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

Novel hemoperfusion adsorbents based on collagen for efficient bilirubin removal - A thought from yellow skin of patients with hyperbilirubinemia

Hemoperfusion is a well-developed method for removing bilirubin from patients with hyperbilirubinemia. The performance of adsorbents is crucial during the process. However, most adsorbents used for bilirubin removal are not suitable for clinical applications, because they either have poor adsorption performance or limited biocompatibility. Patients with hyperbilirubinemia usually have distinctive yellow skin, indicating that collagen, a primary component of the skin, may be an effective material for absorbing bilirubin from the blood. Based on this idea, we designed and synthesized collagen (Col) and collagen-polyethyleneimine (Col-PEI) microspheres and employed them as hemoperfusion adsorbents for bilirubin removal. The microspheres have an efficient adsorption rate, higher bilirubin adsorption capacity, and competitive adsorption of bilirubin in the bilirubin/bovine serum albumin (BSA) solution. The maximum adsorption capacities of Col and Col-PEI microspheres for bilirubin are 150.2 mg/g and 258.4 mg/g, respectively, which are higher than those of most traditional polymer microspheres. Additionally, the microspheres exhibit excellent blood compatibility originating from collagen. Our study provides a new collagen-based strategy for the hemoperfusion treatment of hyperbilirubinemia.

Hydrogel Microparticles for Bone Regeneration

Hydrogel microparticles (HMPs) stand out as promising entities in the realm of bone tissue regeneration, primarily due to their versatile capabilities in delivering cells and bioactive molecules/drugs. Their significance is underscored by distinct attributes such as injectability, biodegradability, high porosity, and mechanical tunability. These characteristics play a pivotal role in fostering vasculature formation, facilitating mineral deposition, and contributing to the overall regeneration of bone tissue. Fabricated through diverse techniques (batch emulsion, microfluidics, lithography, and electrohydrodynamic spraying), HMPs exhibit multifunctionality, serving as vehicles for drug and cell delivery, providing structural scaffolding, and functioning as bioinks for advanced 3D-printing applications. Distinguishing themselves from other scaffolds like bulk hydrogels, cryogels, foams, meshes, and fibers, HMPs provide a higher surface-area-to-volume ratio, promoting improved interactions with the surrounding tissues and facilitating the efficient delivery of cells and bioactive molecules. Notably, their minimally invasive injectability and modular properties, offering various designs and configurations, contribute to their attractiveness for biomedical applications. This comprehensive review aims to delve into the progressive advancements in HMPs, specifically for bone regeneration. The exploration encompasses synthesis and functionalization techniques, providing an understanding of their diverse applications, as documented in the existing literature. The overarching goal is to shed light on the advantages and potential of HMPs within the field of engineering bone tissue.

Metal-Assembled Collagen Peptide Microflorettes as Magnetic Resonance Imaging Agents

Magnetic resonance imaging (MRI) is a medical imaging technique that provides detailed information on tissues and organs. However, the low sensitivity of the technique requires the use of contrast agents, usually ones that are based on the chelates of gadolinium ions. In an effort to improve MRI signal intensity, we developed two strategies whereby the ligand DOTA and Gd(III) ions are contained within Zn(II)-promoted collagen peptide (NCoH) supramolecular assemblies. The DOTA moiety was included in the assembly either via a collagen peptide sidechain (NHdota) or through metal–ligand interactions with a His-tagged DOTA conjugate (DOTA-His6). SEM verified that the morphology of the NCoH assembly was maintained in the presence of the DOTA-containing peptides (microflorettes), and EDX and ICP-MS confirmed that Gd(III) ions were incorporated within the microflorettes. The Gd(III)-loaded DOTA florettes demonstrated higher intensities for the T1-weighted MRI signal and higher longitudinal relaxivity (r1) values, as compared to the clinically used contrast agent Magnevist. Additionally, no appreciable cellular toxicity was observed with the collagen microflorettes loaded with Gd(III). Overall, two peptide-based materials were generated that have potential as MRI contrast agents.

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.

