The repair of critical-size defects with porous hydroxyapatite/polyamide nanocomposite: an experimental study in rabbit mandibles

Functional Approaches in Promoting Vascularization and Angiogenesis in Bone Critical-Sized Defects via Delivery of Cells, Growth Factors, Drugs, and Particles

Critical-sized bone defects, or CSDs, are defined as bone defects that cannot be regenerated by themselves and require surgical intervention via employing specific biomaterials and a certain regenerative strategy. Although a variety of approaches can be used to treat CSDs, poor angiogenesis and vascularization remain an obstacle in these methods. The complex biological healing of bone defects depends directly on the function of blood flow to provide sufficient oxygen and nutrients and the removal of waste products from the defect site. The absence of vascularization can lead to non-union and delayed-union defect development. To overcome this challenge, angiogenic agents can be delivered to the site of injury to stimulate vessel formation. This review begins by introducing the treatment methods for CSDs. The importance of vascularization in CSDs is subsequently highlighted. Delivering angiogenesis agents, including relevant growth factors, cells, drugs, particles, cell secretion substances, their combination, and co-delivery to CSDs are fully explored. Moreover, the effects of such agents on new bone formation, followed by vessel formation in defect areas, are evaluated.

Comparing the effect of demineralized versus hybrid dentin matrices on inducing bone regeneration in New Zealand white rabbits' Mandibular defect

OBJECTIVES

The aim of this study was to compare the effect of using demineralized dentin matrix (DDM) versus hybrid dentin matrices; Demineralized and undemineralized dentin particles (DDM +UDDM) on inducing bone regeneration in mandibular defects.

DESIGN

The study was conducted on fifty adult New Zealand rabbits, twenty for preparation of experimental materials and thirty for surgical procedures. They were randomly assigned into 3 equal groups as follow one control group: no treatment and two experimental groups including demineralized group: treated with DDM only; and hybrid group: treated with a hybrid of (50% DDM+50% UDD). A rounded critical size defect (10 mm in diameter- 5 mm in depth) was created in the body of mandible. After 3- and 6-weeks post-surgery, the bone regeneration was evaluated by light microscope, scanning electron microscope and histomorphometry.

RESULTS

Histological, histomorphometrical observation and SEM revealed that both dentin matrices had largely resorbed and induced new bone formation at both experimental groups compared to the control group, with statistically higher percentage of new bone formation in the hybrid group.

CONCLUSION

We concluded that although both dentin matrices induced new bone formation; however, hybrid dentin matrix yielded better results compared to DDM group.

Rabbit calvarial and mandibular critical-sized bone defects as an experimental model for the evaluation of craniofacial bone tissue regeneration

INTRODUCTION

Many studies have aimed to investigate the regeneration potential of bone substitutes through animal models at different defect sites, where the bone healing mechanism varies due to developmental, structural and functional differences. This study aims to develop a rabbit model with two functionally different (non-load-bearing calvarias and load-bearing mandibular) critical-sized defects (CSD) in one rabbit.

MATERIAL & METHOD

The comparison of the "gold standard" autograft to a sham (no graft) control was undertaken in order to validate this model; at the same time, a 3D-printed biphasic calcium phosphate scaffold was implanted to test its utility in the evaluation of new bone substitute materials. Twenty rabbits were selected with both a 10 mm calvaria defect and a 11 mm bicortical semi-cylindrical mandibular defect. The animals were euthanized at 4 and 12 weeks once surgery, microcomputed tomography and histological analysis had been performed.

RESULTS

In the case of the calvaria, the results for the non-healing sham group compared with the healing of those that had undergone the autograft validated the CSD model. But the mandibular defect was not validated, due to the particularity of mandible high mechanical stress and infectious risk.

DISCUSSION

This study showed for the first time that rabbits have a high tolerance for the bilateral double-site CSD model under consideration; and further studies are essential to modify and improve the design of mandibular CSD.

Bilateral double site (calvarial and mandibular) critical-size bone defect model in rabbits for evaluation of a craniofacial tissue engineering constructs

Most existing preclinical models for evaluating the biosafety and bone-regeneration efficacy of innovative bone substitute materials (BSMs) or tissue engineering (TE) constructs only consisted of a single-site defect and the anatomical locations of defect varied drastically. While the compelling evidence showed that the bone healing pattern is location-dependent, owing to developmental, structural, and functional differences of anatomical locations, this is particularly true for the craniofacial region. Taking this into account, the bone healing efficiency of a BSM shown at one anatomical defect location cannot ensure the same impact at another. This prompted us to develop, for the first time, a model of bilateral critical-sized defect (CSD) at two distinctly different locations (non-load-bearing parietal calvaria and load-bearing mandibular body) co-existing in one rabbit to reduce the number of animals needed and avoid the influence of interindividual variability and evaluation bias on comparisons.

