In vivo experimental study on bone regeneration in critical bone defects using an injectable biodegradable PLA/PGA copolymer

Clinical Treatment Progress for Large Metacarpal and Phalangeal Bone Defects

Large metacarpal and phalangeal bone defects are a hot topic for orthopedic surgeons due to its high clinical incidence, disability rate, and postsurgical amputation rate, along with its difficult treatment, long treatment course, high cost, and poor effect, all of which have a negative impact on the appearance and function of the patient's hands. There are currently a variety of treatment options for large metacarpal and phalangeal bone defects, each with its own benefits and drawbacks. However, there is no treatment method capable of perfectly resolving all the problems of patients with these defects. In this paper, the authors introduce several common plans for and progress of large metacarpal and phalangeal bone defect treatment.

Engineering Innervated Musculoskeletal Tissues for Regenerative Orthopedics and Disease Modeling

Musculoskeletal (MSK) disorders significantly burden patients and society, resulting in high healthcare costs and productivity loss. These disorders are the leading cause of physical disability, and their prevalence is expected to increase as sedentary lifestyles become common and the global population of the elderly increases. Proper innervation is critical to maintaining MSK function, and nerve damage or dysfunction underlies various MSK disorders, underscoring the potential of restoring nerve function in MSK disorder treatment. However, most MSK tissue engineering strategies have overlooked the significance of innervation. This review first expounds upon innervation in the MSK system and its importance in maintaining MSK homeostasis and functions. This will be followed by strategies for engineering MSK tissues that induce post-implantation in situ innervation or are pre-innervated. Subsequently, research progress in modeling MSK disorders using innervated MSK organoids and organs-on-chips (OoCs) is analyzed. Finally, the future development of engineering innervated MSK tissues to treat MSK disorders and recapitulate disease mechanisms is discussed. This review provides valuable insights into the underlying principles, engineering methods, and applications of innervated MSK tissues, paving the way for the development of targeted, efficacious therapies for various MSK conditions.

Silicone rubber sealed channel induced self-healing of large bone defects: Where is the limit of self-healing of bone?

Background

Large defects of long tubular bones due to severe trauma, bone tumor resection, or osteomyelitis debridement are challenging in orthopedics. Bone non-union and other complications often lead to serious consequences. At present, autologous bone graft is still the gold standard for the treatment of large bone defects. However, autologous bone graft sources are limited. Silicon rubber (SR) materials are widely used in biomedical fields, due to their safety and biocompatibility, and even shown to induce nerve regeneration.

Materials and methods

We extracted rat bone marrow mesenchymal stem cells (BMMSCs) in vitro and verified the biocompatibility of silicone rubber through cell experiments. Then we designed a rabbit radius critical sized bone defect model to verify the effect of silicone rubber sealed channel inducing bone repair in vivo.

Results

SR sealed channel could prevent the fibrous tissue from entering the fracture end and forming bone nonunion, thereby inducing self-healing of long tubular bone through endochondral osteogenesis. The hematoma tissue formed in the early stage was rich in osteogenesis and angiogenesis related proteins, and gradually turned into vascularization and endochondral osteogenesis, and finally realized bone regeneration.

Conclusions

In summary, our study proved that SR sealed channel could prevent the fibrous tissue from entering the fracture end and induce self-healing of long tubular bone through endochondral osteogenesis. In this process, the sealed environment provided by the SR channel was key, and this might indicate that the limit of self-healing of bone exceeded the previously thought.

The translational potential of this article

This study investigated a new concept to induce the self-healing of large bone defects. It could avoid trauma caused by autologous bone extraction and possible rejection reactions caused by bone graft materials. Further research based on this study, including the innovation of induction materials, might invent a new type of bone inducing production, which could bring convenience to patients. We believed that this study had significant meaning for the treatment of large bone defects in clinical practice.

Efficient drug supply in stem cell cytosol via pore-forming saponin nanoparticles promotes in vivo osteogenesis and bone regeneration

Directional differentiation of stem cells is a key step in stem cell therapy. In this study, we developed saponin-based nanoparticles (Ad-SNPs) containing dexamethasone (Dex) and alpha-lipoic acid (ALA) to promote osteogenic differentiation of human mesenchymal stem cells (hMSCs) and bone regeneration. The Ad-SNPs can achieve rapid cellular uptake through a pore-forming effect without cytotoxic cationic charges. They also provide extended retention in cell cytosol due to their uptake route. These properties are advantageous in efficiently supplying drugs to the hMSCs. The combination of Dex and ALA facilitated mitochondrial fusion and prevented reactive oxygen species-induced DNA damage. It also helped to preserve mitochondrial dynamics, and the efficient supply of it provided by the Ad-SNPs induced differentiation of hMSCs into osteoblasts. The Ad-SNPs showed outstanding performance in osteoblast differentiation, maturation, and mineralization in 3D culture compared with NPs without saponin and with free drugs. When Ad-SNP-treated hMSCs were tested in a rat femoral bone defect model, they showed the fastest regeneration of bones and complete repair in the shortest period among all groups. To the best of our knowledge, this study is the first application of pore-forming saponin-based NPs with rapid cellular uptake and extended retention to stem cell therapy, and we demonstrated their promising potential in bone regeneration and efficient delivery of Dex and ALA.

