Bone formation in transforming growth factor beta-I-loaded titanium fiber mesh implants

Serum TNF-α level and probing depth as a combined indicator for peri-implant disease

Peri-implant disease (PID) is a general term for inflammatory diseases of soft and hard tissues that occur around implants, including peri-implant mucositis and peri-implantitis. Cytokines are a class of small molecule proteins, which have various functions such as regulating innate immunity, adaptive immunity, and repairing damaged tissues. In order to explore the characteristics and clinical significance of tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-10, and tumor growth factor (TGF)-β1 expression levels in serum of patients with peri-implant disease, 31 patients with PID and 31 patients without PID were enrolled. The modified plaque index (mPLI), modified sulcus bleeding index (mSBI), and peri-implant probing depth (PD) were recorded. The levels of serum TNF-α, IL-6, IL-10, and TGF-β1 were detected by ELISA. TNF-α, mPLI, mSBI, and PD levels were significantly higher in the PID group. TGF-β1 levels were significantly higher in the control group. There was a significant positive correlation between TNF-α and mPLI, mSBI, and PD. TGF-β1 was negatively associated with TNF-α, mPLI, mSBI, and PD. Multiple logistic regression analysis showed that TNF-α and PD were risk factors for the severity of PID. The receiver operating curve analysis showed that high TNF-α levels (cut-off value of 140 pg/mL) and greater PD values (cut-off value of 4 mm) were good predictors of PID severity with an area under the curve of 0.922. These results indicated that TNF-α and PD can be used as a biological indicator for diagnosing the occurrence and progression of PID.

Histological evaluation of titanium fiber mesh-coated implants in a rabbit femoral condyle model

OBJECTIVES

This study was aimed to comparatively evaluate new bone formation into the pores of a flexible titanium fiber mesh (TFM) applied on the surface of implant.

METHODS

Twenty-eight custom made cylindrical titanium implants (4 ×10 mm) with and without a layer of two different types of TFM (fiber diameter of 22 µm and 50 µm, volumetric porosity ~70%) were manufactured and installed bilaterally in the femoral condyles of 14 rabbits. The elastic modulus for these two TFM types was ~20 GPa and ~5 GPa respectively, whereas the solid titanium was ~110 GPa. The implants (Control, TFM-22, TFM-50) were retrieved after 14 weeks of healing and prepared for histological assessment. The percentage of the bone area (BA%), the bone-to-implant contact (BIC%) and amount were determined.

RESULTS

Newly formed bone into mesh porosity was observed for all three types of implants. Histomorphometric analyses revealed significantly higher (~2.5 fold) BA% values for TFM-22 implants (30.9 ± 9.5%) compared to Control implants (12.7 ± 6.0%), whereas BA% for TMF-50 did not significantly differ compared with Control implants. Furthermore, both TFM-22 and TFM-50 implants showed significantly higher BIC% values (64.9 ± 14.0%, ~2.5 fold; 47.1 ± 14.1%, ~2 fold) compared to Control (23.6 ± 17.4%). Finally, TFM-22 implants showed more and thicker trabeculae in the peri-implant region.

SIGNIFICANCE

This in vivo study demonstrated that implants with a flexible coating of TFM improve bone formation within the inter-fiber space and the peri-implant region.

Proteomic and genomic analysis of acid dentin lysate with focus on TGF-β signaling

Particulate autologous tooth roots are increasingly used for alveolar bone augmentation; however, the proteomic profile of acid dentin lysate and the respective cellular response have not been investigated. Here we show that TGF-β1 is among the 226 proteins of acid dentin lysate (ADL) prepared from porcine teeth. RNA sequencing identified 231 strongly regulated genes when gingival fibroblasts were exposed to ADL. Out of these genes, about one third required activation of the TGF-β receptor type I kinase including interleukin 11 (IL11) and NADPH oxidase 4 (NOX4). Reverse transcription-quantitative polymerase chain reaction and immunoassay confirmed the TGF-β-dependent expression of IL11 and NOX4. The activation of canonical TGF-β signaling by ADL was further confirmed by the phosphorylation of Smad3 and translocation of Smad2/3, using Western blot and immunofluorescence staining, respectively. Finally, we showed that TGF-β activity released from dentin by acid lysis adsorbs to titanium and collagen membranes. These findings suggest that dentin particles are a rich source of TGF-β causing a major response of gingival fibroblasts.

Advances in Growth Factor Delivery for Bone Tissue Engineering

Shortcomings related to the treatment of bone diseases and consequent tissue regeneration such as transplants have been addressed to some extent by tissue engineering and regenerative medicine. Tissue engineering has promoted structures that can simulate the extracellular matrix and are capable of guiding natural bone repair using signaling molecules to promote osteoinduction and angiogenesis essential in the formation of new bone tissues. Although recent studies on developing novel growth factor delivery systems for bone repair have attracted great attention, taking into account the complexity of the extracellular matrix, scaffolding and growth factors should not be explored independently. Consequently, systems that combine both concepts have great potential to promote the effectiveness of bone regeneration methods. In this review, recent developments in bone regeneration that simultaneously consider scaffolding and growth factors are covered in detail. The main emphasis in this overview is on delivery strategies that employ polymer-based scaffolds for spatiotemporal-controlled delivery of both single and multiple growth factors in bone-regeneration approaches. From clinical applications to creating alternative structural materials, bone tissue engineering has been advancing constantly, and it is relevant to regularly update related topics.

