Effects of gamma irradiation on osteoinduction associated with demineralized bone matrix

Effect of gamma and Ultraviolet-C sterilization on BMP-7 level of indigenously prepared demineralized freeze-dried bone allograft

The presence of bone morphogenetic proteins in demineralized freeze-dried bone allograft (DFDBA) are responsible for developing hard tissues in intraosseous defects. The most common mode of sterilization of bone allografts, i.e., Gamma rays, have dramatic effects on the structural and biological properties of DFDBA, leading to loss of BMPs. Ultraviolet-C radiation is a newer approach to sterilize biodegradable scaffolds, which is simple to use and ensures efficient sterilization. However, UV-C radiation has not yet been effectively studied to sterilize bone allografts. This study aimed to compare and evaluate the effectiveness of Gamma and Ultraviolet-C rays in sterilizing indigenously prepared DFDBA and assess their effect on the quantity of BMP-7 present in the allograft. DFDBA samples from non-irradiated, gamma irradiated, and UV-C irradiated groups were tested for BMP-7 level and samples sterilized with gamma and UV-C rays were analysed for sterility testing. The estimated mean BMP-7 level was highest in non-irradiated DFDBA samples, followed by UV-C irradiated, and the lowest in gamma irradiated samples. Our study concluded that UV-C rays effectively sterilized DFDBA as indicated by negative sterility test and comprised lesser degradation of BMP-7 than gamma irradiation.

Effects of processing and gamma radiation on mechanical properties and organic composition of frozen, freeze-dried and demineralised human cortical bone allograft

Bone processing and radiation were reported to influence mechanical properties of cortical bones due in part to structural changes and denaturation of collagen composition. This comparative study was to determine effects of bone processing on mechanical properties and organic composition, and to what extent the radiation damaging after each processing. Human femur cortical bones were processed by freezing, freeze-drying and demineralisation and then gamma irradiated at 5, 15, 20, 25 and 50 kGy. In the compression test, freeze drying significantly decreased the Young's Modulus by 15%, while demineralisation reduced further by 90% (P < 0.05) when compared to the freezing. Only demineralisation significantly reduced ultimate strength of bone by 93% (P < 0.05). In the bending test, both freeze drying and demineralisation significantly reduced the ultimate strength and the work to failure. Radiation at 25 kGy showed no effect on compression for ultimate strength in each processing group. However, high dose of 50 kGy significantly reduced bending ultimate strength by 47% in demineralisation group. Alterations in collagen in bones irradiated at 25 and 50 kGy showed by the highest peak of the amide I collagen in the Fourier Transfer Infra-Red spectra indicating more collagen was exposed after calcium was removed in the demineralised bone, however radiation showed no effect on the collagen crosslink. The study confirmed that demineralisation further reduced the ability to resist deformation in response to an applied force in freeze-dried bones due to calcium reduction and collagen composition. Sterilisation dose of 25 kGy has no effect on mechanical properties and collagen composition of the processed human cortical bone.

Acetabular fixation in total hip arthroplasty in the previously irradiated pelvis: a review of basic science and clinical outcomes

Radiation therapy is a common primary, adjuvant, or palliative treatment for many intrapelvic tumors, including primary gastrointestinal, genitourinary, and hematopoietic tumors, as well as metastatic disease to bone. Radiation has well documented microbiologic and clinical effects on bone ranging from radiation osteitis to early degenerative changes of the hip joint and avascular necrosis of the femoral head. Conventional total hip arthroplasty methods have demonstrated high rates of failure in this population, with historical data describing aseptic loosening rates as high as 44-52%, as radiation have been shown to preferentially diminish osteoblast and osteocyte number and function and limit capacity for both cement interdigitation and biologic bony ingrowth. A review of the clinical literature suggests that patients with prior pelvic irradiation are at higher risk for both septic and aseptic loosening of acetabular components, as well as lower postoperative Harris Hip Score (HHS) when compared to historical controls. With limited evidence, trabecular metal shells with multi-screw fixation and cemented polyethene liners, as well as cemented cup-cage constructs both appear to be durable acetabular fixation options, though the indications for each remains elusive. Further prospective data are needed to better characterize this difficult clinical problem.

