Biodegradation and biocompatibility of a guided tissue regeneration barrier membrane formed from a liquid polymer material

Engineering periodontal tissue interfaces using multiphasic scaffolds and membranes for guided bone and tissue regeneration

Periodontal diseases are one of the greatest healthcare burdens worldwide. The periodontal tissue compartment is an anatomical tissue interface formed from the periodontal ligament, gingiva, cementum, and bone. This multifaceted composition makes tissue engineering strategies challenging to develop due to the interface of hard and soft tissues requiring multiphase scaffolds to recreate the native tissue architecture. Multilayer constructs can better mimic tissue interfaces due to the individually tuneable layers. They have different characteristics in each layer, with modulation of mechanical properties, material type, porosity, pore size, morphology, degradation properties, and drug-releasing profile all possible. The greatest challenge of multilayer constructs is to mechanically integrate consecutive layers to avoid delamination, especially when using multiple manufacturing processes. Here, we review the development of multilayer scaffolds that aim to recapitulate native periodontal tissue interfaces in terms of physical, chemical, and biological characteristics. Important properties of multiphasic biodegradable scaffolds are highlighted and summarised, with design requirements, biomaterials, and fabrication methods, as well as post-treatment and drug/growth factor incorporation discussed.

Injectable Hydrogel Membrane for Guided Bone Regeneration

In recent years, multicomponent hydrogels such as interpenetrating polymer networks (IPNs) have emerged as innovative biomaterials due to the synergistic combination of the properties of each network. We hypothesized that an innovative non-animal IPN hydrogel combining self-setting silanized hydroxypropyl methylcellulose (Si-HPMC) with photochemically cross-linkable dextran methacrylate (DexMA) could be a valid alternative to porcine collagen membranes in guided bone regeneration. Calvaria critical-size defects in rabbits were filled with synthetic biphasic calcium phosphate granules in conjunction with Si-HPMC; DexMA; or Si-HPMC/DexMA experimental membranes; and in a control group with a porcine collagen membrane. The synergistic effect obtained by interpenetration of the two polymer networks improved the physicochemical properties, and the gel point under visible light was reached instantaneously. Neutral red staining of murine L929 fibroblasts confirmed the cytocompatibility of the IPN. At 8 weeks, the photo-crosslinked membranes induced a similar degree of mineral deposition in the calvaria defects compared to the positive control, with 30.5 ± 5.2% for the IPN and 34.3 ± 8.2% for the collagen membrane. The barrier effect appeared to be similar in the IPN test group compared with the collagen membrane. In conclusion, this novel, easy-to-handle and apply, photochemically cross-linkable IPN hydrogel is an excellent non-animal alternative to porcine collagen membrane in guided bone regeneration procedures.

Advance of Nano-Composite Electrospun Fibers in Periodontal Regeneration

Periodontitis is considered to be the main cause of tooth loss, which affects about 15% of the adult population around the world. Scaling and root-planning are the conventional treatments utilized to remove the contaminated tissue and bacteria, but eventually lead to the formation of a poor connection—long junctional epithelium. Therefore, regenerative therapies, such as guided tissue/bone regeneration (GTR/GBR) for periodontal regeneration have been attempted. GTR membranes, acting as scaffolds, create three-dimensional (3D) environment for the guiding of cell attachment, proliferation and differentiation, and play a significant role in periodontal regeneration. Nano-composite scaffolds based on electrospun nanofibers have gained great attention due to their ability to emulate natural extracellular matrix (ECM) that affects cell survival, attachment and reorganization. Promoted protein absorption, cellular reactions, activation of specific gene expression and intracellular signaling, and high surface area to volume ratio are also important properties of nanofibrous scaffolds. Moreover, several bioactive components, such as bioceramics and functional polymers can be easily blended into nanofibrous matrixes to regulate the physical-chemical-biological properties and regeneration abilities. Simultaneously, functional growth factors, proteins and drugs are also incorporated to regulate cellular reactions and even modify the local inflammatory microenvironment, which benefit periodontal regeneration and functional restoration. Herein, the progress of nano-composite electrospun fibers for periodontal regeneration is reviewed, including fabrication methods, compound types and processes, and surface modifications, etc. Significant proof-of-concept examples are utilized to illustrate the results of material characteristics, cellular interactions and periodontal regenerations. Finally, the existing limitations of nano-composite electrospun fibers and the development tendencies in future are also discussed.