Acid bone lysates reduce bone regeneration in rat calvaria defects

Acid bone lysates (ABLs) represent the growth factors and other molecules released during autologous graft resorption. However, the impact of these bone-derived growth factors on the healing of bone defects has not yet been investigated. The aim of the present study was, therefore, to examine the impact of ABLs adsorbed to collagen membranes on bone regeneration. To this end, in 16 female Sprague Dawley rats, a standardized 5-mm-diameter critical size defect on the calvarial bone was created. The defects were covered with collagen membranes that had been soaked either in serum-free media or ABLs followed by lyophilization. After a healing period of 4 weeks, micro-computed tomography (μCT) and histological analyses by means of undecalcified thin ground sections were performed. μCT analysis of the inner 4 mm of the calvaria defect showed a greater bone defect coverage in the control group when compared to ABL group, 29.8% (confidence interval [CI]: 17.7-50.3) versus 5.6% (CI: 1.0-29.8, p = .03), respectively. Moreover, we found significantly more absolute bone volume (BV) in the control group when compared to ABL group, 0.59 mm³ (CI: 0.27-1.25) versus 0.07 mm³ (CI: 0.06-0.59, p = .04), respectively. Histomorphometry confirmed these findings with a relative BV in the central compartment of 14.1% (CI: 8.4-20.6) versus 5.6% (CI: 3.4-7.9, p = .004), respectively. These findings indicate that bone-derived growth factors contained in ABLs are able to attenuate bone regeneration within collagen membranes.

Mediating bone regeneration by means of drug eluting implants: From passive to smart strategies

In addition to excellent biocompatibility and mechanical performance, the new generation of bone and craniofacial implants are expected to proactively contribute to the regeneration process and dynamically interact with the host tissue. To this end, integration and sustained delivery of therapeutic agents has become a rapidly expanding area. The incorporated active molecules can offer supplementary features including promoting oteoconduction and angiogenesis, impeding bacterial infection and modulating host body reaction. Major limitations of the current practices consist of low drug stability overtime, poor control of release profile and kinetics as well as complexity of finding clinically appropriate drug dosage. In consideration of the multifaceted cascade of bone regeneration process, this research is moving towards dual/multiple drug delivery, where precise control on simultaneous or sequential delivery, considering the possible synergetic interaction of the incorporated bioactive factors is of utmost importance. Herein, recent advancements in fabrication of synthetic load bearing implants equipped with various drug delivery systems are reviewed. Smart drug delivery solutions, newly developed to provide higher tempo-spatial control on the delivery of the pharmaceutical agents for targeted and stimuli responsive delivery are highlighted. The future trend of implants with bone drug delivery mechanisms and the most common challenges hindering commercialization and the bench to bedside progress of the developed technologies are covered.

In vitro culture of hFOB1.19 osteoblast cells on TGF-β1-SF-CS three-dimensional scaffolds

The aim of the present study was to examine the biocompatibility of transforming growth factor-β1-silk fibroin-chitosan (TGF-β1-SF-CS) scaffolds. In order to provide an ideal scaffold for use in bone tissue engineering, TGF-β1 was introduced into the SF-CS scaffold in order to reconstruct a three dimensional scaffold, following which hFOB1.19 osteoblast cells were seeded onto TGF-β1-SF-CS and SF-CS scaffolds. On the TGF-β1-SF-CS and SF-CS scaffolds, the cell adhesion rate increased in a time-dependent manner. Scanning electron microscopy revealed that the cells grew actively and exhibited normal morphological features with multiple fissions, and granular and filamentous substrates were observed surrounding the cells. In addition, the cell microfilaments were closely connected with the scaffolds. The cells exhibited attached growth on the surfaces of the scaffolds, however, the growth also extended into the scaffolds. Cell Counting Kit-8 and ALP analyses revealed that TGF-β1 significantly promoted the growth and proliferation of the hFOB1.19 osteoblast cells in the SF-CS scaffolds, and the enhancement of osteoblast cell proliferation and activity by TGF-β1 occurred in a time-dependent manner. The TGF-β1-SF-CS composite material may offer potential as an ideal scaffold material for bone tissue engineering.

Sustained delivery of bioactive TGF-β1 from self-assembling peptide hydrogels induces chondrogenesis of encapsulated bone marrow stromal cells

Tissue engineering strategies for cartilage defect repair require technology for local targeted delivery of chondrogenic and anti-inflammatory factors. The objective of this study was to determine the release kinetics of transforming growth factor β1 (TGF-β1) from self-assembling peptide hydrogels, a candidate scaffold for cell transplant therapies, and stimulate chondrogenesis of encapsulated young equine bone marrow stromal cells (BMSCs). Although both peptide and agarose hydrogels retained TGF-β1, fivefold higher retention was found in peptide. Excess unlabeled TGF-β1 minimally displaced retained radiolabeled TGF-β1, demonstrating biologically relevant loading capacity for peptide hydrogels. The initial release from acellular peptide hydrogels was nearly threefold lower than agarose hydrogels, at 18% of loaded TGF-β1 through 3 days as compared to 48% for agarose. At day 21, cumulative release of TGF-β1 was 32-44% from acellular peptide hydrogels, but was 62% from peptide hydrogels with encapsulated BMSCs, likely due to cell-mediated TGF-β1 degradation and release of small labeled species. TGF-β1 loaded peptide hydrogels stimulated chondrogenesis of young equine BMSCs, a relevant preclinical model for treating injuries in young human cohorts. Self-assembling peptide hydrogels can be used to deliver chondrogenic factors to encapsulated cells making them a promising technology for in vivo, cell-based regenerative medicine.

