Healing of experimentally created defects: a review

Functionalized Periosteum-Derived Microsphere-Hydrogel with Sequential Release of E7 Short Peptide/miR217 for Large Bone Defect Repairing

Large bone defects are still a persistent challenge in orthopedics. The availability limitations and associated complications of autologous and allogeneic bone have prompted an increasing reliance on tissue engineering and regenerative medicine. In this study, we developed an injectable scaffold combining an acellular extracellular periosteal matrix hydrogel with poly(d,l-lactate-co-glycol-acetate) microspheres loaded with the E7 peptide and miR217 (miR217/E7@MP-GEL). Characterization of the composites included morphological analysis by scanning electron microscopy, degradation and swelling tests, in vitro and in vivo biological evaluation, and the biological activity evaluation of mesenchymal stem cells (MSCs) through their effects on cell recruitment, proliferation, and osteogenic differentiation. The designed hydrogels demonstrated good physical and chemical properties that are cytocompatible and suitable for cell recruitment. In vitro studies confirmed the high biological activity of the release agent, which markedly enhanced the proliferation and osteogenic differentiation of MSCs. In vivo application to a rat model of a femur defect exhibited a significant increase in bone volume and density over 7 weeks, resulting in enhanced bone regeneration. Acellular periosteum-based hydrogels combined with the E7 peptide and miR217-loaded poly(d,l-lactate-co-glycol-acetate) microspheres can promote effective bone regeneration through the recruitment, proliferation, and osteogenic differentiation of MSCs, which provides a promising approach for the treatment of large bone defects.

Guided Bone Regeneration Using Barrier Membrane in Dental Applications

Guided bone regeneration (GBR) is a widely used technique in preclinical and clinical studies due to its predictability. Its main purpose is to prevent the migration of soft tissue into the osseous wound space, while allowing osseous cells to migrate to the site. GBR is classified into two main categories: resorbable and non-resorbable membranes. Resorbable membranes do not require a second surgery but tend to have a short resorption period. Conversely, non-resorbable membranes maintain their mechanical strength and prevent collapse. However, they require removal and are susceptible to membrane exposure. GBR is often used with bone substitute graft materials to fill the defect space and protect the bone graft. The membrane can also undergo various modifications, such as surface modification and biological factor loading, to improve barrier functions and bone regeneration. In addition, bone regeneration is largely related to osteoimmunology, a new field that focuses on the interactions between bone and the immune system. Understanding these interactions can help in developing new treatments for bone diseases and injuries. Overall, GBR has the potential to be a powerful tool in promoting bone regeneration. Further research in this area could lead to advancements in the field of bone healing. This review will highlight resorbable and non-resorbable membranes with cellular responses during bone regeneration, provide insights into immunological response during bone remodeling, and discuss antibacterial features.

Guided Tissue and Bone Regeneration Membranes: A Review of Biomaterials and Techniques for Periodontal Treatments

This comprehensive review provides an in-depth analysis of the use of biomaterials in the processes of guided tissue and bone regeneration, and their indispensable role in dental therapeutic interventions. These interventions serve the critical function of restoring both structural integrity and functionality to the dentition that has been lost or damaged. The basis for this review is laid through the exploration of various relevant scientific databases such as Scopus, PubMed, Web of science and MEDLINE. From a meticulous selection, relevant literature was chosen. This review commences by examining the different types of membranes used in guided bone regeneration procedures and the spectrum of biomaterials employed in these operations. It then explores the manufacturing technologies for the scaffold, delving into their significant impact on tissue and bone regenerations. At the core of this review is the method of guided bone regeneration, which is a crucial technique for counteracting bone loss induced by tooth extraction or periodontal disease. The discussion advances by underscoring the latest innovations and strategies in the field of tissue regeneration. One key observation is the critical role that membranes play in guided reconstruction; they serve as a barrier, preventing the entry of non-ossifying cells, thereby promoting the successful growth and regeneration of bone and tissue. By reviewing the existing literature on biomaterials, membranes, and scaffold manufacturing technologies, this paper illustrates the vast potential for innovation and growth within the field of dental therapeutic interventions, particularly in guided tissue and bone regeneration.

Radiographic Analysis of Graft Dimensional Changes after Lateral Maxillary Sinus Augmentation with Heterologous Materials and Simultaneous Implant Placement: A Retrospective Study in 18 Patients

Background: This investigation aimed to radiographically assess the variations of graft dimension following maxillary sinus augmentation by the lateral approach. Methods: Eighteen patients (seven males), with a mean age at surgery of 66.5 ± 9.8 (range 52−82) years, were unilaterally treated. Thirty-five dental implants were positioned in the posterior maxilla simultaneously to grafting with heterologous biomaterials. Intraoral radiographs taken at the time of surgery, after six months, and at the longest follow-up (up to nine years after implant placement) were analyzed. The following distances were measured: mesio-distal width of the graft, vertical distance from implant apex to most coronal level of the graft, distance from the mesial aspect of the (mesial) implant to the mesial graft extension; distance from the distal aspect of the (distal) implant to the distal graft extension, and graft height along the implant axis. The dimensional changes with respect to baseline, after six months and at the longest follow-up were calculated. Results: The patient-based mean follow-up was 38.3 ± 30.1 months (range 12−108 months). The mean residual bone height at the mesial and distal aspect of the implants was 3.19 ± 2.05 mm and 2.65 ± 1.60 mm, respectively (p = 0.38). The mean graft width at baseline was 27.95 ± 5.23 mm, and the mean graft width reduction was 10.2 ± 12.7% (2.98 ± 3.62 mm) and 11.3 ± 14.4% (3.36 ± 4.08 mm) at six months and at the latest follow-up. The change was significant at six months (p = 0.005), but did not show significant further variation (p = 0.11). On the mesial and distal aspect, the mean graft extension decreased by 1.56 ± 2.67 mm and 0.84 ± 2.71 mm at the latest follow-up. No significant difference between mesial and distal changes was found (p = 0.24), suggesting that the biomaterial is resorbed homogeneously on both sides. The mean graft height was 11.92 ± 2.53 mm at baseline and decreased by 9.3 ± 9.05% (1.11 ± 1.09 mm) at six months (p < 0.001). Non-significant further changes were found at the latest follow-up (p = 0.10). Conclusions: after early remodeling, heterologous bone substitutes showed a good dimensional stability in the mid-term for maxillary sinus augmentation.

