Biomedical subjects

Wouter J A Dhert

Publications and source records attributed to Wouter J A Dhert.

At least 19 recordsLinked to original sources

PubMed2006

Analysis of ectopic and orthotopic bone formation in cell-based tissue-engineered constructs in goats.

Despite decades of extensive research, the application of cell-based bone tissue engineering in clinically relevant models remains challenging. To improve effectiveness, a better understanding of how the technique should work is crucial. In the current study, we investigated the onset time, rate, location and direction of bone formation in ectopically and orthotopically implanted clinically sized tissue-engineered constructs to gain insight the mechanism behind it. Bone marrow stromal cells (BMSCs) were obtained from 10 goats, culture expanded and cryopreserved. Porous biphasic calcium phosphate (BCP) disks of 17mmx6mm were per-operatively seeded with BMSCs or left empty. Both conditions were implanted intramuscularly and in bilateral critical-sized iliac wing defects. Fluorochromes were administered at 3, 5 and 7 weeks and samples were retrieved after 9 weeks. Histology showed abundant and homogeneous bone formation throughout the intramuscular BMSC samples and little bone in the controls. Histomorphometry and measurements of the fluorochrome labels of the ectopical BMSC samples indicated that osteogenesis started at the periphery and subsequent osteoconduction filled the whole scaffold within 7 weeks. In the orthotopically implanted disks, there was good integration with the surrounding bone, but minimal bone in the center of the implants, in both conditions. Bone was only derived from the interface with the surrounding bone, there was no early bone at the surfaces in contact to soft tissue as was seen in the ectopical samples. Apparently cell survival was minimal and insufficient for relevant additional bone formation. However, the speed of integration with surrounding bone and subsequent bone apposition on the BMSC-seeded orthotopic scaffolds were found to be significantly enhanced, which may be relevant especially in challenging environments.

Animals↗

PubMed2006

The effect of cell-based bone tissue engineering in a goat transverse process model.

A disadvantage of traditional posterolateral spinal fusion models is that they are highly inefficient for screening multiple conditions. We developed a multiple-condition model that concentrates on the initial process of bone formation from the transverse process and not on a functional fusion. The effect of bone marrow stromal cells (BMSCs) in four different porous ceramic scaffolds was investigated in this setting. Polyacetal cassettes were designed to fit on the goat transverse process and house four different ceramic blocks, i.e: hydroxyapatite (HA) sintered at 1,150 degrees and 1,250 degrees; biphasic calcium phosphate (BCP) and tricalcium phosphate (TCP). Goat BMSCs (n=10) were cultured and per-operatively seeded autologeously on one of two cassettes implanted per animal. The cassettes were bilaterally mounted on the dorsum of decorticated L2-processes for 9 weeks. To asses the dynamics of bone formation, fluorochrome labels were administered and histomorphometry focused on the distribution of bone in the scaffolds. A clear difference in the extent of bone ingrowth was determined for the different scaffold types. An obvious effect of BMSC seeding was observed in three of four scaffold types, especially in scaffold regions adjacent to the overlying muscle. Generally, the BCP and TCP scaffolds showed better osteoconduction and an increased response to BMSCs administration. In conclusion the model provides a reliable and highly efficient method to study bone formation in cell-based tissue engineering. An effect of cell administration was obvious in three of the four scaffold materials.

Animals↗

PubMed2006

Cement augmentation techniques in traumatic thoracolumbar spine fractures.

STUDY DESIGN: Review of human cadaveric and in vivo animal studies and clinical trial. OBJECTIVE: To develop less invasive surgical techniques for reconstruction of the anterior column in thoracolumbar fractures. SUMMARY OF BACKGROUND DATA: Persistent central endplate depression can cause anterior column insufficiency after posterior surgery for traumatic thoracolumbar fractures. Reduction of the central endplate followed by intravertebral cement augmentation could restore weight-bearing capacity. MATERIALS AND METHODS: In human cadaveric burst fracture models, balloon-assisted endplate reduction (BAER) and vertebroplasty techniques have been investigated in terms of their safety and biomechanical properties. The histologic properties of different cement polymers were studied in an animal vertebral body and endplate defect model. In addition, the clinical outcome of percutaneous cement augmentation in the setting of a burst fracture examining the BAER technique and vertebroplasty with adjunctive posterior pedicle screw fixation is reviewed. RESULTS: These techniques have proven to be safe and effective, although cement leakage outside the confines of the vertebral body may occur. Calcium phosphate cements are preferable over methylmethacrylate because of their in vivo histologic properties. Using the BAER technique and posterior pedicular fixation, anterior vertebral height restoration is possible. Following balloon removal, some loss of fracture height restoration is observed. Further loss of vertebral height reduction was not observed following cement curing clinically. CONCLUSIONS: These studies show that less invasive anterior vertebral reconstruction using percutaneous cement augmentation techniques is feasible following traumatic vertebral fractures.

