Collagen microparticles: carriers for glucocorticosteroids

Current Trends in Gelatin-Based Drug Delivery Systems

Gelatin is a highly versatile natural polymer, which is widely used in healthcare-related sectors due to its advantageous properties, such as biocompatibility, biodegradability, low-cost, and the availability of exposed chemical groups. In the biomedical field, gelatin is used also as a biomaterial for the development of drug delivery systems (DDSs) due to its applicability to several synthesis techniques. In this review, after a brief overview of its chemical and physical properties, the focus is placed on the commonly used techniques for the development of gelatin-based micro- or nano-sized DDSs. We highlight the potential of gelatin as a carrier of many types of bioactive compounds and its ability to tune and control select drugs' release kinetics. The desolvation, nanoprecipitation, coacervation, emulsion, electrospray, and spray drying techniques are described from a methodological and mechanistic point of view, with a careful analysis of the effects of the main variable parameters on the DDSs' properties. Lastly, the outcomes of preclinical and clinical studies involving gelatin-based DDSs are thoroughly discussed.

Potential Use of 3D CORAGRAF-Loaded PDGF-BB in PLGA Microsphere Seeded Mesenchymal Stromal Cells in Enhancing the Repair of Calvaria Critical-Size Bone Defect in Rat Model

Our previous study evidenced that the 3D CORAGRAF loaded with PLGA microsphere constitutes PDGF-BB can support cell attachment and proliferation and can induce an osteogenic commitment of mesenchymal stromal cells in the in vitro condition. However, how this construct can perform in pathophysiological conditions in terms of repairing critical bone defects is yet to be understood. A study was therefore conducted to investigate the regeneration potential of calvaria critical-size defects using CORAGRAF + PLGA with PDGF-BB + mesenchymal stromal cells (MSCs) in a rat model. A 5 mm critical bone defect was created on calvaria of 40 male Sprague-Dawley rats. CORAGRAF incorporated either with or without PDGF-BB and seeded with rat bone-marrow-derived MSCs was implanted at the defect region. The bone regeneration potential of implanted constructs was assessed using micro-CT imaging and histological staining in weeks 4 and 8. The micro-CT images indicated a significant closure of defects in the cranial bone of the rats treated with 3D CORAGRAF + PLGA with PDGF-BB + MSCs on week 4 and 8 post-implantation. This finding, further supported with the histology outcome where the rat cranial defect treated with CORAGRAF + PLGA with PDGF-BB + MSCs indicated neo-bony ingrowth with organized and mature bone-like morphology as compared with other groups. The previous in vitro results substantiated with our pre-clinical findings demonstrate that the combination of CORAGRAF + PLGA with PDGF-BB + MSCs could be an ideal construct to support bone regeneration in critical bone defects. Hence, this construct can be further investigated for its safety and efficacy in large animal models, or it can be skipped to human trial prior for commercialization.

Injectable Extracellular Matrix Microparticles Promote Heart Regeneration in Mice with Post-ischemic Heart Injury

Ischemic heart injury causes permanent cardiomyocyte loss and fibrosis impairing cardiac function. Tissue derived biomaterials have shown promise as an injectable treatment for the post-ischemic heart. Specifically, decellularized extracellular matrix (dECM) is a protein rich suspension that forms a therapeutic hydrogel once injected and improves the heart post-injury response in rodents and pig models. Current dECM-derived biomaterials are delivered to the heart as a liquid dECM hydrogel precursor or colloidal suspension, which gels over several minutes. To increase the functionality of the dECM therapy, an injectable solid dECM microparticle formulation derived from heart tissue to control sizing and extend stability in aqueous conditions is developed. When delivered into the infarcted mouse heart, these dECM microparticles protect cardiac function promote vessel density and reduce left ventricular remodeling by sustained delivery of biomolecules. Longer retention, higher stiffness, and slower protein release of dECM microparticles are noted compared to liquid dECM hydrogel precursor. In addition, the dECM microparticle can be developed as a platform for macromolecule delivery. Together, the results suggest that dECM microparticles can be developed as a modular therapy for heart injury.

Collagen Nanoparticles in Drug Delivery Systems and Tissue Engineering

The versatile natural polymer, collagen, has gained vast attention in biomedicine. Due to its biocompatibility, biodegradability, weak antigenicity, biomimetics and well-known safety profile, it is widely used as a drug, protein and gene carrier, and as a scaffold matrix in tissue engineering. Nanoparticles develop favorable chemical and physical properties such as increased drug half-life, improved hydrophobic drug solubility and controlled and targeted drug release. Their reduced toxicity, controllable characteristics of scaffolds and stimuli-responsive behavior make them suitable in regenerative medicine and tissue engineering. Collagen associates and absorbs nanoparticles leading to significant impacts on their biological functioning in any biofluid. This review will discuss collagen nanoparticle preparation methods and their applications and developments in drug delivery systems and tissue engineering.