In Vitro and In Vivo Studies of Hydrophilic Electrospun PLA95/β-TCP Membranes for Guided Tissue Regeneration (GTR) Applications

The guided tissue regeneration (GTR) membrane is a barrier intended to maintain a space for alveolar bone and periodontal ligament tissue regeneration but prevent the migration of fast-growing soft tissue into the defect sites. This study evaluated the physical properties, in vivo animal study, and clinical efficacy of hydrophilic PLA95/β-TCP GTR membranes prepared by electrospinning (ES). The morphology and cytotoxicity of ES PLA95/β-TCP membranes were evaluated by SEM and 3-(4,5-cimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) respectively. The cementum and bone height were measured by an animal study at 8 and 16 weeks after surgery. Fifteen periodontal patients were selected for the clinical trial by using a commercial product and the ES PLA95/β-TCP membrane. Radiographs and various indexes were measured six months before and after surgery. The average fiber diameter for this ES PLA95/β-TCP membrane was 2.37 ± 0.86 µm. The MTT result for the ES PLA95/β-TCP membrane showed negative for cytotoxicity. The significant differences in the cementum and bone height were observed between empty control and the ES PLA95/β-TCP membrane in the animal model (p < 0.05). Clinical trial results showed clinical attachment level (CAL) of both control and ES PLA95/β-TCP groups, with a significant difference from the pre-surgery results after six months. This study demonstrated that the ES PLA95/β-TCP membrane can be used as an alternative GTR membrane for clinical applications.

In situ photochemical crosslinking of hydrogel membrane for Guided Tissue Regeneration

OBJECTIVE

Periodontitis is an inflammatory disease that destroys the tooth-supporting attachment apparatus. Guided tissue regeneration (GTR) is a technique based on a barrier membrane designed to prevent wound space colonization by gingival cells. This study examined a new formulation composed of two polymers that could be photochemically cross-linked in situ into an interpenetrated polymer network (IPN) forming a hydrogel membrane.

METHODS

We synthetized and characterized silanized hydroxypropyl methylcellulose (Si-HPMC) for its cell barrier properties and methacrylated carboxymethyl chitosan (MA-CMCS) for its degradable backbone to use in IPN. Hydrogel membranes were cross-linked using riboflavin photoinitiator and a dentistry visible light lamp. The biomaterial's physicochemical and mechanical properties were determined. Hydrogel membrane degradation was evaluated in lysozyme. Cytocompatibility was estimated by neutral red uptake. The cell barrier property was studied culturing human primary gingival fibroblasts or human gingival explants on membrane and analyzed with confocal microscopy and histological staining.

RESULTS

The IPN hydrogel membrane was obtained after 120s of irradiation. The IPN showed a synergistic increase in Young moduli compared with the single networks. The CMCS addition in IPN allows a progressive weight loss compared to each polymer network. Cytocompatibility was confirmed by neutral red assay. Human cell invasion was prevented by hydrogel membranes and histological sections revealed that the biomaterial exhibited a barrier effect in contact with soft gingival tissue.

SIGNIFICANCE

We demonstrated the ability of an innovative polymer formulation to form in situ, using a dentist's lamp, an IPN hydrogel membrane, which could be an easy-to-use biomaterial for GTR therapy.

Advanced Scaffolds for Dental Pulp and Periodontal Regeneration

No current therapy promotes root canal disinfection and regeneration of the pulp-dentin complex in cases of pulp necrosis. Antibiotic pastes used to eradicate canal infection negatively affect stem cell survival. Three-dimensional easy-to-fit antibiotic-eluting nanofibers, combined with injectable scaffolds, enriched or not with stem cells and/or growth factors, may increase the likelihood of achieving predictable dental pulp regeneration. Periodontitis is an aggressive disease that impairs the integrity of tooth-supporting structures and may lead to tooth loss. The latest advances in membrane biomodification to endow needed functionalities and technologies to engineer patient-specific membranes/constructs to amplify periodontal regeneration are presented.

Natural graft tissues and synthetic biomaterials for periodontal and alveolar bone reconstructive applications: a review

Periodontal disease is categorized by the destruction of periodontal tissues. Over the years, there have been several clinical techniques and material options that been investigated for periodontal defect repair/regeneration. The development of improved biomaterials for periodontal tissue engineering has significantly improved the available treatment options and their clinical results. Bone replacement graft materials, barrier membranes, various growth factors and combination of these have been used. The available bone tissue replacement materials commonly used include autografts, allografts, xenografts and alloplasts. These graft materials mostly function as osteogenic, osteoinductive and/or osteoconductive scaffolds. Polymers (natural and synthetic) are more widely used as a barrier material in guided tissue regeneration (GTR) and guided bone regeneration (GBR) applications. They work on the principle of epithelial cell exclusion to allow periodontal ligament and alveolar bone cells to repopulate the defect before the normally faster epithelial cells. However, in an attempt to overcome complications related to the epithelial down-growth and/or collapse of the non-rigid barrier membrane and to maintain space, clinicians commonly use a combination of membranes with hard tissue grafts. This article aims to review various available natural tissues and biomaterial based bone replacement graft and membrane options used in periodontal regeneration applications.

