Bone formation in transforming growth factor beta-1-coated porous poly(propylene fumarate) scaffolds

This study determined the bone growth into pretreated poly(propylene fumarate) (PPF) scaffolds implanted into a subcritical size, rabbit cranial defect. PPF scaffolds were constructed by using a photocrosslinking-porogen leaching technique. These scaffolds were then either prewetted (PPF-Pw), treated with RF glow-discharge (PPF-Gd), coated with fibronectin (PPF-Fn), or coated with rhTGF-beta1 (PPF-TGF-beta1). One of each scaffold type was then placed into the cranium of nine rabbits. The rabbits were sacrificed after 8 weeks, and the scaffolds were retrieved for histological analysis. The most bone formation was present in the PPF-TGF-beta1 implants; the newly formed bone had a trabecular appearance together with bone marrow-like tissue. Little or no bone formation was observed in implants without rhTGF-beta1. These histological findings were confirmed by image analysis. Bone surface area, bone area percentage, pore fill percentage, and pore area percentage were significantly higher in the rhTGF-beta1-coated implants than in the noncoated implants. No statistical difference was seen between the PPF-Fn, PPF-Pw, or PPF-Gd scaffolds for these parameters. Quadruple fluorochrome labeling showed that in PPF-TGF-beta1 implants bone formation mainly started in the interior of a pore and proceeded toward the scaffold. We conclude that (a) PPF-TGF-beta1 scaffolds can indeed adequately induce bone formation in porous PPF, and (b) PPF scaffolds prepared by the photocrosslinking-porogen leaching technique are good candidates for the creation of bone graft substitutes.     

Improved bone anchorage of hydroxypatite coated implants compared with tricalcium-phosphate coated implants in trabecular bone in dogs

Tricalcium phosphate (TCP) and hydroxyapatite (HA) ceramic coatings are bioactive coatings that have been shown to stimulate bone apposition onto ceramic-coated implants. TCP and HA ceramics have well-documented differences in physical properties, but both types of ceramics are used for stimulation of bone ongrowth to cementless endo-prosthetic components clinically. However, little is known about the difference in osteoconductive properties between these coatings when inserted into trabecular bone in a controlled experimental situation. Unloaded cylindrical gritblasted titanium (Ti-6A1-4V) implants (6 x 10 mm) coated with either hydroxyapatite (HA) or tricalcium phosphate (TCP) ceramic were inserted into the proximal humerus of 20 skeletally mature dogs. The implants were initially surrounded by a 2 mm gap. Each animal received one HA-coated implant and one TCP-coated implant. All dogs were sacrificed 6 weeks after surgery. Results were evaluated by histomorphometry and mechanical push-out test. Push-out tests demonstrated that HA-coated implants were 10-fold stronger fixated in comparison to TCP-coated implant. Bone ongrowth was significantly higher for HA-coated implants compared to TCP-coated implants. Bone volume in the gap showed a tendency to less bone volume around HA-coated implants compared to TCP-coated implants but this difference was insignificant. As expected almost all of the TCP coating were resorbed after 6 weeks and almost none of the HA coating. HA-coated implants with a grit-blasted surface provide a favorable early mechanical implant anchorage most likely due to superior ceramic stability compared to TCP-coated implants.     

Functionalization of dental implant surfaces using adhesion molecules

The aim of the present study was to test the hypothesis that organic coating of titanium screw implants that provides binding sites for integrin receptors can enhance periimplant bone formation. Ten adult female foxhounds received experimental titanium screw implants in the mandible 3 months after removal of all premolar teeth. Four types of implants were evaluated in each animal: (1) implants with machined titanium surface, (2) implants coated with collagen I, (3) implants with collagen I and cyclic RGD peptide coating (Arg-Gly-Asp) with low RGD concentrations (100 micromol/mL), and (4) implants with collagen I and RGD coating with high RGD concentrations (1000 micromol/mL). Periimplant bone regeneration was assessed histomorphometrically after 1 and 3 months in five dogs each by measuring bone implant contact (BIC) and the volume density of the newly formed periimplant bone (BVD). After 1 month, BIC was significantly enhanced only in the group of implants coated with the higher concentration of RGD peptides (p = 0.026). Volume density of the newly formed periimplant bone was significantly higher in all implants with organic coating. No significant difference was found between collagen coating and RGD coatings. After 3 months, BIC was significantly higher in all implants with organic coating than in implants with machined surfaces. Periimplant BVD was significantly increased in all coated implants in comparison to machined surfaces also. It was concluded that organic coating of machined screw implant surfaces providing binding sites for integrin receptors can enhance bone implant contact and periimplant bone formation.     

