Enhanced guided bone regeneration by controlled tetracycline release from poly(L-lactide) barrier membranes

Improving bactericidal performance of implant composite coatings by synergism between Melittin and tetracycline

Methicillin resistance Staphylococcus aureus bacteria (MRSA) are serious hazards of bone implants. The present study was aimed to use the potential synergistic effects of Melittin and tetracycline to prevent MRSA associated bone implant infection. Chitosan/bioactive glass nanoparticles/tetracycline composite coatings were deposited on hydrothermally etched titanium substrate. Melittin was then coated on composite coatings by drop casting method. The surfaces were analyzed by FTIR, XRD, and SEM instruments. Tetracycline in coatings revealed multifunctional behaviors include bone regeneration and antibacterial activity. Releasing ALP enzyme from MC3T3 cells increased by tetracycline, so it is suitable candidate as osteoinductive and antibacterial agent in orthopedic implants coatings. Melittin increased the proliferation of MC3T3 cells. Composite coatings with combination of tetracycline and Melittin eradicate all MRSA bacteria, while coatings with one of them could no t eradicate all of the bacteria. In conclusion, chitosan/bioactive glass/tetracycline/Melittin coating can be suggested as a multifunctional bone implant coating because of its osteogenic and promising antibacterial activity. Graphical abstract.

Antibiotic-Loaded Polymeric Barrier Membranes for Guided Bone/Tissue Regeneration: A Mini-Review

Polymeric membranes are frequently used for bone regeneration in oral and periodontal surgery. Polymers provide adequate mechanical properties (i.e., Young’s modulus) to support oral function and also pose some porosity with interconnectivity to permit for cell proliferation and migration. Bacterial contamination of the membrane is an event that may lead to infection at the bone site, hindering the clinical outcomes of the regeneration procedure. Therefore, polymeric membranes have been proposed as carriers for local antibiotic therapy. A literature search was performed for papers, including peer-reviewed publications. Among the different membranes, collagen is the most employed biomaterial. Collagen membranes and expanded polytetrafluoroethylene loaded with tetracyclines, and polycaprolactone with metronidazole are the combinations that have been assayed the most. Antibiotic liberation is produced in two phases. A first burst release is sometimes followed by a sustained liberation lasting from 7 to 28 days. All tested combinations of membranes and antibiotics provoke an antibacterial effect, but most of the time, they were measured against single bacteria cultures and usually non-specific pathogenic bacteria were employed, limiting the clinical relevance of the attained results. The majority of the studies on animal models state a beneficial effect of these antibiotic functionalized membranes, but human clinical assays are scarce and controversial.

Bio-mimicked guided tissue regeneration/guided bone regeneration membranes with hierarchical structured surfaces replicated from teak leaf exhibits enhanced bioactivity

Bio-mimicked GTR/GBR membranes with hierarchical structured surfaces were developed by direct and indirect replication of teak leaf surface. The membranes were fabricated using solvent casting method with customized templates. The surfaces obtained were those with micro-trichomes (MTS) and micro-depression (MDS) that resembled a whorling pattern. Structural details of the fabricated membrane surfaces were studied under stereomicroscope and scanning electron microscopy. Surface roughness, water wetting angle, water uptake, and degradation properties of the membranes were examined. The effects of the micro-patterned hierarchical structure on in vitro bioactivities of human osteoblast-like cells (MG63) and human gingival fibroblast cells HGF1-RT1 were studied. In vivo study carried out on rat skulls to assess the response of surrounding tissues for 4 weeks showed that the bio-mimicked MTS and MDS membrane surfaces enhanced the cell proliferation. The proliferation significantly increased with increasing surface roughness and decreasing contact angle. There was also an evidence of rapid new bone maturation with membranes with MTS. It is thus suggested that the teak leaf mimicked whorling patterned hierarchical structured surface is an important design for enhancing bioactivity.

Development of Zoledronic Acid Containing Biomaterials for Enhanced Guided Bone Regeneration

In recent years, biomaterial-based treatments, also called guided bone regeneration (GBR), which aim to establish a bone regeneration site and prevent the migration of gingival connective tissue and / or peripheral epithelium through the defective area during periodontal surgical procedures have come to the fore. In this report, we have developed a nanoparticle bearing thermosensitive in situ gel formulation of Pluronic F127 and poly(D,L-lactic acid) based membrane to reveal their utilization at GBR by in-vivo applications. In addition, the encouragement of the bone formation in defect area via inhibition of osteoclastic activity is intended by fabrication these biodegradable biomaterials at a lowered Zoledronic Acid (ZA) dose. Both of the developed materials remained stable under specified stability conditions (25 °C, 6 months) and provided the extended release profile of ZA. The in-vivo efficacy of nanoparticle bearing in situ gel formulation, membrane formulation and simultaneous application for guided bone regeneration was investigated in New Zealand female rabbits with a critical size defect of 0.5 × 0.5 cm in the tibia bone for eight weeks. Based on the histopathological findings, lamellar bone and primarily woven bone formations were observed after 8 weeks of post-implantation of both formulations, while fibrosis was detected only in the untreated group. Lamellar bone growth was remarkably achieved just four weeks after the simultaneous application of formulations. Consequently, the simultaneous application of ZA-membrane and ZA-nanoparticles loaded in-situ gel formulations offers enhanced and faster GBR therapy alternatives.

Preventive antibiotic therapy in bone augmentation procedures in oral implantology: A systematic review

INTRODUCTION

Since the beginning of Oral Implantology, preventive antibiotic therapy has been routinely prescribed. However, at present, due to the growing appearance of antimicrobial resistance, its use has been questioned, generating a great debate and an emerging controversy. The present systematic review aims to analyze the scientific literature to determine whether the preventive prescription of antibiotics in augmentation procedures with the insertion of implants in one or two phases decreases the incidence of postoperative infections and/or the survival rate of the implants.