Guided Tissue Regeneration in Four Teeth Using a Liquid Polymer Membrane

Periodontal disease is one of the most common diseases diagnosed in dogs and cats. Guided tissue regeneration (GTR) is a treatment alternative to extraction of strategically important teeth. The barrier membrane used in the GTR procedure is of key importance. The purpose of this case series was to evaluate a liquid polymer gel as a membrane for GTR. The polymer gel ( N-methyl-2-pyrrolidone and poly [DL-lactide]) combined with 8.5% doxycycline hyclate was used in place of a traditional membrane in 4 teeth. The teeth were re-examined 6 months postoperatively for radiographic evaluation. A decrease in probing depth and new alveolar bone formation was seen 6 months postoperatively. Improvement in periodontal disease stage was seen in 2 of the 4 teeth. Larger controlled trials with histopathologic evaluation are indicated to further assess the use of this polymer as a membrane in GTR. However, the clinical outcomes of all 4 treated teeth were considered successful.

Injectable formulations of poly(lactic acid) and its copolymers in clinical use

Poly(lactic acid) and its copolymers have revolutionized the field of drug delivery due to their excellent biocompatibility and tunable physico-chemical properties. These copolymers have served the healthcare sector by contributing many products to combat various diseases and for biomedical applications. This article provides a comprehensive overview of clinically used products of poly(lactic acid) and its copolymers. Multi-dimension information covering product approval, formulation aspects and clinical status is described to provide a panoramic overview of each product. Moreover, leading patented technologies and various clinical trials on these products for different applications are included. This review focuses on marketed injectable formulations of PLA and its copolymers.

Characterization of the release profile of doxycycline by PLGA microspheres adjunct to non-surgical periodontal therapy

The aim of this pilot study was to assess the release of locally delivered doxycycline by poly (l-lactide-co-glycolide) (PLGA) microspheres in the periodontal pocket of patients with chronic periodontitis, treated by non-surgical periodontal therapy. Nineteen sites of non-adjacent teeth of four different patients were evaluated. Five milligram of PLGA microspheres loaded with 16 doxycycline hyclate (DOX) was administered per periodontal site. To quantify DOX released into the periodontal pocket, gingival crevicular fluid (GCF) was collected from the sites on days 2, 5, 7, 10, 15, and 20 after DOX application, and high-performance liquid chromatography was performed. Data were statistically assessed by ANOVA/Tukey test. At days 2, 5, and 7, the DOX concentration was stably sustained (23.33 ± 1.38, 23.4 ± 1.82, and 22.75 ± 1.33 μg/mL, respectively), with no significant differences over these assessment times (p > 0.05). At days 10 and 15, a tendency was observed toward a decrease in DOX concentration (21.74 ± 0.91 and 20.53 ± 4.88 μg/mL, respectively), but a significant decrease in GCF drug concentration (19.69 ± 4.70 μg/mL) was observed only on day 20. The DOX delivery system developed demonstrated a successful sustained release after local administration, as an adjunct to non-surgical periodontal therapy.

Biomaterials for periodontal regeneration: a review of ceramics and polymers

Periodontal disease is characterized by the destruction of periodontal tissues. Various methods of regenerative periodontal therapy, including the use of barrier membranes, bone replacement grafts, growth factors and the combination of these procedures have been investigated. The development of biomaterials for tissue engineering has considerably improved the available treatment options above. They fall into two broad classes: ceramics and polymers. The available ceramic-based materials include calcium phosphate (eg, tricalcium phosphate and hydroxyapatite), calcium sulfate and bioactive glass. The bioactive glass bonds to the bone with the formation of a layer of carbonated hydroxyapatite in situ. The natural polymers include modified polysaccharides (eg, chitosan,) and polypeptides (collagen and gelatin). Synthetic polymers [eg, poly(glycolic acid), poly(L-lactic acid)] provide a platform for exhibiting the biomechanical properties of scaffolds in tissue engineering. The materials usually work as osteogenic, osteoconductive and osteoinductive scaffolds. Polymers are more widely used as a barrier material in guided tissue regeneration (GTR). They are shown to exclude epithelial downgrowth and allow periodontal ligament and alveolar bone cells to repopulate the defect. An attempt to overcome the problems related to a collapse of the barrier membrane in GTR or epithelial downgrowth is the use of a combination of barrier membranes and grafting materials. This article reviews various biomaterials including scaffolds and membranes used for periodontal treatment and their impacts on the experimental or clinical management of periodontal defect.