A better roadmap for designing novel bioactive glasses: effective approaches for the development of innovative revolutionary bioglasses for future biomedical applications

The introduction of bioactive glasses (BGs) precipitated a paradigm shift in the medical industry and opened the path for the development of contemporary regenerative medicine driven by biomaterials. This composition can bond to live bone and can induce osteogenesis by the release of physiologically active ions. 45S5 BG products have been transplanted effectively into millions of patients around the world, primarily to repair bone and dental defects. Over the years, many other BG compositions have been introduced as innovative biomaterials for repairing soft tissue and delivering drugs. When research first started, many of the accomplishments that have been made today were unimaginable. It appears that the true capacity of BGs has not yet been realized. Because of this, research involving BGs is extremely fascinating. However, to be successful, it requires interdisciplinary cooperation between physicians, glass chemists, and bioengineers. The present paper gives a picture of the existing clinical uses of BGs and illustrates key difficulties deserving to be faced in the future. The challenges range from the potential for BGs to be used in a wide variety of applications. We have high hopes that this paper will be of use to both novice researchers, who are just beginning their journey into the world of BGs, as well as seasoned scientists, in that it will promote conversation regarding potential additional investigation and lead to the discovery of innovative medical applications for BGs.

Advantages of agarose on alginate for the preparation of polysaccharide/hydroxyapatite porous bone scaffolds compatible with a proline-rich antimicrobial peptide

The optimized proline-rich antimicrobial peptide B7-005 was loaded on bone scaffolds based on polysaccharides and hydroxyapatite. Alginate was firstly chosen in order to exploit its negative charges, which allowed an efficient B7-005 loading but hindered its release, due to the strong interactions with the positive charged peptide. Hence, alginate was substituted with agarose which allowed to prepare scaffolds with similar structure, porosity, and mechanical performance than the ones prepared with alginate and hydroxyapatite. Moreover, agarose scaffolds could release B7-005 within the first 24 h of immersion in aqueous environment. The peptide did not impaired MG-63 cell adhesion and proliferation in the scaffold, and a positive cell proliferation trend was observed up to two weeks. The released B7-005 was effective against the pathogensE. coli, K. pneumoniae, andA. baumannii, but not againstS. aureusandP. aeruginosa, thus requiring further tuning of the system to improve its antimicrobial activity.

Characterization of the Masquelet Induced Membrane Technique in a Murine Segmental Bone Defect Model

Objective  To reproduce in an animal model the surgical technique of Masquelet used in the treatment of critical bone defects and to analyze the characteristics of the membrane formed around the bone cement. Methods  A 10mm critical defect was created in the femoral shaft of 21 Sprague-Dawley rats. After resection of the central portion of the diaphysis, the defect was stabilized with a Kirschner wire introduced through the medullary canal and with the interposition of a bone cement spacer. After 2, 4, and 6 weeks of the surgical procedure, the animals were euthanized and evaluated on radiographs of the posterior limb regarding the size of the defect, alignment and stability of the osteosynthesis. The membranes formed around the spacer were subjected to histological analysis to assess thickness, connective tissue maturation and vascular density. Results  Over time, the membranes initially made up of loose connective tissue were replaced by membranes represented by dense connective tissue, rich in thick collagen fibers. At six weeks, membrane thickness was greater (565 ± 208μm) than at four (186.9 ± 70.21μm, p = 0.0002) and two weeks (252.2 ± 55.1μm, p = 0.001). All membranes from the initial time showed foci of osteogenic differentiation that progressively reduced over time. Conclusion  In addition to the structural and protective function of the membrane, its intrinsic biological characteristics can actively contribute to bone regeneration. The biological activity attributed by the presence of foci of osteogenesis confers to the membrane the potential of osteoinduction that favors the local conditions for the integration of the bone graft.

Scaphoid Bone Nonunions: Clinical and Functional Outcomes of Collagen/PGA Scaffolds and Cell-Based Therapy

In this study, the procedure for treating the nonunion complication of scaphoid fractures using collagen/poly glycolic acid (CPGA) scaffolds with bone marrow mesenchymal stem cell (BM-MSC) therapy was adopted and compared with the commonly employed autologous bone tissue graft. With conducting a two-armed clinical trial, 10 patients with scaphoid nonunions were enrolled in this investigation. Patients were randomly assigned to two groups treated with (1) CPGA + cell therapy and (2) autologous iliac crest bone graft standard therapy. Treatment outcomes were evaluated three months after surgery, measuring the grip and pinch strengths and wrist range of motion, with two questionnaires: Patient-Rated Wrist Evaluation (PRWE) and Quick form of Disabilities of the Arm, Shoulder, and Hand (QDASH). We have also assessed the union rate using clinical and radiologic healing criteria one and three months post-operatively. Restorative effects of CPGA + cell therapy were similar to those of the autologous bone graft standard therapy, except for the grip strength (P = 0.048) and QDASH score (P = 0.044) changes, which were higher in the CPGA + cell therapy group. Three months following the surgery, radiographic images and computed tomography (CT) scans also demonstrated that the scaphoid union rate in the test group was comparable to that of scaphoids treated with the standard autograft method. Our findings demonstrate that the CPGA + cell therapy is a potential alternative for bone grafting in the treatment of bone nonunions.