Radiographic Analysis of Graft Dimensional Changes in Transcrestal Maxillary Sinus Augmentation: A Retrospective Study

Background. The maxillary sinus lift is a popular and predictable technique associated with implant-supported rehabilitation of the severely atrophic maxilla. The aim of the present retrospective study was to investigate the effectiveness of transcrestal maxillary sinus augmentation and the graft resorption pattern using different heterologous bone substitutes. Methods. A total of 75 sinus-grafting procedures were performed and 89 implants were placed in 66 patients, 24 males and 42 females, with mean age 67.9 ± 10.64 years (range 43−84 years). Nineteen subjects were smokers. The mean follow-up period was 93.33 ± 54.71 months (range 14−240 months). Clinical and radiographical evaluations were performed. Graft height and width were measured at baseline and at the latest follow-up. Results. Mesiodistal and vertical resorption averaged 9.3 ± 20.7% (standard deviation), and 5.04 ± 9.9% of the postoperative size, respectively, considering the graft as the unit. Linear regression analysis showed that graft resorption in both the vertical and the mesiodistal dimension is independent of the follow-up time. Conversely, there was a trend for greater resorption when increasing the postoperative graft size, in both vertical (p = 0.001) and horizontal (p = 0.007) dimensions. When grouping the dimensional changes by graft particle size (only small (<300 μm) particles, combination of small and medium (>500 μm)/large (>1000 μm) particles, and only medium/large particles), there was a trend for greater resorption associated with smaller particles, but it was not significant; neither in the mesiodistal nor in the vertical dimension (p = 0.17 and p = 0.25, respectively). No implant was lost during the observation period. In conclusion, the transcrestal technique for maxillary sinus augmentation documented a high level of predictability. The low clinical morbidity and the contextual dental implant positioning is clinically useful in relation to a significant reduction of the time required for implant restoration, a consistent decrease of the number of surgical phases, and a cost-effectiveness approach for the rehabilitation. The graft resorption pattern in all cases was compatible with persistent implant protection and support.

A review on bovine hydroxyapatite; extraction and characterization

High rate of bone grafting surgeries emphasizes the need for optimal bone substitutes. Biomaterials mimicking the interconnected porous structure of the original bone with osteoconductive and osteoinductive capabilities have long been considered. Hydroxyapatite (HA), as the main inorganic part of natural bone, has exhibited excellent regenerative properties in bone tissue engineering. This manuscript reviews the HA extraction methods from bovine bone, as one of the principal biosources. Essential points in the extraction process have also been highlighted. Characterization of the produced HA through gold standard methods such as XRD, FTIR, electron microscopies (SEM and TEM), mechanical/thermodynamic tests, and bioactivity analysis has been explained in detail. Finally, future perspectives for development of HA constructs are mentioned.

Barrier membranes for tissue regeneration in dentistry

Background: In dentistry, barrier membranes are used for guided tissue regeneration (GTR) and guided bone regeneration (GBR). Various membranes are commercially available and extensive research and development of novel membranes have been conducted. In general, membranes are required to provide barrier function, biosafety, biocompatibility and appropriate mechanical properties. In addition, membranes are expected to be bioactive to promote tissue regeneration. Objectives: This review aims to organize the fundamental characteristics of the barrier membranes that are available and studied for dentistry, based on their components. Results: The principal components of barrier membranes are divided into nonbiodegradable and biodegradable materials. Nonbiodegradable membranes are manufactured from synthetic polymers, metals or composites of these materials. The first reported barrier membrane was made from expanded polytetrafluoroethylene (e-PTFE). Titanium has also been applied for dental regenerative therapy and shows favorable barrier function. Biodegradable membranes are mainly made from natural and synthetic polymers. Collagens are popular materials that are processed for clinical use by cross-linking. Aliphatic polyesters and their copolymers have been relatively recently introduced into GTR and GBR treatments. In addition, to improve the tissue regenerative function and mechanical strength of biodegradable membranes, inorganic materials such as calcium phosphate and bioactive glass have been incorporated at the research stage. Conclusions: Currently, there are still insufficient guidelines for barrier membrane choice in GTR and GBR, therefore dentists are required to understand the characteristics of barrier membranes.

Evaluation of single-dose applied teriparatide effect on bone healing with histomorphometric and micro-ct analysis

The aim of the present study was to evaluate the effects of a single dose of locally administered teriparatide (TP) on healing critical-sized defects in rat mandibles through histomorphometric and microcomputed tomography (micro-CT) analyses. In this study, 48 Sprague-Dawley rats were used. The experimental animals were divided into 4 groups as follows: Group 1 had empty defects, Group 2 received autografts, Group 3 received allografts, and Group 4 received allografts combined with 40 μg of TP. Eight weeks after the surgical procedure, all rats were sacrificed, and all specimens were evaluated using micro-CT and histomorphometric analyses. The results of the histomorphometric analysis showed that Group 4 had the most new bone area (0.85 mm² ± 0.13 mm²) (p = 0.002) and the highest number of osteoblasts (86.61 ± 4.86) (p = 0.001). In addition, the results of the micro-CT analysis showed that Group 4 had the highest bone volume/total volume (23.27% ± 0.15%) (p = 0.001). The histomorphometric and micro-CT values of Group 2 were higher than those of Group 1 but lower than those of Group 3 and Group 4. The results of the study show that a single dose of locally administered TP has a positive effect on the integration of allografts. However, further studies are necessary to identify the mechanism of action and the effective minimum and maximum doses of locally administered TP.

Scaffolds of PCL combined to bioglass: synthesis, characterization and biological performance

Biomaterials may be useful in filling lost bone portions in order to restore balance and improve bone regeneration. The objective of this study was to produce polycaprolactone (PCL) membranes combined with two types of bioglass (Sol-Gel and melt-quenched) and determine their physical and biological properties. Membranes were produced through electrospinning. This study presented three experimental groups: pure PCL membranes, PCL-Melt-Bioglass and PCL-Sol-gel-Bioglass. Membranes were characterized using Scanning Electron Microscopy, Fourier Transform Infrared Spectrophotometry (FTIR), Energy-Dispersive Spectroscopy and Zeta Potential. The following in vitro tests were performed: MTT assay, alkaline phosphatase activity, total protein content and mineralization nodules. Twenty-four male rats were used to observe biological performance through radiographic, fracture energy, histological and histomorphometric analyses. The physical and chemical analysis results showed success in manufacturing bioactive membranes which significantly enhanced cell viability and osteoblast differentiation. The new formed bone from the in vivo experiment was similar to that observed in the control group. In conclusion, the electrospinning enabled preparing PCL membranes with bioglass incorporated into the structure and onto the surface of PCL fibers. The microstructure of the PCL membranes was influenced by the bioglass production method. Both bioglasses seem to be promising biomaterials to improve bone tissue regeneration when incorporated into PCL.