24 healthy adult male New Zealand White rabbits were randomly assigned to a group, either control, autograft (considered the “gold standard”) or a clinically relevant BSM (biphasic calcium phosphate granules) (BCPg, Mastergraft®, Medronics). The full-thickness cylindrical calvarial defect (ø10 mm) on frontoparietal region and mandibular composite defect (ø11 mm) on the body of the mandible were created bilaterally using low-speed drilling with saline irrigation. The defect on one side was filled with autograft debris or BCPg, and the other side was no graft (empty). Following the euthanasia of animals at the predetermined intervals (4w and 12w), the defect zones were examined macroscopically and then sampled and processed for microcomputed tomography (microCT) and histological analysis.

All surgeries went uneventfully, and all rabbits recovered slowly but steadily. No symptoms of infection or inflammation associated with the defect were observed during the experiment. At 4w and 12w, macroscopic views of all defect sites were clean without any signs of necrosis or abscess, and no intraoral communication was found. The analysis of microCT and histological findings showed the non-healing nature of the empty defect, thereby both calvaria and mandible CSDs can be validated. The study of the application of BCPg in this defect model highlighted good osteointegration and excellent osteoconductive properties but compromised the osteoinductive properties of this material (compared with autograft).

To conclude, this novel double-site CSD model holds great promise in the application for preclinical evaluation of BSMs, TE construct, etc. With a reduced number of animals in use, and lower interindividual variability and evaluation bias for comparisons.

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A novel rabbit model of bilateral critical-sized defect co-existing at two distinctly different locations was developed.

Preliminary report of the outcomes and indications of single approach, double-channel core decompression with structural bone support and bone grafting for osteonecrosis of the femoral head

Background

To report the outcomes of the single approach to double-channel core decompression and bone grafting with structural bone support (SDBS) for osteonecrosis of the femoral head (ONFH) and define the indications.

Methods

One-hundred-and-thirty-nine hips in 96 patients (79 males, 17 females; mean age 37.53±10.31 years, range 14–58 years; mean body mass index 25.15±3.63 kg/m²) were retrospectively analysed. The Harris hip score (HHS) was used to assess hip function, and radiographs were used to assess the depth of femoral head collapse. Treatment failure was defined as the performance of total hip arthroplasty (THA). The variables assessed as potential risk factors for surgical failure were: aetiology, Japanese Osteonecrosis Investigation Committee (JIC) type, age, and Association Research Circulation Osseous (ARCO) stage. Complications were recorded.

Results

The mean follow-up time was 29.26±10.02 months. The HHS increased from 79.00±13.61 preoperatively to 82.01±17.29 at final follow-up (P=0.041). The average HHS improvement was 3.00±21.86. The combined excellent and good rate at final follow-up (65.6%) was significantly higher than that before surgery (34.5%) (P<0.05). On radiographic evaluation, 103 (74.1%) hips remained stable, while 36 (25.9%) had femoral head collapse or aggravation of ONFH. THA was performed in 18 hips. Thus, the overall femoral head survival rate was 87.05% (121/139). The success rate was adversely affected by JIC type, but not by aetiology, age, or ARCO stage. The only complication was a subtrochanteric fracture in one patient.

Conclusion

The SDBS may be an effective method to delay or even terminate the natural progression of ONFH, especially for patients with JIC types B and C1. The SDBS represents a new option for treating early-stage ONFH.

Nano-Hydroxyapatite as a Delivery System for Promoting Bone Regeneration In Vivo: A Systematic Review

Nano-hydroxyapatite (nHA) has been widely used as an orthopedic biomaterial and vehicle for drug delivery owing to its chemical and structural similarity to bone minerals. Several studies have demonstrated that nHA based biomaterials have a potential effect for bone regeneration with very minimal to no toxicity or inflammatory response. This systematic review aims to provide an appraisal of the effectiveness of nHA as a delivery system for bone regeneration and whether the conjugation of proteins, antibiotics, or other bioactive molecules to the nHA further enhances osteogenesis in vivo. Out of 282 articles obtained from the literature search, only 14 articles met the inclusion criteria for this review. These studies showed that nHA was able to induce bone regeneration in various animal models with large or critical-sized bone defects, open fracture, or methicillin-resistant Staphylococcus aureus (MRSA)-induced osteomyelitis. The conjugations of drugs or bioactive molecules such as bone-morphogenetic protein-2 (BMP-2), vancomycin, calcitriol, dexamethasone, and cisplatin were able to enhance the osteogenic property of nHA. Thus, nHA is a promising delivery system for a variety of compounds in promoting bone regeneration in vivo.