Transforming growth factor-beta1 incorporated during setting in calcium phosphate cement stimulates bone cell differentiation in vitro

Growth stimulation of periimplant tissues by growth factors like transforming growth factor-beta1 (TGF-beta1) may increase the indication for and success of implant use. Calcium phosphate as a material for implants or for coating of implants is known for its good biologic interaction with bone. Therefore, calcium phosphate implants combined with TGF-beta1 might improve osseointegration. In this study we hypothesise that the addition of recombinant human TGF-beta1 (rhTGF-beta1) to calcium phosphate cement (CPC) affects the differentiation of bone cells growing on the cement layer. rhTGF-beta1 incorporated during setting in a CPC layer at 20 ng rhTGF-beta1/60 mg cement was found to be gradually released into tissue culturing medium leading to a 20% release after 24 h. Two cell populations were obtained from collagenase-treated fragments of adult rat long bones: preosteoblastic cells, which were released by the collagenase treatment, and osteoblastic cells, which grew from the collagenase-stripped bone fragments. Both cell populations were tested for their osteoblastic characteristic phenotype by measuring their alkaline phosphatase (ALP) activity after vitamin D treatment and cyclic AMP after parathyroid hormone stimulation. After preculture the cells were plated on a layer of CPC containing 0 (control), 10, or 20 ng rhTGF-beta1/60 mg CPC. Bone cell differentiation was analyzed after 10 days by measuring the ALP activity, as well as the protein content of the cell layer. Incorporation of rhTGF-beta1 in the CPC did not change the ALP activity in osteoblastic cells, but a significant (analyzed by multivariate analysis of variance) increase was observed in preosteoblastic cells. Incorporation of 10 ng of rhTGF-beta1 in 60 mg of CPC increased the ALP activity in preosteoblastic cells by threefold and 20 ng rhTGF-beta1/60 mg CPC increased it by fivefold. The total protein content was not affected by rhTGF-beta1 in either of the cell populations. We conclude that rhTGF-beta1 incorporated during setting in CPC stimulates the differentiation of preosteoblastic cells in vitro. These results provide a basis for further studies on the use of this combination as an implant material in vivo.     

局部应用阿伦膦酸钠对非负荷期种植体骨结合影响的X射线观察*

背景：阿伦膦酸钠作为第3代二膦酸盐,具有很强的抑制骨吸收的能力。 目的：研究阿伦膦酸钠对非负荷期种植体周围骨结合的影响。 方法：取健康成年Beagle犬6只,随机等分为实验组和对照组,选取每犬的双侧下颌第二、四前磨牙共计24牙位,于实验第1,29,43,50天分别行即刻种植手术。实验组于种植体周围局部注射阿伦膦酸钠,对照组注射生理盐水,每周2次。 结果与结论：于实验第57天进行X射线显示种植体骨结合情况良好,实验组2周时即可见到种植体周围骨小梁的形成,明显早于对照组。提示阿伦膦酸钠可促进种植体周围骨组织中骨小梁的早期形成,从而影响种植体周围骨改建,提高非负荷期种植体周围骨结合。     

Histological and histomorphometrical comparative study of the degradation and osteoconductive characteristics of alpha- and beta-tricalcium phosphate in block grafts