From two stages to one: acceleration of the induced membrane (Masquelet) technique using human acellular dermis for the treatment of non-infectious large bone defects

Introduction

The induced membrane technique for the treatment of large bone defects is a two-step procedure. In the first operation, a foreign body membrane is induced around a spacer, then, in the second step, several weeks or months later, the spacer is removed and the Membrane pocket is filled with autologous bone material. Induction of a functional biological membrane might be avoided by initially using a biological membrane. In this study, the effect of a human acellular dermis (hADM, Epiflex, DIZG gGmbH) was evaluated for the treatment of a large (5 mm), plate-stabilised femoral bone defect.

Material and Methods

In an established rat model, hADM was compared to the two-stage induced membrane technique and a bone defect without membrane cover. Syngeneous spongiosa from donor animals was used for defect filling in all groups. The group size in each case was n = 5, the induction time of the membrane was 3–4 weeks and the healing time after filling of the defect was 8 weeks.

Results

The ultimate loads were increased to levels comparable with native bone in both membrane groups (hADM: 63.2% ± 29.6% of the reference bone, p < 0.05 vs. no membrane, induced membrane: 52.1% ± 25.8% of the reference bone, p < 0.05 vs. no membrane) and were significantly higher than the control group without membrane (21.5%). The membrane groups were radiologically and histologically almost completely bridged by new bone formation, in contrast to the control Group where no closed osseous bridging could be observed.

Conclusion

The use of the human acellular dermis leads to equivalent healing results in comparison to the two-stage induced membrane technique. This could lead to a shortened therapy duration of large bone defects.

Resorbable Versus Nonresorbable Membranes: When and Why?

Guided bone-regeneration techniques use either resorbable or nonresorbable membrane. Ideal membrane material should be biocompatible with tissue integration, be able to create and maintain space, be occlusive with selective permeability, and have good handling properties. Commercially available nonresorbable membranes are Gor-tex (e-PTFE), Cytoplast (d-PTFE), and titanium mesh. Resorbable membranes are available as natural and synthetic. Clinical trials, a systematic review and meta-analysis have shown no statistically significant difference in most clinical indications between both types of membrane. The choice of membrane varies according to the choice of grafting materials and nature of defect.

* 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.

Nanomaterials for Tissue Engineering In Dentistry

The tissue engineering (TE) of dental oral tissue is facing significant changes in clinical treatments in dentistry. TE is based on a stem cell, signaling molecule, and scaffold triad that must be known and calibrated with attention to specific sectors in dentistry. This review article shows a summary of micro- and nanomorphological characteristics of dental tissues, of stem cells available in the oral region, of signaling molecules usable in TE, and of scaffolds available to guide partial or total reconstruction of hard, soft, periodontal, and bone tissues. Some scaffoldless techniques used in TE are also presented. Then actual and future roles of nanotechnologies about TE in dentistry are presented.

Bone regeneration using injectable BMP-7 loaded chitosan microparticles in rat femoral defect

Injectable chitosan microparticles were prepared using a simple coacervation method under physiologically friendly conditions by eliminating oil or toxic chemical, and employing low temperature and pressure for growth factor stability. Amount of 200 ng of bone morphogenetic protein-7 (BMP-7) was incorporated in the chitosan microparticles by two methods: encapsulating and coating techniques. These microparticles were tested in vivo to determine the biological response in a rat femoral bone defect at 6 and 12 weeks. Four groups (n=10) were tested which include two groups for BMP-7 incorporated microparticles (by two techniques), microparticles without BMP-7, and defect itself (negative control). Healthy bone formation was observed around the microparticles, which were only confined to the defect site and did not disperse. Histology indicated minor inflammatory response around the microparticles at 6 weeks, which reduced by 12 weeks. Micro-CT analysis of bone surface density and porosity was found to be significantly more (p<0.05) for microparticles containing groups, in comparison with controls, which suggests that the new bone formed in the presence of microparticles is more interconnected and porous. Collagen fibrils analysis conducted using multiphoton microscopy showed significant improvement in the formation of bundled collagen area (%) in microparticles containing groups in comparison with controls, indicating higher cross-linking between the fibrils. Microparticles were biocompatible and did not degrade in the 12 week implant period.

Comparison of platelet rich plasma and synthetic graft material for bone regeneration after third molar extraction

Aims:

To compare the efficacy of Platelet rich plasma and synthetic graft material for bone regeneration after bilateral third molar extraction.

Material and Methods:

This study was conducted in 10 patients visiting the outpatient department of Oral & Maxillofacial Surgery, Yenepoya Dental College & Hospital. Patients requiring extraction of bilateral mandibular third molars were taken for the study. Following extraction, PRP (Platelet Rich Plasma) was placed in one extraction socket and synthetic graft material in form granules [combination of Hydroxyapatite (HA) and Bioactive glass (BG)] in another extraction socket. The patients were assessed for postoperative pain and soft tissue healing. Radiological assessment of the extraction site was done at 8, 12 and 16 weeks interval to compare the change in bone density in both the sockets.

Results:

Pain was less on PRP site when compared to HA site. Soft tissue evaluation done using gingival healing index given by Landry et al showed better healing on PRP site when compared to HA site. The evaluation of bone density by radiological assessment showed the grey level values calculated at 4 months at the PRP site were comparatively higher than HA site.

Conclusion:

The study showed that the platelet rich plasma is a better graft material than synthetic graft material in terms of soft tissue and bone healing. However a more elaborate study with a larger number of clinical cases is very much essential to be more conclusive regarding the efficacy of both the materials.

Biomaterial-Stabilized Soft Tissue Healing for Healing of Critical-Sized Bone Defects: the Masquelet Technique

Critical-sized bone defects present a significant burden to the medical community due to their challenging treatment. However, a successful limb-salvaging technique, the Masquelet Technique (MT), has significantly improved the prognosis of many segmental bone defects in helping to restore form and function. Although the Masquelet Technique has proven to be clinically effective, the physiology of the healing it induces is not well understood. Multiple modifiable factors have been implicated by various surgical and research teams, but no single factor has been proven to be critical to the success of the Masquelet Technique. In this review the most recent clinical and experimental evidence that supports and helps to decipher the traditional Masquelet, as well as the modifiable factors and their effect on the success of the technique are discussed. In addition, future developments for the integration of the traditional Masquelet Technique with the use of alternative biomaterials to increase the effectiveness and expand the clinical applicability of the Masquelet Technique are reviewed.