The effect of loading in regenerated bone in dehiscence defects following a combined approach of bone grafting and GBR

OBJECTIVES

To evaluate by histology the effect of loading on the regenerated bone at dehiscence type defects around implants when treated with a combined approach of bone grafting and guided bone regeneration (GBR).

MATERIALS AND METHODS

In twelve Göttingen mini-pigs, the lower premolars and first molars were extracted and the alveolar process was reduced in width. After 3 months, two Straumann SLActive (Straumann AG, Basel, Switzerland) implants were placed in each hemi-mandible. Twelve implants were placed into the reduced alveolar ridge (group P) with no further defect or treatment on the site, while on 36 implants, buccal dehiscence defects were created and treated as follows: Group T1: synthetic bone substitute (Straumann Bone Ceramic, SBC, Straumann AG). Group T2: SBC with a polyethylene glycol membrane (Straumann MembraGel, Straumann AG); Group N: the dehiscence remained untreated. Three months following implantation, long, custom-made, healing abutments were placed in one hemi-mandible only to ensure functional loading. After 2 months, histological analysis was performed.

RESULTS

A trend for lower residual defect height and higher bone-to-implant contact was observed in the loaded sites compared with non-loaded sites in groups P, T1 and N. In group T2, the opposite effect was observed. In terms of bone formation, sites treated with SBC grafting and GBR (group T2) exhibited the largest surface area of regenerated bone followed by T1 and N. Significant resorption of the graft particles was noted in group T2 and the graft surface area occupied by SBC was significantly higher in group T1 compared with group T2 (P < 0.05).

CONCLUSIONS

Loading may have a positive effect on bone-to-implant contact in implants inserted in pristine bone or inserted in dehiscence sites and treated by grafting/no grafting.

Evaluation of a new biodegradable membrane to prevent gingival ingrowth into mandibular bone defects in minipigs

OBJECTIVE

The aim of this study was to test whether a synthetic, biodegradable membrane made of polyethylene glycol (PEG) can prevent soft-tissue ingrowth into alveolar defects.

MATERIAL AND METHODS

In each of 16 minipigs, three mandibular premolars were bilaterally extracted. Three months later, acute standardized defects (diameter 8 mm, depth 8 mm) were prepared. Four treatment modalities were randomly allocated to the defects: (1) PEG membrane plus collagen sponge, (2) polylactide (PLA) membrane plus collagen sponge, (3) collagen sponge alone, and (4) empty defect. Animals were sacrificed at 10 days (n=5), 21 days (n=5), or 2 months (n=6) after treatment. Qualitative and quantitative histological evaluations of soft-tissue ingrowth and bone regeneration were performed on nondecalcified ground sections. For statistical analysis, the Mann-Whitney-Wilcoxon test, the Kruskal-Wallis, and the paired t-test were applied. P-values were adjusted using the Dunnett-Hsu adjustment.

RESULTS

At 10 days, the PEG membrane group showed the least soft-tissue ingrowth (mean value -0.75 mm; range -1.35 to -0.10), followed by the PLA membrane group -0.18 mm (-0.80 to 0.44), the collagen group 0.04 mm (-0.65 to 0.73), and the empty defects 0.60 mm (-0.08 to 1.29). Statistically significant differences were observed between the PEG membrane group and the empty defects (P<0.05). At 21 days, the highest percentage of newly formed bone was found in the PEG membrane group (mean 28.4%; range 21.6-35.2) compared with 23.7% (16.9-30.5; PLA membrane), 15.2% (8.2-22.2; collagen group), and 21.6% (14.5-28.8; empty defects). Statistically significant differences were only found between the PEG membrane group and the collagen group (P<0.05). At 2 months, the tested parameters revealed no statistically significant differences between the groups.

CONCLUSION

The experimental PEG membrane applied in the present study successfully prevented collapse of the covering soft tissues to a degree similar to the PLA membrane. The combination of a collagen sponge and the PEG membrane showed the least soft-tissue ingrowth at 10 days and promoted more bone formation at 21 days.