The purpose of the present study was to compare alpha- and beta-tricalcium phosphate (TCP) as bone graft material for augmenting highly resorbed alveolar ridges. The cranial bones of 15 rabbits were used. Three titanium chambers filled with porous blocks of alpha-TCP, beta-TCP, or blood clots were placed in each slit. The two TCP blocks had similar inner/outer structures and purities. Animals were sacrificed after 2, 4, and 8 weeks. Specimens were embedded in polyester resin as nondecalcified specimens, and evaluated both histologically and histomorphometrically. In both TCP groups, blocks had hardly degraded at 2 weeks while in the alpha-TCP group, the block had notably started degrading after 4 weeks. In the beta-TCP group, degradation began at 4 weeks and this degradation had increased just slightly after 8 weeks. The alpha-TCP block degraded significantly more than the beta-TCP block. Residual alpha-TCP particles surrounded by newly formed bone decreased over time, and both particles and newly formed bone were simultaneously absorbed by osteoclast-like cells. These observations suggest that residual alpha-TCP particles surrounded by newly formed bone may disappear progressively from bone and could be incorporated into the bone remodeling cycle in combination with newly formed bone.     

A modified rhTGF-beta1 and rhBMP-2 are effective in initiating a chondro-osseous differentiation pathway in bone marrow cells cultured in vitro

Rat bone marrow cells were cultured in vitro in a collagen-gel medium at 0.5% fetal bovine serum concentration for 10 days in the presence of recombinant human transforming growth factor-beta-1, genetically engineered to contain a collagen binding domain (rhTGF-beta1-F2), or a commercial rhTGF-beta1. To compare the effects of TGF-betas with other growth factors in which the osteogenic capacity has been widely documented, a recombinant human bone morphogenetic protein (rhBMP-2) was evaluated. Once serum conditions compatible with growth were re-established, the selected cells were cultured for 6 more days in the presence of the growth factor. In the last 2 days, dexamethasone (dex) and beta-glycerophosphate (beta-GP) were added to promote osteogenesis. After this 16-day period, cells were placed into diffusion chambers or demineralized bone matrix (DBM) implants, and implanted subdermally on the backs of rats for 28 days. Biochemical, histological, and immunohistochemistry analysis provided evidence of cartilage (commercial rhTGF-beta1-treated cells), osteoid (rhTGF-beta1-F2-treated cells), and bone tissues (rhBMP-2 treated cells), inside the diffusion chambers, whereas bone, cartilage, and osteoid were observed inside the DBM implants under any of the three growth factors effect. Our study advances the technology capable of selecting a cell population from bone marrow that, in the presence of rhTGF-beta1 or rhBMP-2 in vitro, achieves chondro-osteogenic potential in vitro and in vivo.     

BMP-2 incorporated in a tricalcium phosphate bone substitute enhances bone remodeling in sheep

Bone morphogenetic protein-2 (BMP-2) is a well-known osteoinductive protein, which requires a carrier for local application. As an alternative to the previously described carriers, an in situ hardening, resorbable, and osteoconductive beta-tricalcium phosphate cement (TCP) is tested. Trepanation defects in the bovine distal femoral epiphysis are filled with a composite consisting of TCP and 200 microg rhBMP-2 per cm3 TCP, autologous bone graft, pure TCP, or left empty. A radiological follow-up is performed after 7 weeks and 3 months. The sheep are euthanized and bone samples are analyzed by microradiography, histology, and histomorphometry. Microradiography and histology show similar results for pure TCP and the composite. The defects are filled with trabecular bone and newly formed bone is in close contact with the remaining TCP-particles. The majority of the cement is resorbed, in the composite group the amount of remaining cement particles is reduced. Defects treated with autologous bone graft are filled completely, while untreated defects shows only a small amount of bone originating from the rim of the defect. Histomorphometry of the defects treated with pure TCP shows a significantly increased bone content in comparison to defects treated with the composite or autologous bone graft. Analysis of the remaining cement particles shows significantly less cement in the TCP/rhBMP-2 group in comparison to pure TCP. The sum of bone and cement content in the rhBMP-2 group shows amounts comparable to the calcified structures found following autologous bone grafting. The addition of rhBMP-2 to the TCP leads to faster remodeling of the defect comparable to autologous bone graft, while defects treated with pure TCP are not completely remodeled.     

