Biodegradable microspheres for protein delivery

Polyelectrolyte complex of chondroitin sulfate and peptide with lower pI value in poly(lactide-co-glycolide) microsphere for stability and controlled release

A polyelectrolyte complex between a therapeutic peptide and chargeable polymer was applied to prevent peptide denaturation in poly(lactide-co-glycolide) (PLGA) microspheres. Chondroitin sulfate A (CsA) was employed as a polymeric additive for the formation of an ionic complex with insulin (InS). The complex prepared at pH 3.0 evidenced a nano-size in the range of 100-400 nm with a mono distribution. The stability of InS in the complex in an organic/water (O/W) interface was verified via RP-HPLC. The insulin in the complex evidenced a retention time almost identical to native InS, whereas free insulin did not evidence such a retention time. On the basis of these studies, PLGA microspheres including a complex with various CsA/InS ratios were prepared via a double-emulsion method (PLGA/CsA MS). InS loading efficiency in the system is higher than that of the microspheres without CsA. The system evidenced a lower initial burst and, following the initial burst, continuous release kinetics for 30 days. Circular dichroism (CD) spectra demonstrated that the insulin in PLGA/CsA MS is more stable than the PLGA-only microspheres (PLGA/only MS) for 20 days. These results indicate that the complex system with CsA is useful for the long-term delivery of peptides with lower pI values.

Novel electrohydrodynamic preparation of porous chitosan particles for drug delivery

Uniform spherical chitosan particles of size <10 microm in diameter are important in drug delivery applications due to their excellent biocompability and biodegradability. A high concentration of chitosan in the particles can help to control the release of drugs and methods for processing high viscosity chitosan solutions are therefore required. In principle, any type of polymer, whether hydrophobic or hydrophilic, can be electrosprayed to obtain monodisperse particles of diameter <10 microm. In practice, however, electrospraying of biopolymers having viscosities of >100 mPa s results in particles >10 microm diameter. In this study, by reducing surface tension of a high viscosity chitosan suspension, it was found that smaller diameter particles could be prepared. Chitosan solutions were electrosprayed in the stable cone-jet mode to systematically study the relationship between particle diameter, viscosity and surface tension. Increasing viscosity resulted in larger diameter particles with a broad size distribution, but decreasing surface tension had the opposite effect. Results show that a chitosan solution having a viscosity of approximately 80 mPa s can be used to prepare chitosan particles of diameter approximately 2.5 microm which on drying reduced to particles of 500 nm.

Evaluation of albumin microspheres as oral delivery system for Mycobacterium tuberculosis vaccines

Mucosal immunization has been suggested to be the best option for preventing Mycobacterium tuberculosis infection. The purpose of this study was to develop albumin microspheres containing Mycobacterium tuberculosis antigens and to determine if oral administration of the microspheres can induce antigen-specific mucosal and systemic immune responses. Albumin microspheres containing Mycobacterium tuberculosis dead cells and cell lysate were prepared. The physico-chemical characteristics of the formulations were determined and the microspheres were administered to animal models to evaluate the induction of immune responses to the antigens. The results showed that the particle sizes, zeta potential and dissolution pattern of the microspheres were ideal for oral delivery of vaccines. In vivo studies showed high production of antigen-specific antibody production in serum, nasal, salivary and faecal samples. From the results of the study, it can be concluded that oral administration of Mycobacterium tuberculosis microspheres was successful in inducing antigen-specific systemic and mucosal immune responses.

