Bone regeneration by transforming growth factor beta1 released from a biodegradable hydrogel

Novel strategy for the control of postoperative pain: long-lasting effect of an implanted analgesic hydrogel in a rat model of postoperative pain

BACKGROUND

The administration of nonsteroidal anti-inflammatory drugs (NSAIDs) is the most common nonopioid analgesic currently used for postoperative pain management. We tested the sustained analgesic effect of ketoprofen emanating from a biodegradable gelatin hydrogel in a rat model of postoperative pain.

METHODS

A sheet of analgesic-infiltrated hydrogel was inserted below the plantaris muscle at the end of surgery. Mechanical thresholds were measured by use of von Frey filaments before and 2 weeks after the operation. The effect of ketoprofen on the postoperative pain was also assessed immunohistochemically by assessing microglial activation in the spinal cord with anti-OX-42 and phosphorylated p38 mitogen-activated protein kinase antibodies.

RESULTS

Implantation of ketoprofen-infiltrated gelatin hydrogel exerted a sustained analgesic effect for 1 week after the operation. Preemptive analgesia with zaltoprofen, another NSAID, produced an additive analgesic effect in conjunction with the ketoprofen-infiltrated hydrogel. Microglial activation was attenuated by the treatment with ketoprofen-infiltrated hydrogel on day 3 after the incision.

CONCLUSIONS

These results demonstrate that ketoprofen was effective in reducing mechanical hypersensitivity for 1 week in a rat model of postoperative pain and that the implantation of NSAID-infiltrated gelatin hydrogel may serve as a useful analgesic method for the long-term relief of patients after surgery.

In vivo degradability of hydrogels prepared from different gelatins by various cross-linking methods

This study is an investigation to evaluate the in vivo degradation of gelatin hydrogels in terms of their number of cross-links. Various hydrogels were prepared from acidic gelatin, extracted from bovine bone, porcine skin or fish scale, and basic gelatin, extracted from porcine skin, through four types of cross-linking methods, i.e., glutaraldehyde (GA) or dehydrothermal treatment and ultraviolet (UV) or electron beam irradiation. The water content of hydrogels and their number of cross-links, calculated from the tensile modulus of hydrogels, were evaluated as the measure of hydrogel cross-linking extent. Following subcutaneous implantation of 125I-labeled gelatin hydrogels into mice, the radioactivity remaining was measured at different time intervals to assess the in vivo degradability of hydrogels. Irrespective of the gelatin type and cross-linking method, a good correlation was found between the in vivo degradability of hydrogels and their number of cross-links, which is different from the correlation to their water content. This finding indicates that the degradability of hydrogels is governed by their number of cross-links.

Effect of triple growth factor controlled delivery by a brushite-PLGA system on a bone defect

Bone regeneration is a complex process that involves multiple cell types, growth factors (GFs) and cytokines. A synergistic contribution of various GFs and a crosstalk between their signalling pathways was suggested as determinative for the overall osteogenic outcome. The purpose of this work was to develop a brushite-PLGA system, which controls the release rate of the integrated growth factors (GFs) to enhance bone formation. The brushite cement implants were prepared by mixing a phosphate solid phase with an acid liquid phase. PDGF (250 ng) and TGF-β1 (100 ng) were incorporated into the liquid phase. PLGA microsphere-encapsulated VEGF (350 ng) was pre-blended with the solid phase. VEGF, PDGF and TGF-β1 release kinetics and tissue distributions were determined using iodinated ((125)I) GFs. In vivo results showed that PDGF and TGF-β1 were delivered more rapidly from these systems implanted in an intramedullary defect in rabbit femurs than VEGF. The three GFs released from the brushite-PLGA system remained located around the implantation site (5 cm) with negligible systemic exposure. Bone peak concentrations of approximately 4 ng/g and 1.5 ng/g of PDGF and TGF-β1, respectively were achieved on day 3. Thereafter, PDGF and TGF-β1 concentrations stayed above 1 ng/g during the first week. The scaffolds also provided a VEGF peak concentration of nearly 6 ng/g on day 7 and a local concentration of approximately 1.5 ng/g during at least 4 weeks. Four weeks post implantation bone formation was considerably enhanced with the brushite-PLGA system loaded with each of the three GFs separately as well as with the combination of PDGF and VEGF. The addition of TGF-β1 did not further improve the outcome. In conclusion, the herein presented brushite-PLGA system effectively controlled the release kinetics and localisation of the three GFs within the defect site resulting in markedly enhanced bone regeneration.

Bone healing of critical-sized nasal defects in rabbits by statins in two different carriers

OBJECTIVES

To evaluate bone healing following implantation of a statin with two different carriers in rabbit nasal bone using histological and immunohistochemical methods.

MATERIALS AND METHODS

Twenty adult, male Japanese white rabbits (age: 12-16 weeks, weight: 2.5-3 kg) were used in this study. Five bone circular defects (5 mm in diameter) per rabbit were created in the nasal bone while preserving the nasal membrane. In the experimental groups, 2.5 mg/ml simvastatin dissolved in 0.2 ml water with hydrogel was implanted in one group, 2.5 mg/ml simvastatin dissolved in 0.2 ml water with an atelocollagen sponge (ACS) in the second group with, only the hydrogel in the third group and only an ACS in the fourth group. No material was implanted in the control group. Four animals were killed in each period, at 1, 2, 4, 8 and 12 weeks postoperatively. The parts that had been operated on were removed and prepared for histological assessment. The expression of bone morphogenetic proteins (BMP)-2 and the bone ration was evaluated using histological and immunohistochemical methods.

