of grafted remnants, and 22.72% of medullary spaces. Blood vessels were the 4% of the tissue.

CONCLUSIONS

Data from this study support the use of customized CAD/CAM titanium mesh for regeneration of vital, well-structured, and vascularized alveolar bone.

The synergistic promotion of osseointegration by nanostructure design and silicon substitution of hydroxyapatite coatings in a diabetic model

Accumulating evidence indicates much higher failure rates for biomedical titanium implants in diabetic patients. This phenomenon is attributed to impaired osteoblastic function, suppressed angiogenesis capacity, and abnormal osteoclast activation in diabetic patients. Our previous study demonstrated that titanium implants coated with highly crystalline nanostructured hydroxyapatite (nHA) promoted the osteogenic differentiation of bone marrow stromal cells (BMSCs) and bone-implant osseointegration under healthy conditions. Furthermore, recent studies showed that silicon-substituted biomaterials exhibited excellent osteogenesis and angiogenesis performance while repressing osteoclastogenesis. Hence, we proposed that a combination of nanostructural modification and Si substitution might produce synergetic effects to mitigate the impaired osseointegration of bone implants under diabetes mellitus (DM) conditions. To confirm this hypothesis, titanium implants coated with highly crystalline Si-substituted nHA (Si-nHA) were successfully fabricated via atmospheric plasma spraying combined with hydrothermal treatment. An in vitro study demonstrated that compared to the original HA coating, the nHA coating improved osteogenic and angiogenic differentiation and altered the OPG/RANKL ratio of DM-BMSCs. In addition, the Si-nHA coating further enhanced cell proliferation, improved osteogenic and angiogenic differentiation, and repressed osteoclastogenesis in DM-BMSCs. An in vivo study confirmed that the titanium implants coated with nHA or Si-nHA effectively promoted bone formation and bone-implant osseointegration in a diabetic rabbit model, with the Si-nHA coating exhibiting the best stimulatory effect. Collectively, the results suggest that the nanostructured topography and Si substitution act synergistically to ameliorate the poor bone regeneration and osseointegration associated with DM. Thus, the results provide a promising coating method for dental and orthopedic applications under diabetic conditions.

A partially demineralized allogeneic bone graft: in vitro osteogenic potential and preclinical evaluation in two different intramembranous bone healing models

In skeletal surgical procedures, bone regeneration in irregular and hard-to-reach areas may present clinical challenges. In order to overcome the limitations of traditional autologous bone grafts and bone substitutes, an extrudable and easy-to-handle innovative partially demineralized allogenic bone graft in the form of a paste has been developed. In this study, the regenerative potential of this paste was assessed and compared to its clinically used precursor form allogenic bone particles. Compared to the particular bone graft, the bone paste allowed better attachment of human mesenchymal stromal cells and their commitment towards the osteoblastic lineage, and it induced a pro-regenerative phenotype of human monocytes/macrophages. The bone paste also supported bone healing in vivo in a guide bone regeneration model and, more interestingly, exhibited a substantial bone-forming ability when implanted in a critical-size defect model in rat calvaria. Thus, these findings indicate that this novel partially demineralized allogeneic bone paste that combines substantial bone healing properties and rapid and ease-of-use may be a promising alternative to allogeneic bone grafts for bone regeneration in several clinical contexts of oral and maxillofacial bone grafting.

Effect of platelet-rich and platelet-poor plasma on 3D bone-to-implant contact: a preclinical micro-CT study

BACKGROUND

Bone-to-implant contact ratio (BIC%) plays a critical role in secondary stability of osseointegrated dental implants. The aim of this study was to identify the correlation of 2D/3D micro-CT images with histology as a gold standard for evaluating BIC% and to investigate the influence of the platelet-rich plasma (PRP) and platelet-poor plasma (PPP) on 3D BIC% following delayed implant placement with delayed loading (DIP+DL).