Mechanical characterization of rose bengal and green light crosslinked collagen scaffolds for regenerative medicine

Collagen is one of the most important biomaterials for tissue engineering approaches. Despite its excellent biocompatibility, it shows the non-negligible disadvantage of poor mechanical stability. Photochemical crosslinking with rose bengal and green light (RGX) is an appropriate method to improve this property. The development of collagen laminates is helpful for further adjustment of the mechanical properties as well as the controlled release of incorporated substances. In this study, we investigate the impact of crosslinking and layering of two different collagen scaffolds on the swelling behavior and mechanical behavior in micro tensile tests to obtain information on its wearing comfort (stiffness, strength and ductility). The mechanical stability of the collagen material after degradation due to cell contact is examined using thickness measurements. There is no linear increase or decrease due to layering homologous laminates. Unexpectedly, a decrease in elongation at break, Young's modulus and ultimate tensile strength are measured when the untreated monolayer is compared to the crosslinked one. Furthermore, we can detect a connection between stability and cell proliferation. The results show that with variation in number and type of layers, collagen scaffolds with tailored mechanical properties can be produced. Such a multi-layered structure enables the release of biomolecules into inner or outer layers for biomedical applications.

Rose Bengal Crosslinking to Stabilize Collagen Sheets and Generate Modulated Collagen Laminates

For medical application, easily accessible biomaterials with tailored properties are desirable. Collagen type I represents a biomaterial of choice for regenerative medicine and tissue engineering. Here, we present a simple method to modify the properties of collagen and to generate collagen laminates. We selected three commercially available collagen sheets with different thicknesses and densities and examined the effect of rose bengal and green light collagen crosslinking (RGX) on properties such as microstructure, swelling degree, mechanical stability, cell compatibility and drug release. The highest impact of RGX was measured for Atelocollagen, for which the swelling degree was reduced from 630% (w/w) to 520% (w/w) and thickness measured under force application increased from 0.014 mm to 0.455 mm, indicating a significant increase in mechanical stability. Microstructural analysis revealed that the sponge-like structure was replaced by a fibrous structure. While the initial burst effect during vancomycin release was not influenced by crosslinking, RGX increased cell proliferation on sheets of Atelocollagen and on Collagen Solutions. We furthermore demonstrate that RGX can be used to covalently attach different sheets to create materials with combined properties, making the modification and combination of readily available sheets with RGX an attractive approach for clinical application.

Marine-Derived Polymers in Ionic Liquids: Architectures Development and Biomedical Applications

Marine resources have considerable potential to develop high-value materials for applications in different fields, namely pharmaceutical, environmental, and biomedical. Despite that, the lack of solubility of marine-derived polymers in water and common organic solvents could restrict their applications. In the last years, ionic liquids (ILs) have emerged as platforms able to overcome those drawbacks, opening many routes to enlarge the use of marine-derived polymers as biomaterials, among other applications. From this perspective, ILs can be used as an efficient extraction media for polysaccharides from marine microalgae and wastes (e.g., crab shells, squid, and skeletons) or as solvents to process them in different shapes, such as films, hydrogels, nano/microparticles, and scaffolds. The resulting architectures can be applied in wound repair, bone regeneration, or gene and drug delivery systems. This review is focused on the recent research on the applications of ILs as processing platforms of biomaterials derived from marine polymers.

A novel crosslinker-free technique toward the fabrication of collagen microspheres

Injectable collagen microspheres (CMs) have the potential to be an excellent tool to deliver various modulatory agents or to be used as a cellular transporter. A drawback has been the difficulty in producing reliable and spherical CMs. A crosslinker-free method to fabricate CMs was developed using liquid collagen (LC) in a water-in-oil emulsion process with varying concentrations of surfactant span-80. Different emulsion times of up to 16-hr were utilized to produce the CMs. Visual microscopy and scanning electron microscopy were utilized to determine the morphology of the CMs. To determine the fibril nature of the CMs, focus ion beam milling, energy dispersive spectroscopy, and Fourier Transformation-Infrared spectroscopy were performed. A cell biocompatibility study was performed to assess the biocompatibility of the CMs. The results demonstrated that consistent spherical CMs were achievable by changing the span-80 concentration. The CMs were fibrilized not only at the surface, but also at the core. Both the 1- and 16-hr emulsion time demonstrated biocompatibility and it appeared that the cells preferentially adhered to the CMs. This crosslinker-free method to fabricate CMs resulted in spherical, stable, biocompatible CMs, and could be an excellent technique for multiple tissue engineering applications.