RESULTS

No significant differences were observed between the simvastatin with hydrogel group and the simvastatin with ACS group at 1, 2, 4, 8 and 12 weeks postoperatively regarding expression of BMP-2, although the number of cells that stained positive for BMP-2 in both of the implanted groups increased significantly at 2 and 4 weeks postoperatively in comparison with the control group (P<0.0001). For new bone area ratio, there were no significant differences between the simvastatin with hydrogel groups and the simvastatin with ACS group after 2, 4, 8 and 12 weeks, although these groups showed higher value than control group (P<0.0001).

CONCLUSION

This study suggests that both the simvastatin with hydrogel and simvastatin with ACS implants showed similar BMP-2 expression and new bone formation, and there were no significant differences between the two carriers.

Platelet lysate formulations based on mucoadhesive polymers for the treatment of corneal lesions

Objectives

Growth factors contained in platelet α-granules initiate and modulate tissue repair and are proposed for the treatment of soft and hard-tissue surgical conditions and in the management of non-healing wounds. Platelet lysate is a hemoderivative obtained from platelet-rich plasma and is capable of releasing a pool of growth factors. Many medical and surgical techniques have been proposed for the treatment of corneal lesions; management of these conditions remains problematic and healing with standard protocols is unattainable. The aim of this study was to develop formulations suitable for prolonging the contact of platelet lysate with the damaged cornea for the time necessary to exert a therapeutic effect.

Methods

Two vehicles, one based on polyacrylic acid and one based on chitosan, were autoclaved and loaded with platelet lysate and the resultant formulations were characterized for rheology, mucoadhesion, vehicle compatibility and stability. The proliferation effect was tested on two cell culture types (rabbit corneal epithelial cells and fibroblasts). An in-vitro wound-healing test was performed on fibroblasts. In both cases the formulations were compared with platelet lysate diluted with saline at the same concentration.

Findings

Both formulations maintained the rheological and mucoadhesive properties of the vehicles and the proliferative activity of platelet lysate. The chitosan formulation was able to significantly enhance epithelial cell growth even after storage of up to 2 weeks (in-use conditions), while the polyacrylic acid formulation was less efficient, probably due to the characteristics of the cell model used.

Conclusions

The in-vitro wound-healing test performed on fibroblasts confirmed the differences between the two vehicles. The effect induced by the platelet lysate and chitosan formulation was faster than that of the polyacrylic acid formulation and complete in-vitro wound repair was achieved within 48 h.

Enhanced bone morphogenetic protein-2-induced ectopic and orthotopic bone formation by intermittent parathyroid hormone (1-34) administration

Bone morphogenetic proteins (BMPs) play a central role in local bone regeneration strategies, whereas the anabolic features of parathyroid hormone (PTH) are particularly appealing for the systemic treatment of generalized bone loss. The aim of the current study was to investigate whether local BMP-2-induced bone regeneration could be enhanced by systemic administration of PTH (1-34). Empty or BMP-2-loaded poly(lactic-co glycolic acid)/poly(propylene fumarate)/gelatin composites were implanted subcutaneously and in femoral defects in rats (n = 9). For the orthotopic site, empty defects were also tested. Each of the conditions was investigated in combination with daily administered subcutaneous PTH (1-34) injections in the neck. After 8 weeks of implantation, bone mineral density (BMD) and bone volume were analyzed using microcomputed tomography and histology. Ectopic bone formation and almost complete healing of the femoral defect were only seen in rats that received BMP-2-loaded composites. Additional treatment of the rats with PTH (1-34) resulted in significantly (p < 0.05) enhanced BMD and bone volume in the BMP-2 composites at both implantation sites. Despite its effect on BMD in the humerus and vertebra, PTH (1-34) treatment had no significant effect on BMD and bone volume in the empty femoral defects and the ectopically or orthotopically implanted empty composites. Histological analysis showed that the newly formed bone had a normal woven and trabecular appearance. Overall, this study suggests that intermittent administration of a low PTH dose alone has limited potential to enhance local bone regeneration in a critical-sized defect in rats. However, when combined with local BMP-2-releasing scaffolds, PTH administration significantly enhanced osteogenesis in both ectopic and orthotopic sites.

Bone regeneration using a bone morphogenetic protein-2 saturated slow-release gelatin hydrogel sheet: evaluation in a canine orbital floor fracture model

Bone regeneration methods using bone inductive cytokines show promise, however, due to early diffusion and absorption of single applications of these cytokines, the bone inductive effects are limited. In this study, such a system was applied, using gelatin hydrogel as a carrier to slowly release (bone morphogenetic proteins) BMP-2 over a relatively long period in vivo. By coupling this slow-release system with a biodegradable copolymer, this composite was evaluated by grafting into bone defect sites of a canine orbital floor fracture model. Radio-iodinated BMP-2 incorporated into the gelatin hydrogel carrier and subcutaneously implanted into nude mice showed a similar slow release (approximately, 60% at 3 days and 80% at 14 days) as the radiolabeled hydrogel carrier alone. In contrast, greater than 90% of fluid-injected BMP-2 was lost in the injection site within the first 8 hours. Using a dog model of orbital floor fracture, a complex of BMP-2-saturated gelatin hydrogel and a polylactide-based biodegradable copolymer was implanted into the orbital bone defect. Bone structural analysis, using radiography, histologic examination, and microfocus CT, showed greatly enhanced new bone formation and defect healing at 5 weeks in comparison to implanted biodegradable copolymer directly saturated with the same amount of BMP-2 (no slow-release hydrogel carrier). A trabecular structure resembling that normal bone tissue was restored in the new bone tissue generated by the slow-release constructs. Thus study demonstrates the potential of slow-release BMP-2 for bone healing of difficult defects.