Histological Comparison in Rats between Carbonate Apatite Fabricated from Gypsum and Sintered Hydroxyapatite on Bone Remodeling

Carbonate apatite (CO₃Ap), the form of apatite found in bone, has recently attracted attention. The purpose of the present study was to histologically evaluate the tissue/cellular response toward the low-crystalline CO₃Ap fabricated using a dissolution-precipitation reaction with set gypsum as a precursor. When set gypsum was immersed in a 100°C 1 mol/L Na₃PO₄ aqueous solution for 24 h, the set gypsum transformed into CO₃Ap. Both CO₃Ap and sintered hydroxyapatite (s-HAp), which was used as a control, were implanted into surgically created tibial bone defects of rats for histological evaluation. Two and 4 weeks after the implantation, histological sections were created and observed using light microscopy. The CO₃Ap granules revealed both direct apposition of the bone matrix by osteoblasts and osteoclastic resorption. In contrast, the s-HAp granules maintained their contour even after 4 weeks following implantation which implied that there was a lack of replacement into the bone. The s-HAp granules were sometimes encapsulated with fibrous tissue, and macrophage polykaryon was occasionally observed directly apposed to the implanted granules. From the viewpoint of bone remodeling, the CO₃Ap granules mimicked the bone matrix, suggesting that CO₃Ap may be an appropriate bone substitute.

Evolution of Barrier Membranes in Periodontal Regeneration-"Are the third Generation Membranes really here?"

In the last decades, Guide Tissue Regeneration (GTR) technique has been applied for the treatment of various periodontal defects such as intrabony defects, furcation involvements and localized gingival recession defects. From early days of using membranes with the simple aim of minimizing toxic response in the host, membranes have come a long way. Third generation membranes not only act as barriers but also as delivery devices to release specific agents. Many clinical trials have focused on using membranes as delivery devices for antibiotics and growth factors. In this article we take a brief look at the evolution of barrier membranes and future avenues with regard to third generation membranes.

Incorporation of copper into chitosan scaffolds promotes bone regeneration in rat calvarial defects

The objective of this study was to investigate the effects of a copper loaded chitosan scaffold on bone regeneration in critical-sized calvarial defects in rats. Chitosan scaffolds and copper-chitosan scaffolds were fabricated and characterized by scanning electron microscopy (SEM). Chitosan and copper-chitosan scaffolds were implanted into 5 mm diameter critical-sized calvarial defects in Fisher 344 male rats. Empty defects (no scaffolds) were included as a control. After 4 weeks, the rats were sacrificed for microcomputed tomography (micro-CT) and histological analysis of new bone tissue development. Microscopy images revealed the uniformly porous structure of chitosan and copper-chitosan scaffolds. Significant bone regeneration was noted in the defects treated with copper-chitosan scaffolds when evaluated using micro-CT and histological analysis, when compared with other groups tested. On analysis of the micro-CT scans, an eleven-fold and a two-fold increase in the new bone volume/total volume (BV/TV) % was found in defects treated with the copper-chitosan scaffolds, when compared to empty defects and chitosan scaffolds, respectively. This study demonstrated the suitability of copper-crosslinked chitosan scaffolds for bone tissue engineering and provides the first evidence that inclusion of copper ions in scaffolds can enhance tissue regeneration.

Resorption of bone graft after maxillary sinus grafting and simultaneous implant placement

OBJECTIVES

The purpose of this study was to evaluate the sinus bone graft resorption over 3 years after two-stage implant placement.

MATERIALS AND METHODS

The subjects for this study included 30 patients whose maxillary posterior ridges were too atrophic for implants. Bone-added osteotome sinus floor elevation was used in 15 maxillary sinuses, while the bone graft by lateral approach technique was used in 25 maxillary sinuses. The height from the top of the fixture to the sinus floor was estimated immediately after implant placement and the follow-up period was over 3 years. The surgery was classified with two groups: sinus bone grafting with and without autogenous bone. All implants were placed simultaneously.

RESULTS

The mean vertical bone loss was 3.15±2.95 mm. The survival rate of implants was 94.7%.

CONCLUSION

The amount of bone resorption was not significantly associated with the surgical methods, the type of bone graft materials used, or sinus perforation during surgery.

Guided bone regeneration using acellular bovine pericardium in a rabbit mandibular model: in-vitro and in-vivo studies

BACKGROUND AND OBJECTIVE

To investigate the feasibility of acellular bovine pericardium (BP) for guided bone regeneration (GBR) in vitro and in vivo. The success of GBR relies on the fact that various cellular components possess different migration rates into the defect site and that a barrier membrane plays a significant role in these processes.

MATERIAL AND METHODS

BP membrane was isolated and decellularized using an enzymatic method. The microarchitecture, mechanical properties, cytotoxicity and cell chemotaxis properties of the acellular BP were evaluated in vitro, and the in-vivo efficacy of the acellular BP was also investigated in a rabbit mandibular model.

RESULTS

The acellular BP membrane possessed an interconnected fibrous structure. Glutaraldehyde (GA) treatment was efficient for enhancement of the mechanical properties of the acellular BP bur and resulted in negligible cytotoxicity. After 16 wk, standardized osseous defects created in the rabbit mandible, and covered with acellular BP, were associated with an enhanced deposition of mineralized tissue when compared with defects left to spontaneous healing.

CONCLUSION

GA-treated acellular BP is promising as a barrier membrane for GBR for further in-vivo and clinical studies.

Platelet rich plasma enhances osteoconductive properties of a hydroxyapatite-β-tricalcium phosphate scaffold (Skelite) for late healing of critical size rabbit calvarial defects

The use of platelet rich plasma (PRP) in bone repair remains highly controversial. In this work, we evaluated the effect of lyophilized PRP on bone regeneration when associated with a silicon stabilized hydroxyapatite tricalcium phosphate scaffold in a rabbit calvarial defect (Skelite). Critical defects were created in the calvaria of twenty-four rabbits. The periosteum was removed and the defects were either left empty or filled with allogeneic PRP gel; Skelite particles; Skelite and PRP gel. Four animals were killed after 4 weeks, 10 animals after 8 and 10 after 16 weeks. Specimens were processed for X-ray microtomography (μCT) and for resin embedded histology. μCT analysis revealed significant osteoid-like matrix and new bone deposition in PRP + Skelite group at both 8 and 16 weeks in respect to Skelite alone. Histologically, PRP + Skelite defects were highly cellular with more abundant osteoid deposition and more regular collagen fibres. Moreover, in vitro migration assays confirmed the chemotactic effect of PRP to endothelial and osteoprogenitor cells. We conclude that the addition of PRP influenced the local tissue microenvironment by providing key cryptic factors for regeneration, thereby enhancing progenitor cell recruitment, collagen and bone matrix deposition, and by creating a bridging interface between the scaffold and bone.

Maxillary sinus-floor elevation with nanoporous biphasic bone graft material for early implant placement

BACKGROUND

Insufficient bone height in the posterior maxilla is caused by bone atrophy after tooth extraction and continued pneumatization of the maxillary sinus. To allow for implant placement in this area, external sinus-floor elevations are performed. For this indication, the application of various bone graft materials can be a reliable alternative to autologous bone.