METHODS

Nine beagle dogs were recruited. Following bilateral extraction of mandibular 3rd premolar, 4th premolar, and 1st molar, 54 screw-type titanium implants were inserted and randomly divided into one control and two test groups based on a split-mouth design. The control group involved DIP+DL (n = 18) and both test groups included DIP+DL with local application of PRP (n = 18) and PPP (n = 18). A BIC analysis was performed utilizing 2D histomorphometry and 2D/3D micro-CT. Following identification of correlation between histology and 2D/3D micro-CT images, a 3D micro-CT assessment of the 3D BIC% at three follow-up time-points (1, 3, and 6 months) was carried out for observing the influence of PRP and PPP on BIC.

RESULTS

The 2D micro-CT BIC% values revealed a strong positive correlation with histology (r = 0.98, p < 0.001) and a moderate correlation existed with 3D micro-CT (r = 0. 67, p = 0.005). BIC levels at 1 month and combined influence of PPP and PRP irrespective of time-points revealed significantly higher 3D BIC% compared to the control. However, a reduction in 3D BIC% was observed at the 3rd and 6th month. No significant difference was observed between both PRP and PPP.

CONCLUSIONS

Both 2D and 3D micro-CT demonstrated a potential to be utilized as a complimentary method for assessing BIC compared to the histological gold standard. Overall, both PRP and PPP significantly facilitated bone healing and osseointegration with a higher 3D BIC at follow-up. However, their influence was reduced as the observation period was increased.

Vascular Endothelial Growth Factor: A Translational View in Oral Non-Communicable Diseases

Vascular endothelial growth factors (VEGFs) are vital regulators of angiogenesis that are expressed in response to soluble mediators, such as cytokines and growth factors. Their physiologic functions include blood vessel formation, regulation of vascular permeability, stem cell and monocyte/macrophage recruitment and maintenance of bone homeostasis and repair. In addition, angiogenesis plays a pivotal role in chronic pathologic conditions, such as tumorigenesis, inflammatory immune diseases and bone loss. According to their prevalence, morbidity and mortality, inflammatory diseases affecting periodontal tissues and oral cancer are relevant non-communicable diseases. Whereas oral squamous cell carcinoma (OSCC) is considered one of the most common cancers worldwide, destructive inflammatory periodontal diseases, on the other hand, are amongst the most prevalent chronic inflammatory conditions affecting humans and also represent the main cause of tooth loss in adults. In the recent years, while knowledge regarding the role of VEGF signaling in common oral diseases is expanding, new potential translational applications emerge. In the present narrative review we aim to explore the role of VEGF signaling in oral cancer and destructive periodontal inflammatory diseases, with emphasis in its translational applications as potential biomarkers and therapeutic targets.

Osseointegration Pharmacology: A Systematic Mapping Using Artificial Intelligence

Clinical performance of osseointegrated implants could be compromised by the medications taken by patients. The effect of a specific medication on osseointegration can be easily investigated using traditional systematic reviews. However, assessment of all known medications requires the use of evidence mapping methods. These methods allow assessment of complex questions, but they are very resource intensive when done manually. The objective of this study was to develop a machine learning algorithm to automatically map the literature assessing the effect of medications on osseointegration. Datasets of articles classified manually were used to train a machine-learning algorithm based on Support Vector Machines. The algorithm was then validated and used to screen 599,604 articles identified with an extremely sensitive search strategy. The algorithm included 281 relevant articles that described the effect of 31 different drugs on osseointegration. This approach achieved an accuracy of 95%, and compared to manual screening, it reduced the workload by 93%. The systematic mapping revealed that the treatment outcomes of osseointegrated medical devices could be influenced by drugs affecting homeostasis, inflammation, cell proliferation and bone remodeling. The effect of all known medications on the performance of osseointegrated medical devices can be assessed using evidence mappings executed with highly accurate machine learning algorithms.