Heparinized hydroxyapatite/collagen three-dimensional scaffolds for tissue engineering

Currently, in bone tissue engineering research, the development of appropriate biomaterials for the regeneration of bony tissues is a major concern. Bone tissue is composed of a structural protein, collagen type I, on which calcium phosphate crystals are enclosed. For tissue engineering, one of the most applied strategies consists on the development and application of three dimensional porous scaffolds with similar composition to the bone. In this way, they can provide a physical support for cell attachment, proliferation, nutrient transport and new bone tissue infiltration. Hydroxyapatite is a calcium phosphate with a similar composition of bone and widely applied in several medical/dentistry fields. Therefore, in this study, hydroxyapatite three dimensional porous scaffolds were produced using the polymer replication method. Next, the porous scaffolds were homogeneously coated with a film of collagen type I by applying vacuum force. Yet, due to collagen degradability properties, it was necessary to perform an adequate crosslinking method. As a result, N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) was employed as an efficient and non-toxic crosslinking method in this research. The composites were characterized by means of SEM, DSC and TNBS. Furthermore, heparin was incorporated in order to accomplish sustained delivery of a growth factor of interest namely, bone morphogenetic proteins (BMP-2). BMP-2 binding and release of non-heparinized and heparinized scaffolds was evaluated at specific time points. The incorporation of heparin leads to a reduced initial burst phase when compared to the non heparinized materials. The results show a beneficial effect with the incorporation of heparin and its potential as a localized drug delivery system for the sustained release of growth factors.

Hydroxyapatite nanoparticles as a controlled-release carrier of BMP-2: absorption and release kinetics in vitro

Recently, nanoparticles have been extensively developed as controlled-release carriers; however, there has been little research on hydroxyapatite nanoparticles (HANPs) and their potential applications. In this study, HANPs were investigated as a controlled-release carrier of bone morphogenetic protein-2 (BMP-2), the absorption and release kinetics of which were analyzed in vitro. Different concentrations of BMP-2 solution were used to evaluate the adsorptive properties of HANPs. It was observed that the amount of BMP-2 adsorbed onto HANPs could be as high as 70 mug/mg and that adsorption rate was highly correlated with the concentration of BMP-2 solution used. After absorption, the suspension of HANPs absorbed BMP-2 (HANPs/BMP-2) was incubated at 37 degrees C for 15 days and the release kinetics of BMP-2 from HANPs/BMP-2 was determined daily. The release profile showed sustained release of BMP-2 over the period of the investigation. Collectively, these results suggest that HANPs has the potential to function as a carrier for drug delivery systems and as a scaffold material in bone tissue engineering.

Enhancement of bone formation ex vivo and in vivo by a helioxanthin-derivative

To effectively treat serious bone defects using bone-regenerative medicine, a small chemical compound that potently induces bone formation must be developed. We previously reported on the osteogenic effect of 4-(4-methoxyphenyl)pyrido[40,30:4,5]thieno[2,3-b]pyridine-2-carboxamide (TH), a helioxanthin-derivative, in vitro. Here, we report on TH's osteogenic effects ex vivo and in vivo. TH-induced new bone formation in both calvarial and metatarsal organ cultures. A novel monitoring system of osteoblastic differentiation using MC3T3-E1 cells revealed that TH was released from alpha-TCP bone cement and this release continued for more than one month. Lastly, the implantation of the alpha-TCP carrier containing TH into defects in mouse skull resulted in increased new bone areas within the defects after 4 weeks. A TH-containing scaffold may help establish a more efficient bone regeneration system.

Migration of marrow stromal cells in response to sustained release of stromal-derived factor-1alpha from poly(lactide ethylene oxide fumarate) hydrogels

Stromal derived factor-1alpha (SDF-1alpha) is an important chemokine in stem cell trafficking and plays a critical role in the homing of bone marrow stromal (BMS) cells. However, its use in tissue regeneration is limited by its relatively short half-life and the time-dependent nature of cell homing to the site of injury. The objective of this work was to investigate the release characteristics of SDF-1alpha from degradable poly(lactide ethylene oxide fumarate) (PLEOF) hydrogels and to determine the effect of sustained release of SDF-1alpha on migration of BMS cells. Three PLEOF hydrogels with poly(l-lactide) (PLA) fractions of 6%, 9%, and 24% by weight were synthesized. After the addition of chemokine, the polymerizing mixture was crosslinked to produce SDF-1alpha loaded PLEOF hydrogels. The hydrogels were characterized with respect to sol fraction, water uptake, degradation, SDF-1alpha loading efficiency and release kinetics, and migration rate of bone marrow stromal (BMS) cells. The more hydrophilic hydrogels with 6% and 9% PLA fraction had a pronounced burst release followed by a period of sustained release by diffusion for 21 days. The more hydrophobic hydrogel with 24% PLA fraction had a less pronounced burst release and displayed a slow but constant release by diffusion between days 1 and 9 followed by a fast release by diffusion-degradation from days 9 to 18. The fraction of active SDF-1alpha released from 6%, 9%, and 24% hydrogels after 21 days was 34.3%, 32.3%, and 35.8%, respectively. The migration of BMS cells in response to time-released SDF-1alpha closely followed the protein release kinetics from the hydrogels. The biodegradable PLEOF hydrogel may potentially be useful as a delivery matrix for sustained release of SDF-1alpha in the proliferative phase of healing for recruitment of progenitor cells in tissue engineering applications.