PURPOSE

The aim of this study was to analyze a nanoporous bone graft material under the condition of early implant treatment in sinus floor elevations.

MATERIALS AND METHODS

Sixty-six patients received 94 individual external sinus-floor elevations as a precondition for implant surgery. As grafting material, a synthetic, nanoporous bone graft material consisting of a mixture of nano-hydroxyapatite and nano-β-tricalciumphosphate crystals, combined with blood from the defect side, was used. Depending on the remaining vertical bone height, implant placement was performed either simultaneously with bone augmentation or consecutively in a delayed approach. After a 4-month healing period, the patients received 218 implants and were followed up clinically, radiographically, and histologically. To quantify the bone situation at implant placement, immunohistochemical analysis using tenascin-C was performed.

RESULTS

We achieved an average vertical bone increase of 8.28 mm (SD, 2.59) for the one-stage approach and 10.99 mm (SD, 1.73) for the two-stage approach after sinus-floor elevation. The augmented areas showed mean resorption rates of 10.32% (one stage) and 10.82% (two stages) of vertical graft during the observation period. Immunohistochemical analysis after 4 months of healing showed high tenascin activity, indicating bone growth. Good primary stability was achieved during implant placement. Mean peri-implant marginal bone loss was 0.45 mm (SD, 0.31).

CONCLUSION

After a mean observation time of 21.45 months, the biomaterial showed good osseointegration and bone stability radiographically. Adding to this the positive histological and immunohistochemical findings, we conclude that, after a relatively short 4-month healing period, the biomaterial showed predictable results.

The role of barrier membranes for guided bone regeneration and restoration of large bone defects: current experimental and clinical evidence

Treatment of large bone defects represents a great challenge in orthopedic and craniomaxillofacial surgery. Although there are several methods for bone reconstruction, they all have specific indications and limitations. The concept of using barrier membranes for restoration of bone defects has been developed in an effort to simplify their treatment by offering a single-staged procedure. Research on this field of bone regeneration is ongoing, with evidence being mainly attained from preclinical studies. The purpose of this review is to summarize the current experimental and clinical evidence on the use of barrier membranes for restoration of bone defects in maxillofacial and orthopedic surgery. Although there are a few promising preliminary human studies, before clinical applications can be recommended, future research should aim to establish the 'ideal' barrier membrane and delineate the need for additional bone grafting materials aiming to 'mimic' or even accelerate the normal process of bone formation. Reproducible results and long-term observations with barrier membranes in animal studies, and particularly in large animal models, are required as well as well-designed clinical studies to evaluate their safety, efficacy and cost-effectiveness.

Human mesenchymal stem cells and biomaterials interaction: a promising synergy to improve spine fusion

PURPOSE

Spine fusion is the gold standard treatment in degenerative and traumatic spine diseases. The bone regenerative medicine needs (i) in vitro functionally active osteoblasts, and/or (ii) the in vivo induction of the tissue. The bone tissue engineering seems to be a very promising approach for the effectiveness of orthopedic surgical procedures, clinical applications are often hampered by the limited availability of bone allograft or substitutes. New biomaterials have been recently developed for the orthopedic applications. The main characteristics of these scaffolds are the ability to induce the bone tissue formation by generating an appropriate environment for (i) the cell growth and (ii) recruiting precursor bone cells for the proliferation and differentiation. A new prototype of biomaterials known as "bioceramics" may own these features. Bioceramics are bone substitutes mainly composed of calcium and phosphate complex salt derivatives.

METHODS

In this study, the characteristics bioceramics bone substitutes have been tested with human mesenchymal stem cells obtained from the bone marrow of adult orthopedic patients.

RESULTS

These cellular models can be employed to characterize in vitro the behavior of different biomaterials, which are used as bone void fillers or three-dimensional scaffolds.

CONCLUSIONS

Human mesenchymal stem cells in combination with biomaterials seem to be good alternative to the autologous or allogenic bone fusion in spine surgery. The cellular model used in our study is a useful tool for investigating cytocompatibility and biological features of HA-derived scaffolds.

Scaffolds based bone tissue engineering: the role of chitosan

As life expectancy increases, malfunction or loss of tissue caused by injury or disease leads to reduced quality of life in many patients at significant socioeconomic cost. Even though major progress has been made in the field of bone tissue engineering, present therapies, such as bone grafts, still have limitations. Current research on biodegradable polymers is emerging, combining these structures with osteogenic cells, as an alternative to autologous bone grafts. Different types of biodegradable materials have been proposed for the preparation of three-dimensional porous scaffolds for bone tissue engineering. Among them, natural polymers are one of the most attractive options, mainly due to their similarities with extracellular matrix, chemical versatility, good biological performance, and inherent cellular interactions. In this review, special attention is given to chitosan as a biomaterial for bone tissue engineering applications. An extensive literature survey was performed on the preparation of chitosan scaffolds and their in vitro biological performance as well as their potential to facilitate in vivo bone regeneration. The present review also aims to offer the reader a general overview of all components needed to engineer new bone tissue. It gives a brief background on bone biology, followed by an explanation of all components in bone tissue engineering, as well as describing different tissue engineering strategies. Moreover, also discussed are the typical models used to evaluate in vitro functionality of a tissue-engineered construct and in vivo models to assess the potential to regenerate bone tissue are discussed.

Tensile resistance of mineralized and demineralized rat bones in different regions (calvarial and femur)

The aim of this study was to evaluate the tensile resistance of mineralized and demineralized bones. Twelve mice were used. Specimens were collected and divided into groups 1 and 2, mineralized and demineralized calvarial bone, and groups 3 and 4, mineralized and demineralized femoral bone. There was not a statistically significant difference (analysis of variance) between the regions; however, when comparing the demineralized and mineralized groups, a statistically significant difference (Student test) for the mineralized group was noticed.

Rodent models in bone-related research: the relevance of calvarial defects in the assessment of bone regeneration strategies

In vivo research with animal models has been a preferred experimental system in bone-related biomedical research since, by approximation, it allows relevant data gathering regarding physiological and pathological conditions that could be of use to establish more effective clinical interventions. Animal models, and more specifically rodent models, have been extensively used and have contributed greatly to the development and establishment of a wide range of translational approaches aiming to regenerate the bone tissue. In this regard, the calvarial defect model has found great application in basic and applied research, nonetheless the controversial rationalization for the use of critical size defects - defects that are unable to report spontaneous healing - or subcritical size defects in the proposed applications. Accordingly, this work aims to review the advantages and limitations of the use of rodent models in biomedical bone-related research, emphasizing the problematic issues of the use of calvarial critical and subcritical size defects. Additionally, surgical protocols for the establishment of both defects in rat calvarial bone, as well as the description and exemplification of the most frequently used techniques to access the bone tissue repair, are portrayed.