MATERIAL AND METHODS

The MEDLINE database was searched (via PubMed) with the following keywords: (bone grafting OR alveolar ridge augmentation OR bone graft augmentation OR guided bone regeneration OR bone block) AND (dental implants OR dental implant OR oral implantology) AND (antibiotic prophylaxis OR antibiotics). The criteria used were those described by the PRISMA® Statement. The search was limited to randomised clinical trials, systematic reviews and meta-analyses published in the last 15 years (2005-2020).

RESULTS

After reading the titles and abstracts of the resulting articles, only one systematic review meeting the described criteria and 4 randomised clinical trials were included.

CONCLUSIONS

Prescription of 2 or 3 g of amoxicillin one hour before surgery is recommended to reduce the early failure rate of one-stage implants and to decrease the bacterial load of grafted bone particles in bone augmentation procedures with one or two-stage implants.

Membranes for Guided Bone Regeneration: A Road from Bench to Bedside

Bone resorption can negatively influence the osseointegration of dental implants. Barrier membranes for guided bone regeneration (GBR) are used to exclude nonosteogenic tissues from influencing the bone healing process. In addition to the existing barrier membranes available on the market, a growing variety of membranes for GBR with tailorable physicochemical properties are under preclinical evaluation. Hence, the aim of this review is to provide a comprehensive description of materials used for GBR and to report the main industrial and regulatory aspects allowing the commercialization of these medical devices (MDs). In particular, a summary of the main attributes defining a GBR membrane is reported along with a description of commercially available and under development membranes. Finally, strategies for the scaling-up of the manufacturing process and the regulatory framework of the main MD producers (USA, EU, Japan, China, and India) are presented. The description of the regulatory approval process of GBR membranes is representative of the typical path that medium- to high-risk MDs have to follow for an effective medical translation, which is of fundamental importance to increase the impact of biomedical research on public health.

In vitro evaluation of bilayer membranes of PLGA/hydroxyapatite/β-tricalcium phosphate for guided bone regeneration

Membranes for guided bone regeneration represent valuable resources, preventing fibroblast infiltration and aiding anatomical bone reconstruction. Nonetheless, available membranes lack bone regenerative capacity, suitable mechanical behavior, or adequate degradation profile. Therefore, to overcome these limitations, this study developed bilayer membranes with a dense layer (dry phase inversion) of PLGA (poly(lactic-co-glycolic acid)):HAp (hydroxyapatite) - 95:05 (wt%) - and an electrospun layer of PLGA and HAp:β-TCP (β-tricalcium phosphate) with ratios of 60:40, 70:30 and 85:15 (wt%), evaluating its mechanical, morphological and in vitro properties. The bilayer membranes displayed adequate interlayer adhesion, dense layer pore size of 4.20 μm and electrospun layer with porosity degree of 38.2%, thus capable of preventing fibroblast infiltration while allowing osteoblast migration and nutrient permeation. They also showed T_g of 82 °C and higher storage modulus, which was constant up to 54.6 °C, characteristics important for membrane implantation and use with no mechanical compromise. In vitro degradation mass loss was only 10% after 60 days, a profile suitable for the application requirement. Membranes with calcium phosphates had better osteoblast attachment, proliferation and migration. Taken together, results indicate the great potential of PLGA/HAp/β-TCP bilayer membranes on bone reconstruction with proper degradation profile, morphology, mechanical behavior and bone regenerative capacity.

Barrier membranes: More than the barrier effect?

AIM

To review the knowledge on the mechanisms controlling membrane-host interactions in guided bone regeneration (GBR) and investigate the possible role of GBR membranes as bioactive compartments in addition to their established role as barriers.

MATERIALS AND METHODS

A narrative review was utilized based on in vitro, in vivo and available clinical studies on the cellular and molecular mechanisms underlying GBR and the possible bioactive role of membranes.

RESULTS

Emerging data demonstrate that the membrane contributes bioactively to the regeneration of underlying defects. The cellular and molecular activities in the membrane are intimately linked to the promoted bone regeneration in the underlying defect. Along with the native bioactivity of GBR membranes, incorporating growth factors and cells in membranes or with graft materials may augment the regenerative processes in underlying defects.

CONCLUSION

In parallel with its barrier function, the membrane plays an active role in hosting and modulating the molecular activities of the membrane-associated cells during GBR. The biological events in the membrane are linked to the bone regenerative and remodelling processes in the underlying defect. Furthermore, the bone-promoting environments in the two compartments can likely be boosted by strategies targeting both material aspects of the membrane and host tissue responses.

Novel Bioactive and Therapeutic Dental Polymeric Materials to Inhibit Periodontal Pathogens and Biofilms

Periodontitis is a common infectious disease characterized by loss of tooth-supporting structures, which eventually leads to tooth loss. The heavy burden of periodontal disease and its negative consequence on the patient's quality of life indicate a strong need for developing effective therapies. According to the World Health Organization, 10⁻15% of the global population suffers from severe periodontitis. Advances in understanding the etiology, epidemiology and microbiology of periodontal pocket flora have called for antibacterial therapeutic strategies for periodontitis treatment. Currently, antimicrobial strategies combining with polymer science have attracted tremendous interest in the last decade. This review focuses on the state of the art of antibacterial polymer application against periodontal pathogens and biofilms. The first part focuses on the different polymeric materials serving as antibacterial agents, drug carriers and periodontal barrier membranes to inhibit periodontal pathogens. The second part reviews cutting-edge research on the synthesis and evaluation of a new generation of bioactive dental polymers for Class-V restorations with therapeutic effects. They possess antibacterial, acid-reduction, protein-repellent, and remineralization capabilities. In addition, the antibacterial photodynamic therapy with polymeric materials against periodontal pathogens and biofilms is also briefly described in the third part. These novel bioactive and therapeutic polymeric materials and treatment methods have great potential to inhibit periodontitis and protect tooth structures.