The rabbit as experimental model for research in implant dentistry and related tissue regeneration

The use of rabbits for experimental research has a long historical tradition. The aim of this review consists in outlining the use of the rabbit for research in implant dentistry and related tissue regeneration. Rabbits appear as a first-hand choice for fundamental implant design studies because of their size, easy handling, short life span, and economical aspects in purchasing and sustaining. In the following, the various anatomical sites in the rabbit will be summarized to provide an overview of current possibilities and limitations of this model for bone research in oral implantology.

Dedifferentiated fat cells differentiate into osteoblasts in titanium fiber mesh

Mature adipocyte-derived dedifferentiated fat (DFAT) cells rapidly differentiate into osteoblasts under three-dimensional culture conditions. However, it has not been demonstrated that DFAT cells can differentiate into osteoblasts in a rigid scaffold consisting of titanium fiber mesh (TFM). We examined the proliferation and osteogenic differentiation ability of DFAT cells using TFM as a scaffold. DFAT cells derived from rabbit subcutaneous fat were seeded into TFM and cultured in osteogenic medium containing dexamethasone, L-ascorbic acid 2-phosphate and β-glycerophosphate for 14 days. In scanning electron microscopy (SEM) analysis, well-spread cells covered the titanium fibers on day 3, and appeared to increase in number from day 3 to 7. Numerous globular accretions were found and almost completely covered the fibers on day 14. Cell proliferation, as measured by DNA content in the TFM, was significantly higher on day 7 compared with that of day 1. Osteocalcin and calcium content in the TFM were significantly higher on day 14 compared to those of days 1, 3, and 7, indicating DFAT cells differentiated into osteoblasts. We theorize that globular accretions observed in SEM analysis may be calcified matrix resulting from osteocalcin secreted by osteoblasts binding calcium contained in fetal bovine serum. In this study, we demonstrated that DFAT cells differentiate into osteoblasts and deposit mineralized matrices in TFM. Therefore, the combination of DFAT cells and TFM may be an attractive option for bone tissue engineering.

Porous titanium materials with entangled wire structure for load-bearing biomedical applications

A kind of porous metal-entangled titanium wire material has been investigated in terms of the pore structure (size and distribution), the strength, the elastic modulus, and the mechanical behavior under uniaxial tensile loading. Its functions and potentials for surgical application have been explained. In particular, its advantages over competitors (e.g., conventional porous titanium) have been reviewed. In the study, a group of entangled titanium wire materials with non-woven structure were fabricated by using 12-180 MPa forming pressure, which have porosity in a range of 48%-82%. The pores in the materials are irregular in shape, which have a nearly half-normal distribution in size range. The yield strength, ultimate tensile strength, and elastic modulus are 75 MPa, 108 MPa, and 1.05 GPa, respectively, when its porosity is 44.7%. The mechanical properties decrease significantly as the porosity increases. When the porosity is 57.9%, these values become 24 MPa, 47.5 MPa, and 0.33 GPa, respectively. The low elastic modulus is due to the structural flexibility of the entangled titanium wire materials. For practical reference, a group of detailed data of the porous structure and the mechanical properties are reported. This kind of material is very promising for implant applications because of their very good toughness, perfect flexibility, high strength, adequate elastic modulus, and low cost.

Serum transforming growth factor beta-1 post hip fracture repair in elderly patients

BACKGROUND

To determine the kinetics of serum transforming growth factor beta-1 (TGF-β1) in aged hip fracture patients during a month post-op. and determine its relationship to complications and cognitive status.

METHODS

Forty-one elderly patients were prospectively followed. Serum TGF-β1 was obtained during the first 10h post-fracture (baseline) and pre-surgery, 48-60 h post-op., 7 and 30 days post-op.

RESULTS

Mean age was 81.8±7.7, range 68-97 years. A significant increase in serum TGF-β1 (from baseline) was observed on the seventh day post-op., lasting for at least 1 month (p = 0.004). Sixteen patients experienced post-op. complications. Serum TGF-β1 of patients with complications was significantly higher compared to patients without complications (p = 0.039). More complications were found in impaired mental status (IMS) patients (9/12) compared to cognitively normal patients (10/29), (p = 0.037). However, no differences were found in serum TGF-β1 between IMS and normal patients, nor was a correlation found between age and TGF-β1 production. No differences were found between genders.

CONCLUSIONS

There is a distinct increase in serum TGF-β1, a week post hip fracture repair, lasting for at least a month, which is significantly higher in patients with post-op. complications. TGF-β1 seems to be essential to the healing process post hip fracture repair; still its clinical applications have as yet to be determined.