Current and Advanced Nanomaterials in Dentistry as Regeneration Agents: An Update

In modern dentistry, nanomaterials have strengthened their foothold among tissue engineering strategies for treating bone and dental defects due to a variety of reasons, including trauma and tumors. Besides their finest physiochemical features, the biomimetic characteristics of nanomaterials promote cell growth and stimulate tissue regeneration. The single units of these chemical substances are small-sized particles, usually between 1 to 100 nm, in an unbound state. This unbound state allows particles to constitute aggregates with one or more external dimensions and provide a high surface area. Nanomaterials have brought advances in regenerative dentistry from the laboratory to clinical practice. They are particularly used for creating novel biomimetic nanostructures for cell regeneration, targeted treatment, diagnostics, imaging, and the production of dental materials. In regenerative dentistry, nanostructured matrices and scaffolds help control cell differentiation better. Nanomaterials recapitulate the natural dental architecture and structure and form functional tissues better compared to the conventional autologous and allogenic tissues or alloplastic materials. The reason is that novel nanostructures provide an improved platform for supporting and regulating cell proliferation, differentiation, and migration. In restorative dentistry, nanomaterials are widely used in constructing nanocomposite resins, bonding agents, endodontic sealants, coating materials, and bioceramics. They are also used for making daily dental hygiene products such as mouth rinses. The present article classifies nanostructures and nanocarriers in addition to reviewing their design and applications for bone and dental regeneration.

Mandible Biomechanics and Continuously Erupting Teeth: A New Defect Model for Studying Load-Bearing Biomaterials

Animals with elodont dentition and unfused mandible symphyses are hypothesized to have symmetric incisor morphology. Since these animals maintain their teeth by gnawing, they may provide physiologic feedback on mechanical function when unilateral mandible defects are created that manifest as ipsilateral changes in tooth structure. This defect model would potentially generate important information on the functional/mechanical properties of implants. Rats’ and rabbits’ mandibles and teeth are analyzed with µCT at baseline and post-intervention (n = 8 for each). Baseline incisors were compared. In a unilateral mandible pilot study, defects—ranging from critical size defect to complete ramus osteotomies—were created to assess effect on dentition (rats, n = 7; rabbits, n = 6). Within 90% confidence intervals, animals showed no baseline left/right differences in their incisors. There are apparent dental changes associated with unilateral defect type and location. Thus, at baseline, animals exhibit statistically significant incisor symmetry and there is an apparent relationship between mandible defect and incisor growth. The baseline symmetry proven here sets the stage to study the degree to which hemi-mandible destabilizing procedures result in measurable & reproducible disruption of dental asymmetry. In a validated model, an implant designed to function under load that prevents incisor asymmetry would provide supporting evidence that the implant has clinically useful load-bearing function.

Advances of nanomaterial applications in oral and maxillofacial tissue regeneration and disease treatment

Using bioactive nanomaterials in clinical treatment has been widely aroused. Nanomaterials provide substantial improvements in the prevention and treatment of oral and maxillofacial diseases. This review aims to discuss new progresses in nanomaterials applied to oral and maxillofacial tissue regeneration and disease treatment, focusing on the use of nanomaterials in improving the quality of oral and maxillofacial healthcare, and discuss the perspectives of research in this arena. Details are provided on the tissue regeneration, wound healing, angiogenesis, remineralization, antitumor, and antibacterial regulation properties of nanomaterials including polymers, micelles, dendrimers, liposomes, nanocapsules, nanoparticles and nanostructured scaffolds, etc. Clinical applications of nanomaterials as nanocomposites, dental implants, mouthwashes, biomimetic dental materials, and factors that may interact with nanomaterials behaviors and bioactivities in oral cavity are addressed as well. In the last section, the clinical safety concerns of their usage as dental materials are updated, and the key knowledge gaps for future research with some recommendation are discussed. This article is categorized under: Implantable Materials and Surgical Technologies > Nanomaterials and Implants Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement.

In vivo evaluation of porous nanohydroxyapatite/polyamide 66 struts in a goat cervical fusion model

The hollow cylindrical nanohydroxyapatite/polyamide 66 strut (n-HA/PA66) has been used clinically for anterior cervical reconstruction. However, rates of occurrence of a “radiolucent gap” between the dense strut and adjacent endplates were reported. The aim of this in vivo study was to evaluate the viability and advantages of the novel porous n-HA/PA66 strut. The goat C3/4 partial discectomy and fusion model was built, and two groups of n-HA/PA66 struts were implanted into C3/4: group 1, porous n-HA/PA66 strut; and group 2, hollow cylindrical n-HA/PA66 strut filled with autogenous cancellous bone. CT evaluation was performed to assess the fusion status after 12 and 24 weeks. The cervical spines were harvested. Histomorphological analysis was performed to determine new bone formation. Biomechanical testing was performed to determine range of motion (ROM). CT confirmed the disappearance of the boundary of the porous strut and host bone, while the radiolucent gap remained clearly discernible in the dense strut group. The mean CT fusion scores of the porous group were significantly higher. Histologic evaluation showed that the porous struts promoted better osteointegration. Calcein fluorochrome labelling indicated faster bone ingrowth in the porous struts. Biomechanical tests revealed that the porous struts had significantly reduced micromotion. The porous n-HA/PA66 strut could offer interesting potential for cervical reconstruction after corpectomy.