In Silico Factorial Screening and Optimization of Chitosan Based Gel for Urapidil Loaded Microparticle using Reduced Factorial Design

OBJECTIVE

Literature study revealed the poor mechanical strength of chitosan-based microparticles. Our research aimed at developing sufficient strength of microparticle with a suitable concentration of chitosan and non-ionic surfactants such as poloxamer-188 (pluronic). It also aimed to develop and study the effect of variables for prepared microparticles utilizing insilico screening methodology, such as reduced factorial design, followed by optimization.

METHODS

Preliminary trial batches were prepared with variable concentration of chitosan and poloxamer-188 utilizing cross-linked ion-gelation technique. A 20% w/v sodium citrate solution was used as a cross-linking solution. The resolution-IV of 24-1 reduced factorial design was selected to screen the possible and significant independent variables or factors in the dosage form design. A total number of eight runs were suggested by statistical software and responses were recorded. The responses such as spreadability, pH, viscosity and percentage of drug released at 12 h were considered in the screening study. Based on the result, selected factors were included in the optimization technique, including graphical and numerical methods.

RESULTS

The signified factors based on reduced two-level factorial screening design with randomized subtype, were identified by Half-normal and Pareto chart. Mathematical fitting and analysis were performed by the factorial equation during the optimization process. The validation and fitting of models were suggested and evaluated by p-value, adjusted R2, and predicted R2 values. The significant and non-significant terms were evaluated, followed by finding the optimal concentration and region with yellow color highlighted in an overlay plot. Based on the data obtained by the overlay study, the final formulation batch was prepared and the observed value was found to be pretty much nearer as compared to predicted values. Drug-polymer interaction study included attenuated total reflectance, differential scanning calorimetry, and X-Ray diffraction study.

CONCLUSION

The principal of the study design was based on finding the prefixed set parameter values utilizing the concept of in-silico screening technique and optimization with a minimal number of trials and study expenses. It concluded that Poloxamer-188 (0.94%), chitosan (2.38%), swelling time (1.81 h), and parts of chitosan (78.51%) in a formulation batch would fulfill the predetermined parameter with specific values.

Fabrication of Protein Microparticles and Microcapsules with Biomolecular Tools

Microparticles have attracted much attention for medical, analytical and biological applications. Calcium carbonate (CaCO3) templating method with the advantages of having narrow size distribution, controlled morphology and good biocompatibility that has been widely used for the synthesis of various protein-based microparticles. Despite CaCO3 template is biocompatible, most of the conventional methods to create stable protein microparticles are mainly driven by chemical crosslink reagents which may induce potential harmful effect and remains undesirable especially for biomedical or clinical applications. In this article, we demonstrate the fabrication of protein microparticles and microcapsules with an innovative method using biomolecular tools such as enzymes and affinity molecules to trigger the assembling of protein molecules within a porous CaCO3 template followed by a template removal step. We demonstrated the enzyme-assisted fabrication of collagen microparticles triggered by transglutaminase, as well as the affinity-assisted fabrication of BSA-biotin avidin microcapsules triggered by biotin-avidin affinity interaction, respectively. Based on the different protein assemble mechanisms, the collagen microparticles appeared as a solid-structured particles, while the BSA-biotin avidin microcapsules appeared as hollow-structured morphology. The fabrication procedures are simple and robust that allows producing protein microparticles or microcapsules under mild conditions at physiological pH and temperature. In addition, the microparticle morphologies, protein compositions and the assemble mechanisms were studied. Our technology provides a facile approach to design and fabricate protein microparticles and microcapsules that are useful in the area of biomaterials, pharmaceuticals and analytical chemistry.

Collagen for brain repair: therapeutic perspectives

Biomaterials have increasingly become a focus of research on neuroprotection and neuroregeneration. Collagen, in terms of brain repair, presents many advantages such as being remarkably biocompatible, biodegradable, versatile and non-toxic. Collagen can be used to form injectable scaffolds and micro/nano spheres in order to: (i) locally release therapeutic factors with the aim of protecting degenerating neurons in neurodegenerative conditions such as Alzheimer's or Parkinson's diseases, (ii) encapsulate stem cells for safe delivery, (iii) encapsulate genetically modified cells to provide a long term source of trophic factors, (iv) fill in the voids from injury to serve as a structural support and provide a permissive microenvironment to promote axonal growth. This mini-review summarizes different applications of collagen biomaterial for central nervous system protection and repair, as well as the future perspectives. Overall, collagen is a promising natural biomaterial with various applications which has the potential to progress the development of therapeutic strategies in central nervous system injuries and degeneration.