A new class of inhibitors of peptide sorption and acylation in PLGA

Acylation of peptides occurring within controlled-release depots prepared from copolymers of lactic and glycolic acid (PLGA) is a degradation reaction that may compromise product safety and efficacy. As peptide sorption to PLGA is believed to be a common precursor to peptide acylation, a new method to inhibit acylation is presented involving disruptors of peptide sorption, namely, inorganic divalent cations. Kinetics of sorption of a model peptide, octreotide acetate, to free-acid end-group PLGA was monitored in the presence and absence of water-soluble inorganic divalent cationic salts in HEPES buffer solution (pH 7.4, 37 degrees C). Sorption of cations and octreotide attained pseudo-equilibrium by 24 h. From 24-h sorption isotherms, all cations studied inhibited octreotide sorption to PLGA-the inhibiting effect of the cations increased in the order: Na(+)<Mg(2+)<Ca(2+), Sr(2+)<Ni(2+)<Mn(2+). Long-term inhibition of octreotide sorption in the presence of 15 mM CaCl(2) and MnCl(2) translated to decreased acylated octreotide present in solution by greater than 50% at 21 days incubation, i.e., from 32% in the cation-free control to 14 and 13% for CaCl(2) and MnCl(2), respectively. Over one month in vitro release, PLGA implants encapsulating octreotide acetate and CaCl(2) or MnCl(2) also showed substantial inhibition of acylation relative to no-salt or NaCl controls, and similarly, strong inhibition of acylation upon divalent salt incorporation was observed during solvent extrusion of suspended peptide with polar organic carrier solvents. Hence, disrupting peptide sorption to PLGA with addition of inorganic divalent cations is a simple and viable strategy to inhibit acylation of peptides in PLGA delivery systems.

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.

Strength of hollow hydroxyapatite microspheres prepared by a glass conversion process

Hollow hydroxyapatite (HA) microspheres (diameter = 100-800 microm) were prepared by reacting solid Li(2)O-CaO-B(2)O(3) glass spheres in 0.25 M K(2)HPO(4) solution at 37 degrees C. The influence of subsequent heating on the microstructure, surface area, and compressive strength of the HA microspheres was evaluated using scanning electron microscopy, the BET method, and nano-mechanical testing. The surface area and rupture strength of the as-prepared microspheres were 135 m(2)/g and 1.6 +/- 0.6 MPa, respectively. On heating for 8 h at 600 degrees C, the surface area decreased to 27 m(2)/g, but there was no increase in the compressive strength (1.7 +/- 0.4 MPa). Heating to 800 degrees C (8 h) resulted in a marked decrease in the surface area (to 2.6 m(2)/g) and a sharp increase in the compressive strength (to >35 +/- 8 MPa). These hollow HA microspheres may be useful as devices for drug or protein growth factor delivery or as scaffolds for engineered tissues.

Nanomedicine--challenge and perspectives

The application of nanotechnology concepts to medicine joins two large cross-disciplinary fields with an unprecedented societal and economical potential arising from the natural combination of specific achievements in the respective fields. The common basis evolves from the molecular-scale properties relevant to the two fields. Local probes and molecular imaging techniques allow surface and interface properties to be characterized on a nanometer scale at predefined locations, while chemical approaches offer the opportunity to elaborate and address surfaces, for example, for targeted drug delivery, enhanced biocompatibility, and neuroprosthetic purposes. However, concerns arise in this cross-disciplinary area about toxicological aspects and ethical implications. This Review gives an overview of selected recent developments and applications of nanomedicine.

A unified mathematical model for the prediction of controlled release from surface and bulk eroding polymer matrices

A unified model has been developed to predict release not only from bulk eroding and surface eroding systems but also from matrices that transition from surface eroding to bulk eroding behavior during the course of degradation. This broad applicability is afforded by fundamental diffusion/reaction equations that can describe a wide variety of scenarios including hydration of and mass loss from a hydrolysable polymer matrix. Together, these equations naturally account for spatial distributions of polymer degradation rate. In this model paradigm, the theoretical minimal size required for a matrix to exhibit degradation under surface eroding conditions was calculated for various polymer types and then verified by empirical data from the literature. An additional set of equations accounts for dissolution- and/or degradation-based release, which are dependent upon hydration of the matrix and erosion of the polymer. To test the model's accuracy, predictions for agent egress were compared to experimental data from polyanhydride and polyorthoester implants that were postulated to undergo either dissolution-limited or degradation-controlled release. Because these predictions are calculated solely from readily attainable design parameters, it seems likely that this model could be used to guide the design controlled release formulations that produce a broad array of custom release profiles.