Degradative and mechanical properties of a novel resorbable plating system during a 3-year follow-up in vivo and in vitro

We tested the tissue reactions and mechanical strength of a novel biodegradable craniomaxillofacial plating system, Inion CPS, in the course of degradation. Plates and screws composed of L-lactide, D-lactide and trimethylene carbonate were implanted to the mandible and dorsal subcutis of 12 sheep. The animals were sacrificed at 6-156 weeks. Histological evaluation was done using paraffin and methylmetacrylate techniques. Degradative and mechanical properties during the follow-up were measured both of in vivo and in vitro implants. In light microscopy, the in vivo implant material began to fragment at 52 weeks and could not be detected at 104 weeks. No significant foreign body reactions were seen in the mandibles. The dorsal subcutis disclosed mild reactions, which were, however, not of clinical significance. The implants in vitro maintained their entire mass for 26 weeks and lost 63-80% of the mass by week 104. The inherent viscosity of the implants in vitro and in vivo diminished uniformly. The screws retained their shear strength for 12-16 weeks. The plates maintained their tensile strength for at least 6 weeks. The maximum capacity of the plates in 3-point bending tests diminished gradually by 87% in 26 weeks. In conclusion, the plates and screws examined maintain adequate strength for the healing period of a bone fracture or osteotomy, producing no harmful foreign body reactions.

Novel membrane for guided bone regeneration

Membranes have been clinically used for guided tissue and bone regeneration for decades, but their use in every day clinical practice is rather limited. We developed a biodegradable membrane (InionGTR) composed of polylactide, polyglycolide and trimethylene carbonate aiming to improve the properties of membrane. Before application the membrane is treated with N-methyl-pyrrolidone (NMP) to achieve a rubber like consistency, to allow easy handling and manageability in the clinical setting. After placing the membrane NMP diffuses out from the polymer phase into the water phase. The loss of NMP in the polymer stiffens the membrane up and allows space maintenance in the defect area. In addition the influx and efflux of NMP creates a porous surface on the membrane leading to an improved integration of tissues into the porous surface layers of the InionGTR membrane. Therefore, the use of NMP improves the handling in the clinical setting, and allows tissue integration and space maintenance, both important for the outcome of the treatment.

Levels of platelet activating factor in gingival crevice fluid following periodontal surgical therapy

BACKGROUND AND OBJECTIVE

Elevated levels of platelet activating factor (PAF), a potent inflammatory phospholipid mediator, have been previously detected in gingival tissues and gingival crevice fluid (GCF) in periodontal disease. However, the role of this mediator during wound healing after periodontal surgery remains unclear. The hypothesis, a relationship between PAF levels and periodontal healing, was tested by measuring PAF levels in GCF samples collected from sites that had undergone guided tissue regeneration (GTR) or flap surgery.

MATERIAL AND METHODS

Using a split-mouth design, 30 intrabony defects were randomly assigned to treatment with GTR (group 1) or to flap surgery (group 2). GCF was sampled pre-operatively and at 6-, 12- and 24-wk follow-up evaluation visits. PAF levels in GCF were analyzed by high-performance liquid chromatography (HPLC).

RESULTS

Both treatment modalities significantly reduced the probing pocket depth and improved the clinical attachment level (p < 0.01). Compared with pre-operative values, the GCF volume and PAF levels were significantly decreased at postoperative weeks 6, 12 and 24 in both groups (p < 0.01). There were also significant differences in GCF volume and PAF levels at all time points up to 24 wks in both groups (p < 0.01). No statistically significant differences were observed in any of the parameters investigated between the two groups (p > 0.05).

CONCLUSION

PAF is detectable in GCF by HPLC and showed a continuous decrease at all the time points monitored following periodontal surgical therapy. This suggests that changes in the levels of this mediator in GCF might be useful for monitoring the progress of periodontal repair and regeneration.

In vitro biocompatibility of a novel membrane of the composite poly(vinylidene-trifluoroethylene)/barium titanate