Total flavonoids of rhizoma drynariae ameliorates bone formation and mineralization in BMP-Smad signaling pathway induced large tibial defect rats

Osteogenesis and angiogenesis acts as an essential role in repairing large tibial defects (LTDs). Total flavonoids of rhizoma drynariae (TFRD), a traditional Chinese medicinal herb, is reported to show anabolic effects on fracture healing. However, whether TFRD could improve the bone formation and angiogenesis in LTDs remains unknown. The purpose of this study was to evaluate the effect of TFRD on bone formation and angiogenesis in LTDs in distraction osteogenesis (DO). Using a previously established fracture model, LTD rats was established with circular external fixator (CEF). All rats then randomly divided into TFRD low dosage group (with DO), TFRD medium dosage group (with DO), TFRD high dosage group (with DO), model group (with DO) and blank group (without DO). Twelve weeks after treatment, according to X-ray and Micro-CT, TFRD groups (especially in medium dosage group) can significantly promote the formation of a large number of epiphyses and improve new bone mineralization compared with model group, and the results of HE and Masson staining and in vitro ALP level of BMSC also demonstrated the formation of bone matrix and mineralization in the TFRD groups. Also, angiographic imaging suggested that total flavonoids of TFRD was able to promote angiogenesis in the defect area. Consistently, TFRD significantly increased the levels of BMP-2, SMAD1, SMAD4, RUNX-2, OSX and VEGF in LTD rats based on ELISA and Real-Time PCR. In addition, we found that ALP activity of TFRD medium dosage group reached a peak after 10 days of induction through BMSC cell culture in vitro experiment. TFRD promoted bone formation in LTD through activation of BMP-Smad signaling pathway, which provides a promising new strategy for repairing bone defects in DO surgeries.

Vascular Supply and Bone Marrow Concentrate for the Improvement of Allograft in Bone Defects: A Comparative In Vivo Study

BACKGROUND

Surgical repair of critical-sized bone defects still remains a big challenge in orthopedic surgery. Biological enhancement, such as growth factors or cells, can stimulate a better outcome in bone regeneration driven by well-established treatments such as allogenic bone graft. However, despite the surgical options available, correct healing can be slowed down or compromised by insufficient vascular supply to the injured site.

MATERIALS AND METHODS

In this pilot study, critical size bone defects in rabbit radius were treated with allograft bone, in combination with vascular bundle and autologous bone marrow concentrate seeded onto a commercial collagen scaffold. Microtomographical, histological and immunohistochemical assessments were performed to evaluate allograft integration and bone regeneration.

RESULTS

Results showed that the surgical deviation of vascular bundle in the bone graft, regardless from the addition of bone marrow concentrate, promote the onset of healing process at short experimental times (8 wk) in comparison with the other groups, enhancing graft integration.

CONCLUSION

The surgical procedure tested stimulates bone healing at early times, preserving native bone architecture, and can be easily combined with biological adjuvant.

The Masquelet technique: Current concepts, animal models, and perspectives

Bone reconstruction within a critical-sized defect remains a real challenge in orthopedic surgery. The Masquelet technique is an innovative, two-step therapeutic approach for bone reconstruction in which the placement of a poly (methylmethacrylate) spacer into the bone defect induces the neo-formation of a tissue called "induced membrane." This surgical technique has many advantages and is often preferred to a vascularized bone flap or Ilizarov's technique. Although the Masquelet technique has achieved high clinical success rates since its development by Alain-Charles Masquelet in the early 2000s, very little is known about how the process works, and few animal models of membrane induction have been developed. Our successful use of this technique in the clinic and our interest in the mechanisms of tissue regeneration (notably bone regeneration) prompted us to develop a surgical model of the Masquelet technique in rats. Here, we provide a comprehensive review of the literature on animal models of membrane induction, encompassing the defect site, the surgical procedure, and the histologic and osteogenic properties of the induced membrane. We also discuss the advantages and disadvantages of those models to facilitate efforts in characterizing the complex biological mechanisms that underlie membrane induction.

Enzymatic degradation of hyaluronan hydrogels with different capacity for in situ bio-mineralization

In situ cross-linked hyaluronan (HA) hydrogels with different capacities for biomineralization were prepared and their enzymatic degradation was monitored. Covalent incorporation of bisphosphonates (BPs) into HA hydrogel results in the increased stiffness of the hydrogel in comparison with the unmodified HA hydrogel of the same cross-linking density. The rate of enzymatic degradation of HABP hydrogel was significantly lower than the rate of degradation of control HA hydrogel in vitro. This effect is observed only in the presence of calcium ions that strongly bind to the matrix-anchored BP groups and promote further mineralization of the matrix. The degradation of the hydrogels was followed by noninvasive fluorescence measurements enabled after mild and chemoselective labeling of cross-linkable HA derivatives with a fluorescent tag.

Tuning of the surface biological behavior of poly(L-lactide)-based composites by the incorporation of polyelectrolyte complexes for bone regeneration

Poly(L-lactide)(PLLA)-based composites have been widely used for tissue regeneration. Novel polyelectrolyte complexes (PECs) consisted of carboxymethyl starch sodium (CMS) and chitosan oligosaccharide (COS) was fabricated and evaluated. The results suggested that the CMS/COS-PECs (CC-PECs) distinguished from the original polymers alone, presenting an amorphous structure. Then, the CC-PECs/PLLA composites were prepared by varying the relative amount of CC-PECs in the PLLA-matrix, demonstrated by means of the surface morphology, hydrophilicity, water uptake, in vitro degradability and primary cell responses. The results suggested that the CC-PECs physically attached on the PLLA surface enhanced the formation of the surface seepage network, which could target modification of the surface biological behavior of the materials. The phenomena had been evidenced by the performed tests in respect to hydrophilicity, water uptake and degradation in PBS, which also may provide effective support for cell adhesion and proliferation. Further, the CC-PECs/PLLA surfaces clearly promoted the adhesion and proliferation of MC3T3-E1 cells compared with PLLA materials, indicating excellent cytocompatibility. This study suggested that the CC-PECs/PLLA-50 composite with excellent biological behavior could be a promising candidate for bone repair.