Osteocyte apoptosis, bone marrow adiposity and fibrosis in the irradiated human mandible

Purpose

To assess the effect of radiation therapy on osteocyte apoptosis, osteocyte death, and bone marrow adipocytes in the human mandible and its contribution to the pathophysiology of radiation damage to the mandibular bone.

Methods and Materials

Mandibular cancellous bone biopsies were taken from irradiated patients and nonirradiated controls. Immunohistochemical detection of cleaved caspase-3 was performed to visualize apoptotic osteocytes. The number of apoptotic osteocytes per bone area and per total amount of osteocytes, osteocytes per bone area, and empty lacunae per bone area were counted manually. The percentage fibrotic tissue and adipose tissue per bone marrow area, the percentage bone marrow of total area, and the mean adipocyte diameter (μm) was determined digitally from adjacent Goldner stained sections.

Results

Biopsies of 15 irradiated patients (12 men and 3 women) and 7 nonirradiated controls (5 men and 2 women) were assessed. In the study group a significant increase was seen in the number of empty lacunae, the percentage of adipose tissue of bone marrow area, and the adipocyte diameter. There was no significant difference in bone marrow fibrosis nor apoptotic osteocytes between the irradiated group and the controls.

Conclusions

Irradiation alone does not seem to induce excessive bone marrow fibrosis. The damage to bone mesenchymal stem cells leads to increased marrow adipogenesis and decreased osteoblastogenic potential. Early osteocyte death resulting in avital persisting bone matrix with severely impaired regenerative potential may contribute to the vulnerability of irradiated bone to infection and necrosis.

Effect of Gamma Irradiation on the Osteoinductivity of Demineralized Dentin Matrix for Allografts: A Preliminary Study

Demineralized dentin matrix (DDM) treated with gamma irradiation (GR) has shown promising results as an allograft without any adverse effects in in vivo and clinical studies. The purpose of this study was to evaluate the effects of 15 and 25 kGy GR on the osteoinductive properties of DDM at extra-skeletal sites. As a control group, non-irradiated DDM powder was implanted into the right subcutaneous tissues of the dorsal thigh muscles of 20 nude mice. DDM powder irradiated with 15 and 25 kGy was implanted into the left side. After two and four weeks, the bone mineral density (BMD) was measured with dual-energy X-ray absorptiometry. After confirming osteoblast- and osteoclast-specific activities by alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRAP) staining, a histological analysis was performed to measure the new bone formation and the number of osteoblasts and osteoclast-like cells on the surface of the DDMs. Histomorphometry was used to calculate the new bone formation area on the surface of the DDM particles (DDMs). The BMD in all the groups increased from two and four weeks without statistically significant differences. The osteoblasts were dominantly activated on DDM without GR, and DDM treated with 25 kGy compared to DDM treated with 15 kGy. Among the groups, new bone formation was identified in all the groups at each time point. In conclusion, GR at doses of 15 and 25 kGy does not affect the osteoinductive properties of DDM powder.

Magnesium cationic cue enriched interfacial tissue microenvironment nurtures the osseointegration of gamma-irradiated allograft bone

Regardless of the advancement of synthetic bone substitutes, allograft-derived bone substitutes still dominate in the orthopaedic circle in the treatments of bone diseases. Nevertheless, the stringent devitalization process jeopardizes their osseointegration with host bone and therefore prone to long-term failure. Hence, improving osseointegration and transplantation efficiency remains important. The alteration of bone tissue microenvironment (TME) to facilitate osseointegration has been generally recognized. However, the concept of exerting metal ionic cue in bone TME without compromising the mechanical properties of bone allograft is challenging. To address this concern, an interfacial tissue microenvironment with magnesium cationc cue was tailored onto the gamma-irradiated allograft bone using a customized magnesium-plasma surface treatment. The formation of the Mg cationic cue enriched interfacial tissue microenvironment on allograft bone was verified by the scanning ion-selective electrode technique. The cellular activities of human TERT-immortalized mesenchymal stem cells on the Mg-enriched grafts were notably upregulated. In the animal test, superior osseointegration between Mg-enriched graft and host bone was found, whereas poor integration was observed in the gamma-irradiated controls at 28 days post-operation. Furthermore, the bony in-growth appeared on magnesium-enriched allograft bone was significant higher. The mechanism possibly correlates to the up-regulation of integrin receptors in mesenchymal stem cells under modified bone TME that directly orchestrate the initial cell attachment and osteogenic differentiation of mesenchymal stem cells. Lastly, our findings demonstrate the significance of magnesium cation modified bone allograft that can potentially translate to various orthopaedic procedures requiring bone augmentation.

