Prolonged release from PLGA/HAp scaffolds containing drug-loaded PLGA/gelatin composite microspheres

Progress of gelatin-based microspheres (GMSs) as delivery vehicles of drug and cell

Gelatin has various attractive features as biomedical materials, for instance, biocompatibility, low immunogenicity, biodegradability, and ease of manipulation. In recent years, various gelatin-based microspheres (GMSs) have been fabricated with innovative technologies to serve as sustained delivery vehicles of drugs and genetic materials as well as beneficial bacteria. Moreover, GMSs have exhibited promising potentials to act as both cell carriers and 3D scaffold components in tissue engineering and regenerative medicine, which not only exhibit excellent injectability but also could be integrated into a macroscale construct with the laden cells. Herein, we aim to thoroughly summarize the recent progress in the preparations and biomedical applications of GMSs and then to point out the research direction in future. First, various methods for the fabrication of GMSs will be described. Second, the recent use of GMSs in tumor embolization and in the delivery of cells, drugs, and genetic material as well as bacteria will be presented. Finally, several key factors that may enhance the improvement of GMSs were suggested as delivery vehicles.

BMP-2-releasing gelatin microspheres/PLGA scaffolds for bone repairment of X-ray-radiated rabbit radius defects

The purpose of this research is to assess the feasibility of poly(lactic-co-glycolic) acid (PLGA) incorporating gelatin microspheres (PLGA/GMs scaffold) for enhancing osteogenesis in vitro and at a radius defect of rabbits after X-ray radiation in vivo. After incorporating gelatin microspheres, PLGA scaffold demonstrated improved mechanical properties. Moreover, a sustained release property of recombinant human bone morphogenetic protein-2 (BMP-2) was achieved in BMP-2-releasing PLGA/GMs scaffold. BMP-2-releasing PLGA/GMs scaffold also enhanced proliferation and osteogenesis of rabbit bone mesenchymal stem cells (BMSCs) in vitro, indicating the bioactivity of BMP-2. After finishing X-ray radiation of the radius bone, 20-mm radius bone defects were generated, followed by being implanted with BMP-2-releasing PLGA/GMs scaffolds with or without bone marrow. Both PLGA/GMs scaffolds containing bone marrow or BMP-2 showed more obvious enhancement for bone regeneration than the empty scaffolds (control) at the radius defect. In the X-ray radiated groups, however, the bone regeneration was inhibited either with bone marrow or BMP-2. When combined with bone marrow, the BMP-2 showed significantly high osteogenic effect, regardless of X-ray radiation. It is considered that it is a promising way to repair bone defects even after X-ray radiation by a combination of bone marrow with the BMP-2-releasing PLGA/GMs scaffold.

Synergistic effects of dual growth factor delivery from composite hydrogels incorporating 2-N,6-O-sulphated chitosan on bone regeneration

A promising strategy to accelerate bone generation is to deliver a combination of certain growth factors to the integration site via a controlled spatial and temporal delivery mode. Here, a composite hydrogel incorporating poly(lactide-co-glycolide) (PLGA) microspheres was accordingly prepared to load and deliver the osteogenic rhBMP-2 and angiogenic rhVEGF₁₆₅ in the required manner. In addition, 2-N,6-O-sulphated chitosan (26SCS), which is a synergetic factor of growth factors, was incorporated in the composite hydrogel as well. The system showed a similar release behaviour of the two growth factors regardless of 26SCS inclusion. RhBMP-2 loaded in PLGA microspheres showed a sustained release over a period of 2 weeks, whereas rhVEGF₁₆₅ loaded in hydrogel eluted almost completely from the hydrogel over the first 16 days. Both growth factors retained their efficacy, as quantified with relevant in vitro assays. Moreover, an enhanced cell response was achieved upon the delivery of dual growth factors, compared to that obtained with a single factor. Furthermore, in the presence of 26SCS, the system revealed significantly upregulated alkaline phosphatase activity, human umbilical vein endothelial cell proliferation, sprouting, nitric oxide secretion, and angiogenic gene expression. This study highlighted that the composite hydrogel incorporated with 26SCS appears to constitute a promising approach to deliver multiple growth factors. From our findings, we could also conclude that rhBMP-2 can promote angiogenesis and that the mechanism is worthy of further study in subsequent research.

Safety of bioabsorbable implants in vitro

Background

The aim of the present study was to investigate the safety of bioabsorbable plates and screws in humans.