Postoperative Administration of the Acetylcholinesterase Inhibitor, Donepezil, Interferes with Bone Healing and Implant Osseointegration in a Rat Model

Donepezil is an acetylcholinesterase inhibitor commonly used to treat mild to moderate Alzheimer’s disease. Its use has been associated with increased bone mass in humans and animals. However, the effect of postoperative administration of donepezil on bone healing remains unknown. Therefore, this study aimed to assess the impact of postoperative injection of donepezil on bone healing, titanium-implant osseointegration, and soft tissue healing. Twenty-two Sprague-Dawley rats were randomly assigned to receive a daily dose of either donepezil (0.6 mg/kg) or saline as a control. In each rat, a uni-cortical defect was created in the right tibia metaphysis and a custom-made titanium implant was placed in the left tibiae. After two weeks, rats were euthanized, and their bones were analysed by Micro-CT and histology. The healing of bone defect and implant osseointegration in the rats treated with donepezil were significantly reduced compared to the saline-treated rats. Histomorphometric analysis showed lower immune cell infiltration in bone defects treated with donepezil compared to the saline-treated defects. On the other hand, the healing time of soft tissue wounds was significantly shorter in donepezil-treated rats compared to the controls. In conclusion, short-term administration of donepezil hinders bone healing whereas enhancing soft tissue healing.

Ranitidine Impairs Bone Healing and Implant Osseointegration in Rats' Tibiae

PURPOSE

Ranitidine has been found to have an impact on bone metabolism by suppressing osteoclastogenesis. We hypothesized that the use of ranitidine would impair bone healing and implant osseointegration. This study investigated the effect of postoperative administration of ranitidine on bone healing and osseointegration in rats.

MATERIALS AND METHODS

Twenty-two Sprague-Dawley rats underwent surgery to create a unicortical bone defect in each tibia. A titanium implant was placed on the right tibial defect, whereas the contralateral defect was left unfilled. After surgery, the rats were randomly divided into 2 groups receiving a daily dose of ranitidine or saline solution for 14 days and then euthanized for assessment of bone healing and osseointegration using micro-computed tomography (CT) and histomorphometry.

RESULTS

Micro-CT analysis of the bone defect showed a larger bone defect volume in the ranitidine group (0.82 ± 0.13 μL vs 0.66 ± 0.16 μL, P = .034), thinner cortical thickness (0.54 ± 0.07 mm vs 0.63 ± 0.11 mm, P = .026), and less bone regeneration at the defect site (40% ± 12% vs 57% ± 11%, P = .003). Implant-site micro-CT analysis showed less osseointegration in the ranitidine group (34.1% ± 2.7% vs 43.5% ± 2.1%, P = .014), and implant-site histologic analysis showed less medullary (P = .021), cortical (P = .001), and total (P = .003) bone-implant contact and less peri-implant bone volume-tissue volume (P = .002) in the ranitidine group. Histologic analysis for osteoclastic activity showed a lower number of osteoclasts in the ranitidine group (4.8 ± 2.4 mm^-2 vs 9.1 ± 2.1 mm^-2, P = .026).

CONCLUSIONS

The postoperative use of ranitidine impaired bone healing and osseointegration.

Biocompatibility of polyetheretherketone for the treatment of orbital bone defects

AIM

To investigate the biocompatibility and therapeutic effects of polyetheretherketone (PEEK) on recovery of a rabbit orbital defect.

METHODS

Totally 16 New Zealand rabbits were used to establish an orbital bone defect model and then randomly divided into two groups. PEEK was implanted in the experimental group. The control group was blank, and no substance was implanted. The model rabbits were sacrificed at 4 and 8wk, and examined by general observations, histology, electron microscopy, Western blotting, and real-time polymerase chain reaction.

RESULTS

No infection or rejection occurred after PEEK implantation, and biocompatibility was good. The relative expression of vascular endothelial growth factor (VEGF) protein in the experimental group was significantly higher than that in the control group postoperatively (P<0.05). Bone defect repair in the experimental group was significantly better than that in the control group in the same period and some osteogenesis was observed.

CONCLUSION

PEEK has good biocompatibility and efficacy for the treatment of orbital bone defects in a rabbit model.