Bone healing with an in situ-formed bioresorbable polyethylene glycol hydrogel membrane in rabbit calvarial defects

OBJECTIVES

The aims of this study were to test whether or not the application of an in situ-formed synthetic polyethylene glycol hydrogel (PEG) used as a biodegradable membrane for guided bone regeneration with a variety of graft materials and ambient oxygen or hyperbaric oxygen (HBO) environments would result in enhanced bone regeneration, and to observe the histologic and histomorphometric aspects of bone healing of the calvarial defects with and without a PEG membrane.

STUDY DESIGN

Thirty adult, skeletally mature, male New Zealand white rabbits were randomly divided into 3 groups of 10 animals each. Bilateral 15-mm-diameter critical-size defects were created in the parietal bones of each animal. Group 1 served as a control with unfilled bilateral calvarial defects, group 2 had bilateral calvarial defects filled with morcelized autogenous calvarial bone, and group 3 had bilateral calvarial defects filled with a biphasic calcium phosphate ceramic. One of the calvarial defects was randomly protected with a PEG resorbable liquid membrane in each animal. Five animals from each group underwent a course of HBO treatment (2.4 ATA 100% oxygen for 90 minutes 5 days a week for 4 weeks) and the other 5 served as control and did not receive any supplemental oxygen (normobaric). The animals were killed 6 weeks after their surgery, and their parietal bones were harvested. The specimens were analyzed with microscopic computerized tomography (microCT) scans and histomorphometrics.

RESULTS

The unfilled normobaric control bony defects did not heal, proving the critical-size nature of these defects. The presence of autogenous bone or bone ceramic in the defects increased the bone volume fraction and bone mineral density of the defects (P < .001). The presence of a membrane in the ungrafted and autogenous bone grafted defects resulted in a decrease in the corrected bone volume fraction (P = .002) but not in the bone ceramic grafted defects (P = .580). Bony healing of defects where the membrane was unsupported was compromised; the membrane did not maintain the desired bone regeneration volume with the unfilled and autogenous bone grafted groups. The PEG resorbable liquid membrane worked best with the bone ceramic material. HBO did not ameliorate the healing of the autogenous bone graft or ceramic filled defects in the 6-week time period of this study.

CONCLUSIONS

Although the PEG resorbable liquid membrane is easy to use and forms an occlusive layer, caution is recommended when using the membrane over an unsupported defect. HBO did not ameliorate bony healing with the membrane at the early 6-week time point. The authors recommend future assessment with HBO at the 12-week time point.

Avaliação do potencial osteogênico do periósteo em associação com uma membrana de colágeno

OBJETIVOS: Este trabalho avaliou o potencial osteogênico de enxertos de periósteo livre associado a uma membrana de colágeno. MÉTODOS: Vinte ratos albinos Wistar com idade média de 100 dias foram submetidos à cirurgia para criação de um defeito ósseo de 2,5 a 3,0 mm de comprimento na diáfise das fíbulas. Após 30 dias os animais foram então divididos em dois grupos: Grupo I recebeu o implante de periósteo associado à membrana de colágeno e Grupo II, somente a membrana de colágeno. Os animais foram radiografados antes do implante de periósteo e 15 ou 30 dias após o mesmo. RESULTADOS: Os resultados mostraram que o enxerto de periósteo livre associado à membrana de colágeno não foi eficiente no processo de reparo do defeito ósseo. CONCLUSÃO: Sugere-se que enxertos periosteais não vascularizados não apresentam potencial para formar novo osso. O fato de o enxerto ter sido implantado 30 dias após a criação do defeito ósseo interferiu negativamente no processo de osteogênese.

From natural bone grafts to tissue engineering therapeutics: Brainstorming on pharmaceutical formulative requirements and challenges

Tissue engineering is an emerging multidisciplinary field of investigation focused on the regeneration of diseased or injured tissues through the delivery of appropriate molecular and mechanical signals. Therefore, bone tissue engineering covers all the attempts to reestablish a normal physiology or to speed up healing of bone in all musculoskeletal disorders and injuries that are lashing modern societies. This article attempts to give a pharmaceutical perspective on the production of engineered man-made bone grafts that are described as implantable tissue engineering therapeutics, and to highlight the importance of understanding bone composition and structure, as well as osteogenesis and bone healing processes, to improve the design and development of such implants. In addition, special emphasis is given to pharmaceutical aspects that are frequently minimized, but that, instead, may be useful for formulation developments and in vitro/in vivo correlations.

Fabrication of bioactive glass-ceramic foams mimicking human bone portions for regenerative medicine

A technique for the preparation of bioglass foams for bone tissue engineering is presented. The process is based on the in situ foaming of a bioglass-loaded polyurethane foam as the intermediate step for obtaining a bioglass porous monolith, starting from sol-gel synthesized bioglass powders. The obtained foams were characterized using X-ray diffraction analysis, Fourier transform infrared spectroscopy, and field emission scanning electron microscopy observations. The material was assessed by soaking samples in simulated body fluid and observing apatite layer formation. Diagnostic imaging taken from human patients was used to reconstruct a human bone portion, which was used to mould a tailored scaffold fabricated using the in situ foaming technique. The results confirmed that the obtained bioactive materials prepared with three-dimensional processing are promising for applications in reconstructive surgery tailored to each single patient.

Reconstruction of a mandibular critical-sized defect using iliac graft in rats

OBJECTIVE

To evaluate, histologically and by optical densitometry of radiographs, the healing of a critical-sized defect in the rat mandible filled with iliac graft.

MATERIALS

The study was conducted on 25 adult Wistar rats. With the rats under general anesthesia, a bicortical critical-sized osseous defect was created in the right mandibular ramus and filled with autogenous iliac crest graft. The animals were divided into 5 groups, with 5 rats in each. They were sacrificed after 1, 7, and 14 days, and 1 and 3 months. The mandibles were removed, fixed in formalin, and radiographed. The right hemi-mandibles were decalcified, and sections were cut and stained with hematoxylin and eosin.

RESULTS

Initially, an acute inflammatory process was noted along the graft that was tightly fitted to the defect. Subsequently, intense bone neoformation from external corticals and in the inner spaces of the graft was observed, while medullar spaces were occupied by granulation tissue and osteoblasts. There was remodelation of the receptor site, with a decrease in the graft volume and medullary space, as well as cancellous bone replaced by compact bone. Later, the receptor site was similar to the normal mandible, and only devitalized remnants of corticals of the graft were found. Optical densitometry of radiographs revealed statistically significant differences between experimental and control sites.

CONCLUSIONS

This experimental model is valuable in the study of bone healing. The study showed that autogenous iliac graft promoted healing of the critical-sized defect of the mandible with complete bony remodeling.

