Bone induction by composite of bioerodible polyorthoester and demineralized bone matrix in rats

Universal Hydrogel Carrier Enhances Bone Graft Success: Preclinical and Clinical Evaluation

Orthopedic, maxillofacial, and complex dentoalveolar bone grafting procedures that require donor-site bone harvesting can be associated with post-surgical complications. There has been widespread adoption of exogenously sourced particulate bone graft materials (BGM) for bone regenerative procedures; however, the particulate nature of these materials may lead to compromised healing outcomes, mainly attributed to structural collapse of the BGM, prolonged tissue healing. In this study, a fully synthetic thermoresponsive hydrogel-based universal carrier matrix (TX) that forms flowable and shapable putties with different BGMs while spatially preserving the particles in a 3D scaffold at the implantation site is introduced. The potential synergistic effect of the carrier is investigated in combination with particulate demineralized bone matrix (DBM) in a standard muscle pouch nude mice model (n = 24) as well as in a rabbit femoral critical-sized cortico-cancellous bone defect model (n = 9). Finally, the clinical usability, safety, and efficacy of the carrier for the delivery of deproteinized bovine bone mineral (DBBM) are evaluated in a controlled clinical trial for extraction socket alveolar ridge preservation (ARP) (n = 11 participants). Overall, the TX carrier improved the delivery of different types of BGMs, maintaining these spatially at the implantation site with minimal inflammatory responses, resulting in favorable bone regenerative outcomes.

Comparable bone healing capacity of different bone graft matrices in a rabbit segmental defect model

We compared the bone healing capacity of three different demineralized bone matrix (DBM) products applied using different carrier molecules (hyaluronic acid [HA] vs. carboxymethylcellulose [CMC]) or bone compositions (cortical bone vs. cortical bone and cancellous bone) in a rabbit segmental defect model. Overall, 15-mm segmental defects in the left and right radiuses were created in 36 New Zealand White rabbits and filled with HA-based demineralized cortical bone matrix (DBX), CMC-based demineralized cortical bone matrix (DB) or CMC-based demineralized cortical bone with cancellous bone (NDDB), and the wound area was evaluated at 4, 8, and 12 weeks post-implantation. DBX showed significantly lower radiopacity, bone volume fraction, and bone mineral density than DB and NDDB before implantation. However, bone healing score, bone volume fraction, bone mineral density, and residual bone area at 4, 8, and 12 weeks post-implantation revealed no significant differences in bone healing capacity. Overall, three DBM products with different carrier molecules or bone compositions showed similar bone healing capacity.

Delivery of demineralized bone matrix powder using a thermogelling chitosan carrier

Demineralized bone matrix (DBM) powder is widely used for bone regeneration due to its osteoinductivity and osteoconductivity. However, difficulties with handling, its tendency to migrate from graft sites, and lack of stability after surgery can sometimes limit the clinical utility of this material. In this work, the possibility of using a thermogelling chitosan carrier to deliver DBM powder was assessed. The DBM-thermogelling putty improved handling and formed a gel-like composite in situ at body temperature within a clinically relevant time period. The properties of the formed composite, including morphology, porosity, mechanical properties, equilibrium swelling as well as degradability, are significantly influenced by the ratio of DBM to thermogelling chitosan. The in vitro study showed that the alkaline phosphatase activity of C2C12 cells encapsulated in the composite was steadily increased with culture time. The in vivo study showed that increased DBM content in the DBM-thermogelling chitosan induced ectopic bone formation in a nude rat model. The diffusion of growth factor from the DBM-thermogelling chitosan as well as the host-implant interactions are discussed.

No positive effects of OP-1 device on the incorporation of impacted graft materials after 8 weeks: a bone chamber study in goats

BACKGROUND

Bone morphogenetic proteins (BMPs) have the potential to improve clinical outcome after hip revision surgery by improving graft incorporation and implant fixation. However, impaction of cancellous bone grafts and TCP/HA bone substitute mixed with OP-1 device in a bone chamber in goats in a previous study led to reduced fibrous tissue ingrowth after 4 weeks. New bone formation was not promoted by OP-1. In the current study we examined whether this reduction represented a final loss of ingrowth or was just a delay, and whether the reduction can be overcome and ultimately results in a better late ingrowth.