* Engineering Membranes for Bone Regeneration

This review is focused on the use of membranes for the specific application of bone regeneration. The first section focuses on the relevance of membranes in this context and what are the specifications that they should possess to improve the regeneration of bone. Afterward, several techniques to engineer bone membranes by using "bulk"-like methods are discussed, where different parameters to induce bone formation are disclosed in a way to have desirable structural and functional properties. Subsequently, the production of nanostructured membranes using a bottom-up approach is discussed by highlighting the main advances in the field of bone regeneration. Primordial importance is given to the promotion of osteoconductive and osteoinductive capability during the membrane design. Whenever possible, the films prepared using different techniques are compared in terms of handability, bone guiding ability, osteoinductivity, adequate mechanical properties, or biodegradability. A last chapter contemplates membranes only composed by cells, disclosing their potential to regenerate bone.

Development of multifunctional films for peripheral nerve regeneration

In this study, a poly(lactic acid) (PLLA) porous film with longitudinal surface micropatterns was fabricated by a dry phase inversion technique to be used as potential conduit material for peripheral nerve regeneration applications. The presence of a nerve growth factor (NGF) gradient on the patterned film surface and protein loaded, surface-eroding, biodegradable, and amphiphilic polyanhydride (PA) microparticles within the film matrix, enabled co-delivery of neurotrophic factors with controlled release properties and enhanced neurite outgrowth from PC12 cells. The protein loading capacity of PA particles was increased up to 80% using the spray drying technique, while the surface loading of NGF reached 300ng/cm² through ester-amine interactions. The NGF surface gradient provided initial fast release from the film surface and facilitated directional neurite outgrowth along with the longitudinal micropatterns. Furthermore, the variable backbone chemistry and surface eroding nature of protein-loaded PA microparticles within the film matrix ensured protein stability and enabled controlled protein release. This novel co-delivery strategy yielded tunable diffusion coefficients varying between 6×10^-14 and 1.67×10^-10cm²/min and dissolution constants ranging from 1×10^-4 to 1×10^-3min^-1 with released amounts of ∼100-300ng/mL. This strategy promoted guided neurite extension from PC12 cells of up to 10μm total neurite length per cell in 2days. Overall, this unique strategy can potentially be extended for individually programmed delivery of multiple growth factors through the use of PA microparticle cocktails and can further be investigated for in vivo performance as potential conduit material for peripheral nerve regeneration applications.

STATEMENT OF SIGNIFICANCE

This manuscript focuses on the development of multifunctional degradable polymer films that provide topographic cues for guided growth, surface gradients of growth factors as well as nanoparticles in the films for tunable release of growth factors to enable peripheral nerve regeneration. The combination of cues was designed to overcome limitations of current strategies to facilitate peripheral nerve regeneration. These multifunctional films successfully provided high protein loading capacities while persevering activity, protein gradients on the surface, and tunable release of bioactive nerve growth factor that promoted directional and guided neurite extension of PC12 cells of up to 10μm in 2days. These multifunctional films can be made into conduits for peripheral nerve regeneration.

Electrospun PDLLA/PLGA composite membranes for potential application in guided tissue regeneration

With the aim to explore a membrane system with appropriate degradation rate and excellent cell-occlusiveness for guided tissue regeneration (GTR), a series of poly(D, L-lactic acid) (PDLLA)/poly(D, L-lactic-co-glycolic acid) (PLGA) (100/0, 70/30, 50/50, 30/70, 0/100, w/w) composite membranes were fabricated via electrospinning. The fabricated membranes were evaluated by morphological characterization, water contact angle measurement and tensile test. In vitro degradation was characterized in terms of the weight loss and the morphological change. Moreover, in vitro cytologic research revealed that PDLLA/PLGA composite membranes could efficiently inhibit the infiltration of 293 T cells. Finally, subcutaneous implant test on SD rat in vivo showed that PDLLA/PLGA (70/30, 50/50) composite membranes could function well as a physical barrier to prevent cellular infiltration within 13 weeks. These results suggested that electrospun PDLLA/PLGA (50/50) composite membranes could serve as a promising barrier membrane for guided tissue regeneration due to suitable biodegradability, preferable mechanical properties and excellent cellular shielding effects.

The effects of tetracycline-loaded silk fibroin membrane on proliferation and osteogenic potential of mesenchymal stem cells

BACKGROUND

The main objective of this study was to investigate the effect of tetracycline-loaded silk fibroin membranes (TC-SFMs) on the proliferation and the osteogenic differentiation of human mesenchymal stem cells.

MATERIALS AND METHODS

Four groups (0, 1, 5, and 10% concentration) of TC-SFMs were prepared for the experiments. We investigated cumulative tetracycline (TC) release profile for 7 d. Human gingiva-derived mesenchymal stem cells (GMSCs) were isolated from our previous study and seeded to the TC-SFMs. WST-8 assay (Cell Counting Kit-8; SigmaeAldrich Co, St. Louis, MO), staining of Phalloidin-FITC, and scanning electron microscope analyzed the cellular attachment and viability. Staining of Alizarin Red S (Sigma-Aldrich Co.) and osteogenic marker (osteocalcin) analyzed osteogenic differentiation. Additionally, quantitative polymerase chain reaction measured the expression of osteogenic lineage genes, including bone gamma-carboxyglutamic acid protein, bone sialoprotein, runt-related transcription factor 2, and collagen type I α1 according to TC concentration (0.05, 0.1, 0.25, and 0.5 mg/mL).

