Resultados estéticos en defectos nasales posquirúrgicos regenerados con fibrina autóloga rica en plaquetas y leucocitos / Aesthetic results in post-surgical nasal defects regenerated with autologous platelet- and leukocyte-rich fibrin

Introducción: En la reconstrucción de los defectos cutáneos nasales se han utilizado varias técnicas a nivel mundial. Novedosas prácticas utilizan los concentrados plaquetarios por sus propiedades moduladoras y favorecedoras de la regeneración tisular. Objetivo: Determinar los resultados estéticos asociados al uso de la membrana de fibrina autóloga rica en plaquetas y leucocitos, para la regeneración de defectos cutáneos nasales posquirúrgicos. Métodos: Se realizó un estudio cuasiexperimental, longitudinal y prospectivo en el Servicio de Cirugía Maxilofacial del Hospital Universitario "Arnaldo Milián Castro" de la ciudad de Santa Clara, Villa Clara, Cuba, desde septiembre de 2015 hasta junio de 2019. Se efectuó un muestreo intencional, no probabilístico, de 31 pacientes. A partir de una donación de sangre del paciente, se obtuvo una membrana de fibrina rica en plaquetas y leucocitos, la que fue suturada en el defecto nasal posquirúrgico. Se estudiaron variables como el resultado estético, evaluado sobre la base de parámetros como la elasticidad, el color, el volumen y la superficie. Resultados: La edad media fue 62,71 ± 11,09 años y el 61,29 por ciento de la muestra correspondió al sexo masculino. Mostraron un buen resultado estético el 90,32 por ciento de los pacientes, lo que se asoció de forma significativa al grado de epitelización. Conclusiones: Se obtuvo un buen resultado estético en los pacientes donde se utilizó la membrana de fibrina autóloga rica en plaquetas y leucocitos, con independencia de la presencia de diabetes mellitus y hábitos tóxicos. El resultado estético estuvo asociado significativamente al grado de epitelización y a la edad(AU)

Introduction: In the reconstruction of nasal skin defects, several techniques have been used worldwide. Innovative practices use platelet concentrates for their modulating properties and favoring tissue regeneration. Objective: Determine the aesthetic results associated with the use of autologous fibrin rich in platelets and leukocytes, for the regeneration of post-surgical nasal skin defects. Methods: A quasi-experimental, longitudinal and prospective study was conducted in the Maxillofacial Surgery Service of "Arnaldo Milián Castro" University Hospital in the city of Santa Clara, Villa Clara province, Cuba, from September 2015 to June 2019. An intentional, non-probabilistic sampling of 31 patients was carried out. From a blood donation from the patient, a fibrin membrane rich in platelets and leukocytes was obtained, which was sutured in the post-surgical nasal defect. Variables such as the aesthetic result were studied, evaluated on the basis of parameters such as elasticity, color, volume and surface. Results: The mean age was 62.71 ± 11.09 years and 61.29 percent of the sample corresponded to the male sex. A good aesthetic result was shown by 90.32 percent of the patients, which was significantly associated with the degree of epithelialization. Conclusions: A good aesthetic result was obtained in patients where the fibrin membrane rich in leukocytes and autologous platelets was used, regardless of the presence of diabetes mellitus and toxic habits. The aesthetic result was significantly associated with the degree of epithelialization and age(AU)

The role of bone marrow edema on osteochondral lesions of the talus.

BACKGROUND: To assess the functional and radiological outcomes after arthroscopic talus autologous matrix-induced chondrogenesis (AT-AMIC®) in 2 groups: patients with and without bone marrow edema (BME). METHODS: Thirty-seven patients of which 24 without edema (GNE) and 13 with edema (GE) were evaluated. All patients were treated with AT-AMIC® repair for symptomatic osteochondral talar lesion. Clinical and radiological parameters were evaluated with VAS score for pain, AOFAS and SF-12 at T0 (preoperatively), T1 (6 months), T2 (12 months), T3 (24 months) and MRI and CT-scan at T0, T1, T2 and T3. RESULTS: No patients were lost to the final follow-up. In both groups we found a significant difference for clinical and radiological parameters with ANOVA for repeated measures through four time points (p<0.001). In GNE, AOFAS improved significantly at each follow-up (p<0.05); while CT and MRI showed a significant reduction in lesion size between T1 and T2 and T2 and T3 (p<0.05). In GE, AOFAS improved significantly between T0 and T1 and T2 and T3 (p<0.05); lesion size, measured with CT, decreased between T1 and T2 (p<0.05), while with MRI the lesion showed a reduction at each follow-up (p<0.05). Lesion size was significantly higher both in MRI and CT in GE compared to GNE (p<0.05). In GNE no patients presented edema at T3, while in GE only 23.08% of the patients presented edema at T3. CONCLUSIONS: The study revealed that osteochondral lesions of the talus were characterized by bigger size both in MRI and CT in patients with edema. We conclude that AT-AMIC® can be considered a safe and reliable procedure that allows effective healing, regardless of edema and more than half of patients did not present edema six months after surgery.