METHODS

Bone chambers with impacted allografts and impacted TCP/HA granules mixed with 2 doses of OP-1 device were implanted in proximal medial goat tibias. Impacted allografts and TCP/HA not treated with OP-1 served as controls. After 8 weeks, the incorporation was evaluated using histology and histomorphometry.

RESULTS

Histology revealed evidence of bone graft incorporation, which proceeded in a similar way in both allografts and TCP/HA, with and without the addition of OP-1. After 8 weeks, no difference in bone ingrowth was found between the OP-1 groups and their controls. It was only in the allografts that the addition of OP-1 resulted in more fibrous tissue ingrowth.

INTERPRETATION

We conclude that the previously observed delay in fibrous tissue ingrowth can be only partially overcome.

Bone defect healing with an osteogenic protein-1 device combined with carboxymethylcellulose

One consideration for the practical use and application of osteogenic proteins is an effective method of delivery. This study evaluated a putty-type collagen carrier with recombinant human osteogenic protein-1 (rhOP-1) ability to heal canine critical sized (2.5 cm) ulna segmental defects compared to rhOP-1 with a particulate collagen carrier (OP device). The addition of carboxymethylcellulose (CMC) to the particulate collagen carrier (OPCMC device) to form the putty consistency was evaluated in two doses (3.5 and 1.75 mg rhOP-1/g carrier). The CMC greatly improved the intraoperative handling and site containment of the device. For the one-half dose and full-dose sites there were no statistically significant differences in the radiographic grading of defect healing when treated with the particulate OP-1 device and the device with CMC added. However, there was a dose effect with greater and earlier new bone formation observed with increased rhOP-1. Mechanically, there were no differences between particulate and putty formulations, although again, a significant effect was observed for treatment dose with the full-dose OPCMC device restoring 94% of the strength of the intact ulna compared to only 65% for the identical one-half dose implant. Regardless of rhOP-1 dose, the quality of union grading and total histologic score appearance were improved with the addition of CMC, although differences in histologic scoring were not statistically significant. Overall, the radiographic, mechanical, and histologic bone-healing characteristics with the one-half dose OPCMC device were similar to sites treated with the full-dose OP device. The observed improvement in healing may allow for lesser amounts of the device or a device with less rhOP-1 to be used.

Therapeutic applications of viscous and injectable poly(ortho esters)

Poly(ortho esters) (POE) are hydrophobic and bioerodible polymers that have been investigated for pharmaceutical use since the early 1970s. Among the four described generations of POE, the third (POE III) and fourth (POE IV) are promising viscous and injectable materials which have been investigated in numerous biomedical applications. POE III has been extensively studied for ophthalmic drug delivery, it presents an excellent biocompatibility and is currently being investigated as a vehicle for sustained drug delivery to treat diseases of the posterior segment of the eye. POE IV is distinguishable by a highly reproducible and controlled synthesis, a higher hydrophobicity, and an excellent biocompatibility. It is currently under development for a variety of applications, such as ocular delivery, periodontal disease treatment and applications in veterinary medicine. This review will also focus on new perspectives for this promising family of polymers, such as guided tissue regeneration, treatment of osteoarthritis, as well as peptide and protein delivery.

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.

Biocompatibility and effect on osteogenesis of poly(ortho ester) compared to poly(DL-lactic acid)

Implantation of demineralized bone induces new bone formation by the action of contained growth factors, of which bone morphogenetic proteins are of prime importance. A biodegradable polymer may be used as a carrier for demineralized bone particles or recombinant bone growth factors to prevent displacement of the implant, preserve its volume and shape, and assure sustained release of the incorporated active components. A polymer for this use should be biocompatible and completely absorbed without interfering with the osteogenesis. We investigated the host-tissue response and effect on demineralized bone-induced bone formation by two biodegradable polymers, a poly(ortho ester) and an amorphous low-molecular poly(DL-lactic acid). Both polymers had a plastic consistency, could easily be molded, and adhered well to the demineralized bone particles. Demineralized bone particles were implanted alone and in combination with each of the polymers in the abdominal muscles of 45 male Wistar rats. Four weeks after the operation the implants were recovered and subjected to (85)Sr uptake analysis to quantify bone formation and histologic examination. The poly(ortho ester) provoked little inflammation; it was largely absorbed by 4 weeks, and no qualitative or quantitative effect on bone formation was found. The poly(DL-lactic acid) provoked a chronic inflammation with multinuclear giant cells, macrophages with engulfed material, and proliferating fibroblasts; part of the material was still present, and the bone formation was inhibited.

