Outcomes and complication rates of different bone grafting modalities in long bone fracture nonunions: a retrospective cohort study in 182 patients

Effects of Bone Morphogenetic Protein-2 on Neovascularization During Large Bone Defect Regeneration

Insufficient blood vessel supply is a primary limiting factor for regenerative approaches to large bone defect repair. Recombinant bone morphogenetic protein-2 (BMP-2) delivery induces robust bone formation and has been observed to enhance neovascularization, but whether the angiogenic effects of BMP-2 are due to direct endothelial cell stimulation or due to indirect paracrine signaling remain unclear. In this study, we evaluated the effects of BMP-2 delivery on vascularized bone regeneration and tested whether BMP-2 induces neovascularization directly or indirectly. We found that delivery of BMP-2 (5 μg) enhanced both bone formation and neovascularization in critically sized (8 mm) rat femoral bone defects; however, BMP-2 did not directly stimulate angiogenesis in vitro. In contrast, conditioned medium from both mesenchymal progenitor cells and osteoblasts induced endothelial cell migration in vitro, suggesting a paracrine mechanism of BMP-2 action. Consistent with this inference, codelivery of BMP-2 with endothelial colony forming cells to a heterotopic site, distant from the skeletal stem cell-rich bone marrow niche, induced ossification but had no effect on neovascularization. Taken together, these data suggest that paracrine activation of osteoprogenitor cells is an important contributor to neovascularization during BMP-2-mediated bone regeneration. Impact Statement In this study, we show that bone morphogenetic protein-2 (BMP-2) robustly induces neovascularization during tissue-engineered large bone defect regeneration, and we found that BMP-2 induced angiogenesis, in part, through paracrine signaling from osteoprogenitor cells.

Autograft, Allograft, and Bone Graft Substitutes: Clinical Evidence and Indications for Use in the Setting of Orthopaedic Trauma Surgery

Bone grafts are the second most common tissue transplanted in the United States, and they are an essential treatment tool in the field of acute and reconstructive traumatic orthopaedic surgery. Available in cancellous, cortical, or bone marrow aspirate form, autogenous bone graft is regarded as the gold standard in the treatment of posttraumatic conditions such as fracture, delayed union, and nonunion. However, drawbacks including donor-site morbidity and limited quantity of graft available for harvest make autograft a less-than-ideal option for certain patient populations. Advancements in allograft and bone graft substitutes in the past decade have created viable alternatives that circumvent some of the weak points of autografts. Allograft is a favorable alternative for its convenience, abundance, and lack of procurement-related patient morbidity. Options include structural, particulate, and demineralized bone matrix form. Commonly used bone graft substitutes include calcium phosphate and calcium sulfate synthetics-these grafts provide their own benefits in structural support and availability. In addition, different growth factors including bone morphogenic proteins can augment the healing process of bony defects treated with grafts. Autograft, allograft, and bone graft substitutes all possess their own varying degrees of osteogenic, osteoconductive, and osteoinductive properties that make them better suited for different procedures. It is the purpose of this review to characterize these properties and present clinical evidence supporting their indications for use in the hopes of better elucidating treatment options for patients requiring bone grafting in an orthopaedic trauma setting.

Bone marrow aspirate concentrate with cancellous allograft versus iliac crest bone graft in the treatment of long bone nonunions

Objectives:

The purpose of this study was to compare bone marrow aspirate concentrate (BMAC) with cancellous allograft to iliac crest bone graft (ICBG) in the treatment of long bone nonunions.

Design:

Retrospective cohort study.

Setting:

A single level I trauma center.

Patients:

26 patients with long bone diaphyseal or metaphyseal nonunions with defects >2 mm and treated with open repair and BMAC, compared to 25 patients with long bone diaphyseal or metaphyseal nonunions with defects >2 mm and treated with open repair and ICBG.

Intervention:

Open repair of long bone nonunion using either autologous ICBG or BMAC with cancellous allograft.

Main outcome measure:

Nonunion healing, radiographically measured by the modified Radiographic Union Score for Tibia (mRUST) score. Secondary outcomes included risk factors associated with failed repair.

Results:

The union rates for the BMAC and ICBG cohorts were 75% and 78%, respectively (P = .8). Infection was the only risk factor of statistical significance for failure.

Conclusion:

In this study, we found no significant difference in union rate for long bone nonunions treated with ICBG or BMAC with allograft. BMAC and allograft led to 75% successful healing in this series. Given the heterogeneity of the control group and loss to follow-up, further prospective investigation should be conducted to more rigorously compare BMAC to ICBG for nonunion treatment.

Level of evidence:

III, retrospective cohort.

A parameterised mathematical model to elucidate osteoblast cell growth in a phosphate-glass microcarrier culture

Tissue engineering has the potential to augment bone grafting. Employing microcarriers as cell-expansion vehicles is a promising bottom-up bone tissue engineering strategy. Here we propose a collaborative approach between experimental work and mathematical modelling to develop protocols for growing microcarrier-based engineered constructs of clinically relevant size. Experiments in 96-well plates characterise cell growth with the model human cell line MG-63 using four phosphate glass microcarrier materials. Three of the materials are doped with 5 mol% TiO₂ and contain 0%, 2% or 5% CoO, and the fourth material is doped only with 7% TiO₂ (0% CoO). A mathematical model of cell growth is parameterised by finding material-specific growth coefficients through data-fitting against these experiments. The parameterised mathematical model offers more insight into the material performance by comparing culture outcome against clinically relevant criteria: maximising final cell number starting with the lowest cell number in the shortest time frame. Based on this analysis, material 7% TiO₂ is identified as the most promising.

Effect of Osteoking on the osteogenic and adipogenic differentiation potential of rat bone marrow mesenchymal stem cells in vitro

Background

Bone damage is a condition that affects the quality of life of patients. Mesenchymal stem cells (MSCs) are important for bone repair. Osteoking is a natural compound in traditional Chinese Medicine used to treat bone diseases; however, the effect of Osteoking on the differentiation of MSCs has not been reported. In this study, we aimed to investigate the effect of Osteoking on the osteogenic and adipogenic differentiation potential of rat bone marrow mesenchymal stem cells (rbMSCs).

Methods

The effects of Osteoking on the proliferation and differentiation of rbMSCs were investigated. Different concentrations of Osteoking were prepared, and its cytotoxicity was evaluated by CCK-8 assay. The expression of osteogenic and adipogenic genes were determined, and several staining methods were used to reveal the osteogenic and adipogenic differentiation potential of rbMSCs.