Nanotechnology Scaffolds for Alveolar Bone Regeneration

In oral biology, tissue engineering aims at regenerating functional tissues through a series of key events that occur during alveolar/periodontal tissue formation and growth, by means of scaffolds that deliver signaling molecules and cells. Due to their excellent physicochemical properties and biomimetic features, nanomaterials are attractive alternatives offering many advantages for stimulating cell growth and promoting tissue regeneration through tissue engineering. The main aim of this article was to review the currently available literature to provide an overview of the different nano-scale scaffolds as key factors of tissue engineering for alveolar bone regeneration procedures. In this narrative review, PubMed, Medline, Scopus and Cochrane electronic databases were searched using key words like “tissue engineering”, “regenerative medicine”, “alveolar bone defects”, “alveolar bone regeneration”, “nanomaterials”, “scaffolds”, “nanospheres” and “nanofibrous scaffolds”. No limitation regarding language, publication date and study design was set. Hand-searching of the reference list of identified articles was also undertaken. The aim of this article was to give a brief introduction to review the role of different nanoscaffolds for bone regeneration and the main focus was set to underline their role for alveolar bone regeneration procedures.

Enhancement of Healing of Periodontal Intrabony Defects Using 810 nm Diode Laser and Different Advanced Treatment Modalities: A Blind Experimental Study

BACKGROUND

Low-level laser therapy (LLLT) in the early stage of bone healing was demonstrated as a positive local biostimulative effect. It was also shown that platelet-rich fibrin (PRF) and nanohydroxyapatite alloplast (NanoHA) are effective in treating periodontal intrabony defects.

AIM

The study aimed to evaluate the combined effects of LLLT (810 nm), PRF and NanoHA on induced intrabony periodontal defects healing.

MATERIAL AND METHODS

The study was conducted on 16 defects in 8 adult male rabbits (n = 16) divided into 4 groups; Control non-treated group (C), laser irradiated control group (CL), PRF+NanoHA graft (NanoHA-Graft+PRF) treated group and laser irradiated and treated group (NanoHA-Graft+PRF+L). CT radiography was made at baseline, 15 and 30 days later. The defects were induced in the form of one osseous wall defects of 10 mm height, 4 mm depth between the 1st and the 2nd molars using a tapered fissure drill coupled to a high-speed motor. Statistical analysis was done using ANOVA.

RESULTS

(NanoHA-Graft+PRF+L) group significantly produced bone density higher than C, CL and NanoHA-G+PRF alone.

CONCLUSION

The combination of LLLT+PRF+NanoHA as a treatment modality induced the best results in bone formation in the bone defect more than LLLT alone or PRF+NanoHA alone.

Are critical size bone notch defects possible in the rabbit mandible?

Objectives

Small animal maxillofacial models, such as non-segmental critical size defects (CSDs) in the rabbit mandible, need to be standardized for use as preclinical models of bone regeneration to mimic clinical conditions such as maxillofacial trauma. The objective of this study is the establishment of a mechanically competent CSD model in the rabbit mandible to allow standardized evaluation of bone regeneration therapies.

Materials and Methods

Three sizes of bony defect were generated in the mandibular body of rabbit hemi-mandibles: 12 mm×5 mm, 12 mm×8 mm, and 15 mm×10 mm. The hemi-mandibles were tested to failure in 3-point flexure. The 12 mm×5 mm defect was then chosen for the defect size created in the mandibles of 26 rabbits with or without cautery of the defect margins and bone regeneration was assessed after 6 and 12 weeks. Regenerated bone density and volume were evaluated using radiography, micro-computed tomography, and histology.

Results

Flexural strength of the 12 mm×5 mm defect was similar to its contralateral; whereas the 12 mm×8 mm and 15 mm×10 mm groups carried significantly less load than their respective contralaterals (P<0.05). This demonstrated that the 12 mm×5 mm defect did not significantly compromise mandibular mechanical integrity. Significantly less (P<0.05) bone was regenerated at 6 weeks in cauterized defect margins compared to controls without cautery. After 12 weeks, the bone volume of the group with cautery increased to that of the control without cautery after 6 weeks.