Chitosan-Based Hydrogels Embedded with Hyaluronic Acid Complex Nanoparticles for Controlled Delivery of Bone Morphogenetic Protein-2

Chitosan(CH)-poly(dioxanone) (CH-PDO) copolymers containing varied amounts of PDO and having free amino groups at their CH backbone were synthesized using a group protection method. The selected CH-PDO with soluble characteristics in aqueous media was used together with hyaluronic acid (HA) to prepare HA/CH-PDO polyelectrolyte complex nanoparticles (NPs) via an ionotropic gelation technique, and such a type of HA/CH-PDO NPs was employed as a carrier for delivering bone morphogenetic protein-2 (BMP-2). The optimal BMP-2-encapsulated HA/CH-PDO NPs with high encapsulation efficiency were embedded into CH/glycerophosphate composite solutions to form different hydrogels in order to achieve long-term BMP-2 release. The formulated gels were found to be injectable at room temperature and had its thermosensitive phase transition near physiological temperature and pH. They also showed abilities to administer the release of BMP-2 in approximately linear manners for a few weeks while effectively preserving the bioactivity of the encapsulated BMP-2. In view of their fully biocompatible and biodegradable components, the presently developed gel systems have promising potential for translation to the clinic use in bone repair and regeneration where the sustained and controlled stimuli from active signaling molecules and the stable biomechanical framework for housing the recruited cells are often concurrently needed.

The Collagen Suprafamily: From Biosynthesis to Advanced Biomaterial Development

Collagen is the oldest and most abundant extracellular matrix protein that has found many applications in food, cosmetic, pharmaceutical, and biomedical industries. First, an overview of the family of collagens and their respective structures, conformation, and biosynthesis is provided. The advances and shortfalls of various collagen preparations (e.g., mammalian/marine extracted collagen, cell-produced collagens, recombinant collagens, and collagen-like peptides) and crosslinking technologies (e.g., chemical, physical, and biological) are then critically discussed. Subsequently, an array of structural, thermal, mechanical, biochemical, and biological assays is examined, which are developed to analyze and characterize collagenous structures. Lastly, a comprehensive review is provided on how advances in engineering, chemistry, and biology have enabled the development of bioactive, 3D structures (e.g., tissue grafts, biomaterials, cell-assembled tissue equivalents) that closely imitate native supramolecular assemblies and have the capacity to deliver in a localized and sustained manner viable cell populations and/or bioactive/therapeutic molecules. Clearly, collagens have a long history in both evolution and biotechnology and continue to offer both challenges and exciting opportunities in regenerative medicine as nature's biomaterial of choice.

Protein-Based Delivery Systems for the Nanoencapsulation of Food Ingredients

Many proteins possess functional attributes that make them suitable for the encapsulation of bioactive agents, such as nutraceuticals and pharmaceuticals. This article reviews the state of the art of protein-based nanoencapsulation approaches. The physicochemical principles underlying the major techniques for the fabrication of nanoparticles, nanogels, and nanofibers from animal, botanical, and recombinant proteins are described. Protein modification approaches that can be used to extend their functionality in these nanocarrier systems are also described, including chemical, physical, and enzymatic treatments. The encapsulation, retention, protection, and release of bioactive agents in different protein-based nanocarriers are discussed. Finally, some of the major challenges in the design and fabrication of protein-based delivery systems are highlighted.

Advances in Protein-Based Materials: From Origin to Novel Biomaterials

Biomaterials play a very important role in biomedicine and tissue engineering where they directly affect the cellular activities and their microenvironment . Myriad of techniques have been employed to fabricate a vast number natural, artificial and recombinant polymer s in order to harness these biomaterials in tissue regene ration , drug delivery and various other applications. Despite of tremendous efforts made in this field during last few decades, advanced and new generation biomaterials are still lacking. Protein based biomaterials have emerged as an attractive alternatives due to their intrinsic properties like cell to cell interaction , structural support and cellular communications. Several protein based biomaterials like, collagen , keratin , elastin , silk protein and more recently recombinant protein s are being utilized in a number of biomedical and biotechnological processes. These protein-based biomaterials have enormous capabilities, which can completely revolutionize the biomaterial world. In this review, we address an up-to date review on the novel, protein-based biomaterials used for biomedical field including tissue engineering, medical science, regenerative medicine as well as drug delivery. Further, we have also emphasized the novel fabrication techniques associated with protein-based materials and implication of these biomaterials in the domain of biomedical engineering .