Results

Our results show that appropriate concentrations of Osteoking can enhance osteogenic differentiation of rbMSCs and reduce adipogenic differentiation without any effect on proliferation. This may be related to the changes in related gene expression.

Conclusion

Osteoking enhances osteogenic differentiation and inhibits adipogenic differentiation of rbMSCs. Therefore, Osteoking may have a therapeutic potential for treating bone disease caused by changes in differentiation function of MSCs.

Mathematical and computational models for bone tissue engineering in bioreactor systems

Research into cellular engineered bone grafts offers a promising solution to problems associated with the currently used auto- and allografts. Bioreactor systems can facilitate the development of functional cellular bone grafts by augmenting mass transport through media convection and shear flow-induced mechanical stimulation. Developing successful and reproducible protocols for growing bone tissue in vitro is dependent on tuning the bioreactor operating conditions to the specific cell type and graft design. This process, largely reliant on a trial-and-error approach, is challenging, time-consuming and expensive. Modelling can streamline the process by providing further insight into the effect of the bioreactor environment on the cell culture, and by identifying a beneficial range of operational settings to stimulate tissue production. Models can explore the impact of changing flow speeds, scaffold properties, and nutrient and growth factor concentrations. Aiming to act as an introductory reference for bone tissue engineers looking to direct their experimental work, this article presents a comprehensive framework of mathematical models on various aspects of bioreactor bone cultures and overviews modelling case studies from literature.

Application of mesenchymal stem cells to enhance non-union bone fracture healing

ECM components include a number of osteoinductive and osteoconductive factors, which are involved in bone fracture healing. In this study, a combination of adipose derived mesenchymal stem cells (Ad-MSCs), cancellous bone graft (CBG), and chitosan hydrogel (CHI) was applied to the non-union bone fracture and healing effects were evaluated for the first time. After creation of animal models with non-union fracture in rats, they were randomly classified into seven groups. Radiography at 0, 2, 4, and 8 weeks after surgery, indicated the positive effects of Ad-MSCs + CBG + CHI and Ad-MSCs + CBG in treatment of bone fractures as early as 2 weeks after the surgery. These data were confirmed with both biomechanical and histological studies. Gene expression analyses of Vegf and Bmp2 showed a positive effect of Ad-MSCs on vascularization and osteogenic differentiation in all groups receiving Ad-MSCs, as shown by real-time PCR. Immunofluorescence analysis and RT-PCR results indicated existence of human Ad-MSCs in the fractured region 8 weeks post-surgery. In conclusion, we suggest that application of Ad-MSCs, CBG, and CHI, could be a suitable combination for osteoinduction and osteoconduction to improve non-union bone fracture healing. Further investigations are required to determine the exact mechanisms involved in this process before moving to clinical studies. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 301-311, 2019.

Assessment of the degradation rates and effectiveness of different coated Mg-Zn-Ca alloy scaffolds for in vivo repair of critical-size bone defects

Surgical repair of bone defects remains challenging, and the search for alternative procedures is ongoing. Devices made of Mg for bone repair have received much attention owing to their good biocompatibility and mechanical properties. We developed a new type of scaffold made of a Mg-Zn-Ca alloy with a shape that mimics cortical bone and can be filled with morselized bone. We evaluated its durability and efficacy in a rabbit ulna-defect model. Three types of scaffold-surface coating were evaluated: group A, no coating; group B, a 10-μm microarc oxidation coating; group C, a hydrothermal duplex composite coating; and group D, an empty-defect control. X-ray and micro-computed tomography(micro-CT) images were acquired over 12 weeks to assess ulnar repair. A mechanical stress test indicated that bone repair within each group improved significantly over time (P < 0.01). The degradation behavior of the different scaffolds was assessed by micro-CT and quantified according to the amount of hydrogen gas generated; these measurements indicated that the group C scaffold better resisted corrosion than did the other scaffold types (P < 0.05). Calcein fluorescence and histology revealed that greater mineral densities and better bone responses were achieved for groups B and C than for group A, with group C providing the best response. In conclusion, our Mg-Zn-Ca-alloy scaffold effectively aided bone repair. The group C scaffold exhibited the best corrosion resistance and osteogenesis properties, making it a candidate scaffold for repair of bone defects.

Tissue Engineering and Cell-Based Therapies for Fractures and Bone Defects

Bone fractures and segmental bone defects are a significant source of patient morbidity and place a staggering economic burden on the healthcare system. The annual cost of treating bone defects in the US has been estimated to be $5 billion, while enormous costs are spent on bone grafts for bone injuries, tumors, and other pathologies associated with defective fracture healing. Autologous bone grafts represent the gold standard for the treatment of bone defects. However, they are associated with variable clinical outcomes, postsurgical morbidity, especially at the donor site, and increased surgical costs. In an effort to circumvent these limitations, tissue engineering and cell-based therapies have been proposed as alternatives to induce and promote bone repair. This review focuses on the recent advances in bone tissue engineering (BTE), specifically looking at its role in treating delayed fracture healing (non-unions) and the resulting segmental bone defects. Herein we discuss: (1) the processes of endochondral and intramembranous bone formation; (2) the role of stem cells, looking specifically at mesenchymal (MSC), embryonic (ESC), and induced pluripotent (iPSC) stem cells as viable building blocks to engineer bone implants; (3) the biomaterials used to direct tissue growth, with a focus on ceramic, biodegradable polymers, and composite materials; (4) the growth factors and molecular signals used to induce differentiation of stem cells into the osteoblastic lineage, which ultimately leads to active bone formation; and (5) the mechanical stimulation protocols used to maintain the integrity of the bone repair and their role in successful cell engraftment. Finally, a couple clinical scenarios are presented (non-unions and avascular necrosis—AVN), to illustrate how novel cell-based therapy approaches can be used. A thorough understanding of tissue engineering and cell-based therapies may allow for better incorporation of these potential therapeutic approaches in bone defects allowing for proper bone repair and regeneration.