Biological repair of thyroid cartilage defects by osteogenic protein-1 (bone morphogenetic protein-7) in dog

The efficacy of human recombinant osteogenic protein-1 (OP-1; bone morphogenetic protein-7) in regeneration of dog larynx was examined by treating thyroid cartilage defects (1.5 cm2) in dogs with thyroid allografts covered with host perichondrium or fascia. Prior to implantation allografts were frozen, thawed and demineralized. The treatment groups were as follows: I--Allograft control implant (n = 3); II--Implants coated with 500 micrograms OP-1 (n = 4); III--Implants coated with 100 micrograms OP-1 (n = 3); IV--Implants coated with 500 micrograms OP-1 and covered with neck fascia (n = 3); and V--Implants extracted with 1 M NaCl and guanidine hydrochloride, and coated with 500 micrograms OP-1 (n = 4). Dogs were sacrificed four months following surgery. Each larynx was removed, carefully dissected and a three-dimensional reconstruction of the defect area was performed on serial sections. The results revealed that the implants of control dogs remained intact with no apparent reduction in size and new tissue formation. OP-1 enriched thyroid allografts, dose dependently induced bone, cartilage and ligament-like structures comprising up to 80% of the total regenerated defect area. Boundaries of the defects healed by formation of new bone when bone resided within the old thyroid cartilage layers. Old cartilage not containing bone within its layers healed by complete integration with newly formed cartilage. Both new bone and cartilage were embedded into layers of new ligament-like tissue which expressed specific morphologic and molecular markers. The three newly formed tissues were tightly connected into a "bone-cartilage-ligament continuum" of tissues, suggesting that OP-1 served as a multiple tissue morphogen in this specific microenvironment.     

Adsorption and release of insulin-like growth factor-I on porous tricalcium phosphate implant

In order to develop bone substitutes, the design of biomaterials like calcium phosphate ceramic loaded with bone growth factor are of great interest. However, it is necessary to control the amount of growth factor adsorbed onto ceramics and the kinetics of its release. Radiolabeling of insulin-like growth factor-I (IGF-I) with 125-iodine ([(125)I]-IGF-I) and its adsorption onto porous tricalcium phosphate (TCP) cylinders enabled us to establish the time-adsorption and time-release curves using various concentrations of IGF-I. The adsorption curve increased rapidly and then flattened out at 72 h; 90% of the maximum was already reached at 24 h; and 20% of the adsorbed IGF-I was released in water within 4 days. In human serum the release was faster at 82% within 4 days. In vivo evaluation on an animal model was then performed. Rabbits' bilateral femoral cylindrical bone defects were filled with the TCP cylinders, which were either carrying IGF-I or implanted alone as a control in each rabbit. Bone turnover and ceramic resorption were stimulated by IGF-I loaded TCP according to standard radiography, dual-energy X-ray absorptiometry, histology, and histomorphometry.     

Mechanical and histological evaluations of hydroxyapatite-coated and noncoated Ti6Al4V implants in tibia bone

This paper evaluates the behavior of hydroxyapatite (HAP) coated and noncoated Ti6Al4V implants in dog tibia after 3 and 5 months implantation. HPA-coated implants were obtained by plasma spraying. XRD, SEM, and EPMA were employed to estimate the coating characteristics and their behavior in vivo. Investigation of material characteristics showed that the as-received coatings consisted mainly of amorphism and HAP phase. Other phases such as TCP and CaO were identified due to thermal changes of HAP particles in plasma flame. SEM micrographs showed a typical microstructure of plasma-sprayed coating. The as-received coating was formed by well-melted pancake-like splats that lead to a dense coating with a rough surface. Lamellar structure, micropores, and microcracks, observed inside the coating, are characteristic of plasma spraying. Push-out tests revealed that HAP coating had a significant promotion of interfacial shear strength. The shear strength between bone and HAP-coated implants was much higher than that between bone and noncoated implants due to the different bone-implant interfaces formed after implantation. SEM observation revealed a direct attachment between HAP coating and newly formed bone. However, noncoated implants were separated from newly formed bone by fibrous tissues. Ti ions were found to be released into the surrounding environment after long time immersion in body fluid, and thus caused low shear strength. Prolongation of implantation time had different effects on shear strength. It improved the shear strength between HAP-coated implant and newly formed bone. However, it had little effect on that between noncoated implant and surrounding tissues.     