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A modified interfacial Mg TME was tailored onto the GI allograft bone matrix without compromising the mechanical properties.

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The SIET were applied to recognize the Mg²⁺-cue enriched interfacial TME on the surface of the Mg-treated bone allograft.

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The rodent model that is analogous to the clinical use of allograft bone were applied to charaterize the osseointegration.

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The boundary of the Mg-enriched allograft bone was already unable to be identified and become homogeneous at D28 post-op.

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The Mg²⁺-cue enriched interfacial TME is able to convince the upregulation of several integrin receptors of MSCs.

PEGylated Coating Affects DBM Osteoinductivity In Vivo by Changing Inflammatory Responses

PEGylation is a widely used modification in device coating or drug delivery by combing materials with poly(ethylene glycol) (PEG). In the present study, a well-established rat ectopic bone formation model was used to elucidate how PEGylated coating affects demineralized bone matrix (DBM) osteoinductivity in vivo by changing the inflammation events at the early phase of implantation. A range of cell-matrix interactions was characterized at the cellular and functional levels, including growth factor activity and kinetics, immune cell migration and activation, and bone formation in vivo. After 28 days, DBM's bone formation potential decreased in groups with increasing PEG concentration in the gelatin carrier. The increasing PEG concentration did not affect DBM's osteoinductive growth factor release or activity. However, increasing PEG cross-linking concentration resulted in decreased DBM-related early phase inflammatory reactions, reduced neutrophil infiltration, decreased coating material degradation, lowered the total number and active mast cells, and decreased CD80+ macrophage expression. Understanding and controlling cell-material responses may improve the design and development of functional medical devices.

In vitro analysis of the influence of mineralized and EDTA-demineralized allogenous bone on the viability and differentiation of osteoblasts and dental pulp stem cells

Grafting based on both autogenous and allogenous human bone is widely used to replace areas of critical loss to induce bone regeneration. Allogenous bones have the advantage of unlimited availability from tissue banks. However, their integration into the remaining bone is limited because they lack osteoinduction and osteogenic properties. Here, we propose to induce the demineralization of the allografts to improve these properties by exposing the organic components. Allografts fragments were demineralized in 10% EDTA at pH 7.2 solution. The influence of the EDTA-DAB and MAB fragments was evaluated with respect to the adhesion, growth and differentiation of MC3'T3-E1 osteoblasts, primary osteoblasts and dental pulp stem cells (DPSC). Histomorphological analyses showed that EDTA-demineralized fragments (EDTA-DAB) maintained a bone architecture and porosity similar to those of the mineralized (MAB) samples. BMP4, osteopontin, and collagen III were also preserved. All the cell types adhered, grew and colonized both the MAB and EDTA-DAB biomaterials after 7, 14 and 21 days. However, the osteoblastic cell lines showed higher viability indexes when they were cultivated on the EDTA-DAB fragments, while the MAB fragments induced higher DPSC viability. The improved osteoinductive potential of the EDTA-DAB bone was confirmed by alkaline phosphatase activity and calcium deposition analyses. This work provides guidance for the choice of the most appropriate allograft to be used in tissue bioengineering and for the transport of specific cell lineages to the surgical site.