Segmental bone replacement via patient-specific, three-dimensional printed bioresorbable graft substitutes and their use as templates for the culture of mesenchymal stem cells under mechanical stimulation at various frequencies

The treatment of large segmental bone defects remains a challenge as infection, delayed union, and nonunion are common postoperative complications. A three-dimensional printed bioresorbable and physiologically load-sustaining graft substitute was developed to mimic native bone tissue for segmental bone repair. Fabricated from polylactic acid, this graft substitute is novel as it is readily customizable to accommodate the particular size and location of the segmental bone of the patient to be replaced. Inspired by the structure of the native bone tissue, the graft substitute exhibits a gradient in porosity and pore size in the radial direction and exhibit mechanical properties similar to those of the native bone tissue. The graft substitute can serve as a template for tissue constructs via seeding with stem cells. The biocompatibility of such templates was tested under in vitro conditions using a dynamic culture of human mesenchymal stem cells. The effects of the mechanical loading of cell-seeded templates under in vitro conditions were assessed via subjecting the tissue constructs to 28 days of daily mechanical stimulation. The frequency of loading was found to have a significant effect on the rate of mineralization, as the alkaline phosphatase activity and calcium deposition were determined to be particularly high at the typical walking frequency of 2 Hz, suggesting that mechanical stimulation plays a significant role in facilitating the healing process of bone defects. Utilization of such patient-specific and biocompatible graft substitutes, coupled with patient's bone marrow cells seeded and exposed to mechanical stimulation of 2 Hz have the potential of reducing significant volumes of cadaveric tissue required, improving long-term graft stability and incorporation, and alleviating financial burdens associated with delayed or failed fusions of long bone defects.

In situ bone tissue engineering via ultrasound-mediated gene delivery to endogenous progenitor cells in mini-pigs

More than 2 million bone-grafting procedures are performed each year using autografts or allografts. However, both options carry disadvantages, and there remains a clear medical need for the development of new therapies for massive bone loss and fracture nonunions. We hypothesized that localized ultrasound-mediated, microbubble-enhanced therapeutic gene delivery to endogenous stem cells would induce efficient bone regeneration and fracture repair. To test this hypothesis, we surgically created a critical-sized bone fracture in the tibiae of Yucatán mini-pigs, a clinically relevant large animal model. A collagen scaffold was implanted in the fracture to facilitate recruitment of endogenous mesenchymal stem/progenitor cells (MSCs) into the fracture site. Two weeks later, transcutaneous ultrasound-mediated reporter gene delivery successfully transfected 40% of cells at the fracture site, and flow cytometry showed that 80% of the transfected cells expressed MSC markers. Human bone morphogenetic protein-6 (BMP-6) plasmid DNA was delivered using ultrasound in the same animal model, leading to transient expression and secretion of BMP-6 localized to the fracture area. Micro-computed tomography and biomechanical analyses showed that ultrasound-mediated BMP-6 gene delivery led to complete radiographic and functional fracture healing in all animals 6 weeks after treatment, whereas nonunion was evident in control animals. Collectively, these findings demonstrate that ultrasound-mediated gene delivery to endogenous mesenchymal progenitor cells can effectively treat nonhealing bone fractures in large animals, thereby addressing a major orthopedic unmet need and offering new possibilities for clinical translation.

Human bone graft cytocompatibility with mesenchymal stromal cells is comparable after thermal sterilization and washing followed by γ-irradiation: an in vitro study

Human bone allografts present a better alternative to autografts in terms of minimization of the harvesting procedure complications. Prior to the use in clinical applications, they require sterilization which aims to reduce bioburden. This often comes at the expense of their biological properties as carriers of cells. In this study, we evaluated the cytocompatibility of human bone allografts processed and sterilized by three different methods with mesenchymal stromal cells. Bone morphology, biological and biochemical properties of the extracted bone-conditioned medium and viability of cells were assessed. We found that chemical sterilization had a strong negative effect on cell viability, whereas thermal sterilization and washing with subsequent γ-irradiation both resulted in a bone graft compatible with the progenitor cells. Moreover, washing of the bone prior to sterilization allowed solid removal of cell debris and other bone marrow components. Taken together, our findings demonstrate the importance of a proper choice of the bone graft processing method for the production of the biomaterial suitable for tissue engineering.

Pedicled iliac crest bone flap transfer for the treatment of upper femoral shaft fracture nonunion: An anatomic study and clinical applications

PURPOSE

We present the results of a study on the anatomy of the ascending branch of the lateral circumflex femoral artery (AB-LCFA) and the use of the pedicled iliac bone flap transfer perfused by AB-LCFA combined with external fixation for the treatment of the nonunion of upper femoral shaft fractures.

METHODS

The orientation, diameter, length, and distribution of the AB-LCFA from 40 lower limbs of adult cadavers were dissected and measured. From 2000 to 2012, 13 patients with nonunion of upper femoral shaft fractures underwent pedicled iliac bone flap transfer perfused by the AB-LCFA combined with external fixation. The time of bone fracture union was recorded based on X-ray examination. The functional results of the femoral shaft were evaluated by the Klemm classification.

RESULTS

The lateral circumflex femoral artery (LCFA) divided into ascending, transverse, and descending branches in 32 specimens (80%). The diameter of the AB-LCFA at the origin was 3.15 ± 0.9 mm and the length of the AB-LCFA was 8.51 ± 3.06 cm. The postoperative course of the procedure was uneventful in all 13 patients. The average follow-up was 15 months. Bone union was achieved in all patients and the average union time was 5.3 months. 12 patients achieved excellent or good functional results based on the Klemm classification.

CONCLUSION

The AB-LCFA has a consistent orientation and abundant blood flow. The transfer of the iliac crest bone flap perfused by the AB-LCFA while combined with external fixation could be an option for treating the nonunion of upper femoral shaft fractures.

Radial extracorporeal shock wave therapy is efficient and safe in the treatment of fracture nonunions of superficial bones: a retrospective case series

BACKGROUND

A substantial body of evidence supports the use of focused extracorporeal shock wave therapy (fESWT) in the non-invasive treatment of fracture nonunions. On the other hand, virtually no studies exist on the use of radial extracorporeal shock wave therapy (rESWT) for this indication.

METHODS

We retrospectively analyzed 22 patients treated with rESWT for fracture nonunions of superficial bones that failed to heal despite initial surgical fixation in most cases. Radial extracorporeal shock wave therapy was applied without anesthesia in three rESWT sessions on average, with one rESWT session per week and 3000 radial extracorporeal shock waves at an energy flux density of 0.18 mJ/mm² per session. Treatment success was monitored with radiographs and clinical examinations.

RESULTS

Six months after rESWT radiographic union was confirmed in 16 out of 22 patients (73%), which is similar to the success rate achieved in comparable studies using fESWT. There were no side effects. The tibia was the most common treatment site (10/22) and 70% of tibia nonunions healed within 6 months after rESWT. Overall, successfully treated patients showed a mean time interval of 8.8 ± 0.8 (mean ± standard error of the mean) months between initial fracture and commencement of rESWT whereas in unsuccessfully treated patients the mean interval was 26.0 ± 10.1 months (p < 0.05). In unsuccessful tibia cases, the mean interval was 43.3 ± 13.9 months.

