Effect of freeze-dried poly-L-lactic acid discs mixed with bone morphogenetic protein on the healing of rat skull defects

Biological Evaluation of Flexible Polyurethane/Poly l-Lactic Acid Composite Scaffold as a Potential Filler for Bone Regeneration

Degradable bone graft substitute for large-volume bone defects is a continuously developing field in orthopedics. With the advance in biomaterial in past decades, a wide range of new materials has been investigated for their potential in this application. When compared to common biopolymers within the field such as PLA or PCL, elastomers such as polyurethane offer some unique advantages in terms of flexibility. In cases of bone defect treatments, a flexible soft filler can help to establish an intimate contact with surrounding bones to provide a stable bone-material interface for cell proliferation and ingrowth of tissue. In this study, a porous filler based on segmented polyurethane incorporated with poly l-lactic acid was synthesized by a phase inverse salt leaching method. The filler was put through in vitro and in vivo tests to evaluate its potential in acting as a bone graft substitute for critical-sized bone defects. In vitro results indicated there was a major improvement in biological response, including cell attachment, proliferation and alkaline phosphatase expression for osteoblast-like cells when seeded on the composite material compared to unmodified polyurethane. In vivo evaluation on a critical-sized defect model of New Zealand White (NZW) rabbit indicated there was bone ingrowth along the defect area with the introduction of the new filler. A tight interface formed between bone and filler, with osteogenic cells proliferating on the surface. The result suggested polyurethane/poly l-lactic acid composite is a material with the potential to act as a bone graft substitute for orthopedics application.

Oxysterols enhance osteoblast differentiation in vitro and bone healing in vivo

Oxysterols, naturally occurring cholesterol oxidation products, can induce osteoblast differentiation. Here, we investigated short-term 22(S)-hydroxycholesterol + 20(S)-hydroxycholesterol (SS) exposure on osteoblastic differentiation of marrow stromal cells. We further explored oxysterol ability to promote bone healing in vivo. Osteogenic differentiation was assessed by alkaline phosphatase (ALP) activity, osteocalcin (OCN) mRNA expression, mineralization, and Runx2 DNA binding activity. To explore the effects of osteogenic oxysterols in vivo, we utilized the critical-sized rat calvarial defect model. Poly(lactic-co-glycolic acid) (PLGA) scaffolds alone or coated with 140 ng (low dose) or 1400 ng (high dose) oxysterol cocktail were implanted into the defects. Rats were sacrificed at 6 weeks and examined by three-dimensional (3D) microcomputed tomography (microCT). Bone volume (BV), total volume (TV), and BV/TV ratio were measured. Culture exposure to SS for 10 min significantly increased ALP activity after 4 days, while 2 h exposure significantly increased mineralization after 14 days. Four-hour SS treatment increased OCN mRNA measured after 8 days and nuclear protein binding to an OSE2 site measured after 4 days. The calvarial defects showed slight bone healing in the control group. However, scaffolds adsorbed with low or high-dose oxysterol cocktail significantly enhanced bone formation. Histologic examination confirmed bone formation in the defect sites grafted with oxysterol-adsorbed scaffolds, compared to mostly fibrous tissue in control sites. Our results suggest that brief exposure to osteogenic oxysterols triggered events leading to osteoblastic cell differentiation and function in vitro and bone formation in vivo. These results identify oxysterols as potential agents in local and systemic enhancement of bone formation.

Evaluation of pluronic polyols as carriers for grafting materials: study in rat calvaria defects

BACKGROUND

Pluronic polyols are a family of non-ionic surfactants currently used as drug carriers for antibiotic, anti-inflammatory, and anti-neoplastic agents. Therapeutic administration of non-ionic surface-active agents is known to facilitate early collagen synthesis and microcirculation, thus promoting wound healing. The purpose of this study was to determine the in vivo effects of pluronic polyols combined with either an allograft or an alloplast on the healing of critical-sized calvarial defects.

METHODS

One hundred fifty (150) adult (95 to 105 days old) male Sprague-Dawley rats weighing between 375 and 425 g were randomly and evenly assigned to each of 15 separate treatment groups and anesthetized, and 8 mm calvarial critical-sized defects were created. Pluronic F-68 (F-68) or pluronic F-127 (F-127) was administered either topically or systemically and in conjuction with demineralized bone powder (DBP), tricalcium phosphate (TCP), or non-grafted controls. Pluronic polyols are easily mixed with either DBP or TCP to improve handling ease. Calvaria were harvested at 12 weeks postsurgery and evaluated histomorphometrically, by contact radiography with subsequent densitometric analysis, through energy spectrometry utilizing a scanning electron microscope, and by fluorescent microscopy.

