Net-shaped hydroxyapatite implants for release of agents modulating periodontal-like tissues

Transplantable delivery systems for in situ controlled release of bisphosphonate in orthopedic therapy

IMPORTANCE OF THE FIELD

Bisphosphonates (BPs), structurally similar to pyrophosphates and functionally superior in restraining osteoclast-induced bone resorption, have been widely used as clinical drugs in the treatment of osteoporosis, bone voids and associated inflammation. However, owing to their high aqueous solubility and the consequently high rate of loss during oral administration, the loading and targeting of BPs pose major challenges in practice. Alternative delivery routes such as nasal, subcutaneous/intramuscular injection have contributed little to improving the bioavailiability and efficacy of BPs. To improve and optimize the delivery efficiency and efficacy of BPs, numerous strategies have been developed and adopted. Studies on controlled release of BPs provide important information on the fabrication of BP delivery systems for in situ treatment. As BPs play an important therapeutic role in osteoporosis and similar diseases, it has become essential and vital to survey various reported fabrication methodologies of these systems and the consequential orthopedic treatments so as to keep abreast with advances in their clinical use.

AREAS COVERED IN THIS REVIEW

Transplantable delivery systems for controlled release of BP are reviewed from literature published since 2000. The fabrication pathways and the release of BPs from various material systems are discussed in case studies. Recent progress in CaP models based on the strong and specific chelation between BPs and calcium phosphate crystals is highlighted.

WHAT THE READER WILL GAIN

This review offers an outline of the advances in BP controlled release and delivery systems for orthopedic therapy.

TAKE HOME MESSAGE

Understanding the cutting-edge BP controlled release and delivery systems for in situ treatment is key to the successful design of a more promising and perfect delivery system for orthopedic therapy. Moreover, developing such delivery systems incorporating the numerous advantages of BPs and controlled release environment requires substantially more flexible models to control better the fate of BP drugs.

Controlled release of bisphosphonate from a calcium phosphate biomaterial inhibits osteoclastic resorption in vitro

Calcium phosphate biomaterials such as calcium deficient apatite (CDA) have been contemplated as carrier for delivery of bisphosphonate in bone tissues. In the present work, we have investigated the in vitro biological properties of Zoledronate-loaded CDA. CDA was loaded with zoledronate according to a previously described coating process. 31P MAS NMR spectra demonstrated the effective loading of zoledronate onto CDA. Using 14C labeled zoledronate, we then demonstrated the in vitro release of zoledronate from CDA. In a first set of experiments, we confirmed that Zoledronate reduced the number of TRAP-, vitronectin receptor-, and F-actin ring-positive cells as well as the resorption activity of osteoclasts obtained from a total rabbit bone cell culture. Interestingly, Zoledronate-loaded CDA and its extractive solutions decreased the osteoclastic resorption. Finally, zoledronate-loaded CDA did not affect the viability and alkaline phosphatase activity of primary osteoblastic cells. These data demonstrate that CDA is effective for loading and release of zoledronate. The released zoledronate inhibited osteoclastic resorption without affecting osteoblasts. Our findings therefore suggest that such a drug delivery system would allow an increase in the efficiency of bisphosphonates by being locally available. Further experiments are now required to evaluate the in vivo antiresorptive activity of this concept.

Novel biomaterials for bisphosphonate delivery

One type of gem-bisphosphonate (Zoledronate) has been chemically associated onto calcium phosphate (CaP) compounds of various compositions. For that purpose, CaP powders of controlled granulometry have been suspended in aqueous Zoledronate solutions of variable concentrations. Using mainly (31)P NMR spectroscopy, two different association modes have been observed, according to the nature of the CaP support and/or the initial concentration of the Zoledronate solution. beta-tricalcium phosphate (beta-TCP) and mixtures of hydroxyapatite and beta-TCP (BCPs) appear to promote Zoledronate-containing crystals formation. On the other hand, at concentrations <0.05 mol l(-1) CDAs (calcium deficients apatites) seem to undergo chemisorption of the drug through a surface adsorption process, due to PO(3) for PO(4) exchange, that is well described by Freundlich equations. At concentrations >0.05 mol l(-1), crystalline needles of a Zoledronate complex form onto the CDAs surface. The ability of such materials to release Zoledronate, resulting in the inhibition of osteoclastic activity, was shown using a specific in vitro bone resorption model.

Bone regeneration of localized chronic alveolar defects utilizing cell binding peptide associated with anorganic bovine-derived bone mineral: a clinical and histological study

BACKGROUND

Osteoinduction to treat osseous defects has been attempted by several means. Some clinical studies have demonstrated that a synthetic cell binding peptide (P-15) with anorganic bovine derived bone matrix (ABM) has the ability to enhance bone regeneration. These studies suggest that more histological data are necessary to better understand this process. We have developed a Class III chronic alveolar defect animal model to investigate space-maintaining regenerative materials. The objective of this study was to clinically and histologically evaluate the use of P-15/ABM with or without a bioabsorbable membrane (M) to regenerate localized chronic alveolar ridge defects in dogs.