CONCLUSIONS

Radial extracorporeal shock wave therapy appears to be an effective and safe alternative in the management of fracture nonunions of superficial bones if diagnosed early and no fESWT device is available. The promising preliminary results of the present case series should encourage the implementation of randomized controlled trials for the early use of rESWT in fracture nonunions.

3D- Printed Poly(ε-caprolactone) Scaffold Integrated with Cell-laden Chitosan Hydrogels for Bone Tissue Engineering

Synthetic polymeric scaffolds are commonly used in bone tissue engineering (BTE) due to their biocompatibility and adequate mechanical properties. However, their hydrophobicity and the lack of specific cell recognition sites confined their practical application. In this study, to improve the cell seeding efficiency and osteoinductivity, an injectable thermo-sensitive chitosan hydrogel (CSG) was incorporated into a 3D-printed poly(ε-caprolactone) (PCL) scaffold to form a hybrid scaffold. To demonstrate the feasibility of this hybrid system for BTE application, rabbit bone marrow mesenchymal stem cells (BMMSCs) and bone morphogenetic protein-2 (BMP-2) were encapsulated in CSG. Pure PCL scaffolds were used as controls. Cell proliferation and viability were investigated. Osteogenic gene expressions of BMMSCs in various scaffolds were determined with reverse transcription polymerase chain reaction (RT-PCR). Growth factor releasing profile and mechanical tests were performed. CCK-8 assay confirmed greater cell retention and proliferation in chitosan and hybrid groups. Confocal microscopy showed even distribution of cells in the hybrid system. After 2-week osteogenic culture in vitro, BMMSCs in hybrid and chitosan scaffolds showed stronger osteogenesis and bone-matrix formation. To conclude, chitosan/PCL hybrid scaffolds are a favorable platform for BTE due to its capacity to carry cells and drugs, and excellent mechanical strength.

Risk Factors for Failure of Bone Grafting of Tibia Nonunions and Segmental Bone Defects: A New Preoperative Risk Assessment Score

OBJECTIVE

To develop a clinically useful prediction model of success at the time of surgery to promote bone healing for established tibial nonunion or traumatic bone defects.

DESIGN

Retrospective case controlled.

SETTING

Level 1 trauma center.

PATIENTS

Adult patients treated with surgery for established tibia fracture nonunion or traumatic bone defects from 2007 to 2016. Two hundred three patients met the inclusion criteria and were available for final analysis.

INTERVENTION

Surgery to promote bone healing of established tibia fracture nonunion or segmental defect with plate and screw construct, intramedullary nail fixation, or multiplanar external fixation.

MAIN OUTCOME MEASURES

Failure of the surgery to promote bone healing that was defined as unplanned revision surgery for lack of bone healing or deep infection. No patients were excluded who had a primary outcome event.

RESULTS

Multivariate logistic modeling identified 5 significant (P < 0.05) risk factors for failure of the surgery to promote bone healing: (1) mechanism of injury, (2) Increasing body mass index, (3) cortical defect size (mm), (4) flap size (cm), and (5) insurance status. A prediction model was created based on these factors and awarded 0 points for fall, 17 points for high energy blunt trauma (OR = 17; 95% CI, 1-286, P = 0.05), 22 points for industrial/other (OR = 22; 95% CI, 1-4, P = 0.04), and 28 points for ballistic injuries (OR = 28; 95% CI, 1-605, P = 0.04). One point is given for every 10 cm of flap size (OR = 1; 95% CI, 1-1.1, P < 0.001), 10 mm of mean cortical gap distance (OR = 1; 95% CI, 1-2, P = 0.004), and 10 units BMI, respectively (OR = 1.5; 95% CI, 1-3, P = 0.16). Two points are awarded for Medicaid or no insurance (OR = 2; 95% CI, 1-5, P = 0.035) and 3 points for Medicare (3; 95% CI, 1-9, P = 0.033). Each 1-point increase in risk score was associated with a 6% increased chance of requiring at least 1 revision surgery (P < 0.001).

CONCLUSIONS

This study presents a clinical score that predicts the likelihood of success after surgery for tibia fracture nonunions or traumatic bone defects and may help clinicians better determine which patients are likely to fail these procedures and require further surgery.

Effect of Freeze-Dried Allograft Bone With Human Basic Fibroblast Growth Factor Containing a Collagen-Binding Domain From Clostridium histolyticum Collagenase on Bone Formation After Lumbar Posterolateral Fusion Surgery in Rats

STUDY DESIGN

An experimental study.

OBJECTIVE

To evaluate the effectiveness of freeze-dried bone allograft (FDBA) with basic fibroblast growth factor (bFGF) fused with the polycystic kidney disease domain (PKD) and the collagen-binding domain (CBD) of Clostridium histolyticum collagenase, for the acceleration of lumbar posterolateral fusion in rats.

SUMMARY OF BACKGROUND DATA

Reports indicate bFGF is an effective growth factor with osteogenic potential for promoting bone regeneration, although its efficiency decreases rapidly following its diffusion in body fluid from the host site. We developed a bFGF fusion protein containing the PKD and the CBD of C histolyticum collagenase (bFGF-PKD-CBD), which markedly enhanced bone formation at a relatively low concentration when applied to the surface of rat femurs in a previous study. The potential of this novel protein to accelerate bone fusion in a rat model of lumbar posterolateral fusion has yet to be investigated.

METHODS

Bilateral L4-L5 posterolateral fusions were performed, using 150 mg of FDBA powder per side. A total of 20 male Sprague-Dawley rats weighing 200 to 250 g/each were divided into two groups of 10 rats: FDBA was incubated with either phosphate-buffered saline (control group) or 0.58 nmol bFGF-PKD-CBD (bFGF-PKD-CBD group) before fusion surgery. The effect of bFGF-PKD-CBD was estimated using radiographs, microcomputed tomography, and histology (hematoxylin-eosin and von Kossa staining).

RESULTS

Both grafted bone volume in the posterolateral lesion and the volume of new bone formation on the surface of laminae and spinal processes were significantly higher in the bFGF-PKD-CBD group than in the control group. Histologically, new bone formation and surrounding chondrocytes and fibroblasts were prominent in the bFGF-PKD-CBD group.

CONCLUSION

FDBA infused with bFGF-PKD-CBD may be a promising material for accelerating spinal fusion, and the FDBA-based delivery system for localizing bFGF-PKD-CBD may offer novel therapeutic approaches to augment spinal fusion.

LEVEL OF EVIDENCE

N/A.