Evaluation of Spontaneous Bone Regeneration after Enucleation of Large Cysts of the Jaws using Radiographic Computed Software

Introduction

Spontaneous regeneration of bone is commonly seen in the small surgical defects caused by enucleation of cysts. However, in case of large surgical defects caused by the enucleation, spontaneous regeneration of bone is a rare phenomenon and it depends on factors, such as age of the patient, intact periosteum, and proper stabilization.

Materials and methods

The study included 16 patients, who reported to the department of oral and maxillofacial surgery with the complaint of pain and swelling in the jaws diagnosed as cyst. The sample included equal numbers of male and female subjects aged between 15 and 40 years. Panoramic radiographs were taken pre- and postoperatively on day 2 of the enucleation.

The dimensions of the cyst were evaluated on the radiograph according to the proforma.

Subsequent radiographs were taken at regular intervals of 1.5, 3, and 6 months using standard parameters and were analyzed using MCID™ analysis software of imaging research.

Results

Mean reduction was seen in up to 39 and 60% in the cystic cavity size and increase in the mean density up to 59 and 90.2% at 3 and 6 months intervals respectively.

Conclusion

Spontaneous bone regeneration was seen even after primary closure of the large cystic defect without the need for placement of foreign substances or grafts and it also eliminated the complications resulting from placement of foreign substance. Further studies are required in a larger sample with longer follow-up durations to confirm the outcome of the present work for the benefit of patients.

Clinical significance

The present study depicted that spontaneous bone regeneration can occur with accepted results after simple enucleation of jaw cyst without the aid of any graft material. Hence, simple enucleation may be considered as a first line of treatment modality for cystic lesion of the jaws. This simplifies the surgical procedure, decreases the economic and biologic costs, and reduces the risk of postoperative complications. Follow-up is necessary along with patient's compliance for the success of treatment.

How to cite this article

Wagdargi SS, Rai KK, Arunkumar KV, Katkol B, Arakeri G. Evaluation of Spontaneous Bone Regeneration after Enucleation of Large Cysts of the Jaws using Radiographic Computed Software. J Contemp Dent Pract 2016;17(6):489-495.

Animal Models for Evaluation of Bone Implants and Devices

Bone implants and devices are a rapidly growing field within biomedical research, and implants have the potential to significantly improve human and animal health. Animal models play a key role in initial product development and are important components of nonclinical data included in applications for regulatory approval. Pathologists are increasingly being asked to evaluate these models at the initial developmental and nonclinical biocompatibility testing stages, and it is important to understand the relative merits and deficiencies of various species when evaluating a new material or device. This article summarizes characteristics of the most commonly used species in studies of bone implant materials, including detailed information about the relevance of a particular model to human bone physiology and pathology. Species reviewed include mice, rats, rabbits, guinea pigs, dogs, sheep, goats, and nonhuman primates. Ultimately, a comprehensive understanding of the benefits and limitations of different model species will aid in rigorously evaluating a novel bone implant material or device.

The promotion of angiogenesis induced by three-dimensional porous beta-tricalcium phosphate scaffold with different interconnection sizes via activation of PI3K/Akt pathways

The porous architectural characteristics of biomaterials play an important role in scaffold revascularization. However, no consensus exists regarding optimal interconnection sizes for vascularization and its scaffold bioperformance with different interconnection sizes. Therefore, a series of disk-type beta-tricalcium phosphates with the same pore sizes and variable interconnections were produced to evaluate how the interconnection size influenced biomaterial vascularization in vitro and in vivo. We incubated human umbilical vein endothelial cells on scaffolds with interconnections of various sizes. Results showed that scaffolds with a 150 μm interconnection size ameliorated endothelial cell function evidenced by promoting cell adhesion and migration, increasing cell proliferation and enhancing expression of platelet-endothelial cell adhesion molecules and vascular endothelial growth factor. In vivo study was performed on rabbit implanted with scaffolds into the bone defect on femoral condyles. Implantation with scaffolds with 150 μm interconnection size significantly improved neovascularization as shown by micro-CT as compared to scaffolds with 100 and 120 μm interconnection sizes. Moreover, the aforementioned positive effects were abolished by blocking PI3K/Akt/eNOS pathway with LY-294002. Our study explicitly demonstrates that the scaffold with 150 μm interconnection size improves neovascularization via the PI3K/Akt pathway and provides a target for biomaterial inner structure modification to attain improved clinical performance in implant vascularization.

Use of perfusion bioreactors and large animal models for long bone tissue engineering

Tissue engineering and regenerative medicine (TERM) strategies for generation of new bone tissue includes the combined use of autologous or heterologous mesenchymal stem cells (MSC) and three-dimensional (3D) scaffold materials serving as structural support for the cells, that develop into tissue-like substitutes under appropriate in vitro culture conditions. This approach is very important due to the limitations and risks associated with autologous, as well as allogenic bone grafiting procedures currently used. However, the cultivation of osteoprogenitor cells in 3D scaffolds presents several challenges, such as the efficient transport of nutrient and oxygen and removal of waste products from the cells in the interior of the scaffold. In this context, perfusion bioreactor systems are key components for bone TERM, as many recent studies have shown that such systems can provide dynamic environments with enhanced diffusion of nutrients and therefore, perfusion can be used to generate grafts of clinically relevant sizes and shapes. Nevertheless, to determine whether a developed tissue-like substitute conforms to the requirements of biocompatibility, mechanical stability and safety, it must undergo rigorous testing both in vitro and in vivo. Results from in vitro studies can be difficult to extrapolate to the in vivo situation, and for this reason, the use of animal models is often an essential step in the testing of orthopedic implants before clinical use in humans. This review provides an overview of the concepts, advantages, and challenges associated with different types of perfusion bioreactor systems, particularly focusing on systems that may enable the generation of critical size tissue engineered constructs. Furthermore, this review discusses some of the most frequently used animal models, such as sheep and goats, to study the in vivo functionality of bone implant materials, in critical size defects.