Clinical and biometrical 12-month follow-up in patients after reconstruction of the sural nerve biopsy defect by the collagen-based nerve guide Neuromaix.

Many new strategies for the reconstruction of peripheral nerve injuries have been explored for their effectiveness in supporting nerve regeneration. However only a few of these materials were actually clinically evaluated and approved for human use. This open, mono-center, non-randomized clinical study summarizes the 12-month follow-up of patients receiving reconstruction of the sural nerve biopsy defect by the collagen-based nerve guide Neuromaix. Neuromaix was implanted as a micro-structured, two-component scaffold bridging 20-40 mm nerve defects after sural nerve biopsy in twenty patients (eighteen evaluated, two lost in follow-up). Safety of the material was evaluated by clinical examination of wound healing. Performance was assessed by sensory testing of modalities, pain assessment, and palpation for the Hoffmann-Tinel's sign as well as demarcating the asensitive area at each follow-up visit. Every patient demonstrated uneventful wound healing during the complete 12-month time course of the study. Two patients reported complete return of sensation, whereas eleven out of eighteen patients reported a positive Hoffmann-Tinel's sign at the lower leg with simultaneous reduction of the asensitive area by 12 months. Our data show that Neuromaix can be implanted safely in humans to bridge sural nerve gaps. No procedure-related, adverse events, or severe adverse events were reported. These first clinical data on Neuromaix provide promising perspectives for the bridging of larger nerve gaps in combined nerves, which should be investigated more through extensive, multi-center clinical trials in the near future.

The transpedicular surgical approach for the development of intervertebral disc targeting regenerative strategies in an ovine model.

PURPOSE: To investigate the suitability of the transpedicular approach (TPA) in a sheep model of IVD regenerative strategies METHODS: 24 IVD from four sheep were used. TPA and biopsies of the Nucleus pulposus (NP) were performed in 18 IVD (6 IVD control). Seven discographies were performed to assess the feasibility of injecting contrast agent. MRI, micro-CT scan, and histological analyses were performed and the accuracy of the TPA was evaluated. The effects on the vertebra and endplates were analyzed. RESULTS: 83% of our biopsies or injections were located in the NP. Osseous fragments in IVD were observed in 50%. We observed two cases (11%) of rostral endplate fracture and five cases (27%) of breaching of the cortical pedicle and encroachment into the spinal canal. Two cases of perivertebral venous embolism and two of backflow through the canal of the TPA inside the vertebra were noted. Significant damage occurred to the bone structure of the vertebra and to the rostral endplate on which the IVD had been inserted. CONCLUSIONS: TPA induces damage to the endplates, and it may lead to neurological impairment and leakage of injected materials into the systemic circulation. These adverse effects must be fully considered before proceeding with TPA for IVD regenerative strategies.

A systematic review of animal and clinical studies on the use of scaffolds for urethral repair.

Replacing urethral tissue with functional scaffolds has been one of the challenging problems in the field of urethra reconstruction or repair over the last several decades. Various scaffold materials have been used in animal studies, but clinical studies on use of scaffolds for urethral repair are scarce. The aim of this study was to review recent animal and clinical studies on the use of different scaffolds for urethral repair, and to evaluate these scaffolds based on the evidence from these studies. PubMed and OVID databases were searched to identify relevant studies, in conjunction with further manual search. Studies that met the inclusion criteria were systematically evaluated. Of 555 identified studies, 38 were included for analysis. It was found that in both animal and clinical studies, scaffolds seeded with cells were used for repair of large segmental defects of the urethra, such as in tubular urethroplasty. When the defect area was small, cell-free scaffolds were more likely to be applied. A lot of pre-clinical and limited clinical evidence showed that natural or artificial materials could be used as scaffolds for urethral repair. Urinary tissue engineering is still in the immature stage, and the safety, efficacy, cost-effectiveness of the scaffolds are needed for further study.