Long-term outcome following additional rhBMP-7 application in revision surgery of aseptic humeral, femoral, and tibial shaft nonunion

Background

Surgical revision concepts for the treatment of aseptic humeral, femoral, and tibial diaphyseal nonunion were evaluated. It was analyzed if the range of time to bone healing was shorter, and if clinical and radiological long-term outcome was better following application of additional recombinant human Bone Morphogenetic Protein-7 (rhBMP-7) compared to no additional rhBMP-7 use.

Methods

In a retrospective comparative study between 06/2006 and 05/2013, 112 patients diagnosed with aseptic diaphyseal humerus (22 patients), femur (41 patients), and tibia (49 patients) nonunion were treated using internal fixation and bone graft augmentation. For additional stimulation of bone healing, growth factor rhBMP-7 was locally administered in 62 out of 112 patients. Follow-up studies including clinical and radiological assessment were performed at regular intervals as well as after at least one year following nonunion surgery.

Results

One hundred and two out of 112 (humerus: 19, femur: 37, tibia: 47) nonunion healed within 12 months after revision surgery without any significant differences between the cohort groups. According to the DASH outcome measure for the humerus (p = 0.679), LEFS for the femur (p = 0.251) and the tibia (p = 0.946) as well as to the SF-12 for all entities, no significant differences between the treatment groups were found.

Conclusions

Aseptic diaphyseal nonunion in humerus, femur, and tibia healed irrespectively of additional rhBMP-7 application. Moreover, the results of this study suggest that successful nonunion healing can be linked to precise surgical concepts using radical removal of nonunion tissue, stable fixation and restoration of axis, length and torsion, rather than to the additional use of signaling proteins.

Trial registration

This clinical trial was conducted according to ICMJE guidelines as well as to the approval of the National Medical Board (Ethics Committee of the Bavarian State Chamber of Physicians; TRN: 2016-104) and has been retrospectively registered with the German Clinical Trails Register (TRN: DRKS00012652).

Comparative Study of Proximal Tibia and Iliac Crest Bone Graft Donor Sites in Treatment of Orthopaedic Pathologies

Introduction: Bone graft is harvested from bone and used to stimulate bone healing due to its properties. The aims of the study were to compare the quantity of graft harvested from proximal tibia and iliac crest, and the complications at these donor sites. Materials and Methods: This was a prospective study carried out on all consecutive patients who had orthopaedic procedures that required bone grafting at the study centre, from April, 2015 to March, 2016. Results: During the study period, 86 patients were recruited; 43 of these patients had bone graft harvested from the proximal tibia, while the other 43 patients had graft harvested from the iliac crest. There were 53 males, and 33 females. Mean age of patients was 41.2 ± 11 years and 40.8 ± 16 years, for proximal tibia and iliac crest group respectively. Average compressed volume of graft harvested from proximal tibia and iliac crest were 7cm³ and 5.5cm³ respectively. Non-unions were the commonest indications for bone grafting, femur was the commonest bone requiring bone grafting. Complications such as primary haemorrhage, pain and surgical site infection were commoner with iliac crest than proximal tibia donor sites, however bone graft harvested from both proximal tibia and iliac crest provided adequate bone union of the indicated procedure. Conclusion: Larger quantity of graft can be harvested from proximal tibia than the iliac crest. Though graft harvested from both the proximal tibia and the iliac crest have good healing properties, the proximal tibia donor site gave less complication than the iliac crest.

Treatment of aseptic non-union after intramedullary nailing without removal of the nail

Failure of bone healing after intramedullary nailing of a diaphyseal long bone fracture is a severe complication that requires an effective management to ensure the best chances for successful bone-union and termination of a long period of incapacity and morbidity for the sufferers. Traditional procedures require removal of the existing nail and re-fixation with wider nail, plate or external fixation constructs. The concept that bone union can be obtained with the existing nail in situ is gaining popularity as its removal adds trauma and potential complications and prolongs the operating time. This article reviews all techniques that have been proposed for the management of aseptic diaphyseal long bone non-unions that stimulate bone healing without removing the existing nail.

Injectable hydrogels for cartilage and bone tissue engineering

Tissue engineering has become a promising strategy for repairing damaged cartilage and bone tissue. Among the scaffolds for tissue-engineering applications, injectable hydrogels have demonstrated great potential for use as three-dimensional cell culture scaffolds in cartilage and bone tissue engineering, owing to their high water content, similarity to the natural extracellular matrix (ECM), porous framework for cell transplantation and proliferation, minimal invasive properties, and ability to match irregular defects. In this review, we describe the selection of appropriate biomaterials and fabrication methods to prepare novel injectable hydrogels for cartilage and bone tissue engineering. In addition, the biology of cartilage and the bony ECM is also summarized. Finally, future perspectives for injectable hydrogels in cartilage and bone tissue engineering are discussed.

Treatment of Distal Femur Nonunion Following Initial Fixation with a Lateral Locking Plate

OBJECTIVE

To report and evaluate the outcomes of patients undergoing definitive treatment for distal femur nonunion after initial treatment with a locking plate.

METHODS

Fourteen patients who had undergone definitive treatment at an academic Level 1 trauma center from May 2007 to December 2013 for distal femur nonunion were identified from a fracture database. Thirteen of them were female; the average age was 65 years (range, 50-84 years). Ten patients had sustained their injuries in falls at ground level, and four in motor vehicle accidents. Twelve patients were obese (body mass index ≥30), 10 had diabetes, none were current smokers, and one had an open fracture classified as type IIIa according to the Gustilo-Anderson classification system for open fractures. The fractures were classified according to the AO classification system for distal femur fractures; there were three type 33-A1, six 33-A2, two 33-A3 and three 33-C3 fractures. Methods of definitive treatment involved open reduction and internal fixation (ORIF) revision, medial plating, bone grafting and the use of other biologic materials.

RESULTS

Eight of the 14 patients (57%) achieved union during follow-up. Definitive treatment for nonunion involved ORIF revision in 11 cases. Three patients who did not undergo ORIF revision were treated with iliac crest stem cell autografts, bone graft substitutes or recombinant human-bone morphogenetic protein-2 (rh-BMP-2). Other treatments included rh-BMP-2 (12 cases), iliac crest bone autograft (five), iliac crest stem cell autograft (two), crushed cancellous bone allograft (three), CaSO 4 and tricalcium phosphate bone graft substitute (two) and demineralized bone matrix (one). The average time from definitive treatment to union was 19 weeks (range, 12-51 weeks). Two of the 11 cases who underwent ORIF revision had medial plates added to improve biomechanical stability and prevent varus collapse. This was also performed in one patient with a grade III open type 33-C3 fracture and one with a closed 33-A2 fracture. Five study patients had comminuted fractures. Two had type 33-A3 and three type 33-C3 fractures. Both patients with 33-A3 fractures and 2 two with 33-C3 fractures had persistent nonunion at the end of follow-up.