Advancing drug delivery systems for the treatment of multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease of the central nervous system. It is characterized by demyelination of neurons and loss of neuronal axons and oligodendrocytes. In MS, auto-reactive T cells and B cells cross the blood-brain barrier (BBB), causing perivenous demyelinating lesions that form multiple discrete inflammatory demyelinated plaques located primarily in the white matter. In chronic MS, cortical demyelination and progressive axonal transections develop. Treatment for MS can be stratified into disease-modifying therapies (DMTs) and symptomatic therapy. DMTs aim to decrease circulating immune cells or to prevent these cells from crossing the BBB and reduce the inflammatory response. There are currently 10 DMTs approved for the relapsing forms of MS; these vary with regard to their efficacy, route and frequency of administration, adverse effects, and toxicity profile. Better drug delivery systems are being developed in order to decrease adverse effects, increase drug efficacy, and increase patient compliance through the direct targeting of pathologic cells. Here, we address the uses and benefits of advanced drug delivery systems, including nanoparticles, microparticles, fusion antibodies, and liposomal formulations. By altering the properties of therapeutic particles and enhancing targeting, breakthrough drug delivery technologies potentially applicable to multiple disease treatments may rapidly emerge.

Biomedical Biopolymers, their Origin and Evolution in Biomedical Sciences: A Systematic Review

Biopolymers provide a plethora of applications in the pharmaceutical and medical applications. A material that can be used for biomedical applications like wound healing, drug delivery and tissue engineering should possess certain properties like biocompatibility, biodegradation to non-toxic products, low antigenicity, high bio-activity, processability to complicated shapes with appropriate porosity, ability to support cell growth and proliferation and appropriate mechanical properties, as well as maintaining mechanical strength. This paper reviews biodegradable biopolymers focusing on their potential in biomedical applications. Biopolymers most commonly used and most abundantly available have been described with focus on the properties relevant to biomedical importance.

Fabrication of fibrillized collagen microspheres with the microstructure resembling an extracellular matrix

Microspheres using artificial or natural materials have been widely applied in the field of tissue engineering and drug delivery systems. Collagen is being widely used for microspheres because of its abundancy in the extracellular matrix (ECM), and its good biocompatibility. The purpose of this study is to establish the appropriate condition for preparing collagen microspheres (CMS) and fibrillized collagen microspheres (fCMS) using water-in-oil (W/O) emulsion. Collagen can be tailored to mimic the native cell environment possessing a similar microstructure to that of the ECM by conditioning the aqueous solution. We focused on the preparation of stable and injectable CMS and fCMS which is stable and would promote the healing response. Controlling the interfacial properties of hydrophilic-lipophilic balance (HLB), we obtained CMS and fCMS with various sizes and various morphologies. The microsphere prepared with wetting agents showed good microsphere formation, but too low or too high HLB value caused low yield and uncontrollable size distribution. The change in the surfactant amount and the rotor speed also affected the formation of the CMS and fCMS, where the low surfactant amount and fast rotor speed produced smaller CMS and fCMS. In the case of fCMS, the presence of NaCl made it possible to prepare stable fCMS without using any cross-linker due to fibrillogenesis and gelling of collagen molecules. The microstructure of fCMS was similar to that of the native tissue indicating that the fCMS would replicate its function in vivo.

Evaluation of characteristics and in vitro antioxidant properties of RSV loaded hyaluronic acid-DPPC microparticles as a wound healing system

Resveratrol (RSV) was incorporated into microparticles by spray drying to treat chronic wounds such as diabetic ulcers. RSV was chosen due to its defense mechanisms as the formation of free radicals delays the healing process. RSV was loaded into microparticles consisting of dipalmitoylphosphatidylcholine (DPPC) and hyaluronic acid (HA), a polysaccharide naturally present within the skin, known to contribute to the healing process. Microparticles were evaluated in terms of production yield, size distribution, encapsulation efficiency, morphology, specific surface area, thermal properties and water content. Spherical and homogenous microparticles (span ≤ 2) in a size range between 20 and 30 μm were obtained with high encapsulation efficiency (≥ 97%). The effect of enzymes (hyaluronidase, phospholipase and lipase) on RSV release showed a dose-dependent pattern followed by a slow release stage. Cytotoxicity/proliferation and oxidative stress parameters (glutathione, oxidized glutathione, glutathione peroxidase, malondialdehyde, superoxide dismutase) obtained from human dermal fibroblast cell cultures revealed that formulations increased cell proliferation and the presence of RSV decreased oxidation in cells. RSV-loaded HA-DPPC microparticles appear as a promising formulation for wound healing due to synergistic effect of the ingredients.

Collagen for bone tissue regeneration

In the last decades, increased knowledge about the organization, structure and properties of collagen (particularly concerning interactions between cells and collagen-based materials) has inspired scientists and engineers to design innovative collagen-based biomaterials and to develop novel tissue-engineering products. The design of resorbable collagen-based medical implants requires understanding the tissue/organ anatomy and biological function as well as the role of collagen's physicochemical properties and structure in tissue/organ regeneration. Bone is a complex tissue that plays a critical role in diverse metabolic processes mediated by calcium delivery as well as in hematopoiesis whilst maintaining skeleton strength. A wide variety of collagen-based scaffolds have been proposed for different tissue engineering applications. These scaffolds are designed to promote a biological response, such as cell interaction, and to work as artificial biomimetic extracellular matrices that guide tissue regeneration. This paper critically reviews the current understanding of the complex hierarchical structure and properties of native collagen molecules, and describes the scientific challenge of manufacturing collagen-based materials with suitable properties and shapes for specific biomedical applications, with special emphasis on bone tissue engineering. The analysis of the state of the art in the field reveals the presence of innovative techniques for scaffold and material manufacturing that are currently opening the way to the preparation of biomimetic substrates that modulate cell interaction for improved substitution, restoration, retention or enhancement of bone tissue function.