Unique bone marrow blood vessels couple angiogenesis and osteogenesis in bone homeostasis and diseases

Blood vessels serve as a versatile transport system and play crucial roles in organ development, regeneration, and stem cell behavior. In the skeletal system, certain capillaries support perivascular stem cells or osteoprogenitor cells and thereby regulate bone formation. Recent studies reported that a specialized capillary subtype, termed type H vessels, is shown to couple angiogenesis and osteogenesis in rodents and humans. They can be distinguished by specific cell surface markers, as the endothelial cells in the metaphysis and endosteum highly express the junctional protein CD31 and the sialoglycoprotein endomucin. Here, we provide an overview of the role of type H vessels in bone homeostasis and summarize their linkage with various cytokines to control bone cell behavior and bone formation. We also discuss the potential clinical application for bone disorders by targeting these specific vessels according to their physiological and pathobiological settings.

Anti-Vascular Endothelial Growth Factors as a Potential Risk for Implant Failure: A Clinical Report

Knowledge of the risk factors for implant osseointegration is essential for clinical decision-making and optimizing treatment success. This clinical report presents a rare case of implant failure in a patient who received intravitreal injections of a vascular endothelial growth factor (VEGF) inhibitor for the treatment of age-related macular degeneration. Following CARE guidelines, the report presents a case rehabilitated with a mandibular 2-implant overdenture using the immediate-loading protocol and standard procedures. The implants failed within six weeks of immediate loading although primary stability (≥50 Ncm) was achieved during surgery and clinical follow-ups did not show any deviance from standard implant care or patient-related complications. Further investigation suggested that the intake of a VEGF inhibitor may be the cause of failure. This clinical report highlights the importance of systemic risk factors in implant success and their consideration during planning for implant-assisted treatment.

Vascular endothelial growth factor pathway promotes osseointegration and CD31hiEMCNhi endothelium expansion in a mouse tibial implant model: an animal study

AIMS

It is increasingly appreciated that coordinated regulation of angiogenesis and osteogenesis is needed for bone formation. How this regulation is achieved during peri-implant bone healing, such as osseointegration, is largely unclear. This study examined the relationship between angiogenesis and osteogenesis in a unique model of osseointegration of a mouse tibial implant by pharmacologically blocking the vascular endothelial growth factor (VEGF) pathway.

MATERIALS AND METHODS

An implant was inserted into the right tibia of 16-week-old female C57BL/6 mice (n = 38). Mice received anti-VEGF receptor-1 (VEGFR-1) antibody (25 mg/kg) and VEGF receptor-2 (VEGFR-2) antibody (25 mg/kg; n = 19) or an isotype control antibody (n = 19). Flow cytometric (n = 4/group) and immunofluorescent (n = 3/group) analyses were performed at two weeks post-implantation to detect the distribution and density of CD31^hiEMCN^hi endothelium. RNA sequencing analysis was performed using sorted CD31^hiEMCN^hi endothelial cells (n = 2/group). Osteoblast lineage cells expressing osterix (OSX) and osteopontin (OPN) were also detected with immunofluorescence. Mechanical pull-out testing (n = 12/group) was used at four weeks post-implantation to determine the strength of the bone-implant interface. After pull-out testing, the tissue attached to the implant surface was harvested. Whole mount immunofluorescent staining of OSX and OPN was performed to determine the amount of osteoblast lineage cells.

RESULTS

Flow cytometry revealed that anti-VEGFR treatment decreased CD31^hiEMCN^hi vascular endothelium in the peri-implant bone versus controls at two weeks post-implantation. This was confirmed by the decrease of CD31 and endomucin (EMCN) double-positive cells detected with immunofluorescence. In addition, treated mice had more OPN-positive cells in both peri-implant bone and tissue on the implant surface at two weeks and four weeks, respectively. More OSX-positive cells were present in peri-implant bone at two weeks. More importantly, anti-VEGFR treatment decreased the maximum load of pull-out testing compared with the control.