RESULTS

There was a significant difference in the percentage of bone fill among the control, TCP, and DBP only groups, P <0.05. The only significant difference within any of these groups was between the TCP control and TCP plus systemic F-127, P<0.05.

CONCLUSIONS

Although there were isolated differences, the overall trend was that the pluronic polyol and the mode of administration did not result in a significant change in bone wound healing as measured by the percentage of bone fill. Pluronic polyols may be considered as carriers for osseous graft materials.

Enhancement of bone growth by sustained delivery of recombinant human bone morphogenetic protein-2 in a polymeric matrix

PURPOSE

The purpose of this study was to develop a polymeric sustained delivery system for recombinant human bone morphogenetic protein-2 (BMP-2) and to evaluate local bone growth induced by the sustained release of BMP-2 in an animal model.

METHODS

BMP-2 was incorporated in biodegradable poly(D,L-lactide-co-glycolide) (PLGA) microspheres to obtain different release rates. Two sustained and an immediate release implants were produced by suspending the BMP-2 loaded PLGA microspheres in aqueous sodium carboxymethylcellulose (CMC), lyophilizing, and cutting the dried materials to the size of the animal bone defects. The local in vivo release at the implantation site in rat calvarial defects was determined by gamma scintigraphy using radiolabeled BMP-2. The local bone induction in the critical size of rabbit calvarial defects was evaluated six weeks post implantation.

RESULTS

The immediate release implant showed about 65% initial drug release within 24 h and the remaining BMP-2 quickly exhausted from the implantation site within 7 days. The sustained release implants, showing 45-55% initial release followed by a prolonged release for 21 days, released a greater amount of BMP-2 at the implantation site and maintained higher serum BMP-2 for the longer period of time compared to the immediate release implant. Significant bone growth was observed in all BMP-2 treated defects while the defects without treatment or with BMP-2-free implant showed minimal bone healing. 75-79% of rabbit calvarial defect area was healed with newly induced bone matrix by the sustained release implants in 6 weeks as compared to 45% recovery from the immediate release implant.

CONCLUSION

The sustained delivery of BMP-2 based on the biodegradable PLGA microsphere system resulted in faster and more complete bone healing in the animal model.

Osteogenic evaluation of glutaraldehyde crosslinked gelatin composite with fetal rat calvarial culture model

The cytotoxicity of the synthetic bone substitute composed of tricalcium phosphate and glutaraldehyde crosslinked gelatin (GTG) were evaluated by osteoblast cell culture. In a previous study, the GTG composites were soaked in distilled water for 1, 2, 4, 7, 14, 28, and 42 days, and then the solutions (or extracts) were cocultured with osteoblasts to evaluate the cytotoxicity of GTG composites by alive cell counting. In this study, the extracts were cocultured with the osteoblasts; thereafter, the concentration of transforming growth factor-beta (TGF-beta1) and prostaglandin E2 (PGE2) in the medium was analyzed to strictly reflect the biological effects of GTG composites on the growth of osteoblasts. In order to investigate the osteoconductive potential of the GTG composites on new bone formation in a relative short term, a model of neonatal rat calvarial organ culture was designed prior to animal experiments. Three experimental materials of 4, 8, and 12% GTG composites were evaluated by fetal rat calvarial organ culture for their ability for bone regeneration. Deproteinized bovine and porcine cancellous bone matrixes were used as the controlled materials. All the organ culture units were maintained in cultured medium for 5 weeks. Following the culture period, the morphology of tissue was observed under an optical microscope, and the quantitative evaluation of the new generation bone was determined by using a semiautomatic histomorphometeric method. Except in the initial 4 days, the concentration of TGF-beta1 of 4% and 8% GTG composites was higher than that of the blank group for all the other experimental time periods. The PGE2 concentration for 4% and 8% GTG composites was lower than that of the blank group. It revealed that the 4% and 8% GTG composites would not lead to inflammation and would promote osteoblast growth. The morphology and activity of the osteoblasts were not transformed or changed by the 2 GTG composites. For the 12% GTG composite, the performance of the in vitro condition was inferior to the blank group and the other 2 GTG composites. Although the concentration of TGF-beta1 and PGE2 was gradually back to normal after 14 days, the morphology of the osteoblasts was abnormal with features such as contracted cytoplast structures. The osteoblast was damaged perhaps in the initial stage. We suggested that the 4% and 8% GTG composites should be soaked in distilled water at least for 4 days before medical applications. The 12% GTG composite and the composites with a concentration of glutaraldehyde solution higher than 12% were not recommended as a medical prostheses in any condition. The fetal rat calvaria culture also showed the same results with the analysis of TGF-beta1 and PGE2. From the study, we could predict the results of animal experiments in the future.