A New Method for Partial Breast Reconstruction: 3-Year New Zealand Experience

In New Zealand, oncoplastic surgery is common, but partial breast reconstruction presents challenges for radiation therapy targeting. Tissue rearrangement creates ambiguity when targeting the tumor bed, with resultant overestimation of treatment volumes. Thus, adoption of advanced methods of radiation therapy have been hindered. This pilot study describes use of a novel three-dimensional implant that provides a scaffolding for tissue ingrowth during partial breast reconstruction and delineates the tumor bed more precisely to assist radiation planning and mammographic surveillance. After informed consent, 15 women were implanted with the three-dimensional bioabsorbable implant. The device was sutured to the tumor bed during lumpectomy, and tissue flaps were mobilized and attached to the implant. Visualization of the marker and radiation treatment volumes were recorded and compared. The implant provided volume replacement and helped to maintain breast contour. Cosmetic outcomes were excellent; no device- or radiation-related complications occurred. One patient had a postoperative hematoma that resolved after percutaneous drainage; there were no postoperative infections. Three-year follow-up shows no tumor recurrences and no untoward effects. When compared to conventional radiation targeting, use of the implant showed that a greater than 50 percent reduction in treatment volume was possible in some cases. Three-year mammograms show no significant artifact, normal tissue ingrowth, and minimal fibrosis. This study describes a method of oncoplastic breast reconstruction using an implantable device that marks the site of tumor excision and provides for volume replacement with tissue ingrowth. Patients tolerated it well, and radiation therapy planning, positioning, and treatment were facilitated.

Nasal Dorsal Augmentation with Freeze-Dried Allograft Bone: 10-Year Comprehensive Review

Supplemental Digital Content is available in the text.

Background:

The aim of this study was to evaluate freeze-dried cortical allograft bone for nasal dorsal augmentation. The 42-month report on 18 patients was published in 2009 in Plastic and Reconstructive Surgery with 89 percent success at level II evidence, and this article is the 10-year comprehensive review of 62 patients.

Methods:

All grafts met standards recommended by the American Association of Tissue Banks, the U.S. Food and Drug Administration, and the Centers for Disease Control and Prevention. Objective evaluation of the persistence of graft volume was obtained by cephalometric radiography, cone beam volumetric computed tomography, and computed tomography at up to 10 years. Vascularization and incorporation of new bone elements within the grafts were demonstrated by fluorine-18 sodium fluoride positron emission tomography at up to 10 years. Subjective estimation of graft volume persisting up to 10 years was obtained by patient response to a query conducted by an independent surveyor.

Results:

The authors report objective proof of persistence of volume alone or combined with proof of neovascularization in 16 of 19 allografts. The authors report the patient’s subjective opinion of volume persistence in 37 of 43 grafts. The dorsal augmentation was assessed overall to be successful in 85 percent of 62 patients evaluated between 1 and 10 years, with a mean of 4.7 years.

Conclusions:

Freeze-dried allograft bone is a safe and equal alternative for dorsal augmentation without donor-site morbidity. Further studies are needed to (1) confirm these findings for young patients needing long-term reconstruction, and (2) partially demineralize allograft bone to allow carving with a scalpel.

CLINICAL QUESTION/LEVEL OF EVIDENCE:

Therapeutic, IV.

Amino acid composition in determination of collagen origin and assessment of physical factors effects

The amino acid composition of collagen is a characteristic feature of this protein. Collagen, irrespective of its origin, contains 19 amino acids, including hydroxyproline which does not occur in other proteins. Its atypical amino acid composition is characterized by high content of proline and glycine, as well as the absence of cysteine. This paper shows the comparison of qualitative composition of amino acids of fish skin (FS) collagen, bovine Achilles tendon (BAT) collagen, and bone collagen. Results demonstrate that FS collagen as well as BAT collagen contains no cysteine and significantly different amount of hydroxyproline. In BAT collagen hydroxyproline content is 30% higher than hydroxyproline content of FS collagen. In bone collagen the amount of hydroxyproline is two times more than in FS collagen. Furthermore, it is shown that sensitivity to radiation of individual amino acids varies and depends on the absorbed dose of ionizing radiation. The changes observed in the amino acid composition become very intense for the doses of 500kGy and 1000kGy.

The available evidence on demineralised bone matrix in trauma and orthopaedic surgery: A systematic review

Objectives

The aim of this systematic literature review was to assess the clinical level of evidence of commercially available demineralised bone matrix (DBM) products for their use in trauma and orthopaedic related surgery.

Methods

A total of 17 DBM products were used as search terms in two available databases: Embase and PubMed according to the Preferred Reporting Items for Systematic Reviews and Meta Analyses statement. All articles that reported the clinical use of a DBM-product in trauma and orthopaedic related surgery were included.