RESULTS

The release of TC from TC-SFMs plateaued and neared completion in 24 h. Significantly higher viability was noted achieved in 1% and 5% TC-SFMs. The morphology of GMSCs on TC-SFMs at 0% and 1% concentration showed spindle shapes, but cells in 10% TC-SFMs appeared spheroid. During Alizarin Red S staining at 21 d of osteogenic differentiation, calcium and osteocalcin formation were significantly lower in the 10% TC-SFM group than in the 0, 1, and 5 groups. Compared with the control group, bone gamma-carboxyglutamic acid protein showed significantly low expression rate at TC concentration ≥0.05 mg/mL. Bone sialoprotein was low at TC concentration ≥0.1 mg/mL. Likewise, runt-related transcription factor 2 and collagen type I α1 were low at TC concentration of 0.5 mg/mL.

CONCLUSIONS

Within the limits of this study, 1% and 5% TC-SFMs showed higher proliferation and osteogenic potential of GMSCs than 10% TC-SFM. Therefore, the use of 1% to 5% range of TC may be more suitable to silk fibroin membrane for stem cell tissue engineering.

Biocompatibility and cytotoxic evaluation of drug-loaded biodegradable guided tissue regeneration membranes

BACKGROUND

In periodontology, Guided Tissue Regeneration (GTR) is based on the concept of providing a space for entry of cells with regenerative potential into the wound environment to initiate the regeneration of structures lost due to periodontal disease. First generation GTR membranes were primarily non-absorbable membranes like expanded polytetrafluorethylene which required a second surgery for its removal. This led researchers to explore absorbable materials like collagen and synthetic biodegradable polymers to fabricate GTR membranes. In the present study, biodegradable Polylactic acid (PLA) is used to fabricate membranes with the potential to be used for GTR therapy.

MATERIALS AND METHODS

Biocompatibility of the PLA membranes were evaluated in a subcutaneous guinea pig model. Antimicrobial effect of the drug-loaded PLA membranes were assessed against a drug-resistant Staphylococcus aureus bacterial isolate. The cytocompatibility of the drug-loaded membranes were evaluated using HeLa cell lines.

RESULTS

The PLA membranes were shown to be biocompatible. The drug-loaded PLA membranes showed significant activity against the bacterial isolate. Among the drug-loaded membranes, tetracycline-loaded membrane showed minimal cellular toxicity.

CONCLUSION

The results of this study indicate that biodegradable drug-releasing polylactide membranes have the potential to be used for periodontal regeneration. It has the necessary characteristics of a GTR membrane like biocompatibility, space maintaining ability, and tissue integration. Among the various antimicrobial agents loaded in the PLA membranes, tetracycline-loaded membranes exhibited minimal cellular toxicity against HeLa cells; at the same time showing significant activity against a pathogenic bacterium.

Ammonium bicarbonate as porogen to make tetracycline-loaded porous bioresorbable membranes for dental guided tissue regeneration: failure due to tetracycline instability

The goal of this work was to manufacture a bioresorbable porous membrane aimed at both promoting osseous regeneration in oral surgery and delivering an antibiotic drug locally. The selected design consisted of a porous poly (D,L-lactic acid) matrix having a closed smooth face on one side to prevent inner migration of conjunctive and epithelial cells, and the rest of the membrane presenting open porosity to allow in-growth of osseous neotissue. The antibiotic drug was tetracycline because of its large antibacterial spectrum and its osteogenetic activity. Solvent casting/particulate leaching and gas foaming/salt leaching methods were selected to create the porosity, and ammonium bicarbonate was selected as thermosensitive water-soluble porogen because other studies reported that sodium chloride was difficult to remove totally. One-side-skinned, porous permeable membranes were successfully obtained. However, deleterious alterations of the drug were observed that were assigned to the basicity of the porogen, thus precluding any practical use in vivo.

A novel spatially designed and functionally graded electrospun membrane for periodontal regeneration

A periodontal membrane with a graded structure allows tailoring of the layer properties to design a material system that will retain its physical, chemical and mechanical characteristics for a period long enough to optimize periodontal regeneration. In this work a novel functionally graded membrane (FGM) was designed and fabricated via sequential multilayer electrospinning. The FGM consists of a core layer (CL) and two functional surface layers (SLs) interfacing with bone (nano-hydroxyapatite, n-HAp) and epithelial (metronidazole, MET) tissues. The CL comprises a neat poly(DL-lactide-co-ε-caprolactone) (PLCL) layer surrounded by two composite layers composed of a protein/polymer ternary blend (PLCL:PLA:GEL). Electrospinning parameters involved in fabrication of the individual layers (i.e. neat PLCL, ternary blend, PLA:GEL+10%n-HAp and PLA:GEL+25%MET) were optimized to obtain fibrous layers free of beads. Morphology, structure and mechanical property studies were carried out on each electrospun layer. The individual fiber morphology and roughness of the functional SLs, which are the n-HAp containing and drug-incorporating layers were evaluated by atomic force microscopy. The CL structure demonstrated higher strength (8.7 MPa) and a more elastic behavior (strain at break 357%) compared with the FGM (3.5 MPa, 297%). Incorporation of n-HAp to enhance osteoconductive behavior and MET to combat periodontal pathogens led to a novel FGM that holds promise at solving the drawbacks of currently available membranes.