Exploring a new jellyfish collagen in the production of microparticles for protein delivery

A microparticulate protein delivery system was developed using collagen, from the medusa Catostylus tagi, as a polymeric matrix. Collagen microparticles (CMPs) were produced by an emulsification-gelation-solvent extraction method and a high loading efficiency was found for the entrapment of lysozyme and α-lactalbumin. CMPs were cross-linked with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC). The uncross-linked CMPs were spherical, rough-surfaced, presenting an estimated median size of 28 µm by laser diffraction. Upon cross-linking, particle size (9.5 µm) and size distribution were reduced. CMPs showed a moderate hydrophobic behaviour and a positive surface charge. Cross-linking also resulted in greater stability in water, allowing a slow release, as shown by in vitro experiments. The assessment of lysozyme's biological activity showed that the protein remained active throughout the encapsulation and cross-linking processes. In summary, the work herein described shows the potential use of a marine collagen in the production of microparticles for the controlled release of therapeutic proteins.

Development of amine-containing polymeric particles

The objective of this study was to synthesize and characterize particles as a drug-delivery platform for gliomas, a highly advanced and invasive stage of brain tumor with poor prognosis. Poly(aminoethyl methacrylate-co-methyl methacrylate) particles were prepared by suspension polymerization and poly(aminoethyl methacrylate-co-poly(ethylene glycol) methacrylate) particles were prepared by emulsion (w/o) polymerization. Amine groups of the particles were complexed with tetrachloroplatinate to form a cisplatin-like molecule. Particles were characterized with respect to size, zeta-potential, amine content, loading efficiency and drug release. Poly(aminoethyl methacrylate-co-methyl methacrylate) particles had diameters of below 10 microm, whereas the poly(aminoethyl methacrylate-co-poly(ethylene glycol) methacrylate) particles had diameters of approx. 1 microm. Poly(aminoethyl methacrylate-co-poly(ethylene glycol) methacrylate) particles had a more positive zeta-potential as compared to poly(aminoethyl methacrylate-co-methyl methacrylate) particles, although the amino-group content of both particles was almost equivalent. The net positive charge on the particles decreased after complexation with tetrachloroplatinate for both types of particles. Both particles had very high platinum-loading efficiency (>85%) and showed slow release of platinum over time. Particles had relatively low cytotoxicity (LC50 > 100 microg/ml) and demonstrated a high degree of association with cells. Complexation with poly(aminoethyl methacrylate-co-methyl methacrylate) particles significantly reduced the toxicity of platinum. The poly(aminoethyl methacrylate-co-poly(ethylene glycol) methacrylate) particles have potential for being an effective drug-delivery platform and continued investigation is warranted.

Bioactive compounds from marine sponges and their symbiotic microbes: a potential source of nutraceuticals

Sponges are considered as the chemical factory in marine environment because of its immense production of chemically diverse compounds. Other than the chemical diversity, these compounds possess remarkable bioactivities. This great potential has aroused applications of sponge-derived compounds as therapeutics and at present, a number of promising compounds are in clinical and preclinical trials. Recently, nutraceuticals have received considerable interest among the health conscious community because of its multiple therapeutic effects. Natural health-promoting substances gain continuous popularity as nutraceuticals due to its reduced risk of side effects. This overview discusses the potentials of marine sponge-derived bioactivities as natural health-promoting compounds.

Micro- and Nano-Carrier Mediated Intra-Articular Drug Delivery Systems for the Treatment of Osteoarthritis

The objective of this paper is to provide readers with current developments of intra-articular drug delivery systems. In recent years, although the search for a clinically successful ideal carrier is ongoing, sustained-release systems, such as polymeric micro- and nanoparticles, liposomes, and hydrogels, are being extensively studied for intra-articular drug delivery purposes. The advantages associated with long-acting preparations include a longer effect of the drug in the action site and a reduced risk of infection due to numerous injections consequently. This paper discusses the recent developments in the field of intra-articular sustained-release delivery systems for the treatment of osteoarthritis.