Results

The literature search resulted in 823 manuscripts of which 64 manuscripts met the final inclusion criteria. The included manuscripts consisted of four randomised controlled trials (level I), eight cohort studies (level III) and 49 case-series (level IV). No clinical studies were found for ten DBM products, and most DBM products were only used in combination with other grafting materials. DBM products were most extensively investigated in spinal surgery, showing limited level I evidence that supports the use Grafton DBM (Osteotech, Eatontown, New Jersey) as a bone graft extender in posterolateral lumbar fusion surgery. DBM products are not thoroughly investigated in trauma surgery, showing mainly level IV evidence that supports the use of Allomatrix (Wright Medical, London, United Kingdom), DBX (DePuy Synthes, Zuchwil, Switzerland), Grafton DBM, or OrthoBlast (Citagenix Laval, Canada) as bone graft extenders.

Conclusions

The clinical level of evidence that supports the use of DBM in trauma and orthopaedic surgery is limited and consists mainly of poor quality and retrospective case-series. More prospective, randomised controlled trials are needed to understand the clinical effect and impact of DBM in trauma and orthopaedic surgery.

Cite this article: J. van der Stok, K. A. Hartholt, D. A. L. Schoenmakers, J. J. C. Arts. The available evidence on demineralised bone matrix in trauma and orthopaedic surgery: A systemati c review. Bone Joint Res 2017;6:423–432. DOI: 10.1302/2046-3758.67.BJR-2017-0027.R1.

Disinfection of human musculoskeletal allografts in tissue banking: a systematic review

Musculoskeletal allografts are typically disinfected using antibiotics, irradiation or chemical methods but protocols vary significantly between tissue banks. It is likely that different disinfection protocols will not have the same level of microorganism kill; they may also have varying effects on the structural integrity of the tissue, which could lead to significant differences in terms of clinical outcome in recipients. Ideally, a disinfection protocol should achieve the greatest bioburden reduction with the lowest possible impact on tissue integrity. A systematic review of three databases found 68 laboratory and clinical studies that analyzed the microbial bioburden or contamination rates of musculoskeletal allografts. The use of peracetic acid–ethanol or ionizing radiation was found to be most effective for disinfection of tissues. The use of irradiation is the most frequently published method for the terminal sterilization of musculoskeletal allografts; it is widely used and its efficacy is well documented in the literature. However, effective disinfection results were still observed using the BioCleanse™ Tissue Sterilization process, pulsatile lavage with antibiotics, ethylene oxide, and chlorhexidine. The variety of effective methods to reduce contamination rate or bioburden, in conjunction with limited high quality evidence provides little support for the recommendation of a single bioburden reduction method.

Evaluation of the effect of a gamma irradiated DBM-pluronic F127 composite on bone regeneration in Wistar rat

Demineralized bone matrix (DBM) is widely used for bone regeneration. Since DBM is prepared in powder form its handling properties are not optimal and limit the clinical use of this material. Various synthetic and biological carriers have been used to enhance the DBM handling. In this study we evaluated the effect of gamma irradiation on the physical-chemical properties of Pluronic and on bone morphogenetic proteins (BMPs) amount in DBM samples. In vivo studies were carried out to investigate the effect on bone regeneration of a gamma irradiated DBM-Pluronic F127 (DBM-PF127) composite implanted in the femur of rats. Gamma irradiation effects (25 kGy) on physical-chemical properties of Pluronic F127 were investigated by rheological and infrared analysis. The BMP-2/BMP-7 amount after DBM irradiation was evaluated by ELISA. Bone regeneration capacity of DBM-PF127 containing 40% (w/w) of DBM was investigated in transcortical holes created in the femoral diaphysis of Wistar rat. Bone porosity, repaired bone volume and tissue organization were evaluated at 15, 30 and 90 days by Micro-CT and histological analysis. The results showed that gamma irradiation did not induce significant modification on physical-chemical properties of Pluronic, while a decrease in BMP-2/BMP-7 amount was evidenced in sterilized DBM. Micro-CT and histological evaluation at day 15 post-implantation revealed an interconnected trabeculae network in medullar cavity and cellular infiltration and vascularization of DBM-PF127 residue. In contrast a large rate of not connected trabeculae was observed in Pluronic filled and unfilled defects. At 30 and 90 days the DBM-PF127 samples shown comparable results in term of density and thickness of the new formed tissue respect to unfilled defect. In conclusion a gamma irradiated DBM-PF127 composite, although it may have undergone a significant decrease in the concentration of BMPs, was able to maintains bone regeneration capability.