CONCLUSIONS

Definitive treatment of distal femur nonunion after initial treatment with a locking plate had a low rate of success in this study, suggesting that this procedure is ineffective as a definitive treatment for distal femur nonunion.

Congenital pseudarthrosis of the clavicle: a report on 27 cases

HYPOTHESIS

We aimed to report our experience in treating congenital pseudarthrosis of the clavicle (CPC).

MATERIALS AND METHODS

A retrospective search of the archive of our institute was performed; 27 cases (12 male and 15 female patients) affected by CPC were recorded. Among these patients, 19 underwent surgical intervention for cosmetic appearance between 1960 and 2015. Of 19 patients, 18 were treated by pseudarthrosis resection and stabilization with a Kirschner wire, whereas in 1 case, the osteosynthesis was performed with a plate. Iliac crest bone autograft was used in 15 patients, whereas 4 patients were treated with a fibular allograft.

RESULTS

The mean follow-up period was 36.3 ± 49.1 months. Bone healing was achieved in 14 of 19 operated cases (74%); none of the patients had complaints regarding cosmetic abnormalities or unesthetic appearance. All the operated patients were pain free, range of motion was complete, and no other subjective anomalies were found. No vascular or neurologic complications were observed. However, the use of allograft was associated with high rates of nonunion in this case series (P = .037).

CONCLUSION

CPC can be satisfactorily treated by K-wire fixation and autologous iliac crest bone grafting, which showed better results in terms of functional and cosmetic outcome.

Delivery vehicle effects on bone regeneration and heterotopic ossification induced by high dose BMP-2

Bone morphogenetic protein-2 (BMP-2), delivered on absorbable collagen sponge, is frequently used to treat bone defects. However, supraphysiological BMP-2 doses are common and often associated with complications such as heterotopic ossification and inflammation, causing pain and impaired mobility. This has prompted investigations into strategies to spatially control bone regeneration, for example growth factor delivery in appropriate scaffolds. Our objective was to investigate the spatiotemporal effects of high dose BMP-2 on bone regeneration as a function of the delivery vehicle. We hypothesized that an alginate delivery system would spatially restrict bone formation compared to a collagen sponge delivery system. In vitro, BMP-2 release was accelerated from collagen sponge compared to alginate constructs. In vivo, bone regeneration was evaluated over 12weeks in critically sized rat femoral segmental defects treated with 30μg rhBMP-2 in alginate hydrogel or collagen sponge, surrounded by perforated nanofiber meshes. Total bone volume, calculated from micro-CT reconstructions, was higher in the alginate group at 12weeks. Though bone volume within the central defect region was greater in the alginate group at 8 and 12weeks, heterotopic bone volume was similar between groups. Likewise, mechanical properties from ex vivo torsional testing were comparable between groups. Histology corroborated these findings and revealed heterotopic mineralization at 2weeks post-surgery in both groups. Overall, this study recapitulated the heterotopic ossification associated with high dose BMP-2 delivery, and demonstrated that the amount and spatial pattern of bone formation was dependent on the delivery matrix.

STATEMENT OF SIGNIFICANCE

Alginate hydrogel-based BMP-2 delivery has induced better spatiotemporal bone regeneration in animals, compared to clinically used collagen sponge, at lower BMP-2 doses. Lack of clear dose-response relationships for BMP-2 vis-à-vis bone regeneration has contributed to the use of higher doses clinically. We investigated the potential of the alginate system, with comparatively favorable BMP-2 release-kinetics, to reduce heterotopic ossification and promote bone regeneration, when used with a high BMP-2 dose. While defect mineralization improved with alginate hydrogel, the initial high-release phase and likely early tissue exposure to BMP-2 appeared sufficient to induce heterotopic ossification. The characterization presented here should provide the framework for future evaluations of strategies to optimize bone formation and minimize adverse effects of high dose BMP-2 therapy.

Enhancing the proliferation of MC3T3-E1 cells on casein phosphopeptide-biofunctionalized 3D reduced-graphene oxide/polypyrrole scaffolds

The CPP-biofunctionalized 3D rGO/PPY scaffold can greatly boost the proliferation and differentiation of MC3T3-E1 cells, especially the 3D rGO/PPY/CPP20 scaffold.

Stem and progenitor cells: advancing bone tissue engineering

Unlike many other postnatal tissues, bone can regenerate and repair itself; nevertheless, this capacity can be overcome. Traditionally, surgical reconstructive strategies have implemented autologous, allogeneic, and prosthetic materials. Autologous bone--the best option--is limited in supply and also mandates an additional surgical procedure. In regenerative tissue engineering, there are myriad issues to consider in the creation of a functional, implantable replacement tissue. Importantly, there must exist an easily accessible, abundant cell source with the capacity to express the phenotype of the desired tissue, and a biocompatible scaffold to deliver the cells to the damaged region. A literature review was performed using PubMed; peer-reviewed publications were screened for relevance in order to identify key advances in stem and progenitor cell contribution to the field of bone tissue engineering. In this review, we briefly introduce various adult stem cells implemented in bone tissue engineering such as mesenchymal stem cells (including bone marrow- and adipose-derived stem cells), endothelial progenitor cells, and induced pluripotent stem cells. We then discuss numerous advances associated with their application and subsequently focus on technological advances in the field, before addressing key regenerative strategies currently used in clinical practice. Stem and progenitor cell implementation in bone tissue engineering strategies have the ability to make a major impact on regenerative medicine and reduce patient morbidity. As the field of regenerative medicine endeavors to harness the body's own cells for treatment, scientific innovation has led to great advances in stem cell-based therapies in the past decade.

Refixation, allograft and adjuvant cell therapy to treat nonunion of the femoral neck in a child

INTRODUCTION

Idiopathic posttraumatic nonunion is a rare condition in children; the treatment of this complication is still controversial in this peculiar population.

CASE REPORT

We report a case of a subcapital type II femoral neck fracture, in a 12-year-old boy, which was initially treated by internal fixation and subsequently went on to a nonunion at the femoral neck, in absence of infection or other disease.1 year after index surgery we performed surgical debridement and refixation with plate and bone allograft, added with autologous bone marrow aspiration concentrate (BMAC) and platelet-rich fibrin (PRF).After 3 months the nonunion healed and the boy was allowed full weight-bearing.

CONCLUSIONS

Combined surgery and adjuvant cell therapy can be considered an option of treatment in nonunion of the femoral neck in the paediatric population.