Fabrication and biocompatibility of an antimicrobial composite membrane with an asymmetric porous structure

A composite slurry from silver ion-substituted nano-hydroxyapatite, titania nano-particles and polyamide 66 (Ag-nHA/TiO(2)/PA66) was prepared and used to fabricate a novel antimicrobial membrane with a gradient porous structure for guided bone regeneration (GBR). Subsequently, assays were performed to determine the cytocompatibility, as well as the bone biocompatibility of the prepared membranes. To investigate the cytocompatibility of the Ag-nHA/TiO(2)/PA66 membrane, in vitro studies were done with osteoblast-like cells (MG63) and the viability, alkaline phosphatase activity (ALP) and morphology of cells cultured on the membrane were determined. The bone biocompatibility of the membranes was finally assessed in animal experiments, in which nano-hydroxyapatite/polyamide 66 (nHA/PA66) and pure polyamide 66 (PA66) membranes were compared. The in vitro cell-culture experiments showed that Ag-nHA/TiO(2)/PA66 antimicrobial membrane evoked good cell affinity and cytocompatibility. The in vivo study showed that Ag-nHA/TiO(2)/PA66 asymmetric porous barrier membrane resulted in complete closure of 5-mm bone defects as created in the skull of rats after 8 weeks of implantation. In conclusion, the Ag-nHA/TiO(2)/PA66 membrane has the potential to be applied in GBR, especially in infected tissue or areas with high bacteria concentration.

Biomaterial and antibiotic strategies for peri-implantitis: a review

Dental implants have 89% plus survival rates at 10-15 years, but peri-implantitis or dental implant infections may be as high as 14%. Peri-implantitis can limit clinical success and impose health and financial burdens to patients and health providers. The pathogenic species associated with periodontitis (e.g., Fusobacterium ssp, A. actinomycetemcomitans, P. gingivalis) are also associated with peri-implantitis. Incidence of peri-implantitis is highest within the first 12 months after implantation, and is higher in patients who smoke or have poor oral health as well as with calcium-phosphate-coated or surface-roughened implants. Biomaterial therapies using fibers, gels, and beads to deliver antibiotics have been used in the treatment of Peri-implantitis though clinical efficacy is not well documented. Guided tissue regeneration membranes (e.g., collagen, poly-lactic/glycolic acid, chitosan, ePTFE) loaded with antimicrobials have shown success in reosseointegrating infected implants in animal models but have not been proven in humans. Experimental approaches include the development of anti-bioadhesion coatings, coating surfaces with antimicrobial agents (e.g., vancomycin, Ag, Zn) or antimicrobial releasing coatings (e.g., calcium phosphate, polylactic acid, chitosan). Future strategies include the development of surfaces that become antibacterial in response to infection, and improvements in the permucosal seal. Research is still needed to identify strategies to prevent bacterial attachment and enhance normal cell/tissue attachment to implant surfaces.

Drug controlled release from structured bioresorbable films used in medical devices--a mathematical model

A mathematical model for predicting drug release profiles from structured bioresorbable films was developed and studied. These films, which combine good mechanical properties with desired drug release profiles, are designed for use in various biomedical applications. Our structured polymer/drug films are prepared using a promising technique for controlling the drug location/dispersion in the film. The present model was used for predicting drug release profiles from two film types that is films in which the drug is located on the surface (A-type) and films in which the drug is located in the bulk (B-type). The model is based on Fick's 2nd law of diffusion and assumes that the drug release profile from the films is affected by the host polymer's characteristics, the drug location/dispersion in the film and the drug's characteristics. This semiempirical model uses the weight loss profile of the host polymers as well as the change in their degree of crystallinity with degradation. Our study indicates that the model correlates well with in vitro release results, exhibiting a mean error of less than 7% for most studied cases. It also shows that the host polymer's degradation has a greater effect on the drug release profile than the degree of crystallinity. This new model exhibits a potential for simulating the release profile of bioactive agents from structured films for a wide variety of biomedical applications.

Structured Drug-eluting Bioresorbable Films: Microstructure and Release Profile

Bioresorbable drug-eluting films can be used in many biomedical applications. Examples for such applications include biodegradable medical support devices which combine mechanical support with drug release and antibiotic-eluting film coatings for prevention of bacterial infections associated with orthopedic implants or during gingival healing. In the current study, bioresorbable drug-loaded polymer films are prepared by solution processing. Two film structures are studied: A polymer film with large drug crystals located on its surface (A-type) and a polymer film with small drug particles and crystals distributed within the bulk (B-type). The basic mode of drug dispersion/location in the film (A or B-type) is found to be determined mainly by the process of film formation and depends mainly on the solvent evaporation rate, whereas the drug's hydrophilicity has a minor effect on this structuring process. Most release profiles from A-type films exhibit a burst effect of ~30% and a second release stage that occurs at an approximately constant rate and is determined mainly by the polymer weight loss rate. An extremely high burst release is exhibited only by a very hydrophilic drug. The matrix (monolithic) nature of the B-type film enables release profiles that are determined mainly by the host polymer's degradation profile, with a very low burst effect in most of the studied systems. In addition to the drug location/ dispersion in the film, the host polymer and drug type also strongly affect the drug's release profile from the film. It has been demonstrated that appropriate selection of the process parameters and film components (polymer and drug) can yield film structures with desirable drug release behaviors. This can lead to the engineering of new bioresorbable drug-eluting film-based implants for various applications.