Pre-clinical in vivo evaluation of orthopaedic bioabsorbable devices

The presence of bioabsorbable materials in orthopaedics has grown significantly over the past two decades with applications in fracture fixation, bone replacement, cartilage repair, meniscal repair, fixation of ligaments, and drug delivery. Numerous biocompatible, biodegradable polymers are now available for both experimental and clinical use. Not surprisingly, there have been a wealth of studies investigating the biomechanical properties, biocompatibility, degradation characteristics, osteoconductivity, potential toxicity, and histologic effects of various materials. Promising results have been reported in the areas of fracture fixation, ligament repair, and drug delivery. In this article we review the pre-clinical in vivo testing of bioabsorbable devices with particular emphasis on implants used for these applications.

Experience with freeze-dried PGLA/HA/rhBMP-2 as a bone graft substitute

We investigated bone induction by recombinant human bone morphogenetic protein-2 in rodents. The purpose of this study was to evaluate the osteoinductive potential of a resorbable bone substitute fabricated from freeze-dried poly(glycolic acid-co-lactic acid) (PGLA) mixed with hydroxyapatite particles incorporated with bone morphogenetic protein-2 in skull defects of rats (FD-PGLA/HA/rhBMP-2). The FD-PGLA/HA/rhBMP-2 composite or as a control, the FD-PGLA/HA by itself were implanted in skull defects (psi 8 mm) of rats. The samples were harvested at 2 or 4 weeks postoperatively and were studied radiographically and histologically. Four weeks after implantation, the FD-PGLA/HA/rhBMP-2 discs were completely replaced by newly-formed bone possessing bone marrow. In contrast, the defects implanted with FD-PGLA/HA were filled only with fibrous connective tissue. The results suggest that the FD-PGLA/HA/rhBMP-2 composite could be an optimum bone substitute with osteoinductive potential and could function as an alternative bone graft material for autogenous bone in humans.

Porcine fetal enamel matrix derivative enhances bone formation induced by demineralized freeze dried bone allograft in vivo

BACKGROUND

Embryonic enamel matrix proteins are involved in the formation of acellular cementum during development of the periodontal attachment apparatus, suggesting that these proteins might be used clinically to promote periodontal regeneration. At present, it is unknown if these proteins are osteoinductive, osteoconductive, or osteopromotive. To address this question, we examined the ability of a commercially prepared embryonic porcine enamel matrix derivative to induce new bone formation in nude mouse calf muscle, or to enhance the bone induction ability of a demineralized freeze-dried bone allograft (DFDBA).

METHODS

Porcine fetal enamel matrix derivative (EMD) was implanted bilaterally in the calf muscle of 4 male Nu/Nu mice per treatment group (N = 8 implants): 2 mg EMD alone; 4 mg EMD alone; inactive human DFDBA alone; inactive DFDBA + 2 mg EMD; inactive DFDBA + 4 mg EMD; active DFDBA alone; active DFDBA + 2 mg EMD; and active DFDBA + 4 mg EMD. Implants were harvested after 56 days and examined histologically for bone induction using a semi-quantitative score and histomorphometrically for area of new bone, cortical bone, bone marrow, and residual DFDBA.

RESULTS

Implants containing inactive DFDBA, 2 mg EMD, 4 mg EMD, and inactive DFDBA + 2 or 4 mg EMD did not induce new bone. Active DFDBA and active DFDBA + 2 mg EMD induced new bone to a similar extent. In contrast, active DFDBA + 4 mg EMD resulted in enhanced bone induction, area of new bone, and cortical bone. Residual DFDBA was also increased in this group.

CONCLUSIONS

EMD is not osteoinductive. However, it is osteopromotive, due in part to its osteoconductive properties, but a threshold concentration is required.

Experimental computer-assisted alloplastic sandwich augmentation of the atrophic mandible

PURPOSE

This study evaluated the effectiveness of a technique that combined computer-aided surgery with alloplastic augmentation and implant-borne prosthodontic rehabilitation of the atrophic mandible.