Migration of marrow stromal cells in response to sustained release of stromal-derived factor-1alpha from poly(lactide ethylene oxide fumarate) hydrogels

Stromal derived factor-1alpha (SDF-1alpha) is an important chemokine in stem cell trafficking and plays a critical role in the homing of bone marrow stromal (BMS) cells. However, its use in tissue regeneration is limited by its relatively short half-life and the time-dependent nature of cell homing to the site of injury. The objective of this work was to investigate the release characteristics of SDF-1alpha from degradable poly(lactide ethylene oxide fumarate) (PLEOF) hydrogels and to determine the effect of sustained release of SDF-1alpha on migration of BMS cells. Three PLEOF hydrogels with poly(l-lactide) (PLA) fractions of 6%, 9%, and 24% by weight were synthesized. After the addition of chemokine, the polymerizing mixture was crosslinked to produce SDF-1alpha loaded PLEOF hydrogels. The hydrogels were characterized with respect to sol fraction, water uptake, degradation, SDF-1alpha loading efficiency and release kinetics, and migration rate of bone marrow stromal (BMS) cells. The more hydrophilic hydrogels with 6% and 9% PLA fraction had a pronounced burst release followed by a period of sustained release by diffusion for 21 days. The more hydrophobic hydrogel with 24% PLA fraction had a less pronounced burst release and displayed a slow but constant release by diffusion between days 1 and 9 followed by a fast release by diffusion-degradation from days 9 to 18. The fraction of active SDF-1alpha released from 6%, 9%, and 24% hydrogels after 21 days was 34.3%, 32.3%, and 35.8%, respectively. The migration of BMS cells in response to time-released SDF-1alpha closely followed the protein release kinetics from the hydrogels. The biodegradable PLEOF hydrogel may potentially be useful as a delivery matrix for sustained release of SDF-1alpha in the proliferative phase of healing for recruitment of progenitor cells in tissue engineering applications.

Icariin: a potential osteoinductive compound for bone tissue engineering

To effectively treat bone diseases using bone regenerative medicine, there is an urgent need to develop safe and cheap drugs that can potently induce bone formation. Here, we demonstrate the osteogenic effects of icariin, the main active compound of Epimedium pubescens. Icariin induced osteogenic differentiation of preosteoblastic cells. The combination of icariin and a helioxanthin-derived small compound synergistically induced osteogenic differentiation of MC3T3-E1 cells to a similar extent to bone morphogenetic protein-2. Icariin enhanced the osteogenic induction activity of bone morphogenetic protein-2 in a fibroblastic cell line. Mineralization was enhanced by treatment with a combination of icariin and calcium-enriched medium. The in vivo anabolic effect of icariin was confirmed in a mouse calvarial defect model. Eight-week-old male C57BL/6N mice were transplanted with icariin-calcium phosphate cement (CPC) tablets or CPC tablets only (n = 5 for each), and bone regeneration was evaluated after 4 and 6 weeks. Significant new bone formation was observed in the icariin-CPC group at 4 weeks, and the new bone thickness had increased by 6 weeks. Obvious blood vessel formation was observed in the icariin-induced new bone. Treatment of senescence-accelerated mouse prone 1 and senescence-accelerated mouse prone 6 models further demonstrated that icariin was able to enhance bone formation in vivo. Therefore, icariin is a strong candidate for an osteogenic compound for use in bone tissue engineering.

Delivery systems for bone growth factors — the new players in skeletal regeneration

Given the challenge of an increasing elderly population, the ability to repair and regenerate traumatised or lost tissue is a major clinical and socio-economic need. Pivotal in this process will be the ability to deliver appropriate growth factors in the repair cascade in a temporal and tightly regulated sequence using appropriately designed matrices and release technologies within a tissue engineering strategy. This review outlines the current concepts and challenges in growth factor delivery for skeletal regeneration and the potential of novel delivery matrices and biotechnologies to influence the healthcare of an increasing ageing population.

Drug releasing systems in cardiovascular tissue engineering

Heart disease and atherosclerosis are the leading causes of morbidity and mortality worldwide. The lack of suitable autologous grafts has produced a need for artificial grafts; however, current artificial grafts carry significant limitations, including thrombosis, infection, limited durability and the inability to grow. Tissue engineering of blood vessels, cardiovascular structures and whole organs is a promising approach for creating replacement tissues to repair congenital defects and/or diseased tissues. In an attempt to surmount the shortcomings of artificial grafts, tissue-engineered cardiovascular graft (TECVG), constructs obtained using cultured autologous vascular cells seeded onto a synthetic biodegradable polymer scaffold, have been developed. Autologous TECVGs have the potential advantages of growth, durability, resistance to infection, and freedom from problems of rejection, thrombogenicity and donor scarcity. Moreover polymers engrafted with growth factors, cytokines, drugs have been developed allowing drug-releasing systems capable of focused and localized delivery of molecules depending on the environmental requirements and the milieu in which the scaffold is placed. A broad range of applications for compound-releasing, tissue-engineered grafts have been suggested ranging from drug delivery to gene therapy. This review will describe advances in the development of drug-delivery systems for cardiovascular applications focusing on the manufacturing techniques and on the compounds delivered by these systems to date.

Basic fibroblast growth factor suspended in Matrigel improves titanium implant fixation in ovariectomized rats

Basic fibroblast growth factor (bFGF) has high potential for tissue regeneration; however, its in vivo effects are unpredictable due to the short-term survival. This study sought to evaluate the effects of bFGF suspended in Matrigel on the implant fixation in ovariectomized (OVX) rats. In vitro, the release kinetics of bFGF was tested using an immuno-ligand-assay. In vivo, eighty titanium implants were randomly divided into 4 groups and inserted in the tibiae of forty OVX rats: no treatment group, bFGF alone group, Matrigel alone group and bFGF+Matrigel group. At 3 months after implantation, tibiae were examined by histology, micro-CT and push-out test. We found that Matrigel could prolong the life span of bFGF in vitro with a sustained release during the 21 days. In vivo, bFGF or Matrigel alone had little effect on the fixation of implant in OVX rats, but bFGF suspended in Matrigel induced nearly 2-fold of peri-implant new bone formation and 4-fold of implant mechanical stability when compared to other 3 groups. The results of this study suggest that Matrigel could be used as a carrier of bFGF and prolonged its release around implant, which may improve implant fixation, especially in site of post-menopausal osteoporosis.