The Influence of Platelet-Derived Growth Factor and Bone Morphogenetic Protein Presentation on Tubule Organization by Human Umbilical Vascular Endothelial Cells and Human Mesenchymal Stem Cells in Coculture

A three-dimensional in vitro Matrigel plug was used as a model to explore delivery patterns of platelet-derived growth factor (PDGF) and bone morphogenetic protein-2 (BMP-2) to a coculture of human mesenchymal and endothelial cells. While BMP-2 is well recognized for its role in promoting fracture healing through proliferation and differentiation of osteoclast precursors, it is not a growth factor known to promote the process of angiogenesis, which is also critical for complete bone tissue repair. PDGF, in contrast, is a known regulator of angiogenesis, and also a powerful chemoattractant for osteoblast precursor cells. It has been suggested that presentation of PDGF followed by BMP may better promote vascularized bone tissue formation. Yet, it is unclear as to how cells would respond to various durations of delivery of each growth factor as well as to various amounts of overlap in presentation in terms of angiogenesis. Using a three-dimensional in vitro Matrigel plug model, we observed how various presentation schedules of PDGF and BMP-2 influenced tubule formation by human mesenchymal stem cells and human umbilical vascular endothelial cells. We observed that sequential presentation of PDGF to BMP-2 led to increased tubule formation over simultaneous delivery of these growth factors. Importantly, a 2-4 day overlap in the sequential presentation of PDGF and BMP-2 increased tubule formation as compared with groups with zero or complete growth factor overlap, suggesting that a moderate amount of angiogenic and osteogenic growth factor overlap may be beneficial for processes associated with angiogenesis.

The multifactorial aetiology of fracture nonunion and the importance of searching for latent infection

Objectives

A successful outcome following treatment of nonunion requires the correct identification of all of the underlying cause(s) and addressing them appropriately. The aim of this study was to assess the distribution and frequency of causative factors in a consecutive cohort of nonunion patients in order to optimise the management strategy for individual patients presenting with nonunion.

Methods

Causes of the nonunion were divided into four categories: mechanical; infection; dead bone with a gap; and host. Prospective and retrospective data of 100 consecutive patients who had undergone surgery for long bone fracture nonunion were analysed.

Results

A total of 31% of patients had a single attributable cause, 55% had two causes, 14% had three causes and 1% had all four. Of those (31%) with only a single attributable cause, half were due to a mechanical factor and a quarter had dead bone with a gap. Mechanical causation was found in 59% of all patients, dead bone and a gap was present in 47%, host factors in 43% and infection was a causative factor in 38% of patients.

In all, three of 58 patients (5%) thought to be aseptic and two of nine (22%) suspected of possible infection were found to be infected. A total of 100% of previously treated patients no longer considered to have ongoing infection, had multiple positive microbiology results.

Conclusion

Two thirds of patients had multiple contributing factors for their nonunion and 5% had entirely unexpected infection. This study highlights the importance of identifying all of the aetiological factors and routinely testing tissue for infection in treating nonunion. It raises key points regarding the inadequacy of a purely radiographic nonunion classification system and the variety of different definitions for atrophic nonunion in the current mainstream classifications used for nonunion.

Cite this article: L. Mills, J. Tsang, G. Hopper, G. Keenan, A. H. R. W. Simpson. The multifactorial aetiology of fracture nonunion and the importance of searching for latent infection. Bone Joint Res 2016;5:512–519. DOI: 10.1302/2046-3758.510.BJR-2016-0138.

Amorphous polyphosphate/amorphous calcium carbonate implant material with enhanced bone healing efficacy in a critical-size defect in rats

In this study the effect of amorphous calcium carbonate (ACC) microparticles and amorphous calcium polyphosphate (polyP) microparticles (termed aCa-polyP-MP) on bone mineral forming cells/tissue was investigated in vitro and in vivo. The ACC particles (termed ACC-P10-MP) were prepared in the presence of Na-polyP. Only the combinations of polyP and ACC microparticles enhanced the proliferation rate of human mesenchymal stem cells (MSCs). Gene expression studies revealed that ACC causes an upregulation of the expression of the cell membrane-associated carbonic anhydrase IX (CA IX; formation of ACC), while the transcript level of the alkaline phosphatase (ALP; liberation of orthophosphate from polyP) changes only relatively little. In contrast, aCa-polyP-MP primarily induces ALP expression. If both components are applied together a strong stimulation of expression of both marker genes is observed. In order to investigate whether ACC also enhances bone regeneration induced by polyP in vivo, the particles were encapsulated into PLGA (poly(d,l-lactide-co-glycolide)) microspheres (diameter ~800 μm) and implanted into rat critical-size calvarial defects. The studies revealed that animals that received aCa-polyP-MP microspheres showed an increased rate of regeneration compared to β-tri-calcium phosphate (β-TCP) controls. This effect is even accelerated if microspheres with both aCa-polyP-MP and ACC-P10-MP (1 : 1 weight ratio) are applied, resulting in an almost complete restoration of the defect area after 12 weeks. qRT-PCR analyses of tissue sections through the regeneration zone with microspheres containing both aCa-polyP-MP and ACC-P10-MP revealed a significantly higher upregulation of expression of the marker genes compared to each of the components alone. The Young's moduli for microspheres containing aCa-polyP-MP (1.74 MPa) and aCa-polyP-MP/ACC-P10-MP (2.38 MPa) were markedly higher compared to β-TCP-controls (0.63 mPa). Our results show that the combined application of ACC and Ca-polyP (both in the amorphous state) opens new strategies for the development of regenerative implants for the reconstruction of bone defects.

Combination of calcium sulfate and simvastatin-controlled release microspheres enhances bone repair in critical-sized rat calvarial bone defects

Most allogenic bone graft substitutes have only osteoconductive properties. Developing new strategies to improve the osteoinductive activity of bone graft substitutes is both critical and practical for clinical application. Previously, we developed novel simvastatin-encapsulating poly(lactic-co-glycolic acid) microspheres (SIM/PLGA) that slowly release simvastatin and enhance fracture healing. In this study, we combined SIM/PLGA with a rapidly absorbable calcium sulfate (CS) bone substitute and studied the effect on bone healing in critical-sized calvarial bone defects in a rat model. The cytotoxicity and cytocompatibility of this combination was tested in vitro using lactate dehydrogenase leakage and a cell attachment assay, respectively. Combination treatment with SIM/PLGA and the CS bone substitute had no cytotoxic effect on bone marrow stem cells. Compared with the control, cell adhesion was substantially enhanced following combination treatment with SIM/PLGA and the CS bone substitute. In vivo, implantation of the combination bone substitute promoted healing of critical-sized calvarial bone defects in rats; furthermore, production of bone morphogenetic protein-2 and neovascularization were enhanced in the area of the defect. In summary, the combination of SIM/PLGA and a CS bone substitute has osteoconductive and osteoinductive properties, indicating that it could be used for regeneration of bone in the clinical setting.