MATERIALS AND METHODS

Computed tomographic (CT) data from an atrophic cadaver mandible were transferred to a computer-aided design (CAD) system that prepared an anterior sandwich osteotomy. The cranial segment was moved upward and backward to provide an ideal alveolar relationship, and the geometry of the intermediate space was used to design a titanium implant. Furthermore, a surgical template was derived for the osteotomies, and insertion of dental implants was planned to stabilize both the transposed bone and the intermediate implant on the bony base. An identical implant for augmentation was also fabricated from poly-D,L-lactide in a mold as a possible resorbable carrier for osteoinductive proteins.

RESULTS

The experimental surgery was successfully performed with maximum precision on the dried mandible. The fabrication of an implant made out of poly-D,L-lactide for the same purpose was also possible.

CONCLUSIONS

This preliminary experiment showed that it is possible to use CAD/computer-aided manufacturing (CAM) technology to prepare a prefabricated template and a corresponding titanium implant for mandibular augmentation with a high degree of exactness. Dental implants could be planned and integrated in this procedure as well. The fabrication of a mold using this method also provided the opportunity to give a complex shape to possible carriers of osteoinductive substances.

New synthetic absorbable polymers as BMP carriers: plastic properties of poly-D,L-lactic acid-polyethylene glycol block copolymers

Bone morphogenetic proteins (BMPs) are biologically active molecules capable of eliciting new bone formation. In combination with biomaterials, these proteins can be used in a clinical setting as bone-graft substitutes to promote bone repair. To find new synthetic absorbable polymers with plastic nature that can be used as BMP-carrier materials, six types of poly-D,L-lactic acid-polyethylene glycol block copolymer (PLA-PEG) with various molecular weights of PLA and PEG were synthesized. These were PLA6, 500-PEG3,000 (P-1), PLA11,500-PEG3,000 (P-2), PLA17,500-PEG3,000 (P-3), PLA6,500-PEG1,000 (P-4), PLA15,000-PEG8,000 (P-5), and PLA8, 500-PEG1,000 (P-6). Fifty milligrams of these polymers was mixed with 0 microg (control) or 5, 10, or 20 microg of recombinant human BMP-2 (rhBMP-2). These pellets were implanted into the dorsal muscle pouches of 144 mice (six pellets consisting of the same polymer and dose of rhBMP-2 for a specific group). Three weeks after surgery, the pellets were harvested and examined by radiographic and histological methods. All P-1 pellets with 10 or 20 microg of rhBMP-2 showed bone formation with hematopoietic marrow and bony trabeculae, as did one third of those with 5 microg of rhBMP-2. The incidence of new bone formation with P-2 pellets or that of P-5 pellets was lower than that of P-1 pellets. No bone was formed in any other type of pellet. These results indicated that the PLA6, 500-PEG3,000 polymer with plastic properties was found to work well as a BMP carrier.

Potential of porous poly-D,L-lactide-co-glycolide particles as a carrier for recombinant human bone morphogenetic protein-2 during osteoinduction in vivo

Several different biodegradable bone graft materials are in clinical or preclinical use for the repair of bone defects in orthopedics, maxillofacial surgery, and periodontics. This study tested the hypothesis that poly-D,L-lactide-co-glycolide copolymer (PLG) can be used as an effective carrier of recombinant human bone morphogenetic protein-2 (rhBMP-2) and that the composite has osteoinductive ability. Porous PLG rods were shredded to a particle size ranging from 250 to 850 microm. Active and inactive demineralized freeze-dried bone allografts (DFDBA) with a comparable particle size were used as positive and negative controls, respectively. PLG particles were treated with vehicle or with 5 or 20 microg rhBMP-2. DFDBA and PLG particles were placed in gelatin capsules, mixed with vehicle or rhBMP-2, and implanted at intramuscular sites in male Nu/Nu (nude) mice. Each mouse underwent bilateral implantation with implants of the same formulation, resulting in five groups of four mice per group: active DFDBA, inactive DFDBA, PLG, PLG + 5 microg rhBMP-2, and PLG + 20 microg rhBMP-2. After 56 days, the implants were recovered and processed for histology. Bone induction was assessed by use of a semiquantitative scoring system based on the amount of new bone formed in representative histological sections. Histomorphometry was also used to measure the area of new bone formed and the area of residual implant material. The results showed that active DFDBA induced the formation of ossicles containing new bone with bone marrowlike tissue, whereas inactive DFDBA or PLG particles alone did not induce new bone. The addition of rhBMP-2 to PLG particles resulted in new bone formation that had a greater bone induction score than active DFDBA. Moreover, the histomorphometric analysis showed that the addition of rhBMP-2 to PLG particles induced the formation of a greater area of new bone and bone marrowlike tissue than active DFDBA. The resorption of the PLG particles was markedly increased with the addition of rhBMP-2, suggesting that rhBMP-2 may attract and regulate resorptive cells at the implantation site. The results of the present study indicate that PLG copolymers are good carriers for BMP and promote the induction of new bone formation. Further, the PLG copolymers with rhBMP-2 had a greater effect in inducing new bone formation and resorbing the implanted material than active DFDBA alone.