Prevention of pulmonary metastasis from subcutaneous tumors by binary system-based sustained delivery of catalase

Catalase delivery can be effective in inhibiting reactive oxygen species (ROS)-mediated acceleration of tumor metastasis. Our previous studies have demonstrated that increasing the plasma half-life of catalase by pegylation (PEG-catalase) significantly increases its potency of inhibiting experimental pulmonary metastasis in mice. In the present study, a biodegradable gelatin hydrogel formulation was used to further increase the circulation time of PEG-catalase. Implantation of (111)In-PEG-catalase/hydrogel into subcutaneous tissues maintained the radioactivity in plasma for more than 14 days. Then, the effect of the PEG-catalase/hydrogel on spontaneous pulmonary metastasis of tumor cells was evaluated in mice with subcutaneous tumor of B16-BL6/Luc cells, a murine melanoma cell line stably expressing luciferase. Measuring luciferase activity in the lung revealed that the PEG-catalase/hydrogel significantly (P<0.05) inhibited the pulmonary metastasis compared with PEG-catalase solution. These findings indicate that sustaining catalase activity in the blood circulation achieved by the use of pegylation and gelatin hydrogel can reduce the incidence of tumor cell metastasis.

Non-invasive monitoring of BMP-2 retention and bone formation in composites for bone tissue engineering using SPECT/CT and scintillation probes

Non-invasive imaging can provide essential information for the optimization of new drug delivery-based bone regeneration strategies to repair damaged or impaired bone tissue. This study investigates the applicability of nuclear medicine and radiological techniques to monitor growth factor retention profiles and subsequent effects on bone formation. Recombinant human bone morphogenetic protein-2 (BMP-2, 6.5 microg/scaffold) was incorporated into a sustained release vehicle consisting of poly(lactic-co-glycolic acid) microspheres embedded in a poly(propylene fumarate) scaffold surrounded by a gelatin hydrogel and implanted subcutaneously and in 5-mm segmental femoral defects in 9 rats for a period of 56 days. To determine the pharmacokinetic profile, BMP-2 was radiolabeled with (125)I and the local retention of (125)I-BMP-2 was measured by single photon emission computed tomography (SPECT), scintillation probes and ex vivo scintillation analysis. Bone formation was monitored by micro-computed tomography (microCT). The scaffolds released BMP-2 in a sustained fashion over the 56-day implantation period. A good correlation between the SPECT and scintillation probe measurements was found and there were no significant differences between the non-invasive and ex-vivo counting method after 8 weeks of follow up. SPECT analysis of the total body and thyroid counts showed a limited accumulation of (125)I within the body. Ectopic bone formation was induced in the scaffolds and the femur defects healed completely. In vivo microCT imaging detected the first signs of bone formation at days 14 and 28 for the orthotopic and ectopic implants, respectively, and provided a detailed profile of the bone formation rate. Overall, this study clearly demonstrates the benefit of applying non-invasive techniques in drug delivery-based bone regeneration strategies by providing detailed and reliable profiles of the growth factor retention and bone formation at different implantation sites in a limited number of animals.

Porous nano-HA/collagen/PLLA scaffold containing chitosan microspheres for controlled delivery of synthetic peptide derived from BMP-2

It is advantageous to incorporate controlled growth factor delivery into tissue engineering strategies. The purpose of the present study was to develop a novel tissue engineering scaffold with the capability of controlled releasing BMP-2-derived synthetic peptide. Porous nano-hydroxyapatite/collagen/poly(L-lactic acid)/chitosan microspheres (nHAC/PLLA/CMs) composite scaffolds containing different quantities of chitosan microspheres (CMs) were prepared by a thermally induced phase separation method. Dioxane was used as the solvent for PLLA. Introduction of less than 30% of CMs (on PLLA weight basis) did not remarkably affect the morphology and porosity of the nHAC/PLLA/CMs scaffolds. However, as the microspheres contents increased to 50%, the porosity of the composite decreased rapidly. The compressive modulus of the composite scaffolds increased from 15.4 to 25.5 MPa, while the compressive strength increased from 1.42 to 1.63 MPa as the microspheres contents increased from 0% to 50%. The hydrolytic degradation and synthetic peptide release kinetics in vitro were investigated by incubation in phosphate buffered saline solution (pH 7.4). The results indicated that the degradation rate of the scaffolds was increased with the enhancement of CMs dosage. The synthetic peptide was released in a temporally controlled manner, depending on the degradation of both incorporated chitosan microspheres and PLLA matrix. In vitro bioactivity assay revealed that the encapsulated synthetic peptide was biologically active as evidenced by stimulation of rabbit marrow mesenchymal stem cells (MSCs) alkaline phosphatase (ALP) activity. The successful microspheres-scaffold system offers a new delivery method of growth factors and a novel scaffold design for bone regeneration.

Development of high-throughput screening system for osteogenic drugs using a cell-based sensor

To effectively treat osteoporosis and other bone-loss disorders, small compounds that potently induce bone formation are needed. The present study initially attempted to establish a monitoring system that could detect osteogenic differentiation easily, precisely, and noninvasively. For this purpose, we established pre-osteoblastic MC3T3E1 cells stably transfected with the GFP reporter gene driven by a 2.3 kb fragment of rat type I collagen promoter (Col1a1GFP-MC3T3E1). Among these cells, we selected a clone that fluoresced upon osteogenic stimulation by BMP2. The GFP fluorescence intensity corresponded well to the intensity of alkaline phosphatase (ALP) staining and to the level of osteocalcin (Oc) mRNA. Using this system, we screened natural and synthetic compound libraries and thus identified an isoflavone derivative, glabrisoflavone (GI). GI induced ALP staining and Oc mRNA in a dose-dependent manner. The Col1a1GFP-MC3T3E1 system may be useful for identifying novel osteogenic drugs.