Histomorphometrical analysis of new bone obtained by distraction osteogenesis and osteogenesis by periosteal distraction in rabbits

The aim of this study was to compare histomorphometrically the new bone tissue obtained using two different distraction methods, and evaluate these two methods in terms of their advantages and disadvantages. In 36 New Zealand adult male rabbits, divided into two groups, a gradual distraction was performed using a device placed on the lateral surface of the mandibular corpus. In one group osteotomy was not performed and osteogenesis by periosteal distraction (OPD) only was used. In the other group, conventional distraction osteogenesis (DO) was performed. After a 7-day latent phase, the same distraction protocol was applied to both groups. Each group of rabbits was further divided into three sub-groups killed on the 15th, 30th and 60th days of the consolidation period, and histological analysis was performed. The mean extent of newly formed bone tissue was 14.4 mm2 in the OPD groups and 25.4 mm2 in the DO groups. When compared statistically, there were significant differences between all the DO and OPD sub-groups. The newly formed bone tissue obtained by OPD was rich in interstitial fatty tissue. These results indicate that bone tissue newly formed by OPD is not suitable for occlusal forces.

Tyrosine-derived polycarbonate membrane in treating mandibular bone defects. An experimental study

This study was designed to evaluate the suitability of a novel bioabsorbable material in treating bone defects. A poly(desaminotyrosyl-tyrosine-ethyl ester carbonate) (PDTE carbonate) membrane (thickness 0.2-0.3 mm) was implanted into the mandibular angle of 20 New Zealand White rabbits to cover a through-and-through defect (12 x 6 mm). In group 1, the defects were left unfilled but covered with membrane and in group 2 the defects were filled with bioactive glass mesh and covered with membrane, too. Controls were left uncovered and unfilled. The animals were followed for 6, 12, 24 and 52 weeks, respectively. The material was evaluated by qualitative analysis of histological reactions and newly formed bone. We found that PDTE carbonate elicited a modest foreign body reaction in the tissues, which was uniform throughout the study. New bone formation was seen in all samples after six weeks. Group 1 had more new bone formation until 24 weeks and after this the difference settled. Based on findings of this study it was concluded that PDTE carbonate membranes have good biocompatibility and are sufficient to enhance bone growth without additional supportive matrix.

Collagen-apatite nanocomposite membranes for guided bone regeneration

Collagen-apatite nanocomposite is regarded as a potential biomaterial because of its composition and structure, which are similar to those of human hard tissues. However, there have been few investigations of its mechanical and biological benefits in direct comparison with a collagen equivalent. Herein, we successfully produced a biomedical membrane made of a nanocomposite, and systemically evaluated the mechanical, chemical, and biological properties of the nanocomposite in comparison with those of pure collagen. The results showed that significant improvements were achieved by the nanocomposite approach, particularly in terms of the mechanical strength and chemical stability. The present findings point to the potential usefulness of the collagen-apatite nanocomposite membrane in the field of guided bone regeneration (GBR).

Changes of mineralization of free autogenous bone grafts used for sinus floor elevation

For augmentations before implant placement in areas of minor bone quantity, autogenous bone is considered the reference to all bone substitutes used alternatively. Autogenous bone transplants originate from various donor areas and can be prepared in different ways before augmentation. They may either be used as block grafts or may be milled to granules that can be used solitarily or in combination with a bone substitute. In a prospective study, 61 patients of the Maxillofacial Surgery Department of our University receiving two-stage sinus floor elevation because of insufficient bone supply were randomly selected. At first-stage surgery, the local augmentation procedure, monocortical probes were obtained on the site of bone harvesting. At second-stage surgery, the implant insertion 6 months after the elevation procedure, bone cores were harvested in the areas of implant placement. Donor regions were the following three areas: the posterior (N=28) and anterior pelvic region (N=15) and the chin region (N=18). The implanted bone in all three groups was particulated to granules of 2-3 mm(2) using a bone mill. All biopsies were analyzed by means of microradiography. The anterior pelvic bone grafts showed a mineralized tissue grade of 35.1+/-7.6% before milling and augmentation. The posterior pelvic bone grafts exhibited a mineralization of 30.7+/-9.5% and the chin bone grafts 74.6+/-8.6%. At second-stage surgery after 6 months, the mineralization was 36.1+/-7.59% in the areas where bone grafts from the anterior pelvic crest were used. Probes harvested from sites with posterior pelvic bone augmentations showed a mineralization rate of 34.5+/-6.5%, and sites were chin bone grafts were applied expressed a mineralization of 54+/-8.6% (P=0.003 compared with the pre-operative value). The comparison of the microradiographical results demonstrated significant differences in the mineralization grades depending on the origin of the graft. The origin of the grafts and their remodeling influenced the mineralization rates found at 6 months. How these data may influence the long-term clinical outcome considering implant survival and bone resorption has to be examined in further long-term studies.

Evaluation of substitutes for bone: comparison of microradiographic and histological assessments

We created defects of standard size in the frontal bones of adult pigs and filled them with four different materials. On six occasions (at 1, 2, 4, 8, 12, and 26 weeks), samples were harvested, and evaluated by computing microradiographic images. We examined the specimens histologically as controls. After insertion of anorganic materials, microradiographic evaluation was easy and precise, and there were no significant differences between them and the histological controls (p=0.2). A quantitative evaluation of chemically sterilised bone by computer was not possible for more than 4 weeks.

The effect of a biphasic ceramic on calvarial bone regeneration in rats

Bioactive ceramics (calcium phosphate ceramics, hydroxyapatite ceramics) are now extensively used in oral surgery. The purpose of this study was to assess the effect of a new biphasic ceramic (Ceraform) on the osteogenesis in a rat calvarial defect model. Fifteen Wistar rats were used in this study. Two symmetrical 3-mm wide defects were created in the skull of each rat. The left defect was left empty as a control and the right defect was filled with the ceramic. The rats were sacrificed at day 30, and the calvarial specimens were processed for qualitative and quantitative histological examinations. The material exhibited no adverse effects, but no bone healing was noted either. No statistical difference regarding bone regeneration was observed between the 2 defects (P > .05). This study showed that Ceraform did not elicit any inflammatory reaction; however, it had no effect on bone regeneration, and this material seems suitable only as a space-maintaining material.

Stability of autogenous bone grafts after sinus lift procedures: a comparative study between anterior and posterior aspects of the iliac crest and an intraoral donor site

BACKGROUND

Autologous bone is the standard material used for augmentations in oral-maxillofacial surgery. Depending on the origin of the graft, subsequent bone resorption may vary.

STUDY DESIGN

This prospective study evaluated 57 patients receiving 2-stage sinus floor augmentations. Monocortical samples were taken at the site of bone harvesting, including the posterior (n = 28) and anterior pelvic (n = 15) and retromolar (n = 14) regions. At second-stage surgery, 6 months after the implant insertion, bone cores were harvested at the site of implant placement. All samples were analyzed by microradiography.