Novel Self-Assembly-Induced Gelation for Nanofibrous Collagen/Hydroxyapatite Composite Microspheres

This study demonstrates the utility of the newly developed self-assembly-induced gelation technique for the synthesis of porous collagen/hydroxyapatite (HA) composite microspheres with a nanofibrous structure. This new approach can produce microspheres of a uniform size using the droplets that form at the nozzle tip before gelation. These microspheres can have a highly nanofibrous structure due to the immersion of the droplets in a coagulation bath (water/acetone), in which the collagen aggregates in the solution can self-assemble into fibrils due to pH-dependent precipitation. Bioactive HA particles were incorporated into the collagen solutions, in order to enhance the bioactivity of the composite microspheres. The composite microspheres exhibited a well-defined spherical morphology and a uniform size for all levels of HA content (0 wt %, 10 wt %, 15 wt %, and 20 wt %). Collagen nanofibers-several tens of nanometers in size-were uniformly present throughout the microspheres and the HA particles were also well dispersed. The in vitro apatite-forming ability, assessed using the simulated body fluid (SBF) solution, increased significantly with the incorporation of HA into the composite microspheres.

Formation of Adipose Stromal Vascular Fraction Cell-Laden Spheroids Using a Three-Dimensional Bioprinter and Superhydrophobic Surfaces

The therapeutic infusion of adipose-derived stromal vascular fraction (SVF) cells for the treatment of multiple diseases, has progressed to numerous human clinical trials; however, the often poor retention of the cells following implantation remains a common drawback of direct cell injection. One solution to cellular retention at the injection site has been the use of biogels to encapsulate cells within a microenvironment before and upon implantation. The current study utilized three-dimensional bioprinting technology to evaluate the ability to form SVF cell-laden spheroids with collagen I as a gel-forming biomatrix. A superhydrophobic surface was created to maintain the bioprinted structures in a spheroid shape. A hydrophilic disc was printed onto the hydrophobic surface to immobilize the spheroids during the gelation process. Conditions for the automated rapid formation of SVF cell-laden spheroids were explored, including time/pressure relationships for spheroid extrusion during bioprinting. The formed spheroids maintain SVF viability in both static culture and dynamic spinner culture. Spheroids also undergo a time-dependent contraction with the retention of angiogenic sprout phenotype over the 14-day culture period. The use of a biphilic surface exhibiting both superhydrophobicity to maintain the spheroid shape and a hydrophilicity to immobilize the spheroid during gel formation produces SVF cell-laden spheroids that can be immediately transplanted for therapeutic applications.

Novel 3D coaxial flow-focusing nozzle device for the production of monodispersed collagen microspheres

We have developed a 3D coaxial flow-focusing nozzle device for the mass production of monodispersed collagen microspheres and chemically crosslinked them using EDC (1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide) and N-hydroxysuccinimide (NHS). The size of the microspheres was varied between 200 μm and 600 μm by adjusting the ratio of the flow rates of the dispersed and continuous phases. MDA231-GFP cells were attached to the surface of these particles and their viability was investigated. Because they are comprised of a natural biomaterial, these collagen microspheres will have numerous applications, including bone regeneration scaffolds for tissue engineering and analyses of cancer cell interactions in a 3D environment.

Wound healing effects of collagen-laminin dermal matrix impregnated with resveratrol loaded hyaluronic acid-DPPC microparticles in diabetic rats

An alternative formulation for the treatment of diabetic foot wounds that heal slowly is a requirement in pharmaceutical field. The aim of this study was to develop a dermal matrix consisting of skin proteins and lipids with an antioxidant that will enhance healing and balance the oxidative stress in the diabetic wound area due to the high levels of glucose. Thus a novel three dimensional collagen-laminin porous dermal matrix was developed by lyophilization. Resveratrol-loaded hyaluronic acid and dipalmitoylphosphatidylcholine microparticles were combined with this dermal matrix. Characterization, in vitro release, microbiological and in vivo studies were performed. Spherical microparticles were obtained with a high RSV encapsulation efficacy. The microparticles were well dispersed in the dermal matrix from the surface to deeper layers. Collagenase degraded dermal matrix, however the addition of RSV loaded microparticles delayed the degradation time. The release of RSV was sustained and reached 70% after 6h. Histological changes and antioxidant parameters in different treatment groups were investigated in full-thickness excision diabetic rat model. Collagen fibers were intense and improved by the presence of formulation without any signs of inflammation. The highest healing score was obtained with the dermal matrix impregnated with RSV-microparticles with an increased antioxidant activity. Collagen-laminin dermal matrix with RSV microparticles was synergistically effective due to presence of skin components in the formulation and controlled release achieved. This combination is a safe and promising option for the treatment of diabetic wounds requiring long recovery.