Methods

For this purpose, an implant system based on [poly(lactic-co-glycolic acids)(85:15)] was designed. The system was tested for pH, temperature, and swelling and then its surface morphology was analyzed for surface porosity using environmental electron microscopy. Then, the effects of this bioabsorbable system on the viability and profileration of osteocytes were examined on a molecular level via in vitro experiments. A [poly(lactic-co-glycolic acids)(90:10)] bioabsorbable implant, which is commercially available and used in orthopedic surgery, was used as control group. For the statistical evaluation of the data obtained in the present study, the groups were compared by Tukey HSD test following ANOVA. The significance level was set as p < 0.05.

Results

It was observed that the osteocytes cultivated on the PLGA system designed in the present study included more live cells and allowed more proliferation compared to the control.

Conclusion

One of the criteria in the selection of implants for orthopedic surgery is that a good implant should not need removal and thus a second surgery. In the present study, a bioabsorbable implant was designed considering this criterion. The present study is the first step to prove the safety of this new design by in vitro toxicity and viability experiments.

Controlled drug release for tissue engineering

Tissue engineering is often referred to as a three-pronged discipline, with each prong corresponding to 1) a 3D material matrix (scaffold), 2) drugs that act on molecular signaling, and 3) regenerative living cells. Herein we focus on reviewing advances in controlled release of drugs from tissue engineering platforms. This review addresses advances in hydrogels and porous scaffolds that are synthesized from natural materials and synthetic polymers for the purposes of controlled release in tissue engineering. We pay special attention to efforts to reduce the burst release effect and to provide sustained and long-term release. Finally, novel approaches to controlled release are described, including devices that allow for pulsatile and sequential delivery. In addition to recent advances, limitations of current approaches and areas of further research are discussed.

Recent advances in the use of gelatin in biomedical research

The biomacromolecule, gelatin, has increasingly been used in biomedicine-beyond its traditional use in food and cosmetics. The appealing advantages of gelatin, such as its cell-adhesive structure, low cost, off-the-shelf availability, high biocompatibility, biodegradability and low immunogenicity, among others, have made it a desirable candidate for the development of biomaterials for tissue engineering and drug delivery. Gelatin can be formulated in the form of nanoparticles, employed as size-controllable porogen, adopted as surface coating agent and mixed with synthetic or natural biopolymers forming composite scaffolds. In this article, we review recent advances in the versatile applications of gelatin within biomedical context and attempt to draw upon its advantages and potential challenges.

Mesoporous bioactive glass surface modified poly(lactic-co-glycolic acid) electrospun fibrous scaffold for bone regeneration

A mesoporous bioactive glass (MBG) surface modified with poly(lactic-co-glycolic acid) (PLGA) electrospun fibrous scaffold for bone regeneration was prepared by dip-coating a PLGA electrospun fibrous scaffold into MBG precursor solution. Different surface structures and properties were acquired by different coating times. Surface morphology, chemical composition, microstructure, pore size distribution, and hydrophilicity of the PLGA-MBG scaffold were characterized. Results of scanning electron microscopy indicated that MBG surface coating made the scaffold rougher with the increase of MBG content. Scaffolds after MBG modification possessed mesoporous architecture on the surface. The measurements of the water contact angles suggested that the incorporation of MBG into the PLGA scaffold improved the surface hydrophilicity. An energy dispersive spectrometer evidenced that calcium-deficient carbonated hydroxyapatite formed on the PLGA-MBG scaffolds after a 7-day immersion in simulated body fluid. In vitro studies showed that the incorporation of MBG favored cell proliferation and osteogenic differentiation of human mesenchymal stem cells on the PLGA scaffolds. Moreover, the MBG surface-modified PLGA (PLGA-MBG) scaffolds were shown to be capable of providing the improved adsorption/release behaviors of bone morphogenetic protein-2 (BMP-2). It is very significant that PLGA-MBG scaffolds could be effective for BMP-2 delivery and bone regeneration.

Combination of aligned PLGA/Gelatin electrospun sheets, native dental pulp extracellular matrix and treated dentin matrix as substrates for tooth root regeneration