Influence of biphasic β-TCP with and without the use of collagen membranes on bone healing of surgically critical size defects. A radiological, histological, and histomorphometric study

OBJECTIVES

The aim of this study was to investigate, by means of radiological and histomorphometric analysis, the effect of resorbable collagen membranes on critical size defects (CSD) in rabbit tibiae filled with biphasic calcium phosphate.

MATERIALS AND METHODS

Three CSD of 6 mm diameter were created in both tibiae of 20 New Zealand rabbits and divided into three groups according to the filling material: Group A (Ossceram), Group B (Ossceram plus Alveoprotect membrane), and Group C (unfilled control group). Five animals from each group were sacrificed after 15, 30, 45, and 60 days. Anteroposterior and lateral radiographs were taken. Samples were processed for observation under light microscopy.

RESULTS

At the end of treatment, radiological analysis found that cortical defect closure was greater in Group B than Group A, and radiopacity was clearly lower and more heterogeneous in the Group A cortical defects than in Group B. There was no cortical defect closure in Group C. Histomorphometric evaluation showed significant differences in newly formed bone and cortical closure in Group B compared with Groups A and C, with the presence of higher density newly formed bone in cortical and medullar zones. There was no cortical defect closure or medullar bone formation in Group C.

CONCLUSIONS

Biphasic calcium phosphate functioned well as a scaffolding material allowing mineralized tissue formation. Furthermore, the addiction of absorbable collagen membranes enhanced bone gain compared with non-membrane-treated sites.

Bioelectric modulation of wound healing in a 3D in vitro model of tissue-engineered bone

Long-standing interest in bioelectric regulation of bone fracture healing has primarily focused on exogenous stimulation of bone using applied electromagnetic fields. Endogenous electric signals, such as spatial gradients of resting potential among non-excitable cells in vivo, have also been shown to be important in cell proliferation, differentiation, migration, and tissue regeneration, and may therefore have as-yet unexplored therapeutic potential for regulating wound healing in bone tissue. To study this form of bioelectric regulation, there is a need for three-dimensional (3D) in vitro wound tissue models that can overcome limitations of current in vivo models. We present a 3D wound healing model in engineered bone tissue that serves as a pre-clinical experimental platform for studying electrophysiological regulation of wound healing. Using this system, we identified two electrophysiology-modulating compounds, glibenclamide and monensin, that augmented osteoblast mineralization. Of particular interest, these compounds displayed differential effects in the wound area compared to the surrounding tissue. Several hypotheses are proposed to account for these observations, including the existence of heterogeneous subpopulations of osteoblasts that respond differently to bioelectric signals, or the capacity of the wound-specific biochemical and biomechanical environment to alter cell responses to electrophysiological treatments. These data indicate that a comprehensive characterization of the cellular, biochemical, biomechanical, and bioelectrical components of in vitro wound models is needed to develop bioelectric strategies to control cell functions for improved bone regeneration.

Engineering a biocompatible scaffold with either micrometre or nanometre scale surface topography for promoting protein adsorption and cellular response

Surface topographical features on biomaterials, both at the submicrometre and nanometre scales, are known to influence the physicochemical interactions between biological processes involving proteins and cells. The nanometre-structured surface features tend to resemble the extracellular matrix, the natural environment in which cells live, communicate, and work together. It is believed that by engineering a well-defined nanometre scale surface topography, it should be possible to induce appropriate surface signals that can be used to manipulate cell function in a similar manner to the extracellular matrix. Therefore, there is a need to investigate, understand, and ultimately have the ability to produce tailor-made nanometre scale surface topographies with suitable surface chemistry to promote favourable biological interactions similar to those of the extracellular matrix. Recent advances in nanoscience and nanotechnology have produced many new nanomaterials and numerous manufacturing techniques that have the potential to significantly improve several fields such as biological sensing, cell culture technology, surgical implants, and medical devices. For these fields to progress, there is a definite need to develop a detailed understanding of the interaction between biological systems and fabricated surface structures at both the micrometre and nanometre scales.

Serum albumin enhances bone healing in a nonunion femoral defect model in rats: a computer tomography micromorphometry study

PURPOSE

Blood-derived proliferative factors such as platelet rich plasma or activated plasma are promising adjuvants for bone grafts. Our earlier studies showed that serum albumin itself can markedly enhance the proliferation of stem cells on bone allograft and postulated that albumin coating alone may improve bone graft integration in vivo.

METHODS

Two femoral defect models were performed in adult male Wistar rats. In the critical size model a six millimetre gap was created in the midshaft of the femur and fixed with plate and screws, while a nonunion model was established by the interposition of a spacer in the osteotomy for four weeks which resulted in compromised healing and nonunion. Albumin coated and uncoated grafts were placed into the defects. Bone healing and morphometry were evaluated by μCT and histology four weeks after implantation of the grafts.

RESULTS

In the critical size model none of the bone grafts were able to bridge the defect, and graft resorption was the typical outcome. In the nonunion model regular uncoated grafts had a low union rate (two out of six), which increased markedly when albumin coating was applied (six out of eight). Trabecular thickness and pattern factor improved significantly in the albumin coated group versus uncoated or empty controls.