Study of controlled tetracycline release from porous calcium phosphate/polyhydroxybutyrate composites

Porous calcium phosphate ceramics were prepared by sintering of mixtures of nanocrystalline apatitic calcium phosphate and fibrous natural cotton cellulose after pressing at temperatures of 1150 °C and 1250 °C. Micro-and macropores were present in microstructures of ceramic samples. The microstructures of porous ceramics were similar to those observed in bone tissues and fiber-like randomly oriented texture was observed in ceramics. Polyhydroxybutyrate (PHB) biopolymer layers are distributed homogeneously in the samples after evaporation of the diluent (chloroform) from the PHB vacuum impregnated porous samples. The tetracycline (TTC) release rate decreases with the content of polyhydroxybutyrate in the ceramic samples, which corresponds to the rise in amount of biopolymer displaced in the pores of ceramics. The concentration of TTC in the phosphate buffer saline solution varies almost linearly with time after the first seven hours from the start of the release of the calcium phosphate ceramic samples with 2.4 mass % of polyhydroxybutyrate. The initial burst effect was significantly depressed by the preparation method used.

In vitro evaluation of poly[bis(ethyl alanato)phosphazene] as a scaffold for bone tissue engineering

Polyphosphazenes with amino acid ester as side groups are biocompatible polymers that could provide valid scaffolds for cell growth. In the present study we investigate the adhesion and growth of osteoblasts obtained from rat bone marrow on matrices composed of thin fibers of poly[bis(ethyl alanato)phosphazene] (PAlaP), poly(d,l-lactic acid) (PDLLA), or PAlaP/PDLLA blend. Our data show that scaffolds of PAlaP or PAlaP/PDLLA blend enhanced the cell adhesion and growth in comparison with that observed in cultures seeded on polystyrene tissue culture plates. Although collagenase-digestible protein synthesis remained unchanged, all scaffolds induced a decrease in alkaline phosphatase activity, suggesting that osteoblasts are in the proliferation phase. Both PAlaP and PAlaP blended with PDLLA may represent a new and interesting substrate for bone tissue engineering.

New frontiers in calvarial reconstruction: integrating computer-assisted design and tissue engineering in cranioplasty

Repair of large and complex calvarial defects remains a particular challenge for reconstruction. The paucity of techniques and materials emphasizes the need for alternative bone formation strategies. Recent integrative approaches suggest that successful reconstruction requires interdisciplinary teams, with surgeons interacting with imaging experts, materials scientists, and engineers. In this review, the authors present an overview of current materials used in calvarial reconstruction. Subsequently, progress in computer-designed prostheses, tissue engineering, and osteoinduction strategies is discussed. Finally, the authors discuss their experience with the integration of computer-aided fabrication of customized implants and tissue engineering for calvarial reconstruction.

Dexamethasone loaded bioresorbable films used in medical support devices: structure, degradation, crystallinity and drug release

Bioresorbable polymer films containing dexamethasone (DM) were prepared using a solution processing technique. Investigation of the films focused on cumulative DM release as affected by film morphology (drug location/dispersion in the film) and degradation processes. Two film structures were studied: A-type, a polymer film with large drug crystals located on the film's surface, and B-type, a polymer film with small drug particles and crystals distributed within the bulk. The effect of the polymer's degree of crystallinity on the drug release profile was also studied. Prototypical applications of these films are biodegradable medical support devices which combine mechanical support with drug release. In most of our studied systems the drug release profile from the film is determined mainly by both drug location/dispersion in the film and the polymer's weight loss rate. All release profiles from A-type films exhibited a burst effect of approximately 30%, accompanied by a second release phase at a constant rate, whereas the release profiles from B-type films were determined mainly by the degradation profile of the host polymer, and did not exhibit any burst effect. A high degree of crystallinity is important for the current application, since good mechanical properties are required. This contributes to slower drug release rates, mainly at relatively low weight losses, whereas at high weight losses, where a porous structure is created, the crystallinity almost does not affect the rate of drug release. The shape of the porous structure that develops with degradation also affects the drug release profile from the B-type films.

The effects of guided tissue regeneration (GTR) on modified Le Fort I osteotomy healing in rabbits

Osteogenesis following surgery depends on the osteoblasts at the wound site. Fibrous nonunions may be the result of differential and rapid migration of fibroblasts compared to osteoblasts into the wound. The present study was designed to test this hypothesis through the use of guided tissue regeneration (GTR) in a rabbit model. Bilateral, Le Fort I osteotomies (n=20) were produced in the maxillae of 10 New Zealand White rabbits. The segments were advanced 6mm and rigidly fixed using microplates and screws. One side was covered with a resorbable collagen membrane or left uncovered. Rabbits were followed for four weeks with radiographs and the maxillae were harvested for histology. Cephalometry revealed that membrane-covered defects had significantly (P<0.01) reduced defect area (by approximately 70%) compared to uncovered defects. Histologically, membrane-covered defects showed more organized osteogenesis and less fibrous tissue than uncovered defects. Histomorphometry revealed that membrane covered defects had significantly (P<0.05) reduced defect areas (by approximately 20%) compared to uncovered defects. While findings suggest that GTR can facilitate osseous wound healing in Le Fort I osteotomies, results also caution against relying exclusively on two-dimensional radiography to assess bony wound healing in lieu of three-dimensional imaging and evaluations.

Assessment of Bone Repair Associated with the Use of Organic Bovine Bone and Membrane Irradiated at 830 nm

OBJECTIVE

The aim of the present investigation was to assess histologically the effect of LLLT (GaAIAs, 830 nm, 40 mW, CW, (Phi) approximately 0.6 mm, 16 J/cm(2) per session) on the repair of surgical defects created in the femur of the Wistar Albinus rat. The defects were filled to lyophilized bovine bone (Gen-ox), organic matrix) associated or not to GTR (Gen-derm).