Effect of sterilization on structural and material properties of 3-D silk fibroin scaffolds

The development of porous scaffolds for tissue engineering applications requires the careful choice of properties, as these influence cell adhesion, proliferation and differentiation. Sterilization of scaffolds is a prerequisite for in vitro culture as well as for subsequent in vivo implantation. The variety of methods used to provide sterility is as diverse as the possible effects they can have on the structural and material properties of the three-dimensional (3-D) porous structure, especially in polymeric or proteinous scaffold materials. Silk fibroin (SF) has previously been demonstrated to offer exceptional benefits over conventional synthetic and natural biomaterials in generating scaffolds for tissue replacements. This study sought to determine the effect of sterilization methods, such as autoclaving, heat-, ethylene oxide-, ethanol- or antibiotic-antimycotic treatment, on porous 3-D SF scaffolds. In terms of scaffold morphology, topography, crystallinity and short-term cell viability, the different sterilization methods showed only few effects. Nevertheless, mechanical properties were significantly decreased by a factor of two by all methods except for dry autoclaving, which seemed not to affect mechanical properties compared to the native control group. These data suggest that SF scaffolds are in general highly resistant to various sterilization treatments. Nevertheless, care should be taken if initial mechanical properties are of interest.

Metabolic syndrome in pediatric cancer survivors: a mechanistic review

Pediatric cancer survivors have increased risk of obesity, hypertension, dyslipidemia, and type 2 diabetes, leading to premature cardiovascular disease (CVD). Multiple tissues that are involved in glucose homeostasis and lipid metabolism are adversely affected by chemotherapy. This review highlights the relevant tissue and molecular end-organ effects of therapy exposures and synthesizes the current understanding of the mechanisms underlying CVD risk in this vulnerable population. The review also approaches the topic from a developmental perspective, with the goal of providing a translational approach to identifying the antecedents of overt CVD among survivors of pediatric cancer.

Experimental study of the effect of autologous platelet-rich plasma on the early phases of osteoinduction by allogenic demineralized bone matrix

PURPOSE

To evaluate the effect of autologous platelet-rich plasma (PRP) on the early phases of osteoinduction by allogenic demineralized bone matrix (DBM) in rabbit intramuscular positions.

MATERIALS AND METHODS

Allogenic DBM was produced from bones of 3 healthy rabbits. In each of 6 experimental animals, 0.3 mL autologous PRP was prepared and 2 muscle pouches were created, where 250 mg DBM + PRP (experimental sites) and 250 mg DBM without PRP (control sites) were randomly implanted. Animals were euthanized 3 weeks postoperatively.

RESULTS

Histologic examination revealed uneventful healing in all cases, whereas remineralization of the periphery of the bone graft particles was a constant finding. In both control and experimental sites, fibroblasts and other mesenchymal cells (probably osteoprogenitor cells and preosteoblasts) were observed. The main histological difference was the recolonization of the empty lacunae of the bone graft particles by osteocytes at the control sites. The degradation of the graft at the control sites was statistically significantly quicker, although a statistically significant difference regarding the amount of the newly formed fibrous connective tissue was not observed.

CONCLUSION

The present study demonstrated that in this experimental model, the addition of PRP to DBM had a negative effect on the early phases of osteoinduction at 3 weeks of observation.

Early-stage Pathogenic Sequence of Jaw Osteoradionecrosis in vivo

The mechanism underlying jaw osteoradionecrosis (ORN) is not fully understood, particularly in the early stages. To investigate bone and vessel pathogenesis in the early stages of jaw ORN, we generated a mandibular ORN model in miniature pigs (minipigs) by applying a combination of single-dose 25-Gy irradiation (IR) and tooth extraction. We studied 6 ORN model minipigs and 6 control, non-irradiated minipigs. We measured dynamic morphological changes, bone-remodeling-associated gene expression, sphingomyelinase activity, and local blood flow. Bone remodeling, including bone resorption and new bone formation, was observed within 15 days post-IR. Later, an ORN-related imbalance in bone metabolism gradually occurred, with loss of bone regeneration capacity, collagen collapse, and microvascular obliteration. Within 24 hrs post-IR, sphingomyelinase significantly increased in irradiated tissues. At 1 wk post-IR, local blood flow increased, but at 15 days post-IR, it significantly decreased to 50% below normal levels. This study provided details of the sequential occurrences in early-stage ORN in a large animal model. Our results suggested that reduced local blood flow and consequent hypovascularity may have caused an imbalance in bone remodeling. This suggested that microvessel damage may play a key role in the initiation of ORN.