Animals↗

PubMed2006

Controlled drug release from a novel injectable biodegradable microsphere/scaffold composite based on poly(propylene fumarate).

The ideal biomaterial for the repair of bone defects is expected to have good mechanical properties, be fabricated easily into a desired shape, support cell attachment, allow controlled release of bioactive factors to induce bone formation, and biodegrade into nontoxic products to permit natural bone formation and remodeling. The synthetic polymer poly(propylene fumarate) (PPF) holds great promise as such a biomaterial. In previous work we developed poly(DL-lactic-co-glycolic acid) (PLGA) and PPF microspheres for the controlled delivery of bioactive molecules. This study presents an approach to incorporate these microspheres into an injectable, porous PPF scaffold. Model drug Texas red dextran (TRD) was encapsulated into biodegradable PLGA and PPF microspheres at 2 microg/mg microsphere. Five porous composite formulations were fabricated via a gas foaming technique by combining the injectable PPF paste with the PLGA or PPF microspheres at 100 or 250 mg microsphere per composite formulation, or a control aqueous TRD solution (200 microg per composite). All scaffolds had an interconnected pore network with an average porosity of 64.8 +/- 3.6%. The presence of microspheres in the composite scaffolds was confirmed by scanning electron microscopy and confocal microscopy. The composite scaffolds exhibited a sustained release of the model drug for at least 28 days and had minimal burst release during the initial phase of release, as compared to drug release from microspheres alone. The compressive moduli of the scaffolds were between 2.4 and 26.2 MPa after fabrication, and between 14.9 and 62.8 MPa after 28 days in PBS. The scaffolds containing PPF microspheres exhibited a significantly higher initial compressive modulus than those containing PLGA microspheres. Increasing the amount of microspheres in the composites was found to significantly decrease the initial compressive modulus. The novel injectable PPF-based microsphere/scaffold composites developed in this study are promising to serve as vehicles for controlled drug delivery for bone tissue engineering.

Bone Cements↗

PubMed2006

Towards injectable cell-based tissue-engineered bone: the effect of different calcium phosphate microparticles and pre-culturing.

Bone tissue engineering by combining bone marrow stromal cells (BMSCs) with a porous scaffold is a promising technology. Current major challenges are to upscale the technique for clinical application and to improve the handling characteristics. With respect to minimal invasive surgery, moldable and/or injectable formulations are highly preferable. Ceramic microparticles of different HA/TCP formulations (100/0, 70/30, 60/40, 40/60, and 0/100) with varying surface roughness were sieved to select 200 microg aliquots of the 212-300 microm fraction. Goat BMSCs were seeded on different aliquots one week prior to in vivo implantation. These constructs and remaining cells were cultured for one week. By then, the remaining cells were harvested and resuspended in a specific binder: hyaluronic acid, alginate, or blood plasma, combined with aliquots of 60/40 microparticles peroperatively. All constructs were implanted in nude rats (n = 10) and analyzed for their bone yield histomorphometrically after 6 weeks. All precultured constructs showed consistent bone formation of comparable quantity. No significant differences were observed between the different material compositions. Peroperatively prepared constructs hardly showed any bone formation. The present study demonstrated the osteogenic potential of a tissue- engineered bone substitute made of microparticles of various HA/TCP compositions. There was an obvious advantage when the constructs were pre-cultured.

Alginates↗

PubMed2005

A new in vivo screening model for posterior spinal bone formation: comparison of ten calcium phosphate ceramic material treatments.