Localized paclitaxel delivery

While the search for new antineoplastic agents is in progress, optimization of delivery for existing drugs will remarkably improve the current scenario in the management of cancer. Paclitaxel, a new antineoplastic agent, is one such drug deserving attention in the field of regional drug delivery, offering immense pharmacokinetic as well as therapeutic advantage via localized delivery. The antiangiogenic activity of paclitaxel has been demonstrated using the chick chorioallantoic membrane model (CAM). This review focuses on the antiangiogenic activity of paclitaxel supported by the evidence that angiogenesis inhibitors display potential synergism with cytotoxic agents in the treatment of primary and metastatic cancers. Preclinical trials have confirmed that the biological and cytotoxic effects of paclitaxel on several tumor cell lines are enhanced by the increase in both the drug concentration and the duration of exposure. Sufficient experimental evidence has accumulated to state that localized delivery will exploit the multiple pharmacological effects of paclitaxel in the treatment of refractory and metastatic cancerous diseases. The drug delivery systems, namely, microspheres, surgical pastes and implants, fabricated for localized paclitaxel delivery are reviewed explaining the concept of increased tumor burden alleviating body burden as a consequence of such delivery systems. Some of the preclinical trials are very encouraging and speculate a promising future for these devices in the battle against solid tumors. Finally, the review briefs on the possibilities for better paclitaxel delivery and the future drug delivery systems for localized cancer chemotherapy.

Regeneration of segmental diaphyseal defects in sheep tibiae using resorbable polymeric membranes: a preliminary study

OBJECTIVE

To investigate whether a long bone cortex of well-defined thickness can be regenerated by using an anatomically designed membranous resorbable "tube-in-tube" implant and to establish the functions of membranes in the healing of segmental diaphyseal bone defects larger than the "critical size."

DESIGN

Bone healing in segmental diaphyseal defects larger than the critical size in the sheep tibiae covered with a single porous tubular membrane or implanted with anatomically shaped porous double tube-in-tube membranes was evaluated. Membranes with different pore structures were applied alone and/or in combination with autogenous bone graft.

BACKGROUND

Healing of segmental diaphyseal bone defects in animals can be enhanced by covering the defects with resorbable polylactide membranes. Based on the results of bone healing in defects ten millimeters long in the rabbit radii, it was suggested that the membrane prevents muscle and soft tissue from invading the defect and maintains osteogenic cells and osteogenic substances within the space covered with membrane, thus promoting new bone formation. The functions of membranes may differ, however, depending on the size and the location of the defect and on the experimental species used. Bone defects larger than the critical size may not heal at all, even if membranes are used. The critical-size defect is defined as the smallest bone defect that does not heal spontaneously when covered with polymeric membranes. To heal such defects, it is mandatory that membranes are used in combination with autogenic bone graft and/or a suitable bone substitute. If bone graft is used to fill the defect, the structure and geometry of the covering membrane will determine whether the graft will be vascularized and/or nourished from the surrounding soft tissue and, in consequence, survive. It can be appreciated that bone healing in areas of good vascularity should be more efficient than bone healing in poorly vascularized areas. The influence of all these factors on healing of bone in segmental diaphyseal defects covered with membranes is not known.

METHODS

Four-centimeter-long diaphyseal segmental defects in the tibiae of six- to seven-year-old Swiss mountain sheep were covered with resorbable membranes from poly(LDL-lactide). In Group 1, a single microporous external membrane was used. In Group 2, one microporous membrane was inserted into the medullary cavity at the cut ends of the tibiae (internal membrane), and the other microporous membrane was placed on the outer surface of the cortex (external membrane). In Group 3, a single microporous external membrane was also laser-perforated to produce openings with a diameter in the range of 800 to 900 micrometers. In Group 4, the defect was filled with autogenous cancellous bone graft and covered with a single perforated membrane. In Group 5, one perforated internal membrane was inserted into the medullary cavity at the cut ends of the tibiae, and the other perforated membrane was placed on the outer surface of the cortex. Group 6 was identical to Group 5, except that cancellous bone graft was placed in the space between these two membranes.