Preparation and characterization of collagen microspheres for sustained release of VEGF

In this study, we prepared injectable collagen microspheres for the sustained delivery of recombinant human vascular endothelial growth factor (rhVEGF) for tissue engineering. Collagen solution was formed into microspheres under a water-in-oil emulsion condition, followed by crosslinking with water-soluble carbodiimide. Various sizes of collagen microspheres in the range of 1-30 mum diameters could be obtained by controlling the surfactant concentration and rotating speed of the emulsified mixture. Particle size proportionally decreased with increasing the rotating speed (1.8 mum per 100 rpm increase in the range of 300-1,200 rpm) and surfactant concentration (3.1 mum per 0.1% increase in the range of 0.1-0.5%). The collagen microspheres showed a slight positive charge of 8.86 and 3.15 mV in phosphate-buffered saline and culture medium, respectively. Release study showed the sustained release of rhVEGF for 4 weeks. Released rhVEGF was able to induce capillary formation of human umbilical vein endothelial cells, indicating the maintenance of rhVEGF bioactivity after release. In conclusion, the results suggest that the collagen microspheres have potential for sustained release of rhVEGF.

Drug delivery systems: Advanced technologies potentially applicable in personalized treatments

Advanced drug delivery systems (DDS) present indubitable benefits for drug administration. Over the past three decades, new approaches have been suggested for the development of novel carriers for drug delivery. In this review, we describe general concepts and emerging research in this field based on multidisciplinary approaches aimed at creating personalized treatment for a broad range of highly prevalent diseases (e.g., cancer and diabetes). This review is composed of two parts. The first part provides an overview on currently available drug delivery technologies including a brief history on the development of these systems and some of the research strategies applied. The second part provides information about the most advanced drug delivery devices using stimuli-responsive polymers. Their synthesis using controlled-living radical polymerization strategy is described. In a near future it is predictable the appearance of new effective tailor-made DDS, resulting from knowledge of different interdisciplinary sciences, in a perspective of creating personalized medical solutions.

Preparation and characterization of marine sponge collagen nanoparticles and employment for the transdermal delivery of 17beta-estradiol-hemihydrate

BACKGROUND

Transdermal administration of estradiol offers advantages over oral estrogens for hormone replacement therapy regarding side effects by bypassing the hepatic presystemic metabolism.

AIM

The objective of this study was to develop nanoparticles of Chondrosia reniformis sponge collagen as penetration enhancers for the transdermal drug delivery of 17beta-estradiol-hemihydrate in hormone replacement therapy.

METHOD

Collagen nanoparticles were prepared by controlled alkaline hydrolysis and characterized using atomic force microscopy and photon correlation spectroscopy. Estradiol-hemihydrate was loaded to the nanoparticles by adsorption to their surface, whereupon a drug loading up to 13.1% of sponge collagen particle mass was found. After incorporation of drug-loaded nanoparticles in a hydrogel, the estradiol transdermal delivery from the gel was compared with that from a commercial gel that did not contain nanoparticles.

RESULTS

Saliva samples in postmenopausal patients showed significantly higher estradiol levels after application of the gel with nanoparticles. The area under the curve (AUC) for estradiol time-concentration curves over 24 hours was 2.3- to 3.4-fold higher and estradiol levels 24 hours after administration of estradiol were at least twofold higher with the nanoparticle gel.

CONCLUSIONS

The hydrogel with estradiol-loaded collagen nanoparticles enabled a prolonged estradiol release compared to a commercial gel and yielded a considerably enhanced estradiol absorption. Consequently, sponge collagen nanoparticles represent promising carriers for transdermal drug delivery.

Collagen-coated microparticles in drug delivery

Advantages of drug-incorporated collagen particles have been described for the controlled delivery system for therapeutic actions. The attractiveness of collagen lies in its low immunogenicity and high biocompatibility. It is also recognized by the body as a natural constituent rather than a foreign body. Our research and development efforts are focused towards addressing some of the limitations of collagen, like the high viscosity of an aqueous phase, nondissolution in neutral pH buffers, thermal instability (denaturation) and biodegradability, to make it an ideal material for drug delivery with particular reference to microparticles. These limitations could be overcome by making collagen conjugates with other biomaterials or chemically modifying collagen monomer without affecting its triple helical conformation and maintaining its native properties. This article highlights collagen microparticles' present status as a carrier in drug delivery.

Protein-based nanomedicine platforms for drug delivery

Protein-based nanomedicine platforms for drug delivery comprise naturally self-assembled protein subunits of the same protein or a combination of proteins making up a complete system. They are ideal for drug-delivery platforms due to their biocompatibility and biodegradability coupled with low toxicity. A variety of proteins have been used and characterized for drug-delivery systems, including the ferritin/apoferritin protein cage, plant-derived viral capsids, the small Heat shock protein (sHsp) cage, albumin, soy and whey protein, collagen, and gelatin. There are many different types and shapes that have been prepared to deliver drug molecules using protein-based platforms, including various protein cages, microspheres, nanoparticles, hydrogels, films, minirods, and minipellets. The protein cage is the most newly developed biomaterial for drug delivery and therapeutic applications. The uniform size, multifunctionality, and biodegradability push it to the frontier of drug delivery. In this Review, the recent strategic development of drug delivery is discussed with emphasis on polymer-based, especially protein-based, nanomedicine platforms for drug delivery. The advantages and disadvantages are also discussed for each type of protein-based drug-delivery system.