This study presents a new screening model for evaluating the influence of multiple conditions on the initial process of bone formation in the posterior lumbar spine of a large animal. This model uses cages designed for placement on the decorticated transverse process of the goat lumbar spine. Five conduction channels per cage, each be defined by a different material treatment, are open to both the underlying bone and overlying soft tissue. The model was validated in ten adult Dutch milk goats, with each animal implanted with two cages containing a total of ten calcium phosphate material treatments according to a randomized complete block design. The ten calcium phosphate ceramic materials were created through a combination of material chemistry (BCP, TCP, HA), sintering temperature (low, medium, high), calcination and surface roughness treatments. To monitor the bone formation over time, fluorochrome markers were administered at 3, 5 and 7 weeks and the animals were sacrificed at 9 weeks after implantation. Bone formation in the conduction channels was investigated by histology and histomorphometry of non-decalcified sections using traditional light and epifluorescent microscopy. According to both observed and measured bone formation parameters, materials were ranked in order of increasing magnitude as follows: low sintering temperature BCP (rough and smooth) approximately medium sintering temperature BCP approximately = TCP > calcined low sintering temperature HA > non-calcined low sintering temperature HA > high sintering temperature BCP (rough and smooth) > high sintering temperature HA (calcined and non-calcined). These results agree closely with those obtained in previous studies of osteoconduction and bioactivity of ceramics thereby validating the screening model presented in this study.

Animals↗

PubMed2005

Anterior spinal column augmentation with injectable bone cements.

A vertebral fracture, whether originating from osteoporosis or trauma, can be the cause of pain, disability, deformation and neurological deficit. The treatment of vertebral compression fractures has, for many years until the advent of vertebroplasty, consisted of bedrest and analgesics. Vertebroplasty is a percutaneous technique during which bone cement is injected in a vertebral body to provide immediate pain relief by stabilization. Inflatable bone tamps can, prior to the injection of cement, be used to create a void in the vertebral body, in which case the technique is known as balloon vertebroplasty (or kyphoplasty). The chance of extracorporal cement leakage is smaller for balloon vertebroplasty than for vertebroplasty. Some authors also claim to have gained some correction in vertebral body height or angulation. Both interventions can be used for several indications, including osteoporotic compression fractures and osteolytic lesions of the vertebral body such as myeloma, hemangioma or metastasis, and also for traumatic burst fractures in combination with pedicle screw instrumentation. Polymethyl methacrylate cement is the bone void filler that is used most frequently, although the application of calcium phosphate cements has been studied widely in vitro, in vivo and also in small-scale clinical series. The clinical results of (balloon-) vertebroplasty are favorable with 85-95% of all patients experiencing immediate and long-lasting relief of pain. Serious complications are relatively rare but include neurological deficit and pulmonary embolism. In this paper, both vertebroplasty and balloon vertebroplasty and their respective indications, techniques and results are described in relation with the application and limitations of permanent and resorbable injectable bone cements.

Absorbable Implants↗

PubMed2005

The reduction of endplate fractures during balloon vertebroplasty: a detailed radiological analysis of the treatment of burst fractures using pedicle screws, balloon vertebroplasty, and calcium phosphate cement.

STUDY DESIGN: In a human cadaveric burst fracture model, the amount of endplate fracture reduction after posterior instrumentation and balloon vertebroplasty was investigated quantitatively. OBJECTIVES: To assess, in a burst fracture model, the vertebral body and adjacent disc heights, in parallel sagittal planes with 3-dimensional (3D) rotational x-ray imaging, at various phases during pedicle screw fixation and subsequent balloon vertebroplasty. SUMMARY OF BACKGROUND DATA: In recent human cadaveric thoracolumbar fracture studies, it was found that vertebral body height could be restored significantly with inflatable bone tamps. However, limited quantitative data exist on the amount of fracture reduction that can be achieved and how much of the reduction will be lost after deflation and removal of the bone tamps before the cement is injected. METHODS: Twenty burst fractures were created and balloon vertebroplasty with calcium phosphate cement was performed after pedicle screw instrumentation. A 3D dataset was obtained during the following phases: intact, fractured, after reduction and stabilization with pedicle screws, after inflation of the balloons, after deflation and removal of the balloons, after injection of the cement. The fractured vertebral body and adjacent disc heights were measured from five reconstructed sagittal images and compared for the six phases of the procedure. Furthermore, the difference between the vertebral body height centrally and peripherally was calculated. RESULTS: The mean vertebral body height at the thoracic level was Tintact = 19.5 +/- 2.2 mm, Tfractured = 14.6 +/- 3.8 mm, Treduction = 17.3 +/- 2.2 mm, Tinflation = 20.1 +/- 2.0 mm, Tdeflation = 18.0 +/- 2.0 mm, and Tcement = 17.8 +/- 1.8 mm. The overall change in vertebral body height between these phases was significant (P < 0.001). At the lumbar level the mean vertebral body height was Tintact = 23.2 +/- 3.8 mm, Tfractured = 14.7 +/- 3.0 mm, Treduction = 18.4 +/- 2.5 mm, Tinflation = 23.2 +/- 3.5 mm, Tdeflation = 19.3 +/- 2.3 mm, and Tcement = 20.2 +/- 2.8 mm. The overall change in MCVBH between these phases was also significant (P < 0.001). The increase in vertebral body height resulted in a decrease of the adjacent disc height. No difference was found for the amount of endplate reduction in the center or at the periphery. No leakage of cement was detected in the spinal canal. CONCLUSIONS: Reduction of endplate fractures, both in the center and at the periphery, seems feasible and safe with combined fracture reduction and balloon vertebroplasty. The endplate fracture reduction that was gained by inflation of the bone tamps could not be maintained after deflation.