Assessment of the Safety of Chondrocyte Sheet Implantation for Cartilage Regeneration.

We have previously studied the effects of chondrocyte sheets on the repair and regeneration of articular cartilage by using temperature-responsive culture inserts. On the basis of this work, we succeeded in rapid fabrication of chondrocyte sheets with the use of a coculture method in which inserts were placed between synoviocytes and chondrocytes. Treatment of cartilage defects using layered chondrocyte sheets promotes repair and regeneration; this method is compatible with in vivo osteoarthritis models that reproduce partial-thickness defects. In human stem cell clinical research guidelines, the Ministry of Health, Labour and Welfare (MHLW) approved several applications related to this technology. Indeed, its translation to a clinical setting is already yielding favorable results. In this study, we evaluated the risk of tumorigenesis associated with this treatment and characterized the dynamics of biological processes associated with the posttransplantation cell sheets in vivo. Furthermore, we also confirmed the safety of the procedure by using array comparative genomic hybridization (array CGH) and G-band staining to screen for deleterious genetic aberrations during prolonged subculture of cells. The safety of chondrocytes that were cultured for longer than normal was confirmed by the array CGH and G-band staining results. In addition, tumorigenicity testing confirmed that culture chondrocyte sheets are not tumorigenic. Furthermore, from the evaluation of bioluminescence imaging following implantation of the cell sheets, it was confirmed that the transplanted chondrocytes and synoviocytes remained in the knee joint and did not transfer elsewhere over time. We believe that the technique used in this study is a highly useful method for evaluating the safety of not only chondrocytes but also extensive subculturing in general.

Oestrogen receptor alpha expression in neovaginal tissue of women following modified Abbé-McIndoe technique and in premenopausal women.

The aim of the study was to compare the expression of oestrogen receptor alpha (ERα) in neovaginal tissue of patients with vaginal agenesis following neovaginoplasty using regenerated, oxidised cellulose in premenopausal women. A prospective, observational case-control study was performed on eight patients with vaginal agenesis following modified Abbé-McIndoe neovaginoplasty and 10 control premenopausal women following benign gynaecologic surgery. 6F11 monoclonal antibody was used to determine ERα expression in the vaginal mucosa. Quantitative and qualitative evaluations were performed, respectively, in vaginal epithelium and stroma. The thickness of the vaginal epithelium was determined as the vertical distance between the basal layer cells and the apical surface of the superficial layer. The percentage of ERα-expressing cells was higher in the control group, except in the superficial zone of the epithelium. In the stromal tissue, ERα was detected in only one patient from the neovagina group compared with nine women in the control group. The neovagina group had a statistically thinner epithelium. Our study suggests that women with vaginal agenesis following modified Abbé-McIndoe neovaginoplasty using regenerated oxidised, cellulose experience relatively local hypo-oestrogenism in the first year after surgery, with repercussion in vaginal trophism.

Plasma treatment for improving cell biocompatibility of a biodegradable polymer scaffold for vascular graft applications.

Biodegradable synthetic scaffolds are being evaluated by many groups for the application of vascular tissue engineering. In addition to the choice of the material and the structure of the scaffold, tailoring the surface properties can have an important effect on promoting adequate tissue regeneration. The objective of this study was to evaluate the effect of an increased hydrophilicity of a polycaprolactone vascular graft by treatment with a cold air plasma. To this end, treated and untreated scaffolds were characterized, evaluated in vitro with smooth muscle cells, and implanted in vivo in the rat model for 3 weeks, both in the subcutaneous location and as an aortic replacement. The plasma treatment significantly increased the hydrophilicity of the scaffold, with complete wetting after a treatment of 60 sec, but did not change fiber morphology or mechanical properties. Smooth muscle cells cultured on plasma treated patches adopt a spread out morphology compared to a small, rounded morphology on untreated patches. Subcutaneous implantation revealed a low foreign body reaction for both types of scaffolds and a more extended and dense cellular infiltrate in the plasma treated scaffolds. In the vascular position, the plasma treatment induced a better cellularization of the graft wall, while it did not affect endothelialization rate or intimal hyperplasia. Plasma treatment is therefore an accessible tool to easily increase the biocompatibility of a scaffold and accelerate tissue regeneration without compromising mechanical strength, which are valuable advantages for vascular tissue engineering.