Critical factors in the design of growth factor releasing scaffolds for cartilage tissue engineering

BACKGROUND

Trauma or degenerative diseases of the joints are common clinical problems resulting in high morbidity. Although various orthopedic treatments have been developed and evaluated, the low repair capacities of articular cartilage renders functional results unsatisfactory in the long term. Over the last decade, a different approach (tissue engineering) has emerged that aims not only to repair impaired cartilage, but also to fully regenerate it, by combining cells, biomaterials mimicking extracellular matrix (scaffolds) and regulatory signals. The latter is of high importance as growth factors have the potency to induce, support or enhance the growth and differentiation of various cell types towards the chondrogenic lineage. Therefore, the controlled release of different growth factors from scaffolds appears to have great potential to orchestrate tissue repair effectively.

OBJECTIVE

This review aims to highlight considerations and limitations of the design, materials and processing methods available to create scaffolds, in relation to the suitability to incorporate and release growth factors in a safe and defined manner. Furthermore, the current state of the art of signalling molecules release from scaffolds and the impact on cartilage regeneration in vitro and in vivo is reported and critically discussed.

METHODS

The strict aspects of biomaterials, scaffolds and growth factor release from scaffolds for cartilage tissue engineering applications are considered.

CONCLUSION

Engineering defined scaffolds that deliver growth factors in a controlled way is a task seldom attained. If growth factor delivery appears to be beneficial overall, the optimal delivery conditions for cartilage reconstruction should be more thoroughly investigated.

Non-invasive screening method for simultaneous evaluation of in vivo growth factor release profiles from multiple ectopic bone tissue engineering implants

The purpose of this study was to develop and validate a screening method based on scintillation probes for the simultaneous evaluation of in vivo growth factor release profiles of multiple implants in the same animal. First, we characterized the scintillation probes in a series of in vitro experiments to optimize the accuracy of the measurement setup. The scintillation probes were found to have a strong geometric dependence and experience saturation effects at high activities. In vitro simulation of 4 subcutaneous limb implants in a rat showed minimal interference of surrounding implants on local measurements at close to parallel positioning of the probes. These characteristics were taken into consideration for the design of the probe setup and in vivo experiment. The measurement setup was then validated in a rat subcutaneous implantation model using 4 different sustained release carriers loaded with (125)I-BMP-2 per animal. The implants were removed after 42 or 84 days of implantation, for comparison of the non-invasive method to ex vivo radioisotope counting. The non-invasive method demonstrated a good correlation with the ex vivo counting method at both time-points of all 4 carriers. Overall, this study showed that scintillation probes could be successfully used for paired measurement of 4 release profiles with minimal interference of the surrounding implants, and may find use as non-invasive screening tools for various drug delivery applications.

Biocompatibility issues with modern implants in bone - a review for clinical orthopedics

Skeletal defects may result from traumatic, infectious, congenital or neoplastic processes and are considered to be a challenge for reconstructive surgery. Although the autologous bone graft is still the “gold standard”, there is continuing demand for bone substitutes because of associated disadvantages, such as limited supply and potential donor side morbidity [1]. This is not only true for indications in orthopedic and craniomaxillofacial surgeries, but also in repairing endodontic defects and in dental implantology.

Before clinical use all new bone substitute materials have to be validated for their osseoconductive and - depending on the composition of the material also –inductive ability, as well as for their long-term biocompatibility in bone. Serving this purpose various bone healing models to test osteocompatibility and inflammatory potential of a novel material on one hand and, on the other hand, non-healing osseous defects to assess the healing potential of a bone substitute material have been developed. Sometimes the use of more than one implantation site can be helpful to provide a wide range of information about a new material [2].

Important markers for biocompatibility and inflammatory responses are the cell types appearing after the implantation of foreign material. There, especially the role of foreign body giant cells (FBGC) is discussed controversial in the pertinent literature, such that it is not clear whether their presence marks an incompatibility of the biomaterial, or whether it belongs to a normal degradation behavior of modern, resorbable biomaterials.

This publication is highlighting the different views currently existing about the function of FBGC that appear in response to biomaterials at the implantation sites. A short overview of the general classes of biomaterials, where FBGC may appear as cellular response, is added for clarity, but may not be complete.

Icariin induces osteogenic differentiation in vitro in a BMP- and Runx2-dependent manner

To effectively treat bone diseases using bone regenerative medicine, there is an urgent need to develop safe cheap drugs that can potently induce bone formation. Here, we demonstrate the osteogenic effect of icariin, the main active compound of Epimedium pubescens. Icariin induced osteogenic differentiation in pre-osteoblastic MC3T3-E1 cells and mouse primary osteoblasts. Icariin upregulated the mRNA expression levels of the osteoblast marker genes runt-related transcription factor 2 (Runx2) and inhibitor of DNA-binding 1 (Id-1). The osteogenic effect was inhibited by the introduction of Smad6 or dominant-negative Runx2, as well as Noggin treatment. Furthermore, icariin induced the mRNA expression of bone morphogenetic protein (BMP)-4. These data suggest that icariin exerts its potent osteogenic effect through induction of Runx2 expression, production of BMP-4 and activation of BMP signaling. The extremely low cost of icariin and its high abundance make it appealing for bone regenerative medicine.

Cationized catalase-loaded hydrogel for growth inhibition of peritoneally disseminated tumor cells

A previous study demonstrated that ethylenediamine-conjugated catalase (ED-catalase) inhibits peritoneal dissemination of tumor cells in mice. To increase its inhibitory effects by sustained release, a hydrogel formulation of ED-catalase was prepared using a biodegradable hydrogel consisting of an acidic gelatin with an isoelectric point of 5.0. Although intraperitoneally injected ED-catalase solution rapidly disappeared from the cavity, more than 10% of ED-catalase remained even at 14 days after implantation of ED-catalase/hydrogel into the cavity. Then, the effect of ED-catalase/hydrogel on peritoneal dissemination of tumor cells was evaluated by measuring the luciferase activity of abdominal organs after intraperitoneal inoculation of colon26/Luc, a colon adenocarcinoma stably expressing luciferase. ED-catalase/hydrogel showed a significantly (P<0.05) greater effect on inhibiting the growth of tumor cells than ED-catalase solution, demonstrating the importance of the retention of ED-catalase within the cavity as far as inhibition is concerned. Serial in vivo images of luciferase activity revealed that the ED-catalase/hydrogel significantly (P<0.05) retarded the growth rate of tumor cells. Survival of tumor-bearing mice supported the findings obtained with the luminescence-based analyses. These findings indicate that the sustained release of ED-catalase from hydrogels into the cavity is highly effective in inhibiting the growth of peritoneally disseminated tumor cells.