Controlled delivery of transforming growth factor β1 by self-assembling peptide hydrogels induces chondrogenesis of bone marrow stromal cells and modulates Smad2/3 signaling

Self-assembling peptide hydrogels were modified to deliver transforming growth factor β1 (TGF-β1) to encapsulated bone-marrow-derived stromal cells (BMSCs) for cartilage tissue engineering applications using two different approaches: (i) biotin-streptavidin tethering; (ii) adsorption to the peptide scaffold. Initial studies to determine the duration of TGF-β1 medium supplementation necessary to stimulate chondrogenesis showed that 4 days of transient soluble TGF-β1 to newborn bovine BMSCs resulted in 10-fold higher proteoglycan accumulation than TGF-β1-free culture after 3 weeks. Subsequently, BMSC-seeded peptide hydrogels with either tethered TGF-β1 (Teth-TGF) or adsorbed TGF-β1 (Ads-TGF) were cultured in the TGF-β1-free medium, and chondrogenesis was compared to that for BMSCs encapsulated in unmodified peptide hydrogels, both with and without soluble TGF-β1 medium supplementation. Ads-TGF peptide hydrogels stimulated chondrogenesis of BMSCs as demonstrated by cell proliferation and cartilage-like extracellular matrix accumulation, whereas Teth-TGF did not stimulate chondrogenesis. In parallel experiments, TGF-β1 adsorbed to agarose hydrogels stimulated comparable chondrogenesis. Full-length aggrecan was produced by BMSCs in response to Ads-TGF in both peptide and agarose hydrogels, whereas medium-delivered TGF-β1 stimulated catabolic aggrecan cleavage product formation in agarose but not peptide scaffolds. Smad2/3 was transiently phosphorylated in response to Ads-TGF but not Teth-TGF, whereas medium-delivered TGF-β1 produced sustained signaling, suggesting that dose and signal duration are potentially important for minimizing aggrecan cleavage product formation. Robustness of this technology for use in multiple species and ages was demonstrated by effective chondrogenic stimulation of adult equine BMSCs, an important translational model used before the initiation of human clinical studies.

Fabrication and characterization of a recombinant fibronectin/cadherin bio-inspired ceramic surface and its influence on adhesion and ossification in vitro

This study has investigated the effects of a bio-inspired ceramic surface modified with a novel recombinant protein on surface parameters and cell behavior. The surface of a biphasic calcium phosphate ceramic was functionalized with a recombinant protein spanning the fragments of fibronectin module III7-10 and extracellular domains 1 and 2 of cadherin 11 (rFN/CDH) using a dimethyl-3,3'-dithiobispropionimidate cross-linking method. The surface was characterized by scanning electron microscopy, X-ray photoelectron spectroscopy and protein adsorption and surface density measurements. The material exhibited desirable properties for cell adhesion and proliferation. The effects of the surface on the adhesion and proliferation of human mesenchymal stem cells (hMSC) were investigated using a cell adhesion centrifugal assay and the 3-(4,5-dmethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide method. The data demonstrated that the adhesive capacity and proliferation rate were significantly improved as compared with fibronectin and cadherin positive controls. Moreover, the rFN/CDH bio-inspired ceramic surface also induced osteoblastic differentiation, as evidenced by the higher alkaline phosphatase activity and osteocalcin mRNA expression level of hMSC cultured in osteogenic media for 7-10days. Furthermore, a functional blocking assay with a site-specific antibody against phosphotyrosine 397 (pY397) of focal adhesion kinase revealed that pY397 is involved in adhesion and ossification. These results suggest that the rFN/CDH bio-inspired BCP surface possesses enhanced functionality in adhesion, proliferation and ossification and may be a promising scaffold for tissue engineering.

Improving islet transplantation: a road map for a widespread application for the cure of persons with type I diabetes

PURPOSE OF REVIEW

The widespread application of replacement therapies for type I diabetes is at present limited by the side-effects of systemic immunosuppression. Results obtained in several animal models show that islet encapsulation can control the rejection process without systemic side-effects. However, results have, in general, been disappointing when transferred to large animal models or to humans.

RECENT FINDINGS

Growing insights into how cells respond to mechanical forces and surrounding extracellular matrixes indicate that differences in the Young's modulus (the resistance to deformation) between the implanted biomaterial and surrounding tissues induce inflammation and fibrosis. A valid approach would be to select for implantation a tissue having a higher value of the Young's modulus, for example, bone, allowing direct contact with the highly vascularized bone marrow providing nutrient and oxygen support as well as a rapid distribution of released insulin to the systemic circulation.

SUMMARY

Development of a biochamber with bone-integrating properties will allow initiation of clinical trials with allogeneic human islets, xenogeneic pig islets or insulin-producing cells generated from human embryonic stem cell (hESC)/inducible pluripotent stem cell (iPSC).

Osteoconductive conjugation of bone morphogenetic protein-2 onto titanium/titanium oxide surfaces coated with non-biofouling poly(poly(ethylene glycol) methacrylate)

This paper describes a method for introducing osteoconductivity onto titanium, a widely used material for implants, as well as maintaining its non-biofouling ("bioinert") property, in the aim of increasing bioactivity of titanium for its wider applications to biomedical areas. Titanium substrates were coated with a non-biofouling poly(poly(ethylene glycol) methacrylate) (pPEGMA) by surface-initiated polymerization, and bone morphogenetic protein-2 (BMP-2) was chemically conjugated to the activated pPEGMA films. The non-biofouling property and increased bioactivity of titanium were confirmed by the maintenance of the cellular response of mesenchymal stem cells on the titanium substrates: the BMP-2-conjugated pPEGMA films induced the adhesion and differentiation of mesenchymal stem cells, while non-conjugated pPEGMA films showed the excellent resistance against the adhesion of the cells.