This study was aimed at investigating the in vitro biocompatibility of a novel membrane of the composite poly(vinylidene-trifluoroethylene)/barium titanate (P(VDF-TrFE)/BT). Osteoblastic cells were obtained from human alveolar bone fragments and cultured under standard osteogenic condition until subconfluence. First passaged cells were cultured on P(VDF-TrFE)/BT and expanded polytetrafluoroethylene (e-PTFE--control) membranes in 24-well plates. Cell adhesion and spreading were evaluated at 30 min, and 4 and 24 h. For proliferation assay, cells were cultured for 1, 7, and 10 days. Cell viability was detected by trypan blue at 7 and 10 days. Total protein content and alkaline phosphatase (ALP) activity were measured at 7, 14, and 21 days. Cultures were stained with Alizarin red at 21 days, for detection of mineralized matrix. Data were compared by ANOVA and Student t test. Cell attachment (p = 0.001), cell number (p = 0.001), and ALP activity (p = 0.0001) were greater on P(VDF-TrFE)/BT. Additionally, doubling time was greater on P(VDF-TrFE)/BT (p = 0.03), indicating a decreased proliferation rate. Bone-like nodule formation took place only on P(VDF-TrFE)/BT. The present results showed that both membranes are biocompatible. However, P(VDF-TrFE)/BT presented a better in vitro biocompatibility and allowed bone-like nodule formation. Therefore, P(VDF-TrFE)/BT could be an alternative membrane to be used in guided tissue regeneration.

Guided Tissue Regeneration, Barrier Membranes and Reconstruction of the Cleft Maxillary Alveolus

The use of barrier membranes for bone regeneration is especially beneficial in the case of severely affected soft tissue. One useful indication may be the formation of an effective shell for bone grafts in maxilla cleft defect reconstruction. When selecting a proper material for clinical use, one must consider the safety record, the resorption time and route of elimination, the time of the maintained barrier function, the necessary time of mechanical strength, and costs. Two resorbable collagen membranes, one of single-layer and one of double-layer material, were tested in vitro and in vivo. The tested single-layer membrane is less expensive, but it is also less handling than the double-layer membrane. In vitro, samples were incubated in simulated surgical wound. A complete unambiguous picture of disintegration was not proved histologically in either material in six investigation terms (1-6 weeks). In vivo the effect of the assessed membranes was verified on a group of patients (N = 45) with a cleft. Materials were applied in the reconstruction of the alveolar defect by cancellous bone grafts. The influence on the course of healing was not stated as statistically significant. However, with respect to the costs of double layer membrane, this material was used in the most severe cases.

Locally delivered TGF-beta1 and IGF-1 enhance the fixation of titanium implants: a study in dogs

BACKGROUND

Osteogenic growth factors have been suggested to enhance the fixation of implants used in joint replacement. We examined the effect of locally delivered transforming growth factor-beta1 and insulin-like growth factor-1 in a biodegradable poly (D, L-lactide) coating.

MATERIAL AND METHODS

In a paired study using 9 dogs, unloaded titanium implants surrounded by a 1-mm gap were inserted into the proximal humerus. The growth factors were incorporated in a poly (D, L-lactide) coating at a 1% (w/w) ratio of TGF-beta1 and a 5% (w/w) ratio of IGF-1. Control implants were uncoated. After 4 weeks, the implants were evaluated by mechanical push-out test and by histomorphometry.

RESULTS

A twofold increase was seen in mechanical fixation (strength, stiffness, energy absorption) for the growth factor-treated implants (p = 0.04). Similar results were seen in histomorphometry, as bone ongrowth was 2.5 times higher (p = 0.02), and gap healing was 30-110% higher (p = 0.04) for the growth factor-treated implants than for the control implants. Ongrowth of fibrous tissue was eliminated by the treatment.

INTERPRETATION

TGF-beta-1 and IGF-1, locally delivered in a biodegradable poly(D,L-lactide) coating, enhance the mechanical fixation and osseointegration of titanium implants in cancellous bone, and no fibrous tissue is produced in the growth factor treated implants.

In vivo and in vitro degradation of a novel bioactive guided tissue regeneration membrane

The aim of this study was to assess degradation of a novel bioactive guided tissue regeneration (GTR) membrane and to quantify the concurrent tissue responses. Pieces of membrane composed of poly-l-lactide, poly-d,l-lactide, trimethylenecarbonate and polyglycolide were dipped into an N-methyl-2-pyrroline (NMP) solution and implanted in the mandibles of 10 sheep. The animals were sacrificed at 6-104 weeks. Parallel in vitro degradation was analysed by measuring the inherent viscosity, water absorption and remaining mass. One of the 2 in vitro sets of membranes was prehandled with NMP. At 6-26 weeks in vivo, the gradually more degraded implants were surrounded by a fibrous network. At 52 and 104 weeks, the implants and fibrous networks were non-detectable. Foreign body granulomatous reactions were not observed. In vitro, the mass of the NMP-exposed membranes diminished linearly over the 2-year period down to 10%, while the non-NMP-exposed membrane maintained all their mass for the first 16 weeks. The membranes without NMP had absorbed significantly less water at weeks 4 and 8 than the other group. The inherent viscosity decreased relatively uniformly in the in vitro groups. In conclusion, the in vivo degradation was complete in 12 months with only mild histologic responses; the degradation in vitro may be slower. NMP accelerates the degradation.