Design and characterization of core-shell mPEG-PLGA composite microparticles for development of cell-scaffold constructs.

Appropriate scaffolds capable of providing suitable biological and structural guidance are of great importance to generate cell-scaffold constructs for cell-based tissue engineering. The aim of the present study was to develop composite microparticles with a structure to provide functionality as a combined drug delivery/scaffold system. Composite microparticles were produced by incorporating either alginate/dermatan sulfate (Alg/DS) or alginate/chitosan/dermatan sulfate (Alg/CS/DS) particles in mPEG-PLGA microparticles using coaxial ultrasonic atomization. The encapsulation and distribution of Alg/DS or Alg/CS/DS particles in the mPEG-PLGA microparticles were significantly dependent on the operating conditions, including the flow rate ratio (Qout/Qin) and the viscosity of the polymer solutions (Vout, Vin) between the outer and the inner feeding channels. The core-shell composite microparticles containing the Alg/DS particles or the Alg/CS/DS particles displayed 40% and 65% DS release in 10 days, respectively, as compared to the DS directly loaded microparticles showing 90% DS release during the same time interval. The release profiles of DS correlate with the cell proliferation of fibroblasts, i.e. more sustainable cell growth was induced by the DS released from the core-shell composite microparticles comprising Alg/CS/DS particles. After seeding fibroblasts onto the composite microparticles, excellent cell adhesion was observed, and a successful assembly of the cell-scaffold constructs was induced within 7 days. Therefore, the present study demonstrates a novel strategy for fabrication of core-shell composite microparticles comprising additional particulate drug carriers in the core, which provides controlled delivery of DS and favorable cell biocompatibility; an approach to potentially achieve cell-based tissue regeneration.

Biocompatibility and osteoconduction of macroporous silk fibroin implants in cortical defects in sheep.

The goal of the presented study was to compare the biocompatibility and cellular responses to porous silk fibroin (SF) scaffolds produced in a water-based (UPW) or a solvent based process (HFIP) using two different SF sources. For that reason, four different SF scaffolds were implanted (n=6) into drill hole defects in the cancellous bone of the sheep tibia and humerus. The scaffolds were evaluated histologically for biocompatibility, cell-material interaction, and cellular ingrowth. New bone formation was observed macroscopically and histologically at 8 weeks after implantation. For semiquantitative evaluation, the investigated parameters were scored and statistically analyzed (factorial ANOVA). All implants showed good biocompatibility as evident by low infiltration of inflammatory cells and the absent encapsulation of the scaffolds in connective tissue. Multinuclear foreign body giant cells (MFGCs) and macrophages were present in all parts of the scaffold at the material surface and actively degrading the SF material. Cell ingrowth and vascularization were uniform across the scaffold. However, in HFIP scaffolds, local regions of void pores were present throughout the scaffold, probably due to the low pore interconnectivity in this scaffold type in contrast to UPW scaffolds. The amount of newly formed bone was very low in both scaffold types but was more abundant in the periphery than in the center of the scaffolds and for HFIP scaffolds mainly restricted to single pores.

Adipose-derived stem cells combined with neuregulin-1 delivery systems for heart tissue engineering.

Myocardial infarction (MI) is the leading cause of death worldwide, and extensive research has therefore been performed to find a cure. Neuregulin-1 (NRG) is a growth factor involved in cardiac repair after MI. We previously described how biocompatible and biodegradable microparticles, which are able to release NRG in a sustained manner, represent a valuable approach to avoid problems related to the short half-life after systemic administration of proteins. The effectiveness of this strategy could be improved by combining NRG with several cytokines involved in cardiac regeneration. The present study investigates the potential feasibility of using NRG-releasing particle scaffold combined with adipose-derived stem cells (ADSC) as a multiple growth factor delivery-based tissue engineering strategy for implantation in the infarcted myocardium. NRG-releasing particle scaffolds with a suitable size for intramyocardial implantation were prepared by TROMS. Next, ADSC were adhered to particle scaffolds and their potential for heart administration was assessed in a MI rat model. NRG was successfully encapsulated reaching encapsulation efficiencies of 92.58 ± 3.84%. NRG maintained its biological activity after the microencapsulation process. ADSCs adhered efficiently to particle scaffolds within a few hours. The ADSC-cytokine delivery system developed proved to be compatible with intramyocardial administration in terms of injectability through a 23-gauge needle and tissue response. Interestingly, ADSC-scaffolds were present in the peri-infarted tissue 2 weeks after implantation. This proof of concept study provides important evidence required for future effectiveness studies and for the translation of this approach.