Metallic Scaffolds for Bone Regeneration

Bone tissue engineering is an emerging interdisciplinary field in Science, combining expertise in medicine, material science and biomechanics. Hard tissue engineering research is focused mainly in two areas, osteo and dental clinical applications. There is a lot of exciting research being performed worldwide in developing novel scaffolds for tissue engineering. Although, nowadays the majority of the research effort is in the development of scaffolds for non-load bearing applications, primarily using soft natural or synthetic polymers or natural scaffolds for soft tissue engineering; metallic scaffolds aimed for hard tissue engineering have been also the subject of in vitro and in vivo research and industrial development. In this article, descriptions of the different manufacturing technologies available to fabricate metallic scaffolds and a compilation of the reported biocompatibility of the currently developed metallic scaffolds have been performed. Finally, we highlight the positive aspects and the remaining problems that will drive future research in metallic constructs aimed for the reconstruction and repair of bone.

Electromagnetically enhanced coating of a sintered titanium grid with human SAOS-2 osteoblasts and extracellular matrix

The surface modification of a sintered titanium scaffold could play an important role in bone tissue engineering. In this study we have followed a biomimetic strategy where electromagnetically stimulated human SAOS-2 osteoblasts proliferated and built their extracellular matrix on a sintered titanium grid. In comparison with control conditions (standard cell culture incubator, where no electromagnetic stimulus was detectable), the electromagnetic stimulus (magnetic field, 2 mT; frequency, 75 Hz) increased the cell proliferation and the surface coating with decorin, osteopontin, and type-I collagen. The electromagnetic stimulus aimed at obtaining a better surface coating of the sintered titanium grid in terms of cell colonization and bone matrix. The superficially modified biomaterial could be used, in clinical applications, as an implant for bone repair.

Electromagnetic enhancement of a culture of human SAOS-2 osteoblasts seeded onto titanium fiber-mesh scaffolds

The surface properties of a biomaterial are fundamental to determine the response of the host tissue. In the present study, we have followed a particular biomimetic strategy where electromagnetically stimulated SAOS-2 human osteoblasts proliferated and built a calcified extracellular matrix on a titanium fiber-mesh surface. In comparison with control conditions, the electromagnetic stimulation (magnetic field intensity, 2 mT; frequency, 75 Hz) caused higher cell proliferation and increased surface coating with type-I collagen, decorin, and osteopontin (9.8-fold, 11.3-fold, and 9.5-fold, respectively). Reverse transcriptase-polymerase analysis revealed the electromagnetically upregulated transcription specific for the foregoing matrix proteins and for the growth factor TGF-beta1. The immunofluorescence of type-I collagen, decorin, and osteopontin showed their colocalization in the cell-rich areas. The use of an electromagnetic bioreactor aimed at obtaining the surface modification of the biocompatible metallic scaffold in terms of cell colonization and coating with calcified extracellular matrix. The superficially modified biomaterial could be used, in clinical applications, as an implant for bone repair.

Biomaterials in orthopaedics

At present, strong requirements in orthopaedics are still to be met, both in bone and joint substitution and in the repair and regeneration of bone defects. In this framework, tremendous advances in the biomaterials field have been made in the last 50 years where materials intended for biomedical purposes have evolved through three different generations, namely first generation (bioinert materials), second generation (bioactive and biodegradable materials) and third generation (materials designed to stimulate specific responses at the molecular level). In this review, the evolution of different metals, ceramics and polymers most commonly used in orthopaedic applications is discussed, as well as the different approaches used to fulfil the challenges faced by this medical field.

Physically enhanced coating of a titanium plasma-spray surface with human SAOS-2 osteoblasts and extracellular matrix

Several studies suggest that the modification of a titanium surface could play an important role in bone tissue engineering. In this study we have followed a biomimetic strategy where ultrasonically or electromagnetically stimulated human SAOS-2 osteoblasts proliferated and built their extracellular matrix on a titanium plasma-spray surface. In comparison with control conditions, the ultrasonic stimulus (power, 149 mW; frequency, 1.5 MHz) and the electromagnetic stimulus (magnetic field, 2 mT; frequency, 75 Hz) increased the cell proliferation and the surface coating with type-I collagen. The physical stimuli aimed at obtaining a better modification of the rough titanium plasma-spray surface in terms of cell colonization and coating with bone matrix. The superficially modified biomaterial could be used, in clinical applications, as an implant for bone repair.

Orthotopic bone formation in titanium fiber mesh loaded with platelet-rich plasma and placed in segmental defects

The effect of platelet-rich plasma (PRP) on bone formation was investigated in a rabbit segmental radial defect model. The purpose of the study was to evaluate the bone inductive properties of PRP with titanium fiber mesh and autologous bone chips in a 15-mm rabbit radial defect model. Eighteen New Zealand white rabbits were divided into three groups: I, PRP with autologous bone (PRP-Ti-Bone); II, autologous bone (Ti-Bone); III, control group (Ti). The implants were placed in the radial defect for 12 weeks. After sacrifice, all specimens were harvested for histological, histomorphometrical and radiographic analysis. Histomorphometrical analysis showed that bone formation was higher in the implants with PRP (PRP-Ti-Bone: 37+/-8%) than in those without PRP (Ti-bone: 25+/-6% and Ti: 25+/-5%) after 12 weeks of implantation. It was concluded that PRP has a stimulatory effect on bone formation in titanium fiber mesh filled with autologous bone graft in segmental bone defects. Titanium fiber mesh was also shown to be an excellent scaffold material for the application of autologous bone grafts with or without PRP.