CONCLUSIONS

Our results showed that serum albumin coating of bone grafts can enhance the remodelling and efficacy of treatment in a nonunion model.

New biocomposites based on bioplastic flax fibers and biodegradable polymers

A new generation of entirely biodegradable and bioactive composites with polylactic acid (PLA) or poly-ε-caprolactone (PCL) as the matrix and bioplastic flax fibers as reinforcement were analyzed. Bioplastic fibers contain polyhydroxybutyrate and were obtained from transgenic flax. Biochemical analysis of fibers revealed presence of several antioxidative compounds of hydrophilic (phenolics) and hydrophobic [cannabidiol (CBD), lutein] nature, indicating their high antioxidant potential. The presence of CBD and lutein in flax fibers is reported for the first time. FTIR analysis showed intermolecular hydrogen bonds between the constituents in composite PLA+flax fibers which were not detected in PCL-based composite. Mechanical analysis of prepared composites revealed improved stiffness and a decrease in tensile strength. The viability of human dermal fibroblasts on the surface of composites made of PLA and transgenic flax fibers was the same as for cells cultured without composites and only slightly lower (to 9%) for PCL-based composites. The amount of platelets and Escherichia coli cells aggregated on the surface of the PLA based composites was significantly lower than for pure polymer. Thus, composites made of PLA and transgenic flax fibers seem to have bacteriostatic, platelet anti-aggregated, and non-cytotoxic effect.

The effects of a novel-reinforced bone substitute and Colloss®E on bone defect healing in sheep

Hydroxyappatite-β-tricalciumphosphate (HA/β-TCP) was reinforced with poly(D,L)-lactic acid (PDLLA) to overcome its weak mechanical properties. Two substitutes with porosities of 77% and 81% HA/β-TCP reinforced with 12 wt % PDLLA were tested in compression. The effects of allograft, substitute (HA/β-TCP-PDLLA), Colloss®E, and combination of substitute with Colloss®E on bone formation in vivo were evaluated. Cylindrical critical size defects were created at distal femoral condyles bilaterally in sheep. Titanium implant with concentric gap filling with one of the four materials was inserted. After 9 weeks, the sheep were sacrificed. Implants with surrounding bone were harvested and sectioned into two parts: one for microcomputed tomography scanning and push-out test, and one for histomorphometry. The 77% HA/β-TCP reinforced with PDLLA had similar mechanical properties to human cancellous bone and was significantly stronger than the HA/β-TCP without PDLLA. Microarchitecture of gap mass was significantly changed after implantation for all groups. Allograft had stronger shear mechanical properties than the other three groups, whereas there were no significant differences between the other three groups. Significant new bone formation could be seen in vivo in all four groups and there were no significant differences between them. The PDLLA-reinforced substitute seems to be good alternative substitute material for bone healing in sheep. Further investigations should be performed to validate this novel substitute material.

The enhancement of bone regeneration by a combination of osteoconductivity and osteostimulation using β-CaSiO3/β-Ca3(PO4)2 composite bioceramics

β-Tricalcium phosphate (β-TCP) is osteoconductive, while β-calcium silicate (β-CS) is bioactive with osteostimulative properties. Porous β-CaSiO(3)/β-Ca(3)(PO(4))(2) composite bioceramic scaffolds with various β-TCP:β-CS ratios were designed to combine both osteoconductivity and osteostimulation in order to enhance bone regeneration. The composite scaffolds were implanted in critical sized femur defects (6×12 mm) for 4, 12 and 26weeks with pure β-TCP and β-CS scaffolds as the controls. The in vivo biodegradation and bone regeneration of the specimens were investigated using sequential histological evaluations, immunohistochemical examination and micro-computed tomography technology. The results showed that the scaffolds with 50 and 80 wt.% β-CS dramatically enhanced the amount of newly formed bone and reduced the degradation rate. In contrast, porous β-CS displayed poor new bone formation due to its rapid degradation, while porous β-TCP showed moderate bone regeneration starting on the surface of the implants, due to a lack of osteostimulation. More importantly, the scaffolds with 50 and 80 wt.% β-CS not only had excellent osteoconductivity, but also stimulated rapid bone formation, and they could degrade progressively at a rate matching the regeneration of new bone. In summary, our findings indicated that the degradation rate and bioactivity of β-CS/β-TCP composite bioceramic scaffolds could be adjusted by controlling the ratio of β-CS to β-TCP, suggesting the potential application of β-CS/β-TCP composite bioceramic scaffolds with 50 and 80 wt.% β-CS component in hard tissue regeneration and bone tissue engineering.

Significance of novel bioinorganic anodic aluminum oxide nanoscaffolds for promoting cellular response

Tissue engineering is a multidisciplinary field that can directly benefit from the many advancements in nanotechnology and nanoscience. This article reviews a novel biocompatible anodic aluminum oxide (AAO, alumina) membrane in terms of tissue engineering. Cells respond and interact with their natural environment, the extracellular matrix, and the landscape of the substrate. The interaction with the topographical features of the landscape occurs both in the micrometer and nanoscales. If all these parameters are favorable to the cell, the cell will respond in terms of adhesion, proliferation, and migration. The role of the substrate/scaffold is crucial in soliciting a favorable response from the cell. The size and type of surface feature can directly influence the response and behavior of the cell. In the case of using an AAO membrane, the surface features and porosity of the membrane can be dictated at the nanoscale during the manufacturing stage. This is achieved by using general laboratory equipment to perform a relatively straightforward electrochemical process. During this technique, changing the operational parameters of the process directly controls the nanoscale features produced. For example, the pore size, pore density, and, hence, density can be effectively controlled during the synthesis of the AAO membrane. In addition, being able to control the pore size and porosity of a biomaterial such as AAO significantly broadens its application in tissue engineering.