Aged↗

PubMed2005

Bone displacement and the role of longitudinal ligaments during balloon vertebroplasty in traumatic thoracolumbar fractures.

STUDY DESIGN: In a human cadaveric burst fracture model with and without longitudinal ligament damage, the amount of anterior and posterior bone displacement (ABD, PBD) during balloon vertebroplasty after pedicle-screw instrumentation was investigated quantitatively. OBJECTIVES: To investigate, in a burst fracture model with and without longitudinal ligament damage, the amount of ABD, PBD, and cement leakage at various phases during balloon vertebroplasty in combination with pedicle-screw instrumentation. SUMMARY OF BACKGROUND DATA: The role of intact longitudinal ligaments in traumatic spine fractures, for prevention of bone retropulsion and subsequent reduction, has been discussed in several studies but is still up for debate. In a recent human cadaveric burst fracture study, inflatable bone tamps and calcium phosphate cement were used for the augmentation of the anterior column after pedicle-screw instrumentation. The additional balloon vertebroplasty procedure was found to be feasible and safe, but no data pertaining to unwarranted bone displacement or cement leakage during the procedure are available for burst fractures with damaged longitudinal ligaments. METHODS: Ten thoracic and 10 lumbar burst fractures, with rotation or flexion components, were created, and balloon vertebroplasty with calcium phosphate cement was performed after pedicle-screw instrumentation. Volumetric datasets (using the 3-dimensional (3D) rotational x-ray imaging technique) of the fractures were obtained during the following phases: intact, fractured, after reduction and stabilization with pedicle-screws, after inflation of the balloons, after deflation and removal of the balloons, and after injection of the cement. The amount of ABD and PBD was measured on reconstructed sagittal images and recorded together with the presence of extracorporal cement leakage. The continuity of the longitudinal ligaments was assessed after anatomic dissection. RESULTS: During the balloon vertebroplasty procedure, a significant (P < 0.05) increase of ABD (at both thoracic and lumbar level) and PBD (thoracic level) occurred after inflation of the balloons. After deflation and subsequent injection of the cement, however, the ABD and PBD returned to the preinflation levels. The absolute amount of ABD and PBD (<1 mm) during inflation was considered of little clinical importance. No differences in ABD or PBD were observed for specimens with or without continuity of the corresponding longitudinal ligament, irrespective of the level, at any of the phases during the experiment (P > 0.5 in all cases). A small amount of cement leakage was observed in the psoas compartment of one specimen with intact longitudinal ligaments. CONCLUSIONS: It is suggested that balloon vertebroplasty after pedicle-screw instrumentation may safely be used, in terms of bone displacement and cement leakage, in fracture types where damage to longitudinal ligaments is to be expected.

Aged↗

PubMed2005

Three-dimensional rotational X-ray imaging for spine surgery: a quantitative validation study comparing reconstructed images with corresponding anatomical sections.