BACKGROUND DATA

A major problem on modern Dentistry is the recovery of bone defects caused by trauma, surgical procedures or pathologies. Several types of biomaterials have been used in order to improve the repair of these defects. These materials are often associated to procedures of GTR. Previous studies have shown positive effects of LLLT on the repair of soft tissue wounds, but there are a few on its effects on bone healing.

METHODS

Surgical bone defects were created in 42 animals divided into five groups: Group I (control, 6 animals); Group II (Gen-ox, 9 animals); Group III (Gen-ox + Laser, 9 animals); Group IV (Gen-ox + Gen-derm, 9 animals); Group V (Gen-ox + Gen-derm + Laser, 9 animals). The animals on the irradiated group received 16 J/cm(2) per session divided into four points around the defect (4 J/cm(2)) being the first irradiation immediately after surgery and repeated seven times at every 48 h. The animals were humanly killed after 15, 21, and 30 days.

RESULTS

The results of the present investigation showed histological evidence of improved amount of collagen fibers at early stages of the bone healing (15 days) and increased amount of well organized bone trabeculae at the end of the experimental period (30 days) on irradiated animals compared to non irradiated ones.

CONCLUSIONS

It is concluded that a positive biomodulative effect on the healing process of one defect associated or not to the use of organic lyophilized bone and biological bovine lyophilized membrane on the femur of the rat.

In vitro culture of rat neuromicrovascular endothelial cells on polymeric scaffolds

Polyphosphazenes are polymers possessing a skeleton composed of alternating phosphorous and nitrogen atoms, and two side-moieties linked to each phosphorous atom. Polyphosphazenes with amino acid esters as side-moieties are biocompatible and biodegradable polymers. Two polyphosphazenes, poly[bis(ethyl alanate) phosphazene] and poly[(ethyl phenylalanate)0.8(ethyl alanate)0.8(ethyl glycinate)0.4 phosphazene] (PPAGP) were synthesized, and processed to form small fibers. Their ability to support rat neuromicrovascular endothelial cell (EC) adhesion and growth has been studied, using poly(D,L-lactic acid) as reference compound. Scanning electron microscopy revealed that both poly[bis(ethyl alanate) phosphazene] and PPAGP fibers were thinner than poly(D,L-lactic acid) fibers, and possessed a more irregular and porous surface. All polymers increased EC adhesion, compared with polystyrene, but only polyphosphazenes were able to improve EC growth. The highest increase in EC proliferation was induced by PPAGP, which, as revealed by environmental scanning electron microscopy, was also able to induce ECs to arrange into tubular structures. The conclusion is drawn that PPAGP may provide the best scaffold for engineered blood vessels, because it promotes adhesion, growth, and organization of ECs into capillary-like structures.

A bioresorbable molding mesh for impaction grafting revision hip surgery

Impacted morselized allografts are used to treat bone loss in revision surgery. This technique depends on adequate mechanical support of the graft. Metal support devices function well, but there are disadvantages associated with the use of steel meshes. In this cadaveric, surgical simulation model we investigated the surgical and mechanical suitability of a bioresorbable molding mesh for use in impaction grafting revision surgery. Surgical feasibility was assessed, and mechanical deformation of the mesh during the surgical procedure and postoperative cyclic loading of the specimens were measured with strain gauges. All meshes were surgically usable. The exterior surface deformation of the meshes during the surgical procedure and postoperative mechanical loading did not exceed 4500 microm/m, although the meshes were not damaged in a four-point bending test in which deformations higher than 19,000 microm/m were reached. Therefore, results of this study suggest that this type of bioresorbable mesh seems to have sufficient initial mechanical properties to warrant additional preclinical in vivo study.

Coupling of therapeutic molecules onto surface modified coralline hydroxyapatite

Surface modification and coupling of therapeutic molecules, tetracycline, onto coralline hydroxyapatite (CHA) and their in vitro evaluations were described in this study. Initially, CHA was graft polymerized with glycidylmethacrylate (GMA) using redox initiators and subsequently coupled to tetracycline through epoxy groups. The CHA grafted with polyGMA (CHA-g-PGMA) was characterized by Fourier transform infrared spectroscopy and powder X-ray diffraction (XRD) for proof of grafting. The absorption peaks pertaining to epoxy and ester carbonyl groups were observed for the graft polymer due to PGMA grafting. The XRD results signified that there was no secondary phase in the apatite lattice and crystallinity was also not affected by grafting, which suggested that the PGMA chains were grafted only on the surface of CHA. Drug loading and releasing was evaluated and found that CHA-g-PGMA exhibited higher loading efficiency than CHA. The in vitro release of tetracycline was performed in phosphate buffered saline under physiological condition and the release profiles showed that the tetracycline-containing graft polymer releases the drug for prolonged period as compared to CHA. Based on the experimental results, CHA-g-PGMA appears to be a promising biomaterial for drug delivery.

Enhanced bone augmentation by controlled release of recombinant human bone morphogenetic protein-2 from bioabsorbable membranes

BACKGROUND

The present study was undertaken to determine the effect of recombinant human bone morphogenetic protein-2 (rhBMP-2)-loaded biodegradable membranes on bone augmentation in a rabbit calvarial model.

METHODS

Five microg of rhBMP-2 was loaded into a stiff hemispherical dome membrane made of poly(L-lactide) and tricalcium phosphate (PLLA/TCP). The release kinetics of rhBMP-2 from the membrane were determined in vitro using a human BMP-2 immunoassay. Twelve rhBMP-2-loaded dome membranes (test group) and 12 control dome membranes (control group) were placed on the partial-thickness calvarial defects of 24 rabbits. The animals were sacrificed at 4 and 8 weeks, and undecalcified ground sections were prepared. Newly formed bone area and height were measured histomorphometrically and calculated by percentage ratio to the total submembranous space area and height below the dome.