Nanoindentation study of interfaces between calcium phosphate and bone in an animal spinal fusion model.

Intertransverse process spinal fusion is a common surgical procedure for the treatment of spinal disorders. In the present study, a porous hydroxyapatite (HA)/beta-tricalcium phosphate (beta-TCP) ceramic was tested as graft material using a rabbit lumbar transverse process (L5-L6) fusion model. The porous ceramic blocks were implanted onto the dorsal decorticated surface of the lumbar transverse processes. The specimens were harvested at the seventh week after implantation. Histomorphological observation revealed that the integration of HA/beta-TCP with the host bone of the transverse process occurred by both cancellous bone formation and cartilage formation. Scanning electron microscopy-wavelength dispersive X-ray spectrometry examinations showed significant differences in calcium, phosphorus, and sulfur contents in the newly formed tissues and the porous HA/TCP implants. Nanoindentations were used to evaluate the intrinsic mechanical properties of the implants and the newly formed tissues. The Young's moduli of the newly formed cartilage, new cancellous bone, and HA/TCP, were 0.66 +/- 0.02 GPa, 2.36 +/- 0.50 GPa, and 10.2 +/- 1.21 GPa, respectively. Nanoindentation results revealed degradation of the porous ceramics and incomplete calcification of the new cancellous bone at the seventh week after implantation. Nanoindentation appeared to be a useful technique for assessing the mechanical status of spinal fusion in animal models.     

In vitro change in mechanical strength of beta-tricalcium phosphate/copolymerized poly-L-lactide composites and their application for guided bone regeneration

The bone regenerative properties of calcium phosphate cements (CPCs) may be improved by the addition of growth factors, such as recombinant human transforming growth factor-beta1 (rhTGF-beta1). Previously, we showed that rhTGF-beta1 in CPC stimulated the differentiation of preosteoblastic cells from adult rat long bones. The intermixing of rhTGF-beta1 in CPC, which was subsequently applied to rat calvarial defects, enhanced bone growth around the cement and increased the degradation of the cement. However, it is unknown whether the addition of rhTGF-beta1 changes the material properties of CPC and what the characteristics of the release of rhTGF-beta1 from CPC are. Therefore, we determined in this study the release of rhTGF-beta1, in vitro, from the cement pellets as implanted in the rat calvariae. The possible intervening effects of rhTGF-beta1 intermixing on the clinical compliance of CPC were studied through an assessment of its compressive strength and setting time, as well as its crystallinity, calcium-to-phosphorus ratio, porosity, and microscopic structure. We prepared CPC by mixing calcium phosphate powder (58% alpha-tricalcium phosphate, 25% anhydrous dicalcium phosphate, 8.5% calcium carbonate, and 8.5% hydroxyapatite) with a liquid (3 g/mL). The liquid for standard CPC consisted of water with 4% disodium hydrogen phosphate, whereas the liquid for modified CPC was mixed with an equal amount of 4 mM hydrochloride with 0.2% bovine serum albumin. The hydrochloride liquid contained rhTGF-beta1 in different concentrations for the release experiments. Most of the rhTGF-beta1 incorporated in the cement pellets was released within the first 48 h. For all concentrations of intermixed rhTGF-beta1 (100 ng to 2.5 mg/g of CPC), approximately 0.5% was released in the first 4 h, increasing to 1.0% after 48 h. Further release was only about 0.1% from 2 days to 8 weeks. CPC modification slightly increased the initial setting time at 20 degrees C from 2.6 to 5 min but had no effect on the final setting time of CPC at 20 degrees C or the initial and final setting times at 37 degrees C. The compressive strength was increased from 18 MPa in the standard CPC to 28 MPa in the modified CPC only 4 h after mixing. The compressive strength diminished in the modified CPC between 24 h and 8 weeks from 55 to 25 MPa. No other significant change was found with the CPC modification for rhTGF-beta1. X-ray diffraction revealed that standard and modified CPCs changed similarly from the original components, alpha-tricalcium phosphate and anhydrous dicalcium phosphate, into an apatite cement. The calcium-to-phosphorus ratio, as determined with an electron microprobe, did not differ for standard CPC and modified CPC. Standard and modified CPCs became dense and homogeneous structures after 24 h, but the modified CPC contained more crystal plaques than the standard CPC, as observed with scanning electron microscopy (SEM). SEM and back- scattered electron images revealed that after 8 weeks the cements showed equally and uniformly dense structures with microscopic pores (<1 microm). Both CPCs showed fewer crystal plaques at 8 weeks than at 24 h. This study shows that CPC is not severely changed by its modification for rhTGF-beta1. The prolonged setting time of modified cement may affect the clinical handling but is still within acceptable limits. The compressive strength for both standard and modified cements was within the range of thin trabecular bone; therefore, both CPCs can withstand equal mechanical loading. The faster diminishing compressive strength of modified cement from 24 h to 8 weeks likely results in early breakdown and so might be favorable for bone regeneration. Together with the beneficial effects on bone regeneration from the addition of rhTGF-beta1 to CPC, as shown in our previous studies, we conclude that the envisaged applications for CPC in bone defects are upgraded by the intermixing of rhTGF-beta1. Therefore, the combination of CPC and rhTGF-beta1 forms a promising synthetic bone graft.     