Experimental tissue regeneration by DDS technology of bio-signaling molecules

The medical therapy of tissue regeneration achieved by biomaterial-based tissue engineering has been currently expected as the third option following reconstructive surgery and organ transplantation. The basic idea of this regenerative therapy is to assist the self-healing potentials of body to induce the natural regeneration and repairing of defective or injured tissue. To this end, it is practically important to create a local environment which enables cells to promote their proliferation and differentiation, resulting in the induction of cell-based tissue regeneration. Tissue engineering is a biomedical technology or methodology to build up this regeneration environment by making use of biomaterials. Drug delivery system (DDS) is a biomaterial technology to enhance the in vivo biological functions of bio-signaling molecules (growth factors and genes) for promoted tissue regeneration. This paper overviews the recent status of tissue regeneration therapy based on the DDS technology of bio-signaling molecules.

Matrices and scaffolds for delivery of bioactive molecules in bone and cartilage tissue engineering

Regeneration of bone and cartilage defects can be accelerated by localized delivery of appropriate growth factors incorporated within biodegradable carriers. The carrier essentially allows the impregnated growth factor to release at a desirable rate and concentration, and to linger at injury sites for a sufficient time to recruit progenitors and stimulate tissue healing processes. In addition, the carrier can be formulated to have particular structure to facilitate cellular infiltration and growth. In this review, we present a summary of growth factor delivery carrier systems for bone and cartilage tissue engineering. Firstly, we describe a list of growth factors implicated in repair and regeneration of bone and cartilage by addressing their biological effects at different stages of the healing process. General requirements for localized growth factor delivery carriers are then discussed. We also provide selective examples of material types (natural and synthetic polymers, inorganic materials, and their composites) and fabricated forms of the carrier (porous scaffolds, microparticles, and hydrogels), highlighting the dose-dependent efficacy, release kinetics, animal models, and restored tissue types. Extensive discussion on issues involving currently investigated carriers for bone and cartilage tissue engineering approaches may illustrate future paths toward the development of an ideal growth factor delivery system.

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.

The Regenerative Effects of Platelet-Rich Plasma on Meniscal CellsIn Vitroand ItsIn VivoApplication with Biodegradable Gelatin Hydrogel

The objective of the study was to test the hypothesis that platelet-rich plasma (PRP) enhances meniscal tissue regeneration in vitro and in vivo. In the in vitro study, monolayer meniscal cell cultures were prepared, and 3-(4,5-dimethylthiazol-2yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium inner salt assay and 5-bromo-2'-deoxyuridine assay were performed to assess proliferative behavior in the presence of PRP. Alcian blue assay was performed to assess extracellular matrix (ECM) synthesis. To detect the fibrocartilage-related messenger ribonucleic acid (mRNA) expressions, real-time polymerase chain reaction was performed. In the in vivo study, 1.5-mm-diameter full-thickness defects were created in the avascular region of rabbit meniscus. Gelatin hydrogel (GH) was used as the drug delivery system for PRP growth factors. The defects were filled as follows: Group A, GH with PRP; Group B, GH with platelet-poor plasma; Group C, GH only. Each group was evaluated histologically at 4, 8, and 12 weeks after surgery. PRP stimulated deoxyribonucleic acid synthesis and ECM synthesis (p<0.05). Meniscal cells cultured with PRP showed greater mRNA expression of biglycan and decorin (p<0.05). Histological findings showed that remnants of gelatin hydrogels existed at 4 weeks, indicating that the hydrogels could control release for approximately 4 weeks. Histological scoring of the defect sites at 12 weeks revealed significantly better meniscal repair in animals that received PRP with GH than in the other two groups. These findings suggest that PRP enhances the healing of meniscal defects.

A novel osteogenic helioxanthin-derivative acts in a BMP-dependent manner

To effectively treat serious bone defects using bone regenerative medicine, there is a need for the development of a small chemical compound that potently induces bone formation. We now report a novel osteogenic helioxanthin-derivative, TH. TH induced osteogenic differentiation in MC3T3-E1 cells, mouse primary osteoblasts, and mouse embryonic stem cells. The combination of TH and bone morphogenetic protein (BMP) 2 induced the mRNA expression of osteoblast marker genes and calcification in primary fibroblasts. The TH induced the mRNA of the inhibitor of DNA-binding 1 (Id-1), and its osteogenic effect was inhibited by Smad6 or Noggin. Furthermore, TH induced the mRNA expression of Bmp4 and Bmp6. These data suggest that TH exerts its potent osteogenic effect in a BMP-dependent manner by enhancing the effects of the existing BMPs and/or increasing the expression of Bmp4 and Bmp6. TH may help establish a more efficient bone regeneration system.

Controlled release of platelet growth factors enhances bone regeneration at rabbit calvaria

OBJECTIVE

Platelet-rich plasma (PRP) has been clinically employed to promote bone regeneration. However, few studies have investigated the enhancement of biological function of platelet growth factors after integration of PRP into biomaterials. In this study, the feasibility of gelatin hydrogels for controlled release of platelet growth factors and the consequent enhancement of PRP-induced bone regeneration were evaluated in rabbit calvarial defect.