RESULTS

In vitro release results demonstrated that rhBMP-2 was released consistently over a 4-week period following a high initial burst release on the first day. At both 4 and 8 weeks, histomorphometric analysis revealed that the test group showed significantly higher newly formed bone heights and areas than the control group (P < 0.01). In the control group, new bone height was 36.3% of the dome height and the new bone area reached 8.2% of the submembranous space area at 8 weeks, while the test group reached 87.3% and 35.4%, respectively.

CONCLUSION

These results suggest that the use of rhBMP-2-loaded PLLA/TCP membranes can result in additional bone augmentation, which is due to the osteoinductive properties of rhBMP-2 released from the membrane during healing.

Cell adhesion and morphology in porous scaffold based on enantiomeric poly(lactic acid) graft-type phospholipid polymers

Poly(D-lactic acid) (PDLA) and poly(L-lactic acid) (PLLA) macromonomers were synthesized for preparation of a novel cytocompatible polymer. The cytocompatible polymer was composed of 2-methacryloyloxyethyl phosphorylcholine (MPC), n-butyl methacrylate (BMA), and the enantiomeric PLLA (or PDLA) macromonomer. The degree of polymerization of the lactic acid in the PLLA and PDLA segments was designed to be ca. 20. The copolymer-coated surface was analyzed with static contact angle by water. From the result, the PLLA (or PDLA) segment and MPC unit were located on the coated surface, and the monomer unit in the copolymer was reconstructed by contacting water. Fibroblast cell culture was performed to evaluate cell adhesion on the coated surface, and the cell morphology was observed. The number of cell adhesion is correlated with the PL(D)LA content, and the cell morphology is correlated with the MPC unit content. The porous scaffold was prepared by the formation of a stereocomplex between the PLLA and PDLA, and the cell adhesion and following cell intrusion was then evaluated. The fibroblast cells adhered on the surface and intruded into the scaffold through the connecting pores after 24 h. The cell morphology became round shape from spreading with the decreasing PLLA (or PDLA) content in the copolymer. It is considered that the change in the cell morphology would be induced by the MPC unit as cytocompatible unit. These findings suggest that the porous scaffold makes it possible to have cytocompatibility and to produce three-dimensional tissue regeneration.

Healing patterns in calvarial bone defects following guided bone regeneration in rats. A micro-CT scan analysis

OBJECTIVE

The objective of this study was to evaluate healing patterns of critical-size calvarial bone defects treated according to principles of guided bone regeneration using micro-CT scan analysis. Specifically, the contribution of bone, periosteum and dura mater to the amount and mineralization of newly formed bone was evaluated.

MATERIAL AND METHODS

Surgically induced, critical-size calvarial bone defects in 48 adult male Wistar rats received the following: an occlusive expanded polytetrafluoroethylene (ePTFE) membrane at the exo- and endocranial aspect (OO; n = 12); an occlusive membrane at the exocranial and a perforated membrane at the endocranial aspect (OP; n = 12); a perforated membrane at the exocranial and an occlusive membrane at the endocranial aspect (PO; n = 12); and a perforated membrane at the exo- and endocranial aspect (PP; n = 12). The animals were euthanized at 4 weeks for quantitative analysis of bone volume fraction and mineralization in the region of interest (ROI) as well as in the external, middle and central area of the defect using micro-CT.

RESULTS

Bone volume fraction ranged from 31.4% (OP) to 24.5% (PP). No differences were found among the groups. Bone volume fraction and mineralization in the middle area were significantly greater in group OP than in group PP, and in the central area in group OO and PO than in group PP.

CONCLUSIONS

The results of this study suggest that use of occlusive ePTFE membranes enhances bone formation and maturation in the calvarial skeleton. When occlusion of endo- and exocranial tissues was compromised by membrane perforation, impaired bone formation and mineralization were observed.

Effects of fixation type and guided tissue regeneration on maxillary osteotomy healing in rabbits

PURPOSE

The development of fibrous nonunions after orthognathic surgery is thought to result from an interaction of biomechanical stress and the differential and more rapid migration of fibroblasts (compared with osteoblasts) into the wound site during healing. The present study was designed to test this hypothesis through the manipulation of guided tissue regeneration and osteotomy fixation techniques in an experimental rabbit model.

MATERIALS AND METHODS

Bilateral critical size (4 mm) defects (n = 24) were produced in the maxillae of 12 adult New Zealand white rabbits. The maxillary segments were rigidly or nonrigidly fixed using bone microplates and screws or osteosynthetic wires. The defects were then covered with a resorbable collagen membrane or left uncovered. The rabbits were followed for 4 weeks with the use of serial dorsoventral and lateral oblique cephalographs, and the maxillae were then harvested for histologic analyses.

RESULTS

Radiographic and histomorphometric analyses revealed that rigidly fixed defects, covered with membrane, showed the most rapid and organized new bone formation. The rigidly fixed defects with the membrane averaged approximately 40% more new bone in the osteotomy site compared with the rigidly fixed defects with no membrane. Nonrigidly fixed defects with no membrane showed an ingrowth of fibroblasts and fibrous nonunions.

CONCLUSIONS

These experimental results suggest that an interaction between the decreased fibrous tissue ingrowth through guided tissue regeneration and osteotomy segment stability from rigid fixation prevented postoperative fibrous nonunions and facilitated new bone regeneration and osteotomy site healing in this rabbit model.