Establishment of a preclinical ovine model for tibial segmental bone defect repair by applying bone tissue engineering strategies

Currently, well-established clinical therapeutic approaches for bone reconstruction are restricted to the transplantation of autografts and allografts, and the implantation of metal devices or ceramic-based implants to assist bone regeneration. Bone grafts possess osteoconductive and osteoinductive properties; however, they are limited in access and availability and associated with donor-site morbidity, hemorrhage, risk of infection, insufficient transplant integration, graft devitalization, and subsequent resorption resulting in decreased mechanical stability. As a result, recent research focuses on the development of alternative therapeutic concepts. The field of tissue engineering has emerged as an important approach to bone regeneration. However, bench-to-bedside translations are still infrequent as the process toward approval by regulatory bodies is protracted and costly, requiring both comprehensive in vitro and in vivo studies. The subsequent gap between research and clinical translation, hence, commercialization, is referred to as the "Valley of Death" and describes a large number of projects and/or ventures that are ceased due to a lack of funding during the transition from product/technology development to regulatory approval and subsequently commercialization. One of the greatest difficulties in bridging the Valley of Death is to develop good manufacturing processes and scalable designs and to apply these in preclinical studies. In this article, we describe part of the rationale and road map of how our multidisciplinary research team has approached the first steps to translate orthopedic bone engineering from bench to bedside by establishing a preclinical ovine critical-sized tibial segmental bone defect model, and we discuss our preliminary data relating to this decisive step.

Bone regeneration potential of a soybean-based filler: experimental study in a rabbit cancellous bone defects

Autologous and allogenic bone grafts are considered as materials of choice for bone reconstructive surgery, but limited availability, risks of transmittable diseases and inconsistent clinical performances have prompted the development of alternative biomaterials. The present work compares the bone regeneration potential of a soybean based bone filler (SB bone filler) in comparison to a commercial 50:50 poly(D: ,L: lactide-glycolide)-based bone graft (Fisiograft((R)) gel) when implanted into a critical size defect (6-mm diameter, 10-mm length) in rabbit distal femurs. The histomorphometric and microhardness analyses of femoral condyles 4, 8, 16 and 24 weeks after surgery showed that no significant difference was found in the percentage of both bone repair and bone in-growth in the external, medium and inner defect areas. The SB filler-treated defects showed significantly higher outer bone formation and microhardness results at 24 weeks than Fisiograft((R)) gel (P < 0.05). Soybean-based biomaterials clearly promoted bone repair through a mechanism of action that is likely to involve both the scaffolding role of the biomaterial for osteoblasts and the induction of their differentiation.

The challenge of establishing preclinical models for segmental bone defect research

A considerable number of international research groups as well as commercial entities work on the development of new bone grafting materials, carriers, growth factors and specifically tissue-engineered constructs for bone regeneration. They are strongly interested in evaluating their concepts in highly reproducible large segmental defects in preclinical and large animal models. To allow comparison between different studies and their outcomes, it is essential that animal models, fixation devices, surgical procedures and methods of taking measurements are well standardized to produce reliable data pools and act as a base for further directions to orthopaedic and tissue engineering developments, specifically translation into the clinic. In this leading opinion paper, we aim to review and critically discuss the different large animal bone defect models reported in the literature. We conclude that most publications provide only rudimentary information on how to establish relevant preclinical segmental bone defects in large animals. Hence, we express our opinion on methodologies to establish preclinical critically sized, segmental bone defect models used in past research with reference to surgical techniques, fixation methods and postoperative management focusing on tibial fracture and segmental defect models.

Spontaneous bone healing of the large bone defects in the mandible

Spontaneous healing of large bone defects in the mandibles of 33 patients was studied. Standard postoperative clinical and radiographic examinations were performed immediately after surgery and after 2, 6 and 12 months. They were analysed using a novel relative bone densitometry method and indexes of relative bone healing were established. Spontaneous bone regeneration occurred in all patients clinically, and the computer analysis of radiographs showed that the mean final bone density in the bone defects was 88% of the bone density of the surrounding healthy bone. In the cases of smaller defects (the greatest diameter on panoramic radiographs was 20-30 mm) the final bone density was 97%, while the larger defects finally healed with 84% of the bone density of the surrounding bone. Increased patient age had a negative influence on healing and the shape of the bone defects was more important for healing than their volume. Spontaneous bone healing occurred even in large bone defects in the mandible, therefore this simple treatment with low economic and biological costs should be the treatment of choice, taking into account the patient's age, surgical principles and time of rehabilitation.

Polylactide/polyglycolide copolymer in bone defect healing in humans

This pilot study aims to evaluate the healing of a large defects in the human jawbone filled with a Poly-Lactide-co-Glycolide (PLG) polymer (Fisiograft) by means of clinical, radiological and histological methods and to compare the results with those of platelet-rich plasma (PRP) clot or autologous bone (AB) fillings. Bone cysts, where previous non-surgical treatments failed to promote healing, underwent surgery. Nineteen consenting male patients were randomly split into three groups, packed with PRP, AB or PLG. A core biopsy was performed 4 and 6 months after surgery. All treated defects showed clinical, radiological and histological progresses over time. AB provided the best clinical and histological performance and PLG had overlapping outcomes; PRP filling was statistically different. Six months after surgery, bone activities were enhanced in sites treated with PLG and fairly good with PRP. Additionally, PLG showed some new lamellar formations. In conclusion, outcomes were best with AB graft, but suitable results were achieved using PLG to promote healing of severe bone defects. PLG shows only a delayed regenerative capability but does not require a secondary donor site.