RESULTS

There was no bone healing in Groups 1, 2, 3, and 5. Only in Groups 4 and 6 did the defects heal. In Group 4, new bone was dispersed across the "medullary canal" formed by the membrane. In Group 6, the new bone had grown into the space between the outer and inner membranes, forming the "neocortex."

CONCLUSIONS

The resorbable polymeric implant consisting of two concentric perforated membranes (the tube-in-tube implant) used in combination with cancellous bone graft to treat segmental diaphyseal defects in sheep tibiae allows for the reconstitution of the "neocortex" with well-defined thickness. (ABSTRACT TRUNCATED)

Polyethylene glycol/microfibrillar collagen composite as a new resorbable hemostatic bone wax

Although bone wax is effective at achieving hemostasis, it is nonresorbable, causes a foreign body reaction, and inhibits osteogenesis. We report development of a polyethylene glycol/microfibrillar collagen composite (PEG/MFC) that has inherent hemostatic qualities, is biodegradable, and is compatible with bone repair. PEG/MFC composite (n = 42) was placed in 5 mm cranial defects in New Zealand white rabbits. Hemostasis and healing were compared to unfilled defects (n = 32) and defects filled with standard bone wax (n = 10). Both PEG/MFC and bone wax handled well and stopped bleeding. The polyethylene glycol component was resorbed by 8 h, and the microfibrillar collagen was resorbed over 2 months, eliciting only a minor inflammatory response during the first month. Defects filled with the PEG/MFC composite showed similar amounts of bony regeneration as did unfilled control defects. At 4 weeks, healing bone accounted for 43 +/- 13% in those treated with PEG/MFC and 47 +/- 19% defect area in untreated holes. In contrast, less than 1% of the area was bone in defects filled with bone wax (p < 0.05). PEG/MFC composite provided excellent bony hemostasis and did not inhibit bone growth.

Effect of platelet-derived growth factor-BB on bone formation in calvarial defects: an experimental study in rabbits

The effect of recombinant human platelet-derived growth factor-BB (rhPDGF-BB) on bone healing was examined in calvarial defects in rabbits. Bicortical circular (critical size) defects were prepared in the calvarial bone of 16 rabbits. The defects were closed on the dural side and covered externally with expanded polytetrafluoroethylene membranes to prevent interference with osteogenesis within the defect by the surrounding tissue and to keep the growth factor in place. A single dose of methylcellulose gel (4.4%) with (n = 8) or without rhPDGF-BB (50 micrograms/ml) (n = 8) was applied to the defects, and the bone formation was evaluated after 8 weeks. Healing of defects in both groups was characterized by the presence of newly formed bone along the edges of the original defect and by a central area of fibrous connective tissue. The newly formed bone in the rhPDGF-BB treated defects had a trabecular structure; in contrast, a more compact structure was found in the control defects. In the rhPDGF-BB-treated defects, the bone ingrowth was 51.8 +/- 7.1% compared to 30.5 +/- 3.3% in the control defects. Furthermore, the amount of mineralized tissue was increased 112% in the rhPDGF-BB group. The amount of bone marrow was increased 75% in the rhPDGF-BB-treated defect. The porosity of cortical lamella in the newly formed bone was 84% higher in the rhPDGF-BB-treated defects compared to the control. These results show that administration of a single dose of rhPDGF-BB stimulates bone formation in critical size calvarial defects.

Haemostasis in periradicular surgery

The successful performance of endodontic surgical procedures is predicated on many factors. However, the ability of achieve sustained tissue haemostasis in the surgical site is crucial to the performance of these procedures. This achievement improves vision in the surgical site, minimizes surgical time, enhances the surgical procedures (root-end resection, preparation and filling), and reduces surgical blood loss, postsurgical haemorrhage and postsurgical swelling. A multitude of materials have used in dentistry and medicine to achieve both generalized and localized haemostasis, many without full assessment of their biological implications. The purpose of this paper is to provide a thorough and critical review of these materials from the perspective of surgical endodontics, highlighting their development, application and potential role in achieving proper haemostasis.

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.