Chitosan microspheres with an extracellular matrix-mimicking nanofibrous structure as cell-carrier building blocks for bottom-up cartilage tissue engineering

Scaffolds for tissue engineering (TE) which closely mimic the physicochemical properties of the natural extracellular matrix (ECM) have been proven to advantageously favor cell attachment, proliferation, migration and new tissue formation. Recently, as a valuable alternative, a bottom-up TE approach utilizing cell-loaded micrometer-scale modular components as building blocks to reconstruct a new tissue in vitro or in vivo has been proved to demonstrate a number of desirable advantages compared with the traditional bulk scaffold based top-down TE approach. Nevertheless, micro-components with an ECM-mimicking nanofibrous structure are still very scarce and highly desirable. Chitosan (CS), an accessible natural polymer, has demonstrated appealing intrinsic properties and promising application potential for TE, especially the cartilage tissue regeneration. According to this background, we report here the fabrication of chitosan microspheres with an ECM-mimicking nanofibrous structure for the first time based on a physical gelation process. By combining this physical fabrication procedure with microfluidic technology, uniform CS microspheres (CMS) with controlled nanofibrous microstructure and tunable sizes can be facilely obtained. Especially, no potentially toxic or denaturizing chemical crosslinking agent was introduced into the products. Notably, in vitro chondrocyte culture tests revealed that enhanced cell attachment and proliferation were realized, and a macroscopic 3D geometrically shaped cartilage-like composite can be easily constructed with the nanofibrous CMS (NCMS) and chondrocytes, which demonstrate significant application potential of NCMS as the bottom-up cell-carrier components for cartilage tissue engineering.

Cell-sized condensed collagen microparticles for preparing microengineered composite spheroids of primary hepatocytes

The reconstitution of extracellular matrix (ECM) components in three-dimensional (3D) cell culture environments with microscale precision is a challenging issue. ECM microparticles would potentially be useful as solid particulate scaffolds that can be incorporated into 3D cellular constructs, but technologies for transforming ECM proteins into cell-sized stable particles are currently lacking. Here, we describe new processes to produce highly condensed collagen microparticles by means of droplet microfluidics or membrane emulsification. Droplets of an aqueous solution of type I collagen were formed in a continuous phase of polar organic solvent followed by rapid dissolution of water molecules into the continuous phase because the droplets were in a non-equilibrium state. We obtained highly unique, disc-shaped condensed collagen microparticles with a final collagen concentration above 10% and examined factors affecting particle size and morphology. After testing the cell-adhesion properties on the collagen microparticles, composite multicellular spheroids comprising the particles and primary rat hepatocytes were formed using microfabricated hydrogel chambers. We found that the ratio of the cells and particles is critical in terms of improvement of hepatic functions in the composite spheroids. The presented methodology for incorporating particulate-form ECM components in multicellular spheroids would be advantageous because of the biochemical similarity with the microenvironments in vivo.

A Structurally and Functionally Biomimetic Biphasic Scaffold for Intervertebral Disc Tissue Engineering