Conclusion

An empty defect size of 12 mm×5 mm in the rabbit mandibular model maintains sufficient mechanical stability to not require additional stabilization. However, this defect size allows for bone regeneration across the defect. Cautery of the defect only delays regeneration by 6 weeks suggesting that the performance of bone graft materials in mandibular defects of this size should be considered with caution.

Effect of expanded bone marrow-derived osteoprogenitor cells seeded into polycaprolactone/tricalcium phosphate scaffolds in new bone regeneration of rabbit mandibular defects

The purpose of this study was to assess and evaluate new bone formation in rabbit marginal mandibular defects using expanded bone marrow-derived osteoprogenitor cells seeded in three-dimensional scaffolds of polycaprolactone/tricalcium phosphate (PCL/TCP). Bone marrow was harvested from the rabbit ilium and rabbit bone marrow-derived osteoprogenitor cells were isolated and expanded in standard culture medium and osteogenic medium supplement. The cells were then seeded into the PCL/TCP scaffolds and the cell/scaffold constructions were implanted into prepared defects in rabbit mandibles. PCL/TCP scaffold alone and autogenous bone graft from the mandible were also implanted into the other prepared defects. The specimens were evaluated at 4 and 8 weeks after the implantation using clinical, radiographic, and histological techniques. The results of the experimental group demonstrated more newly formed bone on the surface and in the pores of the PCL/TCP scaffolds. In addition, the osteoblasts, osteocytes, and new bone trabeculae were identified throughout the defects that were implanted with the cell/scaffold constructions. The PCL/TCP alone group was filled mostly with fibrous cells particularly in the middle region with less bone formation. These results would suggest that the derived osteotoprogenitor cells have the potential to form bone tissue when seeded onto PCL/TCP scaffolds.

Custom Repair of Mandibular Bone Defects with 3D Printed Bioceramic Scaffolds

Implanting artificial biomaterial implants into alveolar bone defects with individual shape and appropriate mechanical strength is still a challenge. In this study, bioceramic scaffolds, which can precisely match the mandibular defects in macro and micro, were manufactured by the 3-dimensional (3D) printing technique according to the computed tomography (CT) image. To evaluate the stimulatory effect of the material substrate on bone tissue regeneration in situ in a rabbit mandibular alveolar bone defect model, implants made with the newly developed, mechanically strong ~10% Mg-substituted wollastonite (Ca_90%Mg_10%SiO₃; CSi-Mg10) were fabricated, implanted into the bone defects, and compared with implants made with the typical Ca-phosphate and Ca-silicate porous bioceramics, such as β-tricalcium phosphate (TCP), wollastonite (CaSiO₃; CSi), and bredigite (Bred). The initial physicochemical tests indicated that although the CSi-Mg10 scaffolds had the largest pore dimension, they had the lowest porosity mainly due to the significant linear shrinkage of the scaffolds during sintering. Compared with the sparingly dissolvable TCP scaffolds (~2% weight loss) and superfast dissolvable (in Tris buffer within 6 wk) pure CSi and Bred scaffolds (~12% and ~14% weight loss, respectively), the CSi-Mg10 exhibited a mild in vitro biodissolution and moderate weight loss of ~7%. In addition, the CSi-Mg10 scaffolds showed a considerable initial flexural strength (31 MPa) and maintained very high flexural resistance during soaking in Tris buffer. The in vivo results revealed that the CSi-Mg10 scaffolds have markedly higher osteogenic capability than those on the TCP, CSi, and Bred scaffolds after 16 wk. These results suggest a promising potential application of customized CSi-Mg10 3D robocast scaffolds in the clinic, especially for repair of alveolar bone defects.

Three-dimensionally printed polyetherketoneketone scaffolds with mesenchymal stem cells for the reconstruction of critical-sized mandibular defects

OBJECTIVE

Additive manufacturing offers a tailored approach to tissue engineering by providing anatomically precise scaffolds onto which stem cells and growth factors can be supplied. Polyetherketoneketone (PEKK), an ideal candidate biomaterial, is limited by a poor implant-bone interface but can be functionalized with adipose-derived stem cells (ADSC) to promote integration. This in vivo study examined the interaction of a three-dimensional printed PEKK/ADSC implant within the critical-sized mandibular defect in a rabbit model.

STUDY DESIGN/METHODS

Trapezoidal porous scaffolds with dimensions of 1.5 × 1.0 × 0.5 cm were printed using selective laser sintering. ADSCs were seeded on the scaffolds that were then implanted in marginal defects created in New Zealand rabbits. Rabbits were euthanized at 10- and 20-week intervals. Microcomputed tomography was used to characterize bone ingrowth and was correlated with histological analysis. Stress testing was performed on the scaffolds before and after implantation.