In tissue engineering, scaffold materials provide effective structural support to promote the repair of damaged tissues or organs through simulating the extracellular matrix (ECM) microenvironments for stem cells. This study hypothesized that simulating the ECM microenvironments of periodontium and dental pulp/dentin complexes would contribute to the regeneration of tooth root. Here, aligned PLGA/Gelatin electrospun sheet (APES), treated dentin matrix (TDM) and native dental pulp extracellular matrix (DPEM) were fabricated and combined into APES/TDM and DPEM/TDM for periodontium and dental pulp regeneration, respectively. This study firstly examined the physicochemical properties and biocompatibilities of both APES and DPEM in vitro, and further investigated the degradation of APES and revascularization of DPEM in vivo. Then, the potency of APES/TDM and DPEM/TDM in odontogenic induction was evaluated via co-culture with dental stem cells. Finally, we verified the periodontium and dental pulp/dentin complex regeneration in the jaw of miniature swine. Results showed that APES possessed aligned fiber orientation which guided cell proliferation while DPEM preserved the intrinsic fiber structure and ECM proteins. Importantly, both APES/TDM and DPEM/TDM facilitated the odontogenic differentiation of dental stem cells in vitro. Seeded with stem cells, the sandwich composites (APES/TDM/DPEM) generated tooth root-like tissues after being transplanted in porcine jaws for 12 w. In dental pulp/dentin complex-like tissues, columnar odontoblasts-like layer arranged along the interface between newly-formed predentin matrix and dental pulp-like tissues in which blood vessels could be found; in periodontium complex-like tissues, cellular cementum and periodontal ligament (PDL)-like tissues were generated on the TDM surface. Thus, above results suggest that APES and DPEM exhibiting appropriate physicochemical properties and well biocompatibilities, in accompany with TDM, could make up an ECM microenvironment for tooth root regeneration, which also offers a strategy for complex tissue or organ regeneration.

Photocrosslinked layered gelatin-chitosan hydrogel with graded compositions for osteochondral defect repair

A layered gelatin-chitosan hydrogel with graded composition was prepared via photocrosslinking to simulate the polysaccharide/collagen composition of the natural tissue and mimic the multi-layered gradient structure of the cartilage-bone interface tissue. Firstly, gelatin and carboxymethyl chitosan were reacted with glycidyl methacrylate (GMA) to obtain methacrylated gelatin (Gtn-GMA) and carboxymethyl chitosan (CS-GMA). Then, the mixed solutions of Gtn-GMA in different methacrylation degrees with CS-GMA were prepared to form the superficial, transitional and deep layers of the hydrogel, respectively under the irradiation of ultraviolet light, while polyhedral oligomeric silsesquioxane was introduced in the deep layer to improve the mechanical properties. Results suggested that the pore sizes of the superficial, transitional and deep layers of the layered hydrogel were 115 ± 30, 94 ± 34, 51 ± 12 μm, respectively and their porosities were all higher than 80 %. The compressive strengths of them were 165 ± 54, 565 ± 50 and 993 ± 108 kPa, respectively and the strain of the gradient hydrogel decreased along the thickness direction, similar to the natural tissue. The in vitro cytotoxicity results showed that the hydrogel had good cytocompatibility and the in vivo repair results of osteochondral defect demonstrated remarkable recovery by using the gradient gelatin-chitosan hydrogel, especially when the hydrogel loading transforming growth factor-β1. Therefore, it was suggested that the prepared layered gelatin-chitosan hydrogel in this study could be potentially used to promote cartilage-bone interface tissue repair.

Evaluation of the growth and osteogenic differentiation of ASCs cultured with PL and seeded on PLGA scaffolds

Scaffold serves as an important component of tissue engineering, which facilitates cell attachment, proliferation and differentiation of cultured cells. In this study we aimed to use platelet lysates as a substitute for FBS in culturing and proliferation of human adipose tissue-derived stromal cells (ASCs), which constitute a promising source for cell therapy. We characterized ASCs in the presence of PL, and then we seeded them onto poly(lactic-co-glycolic acid) (PLGA) scaffolds, osteogenic media was used to induce their proliferation and osteogenic differentiation. Gene expression analysis revealed higher expression of osteogenic related genes, immunohistochemical staining showed proper cell attachment, growth and collagen matrix formation with the ability to induce vascularization. In conclusion, expansion of ASCs in PL-supplemented medium could promote cell proliferation and osteogenic differentiation of cells seeded on PLGA scaffolds, therefore it could be considered as a suitable and effective substitute for FBS to be used in clinical applications.

Effect of hydroxyapatite-containing microspheres embedded into three-dimensional magnesium phosphate scaffolds on the controlled release of lysozyme and in vitro biodegradation

The functionality of porous three-dimensional (3D) magnesium phosphate (MgP) scaffold was investigated for the development of a novel protein delivery system and biomimetic bone tissue engineering scaffold. This enhancement can be achieved by incorporation of hydroxyapatite (HA)-containing polymeric microspheres (MSs) into a bulk MgP matrix, and a paste-extruding deposition (PED) system. In this work, the amount of MS and HA was precisely controlled when manufacturing MS-embedded MgP (MS/MgP) composite scaffolds. The main influence was researched in terms of in vitro lysozyme-release, in vitro biodegradation, mechanical properties, and in vitro calcification. The controlled release of lysozyme was indicated, while showing graded release patterns according to HA content. The composite scaffolds degraded gradually with MS content and degradation time. Due to the effect of HA inclusion, the higher HA-containing MS/MgP scaffolds could, not only delay the biodegradation process but also, compensate for the possible loss of mechanical properties. In this regard, it is reasonable to confirm the inverse relationship between biodegradation and corresponding compressive properties. In order to encourage bioactivity and osteoconductivity, the MS/MgP composite scaffolds were subjected to simulated body fluid treatment. Calcium deposition was, in turn, improved with increasing MS and HA content over time. This quantitative result was also proved using morphological and elemental analysis. In summary, a significant transformation of a monolithic MgP scaffold was directed toward a multifunctional bone tissue engineering scaffold equipped with controlled protein delivery, biodegradability, and bioactivity.