Bone Morphogenetic Protein for the Healing of Tibial Fracture: A Meta-Analysis of Randomized Controlled Trials

PURPOSE

To review the evidence from RCTs on clinical outcomes and benefit of acute tibial fracture and nonunion treated with and without BMPs.

MATERIAL

We searched multiple databases (MEDLINE, EMABSE, BIOSIS and Cochrane central) as well as reference lists of articles and contacted authors. Evaluated outcomes included union rate, revision rate, hardware failure and infection. The weighted and standard mean difference (WMD and SMD) or the relative risk (RR) was calculated for continuous or dichotomous data respectively. The quality of the trial was assessed, and meta-analyses were performed with the Cochrane Collaboration's REVMAN 5.0 software.

RESULTS

Eight RCTs involving 1113 patients were included. For acute tibial fracture, BMP group was associated with a higher rate of union (RR, 1.16; 95% CI, 1.04 to 1.30) and a lower rate of revision (RR, 0.68; 95% CI, 0.54 to 0.85) compared with control group. No significant differences were found in rate of hardware failure and infection. The pooled RR for achieving union for tibial fracture nonunion was 0.98 (95% CI, 0.86 to 1.13). There was no significant difference between the two groups in the rate of revision (RR, 0.48; 95% CI, 0.13 to 1.85) and infection (RR, 0.61; 95% CI, 0.37 to 1.02).

CONCLUSION

Study on acute tibial fractures suggests that BMP is more effective that controls, for bone union and for decreasing the rate of surgical revision to achieve union. For the treatment of tibial fracture nonunion, BMP leads to similar results to as autogenous bone grafting. Finally, well-designed RCTs of BMP for tibial fracture treatment are also needed.

Overcoming translational challenges - The delivery of mechanical stimuli in vivo

Despite major medical advances, non-union bone fractures and skeletal defects continue to place significant burden on the patient, the clinicians and the healthcare system as a whole. Current bone substitute approaches are still limited in effectiveness and to date no adequate bone substitute material has been developed for routine clinical application. Tissue engineering presents a novel approach to tackling this clinical burden and developing an acceptable solution for the treatment of skeletal defects. Over the past three decades the field has evolved to appreciate the key biological, material and physical parameters influencing the development of a cell-based tissue engineered therapy and to create associated technologies to exploit such parameters. In recent years a number of therapies have started progressing along the pre-clinical pipeline to build a case for regulatory approval and ultimately clinical adoption. However, little emphasis has been given to the translational challenges faced when moving from "bench-to-bedside". One particular challenge lies in the delivery of functional mechanical stimuli to implanted cell populations to activate and promote osteogenic activities. This review introduces novel bio-magnetic approaches to overcoming this challenge.

Morphogenic Peptides in Regeneration of Load Bearing Tissues

Morphogenic proteins due to their short half-life require high doses of growth factors in regeneration of load bearing tissues which leads to undesirable side effects. These side effects include bone overgrowth, tumor formation and immune reaction. An alternative approach to reduce undesirable side effects of proteins in regenerative medicine is to use morphogenic peptides derived from the active domains of morphogenic proteins or soluble and insoluble components of the extracellular matrix of mineralized load bearing tissues to induce differentiation of progenitor cells, mineralization, maturation and bone formation. In that regard, many peptides with osteogenic activity have been discovered. These include peptides derived from bone morphogenic proteins (BMPs), those based on interaction with integrin and heparin-binding receptors, collagen derived peptides, peptides derived from other soluble ECM proteins such as bone sialoprotein and enamel matrix proteins, and those peptides derived from vasculoinductive and neuro-inductive proteins. Although these peptides show significant osteogenic activity in vitro and increase mineralization and bone formation in animal models, they are not widely used in clinical orthopedic applications as an alternative to morphogenic proteins. This is partly due to the limited availability of data on structure and function of morphogenic peptides in physiological medium, particularly in tissue engineered scaffolds. Due to their amphiphilic nature, peptides spontaneously self-assemble and aggregate into micellar structures in physiological medium. Aggregation alters the sequence of amino acids in morphogenic peptides that interact with cell surface receptors thus affecting osteogenic activity of the peptide. Aggregation and micelle formation can dramatically reduce the active concentration of morphogenic peptides with many-fold increase in peptide concentration in physiological medium. Other factors that affect bioactivity are the non-specific interaction of morphogenic peptides with lipid bilayer of the cell membrane, interaction of the peptide with cell surface receptors that do not specifically induce osteogenesis leading to less-than-optimal osteogenic activity of the peptide, and less-than-optimal interaction of the peptide with osteogenic receptors on the cell surface. Covalent attachment or physical interaction with the tissue engineered matrix can also alter the bioactivity of morphogenic peptides and lead to a lower extent of osteogenesis and bone formation. This chapter reviews advances in discovery of morphogenic peptide, their structural characterization, and challenges in using morphogenic peptides in clinical applications as growth factors in tissue engineered devices for regeneration of load bearing tissues.

Bone tissue engineering via nanostructured calcium phosphate biomaterials and stem cells

Tissue engineering is promising to meet the increasing need for bone regeneration. Nanostructured calcium phosphate (CaP) biomaterials/scaffolds are of special interest as they share chemical/crystallographic similarities to inorganic components of bone. Three applications of nano-CaP are discussed in this review: nanostructured calcium phosphate cement (CPC); nano-CaP composites; and nano-CaP coatings. The interactions between stem cells and nano-CaP are highlighted, including cell attachment, orientation/morphology, differentiation and in vivo bone regeneration. Several trends can be seen: (i) nano-CaP biomaterials support stem cell attachment/proliferation and induce osteogenic differentiation, in some cases even without osteogenic supplements; (ii) the influence of nano-CaP surface patterns on cell alignment is not prominent due to non-uniform distribution of nano-crystals; (iii) nano-CaP can achieve better bone regeneration than conventional CaP biomaterials; (iv) combining stem cells with nano-CaP accelerates bone regeneration, the effect of which can be further enhanced by growth factors; and (v) cell microencapsulation in nano-CaP scaffolds is promising for bone tissue engineering. These understandings would help researchers to further uncover the underlying mechanisms and interactions in nano-CaP stem cell constructs in vitro and in vivo, tailor nano-CaP composite construct design and stem cell type selection to enhance cell function and bone regeneration, and translate laboratory findings to clinical treatments.