Tissue engineering offers high hopes for the treatment of intervertebral disc (IVD) degeneration. Whereas scaffolds of the disc nucleus and annulus have been extensively studied, a truly biomimetic and mechanically functional biphasic scaffold using naturally occurring extracellular matrix is yet to be developed. Here, a biphasic scaffold was fabricated with collagen and glycosaminoglycans (GAGs), two of the most abundant extracellular matrix components in the IVD. Following fabrication, the scaffold was characterized and benchmarked against native disc. The biphasic scaffold was composed of a collagen-GAG co-precipitate making up the nucleus pulposus-like core, and this was encapsulated in multiple lamellae of photochemically crosslinked collagen membranes comprising the annulus fibrosus-like lamellae. On mechanical testing, the height of our engineered disc recovered by ~82-89% in an annulus-independent manner, when compared with the 99% recovery exhibited by native disc. The annulus-independent nature of disc height recovery suggests that the fluid replacement function of the engineered nucleus pulposus core might mimic this hitherto unique feature of native disc. Biphasic scaffolds comprised of 10 annulus fibrosus-like lamellae had the best overall mechanical performance among the various designs owing to their similarity to native disc in most aspects, including elastic compliance during creep and recovery, and viscous compliance during recovery. However, the dynamic mechanical performance (including dynamic stiffness and damping factor) of all the biphasic scaffolds was similar to that of the native discs. This study contributes to the rationalized design and development of a biomimetic and mechanically viable biphasic scaffold for IVD tissue engineering.

Crosslinking biopolymers for biomedical applications

Biomaterials made from proteins, polysaccharides, and synthetic biopolymers are preferred but lack the mechanical properties and stability in aqueous environments necessary for medical applications. Crosslinking improves the properties of the biomaterials, but most crosslinkers either cause undesirable changes to the functionality of the biopolymers or result in cytotoxicity. Glutaraldehyde, the most widely used crosslinking agent, is difficult to handle and contradictory views have been presented on the cytotoxicity of glutaraldehyde-crosslinked materials. Recently, poly(carboxylic acids) that can crosslink in both dry and wet conditions have been shown to provide the desired improvements in tensile properties, increase in stability under aqueous conditions, and also promote cell attachment and proliferation. Green chemicals and newer crosslinking approaches are necessary to obtain biopolymeric materials with properties desired for medical applications.

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.

The effect of crosslinking agent on sustained release of bFGF–collagen microspheres

Initial burst release and loss of bioactivity of drugs are the shortcomings of drug delivery systems (DDSs) used for in vivo treatment.

Nanofibrous microspheres via emulsion gelation and carbonization

Nanofibrous hydrogel microspheres are formed by pH gelation in emulsion droplets, which can then be freeze-dried and carbonized to produce nanofibrous carbon microspheres, showing high performance as electrode materials for supercapacitors.

A review of bioactive release from nerve conduits as a neurotherapeutic strategy for neuronal growth in peripheral nerve injury

Peripheral nerve regeneration strategies employ the use of polymeric engineered nerve conduits encompassed with components of a delivery system. This allows for the controlled and sustained release of neurotrophic growth factors for the enhancement of the innate regenerative capacity of the injured nerves. This review article focuses on the delivery of neurotrophic factors (NTFs) and the importance of the parameters that control release kinetics in the delivery of optimal quantities of NTFs for improved therapeutic effect and prevention of dose dumping. Studies utilizing various controlled-release strategies, in attempt to obtain ideal release kinetics, have been reviewed in this paper. Release strategies discussed include affinity-based models, crosslinking techniques, and layer-by-layer technologies. Currently available synthetic hollow nerve conduits, an alternative to the nerve autografts, have proven to be successful in the bridging and regeneration of primarily the short transected nerve gaps in several patient cases. However, current research emphasizes on the development of more advanced nerve conduits able to simulate the effectiveness of the autograft which includes, in particular, the ability to deliver growth factors.

Multi-modal delivery of therapeutics using biomaterial scaffolds

Functionalisation of biomaterials with therapeutic moieties (proteins, drugs, genes) is a pre-requisite to tissue regeneration and restoration of function following injury or disease.

Strategies for controlled delivery of growth factors and cells for bone regeneration

The controlled delivery of growth factors and cells within biomaterial carriers can enhance and accelerate functional bone formation. The carrier system can be designed with pre-programmed release kinetics to deliver bioactive molecules in a localized, spatiotemporal manner most similar to the natural wound healing process. The carrier can also act as an extracellular matrix-mimicking substrate for promoting osteoprogenitor cellular infiltration and proliferation for integrative tissue repair. This review discusses the role of various regenerative factors involved in bone healing and their appropriate combinations with different delivery systems for augmenting bone regeneration. The general requirements of protein, cell and gene therapy are described, with elaboration on how the selection of materials, configurations and processing affects growth factor and cell delivery and regenerative efficacy in both in vitro and in vivo applications for bone tissue engineering.