RESULTS

All scaffolds were well integrated into adjacent bone. Bone-to-tissue volume increased from 30.34% ( ± 12.46) to 61.27% ( ± 8.24), and trabecular thickness increased from 0.178 mm ( ± 0.069) to 0.331 mm ( ± 0.0306) in the 10- and 20-week groups, respectively, compared to no bone regrowth on the control side (P < 0.05). Histology confirmed integration at the bone-implant interface. Biomechanical testing revealed a compressive resistance 15 times that of bone alone (P < 0.05) CONCLUSION: 3D-printed PEKK scaffolds combined with ADSCs present a promising solution to improve the bone-implant interface and increase the resistance to forces of mastication after mandibular reconstruction.

LEVEL OF EVIDENCE

NA. Laryngoscope, 127:E392-E398, 2017.

Establishing a critical-size mandibular defect model in growing pigs: characterization of spontaneous healing

PURPOSE

A large animal model is desired for preclinical studies aimed at reconstructing severe mandibular skeletal defects using tissue engineering techniques. To identify the size and location requirements for a mandibular critical-size bone defect in growing pigs, the present study investigated the spontaneous healing of surgically created mandibular defects.

MATERIALS AND METHODS

Six 4-month-old domestic pigs were used. In pigs 1 and 2, a 3-, 5-, or 7-cm(3) subperiosteal mandibular defect was created. In pigs 3 to 6, 3- to 5-cm(3) bilateral defects were randomly created at the anterior (apical to the molars) and posterior (mandibular angle) mandibular regions. Spontaneous healing of these defects was assessed by serial computed tomography scans (postoperative week 1, 6, and 12) and histologic analyses.

RESULTS

In pigs 1 and 2, regardless of defect size, the anterior, but not posterior, defects had largely healed. Systematic analyses of pigs 3 to 6 revealed, first, the extent of defect regeneration from spontaneous healing was significantly less in the posterior than in the anterior defects, with about two thirds and one third of the original defect volume remaining, respectively. Second, histologically, the posterior defects had considerably less regeneration and more evident tapering of the new bone than did the anterior defects. Finally, the buccal periosteum had completely regenerated in the anterior defects, but had only partially done so in the posterior defects. Also, the buccal surface contour was moderately concave in the anterior defects, but it was severely concave in the posterior defects.

CONCLUSIONS

Despite robust spontaneous healing of mandibular defects in growing pigs, 5-cm(3) defects in the mandibular angle region without buccal periosteum would be a reasonable critical-size defect model relevant to mandibular defects in adolescent humans.

Delivery of growth factors using a smart porous nanocomposite scaffold to repair a mandibular bone defect

Implantation of a porous scaffold with a large volume into the body in a convenient and safe manner is still a challenging task in the repair of bone defects. In this study, we present a porous smart nanocomposite scaffold with a combination of shape memory function and controlled delivery of growth factors. The shape memory function enables the scaffold with a large volume to be deformed into its temporal architecture with a small volume using hot-compression and can subsequently recover its original shape upon exposure to body temperature after it is implanted in the body. The scaffold consists of chemically cross-linked poly(ε-caprolactone) (c-PCL) and hydroxyapatite nanoparticles. The highly interconnected pores of the scaffold were obtained using the sugar leaching method. The shape memory porous scaffold loaded with bone morphogenetic protein-2 (BMP-2) was also fabricated by coating the calcium alginate layer and BMP-2 on the surface of the pore wall. Under both in vitro and in vivo environmental conditions, the porous scaffold displays good shape memory recovery from the compressed shape with deformed pores of 33 μm in diameter to recover its porous shape with original pores of 160 μm in diameter. In vitro cytotoxicity based on the MTT test revealed that the scaffold exhibited good cytocompatibility. The in vivo micro-CT and histomorphometry results demonstrated that the porous scaffold could promote new bone generation in the rabbit mandibular bone defect. Thus, our results indicated that this shape memory porous scaffold demonstrated great potential for application in bone regenerative medicine.

Safety and Efficiency of Biomimetic Nanohydroxyapatite/Polyamide 66 Composite in Rabbits and Primary Use in Anterior Cervical Discectomy and Fusion

This study was conducted to validate the safety and efficiency of biomimetic nanohydroxyapatite/polyamide 66 (n-HA/PA66) composite in animal model (rabbit) and report its application in anterior cervical discectomy and fusion (ACDF) for 4, 12, and 24 weeks. N-HA/PA66 composite was implanted into one-side hind femur defects and the control defects were kept empty as blank controls. A combination of macroscopic and histomorphometric studies was performed up to 24 weeks postoperatively and compared with normal healing. 60 cervical spondylosis myelopathy and radiculopathy patients who were subjected to ACDF using n-HA/PA66 and PEEK cage were involved in this study with six-month minimum follow-up. Their radiographic (cage subsidence, fusion status, and segmental sagittal alignment (SSA)) and clinical (VAS and JOA scales) data before surgery and at each follow-up were recorded and compared. Nanohydroxyapatite/polyamide 66 composite is safe and effective in animal experiment and ACDF.