Host reaction to poly(2-hydroxyethyl methacrylate) scaffolds in a small spinal cord injury model.

Tissue engineered scaffolds and matrices have been investigated over the past decade for their potential in spinal cord repair. They provide a 3-D substrate that can be permissive for nerve regeneration yet have other roles including neuroprotection, altering the inflammatory cascade and mechanically stabilizing spinal cord tissue after injury. In this study we investigated very small lesions (approx. 0.25 µL in volume) of the dorsal column into which a phase-separated poly(2-hydroxyethyl methacrylate) hydrogel scaffold is implanted. Using fluorescent immunohistochemistry to quantify glial scarring, the poly(2-hydroxyethyl methacrylate) scaffold group showed reduced intensity compared to lesion controls for GFAP and the chondroitin sulfate proteoglycan neurocan after 6 days. However, the scaffold and tissue was also pushed dorsally after 6 days while the scaffold was not integrated into the spinal cord after 28 days. Overall, this small-lesion spinal cord injury model provided information on the host tissue reaction of a TE scaffold while reducing animal discomfort and care.

Micro-structural geometry of thin films intended for the inner lumen of nerve conduits affects nerve repair.

Damage to peripheral nerves can cause significant motor or sensory injuries. In serious cases, a nerve is sacrificed from another part of the body to repair a damaged nerve (autograft). The development of biodegradable polymer conduits may offer an alternative to autografts. This study investigated the surface topography and mechanical properties of smooth, pitted and grooved structures of ultra-thin poly (ε-caprolactone)/poly lactic acid blended, solvent-cast films. We have investigated the effect of the groove shape on cell morphology and alignment. Photolithography and dry/wet etching was used to develop patterned silicon substrates with grooves with accurate geometries (V shaped, sloped walls and square shaped). Using a neural cell line (NG108-15), in vitro experiments confirmed good cell attachment and proliferation on all the polymer scaffolds. Imaging techniques demonstrated that there was different cellular responses and morphology according to the shape of the groove. Studies showed that the geometry, particularly the angle of the slope and the space between grooves, affected cellular responses. In addition, biomechanical studies showed that the patterned films had excellent mechanical properties and were stronger than the natural nerve. The conduit tubes were made by rolling the films around a mandrel and using a thermal welding technique to join the edges. The promising biomechanical and in vitro results demonstrate that nerve cell responses are affected by the shape of longitudinal grooves, and particularly by the angle of the slope of the groove walls.

Lymph node transfer and perinodal lymphatic growth factor treatment for lymphedema.

OBJECTIVE: Our objective was to define the optimal growth factor treatment to be used in combination with lymph node transfer to normalize lymphatic vascular anatomy. BACKGROUND: In the lymph node transfer method, lymphatic anastomoses are expected to form spontaneously. However, lymphangiogenic growth factor therapies have shown promising results in preclinical models of lymphedema. METHODS: The inguinal lymphatic vasculature of pigs was surgically destroyed around the inguinal lymph node. To enhance the regrowth of the lymphatic network in the defected area, adenoviral vascular endothelial growth factor C (VEGF-C) was administered intranodally or perinodally. Control animals received injections of saline or control vector. The lymphangiogenic effect of the growth factor therapy and any potential adverse effects associated with the 2 alternative delivery routes were examined 2 months postoperatively. RESULTS: Both routes of growth factor administration induced robust growth of lymphatic vessels and helped to preserve the structure of the transferred lymph nodes in comparison with the controls. The lymph nodes of the control treated animals regressed in size and their nodal structure was partly replaced by fibro-fatty scar tissue. Intranodally injected adenoviral VEGF-C and adenoviral vector encoding control gene LacZ induced macrophage accumulation inside the node, whereas perinodal administration of VEGF-C did not have this adverse effect. CONCLUSIONS: Lymphangiogenic growth factors improve lymphatic vessel regeneration and lymph node function after lymph node transfer. The perinodal route of delivery provides a basis for future clinical trials in lymphedema patients.