Guided tissue regeneration for using a chitosan membrane: An experimental study in rats

Barrier membranes are employed clinically to deflect the growth of gingival tissues away from root surface. They provide an isolated space over the regions with the defective tissues that allow the relatively slow growing periodontal ligament fibroblasts to be repopulated onto the root surface. Several makes of bioabsorbable membranes are now commercially available. In this study, we have employed chitosan as barrier membrane material and evaluated it for a guided tissue regeneration application. Three types of chitosan membranes: Chi-NaOH, Chi-Na(5)P(3)O(10), and Chi-Na(2)SO(3)(each was gelated by NaOH, crosslinked by Na(5)P(3)O(10) and Na(2)SO(3), respectively), were prepared to be evaluated by the following categories: the mechanical strength to create an effective space, the rapid rate to reach hydrolytic equilibrium in phosphate-buffered solution, and the ease of clinical manipulative operations. Consequently, standardized, transosseous and critical sized skull defects were made in adult rats and the defective regions were covered with the specifically prepared chitosan membranes. After 4 weeks of recovering, varying degrees of bone healing were observed beneath the chitosan membranes in comparison to the control group. The chitosan covered regions showed a clear boundary space between connective tissues and bony tissues. Apparently, this process resulted in a good cell occlusion and beneficial osteogenesis effect to the bone. As for the control group, the bone defect was filled with connective tissue, and a destruction of the integrity of newly formed bone was observed. Among the chitosan membranes tested in this study, Chi-NaOH membrane provided a higher percentage of new bone formation than those from the Chi-Na(5)P(3)O(10) and Chi-Na(2)SO(3) families.

MacroPore resorbable devices in craniofacial surgery

Resorbable polymer implants have become a compelling option in the treatment of acquired and congenital craniofacial deformities. The resorbable polylactide (PLa) and polyglycolide (PGa) polymers in particular have demonstrated excellent safety profile sin multiple in vitro, animal, and clinical studies and are currently being used in a wide variety of craniofacial applications. In this article, the authors discuss the biomaterial properties of PLa and PGa resorbable implants and provide an overview of the use of these polymers in craniofacial surgery. They conclude by relating their experience with an ongoing clinical series using MacroPore PLDLa and FRP implants for various applications,including Le Fort osteotomies, midface/monobloc internal distraction, and craniosynostosis reconstruction.

A novel, non-prostanoid EP2 receptor-selective prostaglandin E2 agonist stimulates local bone formation and enhances fracture healing

CP-533,536, a newly discovered, non-prostanoid EP2 receptor-selective PGE2 agonist, stimulates local bone formation and enhances fracture healing in rat models.

INTRODUCTION

There is a significant medical need for agents that can stimulate local bone formation and enhance fracture healing. We tested the effects of CP-533,536, a newly discovered, non-prostanoid EP2 receptor-selective prostaglandin E2 (PGE2) agonist, in stimulating local bone formation and enhancing fracture healing in rat models.

MATERIALS AND METHODS

In the first model, a single injection of CP-533,536 at doses of 0.3, 1, or 3 mg/kg to the proximal tibial metaphysis of 6-week-old male rats was given on day 1, and the local bone anabolic effect was determined on day 7. We then tested the effects of this compound in inducing bone formation on rat periosteum of the femur. A single dose of 0.3 mg of CP-533,536 incorporated in a poly-(D,L-lactide-co-glycolide) (PLGH) matrix was injected onto the periosteum of the femur in 3-week-old male rats, and local bone formation was determined on day 14. Finally, the ability of CP-533,536 in PLGH matrix in enhancing fracture healing was tested using the rat femoral fracture model. CP-533,536 in PLGH matrix at doses of 0.05, 0.5, or 5 mg was delivered to the local fracture site on the same day of fracture, and its efficacy was evaluated on day 21.