Local delivery of indomethacin by a polyorthoester inhibits reossification of experimental bone defects

Inhibition of orthotopic reossification after surgical removal of bone is sometimes indicated and may be accomplished by implantation of interpositional materials or by systemic administration of indomethacin. However, implantation of nonresorbable foreign material may induce a chronic inflammation and predispose to infections; and systemic administration of indomethacin may induce systemic adverse effects. We studied the effect of local delivery of indomethacin by a bioerodible polyorthoester on the reossification of segmental defects of the radius in rats. We divided 45 Wistar rats into three groups, A-C. A 3.5 mm-long middiaphyseal osteoperiosteal resection of the right radius was made in each rat. The defect was filled with 15 mg of polyorthoester with 5% indomethacin in group A and 15 mg of polyorthoester without drug in group B. No material was implanted in the defects in the group C rats. The rats were killed 50 days postoperatively. The mean area of the residual defects were greater in the defects with the polyorthoester with 5% indomethacin compared with defects with polyorthoester without drug or without implant as judged by computer-assisted area measurements on radiographs. By light microscopy, no inflammation was seen and only traces of the polyorthoester could be detected in the defects filled with the polyorthoester with or without indomethacin. The results of this study suggest that the polyorthoester may be used as a bioerodible system for local delivery of indomethacin to inhibit reossification of skeletal defects without tissue reaction, unabsorbed carrier, or systemic effects.

Assessment in rats of a new bioerodible bone-wax-like polymer

Holes drilled in rats' skull, iliac crest, and tibia were filled with beeswax or with a new, wax-like, bioerodible polyorthoester (Alzamer). Empty drill-holes served as controls. In addition, beeswax and polyorthoester were deposited between the left and the right oblique abdominal muscles, respectively. In muscle, both the beeswax and polyorthoester elicited a transient foreign body reaction. The beeswax was not resorbed in bone or muscle, whereas the polyorthoester was. Bone healing was inhibited in the iliac crest and the tibiae filled with beeswax, whereas holes filled with polyorthoester healed readily.

Bone induction by composites of bioresorbable carriers and demineralized bone in rats: a comparative study of fibrin-collagen paste, fibrin sealant, and polyorthoester with gentamicin

Host tissue response and heterotopic osteoinduction by composites of demineralized bone matrix and three different substances used as bioresorbable carriers implanted in the abdominal muscles were evaluated by strontium 85 uptake and histology 4 weeks postoperatively in 60 male Wistar rats. Both fibrin-collagen paste and fibrin sealant inhibited bone induction and produced a chronic inflammation; part of the fibrin-collagen paste was still present at 4 weeks. Polyorthoester with gentamicin was almost completely absorbed, induced minimal tissue reaction, and did not inhibit osteoinduction.

Fracture healing in rats inhibited by locally administered indomethacin

We studied the inhibitory effect of indomethacin on fracture healing in 135 young, male rats after oral administration compared with local application into the fracture. A closed mid-diaphyseal fracture of the left femur was performed in all the rats. The fractures were not immobilized. In one experiment, half of the animals received indomethacin via a stomach tube (2 mg/kg/day) for 10 days; the controls received only the vehicle. In another experiment, 0.5 mg of indomethacin, contained in a bioerodible polyorthoester gel, was injected into the fracture area in half the rats; in the controls, only the gel was injected. In both experiments, random animals were killed on Days 0, 5, 10, and 20. As assessed by radiographs and manual testing, the same inhibition of fracture healing was found regardless of whether indomethacin was given orally or locally. However, the amount of indomethacin that was applied locally was only one fourth of the total dose given orally; no indomethacin was detected in the serum.

Regeneration of calvarial defects by a composite of bioerodible polyorthoester and demineralized bone in rats

A study was performed to evaluate regeneration of defects in rat calvaria either unfilled or filled with a bioerodible polyorthoester only, demineralized bone only, or a composite of both. At 4 weeks, histological and radiographic studies showed that defects filled with a composite of bioerodible polyorthoester and demineralized bone or demineralized bone alone were bridged by bone. Unfilled defects or defects filled with polyorthoester only did not heal. The polyorthoester caused slight inflammation that subsided by 3 weeks, and only traces of the filler could be detected at 4 weeks. The polyorthoester provided local hemostasis when used either alone or in composites with demineralized bone. The composite implant was moldable, easily contoured, and technically easier to use than demineralized bone alone.