Recent developments of functional scaffolds for craniomaxillofacial bone tissue engineering applications

Autogenous bone grafting remains a gold standard for the reconstruction critical-sized bone defects in the craniomaxillofacial region. Nevertheless, this graft procedure has several disadvantages such as restricted availability, donor-site morbidity, and limitations in regard to fully restoring the complicated three-dimensional structures in the craniomaxillofacial bone. The ultimate goal of craniomaxillofacial bone reconstruction is the regeneration of the physiological bone that simultaneously fulfills both morphological and functional restorations. Developments of tissue engineering in the last two decades have brought such a goal closer to reality. In bone tissue engineering, the scaffolds are fundamental, elemental and mesenchymal stem cells/osteoprogenitor cells and bioactive factors. A variety of scaffolds have been developed and used as spacemakers, biodegradable bone substitutes for transplanting to the new bone, matrices of drug delivery system, or supporting structures enhancing adhesion, proliferation, and matrix production of seeded cells according to the circumstances of the bone defects. However, scaffolds to be clinically completely satisfied have not been developed yet. Development of more functional scaffolds is required to be applied widely to cranio-maxillofacial bone defects. This paper reviews recent trends of scaffolds for crania-maxillofacial bone tissue engineering, including our studies.

Dual delivery of BMP-2 and bFGF from a new nano-composite scaffold, loaded with vascular stents for large-size mandibular defect regeneration

The aim of this study was to investigate the feasibility and advantages of the dual delivery of bone morphogenetic protein-2 (BMP-2) and basic fibroblast growth factor (bFGF) from nano-composite scaffolds (PLGA/PCL/nHA) loaded with vascular stents (PLCL/Col/nHA) for large bone defect regeneration in rabbit mandibles. Thirty-six large bone defects were repaired in rabbits using engineering bone composed of allogeneic bone marrow mesenchymal stem cells (BMSCs), bFGF, BMP-2 and scaffolds composed of PLGA/PCL/nHA loaded with PLCL/Col/nHA. The experiments were divided into six groups: BMSCs/bFGF/BMP-2/scaffold, BMSCs/BMP-2/scaffold, BMSCs/bFGF/scaffold, BMSCs/scaffold, scaffold alone and no treatment. Sodium alginate hydrogel was used as the carrier for BMP-2 and bFGF and its features, including gelling, degradation and controlled release properties, was detected by the determination of gelation and degradation time coupled with a controlled release study of bovine serum albumin (BSA). AlamarBlue assay and alkaline phosphatase (ALP) activity were used to evaluate the proliferation and osteogenic differentiation of BMSCs in different groups. X-ray and histological examinations of the samples were performed after 4 and 12 weeks post-implantation to clarify new bone formation in the mandible defects. The results verified that the use of sodium alginate hydrogel as a controlled release carrier has good sustained release ability, and the combined application of bFGF and BMP-2 could significantly promote the proliferation and osteogenic differentiation of BMSCs (p < 0.05 or p < 0.01). In addition, X-ray and histological examinations of the samples exhibited that the dual release group had significantly higher bone formation than the other groups. The above results indicate that the delivery of both growth factors could enhance new bone formation and vascularization compared with delivery of BMP-2 or bFGF alone, and may supply a promising way of repairing large bone defects in bone tissue engineering.

Calcium orthophosphates in dentistry

Dental caries, also known as tooth decay or a cavity, remains a major public health problem in the most communities even though the prevalence of disease has decreased since the introduction of fluorides for dental care. Therefore, biomaterials to fill dental defects appear to be necessary to fulfill customers' needs regarding the properties and the processing of the products. Bioceramics and glass-ceramics are widely used for these purposes, as dental inlays, onlays, veneers, crowns or bridges. Calcium orthophosphates belong to bioceramics but they have some specific advantages over other types of bioceramics due to a chemical similarity to the inorganic part of both human and mammalian bones and teeth. Therefore, calcium orthophosphates (both alone and as components of various formulations) are used in dentistry as both dental fillers and implantable scaffolds. This review provides brief information on calcium orthophosphates and describes in details current state-of-the-art on their applications in dentistry and dentistry-related fields. Among the recognized dental specialties, calcium orthophosphates are most frequently used in periodontics; however, the majority of the publications on calcium orthophosphates in dentistry are devoted to unspecified "dental" fields.