Ectopic bone formation using osteogenic protein-1 carried by a solution precipitated hydroxyapatite

Solution precipitation of calcium and phosphate is a technique to generate hydroxyapatite [Peri-Apatitetrade mark (PA), Stryker Orthopaedics, Mahwah, NJ] on metal substrate. This study was carried out to determine the capacity of PA to adsorb osteogenic protein-1 (OP-1) and the time course of release, and to determine the osteoinductive activity of OP-1. The adsorption and release studies were conducted with (125)I-labeled OP-1- and PA-coated titanium alloy disks. The results indicate that the adsorption of OP-1 on the PA-coated disks is linear with the concentration of OP-1 up to 5 mg/mL. There is an initial release of 75% to 80% of adsorbed OP-1 within the first hour, and 92% of OP-1 is released in 3 days. The osteoinductive activity of OP-1 was determined in the rat intramuscular ectopic bone formation assay. A total of 24 titanium alloy disks were evenly divided into 3 groups with different treatments for implantation, plain disks (group A), disks coated with PA (group B), and disks coated with PA plus 40 microg OP-1 (group C). Osteogenic protein-1, 40 microg in solution, was injected into the muscle pouch in animals of group D (n = 8). The rats were sacrificed 3 weeks postoperatively and the implants were retrieved. Ectopic bone formation was evaluated with radiography and histology. Results demonstrated that OP-1 induced ectopic bone in all the animals of group C and group D. The titanium alloy disks were surrounded by trabecular bone and marrow tissue. None of the animals of group A or group B showed any evidence of osteoinduction. Our findings indicate that PA can deliver OP-1 directly to titanium alloy implants and maintain the osteoinductive activity of OP-1.     