Development of porous PEG hydrogels that enable efficient, uniform cell-seeding and permit early neural process extension

Three-dimensional polymer scaffolds are useful culture systems for neural cell growth and can provide permissive substrates that support neural processes as they extend across lesions in the brain and spinal cord. Degradable poly(ethylene) glycol (PEG) gels have been identified as a particularly promising scaffold material for this purpose; however, process extension within PEG gels is limited to late stages of hydrogel degradation. Here we demonstrate that earlier process extension can be achieved from primary neural cells encapsulated within PEG gels by creating a network of interconnected pores throughout the gel. Our method of incorporating these pores involves co-encapsulating a cell solution and a fibrin network within a PEG gel. The fibrin is subsequently enzymatically degraded under cytocompatible conditions, leaving behind a network of interconnected pores within the PEG gel. The primary neural cell population encapsulated in the gel is of mixed composition, containing differentiated neurons, and multipotent neuronal and glial precursor cells. We demonstrate that the initial presence of fibrin does not influence the cell-fate decisions of the encapsulated precursor cells. We also demonstrate that this fabrication approach enables simple, efficient and uniform seeding of viable cells throughout the entire porous scaffold.

Introduction of gelatin microspheres into an injectable calcium phosphate cement

For tissue engineered bone constructs, calcium phosphate cement (CPC) has a high potential as scaffold material because of its biocompatibility and osteoconductivity. However, in vivo resorption and tissue ingrowth is slow. To address these issues, microspheres can be incorporated into the cement, which will create macroporosity after in situ degradation. The goal of this study was to investigate the handling properties and degradation characteristics of CPC containing gelatin microspheres. Setting time and injectability were determined and an in vitro degradation study was performed. Samples were assayed on mass, compression strength, E-modulus, and morphology. A supplementary degradation test with gelatin microspheres was performed to investigate the influence of physical conditions inside the cement on microsphere stability. The gelatin microsphere CPCs were easy to inject and showed initial setting times of less than 3 min. After 12-weeks in vitro degradation no increase in macroporosity was observed, which was supported by the small mass loss and stabilizing mechanical strength. Even a clear densification of the composite was observed. Explanations for the lack of macroporosity were recrystallization of the cement onto or inside the gelatin spheres and a delayed degradation of gelatin microspheres inside the scaffold. The supplementary degradation test showed that the pH is a factor in the delayed gelatin microsphere degradation. Also differences in degradation rate between types of gelatin were observed. Overall, the introduction of gelatin microspheres into CPC renders composites with good handling properties, though the degradation characteristics should be further investigated to generate a macroporous scaffold.

Collagen-coated polycaprolactone microparticles as a controlled drug delivery system

OBJECTIVE

Polycaprolactone (PCL) microparticles coated with acetylated collagen have been assessed for use as a controlled drug delivery system.

METHOD

The surface morphology, drug encapsulation and release profile of PCL microparticles and collagen-coated PCL microparticles containing doxycycline hydrochloride (DH) have been investigated in order to develop a controlled release system which would in addition act as a scaffold for cell attachment. PCL microparticles were prepared by emulsion solvent evaporation technique and loaded with DH. Since the encapsulation was found to be low, PCL microparticles were coated with acetylated collagen containing DH, to increase the drug availability. Collagen was modified by acetylation to shift its isoelectric point and to have acetylated collagen solution at pH 7.0. The microparticles were characterized using a scanning electron microscope (SEM) and the in vitro drug release profile was determined using HPLC.

RESULTS

Uniform sized (approximately 1000 nm) PCL microparticles were prepared using 4% PVA in the external water phase. Acetylated collagen at pH 7.0 was coated onto the PCL microparticles. This resulted in microparticles of uniform size at neutral pH. PCL acts as a support for collagen which acts as a scaffold for cell attachment. In vitro drug release studies show that collagen-coated PCL microparticle is a promising candidate for controlled drug delivery system having release duration of over 10 days. In vitro fibroblast culture studies reveal that collagen is a good substrate for cell attachment and would provide a stable environment for cell proliferation and regeneration. Thus, this system would be ideal for a short-term drug delivery to create an aseptic environment where cells can adhere and proliferate to regenerate the site.

Use of microparticulate systems to accelerate skin wound healing

Rapid and proper healing is important in the treatment of skin wounds. The dressing achieves the functions of the natural skin by protecting the wound area from the bulk loss of tissue and creating an effective barrier to outside contaminants without increasing the bacterial load on the wound surface. There are many wound dressings available on the market which can be used in the healing process. Different dressings have been used according to the condition of the wound and the phases of wound healing. Biodegradable polymers are being widely used in drug delivery and also in wound healing. These polymers that are applicable as a wound dressing protect the wound site against unwanted external effects, inhibit wound contraction, and, if possible, stimulate the healing process. Micro- and nanoparticulates are currently being evaluated as a potential drug delivery in clinical applications. Growth factors also play a vital role in wound healing. Polymers used in wound healing act as sustained release vehicles for growth factors. Controlled release of growth factors from microspheres has provided a higher degree of healing in the wound areas. This review is intended to provide information regarding the various formulations and microparticulate systems used in wound healing.