Enhanced in vitro culture of human SAOS-2 osteoblasts on a sand-blasted titanium surface modified with plastic deformation

The titanium surfaces with micro-roughness have been studied to substitute machined titanium, with the focus on enhancing the bone apposition onto the implant. In this study we have followed a biomimetic strategy where human SAOS-2 osteoblasts proliferated and built their extracellular matrix on a sandblasted titanium surface modified with plastic deformation. In comparison with sandblasted titanium surface, the plastic deformation increased the cell proliferation and the surface coating with bone matrix. The superficially modified biomaterial could be used, in clinical applications, as an implant for bone repair.

Bone response and mechanical strength of rabbit femoral defects filled with injectable CaP cements containing TGF-beta 1 loaded gelatin microparticles

This study focused at the potential of transforming growth factor beta 1 (TGF-beta 1) loaded gelatin microparticles to enhance the bone response and mechanical strength of rabbit femoral defects filled with injectable calcium phosphate (CaP)/gelatin microparticle composites. Therefore, TGF-beta1 loaded composites and non-loaded controls were injected in circular defects as created in the femoral condyles of rabbits and were left in place for 4, 8 and 12 weeks. The specimens were evaluated mechanically (push-out test), and morphologically (scanning electron microscopy (SEM), histology, and histomorphometry). The results showed a gradual increase in mechanical strength with increasing implantation periods. Histological and histomorphometrical evaluation showed similar results for both composite formulations regarding histological aspect, new bone formation and bone/implant contact. However, TGF-beta1 loading of the composites demonstrated a significant effect on composite degradation after twelve weeks of implantation. The results of this study showed that CaP/gelatin composites show excellent osteogenic properties and a rapid increase in mechanical strength. The addition of TGF-beta1 significantly enhances the bone remodeling process.

Induction of Myofibroblastic DifferentiationIn Vitroby Covalently Immobilized Transforming Growth Factor-β1

Growth factors are an important tool in tissue engineering. Bone morphogenetic protein-2 and transforming growth factor-beta(1) (TGF-beta(1)) are used to provide bioactivity to surgical implants and tissue substitute materials. Mostly growth factors are used in soluble or adsorbed form. However, simple adsorption of proteins to surfaces is always accompanied by reduced stability and undefined pharmacokinetics. This study aims to prove that TGF-beta(1) can be covalently immobilized to functionalized surfaces, maintaining its ability to induce myofibroblastic differentiation of normal human dermal fibroblasts. In vivo, fibroblasts differentiate to myofibroblasts (MFs) during soft tissue healing by the action of TGF-beta(1). As surfaces for our experiments, we used slides bearing aldehyde, epoxy, or amino groups. For our in vitro cell culture experiments, we used the expression of alpha-smooth muscle actin as a marker for MFs after immunochemical staining. Using the aldehyde and the epoxy slides, we were able to demonstrate the activity of immobilized TGF-beta(1) through a significant increase in MF differentiation rate. A simple immunological test was established to detect TGF-beta(1) on the surfaces. This technology enables the creation of molecular "landscapes" consisting of several factors arranged in a distinct spatial pattern and immobilized on appropriate surfaces.

Matrices and scaffolds for drug delivery in dental, oral and craniofacial tissue engineering

Current treatments for diseases and trauma of dental, oral and craniofacial (DOC) structures rely on durable materials such as amalgam and synthetic materials, or autologous tissue grafts. A paradigm shift has taken place to utilize tissue engineering and drug delivery approaches towards the regeneration of these structures. Several prototypes of DOC structures have been regenerated such as temporomandibular joint (TMJ) condyle, cranial sutures, tooth structures and periodontium components. However, many challenges remain when taking in consideration the high demand for esthetics of DOC structures, the complex environment and yet minimal scar formation in the oral cavity, and the need for accommodating multiple tissue phenotypes. This review highlights recent advances in the regeneration of DOC structures, including the tooth, periodontium, TMJ, cranial sutures and implant dentistry, with specific emphasis on controlled release of signaling cues for stem cells, biomaterial matrices and scaffolds, and integrated tissue engineering approaches.

Transforming growth factor-beta1 release from a porous electrostatic spray deposition-derived calcium phosphate coating

This study evaluated the utilization of a porous coating, derived with electrostatic spray deposition (ESD), as a carrier material for transforming growth factor-beta1 (TGF-beta1). A porous beta-tricalcium phosphate coating was deposited with ESD, and 10 ng of (125) I-labeled TGF-beta1 was loaded on the substrates. A burst release during the first hour of incubation of >90% was observed, in either culture medium or phosphate-buffered saline (PBS). Ninety-nine percent of the growth factor was released after 10 days of incubation. All samples were able to inhibit epithelial cell growth, indicating that the growth factor had remained bioactive after release. Thereafter, osteoblast-like cells were seeded upon substrates with or without 10 ng of TGF-beta1. While proliferation of osteoblast-like cells was increased on TGF-beta1-loaded substrates, differentiation was inhibited or delayed. In conclusion, a porous ESD-derived calcium phosphate coating can be used as a carrier material for TGF-beta1, when a burst release is desired.

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.