CONCLUSION

VEGF pathway controls the coupling of angiogenesis and osteogenesis in orthopaedic implant osseointegration by affecting the formation of CD31^hiEMCN^hi endothelium. Cite this article: Bone Joint J 2019;101-B(7 Supple C):108-114.

Delayed Healing of Tooth Extraction Sockets After Vascular Endothelial Growth Factor Inhibition by Bevacizumab

PURPOSE

This study aimed to explore the effect of the chemotherapeutic agent bevacizumab on the extraction socket healing process in New Zealand rabbits.

MATERIALS AND METHODS

The animals received intraperitoneal bevacizumab treatment for 6 consecutive weeks (3 mg/kg per week). The right mandibular first premolar was extracted in the second week of the experiment, and the jaw bone containing the socket tissues was harvested at the end of the treatment period. The healing of the removed socket was analyzed histologically and radiographically using a micro-computed tomography scan.

RESULTS

Quantitative morphometric and histologic assessments of the healing process of the extraction sockets in rabbits showed a marked (P ≤ .05) decrease in the bone volumetric mass after angiogenesis suppression by bevacizumab therapy (n = 5) compared with the control group (n = 5).

CONCLUSIONS

The results of this study indicate the physiological significance of angiogenesis in extraction socket healing. Moreover, this study highlights the risks and precautions that should be considered in clinical practice in patients undergoing targeted chemotherapy.

3-dimensional visualization of implant-tissue interface with the polyethylene glycol associated solvent system tissue clearing method

OBJECTIVES

Dental implants are major treatment options for restoring teeth loss. Biological processes at the implant-tissue interface are critical for implant osseointegration. Superior mechanical properties of the implant constitute a major challenge for traditional histological techniques. It is imperative to develop new technique to investigate the implant-tissue interface.

MATERIALS AND METHODS

Our laboratory developed the polyethylene glycol (PEG)-associated solvent system (PEGASOS) tissue clearing method. By immersing samples into various chemical substances, bones and teeth could be turned to transparent with intact internal structures and endogenous fluorescence being preserved. We combined the PEGASOS tissue clearing method with transgenic mouse line and other labelling technique to investigate the angiogenesis and osteogenesis processes occurring at the implant-bone interface.

RESULTS

Clearing treatment turned tissue highly transparent and implant could be directly visualized without sectioning. Implant, soft/hard tissues and fluorescent labels were simultaneously imaged in decalcified or non-decalcified mouse mandible samples without disturbing their interfaces. Multi-channel 3-dimensional image stacks at high resolution were acquired and quantified. The processes of angiogenesis and osteogenesis surrounding titanium or stainless steel implants were investigated.

CONCLUSIONS

Both titanium and stainless steel implants support angiogenesis at comparable levels. Successful osseointegration and calcium precipitation occurred only surrounding titanium, but not stainless steel implants. PEGASOS tissue clearing method provides a novel approach for investigating the interface between implants and hard tissue.

Bone extracts immunomodulate and enhance the regenerative performance of dicalcium phosphates bioceramics

Immunomodulation strategies are believed to improve the integration and clinical performance of synthetic bone substitutes. One potential approach is the modification of biomaterial surface chemistry to mimic bone extracellular matrix (ECM). In this sense, we hypothesized that coating synthetic dicalcium phosphate (DCP) bioceramics with bone ECM proteins would modulate the host immune reactions and improve their regenerative performance. To test this, we evaluated the in vitro proteomic surface interactions and the in vivo performance of ECM-coated bioceramic scaffolds. Our results demonstrated that coating DCP scaffolds with bone extracts, specifically those containing calcium-binding proteins, dramatically modulated their interaction with plasma proteins in vitro, especially those relating to the innate immune response. In vivo, we observed an attenuated inflammatory response against the bioceramic scaffolds and enhanced peri-scaffold new bone formation supported by the increased osteoblastogenesis and reduced osteoclastogenesis. Furthermore, the bone extract rich in calcium-binding proteins can be 3D-printed to produce customized hydrogels with improved regeneration capabilities. In summary, bone extracts containing calcium-binding proteins can enhance the integration of synthetic biomaterials and improve their ability to regenerate bone probably by modulating the host immune reaction. This finding helps understand how bone allografts regenerate bone and opens the door for new advances in tissue engineering and bone regeneration. STATEMENT OF SIGNIFICANCE: Foreign-body reaction is an important determinant of in vivo biomaterial integration, as an undesired host immune response can compromise the performance of an implanted biomaterial. For this reason, applying immunomodulation strategies to enhance biomaterial engraftment is of great interest in the field of regenerative medicine. In this article, we illustrated that coating dicalcium phosphate bioceramic scaffolds with bone-ECM extracts, especially those rich in calcium-binding proteins, is a promising approach to improve their surface proteomic interactions and modulate the immune responses towards such biomaterials in a way that improves their bone regeneration performance. Collectively, the results of this study may provide a conceivable explanation for the mechanisms involved in presenting the excellent regenerative efficacy of natural bone grafts.