STUDY DESIGN

Gelatin hydrogels incorporating PRP, PRP-activated thrombin, or an empty gelatin hydrogel were applied to the defect, or the defect was left untreated. Bone regeneration was evaluated by microfocus computed tomography, peripheral quantitative computed tomography, and histological examinations.

RESULTS

Successful bone regeneration was observed at the bone defect applied with the gelatin hydrogel incorporating PRP, which is in marked contrast to other groups.

CONCLUSION

The gelatin hydrogel is a promising material capable of controlled release of platelet growth factors to enhance bone regeneration.

Tailored release of TGF-β1 from porous scaffolds for cartilage tissue engineering

In view of cartilage tissue engineering, the possibility to prepare porous scaffolds releasing transforming growth factor-beta(1) (TGF-beta(1)) in a well controlled fashion was investigated by means of an emulsion-coating method. Poly(ether-ester) multiblock copolymers were used to prepare emulsions containing TGF-beta(1) which were subsequently applied onto prefabricated scaffolds. This approach resulted in defined porous structures (66%) with interconnected porosity, suitable to allow tissue ingrowth. The scaffolds were effectively associated with TGF-beta(1) and allowed to tailor precisely the release of the growth factor from 12 days to more than 50 days by varying the copolymer composition of the coating. An incomplete release was measured by ELISA, possibly linked to the rapid concentration decrease of the protein in solution. The released growth factor retained its biological activity as was assessed by a cell proliferation assay and by the ability of the released protein to induce chondrogenic differentiation of bone marrow-derived mesenchymal stem cells. However, exact bioactivity quantification was rendered difficult by the protein concentration decrease during storage. Therefore, this study confirms the interest of poly(ether-ester) multiblock copolymers for controlled release of growth factors, and indicates that emulsion-coated scaffolds are promising candidates for cartilage tissue engineering applications requiring precise TGF-beta(1) release rates.

Intervertebral Disc Regeneration Using Platelet-Rich Plasma and Biodegradable Gelatin Hydrogel Microspheres

This study evaluated the regenerative effects of platelet-rich plasma (PRP) for the degenerated intervertebral disc (IVD) in vivo. After induction of IVD degeneration in rabbits, we prepared PRP by centrifuging blood obtained from these rabbits. These PRP were injected into the nucleus pulposus (NP) of the degenerated IVDs after impregnation into gelatin hydrogel microspheres that can immobilize PRP growth factors physiochemically and release them in a sustained manner with the degradation of the microspheres. As controls, microspheres impregnated with phosphate-buffered saline (PBS) and PRP without microspheres were similarly injected. Histologically, notable progress in IVD degeneration with time courses was observed in the PBS control, PRP-only, and sham groups. In contrast, progress was remarkably suppressed over the 8-week period in the PRP group. Moreover, in immunohistochemistry, intense immunostaining for proteoglycan in the NP and inner layer of the annulus fibrosus was observed 8 weeks after administration of PRP-impregnated microspheres. Almost all microspheres were indistinct 8 weeks after the injection, and there were no apparent side effects in this study. Our results suggest that the combined administration of PRP and gelatin hydrogel microspheres into the IVD may be a promising therapeutic modality for IVD degeneration.

Effects of rhBMP-2 on cortical strut allograft healing to the femur in revision total hip arthroplasties: an experimental study

We have studied the effects of recombinant human bone morphogenetic protein-2 (rhBMP-2) on cortical strut allograft healing and remodelling in revision hip arthroplasty. Thirty adult New Zealand rabbits underwent bilateral onlay allograft strut procedures to the femur using wires. The left femur (experimental side) received the rhBMP-2 device (1.0-mg rhBMP-2/gelatin composites) interposed between the allograft and host bone, while the right side was grafted with an allograft strut as the control. The femurs and implants were retrieved at 4, 6, and 8 weeks postoperatively. The healing of cortical strut grafts to the femur was enhanced dramatically by the addition of the rhBMP-2 device in radiographic examination, contact radiographic examination, non-decalcification sections, fluorescence tag, and computer-aided image analysis. The remodelling of cortical strut allograft was also accelerated. The new bone formation ratio and radiographic scores of the experimental side were also much higher than the control side at all times. Strut healing with the rhBMP-2 device at 4 weeks postoperatively was superior to the healing in control sides at 8 weeks. Our findings showed that the rhBMP-2 device improved and accelerated the course of cortical strut allograft healing and remodelling with host bone.

A novel poly(ethylene glycol)–fibrinogen hydrogel for tibial segmental defect repair in a rat model

The aim of this study is to investigate regeneration in a segmental bone defect using a novel fibrinogen-based hydrogel material. The use of hydrogels made from poly(ethylene glycol) (PEG) conjugated to fibrinogen for this purpose may be better to conventional fibrin-based materials as it offers an additional degree of control over the structural characteristics and biodegradation of the material. At the same time, it maintains some of the inherent biofunctionality of the fibrinogen molecule. PEGylated fibrinogen hydrogels with various degrees of proteolytic resistance based on PEG and fibrinogen composition were designed for slow, intermediate, and fast biodegradation. The hydrogels were implanted into 7-mm segmental rat tibial defects without additional osteoinductive factors with the rationale that the ingrowth matrix will displace the normal fibrin clot while sustaining a similar healing effect for a longer duration. Histological and X-ray results confirmed that the extent and distribution of newly formed bone in the defect after 5 weeks strongly parallels the biodegradation pattern of the implanted material. When compared to nonunions in animals treated with the fast-degrading implants and untreated control animals, the rats implanted with the intermediate-degrading material exhibited osteoneogenesis. This data supports the hypothesis that the perseverance of the PEGylated fibrinogen material can be synchronized with the optimal healing characteristics of a segmental osseous defect and that the consequent sustained release of fibrinogen fragments facilitates the osteogenic response at the injury site. The PEGylated fibrinogen material may, therefore, be a highly efficacious material for promoting the healing of bone defects and especially nonunion fractures.