The in vitro elution of BMP-7 from demineralized bone matrix

Demineralized bone matrix (DBM) grafts induce new bone formation by locally releasing matrix-associated growth factors, such as bone morphogenetic proteins (BMPs), to the surrounding tissue after implantation. However, the release kinetics of BMPs from DBM lack characterization. Such information can potentially help to improve processing techniques to maximize graft osteoinductive potential, as well as increase understanding of the osteoinductive process itself. We produced DBM with three particle size ranges from bovine cortical bone, i.e., <106, 106-300, and 300-710 μm and extracted 1.5 g of each size range in 40 ml of Sorensen's buffer at room temperature for up to 168 h. The BMP-7 concentration of the DBM and the buffer were measured at each time point using enzyme-linked immunosorbant assay. Based on measurement of the concentration of BMP-7 in the buffer, the 0-8 h elution rate was high, i.e., 3.3, 2.9, and 2.2 ng BMP-7/g DBM h, and for the 8-168 h interval was much lower, at 0.039, 0.15, and 0.11 ng BMP-7/g DBM h for the three size ranges, respectively. By 168 h, there was no indication that elution was nearing completion. Measurement of the residual BMP-7 remaining in the DBM as a function of time yielded unexpected results, i.e., after the BMP-7 content of the DBM declined for the first 4-6 h, it paradoxically increased for the remaining interval. We propose a two-compartment model to help explain these results in terms of the possible distribution of BMP-7 in bone matrix.

Radiation effects on bone healing and reconstruction: interpretation of the literature

OBJECTIVE

Reconstructing irradiated mandibles with biomaterials is still a challenge but little investigated. We collected data that could help us understand studies in the field of regeneration with biomaterials and irradiated bone.

STUDY DESIGN

Systematic review of the literature.

RESULTS

Delay and duration of radiation delivery and total equivalent dose are the most variable parameters in the various studies, resulting in confusion when interpreting the literature. Most reproducible experiments show that radiation reduces osteogenic cell numbers, alters cytokine capacity, and delays and damages bone remodeling. Interindividual variations and how such changes become irreversible lesions are still uncertain. In the case of regeneration using biomaterials, most studies have addressed the question of reconstruction in previously irradiated bone. The results show that osseointegration is often possible, although the failure rate is higher. The sooner the implantation takes place after the end of the radiation, the higher the likelihood of failure. Few studies have focused on primary reconstruction followed by early irradiation, and most of the currently available engineering models would be altered by radiation. Good outcomes have been obtained with bone morphogenetic protein and with total bone marrow transplanation.

CONCLUSION

This review points out the difficulties in achieving reproducible experiments and interpreting literature in this underinvestigated field.

Effects of e-beam radiation, storage, and hydration on osteoinductivity of DBM/AM composite

E-beam irradiation is often used to sterilize medical devices including demineralized bone matrix (DBM) products. In this study, the effect of e-beam on osteoinductivity of a DBM product in hydrous and anhydrous configurations has been evaluated at 0-, 6- and 12-month ambient storage using a nude rat muscle pouch model. The thermal and structural stabilities of DBM and acellular dermal matrix (AM) composites were analyzed using differential scanning calorimetry (DSC) and trypsin digestion assay. Both hydrous and anhydrous DBM/AM composites exhibited osteoinductivity after e-beam irradiation of 15 kGy. After 12-month ambient storage, the osteoinductivity of hydrous DBM/AM was diminished, whereas the anhydrous DBM/AM retained its osteoinductive potential. However, the DSC and trypsin analysis revealed that the DBM in anhydrous DBM/AM was more vulnerable to damage from e-beam irradiation than its hydrous counterpart. This study has found that although the anhydrous DBM has more structural damage than hydrous DBM from e-beam irradiation, it has retained its osteoinductivity better after 1-year ambient storage.