Long-term stable canine mandibular augmentation using autologous bone marrow stromal cells and hydroxyapatite/tricalcium phosphate

Transplants of culture-expanded bone marrow stromal cells (BMSCs) combined with hydroxyapatite/tricalcium phosphate (HA/TCP) scaffolds successfully form cortico-cancellous bone to reconstruct the dog craniofacial skeleton. Yet, these transplants' long-term stability in large animal models has not been evaluated. This study's purpose was the evaluation of long-term BMSC transplant stability when used to augment the mandible. Here, autologous BMSC-HA/TCP transplants were introduced onto the unilateral dog mandible as onlay grafts, while contralateral control mandibles received HA/TCP onlays alone. Quantitative CT (qCT) scans were obtained both early and late after transplantation. Transplants were harvested up to 19 months later for histologic and mechanical analyses. In all dogs, BMSC transplants formed significantly greater amounts of bone over their control counterparts. The new bone formed an extensive union with the underlying mandible. BMSC transplants retained the majority of their initial volume, while control (HA/TCP only) transplants were nearly completely resorbed. By qCT, the extent of newly formed bone could be determined non-invasively. In summary, HA/TCP particles alone undergo a high degree of resorption, while autologous cultured BMSC-HA/TCP transplants provide long-term bony augmentation of the mandible.     

Osteocalcin enhances bone remodeling around hydroxyapatite/collagen composites

The effect of osteocalcin (OC), an extracellular bone matrix protein, on bone healing around hydroxyapatite/collagen composites was investigated. Cylindrical nanocrystalline hydroxyapatite implants of 2.5-mm diameter containing 2.5% biomimetically mineralized collagen type I were inserted press-fit into the tibial head of adult Wistar rats. To one implant group, 10 mug/g OC was added. Six specimens per group were analyzed at 2, 7, 14, 28, and 56 days. After 14 days, newly formed woven bone had reached the implant surface of the OC implants whereas a broad fibrous interface could still be observed around controls. Woven bone was formed directly around both implant groups after 28 days and had been replaced partially by lamellar bone around the OC implants only. No significant differences in total bone contact were seen between both groups after 56 days. The higher number of phagocytosing cells and osteoclasts characterized immunohistochemically with ED1, cathepsin D, and tartate-resistant alkaline phosphatase around the OC implants at the early stages of bone healing suggests an earlier onset of bone remodeling. The earlier and increased expression of bone-specific matrix proteins and multifunctional adhesion proteins (osteopontin, bone sialoprotein, CD44) at the interface around the OC implants indicates that OC may accelerate bone formation and regeneration. This study supports the observations from in vitro studies that OC activates both osteoclasts and osteoblasts during early bone formation.     

Osteogenic protein-1 enhances osseointegration of titanium implants coated with peri-apatite in rabbit femoral defect

This study evaluated the effect of osteogenic protein-1 (OP-1) carried by Peri-Apatite (PA) on bone healing in the gap surrounding implants in a rabbit model. Cylindrical titanium implants (3 x 9 mm) were uniformly coated with PA precipitated from a calcium and phosphate solution. OP-1 solution containing 60 microg OP-1 was directly loaded on the implants immediately before implantation for the experimental group, whereas buffer solution was loaded on the implants for the control. The implant was placed in the distal femur and surrounded by a 1-mm gap. The implants were retrieved and examined 6 weeks after implantation. Mechanical testing (push-out) data showed that OP-1 enhanced implant fixation by 80%. Histomorphometric measurements indicated that bone ingrowth in the initial gap expressed as a percentage of the whole gap was significantly higher in the specimens treated with OP-1 than the control group (25.4% vs. 8.9%, p < 0.05). The percentage of the surface of implants, which was covered by bone, was significantly higher in the OP-1-treated group compared to the control group (65% vs. 25%, p < 0.05). This study suggests that OP-1 can be loaded on orthopedic implants through PA to enhance the osseointegration of orthopedic implant.     

Effect of osteogenic protein 1/collagen composite combined with impacted allograft around hydroxyapatite-coated titanium alloy implants is moderate.