Comparison of micro-computed tomography and histomorphometry in the measurement of bone-implant contact ratios

OBJECTIVE

The purpose of this study was to measure the 3-dimensional (3D) bone-to-implant contact (BIC) ratios calculated with an associated software algorithm on 3D micro-computed tomography (μCT) scans and compare them with measurements made with 2-dimensional histomorphometry.

STUDY DESIGN

For uncomplicated calculation of the 3D BIC ratios, 16 implants (8 grade 2 titanium and 8 grade 4 titanium) with simple cylindrical geometry were inserted into 8 rabbit tibiae; 2 implants were inserted into each tibia. The experimental animals were sacrificed at 2 weeks after surgery. The implants were surgically removed en bloc with surrounding bone. 3D μCT images were acquired and reconstructed, and histomorphometric procedures were performed. The calculated 3D BIC ratios were compared with the histomorphometrically measured BIC ratios.

RESULTS

When the 3D BIC ratios calculated in this study were compared with the BIC ratios measured conventionally by using histologic slides for light microscopy, no significant statistical correlation was found between the 2 ratios (P ≥ .35).

CONCLUSIONS

This study indicated that 3D μCT should be used for more accurate BIC assessment to produce an overall 3D picture for the bone-implant interface.

Ectopic tissue engineered ligament with silk collagen scaffold for ACL regeneration: A preliminary study

Anterior cruciate ligament (ACL) reconstruction remains a formidable clinical challenge because of the lack of vascularization and adequate cell numbers in the joint cavity. In this study, we developed a novel strategy to mimic the early stage of repair in vivo, which recapitulated extra-articular inflammatory response to facilitate the early ingrowth of blood vessels and cells. A vascularized ectopic tissue engineered ligament (ETEL) with silk collagen scaffold was developed and then transferred to reconstruct the ACL in rabbits without interruption of perfusion. At 2weeks after ACL reconstruction, more well-perfused cells and vessels were found in the regenerated ACL with ETEL, which decreased dramatically at the 4 and 12week time points with collagen deposition and maturation. ACL treated with ETEL exhibited more mature ligament structure and enhanced ligament-bone healing post-reconstructive surgery at 4 and 12weeks, as compared with the control group. In addition, the ETEL group was demonstrated to have higher modulus and stiffness than the control group significantly at 12weeks post-reconstructive surgery. In conclusion, our results demonstrated that the ETEL can provide sufficient vascularity and cellularity during the early stages of healing, and subsequently promote ACL regeneration and ligament-bone healing, suggesting its clinic use as a promising therapeutic modality.

STATEMENT OF SIGNIFICANCE

Early inflammatory cell infiltration, tissue and vessels ingrowth were significantly higher in the extra-articular implanted scaffolds than theses in the joint cavity. By mimicking the early stages of wound repair, which provided extra-articular inflammatory stimulation to facilitate the early ingrowth of blood vessels and cells, a vascularized ectopic tissue engineered ligament (ETEL) with silk collagen scaffold was constructed by subcutaneous implantation for 2weeks. The fully vascularized TE ligament was then transferred to rebuild ACL without blood perfusion interruption, and was demonstrated to exhibit improved ACL regeneration, bone tunnel healing and mechanical properties.