RESULTS

Mean retromolar mineralization was 68.7% +/- 8.75%; 35.1% +/- 7.6% in the anterior and 30.7% +/- 9.5% in the posterior iliac crest. Areas augmented with grafts originating from the retromolar region showed a significant decrease to 53.0% +/- 5.15% (P = .001). A stable mineralization of 36.1% +/- 7.59% was found in sites where bone grafts from the anterior pelvic crest were used. Grafts from the posterior pelvis showed a slight increase to 34.5% +/- 6.5%.

CONCLUSION

This prospective clinical study demonstrates the differences in mineralization depending on the origin of autogenous bone. Even after 6 months, these values could still be correlated to the transplants origin.

Maxilla Sinus Grafting With Marine Algae Derived Bone Forming Material: A Clinical Report of Long-Term Results

PURPOSE

Autogenous bone grafting continues to be considered the gold standard for sinus grafting. For the past 15 years the author has used an alternative graft material and followed-up the input/output statistic of implants to evaluate if this material results similar to the autogenous bone graft. Histomorphometric evaluations of graft materials show how much new bone is formed and if the graft material is resorbed.

MATERIALS AND METHODS

In our study we used a marine derived carbonated red algae that is chemically converted into hydroxyapatite (HA). This material is distributed worldwide as the Communauté Européenne approved material AlgiPore (Dentsply Friadent, Mannheim, Germany), as the US Food and Drug Administration approved material C GRAFT (The Clinician Preference LLC, Golden, CO), and the Russian approved material AlgOss (Unexim Co, Moscow, Russia). A total of 209 sinus grafts were performed on 118 patients who presented with a severely resorbed maxillary alveolar process with 1 to 5 mm (mean, 3.6 mm) of remaining bone. The available bone was comparable to Class D bone as described by Simion et al. After 6 months implants were placed and 6 months later the implants were loaded.

RESULTS

From September 5, 1990, to September 1, 2004, the author performed 209 sinus grafts on 118 patients. The longest observation period of loaded implants in this study is 156 months (13 years). Implant loss was 27 out of 614 loaded implants (4.4%), showing a survival rate of 95.6%. Smokers and women over 50 are included. Although AlgiPore/C GRAFT/AlgOss (ACA) undergoes a resorption process, we found only 14% volume loss after 6.4 months compared with 49.5% after 6 months when autogenous bone was used.

CONCLUSION

This retrospective study of over 14 years shows once again that the sinus lift procedure with grafting of the sinus floor and subsequent implant placement is a proven method. This 14-year longitudinal study shows that the marine derived HA material ACA in a mixture with approximately 10% autogenous collector bone and blood or platelet rich plasma is able to enhance enough new bone in 6 months to allow implant osseointegration after 6 more months with a high implant survival rate.

Photocurable hard and porous biomaterials from ROMP precursors cross-linked with diyl radicals

A combination of (ROMP) ring-opening metathesis polymerization and diradical (diyl) cross-linking provides a new access to hard biomaterials and potential artificial bone replacements. ROMP was used to construct soft and pliable linear polymers bearing photolabile diazene functions. After treatment with light, a nitrogen aerosol is released throughout the polymer to create desirable porosity, cross-linking, and hardening in a single step. Nonpolymeric mechanistic work supporting these studies was also examined.

Tyrosine derived polycarbonate membrane is useful for guided bone regeneration in rabbit mandibular defects

Standardized bilateral through-and-through defects (12x6 mm) were created extraorally in the mandibular angle of 18 New Zealand White rabbits. Animals were divided in to three groups (n=6) according to the intended healing time. On the left side, defects were covered with a poly(desaminotyrosyl-tyrosine-ethyl ester carbonate) (PDTE carbonate) membrane wrapped around the inferior border of the mandible and fixed with bioabsorbable sutures. On the right side, the defects were filled with a mesh made of bioactive glass 13-93 and 3 wt% chitosan. The defects were covered with the same membranes. Periosteal flap was sutured over the membrane. Radiographically, bone ingrowth was seen in all specimens at 12 weeks postoperatively. At 24 weeks, completely ossified area remained approximately at the same level as at 12 weeks, but the non-ossified area decreased to almost zero. However, the bioactive glass mesh did not improve the results. Nevertheless, enveloping the defect with PDTE carbonate membrane seemed to play a crucial role in new bone formation. Based on these results, we conclude that tyrosine polycarbonate is a promising new material for guided bone regeneration.

Effect of drying history on swelling properties and cell attachment to oligo(poly(ethylene glycol) fumarate) hydrogels for guided tissue regeneration applications

In these experiments, the effects of the drying history of hydrogels made from a novel polymer, oligo(poly(ethylene glycol) fumarate) (OPF) with two different poly(ethylene glycol) (PEG) molecular weights (approximately 920 (1K) and 9110 (10K) g/mol), were investigated. The hydrogels were either formed, dried and then swelled, representing what may occur in the case of a pre-formed membrane for guided tissue regeneration, or were formed and swelled immediately, as may occur with an injectable material for such applications. Subsequently, swelling properties, sol fraction and polymer network structure (as indicated by differential scanning calorimetry), as well as attachment of human dermal fibroblasts to these hydrogels at 4 and 24 h was examined. It was found that drying before swelling caused a significant reduction in final fold swelling of OPF hydrogels, regardless of OPF formulation or method of drying (air-dried or vacuum-dried) (e.g. PEG 10K swollen first: 13.94 +/- 0.35 vs. vacuum first: 6.53 +/- 0.12; PEG 1K swollen first: 8.99 +/- 0.47 vs. vacuum first: 2.26 +/- 0.08). This decreased swelling correlated to significantly higher cell attachment (% seeded) to these hydrogels at 24 h (PEG 10K vacuum first: 21.1 +/- 4.7% vs. swollen first: 7.1 +/- 5.5%; PEG 1K vacuum first: 58.2 +/- 2% vs. swollen first: 7.4 +/- 2.2%). LIVE/DEAD staining followed by microscopic analysis revealed attached cells were viable, yet rounded, and that, in the case of the PEG 1K dried-first samples, undulations in the surface visible in the hydrated state may have affected cell adhesion. Regardless of treatment, all hydrogels showed significantly less cell attachment than the tissue culture polystyrene control after 24 h (104.9 +/- 4.4%). These results suggest that, by altering the PEG molecular weight used in synthesis, OPF hydrogels may be tailored to produce desired swelling properties and reduce non-specific cell adhesion for either injectable or pre-formed applications, thus providing a potential alternative material for use in guided tissue regeneration procedures.