The Effect of Platelet-Rich Plasma on the Bone Healing around Calcium Phosphate–Coated and Non-coated Oral Implants in Trabecular Bone

The effect of local application of autologous platelet-rich plasma (PRP) on bone healing in combination with the use of titanium implants with 2 different surface configurations was investigated. PRP fractions were obtained from venous blood sample of 6 goats and applied via gel preparation and subsequent installation in the implant site or via dipping of the implant in PRP liquid before insertion. Thirty-six implants (18 non-coated and 18 calcium phosphate (CaP) coated) were placed into the goat femoral condyles (trabecular bone). The animals were sacrificed at 6 weeks after implantation, and implants with surrounding tissue were processed for light microscopical evaluation. In addition to subjective description of the histological findings, histomorphometrical variables were also evaluated (the bone-implant contact and the bone mass adjacent to the implant). Significantly more interfacial bone-to-implant contact was observed for all 3 groups of CaP-coated implants and the titanium / liquid group (non-coated implant with PRP liquid) than for the other 2 non-coated titanium groups (with PRP gel or without PRP). The evaluation of the bone mass close to implant surface indicated that all the groups induced a significant increase of the bone mass except the PRP gel groups. On the basis of the observations, it was concluded that magnetron-sputtered CaP coatings can improve the integration of oral implants in trabecular bone. The additional use of PRP did not offer any significant effect on the bone response to the CaP-coated implants, whereas PRP in a liquid form showed a significant effect on bone apposition to roughened titanium implants during the early post-implantation healing phase.

Heterotopic Bone Formation Around Sintered Porous-Surfaced Ti-6Al-4V Implants Coated with Native Bone Morphogenetic Proteins

PURPOSE

Coating endosseous dental implants with growth factors such as bone morphogenetic proteins (BMPs) may be one way to accelerate and/or enhance the quality of osseointegration. The purpose of this study was to investigate in the murine muscle pouch model whether sintered porous-surfaced titanium alloy implants coated with BMPs would lead to heterotopic bone formation around and within the implant surface geometry.

MATERIALS

Porous-surfaced dental implants were coated with partially purified native human BMPs, with or without a carrier of Poloxamer 407 (BASF Corp., Parsippany, NJ), placed in gelatin capsules and implanted into the hindquarter muscles of mice. Mice were euthanized after 28 days. Sections of retrieved specimens were subsequently prepared for morphometric analysis of bone formation using backscatter electron microscopic images.

RESULTS

Human BMPs, either with or without the carrier of Poloxamer 407, led to bone formation within and outside of the sintered porous implant surface. When the sintered implant surface region was subdivided into inner and outer halves, similar levels of bone ingrowth and contact were seen in the 2 halves. Evidence of bone formation to the depth of the solid implant core (i.e., the deepest level possible) also was seen.

DISCUSSION AND CONCLUSIONS

Sintered porous-surfaced dental implants can be used as substrate for partially purified BMPs in the murine muscle pouch model. With the addition of these osteoinductive factors, the porous implant surface supported bone formation within the surface porosity provided, in some instances, all the way to the solid implant core. The addition of growth factors to a sintered porous surface may be an efficient method for altering locally the healing sequence and quality of bone associated with osseointegration of bone-interfacing implants.

The role of biomaterials in stem cell differentiation: applications in the musculoskeletal system

The capabilities of stem cells continue to be revealed, leading to excitement regarding potential new therapies. Regenerative medicine is an area in which stem cells hold great promise for overcoming the challenge of limited cell sources for tissue repair. Biomaterials play an important role in directing tissue growth and may provide another tool to manipulate and control stem cell behavior. Biomaterials are made from natural or synthetic polymers and can be processed into three-dimensional scaffolds designed to promote cell proliferation and/or differentiation that ultimately produces new tissue. Stem cells will have a significant impact on the fields of regenerative medicine and tissue engineering as a powerful cell source that will work, in conjunction with biomaterials, to treat tissue and organ loss. Herein, we survey our latest research on applying embryonic stem (ES) cells to hydrogel biomaterials for engineering musculoskeletal tissues, emphasizing the unique biomaterial requirements of ES cells for differentiation and tissue development.

Bone-like tissue formation using an equine COLLOSS® E-filled titanium scaffolding material

COLLOSS, a bovine extracellular matrix product containing native BMPs has already shown osteoinductive properties. To overcome problems with risk of transmissable spongiform encephalopathy (TSE) infection, an equine derived version was investigated in this study, named COLLOSS E. Disc- and tube-shaped implants were made from titanium fibre mesh. The central space of tubes was filled and the discs were impregnated with the COLLOSS E material to assess osteo-induction. These implants and non-loaded controls were implanted subcutaneously into the back of Wistar rats. After implantation periods of 2, 8, and 12 weeks, the implants were retrieved and sections were made. Histology showed a thin fibrous capsule surrounding the titanium mesh and a very mild tissue reaction. The disc implants, loaded or non-loaded, showed no bone formation at all. After 2 weeks of implantation 3 out of 5 of the loaded tubes showed bone formation with a mean of 0.3 mm2 areas of new formed bone, after 8 weeks 3 out of 6 and 0.7 mm2, and after 12 weeks this increased to 6 out of 6 and 1.0 mm2. In the non-loaded tubes only connective tissue in growth was seen. In conclusion, it was demonstrated that COLLOSS E material, loaded in a titanium fibre mesh tube shows osteoinductive properties. The effect of COLLOSS E has to be investigated further in orthotopic sites, which resemble more the final clinical application for bone reconstruction.