This study evaluated the effects of osteogenic protein 1/collagen composite (OP-1/col) mixed with impacted allograft around hydroxyapatite (HA)-coated titanium alloy implants in a canine model. The aim of the study was to test different doses of OP-1 growth factor in a collagen composite for stimulatory effect on allograft incorporation around an implant. Unloaded implants were inserted in each proximal humerus of 16 skeletally mature dogs. The cylindrical implants (4 x 9 mm) coated with HA were initially surrounded by a 3-mm gap into which allograft mixed with OP-1/col was impacted. Two different doses of OP-1 were investigated. In eight animals 325 mg OP-1 protein and 130 mg bovine collagen type I as carrier were mixed with the allograft chips.This composite is identical to the clinically used OP-1 device called Novus. In another eight animals a lower dose of 65 mg OP-1 protein and 130 mg bovine collagen type I was used. Control implants placed in the contralateral humerus were surrounded by allograft mixed with collagen carrier only. The dogs were euthanized at 6 weeks. Implant fixation was determined by push-out testing. Bone ingrowth and bone formation were evaluated by quantitative histomorphometry on serial sections of the bone-implant interface. Impacted allograft together with low-dose OP-1 enhanced bone volume in a zone adjacent to HA-coated titanium alloy implants. The high dose had no effect on bone formation. Mechanical fixation, bone ingrowth, and bone volume in the gap near the original trabecular bone were unaffected by both low and high OP-1/col composite. In this model and observation period, the low dose of OP-1/col composite mixed with impacted allograft has a moderate effect on bone healing around HA-coated implants and no effect on implant fixation.     

Tracheal cartilage regeneration and new bone formation by slow release of bone morphogenetic protein (BMP)-2

We investigated the efficiency of bone morphogenetic protein (BMP)-2 released slowly from gelatin sponge for tracheal cartilage regeneration. A 1-cm gap was made in the mid-ventral portion of each of 10 consecutive tracheal cartilages. In the control group (n = 4), the resulting gap was left untreated. In the gelatin group (n = 4), plain gelatin was implanted in the gap. In the BMP-2 group (n = 4), gelatin containing 100 microg BMP-2 was implanted. We euthanatized all dogs in each group at 1, 3, 6, and 12 months after the implantation, respectively, and then examined the implant site macro- and microscopically. In the BMP-2 group, regenerated fibrous cartilage and newly formed bone were observed at 1 and 12 months. Regenerated cartilage was observed at the ends of the host cartilage stumps, with newly formed bone in the middle portion. The gaps were filled with regenerated cartilage and newly formed bone. At 3 and 6 months, regenerated cartilage, but not newly formed bone, was evident. The regenerated cartilage was covered with perichondrium and showed continuity with the host cartilage. We succeeded in inducing cartilage regeneration and new bone formation in canine trachea by slow release of 100 microg BMP-2 from gelatin.     

Biological Repair of Thyroid Cartilage Defects by Osteogenic Protein-1 (Bone Morphogenetic Protein-7) in Dog

The efficacy of human recombinant osteogenic protein-1 (OP-1; bone morphogenetic protein-7) in regeneration of dog larynx was examined by treating thyroid cartilage defects (1.5 cm²) in dogs with thyroid allografts covered with host perichondrium or fascia. Prior to implantation allografts were frozen, thawed and demineralized. The treatment groups were as follows: I - Allograft control implant (n = 3); II - Implants coated with 500 μg OP-1 (n = 4); III - Implants coated with 100 μg OP-1 (n = 3); IV - Implants coated with 500 μg OP-1 and covered with neck fascia (n = 3); and V - Implants extracted with 1M NaCl and guanidine hydrochloride, and coated with 500 μg OP-1 (n = 4). Dogs were sacrificed four months following surgery. Each larynx was removed, carefully dissected and a three-dimensional reconstruction of the defect area was performed on serial sections. The results revealed that the implants of control dogs remained intact with no apparent reduction in size and new tissue formation. OP-1 enriched thyroid allografts, dose dependently induced bone, cartilage and ligament-like structures comprising up to 80% of the total regenerated defect area. Boundaries of the defects healed by formation of new bone when bone resided within the old thyroid cartilage layers. Old cartilage not containing bone within its layers healed by complete integration with newly formed cartilage. Both new bone and cartilage were embedded into layers of new ligament-like tissue which expressed specific morphologic and molecular markers. The three newly formed tissues were tightly connected into a “bone-cartilage-ligament continuum” of tissues, suggesting that OP-1 served as a multiple tissue morphogen in this specific microenvironment.