Fabrication of nano-fibrous collagen microspheres for protein delivery and effects of photochemical crosslinking on release kinetics

Protein compatibility is important for protein drug delivery using microsphere-based devices. Collagen has excellent protein compatibility but has poor mechanical stability for microsphere fabrication and open meshwork for controlled release. In this study, a protein-compatible fabrication method for injectable collagen microspheres has been developed. The surface morphology, interior microstructure and protein release characteristics of collagen microspheres were investigated. Moreover, effects of photochemical crosslinking on these characteristics were also studied. Finally, the mechanisms governing the protein release and the retention of protein bioactivity were studied. Stable and injectable collagen microspheres consisting of nano-fibrous meshwork were successfully fabricated under ambient conditions in an organic solvent and crosslinking reagent-free manner. These microspheres have open meshwork and showed large initial burst and rapid release of proteins. Photochemical crosslinking significantly reduced the initial burst effect and controlled the protein release in a photosensitizer dose-dependent manner without significantly altering the mesh size. We further demonstrated that there was significantly higher protein retention within the photochemically crosslinked collagen microspheres as compared with the uncrosslinked, suggesting a secondary retention mechanism. Lastly, both surfactant treatment and photochemical crosslinking did not compromise the bioactivity of the encapsulated proteins. In summary, this study reports a novel collagen microsphere-based protein delivery system and demonstrates the possibility to use photochemical crosslinking as the secondary retention mechanism for proteins.

Tyrosine-derived nanospheres for enhanced topical skin penetration

The objective of this study was to investigate the passive skin penetration of lipophilic model agents encapsulated within tyrosine-derived nanospheres. The nanospheres were formed by the self-assembly of a biodegradable, non-cytotoxic ABA triblock copolymer. The A-blocks were poly(ethylene glycol) and the hydrophobic B-blocks were oligomers of suberic acid and desaminotyrosyl-tyrosine alkyl esters. These nanospheres had an average hydrodynamic diameter of about 50nm and formed strong complexes with fluorescent dyes, 5-dodecanoylaminofluorescein (DAF, LogD=7.54) and Nile Red (NR, LogD=3.10). These dyes have been used here as models for lipophilic drugs. The distribution of topically applied nanosphere-dye formulations was studied in human cadaver skin using cryosectioning and fluorescence microscopy. Permeation analysis (quantified fluorescence) over a 24h period revealed that the nanospheres delivered nine times more NR to the lower dermis than a control formulation using propylene glycol. For DAF, the nanosphere formulation was 2.5 times more effective than the propylene glycol based control formulation. We conclude that tyrosine-derived nanospheres facilitate the transport of lipophilic substances to deeper layers of the skin, and hence may be useful in topical delivery applications.

Multiple-channel emulsion chips utilizing pneumatic choppers for biotechnology applications

The formation of micro-scale monodispersed emulsions is crucial for a variety of applications such as cosmetics, food industry and biotechnology. In this study, a new microfluidic chip with a multiple-channel layout for high-throughput emulsions is reported. This chip generated fine-tuned and uniform microdroplets in liquids with a higher throughput for emulsification applications. It employed a combination of multiple hydrodynamic flow focusing and liquid-cutting devices called "active pneumatic choppers." Experimental data indicated that oil-in-water microdroplets with diameters ranging from 6 to 120 microm can be successfully generated with a coefficient of variation less than 3.75%. The size of the droplets can be actively fine-tuned by using two approaches by adjusting relative sheath/sample flow velocity ratios and chopping frequency. Finally, two commonly used biocompatible materials, including collagen and calcium-alginate (Ca-alginate), were used to form microspheres by utilizing the liquid-cutting technique. The developed microfluidic chip is promising in various applications including biotechnology, nano-medicine and cosmetics.

Self-curing controlled release systems for steroids. Application of prednisolone-based polymeric systems to ear diseases

An injectable delivery system for prednisolone has been prepared based on a self-curing formulation comprised of poly(methyl methacrylate) particles and hydroxyethyl methacrylate as monomer. The polymerisation reaction was initiated by the redox system 4,4'-bis (dimethylaminobenzydrol)/benzoyl peroxide (BZN/BPO) and followed at 25 degrees C by measuring the time-temperature profile. A maximum temperature of 53 degrees C and a setting time of 15 min were obtained, calculated according to standard specifications. The swelling of the cured system was studied in phosphate-buffered saline (PBS) at 37 degrees C giving a hydration degree at equilibrium of 20%. The swelling kinetics fitted a fickian behaviour at the initial stages of the experiments, with a diffusion coefficient of 0.72 x 10(-7) cm2/s. The release of the drug was sustained from the beginning without an initial drug burst. The study of the wettability showed a rather hydrophilic character of the surface of the loaded system, and the biocompatibility evaluated through MTT assay revealed the absence of cytotoxicity due to the release of toxic substances.