Effects of hesperidin loaded poly(lactic-co-glycolic acid) scaffolds on growth behavior of costal cartilage cells in vitro and in vivo

It has been widely accepted that costal cartilage cells (CCs) have more excellent initial proliferation capacity than articular cartilage cells. Biodegradable synthetic polymer poly(lactic-co-glycolic acid) (PLGA) was approved by Food and Drug Administration. Hesperidin has antifungal, antiviral, antioxidant, anti-inflammatory, and anticarcinogenic properties. Hesperidin loaded (0, 3, 5, and 10 wt.%) PLGA scaffolds were prepared and in vitro and in vivo properties were characterized. Scaffolds were seeded with CCs isolated from rabbit, which were kept in culture to harvest for histological analysis. Hesperidin/PLGA scaffolds were also implanted in nude mice for 7 and 28 days. Assays of 2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfo-phenyl)-2H-tetrazolium, monosodium salt (WST), and scanning electron microscope were carried out to evaluate attachment and proliferation of CCs in hesperidin/PLGA scaffolds. Glycosaminoglycan assay was performed to confirm the effects of hesperidin on extracellular matrix formation. Reverse-transcriptase polymerase chain reaction was carried out to confirm the expression of the specific genes for CCs. In these results, we demonstrated that cell attachment and proliferation on hesperidin/PLGA scaffolds were more excellent compared with on PLGA scaffold. Specially, 5 wt.% hesperidin/PLGA scaffold represented the best results among other scaffolds. Thus, 5 wt.% hesperidin/PLGA scaffold will be applicable to tissue engineering cartilage.

Bone morphogenetic protein-2-impregnated biomimetic scaffolds successfully induce bone healing in a marginal mandibular defect

OBJECTIVES/HYPOTHESIS

To test the osteoregenerative potential and dosing of bone morphogenetic protein-2 (BMP-2)-impregnated biomimetic scaffolds in a rat model of a mandibular defect.

STUDY DESIGN

Prospective study using an animal model.

METHODS

Varied doses of BMP-2 (0.5, 1, 0.5, 0.5 in microspheres, 5, and 15 μg) were absorbed onto a biomimetic scaffold. Scaffolds were then implanted into marginal mandibular defects in rats. Blank scaffolds and unfilled defects were used as negative controls. Two months postoperatively, bone healing was analyzed with microcomputerized tomography (microCT).

RESULTS

MicroCT analysis demonstrated that all doses of BMP-2 induced successful healing of marginal mandibular defects in a rat mandible. Increasing doses of BMP-2 on the scaffolds produced increased tissue healing, with 15 μg demonstrating significantly more healing than all other dosing (P < .01).

CONCLUSIONS

BMP-2-impregnated biomimetic scaffolds successfully induce bone healing in a marginal mandibular defect in the rat. Percentage healing of defect, percentage of bone within healed tissue, and total bone volume are all a function of BMP-2 dosing. There appears to be an optimal dose of 5 μg beyond which there is no increase in bone volume.

LEVEL OF EVIDENCE

NA.

In vivo investigation of ceftiofur-loaded gelatin and PLGA microspheres in beagle dogs

Drug delivery systems based on polymer microspheres have received considerable attention. Ceftiofur sodium and ceftiofur hydrochloride is widely used for the treatment of bacterial diseases in animals but the delivery in vivo has not been reported. In this paper, we report the synthesis of microspheres from gelatin and PLGA, two kinds of typical natural and artificial materials, for loading ceftiofur and the in vivo investigation of the pharmacokinetics in beagle dogs. By controlling the synthesis parameters, gelatin and PLGA microspheres with diameter between 5 and 35 microns were obtained. Assay procedures based on high performance liquid chromatography were evaluated and confirmed. The dogs were randomly divided into three groups, i.e., control group, gelatin group, and PLGA group and administrated via intravenous injection. Plasma concentrations of ceftiofur over time were measured and analyzed. Results indicate that the main kinetic parameters do not show significant difference for the gelatin group and control group, but the area under the curve, plasma half-life, apparent volume of distribution, and clearance ratio of PLGA group show significant difference from the gelatin group and the control group. The PLGA microspheres show a low area under the curve but long time release.