RESULTS AND CONCLUSIONS

A single injection of CP-533,536 at doses of 0.3, 1, or 3 mg/kg to the proximal tibial metaphysis dose-dependently stimulated local lamellar bone formation on trabecular, endocortical, and periosteal surfaces, and thus increased bone mineral content and bone strength at the injected site. Similarly, a single injection of 0.3 mg of CP-533,536 incorporated in PLGH matrix onto the periosteum of the femur induced significantly local bone formation. In the rat femoral fracture model, CP-533,536 in PLGH matrix at doses of 0.05, 0.5, and 5 mg dose-dependently increased callus size, density, and strength compared with PLGH matrix alone. These results show that CP-533,536 stimulates new bone formation on trabecular, endocortical, and periosteal surfaces and enhances fracture healing. These data reveal that EP2 receptor-selective agonists provide therapeutic potential for local bone augmentation, bone repair, and bone healing in humans.

Biodegradable polymer-mediated intratumoral delivery of cisplatin for treatment of human head and neck squamous cell carcinoma in a chimeric mouse model

BACKGROUND

The effectiveness of chemotherapeutic agents is proportional to the dose of the agents at their targets; however, the dose is limited by systemic toxicity. Attempts have been made to improve therapeutic effectiveness by increasing maximum tolerated dose (MTD) of chemotherapeutic agents using various local and regional drug delivery systems. Herein we report the use of an injectable biodegradable polymer to deliver cisplatin for intratumoral treatment of human head and neck squamous cell carcinoma (HNSCC) in a chimeric mouse model. The objectives of this research project were (1) to determine the release kinetics of cisplatin from the polymer delivery system, (2) to identify the MTD of polymer-delivered cisplatin, and (3) to evaluate its therapeutic efficacy.

METHODS

To determine the in vivo release kinetics, cisplatin-loaded polymer was injected subcutaneously into rats. Implants were removed and analyzed for remaining cisplatin by a high-performance liquid chromatography technique. Sera from these rats were assayed for platinum by atomic absorption spectrophotometry. For MTD determination, SCID mice were engrafted subcutaneously with fresh biopsy specimens of HNSCC. Various doses of free or polymer-loaded cisplatin were injected intratumorally. MTD was estimated based on the threshold at which all mice survived. The antitumor efficacy of free and polymer-loaded cisplatin at their respective MTD was assayed on the same chimeric mouse model.

RESULTS

The polymer delivery system released 80% of the loaded cisplatin in vivo over a 7-day period. The polymer-delivered cisplatin exhibited higher MTD (36 mg/kg) than free cisplatin (18 mg/kg) and had a statistically significant tumor suppression effect compared with free cisplatin when used at their respective MTD.

CONCLUSIONS

The polymer delivery system can sustain cisplatin release for a period of 7 days. It can increase MTD and potentially enhance the antitumor efficacy of cisplatin against human head and neck cancers.

An EP2 receptor-selective prostaglandin E2 agonist induces bone healing

The morbidity and mortality associated with impaired/delayed fracture healing remain high. Our objective was to identify a small nonpeptidyl molecule with the ability to promote fracture healing and prevent malunions. Prostaglandin E2 (PGE2) causes significant increases in bone mass and bone strength when administered systemically or locally to the skeleton. However, due to side effects, PGE2 is an unacceptable therapeutic option for fracture healing. PGE2 mediates its tissue-specific pharmacological activity via four different G protein-coupled receptor subtypes, EP1, -2, -3, and -4. The anabolic action of PGE2 in bone has been linked to an elevated level of cAMP, thereby implicating the EP2 and/or EP4 receptor subtypes in bone formation. We identified an EP2 selective agonist, CP-533,536, which has the ability to heal canine long bone segmental and fracture model defects without the objectionable side effects of PGE2, suggesting that the EP2 receptor subtype is a major contributor to PGE2's local bone anabolic activity. The potent bone anabolic activity of CP-533,536 offers a therapeutic alternative for the treatment of fractures and bone defects in patients.

Enzymatic degradation behavior of porous silk fibroin sheets

We investigated the degradation behavior of porous silk fibroin sheets by in vitro enzymatic experiments with alpha-chymotrypsin, collagenase IA, and protease XIV. With 1.0 U/ml protease XIV, 70% of a silk fibroin sheet was degraded within 15 days at 37 degrees C. When the fibroin sheet was exposed to collagenase IA, the amount of Silk II crystalline structure in the sheets decreased slightly, and a small amount of Silk I crystalline structure was formed. When protease XIV was used, almost all Silk II disappeared, but the crystallinity increased overall because the amount of Silk I increased. During digestion with protease XIV, the pore size of the fibroin sheets increased with increasing degradation time, until the sheets finally collapsed and became totally shapeless. The average molecular weight of the products after degradation with the three enzymes followed the order protease XIV < collagenase IA < alpha-chymotrypsin. More than 50% of the products resulting from degradation with protease XIV were free amino acids.