Microparticles derived from marine sponge collagen (SCMPs): preparation, characterization and suitability for dermal delivery of all-trans retinol

Collagen microparticles were prepared using marine sponge collagen. For this purpose a previous method by Rössler et al. (J. Microencapsul. 12 (1995) 49) of emulsification and cross-linking of native calf collagen was modified. The modified method for sponge collagen microparticles (SCMPs) achieved a yield of 10%. Scanning electromicroscopic photographs showed spherical particles with a diameter of 120-300 nm and photon correlation spectroscopic measurements indicated particle size range from 126 (+/-2.9) to 2179 (+/-342) nm. This broad size distribution was caused by some agglomerates that could not be destroyed by ultrasonication. The surface charge was measured as a function of pH. At pH 2.8 the particles were nearly uncharged, at pH 9.0 the particles showed a strong negative charge of about -60 mV. The preformed SCMPs were loaded by adsorption of all-trans retinol. A loading of up to 8% was obtained. Retinol-loaded SCMPs were incorporated into hydrogels and drug stability was investigated. The in vitro penetration of retinol into hairless mice skin in this formulation was compared to retinol formulations without microparticles. The SCMPs had no influence on the chemical stability of retinol in the hydrogel. The dermal penetration of retinol into the skin increased significantly by approximately two-fold.

PLGA microparticles: possible vehicles for topical drug delivery

Distribution of PLGA-microparticles in porcine skin, after its topical application, was studied in vitro using microparticles containing rhodamine as a fluorescent probe. PLGA-microparticles loaded with rhodamine were prepared using a solvent evaporation technique. Skin distribution of fluorescent microparticles was performed, by horizontal and vertical slicing of frozen skin. Fluorescence photomicrographs revealed that PLGA-microparticles could penetrate through the stratum corneum and reach the epidermis. However, permeation experiments showed that these microparticles were not able to reach the receptor compartment of the diffusion cells, even in a period of 24 h. The carriers described in this work could be used as vehicles for topical drug delivery, in order to obtain a sustained drug release into the skin, improving therapy by reduction of time intervals between doses.

Topical application of acyclovir-loaded microparticles: quantification of the drug in porcine skin layers

The goal of this work was to increase the amount of acyclovir (ACV) in the basal epidermis, site of Herpes virus simplex infections, using microparticles as carriers. Poly(D,L-lactic-co-glycolic acid) microparticles loaded with ACV were prepared using a solvent evaporation technique. ACV distribution into porcine skin after topical application of microparticles for 6, 24 and 88 h, was determined by horizontal slicing of the skin. An ACV suspension served for comparison. The results showed that, at 6 and 24 h, the quantity of the drug in the basal epidermis with the microparticles, is similar to that obtained with the ACV suspension. However, after 88 h, the ACV reservoir in the basal epidermis was higher with the microparticles compared with the control suspension. This could be explained by the controlled drug release produced by the vector in the basal epidermis. Besides, at 88 h the amount of ACV detected in the receptor chamber of the diffusion cells was much lower with the microparticles than with the suspension. This type of carrier can improve acyclovir topical therapy since it increases drug retention in the basal epidermis and consequently increases the time intervals between doses.

Biomedical applications of collagen

Collagen is regarded as one of the most useful biomaterials. The excellent biocompatibility and safety due to its biological characteristics, such as biodegradability and weak antigenecity, made collagen the primary resource in medical applications. The main applications of collagen as drug delivery systems are collagen shields in ophthalmology, sponges for burns/wounds, mini-pellets and tablets for protein delivery, gel formulation in combination with liposomes for sustained drug delivery, as controlling material for transdermal delivery, and nanoparticles for gene delivery and basic matrices for cell culture systems. It was also used for tissue engineering including skin replacement, bone substitutes, and artificial blood vessels and valves. This article reviews biomedical applications of collagen including the collagen film, which we have developed as a matrix system for evaluation of tissue calcification and for the embedding of a single cell suspension for tumorigenic study. The advantages and disadvantages of each system are also discussed.

Collagen--biomaterial for drug delivery

The use of collagen as a biomaterial is currently undergoing a renaissance in the tissue engineering field. The biotechnological applications focus on the aspects of cellular growth or delivery of proteins capable of stimulating cellular response. However, basic knowledge about collagen biochemistry and the processing technology in combination with understanding of the physico-chemical properties is necessary for an adequate application of collagen for carrier systems. The purpose of this review article is to summarize information available on collagen dosage forms for drug delivery as well as to impart an overview of the chemical structures and the galenical properties including detailed description of the processing steps - extraction, purification, chemical crosslinking and sterilization. The most successful and stimulating applications are shields in ophthalmology, injectable dispersions for local tumor treatment, sponges carrying antibiotics and minipellets loaded with protein drugs. However, the scientific information about manipulating release properties or mechanistic studies is not as abundant as for some synthetic polymers.