STUDY DESIGN: A validation study was done in which reconstructed three-dimensional rotational x-ray images were quantitatively compared with corresponding anatomic sections. OBJECTIVES: To assess the accuracy of reconstructed images acquired on a three-dimensional rotational x-ray imaging device. SUMMARY OF BACKGROUND DATA: Minimally invasive procedures have proven quite successful as alternatives for a multitude of open treatments. An unfavorable property of this type of procedure is a lack of direct vision of the operating area. Three-dimensional rotational x-ray imaging may be able to merge the advantages of computed tomography and fluoroscopy: real-time two-dimensional projections for fast visual feedback and three-dimensional reconstructions for detailed volumetric imaging of complex anatomy. METHODS: Twenty traumatic thoracolumbar burst fractures were created and underwent pedicle screw instrumentation and balloon vertebroplasty. Subsequently, a three-dimensional dataset was obtained, and the midsagittal image was reconstructed. The specimens were sliced, and photographs were obtained. Multiple parameters on the reconstructed images and photographs were measured two times by two observers using a graphical method. The differences and standard deviations were calculated for the corresponding parameters and for the intraobserver data. RESULTS: The mean difference between the corresponding values ranged between -1.1 and 2.1 mm for all parameters. The standard deviation for the differences per parameter ranged between 1.2 and 3.2 mm. The intraobserver differences ranged from -0.8 to 1.4 mm, and the standard deviation varied between 0.4 and 2.4 mm. CONCLUSIONS: The reconstructed midsagittal images were accurate in all measured parameters. The three-dimensional rotational x-ray technique may prove to be valuable for less invasive spine surgery.

Aged↗

PubMed2005

Balloon vertebroplasty in combination with pedicle screw instrumentation: a novel technique to treat thoracic and lumbar burst fractures.

STUDY DESIGN: Clinical trial (phase II). OBJECTIVES: To assess the feasibility and safety of balloon vertebroplasty after posterior short-segment reduction and fixation for the treatment of traumatic burst fractures. SUMMARY OF BACKGROUND DATA: Hardware failure and loss of reduction after posterior short-segment instrumentation are complications caused by insufficiency of anterior column support. This is due to migration of disc tissue through the endplate into the fractured vertebral body that cannot be restored with posterior instrumentation. METHODS: Patients with traumatic thoracolumbar burst fractures without neurologic deficits were included. After posterior reduction and fixation, bilateral transpedicular balloon reduction of the endplate was performed, and calcium phosphate cement was injected. Preoperative and postoperative Cobb angle and central and anterior height were assessed with radiographs and MRI. RESULTS: Twenty patients underwent surgery without technical difficulties, and a substantial reduction of the endplates could be achieved with the technique. All patients recovered uneventfully, and the neurologic examination revealed no deficits. The postoperative radiographs and magnetic resonance images demonstrated a good fracture reduction and filling of the bone defect without unwarranted bone displacement. The central and anterior height of the vertebral body could be restored to 78 and 91% of the estimated intact height, respectively. Complications were cement leakage in five cases without clinical implications and one wound hematoma. CONCLUSIONS: Transpedicular balloon vertebroplasty for the direct restoration of burst fractures seems feasible in combination with posterior instrumentation. Cement leakage occurred but had no clinical consequences.

Adolescent↗

PubMed2005

Less invasive anterior column reconstruction in thoracolumbar fractures.

Posterior short-segment pedicle screw constructs are commonly used for reduction and fixation of traumatic thoracolumbar spine fractures. Although this technique is usually simple and effective, complications such as loss of fixation or recurrence of deformity are common because of the insufficiency of the damaged anterior column. Anterior approaches to address this deficiency are associated with high morbidity and complications. We have developed a technique to reduce and support the fractured anterior column through a transpedicular approach. Balloon-assisted-endplate-reduction (BAER) followed by vertebroplasty (VTP) with calcium phosphate cement in combination with short segment pedicle screw construct seem to be a safe and effective technique to reconstruct the anterior column in a less invasive manner. In this article, the rationale behind this technique, experimental studies, and the first clinical results are discussed.

Biocompatible Materials↗

PubMed2005

The role of 3-D rotational x-ray imaging in spinal trauma.