Various preparation methods of highly porous hydroxyapatite/polymer nanoscale biocomposites for bone regeneration

Tissue engineering utilizes expertise in the fields of materials science, biology, chemistry, transplantation medicine, and engineering to design materials that can temporarily serve in a structural and/or functional capacity during regeneration of a defect. Hydroxyapatite (HAp) scaffolds are among the most extensively studied materials for this application. However, HAp has been reported to be too weak to treat such defects and, therefore, has been limited to non-load-bearing applications. To capitalize the advantages of HAp and at the same time overcome the drawbacks nanocrystalline HAp (nHAp) is combined with various types of bioactive polymers to generate highly porous biocomposite materials that are used for osteoconduction in the field of orthopedic surgery. In this study we have reviewed nanosized HAp-based highly porous composite materials used for bone tissue engineering, introduced various fabrication methods to prepare nHAp/polymer composite scaffolds, and characterized these scaffolds on the basis of their biodegradability and biocompatibility through in vitro and in vivo tests. Finally, we provide a summary and our own perspectives on this active area of research.

Effects of an antibacterial membrane on osteoblast-like cells in vitro

Infection around membranes is often found in guided bone regeneration (GBR). The excellent antibacterial properties of Ag-nHA-nTiO₂/polyamide-66 (PA66) nanocomposite membranes have been demonstrated previously. The aim of this study was to observe the microstructure of an Ag-nHA-nTiO₂/PA66 membrane and its effects on osteoblast-like cells in vitro. An Ag-nHA-nTiO₂/PA66 membrane was used in the experimental group, and both nHA/PA66 and expanded poly tetrafluroethylene (e-PTFE) membranes were set as control. MG63 osteoblast-like cells were cultured on the three kinds of membrane and tissue culture polystyrene (TCP). The microstructure of the above membranes and the cells adhered on them were detected by scanning electronic microscope (SEM). Cell proliferation was determined by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, cell viability with a cell viability analyzer, and alkaline phosphatase (ALP) activity and Ca²⁺ concentration of osteoblast-like cell matrix by enzyme-linked immunosorbent assay. SEM showed that both Ag-nHA-nTiO₂/PA66 membranes and nHA/PA66 membranes were composed of porous obverse face and smooth opposite face. The e-PTFE membranes showed elliptic surface structure with many tiny lined cracks. The MG63 cells adhered and proliferated well on all three kinds of membranes. Though cell viability on Ag-nHA-nTiO₂/PA66 membranes was significantly lower than that of the control groups (P < 0.05), MTT values, ALP activity, and Ca²⁺ concentration did not differ significantly among the three kinds of membranes (P > 0.05). From these findings, it can be concluded that Ag-nHA-nTiO₂/PA66 membranes are as biocompatible as nHA/ PA66 membranes and TCP, thus may be applied safely in GBR.

Stem cell-biomaterial interactions for regenerative medicine

The synergism of stem cell biology and biomaterial technology promises to have a profound impact on stem-cell-based clinical applications for tissue regeneration. Biomaterials development is rapidly advancing to display properties that, in a precise and physiological fashion, could drive stem-cell fate both in vitro and in vivo. Thus, the design of novel materials is trying to recapitulate the molecular events involved in the production, clearance and interaction of molecules within tissue in pathologic conditions and regeneration of tissue/organs. In this review we will report on the challenges behind translating stem cell biology and biomaterial innovations into novel clinical therapeutic applications for tissue and organ replacements (graphical abstract).

Nano-hydroxyapatite/chitosan sponge-like biocomposite for repairing of rat calvarial critical-sized bone defect

A three-dimensional porous nano-hydroxyapatite (nHA)/chitosan (CS) biocomposite was synthesized. The rod-like nHA grains of 15—30 × 5—10 nm in size were observed by TEM and confirmed by characteristic XRD patterns. The diameters of the interconnecting pores of the nHA/CS biocomposite, determined by SEM, were 120—300 μm. Standard critical-sized calvarial bone defect ( = 6.5 mm) was created in Sprague-Dawley (SD) rats. In group 1, nHA/CS was implanted and in group 2, no implant was made in the defect. After 1 week, the histological assessment of group 1 clearly showed that a large number of living cells were anchored in the pores of the nHA/CS implants. New bone formation, both at the edge and in the center of implants, was found as early as 2 weeks. Histological assays confirmed that the newly formed bone tissue was bioactive and neovascularized. After 5 weeks, the mineral content and volume of the newly formed bone tissue in the defects were significantly greater in group 1 than in group 2 (p < 0.01). These results indicate that implantation of the nHA/CS enhanced the repair of bone defect and confirm the potential of this biocomposite as a bioactive bone grafting substitute.