Angiogenesis Assays for the Evaluation of Angiogenic Properties of Orthopaedic Biomaterials - A General Review

Vascularization is an essential process in bone formation, remodeling and regeneration during both bone development and fracture repair. Vascularization remains a big challenge directly leading to the final success of newly regenerated bone. In this review, the advantages and disadvantages of different angiogenesis assays and bone defect models are described in details for investigating revascularization of materials of interest. Unlike conventional angiogenesis study with growth factors or pharmaceutical molecules performed in two-dimension, special considerations are taken into account whether these assays can be translated for testing three-dimensional implantable devices. Over the years, accurate and quantifiable in vitro, ex vivo and in vivo assays have been extensively demonstrated to be useful in examining how new blood vessels grow. These methods can contribute to the fundamental understanding of angiogenic properties of the materials, but a bone defect model is still pivotal in order to understand the cascade actions of angiogenesis along with bone formation. Finally, angiogenesis and osteogenesis are both complex processes interacting with each other, the choice of which assay to be performed should adequately address the clinical relevance and reflect the sequence of responses of revascularization of the test materials.

Two-Dimensional Magnesium Phosphate Nanosheets Form Highly Thixotropic Gels That Up-Regulate Bone Formation

Hydrogels composed of two-dimensional (2D) nanomaterials have become an important alternative to replace traditional inorganic scaffolds for tissue engineering. Here, we describe a novel nanocrystalline material with 2D morphology that was synthesized by tuning the crystallization of the sodium-magnesium-phosphate system. We discovered that the sodium ion can regulate the precipitation of magnesium phosphate by interacting with the crystal's surface causing a preferential crystal growth that results in 2D morphology. The 2D nanomaterial gave rise to a physical hydrogel that presented extreme thixotropy, injectability, biocompatibility, bioresorption, and long-term stability. The nanocrystalline material was characterized in vitro and in vivo and we discovered that it presented unique biological properties. Magnesium phosphate nanosheets accelerated bone healing and osseointegration by enhancing collagen formation, osteoblasts differentiation, and osteoclasts proliferation through up-regulation of COL1A1, RunX2, ALP, OCN, and OPN. In summary, the 2D magnesium phosphate nanosheets could bring a paradigm shift in the field of minimally invasive orthopedic and craniofacial interventions because it is the only material available that can be injected through high gauge needles into bone defects in order to accelerate bone healing and osseointegration.

Vascular endothelial growth factor and biphasic calcium phosphate in the endosseous healing of femoral defects: An experimental rat study

Background/purpose

The presence of adequate bone volume is a critical factor in rehabilitative dentistry. Despite the use of many promising alloplasts, success in stimulating bone formation has been limited, mostly due to poor local biological response. Growth factors have been introduced to stimulate angiogenesis and new bone formation. This histologic and histomorphometric study aimed to evaluate the effect of vascular endothelial growth factor (VEGF) and a biphasic alloplastic graft material (BA) on the healing of endosseous defects in rats.

Materials and methods

Twenty male Wistar rats were used. Two critical-sized bone defects were created in both the right and left femurs of each rat. Each defect was randomly assigned to be treated with VEGF, BA, or VEGF + BA, or to be left empty as a control. Half of the animals were sacrificed after 1 week, and the remaining half were sacrificed after 2 weeks. Inflammation, necrosis, and new bone areas were evaluated by means of histologic and histomorphometric analyses.

Results

Compared to the control group, defects treated with VEGF alone or in combination with BA showed higher rates of bone formation (33.10–46.60%) on Day 7. Additionally, VEGF significantly reduced inflammation and necrosis (P < 0.001). However, the differences were no longer discernable on Day 14.

Conclusion

VEGF makes a significant contribution to angiogenesis and osteogenesis in the early stages of bone defect healing, and its combination with an osteoconductive grafting material (BA) may further enhance new bone formation.