The most widely used imaging devices in trauma spine surgery are fluoroscopy and computed tomography. Both techniques have their specific pros and cons and expose both patient and operating staff to considerable radiation during image acquisition. Three-dimensional-rotational x-ray imaging (3-DRX) is a relatively new technique in which a C-arm is moved around the patient to allow for an "acquisition run" during which multiple fluoroscopy images are obtained. The images can subsequently be processed on a workstation into a 3-D volume, which can then be manipulated in a similar way to 3-D computed tomography data. The 3-DRX technique combines the advantages of both fluoroscopy and computed tomography: fast visual feedback and high resolution multiplanar reformatted images, respectively, and could be used in an intraoperative setting. In this paper some technical aspects of 3-DRX imaging and its potential role in spinal trauma treatment are presented.

Humans↗

PubMed2004

Development of biodegradable poly(propylene fumarate)/poly(lactic-co-glycolic acid) blend microspheres. I. Preparation and characterization.

We developed poly(propylene fumarate)/poly(lactic-co-glycolic acid) (PPF/PLGA) blend microspheres and investigated the effects of various processing parameters on the characteristics of these microspheres. The advantage of these blend microspheres is that the carbon-carbon double bonds along the PPF backbone could be used for their immobilization in a PPF scaffold. Microspheres containing the model drug Texas red dextran were fabricated using a double emulsion-solvent extraction technique. The effects of the following six processing parameters on the microsphere characteristics were investigated: PPF/PLGA ratio, polymer viscosity, vortex speed during emulsification, amount of internal aqueous phase, use of poly(vinyl alcohol) (PVA) in the internal aqueous phase, and PVA concentration in the external aqueous phase. Our results showed that the microsphere surface morphology was affected most by the viscosity of the polymer solution. Microspheres fabricated with a kinematic viscosity of 39 centistokes had a smooth, nonporous surface. In most microsphere formulations, the model drug was dispersed uniformly in the polymer matrix. For all fabricated formulations, the average microsphere diameter ranged between 19.0 and 76.9 microm. The external PVA concentration and vortex speed had most effect on the size distribution. Entrapment efficiencies varied from 60 to 98% and were most affected by the amount of internal aqueous phase, vortex speed, and polymer viscosity. Overall, we demonstrated the ability to fabricate PPF/PLGA blend microspheres with similar surface morphology, entrapment efficiency, and size distribution as conventional PLGA microspheres.

Biocompatible Materials↗

PubMed2004

Development of biodegradable poly(propylene fumarate)/poly(lactic-co-glycolic acid) blend microspheres. II. Controlled drug release and microsphere degradation.

This article describes the effects of six processing parameters on the release kinetics of a model drug Texas red dextran (TRD) from poly(propylene fumarate)/poly(lactic-co-glycolic acid) (PPF/PLGA) blend microspheres as well as the degradation of these microspheres. The microspheres were fabricated using a double emulsion-solvent extraction technique in which the following six parameters were varied: PPF/PLGA ratio, polymer viscosity, vortex speed during emulsification, amount of internal aqueous phase, use of poly(vinyl alcohol) in the internal aqueous phase, and poly(vinyl alcohol) concentration in the external aqueous phase. We have previously characterized these microspheres in terms of microsphere morphology, size distribution, and TRD entrapment efficiency. In this work, the TRD release profiles in phosphate-buffered saline were determined and all formulations showed an initial burst release in the first 2 days followed by a decreased sustained release over a 38-day period. The initial burst release varied from 5.1 (+/-1.1) to 67.7 (+/-3.4)% of the entrapped TRD, and was affected most by the viscosity of the polymer solution used for microsphere fabrication. The sustained release between day 2 and day 38 ranged from 7.9 (+/-0.8) to 27.2 (+/-3.1)% of the entrapped TRD. During 11 weeks of in vitro degradation, the mass of the microspheres remained relatively constant for the first 3 weeks after which it decreased dramatically, whereas the molecular weight of the polymers decreased immediately upon placement in phosphate-buffered saline. Increasing the PPF content in the PPF/PLGA blend resulted in slower microsphere degradation. Overall, this study provides further understanding of the effects of various processing parameters on the release kinetics from PPF/PLGA blend microspheres thus allowing modulation of drug release to achieve a wide spectrum of release profiles.

Biocompatible Materials↗

PubMed2004

Optimization of bone-tissue engineering in goats.