Effects of added antibiotics on the basic properties of anti-washout-type fast-setting calcium phosphate cement

The effect of added antibiotics on the basic properties of anti-washout-type fast-setting calcium phosphate cement (aw-FSCPC) was investigated in a preliminary evaluation of aw-FSCPC containing drugs. Flomoxef sodium was employed as the antibiotic and was incorporated into the powder-phase aw-FSCPC at up to 10%. The setting time, consistency, wet diametral tensile strength (DTS) value, and porosity were measured for aw-FSCPC containing various amounts of flomoxef sodium. X-ray diffraction (XRD) analysis was also conducted for the identification of products. To evaluate the drug-release profile, set aw-FSCPC was immersed in saline and the released flomoxef sodium was determined at regular intervals. The spread area of the cement paste as an index of consistency of the cement increased progressively with the addition of flomoxef sodium, and it doubled when the aw-FSCPC contained 8% flomoxef sodium. In contrast, the wet DTS value decreased with increase in flomoxef sodium content. Bulk density measurement and scanning electron microscopic observation revealed that the set mass was more porous with the amount of flomoxef sodium contained in the aw-FSCPC. The XRD analysis revealed that formation of hydroxyapatite (HAP) from aw-FSCPC was reduced even after 24 h, when the aw-FSCPC contained flomoxef sodium at > or = 6%. Therefore, the decrease of wet DTS value was thought to be partly the result of the increased porosity and inhibition of HAP formation in aw-FSCPC containing large amounts of flomoxef sodium. The flomoxef sodium release from aw-FSCPC showed the typical profile observed in a skeleton-type drug delivery system (DDS). The rate of drug release from aw-FSCPC can be controlled by changing the concentration of sodium alginate. Although flomoxef sodium addition has certain disadvantageous effects on the basic properties of aw-FSCPC, we conclude that aw-FSCPC is a good candidate for potential use as a DDS carrier that may be useful in surgical operations.

Osteoinductive potential of freeze-dried, biodegradable, poly (glycolic acid-co-lactic acid) disks incorporated with bone morphogenetic protein in skull defects of rats

Biodegradable, porous, polymer implant disks with an osteoinductive potential were prepared by a freeze-drying technique by incorporating bovine bone morphogenetic protein (BMP) in poly (glycolic acid-co-lactic acid) (PGLA). The PGLA disks with and without BMP were implanted in rat skull defects, and the defect sites were studied radiographically and histologically for 2 and 4 weeks after implantation. A quantitative radiographic analysis showed significantly thicker radiopacity for the disks with BMP than those without BMP (P < 0.01). After 2 weeks, chondrogenesis and new bone formation were observed on the BMP-incorporated disks. After 4 weeks, PGLA was completely replaced by new bone in the defects with implantation of the BMP-incorporated disks, whereas the defects implanted with PGLA alone were filled with fibrous connective tissue. The results suggest that BMP-incorporated PGLA is an ideal bone substitute with osteoinductive potential.

Healing of experimentally created defects: a review

Within cranio-maxillofacial surgery and orthopedic surgery a bone graft or a bone substitute is required to recontour or assist bony healing in repair of osseous congenital deformities, or in repair of deformity due to trauma or to surgical excision after elimination of osseous disease processes exceeding a certain size. An autogenous bone graft is the optimal material of choice, however its use is problematic due to donor site morbidity, sparse amounts and uncontrolled resorption. Immunological responses and risk of viral contamination of allogenous and xenogenous bone materials make the use of these materials questionable. Healing and degradation of alloplastic materials are inconsistent with subsequent restricted use. The principle of guided tissue regeneration excluding soft tissue cells from a certain area is not alone sufficient to insure complete bony healing. Recombinant bone morphogenetic proteins have with success been added as adjuncts to already known biomaterials. In the future, inductive materials together with a suitable carrier and a biodegradable membrane may be the choice of bone substitute used within cranio-maxillofacial and orthopaedic surgery.