Tendon regeneration in human and equine athletes: Ubi Sumus-Quo Vadimus (where are we and where are we going to)?

Tendon injuries are one of the most common orthopaedic problems in both human and equine athletes. When a damaged tendon heals naturally, it loses a substantial part of the original strength and elasticity. Therefore, tendons recover structurally (reparation) but not functionally (regeneration) after conservative medical or surgical treatment. Since the structure and matrix composition of human and equine tendons share many similarities, the nature of tendon injuries are also strongly comparable in both species. Therefore, the evaluation of regenerative therapies in horses may have applications for future human medicine and vice versa. The current review focuses briefly on the physiology of human and equine tendon in order to better comprehend the modus operandi of this structure under pathophysiological circumstances. In addition, the reparative effects of conservative medical and surgical interventions are discussed concisely, and an extensive overview is given on the regenerative therapies that are currently being explored. For the latter, the results of equine clinical studies might prove invaluable for gaining additional insights into the treatment of human tendinopathies, since not all of these novel regenerative therapies have been evaluated in humans yet.

Experience of using the bioresorbable copolyester poly(DL-lactide-ε-caprolactone) nerve conduit guide Neurolac™ for nerve repair in peripheral nerve defects: report on a series of 28 lesions.

Synthetic nerve guides are occasionally used to repair nerve defects. The aim of the present work was to analyse the results of Neurolac™ use in a series of 23 patients. We operated on 28 nerve lesions located on various sites: arm (n = 1), elbow (n = 5), forearm (n = 4), wrist (n = 2), palm (n = 5), fingers (n = 11). Defects averaged 11.03 mm and were repaired using Neurolac™. After an average of 21.9 months' follow up (3-45 months), subjective criteria (pain, cold intolerance, Quick DASH) and objective criteria (strength, Weber and Semmes-Weinstein sensitivity tests) were compared with the contralateral side. Average pain score was 2.17/10. Cold intolerance was reported in fifteen cases. Quick DASH averaged 35.37/100. Grip strength averaged 64.62% of the contralateral side. As regards sensitivity, the difference between the two sides was 18.89 on Weber's test, and 46.92 on Semmes-Weinstein. Defect size did not affect the outcomes. We observed eight complications the most serious being two fistulizations of the Neurolac™ device close to a joint and one neuroma. Neurolac™ presents some advantages (resorption, semi-permeability, emergency use, tenseless repair) like other synthetic guides used for nerve regeneration and its transparency constitutes an added benefit. However, some difficulty in its handling and its expensiveness represent real disadvantages. Our results are not in favour of its use in repairing hand nerve defects.

Dual-purpose bone grafts improve healing and reduce infection.

OBJECTIVE: To determine if a dual-purpose bone graft can regenerate bone and reduce infection in highly contaminated bone critical size defects in rats. METHODS: Biodegradable polyurethane (PUR) scaffolds were loaded with recombinant human bone morphogenetic protein-2 (BMP-2) and vancomycin (Vanc). The release kinetics of the BMP-2 were tuned to take advantage of its mechanism of action (ie, an initial burst to recruit cells and sustained release to induce differentiation of the migrating cells). The Vanc release kinetics were designed to protect the graft from contamination until it is vascularized by having a burst for a week and remaining well over the minimum inhibitory concentration for Staphylococcus aureus for 2 months. The bone regeneration and infection reduction capability of these dual-purpose grafts (PUR+Vanc+BMP-2) were compared with collagen sponges loaded with BMP-2 (collagen+BMP-2) and PUR+BMP-2 in infected critical size rat femoral segmental defects. RESULTS: The dual-delivery approach resulted in substantially more new bone formation and a modest improvement in infection than PUR+BMP-2 and collagen+BMP-2 treatments. CONCLUSIONS: The PUR bone graft is injectable, provides a more sustained release of BMP-2 than the collagen sponge, and can release antibiotics for more than 8 weeks. Thus, the dual-delivery approach may improve patient outcomes of open fractures by protecting the osteoinductive graft from colonization until vascularization occurs. In addition, the more optimal release kinetics of BMP-2 may reduce nonunions and the amount of growth factor required.