Successful bone-tissue engineering (TE) has been reported for various strategies to combine cells with a porous scaffold. In particular, the period after seeding until implantation of the constructs may vary between hours and several weeks. Differences between these strategies can be reduced to (a) the presence of extracellular matrix, (b) the differentiation status of the cells, and (c) the presence of residual potentially immunogenic serum proteins. These parameters are investigated in two types of calcium phosphate scaffolds in a goat model of ectopic bone formation. Culture-expanded bone-marrow stromal cells from eight goats were seeded onto two types of hydroxyapatite granules: HA60/400 (60% porosity, 400-microm average pore size) and HA70/800. Scaffolds seeded with cells and control scaffolds were cultured for 6 days in medium containing autologous or semisynthetic serum, in the presence or absence of dexamethasone. Other scaffolds were seeded with cells just before implantation in medium with or without serum. All conditions were implanted autologously in the paraspinal muscles. After 12 weeks, bone had formed in 87% of all TE constructs, as demonstrated by histology. Histomorphometry indicated significantly more bone in the HA70/800 scaffolds. Furthermore, a significant advantage in bone formation was found when the constructs had been cultured for 6 days. In conclusion, both scaffold characteristics (porosity) and TE strategy (culturing of the constructs) were demonstrated to be important for bone TE.

Animals↗

PubMed2004

Osteogenicity of autologous bone transplants in the goat.

BACKGROUND: Little is known about the specific mechanisms that make autologous graft bone (AG) superior to the current alternatives. A potential mechanism is the active bone formation by the osteoprogenitor cells within the AG. However, whether these cells survive the transplantation is questionable, especially in nonvascularized, clinically sized grafts. In the present study, we investigated the role of viability in AG implanted ectopically and orthotopically in the goat. METHODS: Eight goats were operated on twice. At the first operation, pieces of vital or devitalized autologous cortical bone were implanted in the paraspinal muscles. Eight weeks later, corticocancellous plugs were taken from the femoral condyles, morselized, and reimplanted as either vital or devitalized orthotopic grafts. The goats received fluorochrome labels at 5, 7, and 9 weeks after the first operation. At 12 weeks, the goats were killed, and the samples were examined histologically. RESULTS: Ectopically, new bone had formed in both the vital and devitalized grafts. In the vital grafts, all three fluorochrome labels were present, indicating an early osteogenic mechanism. Within the devitalized grafts, only the 9-week label was observed. Histomorphometry indicated significantly more new bone in the vital grafts (10.3% vs. 1.7% in the devitalized grafts, P <0.01). Orthotopically, both vital and devitalized grafts showed new bone. Again, graft viability was advantageous in terms of new bone formation (14.5% vs. 9.3%, P <0.02). CONCLUSION: The cells inside the autologous bone transplants most likely survived transplantation and were capable of initiating and sustaining new bone formation.

Animals↗

PubMed2004

Optimization of bone tissue engineering in goats: a peroperative seeding method using cryopreserved cells and localized bone formation in calcium phosphate scaffolds.

BACKGROUND: Bone tissue engineering by combining cultured bone marrow stromal cells with a porous scaffold is a promising alternative for the autologous bone graft. Drawbacks of the technique include the delay necessary for cell culture and the complicated logistics. We investigated methods to bypass these drawbacks. Furthermore, we investigated the localization of bone formation inside the scaffold. METHODS: Bone marrow stromal cells from seven goats were culture expanded and cryopreserved. One week before surgery, some of the cells were thawed, cultured, and seeded on porous calcium phosphate scaffolds. The constructs were cultured for another week until implantation. The remaining cryopreserved cells were thawed just before implantation and peroperatively resuspended in plasma before combining with the scaffold. Scaffolds impregnated with fresh bone marrow, devitalized cultured constructs, and empty scaffolds served as controls. All samples were implanted in the back muscles of the goats for 9 weeks. RESULTS: Histologic examination showed minimal (<1%) bone in the empty and devitalized scaffolds, 4.2 +/- 5.1 bone area percent in the bone marrow samples, and significantly more bone in both the cultured and peroperatively seeded constructs (11.7 +/- 2.5 and 14.0 +/- 2.0%). The peripheral 350 microm of the implants contained significantly less bone. CONCLUSION: Peroperative preparation of osteogenic constructs with cryopreserved cells is feasible. These constructs yield substantially more bone than the scaffolds alone or scaffolds impregnated with fresh bone marrow. Bone deposition is much less on the scaffold periphery.

Animals↗