In vitro and in vivo behaviour of biodegradable and injectable PLA/PGA copolymers related to different matrices

This study comparatively investigates the in vitro and in vivo behavior of injectable polymeric materials for the treatment of bone defects. The tested materials were three injectable and biodegradable PLA/PGA 50/50 copolymers dispersed in different matrices: Fisograft-gel (GEL) was dispersed in an aqueous matrix of poly-ethyl-glycole (PEG); Slurry2 (SL2) was dispersed in an aqueous matrix of PEG and dextran; and Slurry6 (SL6) was dispersed in a 3% agarose matrix. The biological characterization of these materials was studied by in vitro and in vivo tests: the in vitro test assessed the cellular response in terms of viability, differentiation and synthetic activity, while the in vivo test evaluated the healing capacity of bone defects treated with these biomaterials. GEL and SL2 induced a similar response for viability and differentiation of MG63 osteoblast-like cells after a 7-day culture, while SL6 caused a higher production of both interleukin-6 and type I collagen. Since the results showed that the materials were biocompatible and not cytotoxic in vitro, the in vivo study was carried out: materials were implanted, under general anesthesia, in critical size defects of rabbit femoral condyles; after 4 and 12 weeks, the healing rates and the quality of the regenerated bone were histomorphometrically calculated. The SL2-treated defects healed better at 12 weeks with a more similar microarchitecture of the newly formed bone to normal bone in comparison with other materials, as demonstrated by bone volume fraction and trabecular thickness values.

In vivo study on the healing of bone defects treated with bone marrow stromal cells, platelet-rich plasma, and freeze-dried bone allografts, alone and in combination

The repair of confined trabecular bone defects in rabbits treated by autologous bone marrow stromal cells (BMSC), platelet-rich plasma (PRP), freeze-dried bone allografts (FDBA) alone and in combination (BMSC + PRP; FDBA + BMSC; FDBA + PRP; FDBA + PRP + BMSC) was compared. A critical size defect was created in the distal part of the femurs of 48 adult rabbits. Histology and histomorphometry were used in the evaluation of healing at 2, 4, and 12 weeks after surgery. The healing rate (%) was calculated by measuring the residual bone defect area. Architecture of the newly formed bone was compared with that of bone at the same distal femur area of healthy rabbits. The defect healing rate was higher in PRP + BMSC, FDBA + PRP, FDBA + BMSC, and FDBA + PRP + BMSC treatments, while lower values were achieved with PRP treatment at all experimental times. The highest bone-healing rate at 2 weeks was achieved with FDBA + PRP + BMSC treatment, which resulted significantly different from PRP (p < 0.05) and BMSC (p < 0.05) treatments. At 4 weeks, the bone-healing rate increased except for PRP treatment. Finally, the bone-healing rate of FDBA + PRP, FDBA + BMSC, and FDBA + PRP + BMSC was significantly higher than that of PRP at 12 weeks (p < 0.05). At 12 weeks, significant differences still existed between PRP, BMSC, and FDBA groups and normal bone (p < 0.05). These results showed that the combination of FDBA, BMSC and PRP permitted an acceleration in bone healing and bone remodeling processes.

Preparation of recombinant human bone morphogenetic protein-2 loaded dextran-based microspheres and their characteristics

AIM

To prepare new pharmaceutical forms with sustained delivery properties of recombinant human bone morphogenetic protein-2 (rhBMP2) for tissue engineering and guided tissue regeneration (GTR) use.

METHODS

rhBMP2-loaded dextran-based hydrogel microspheres (rhBMP2-MPs), which aimed to keep rhBMP2 bioactivity and to achieve long-term sustained release of rhBMP2, were prepared by double-phase emulsified condensation polymerization. The physical, chemical performances and biological characteristics of those microspheres were studied both in vitro and in vivo.

RESULTS

The microspheres' average diameter was 30.33+/-4.32 microm with 75.4% ranging from 20 microm to 40 microm and the drug loading and encapsulation efficiency were 7.82% and 82.25%, respectively. The rhBMP2-releasing profiles in vitro showed that rhBMP2 release could be maintained more than 10 d. The rhBMP2-MPs, with good swelling and biodegradation behavior, could be kept for 6 months at below 4 degree without significant characteristic change or bioactivity loss. Cytology studies showed that rhBMP2-MPs could promote the proliferation of periodontal ligament cells (PDLCs) approximately 10 d, while the bioactivity of concentrated rhBMP2 solution could keep no more than 3 d. Scanning electron microscope showed that rhBMP2-MPs could be enchased into the porous structure of calcium phosphate ceremic (CPC) and the eugonic growth of PDLCs in CPC/rhBMP2-MPs scaffolds. Animal experiments indicated that using CPC/rhBMP2-MPs scaffolds could gain more periodontal tissue regeneration than using rhBMP2 compound firsthand with CPC (CPC/rhBMP2).

CONCLUSION

By encapsulating rhBMP2 into dextran-based microspheres, a small quantity of rhBMP2 could achieve equivalent effects to the concentrated rhBMP2 solution and at the same time, could prolong rhBMP2 retention both in vitro and in vivo.