METHODS

Six adult, male mongrel dogs were used in this study. Bilateral, Class III, alveolar defects were surgically produced following extraction of the mandibular second premolar teeth and local reduction of the alveolar ridge. After an 8-week healing interval, mucoperiosteal flaps were elevated. P-15/ABM with or without bioabsorbable membranes were implanted into contralateral defects in 10 sites. Two sites received no biomaterial (controls). Mucoperiosteal flaps were advanced over the P-15/ABM or P-15/ABM/M constructs and sutured. Pre- and postaugmentation clinical evaluation was done utilizing periodontal probes and calipers. The animals were sacrificed 12 weeks postaugmentation and block specimens processed for histologic evaluation.

RESULTS

Clinical results showed no significant statistical augmentation on the control group (0.0 +/- 0.6 mm). In all experimental sites utilizing P-15/ABM or P-15/ABM/M, relevant ridge augmentation was observed (3.6 +/- 2.0 mm and 2.9 +/- 1.9 mm, respectively). Histologically, all experimental sites showed active bone formation with plump osteoblast and osteoid matrix deposition in the treated area. Bone ingrowth filled the area of the defects treated with P-15/ABM/M. Few P-15/ABM particles were seen in the cellular fibrous tissue surrounding the new formed bone trabeculae.

CONCLUSIONS

P-15/ABM with or without membranes can produce a significant clinical ridge augmentation. Bone formation was histologically observed in all test areas. The association of a membrane with P-15/ABM seemed to enhance the process of bone formation.

Effect of a ceramic and a non-ceramic hydroxyapatite on cell growth and procollagen synthesis of cultured human gingival fibroblasts

BACKGROUND

Ceramic hydroxyapatites and non-ceramic hydroxyapatites have been used extensively as alloplastic materials for bone reconstruction. However, different forms of hydroxyapatite induce different types of tissue response.

METHODS

Human gingival fibroblasts (FMM1 cells) were used to analyze ceramic and non-ceramic hydroxyapatite biocompatibility. The cells were grown on surfaces covered either by collagen (control group), collagen plus ceramic hydroxyapatite, or collagen plus non-ceramic hydroxyapatite. Scanning electron microscopy, growth and cell viability curves, and procollagen immunoprecipitation were obtained. For the growth and viability curves, 10(4) cells were seeded on 60 mm dishes. Cells from each group were counted, in triplicate, at 1, 3, 4, 5, and 6 days after seeding using the Trypan blue dye exclusion assay.

RESULTS

The cells grew in close contact with both types of hydroxyapatite particles. No differences were found in the amount of procollagen synthesis among any experimental group. The cultures treated with ceramic hydroxyapatite had a growth delay for the first 5 days. There was no difference in cell viability between the control group and the non-ceramic hydroxyapatite group. However, cultures treated with ceramic hydroxyapatite showed significantly lower viability percentages than the other groups.

CONCLUSIONS

Hydroxyapatite supports cell growth and fibroblast metabolism including collagen production, and hence is biocompatible. Cell viability and structural studies showed that non-ceramic hydroxyapatite has relevant physical and biological properties as an implant material.

Isostatic compression, a new process for incorporating vancomycin into biphasic calcium phosphate: comparison with a classical method

Isostatic compression has rarely been used to load calcium-phosphate biomaterials with therapeutic agents. This report, concerning four processes associating vancomycin, compares isostatic compression with wet granulation, a classical method. In the wet granulation study, vancomycin was associated with biphasic calcium-phosphate (BCP) granules either by adsorption or incorporation with a new granulation. In the isostatic compression study, BCP powder was compressed at 100, 140 and 200 MPa. The blocks obtained were crushed and 200-500 microm, sieved; thus, the vancomycin solution was absorbed on these granules. Compaction of BCP and vancomycin powders gave, after crushing and sieving, granules loaded with vancomycin. In each study, 5% vancomycin was associated with BCP. Vancomycin release profiles were assessed by an in vitro culture chamber dissolution test. Physicochemical studies of BCP and vancomycin showed their structural integrity after isostatic compression. Isostatic compression prolonged vancomycin release time from 3 to 7 days and the release time became greater as isostatic pressure increased, probably because of the porosity decrease of the granules during compression.

Bone and bone substitutes

Bone replacement grafts will play a continuing role in periodontal and other regenerative therapy. Several choices are available to the clinician including autogenous, allogeneic, xenogeneic and a variety of alloplastic materials. Except for fresh autogenous bone, bone replacement graft(s) do not provide the cellular elements necessary for osteogenesis nor can they reliably be considered truly osteoinductive, but instead are mostly osteoconductive, providing a scaffold for bone deposition. Currently, significant decrease in clinical probing depth and gain of clinical attachment have been reported following use of bone replacement grafts when compared to flap debridement surgery alone for periodontal osseous defects. Reported differences among bone replacement grafts (autogenous, allogeneic, xenogeneic, and alloplastic) occur with respect to histological outcomes. Overall, probing depth reduction, attachment level gain and degree of defect fill are similar for all bone replacement grafts.