Recent advances in polymeric microspheres for parenteral drug delivery--part 2

INTRODUCTION

Currently marketed microsphere products are manufactured with the use of organic solvents which have a negative impact on the environment and stability of biological molecules. With recent advances in fabrication technologies, solvent free methods have demonstrated potential for the preparation of microspheres.

AREAS COVERED

New technical advances recently achieved in solvent based microsphere manufacturing processes have allowed for major improvement in product quality and properties. Novel solvent free fabrication methods combined with newly functionalized biodegradable polymers have been explored for their application in the preparation of microspheres containing biological molecules.

EXPERT OPINION

Novel fabrication methods for microspheres have been recently reported but technical challenges and development risks remain high for scale up from bench to industrial commercialization. While the applications of microspheres for delivery of proteins, genes and vaccines have shown promise for clinical use, the approval of newly functionalized polymers as carriers may still face scrutiny on safety and biocompatibility, which can be key factors in securing the regulatory approval of the product.

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

Porous scaffolds that can prolong the release of bioactive factors are urgently required in bone tissue engineering. In this study, PLGA/gelatin composite microspheres (PGMs) were carefully designed and prepared by entrapping poly(L: -lactide-co-glycolide) (PLGA) microspheres (PMs) in gelatin matrix. By mixing PGMs with PLGA solution directly, drug-loaded PLGA/carbonated hydroxyapatite (HAp)/PGMs composite scaffolds were successfully fabricated. In vitro release of fluorescein isothiocyanate-dextran (FD70S) as a model drug from the scaffolds as well as PMs and PGMs was studied by immersing samples in phosphate buffered saline (pH = 7.4) at 37°C for 32 days. Compared with PMs, PGMs and PLGA/HAp/PGMs scaffolds exhibited slow and steady release behavior with constant release rate and insignificantly original burst release. The swelling of PGMs, diffusion of drugs, and degradation of polymer dominated the release behaviors synergistically. The PLGA/HAp/PGMs scaffold offers a novel option for sequential or simultaneous release of several drugs in terms of bone regeneration.

Controlled release of bone morphogenetic protein 2 and dexamethasone loaded in core-shell PLLACL-collagen fibers for use in bone tissue engineering

Electrospun nanofibers mimic the native extracellular matrix of bone and have generated considerable interest in bone tissue regeneration. The aim of this study was to fabricate novel poly(l-lactide-co-caprolactone) (PLLACL), PLLACL/collagen nanofibers blended with bone morphogenetic protein 2 (BMP2) and dexamethasone (DEX) for controlled release during bone tissue engineering (BTE). The morphology, surface hydrophilicity, and mechanical properties of the PLLACL/collagen nanofibrous mats were analyzed by scanning electron microscopy and water contact angle and mechanical stability determination. The performance of the scaffolds was investigated in terms of the viability and morphology of human mesenchymal stromal cells (hMSC) on the nanofibrous mats. BMP2 and DEX were successfully incorporated into PLLACL/collagen nanofibers by means of blending or coaxial electrospinning and the PLLACL/collagen blended fibers proved useful for hMSC culture. Release of the two growth factors from PLLACL/collagen nanofibrous mats in vitro was investigated by UV spectrophotometry. The release profiles for core-shell nanofibers showed more controlled release of the growth factors compared with the blended electrospun fibers. The experimental results show that controlled release of BMP2 and DEX can induce hMSC to differentiate into osteogenic cells for bone tissue engineering. The results imply that PLLACL/collagen nanofibers encapsulating two drugs and/or proteins have great potential in bone tissue engineering.

Natural and Genetically Engineered Proteins for Tissue Engineering

To overcome the limitations of traditionally used autografts, allografts and, to a lesser extent, synthetic materials, there is the need to develop a new generation of scaffolds with adequate mechanical and structural support, control of cell attachment, migration, proliferation and differentiation and with bio-resorbable features. This suite of properties would allow the body to heal itself at the same rate as implant degradation. Genetic engineering offers a route to this level of control of biomaterial systems. The possibility of expressing biological components in nature and to modify or bioengineer them further, offers a path towards multifunctional biomaterial systems. This includes opportunities to generate new protein sequences, new self-assembling peptides or fusions of different bioactive domains or protein motifs. New protein sequences with tunable properties can be generated that can be used as new biomaterials. In this review we address some of the most frequently used proteins for tissue engineering and biomedical applications and describe the techniques most commonly used to functionalize protein-based biomaterials by combining them with bioactive molecules to enhance biological performance. We also highlight the use of genetic engineering, for protein heterologous expression and the synthesis of new protein-based biopolymers, focusing the advantages of these functionalized biopolymers when compared with their counterparts extracted directly from nature and modified by techniques such as physical adsorption or chemical modification.