Influence of RGD-Loaded Titanium Implants on Bone Formation in Vivo

Little is known about the ability of peptide-coated surfaces to influence cell responses in vivo. Many studies have demonstrated that peptide-modified surfaces influence cell responses in vitro. Integrins, which bind specifically short peptide sequences, are responsible for these cell responses. In this way, information can be transmitted to the nucleus through several cytoplasmic signaling pathways. The peptide sequence Arg-Gly-Asp (RGD peptide) plays an important role in osteoblast adhesion. The present study was designed to investigate new bone formation in a porous titanium (Ti) fiber mesh implant, which was coated with cyclic RGD peptide. The RGD-Ti implants were inserted into the cranium of a rabbit and were compared with porous titanium fiber mesh disks without RGD sequence (Ti) and with an open control defect. Histologic and histomorphometric examinations were performed 2, 4, and 8 weeks postoperatively. A significant increase in bone formation, or bone ingrowth, was seen in the RGD-Ti group compared with the Ti group after 4 and 8 weeks. All control defects stayed open in all three periods. It was concluded that the use of cyclic RGD peptide in combination with titanium fiber mesh has a positive effect on bone formation in vivo in a rabbit animal model.

Advances in skeletal tissue engineering with hydrogels

OBJECTIVES

Tissue engineering has the potential to make a significant impact on improving tissue repair in the craniofacial system. The general strategy for tissue engineering includes seeding cells on a biomaterial scaffold. The number of scaffold and cell choices for tissue engineering systems is continually increasing and will be reviewed.

DESIGN

Multilayered hydrogel systems were developed to coculture different cell types and develop osteochondral tissues for applications including the temporomandibular joint.

EXPERIMENTAL VARIABLE

Hydrogels are one form of scaffold that can be applied to cartilage and bone repair using fully differentiated cells, adult and embryonic stem cells.

OUTCOME MEASURE

Case studies represent an overview of our laboratory's investigations.

RESULTS

Bilayered scaffolds to promote tissue development and the formation of more complex osteochondral tissues were developed and proved to be effective.

CONCLUSION

Tissue engineering provides a venue to investigate tissue development of mutant or diseased cells and potential therapeutics.

Bone tissue induction, using a COLLOSS®-filled titanium fibre mesh-scaffolding material

Scaffold materials for bone tissue engineering often are supplemented with bone morphogenetic proteins (BMPs). In the current study we aimed to investigate COLLOSS, a bovine extracellular matrix product containing native BMPs. Hollow cylindrical implants were made, with a length of 10 mm, a 3 mm inner diameter, and a 5 mm outer diameter, from titanium fibre mesh. The central space of the tube was filled with 20 mg COLLOSS. Subsequently, these implants, as well as non-loaded controls, were implanted subcutaneously into the back of Wistar rats, with n=6 for all study groups. After implantation periods of 2, 8, and 12 weeks, tissue-covered implants were retrieved, and sections were made, perpendicular to the long axis of the tube. Histology showed, that all implants were surrounded by a thin fibrous tissue capsule. After 2 weeks of implantation, the COLLOSS material was reduced in size inside the loaded implants, but no bone-like tissue formation was evident. After 8 weeks, in two out of six loaded specimens, new-formed bone- and bone marrow-like tissues could be observed. After 12 weeks, this had increased to five out of six COLLOSS-loaded samples. The amount of bone-like tissue did not differ between 8 and 12 weeks, and on average occupied 15% of the central space of the tube. In the non-loaded control samples, only connective tissue ingrowth was observed. In conclusion, we can say that COLLOSS material loaded in a titanium fibre mesh tube, showed bone-inducing properties. The final efficacy of these osteo-inductive properties has to be confirmed in future large animal studies.

Osteogenic protein-1 enhances osseointegration of titanium implants coated with peri-apatite in rabbit femoral defect

This study evaluated the effect of osteogenic protein-1 (OP-1) carried by Peri-Apatite (PA) on bone healing in the gap surrounding implants in a rabbit model. Cylindrical titanium implants (3 x 9 mm) were uniformly coated with PA precipitated from a calcium and phosphate solution. OP-1 solution containing 60 microg OP-1 was directly loaded on the implants immediately before implantation for the experimental group, whereas buffer solution was loaded on the implants for the control. The implant was placed in the distal femur and surrounded by a 1-mm gap. The implants were retrieved and examined 6 weeks after implantation. Mechanical testing (push-out) data showed that OP-1 enhanced implant fixation by 80%. Histomorphometric measurements indicated that bone ingrowth in the initial gap expressed as a percentage of the whole gap was significantly higher in the specimens treated with OP-1 than the control group (25.4% vs. 8.9%, p < 0.05). The percentage of the surface of implants, which was covered by bone, was significantly higher in the OP-1-treated group compared to the control group (65% vs. 25%, p < 0.05). This study suggests that OP-1 can be loaded on orthopedic implants through PA to enhance the osseointegration of orthopedic implant.

Bone inductive properties of rhBMP-2 loaded porous calcium phosphate cement implants inserted at an ectopic site in rabbits

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is known for its osteoinductive potential in bone tissue engineering. Calcium phosphate (Ca-P) cements are injectable, osteoconductive ceramic materials in which a macroporous structure can be induced during the setting reaction. In this study, the osteoinductive capability of rhBMP-2 loaded porous Ca-P cement was evaluated. Porous Ca-P cement discs were made and loaded with rhBMP-2 in vitro and implanted subcutaneously in the back of New Zealand white rabbits. The implantation period was either 2 or 10 weeks. Histological analysis of retrieved specimens revealed evident bone formation in the rhBMP-2 loaded Ca-P cement discs (pore fill: 18+/-6%) after 10 weeks of implantation. Bone formation occurred only in rhBMP-2 loaded porous Ca-P cement discs. Degradation of the Ca-P cement could not be confirmed after 10 weeks of implantation. The scaffold maintained its shape and stability during this time period. We conclude that porous Ca-P cement is a suitable carrier material for ectopic bone engineering.