The use of micro- and nanospheres as functional components for bone tissue regeneration

During the last decade, the use of micro- and nanospheres as functional components for bone tissue regeneration has drawn increasing interest. Scaffolds comprising micro- and nanospheres display several advantages compared with traditional monolithic scaffolds that are related to (i) an improved control over sustained delivery of therapeutic agents, signaling biomolecules and even pluripotent stem cells, (ii) the introduction of spheres as stimulus-sensitive delivery vehicles for triggered release, (iii) the use of spheres to introduce porosity and/or improve the mechanical properties of bulk scaffolds by acting as porogen or reinforcement phase, (iv) the use of spheres as compartmentalized microreactors for dedicated biochemical processes, (v) the use of spheres as cell delivery vehicle, and, finally, (vi) the possibility of preparing injectable and/or moldable formulations to be applied by using minimally invasive surgery. This article focuses on recent developments with regard to the use of micro- and nanospheres for bone regeneration by categorizing micro-/nanospheres by material class (polymers, ceramics, and composites) as well as summarizing the main strategies that employ these spheres to improve the functionality of scaffolds for bone tissue engineering.

Food protein-stabilized nanoemulsions as potential delivery systems for poorly water-soluble drugs: preparation, in vitro characterization, and pharmacokinetics in rats

Nanoemulsions stabilized by traditional emulsifiers raise toxicological concerns for long-term treatment. The present work investigates the potential of food proteins as safer stabilizers for nanoemulsions to deliver hydrophobic drugs. Nanoemulsions stabilized by food proteins (soybean protein isolate, whey protein isolate, β-lactoglobulin) were prepared by high-pressure homogenization. The toxicity of the nanoemulsions was tested in Caco-2 cells using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide viability assay. In vivo absorption in rats was also evaluated. Food protein-stabilized nanoemulsions, with small particle size and good size distribution, exhibited better stability and biocompatibility compared with nanoemulsions stabilized by traditional emulsifiers. Moreover, β-lactoglobulin had a better emulsifying capacity and biocompatibility than the other two food proteins. The pancreatic degradation of the proteins accelerated drug release. It is concluded that an oil/water nanoemulsion system with good biocompatibility can be prepared by using food proteins as emulsifiers, allowing better and more rapid absorption of lipophilic drugs.

Photochemical crosslinked electrospun collagen nanofibers: synthesis, characterization and neural stem cell interactions

Currently available crosslinking methods for electrospun collagen nanofibers do not preserve the fibrous architecture over prolonged periods of time. In addition, electrospinning of collagen often involves solvents that lead to extensive protein denaturation. In this study, we demonstrate the advantage of acetic acid over 1,1,1,3,3,3 hexafluoroisopropanol (HFP) in preventing collagen denaturation. A novel photochemical crosslinking method using rose bengal as the photoinitiator is also introduced. Using circular dichorism analyses, we demonstrate the fraction of collagen helical structure to be significantly greater in acetic acid-spun fibers than HFP-spun fibers (28.9 +/- 5.9% vs. 12.5 +/- 2.0%, p < 0.05). By introducing 0.1% (w/v) rose bengal into collagen fibers and subjecting these scaffolds to laser irradiation at a wavelength of 514 nm for 100 sec, biodegradable crosslinked scaffolds were obtained. Scaffold degradation as evaluated by soaking crosslinked collagen scaffolds in PBS at 37 degrees C, indicated a mass loss of 47.7 +/- 7.4% and 68.9 +/- 24.7% at day 7 and day 15, respectively. However, these scaffolds retained fibrous architecture for at least 21 days under physiological conditions. Neural stem cell line, C17.2, cultured on crosslinked collagen scaffolds proliferated after 7 days by forming a confluent layer of cells with extensive cellular projections that were indicative of neurite outgrowth. Taken together, these findings support the potential of acetic acid-electrospun photochemical crosslinked collagen nanofibers for neural tissue engineering.

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.