Polymer-based sustained-release dosage forms for protein drugs, challenges, and recent advances

While the concept of using polymer-based sustained-release delivery systems to maintain therapeutic concentration of protein drugs for extended periods of time has been well accepted for decades, there has not been a single product in this category successfully commercialized to date despite clinical and market demands. To achieve successful systems, technical difficulties ranging from protein denaturing during formulation process and the course of prolonged in vivo release, burst release, and incomplete release, to low encapsulation efficiency and formulation complexity have to be simultaneously resolved. Based on this updated understanding, formulation strategies attempting to address these aspects comprehensively were reported in recent years. This review article (with 134 citations) aims to summarize recent studies addressing the issues above, especially those targeting practical industrial solutions. Formulation strategies representative of three areas, microsphere technology using degradable hydrophobic polymers, microspheres made of water soluble polymers, and hydrophilic in vivo gelling systems will be selected and introduced. To better understand the observations and conclusions from different studies for different systems and proteins, physicochemical basis of the technical challenges and the pros and cons of the corresponding formulation methods will be discussed.

Effects of photochemical crosslinking on the microstructure of collagen and a feasibility study on controlled protein release

Photochemical crosslinking is an emerging technique able to modify the physicochemical properties of collagen. However, whether this technique can be used to modify collagen-based structures for drug delivery has not been studied. This study demonstrated that the microporous structure of photochemically crosslinked collagen was affected by rose Bengal and laser energy level. Using the optimized process parameters, the authors fabricated photochemically crosslinked collagen structures encapsulated with sample proteins and demonstrated that photochemical crosslinking reduced the initial burst effect and protein release without compromising the protein bioactivity. The fiber meshwork in collagen structures was also characterized, and it was found that photochemical crosslinking did not significantly alter the mesh size. This study reports the effects of photochemical crosslinking on the microstructure of collagen structures and suggests the feasibility of using photochemically crosslinked collagen structures for controlled protein release.

Physicochemical properties of film-coated melt-extruded pellets

The purpose of this study was to investigate the physicochemical properties of poly(ethylene oxide) (PEO) and guaifenesin containing beads prepared by a melt-extrusion process and film-coated with a methacrylic acid copolymer. Solubility parameter calculations, thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), modulated differential scanning calorimetry (MDSC), X-ray powder diffraction (XRPD) and high performance liquid chromatography (HPLC) were used to determine drug/polymer miscibility and/or the thermal processibility of the systems. Powder blends of guaifenesin, PEO and functional excipients were processed using a melt-extrusion and spheronization technique and then film-coated in a fluidized bed apparatus. Solubility parameter calculations were used to predict miscibility between PEO and guaifenesin, and miscibility was confirmed by SEM and observation of a single melting point for extruded drug/polymer blends during MDSC investigations. The drug was stable following melt-extrusion as determined by TGA and HPLC; however, drug release rate from pellets decreased upon storage in sealed HDPE containers with silica desiccants at 40 degrees C/75% RH. The weight loss on drying, porosity and tortuosity determinations were not influenced by storage. Recrystallization of guaifenesin and PEO was confirmed by SEM and XRPD. Additionally, the pellets exhibited a change in adhesion behaviour during dissolution testing. The addition of ethylcellulose to the extruded powder blend decreased and stabilized the drug release rate from the thermally processed pellets. The current study also demonstrated film-coating to be an efficient process for providing melt-extruded beads with pH-dependent drug release properties that were stable upon storage at accelerated conditions.

Chitosan glutamate nanoparticles for protein delivery: Development and effect on prolidase stability

PURPOSE

To evaluate the feasibility of exploiting ultrasonication coupled with ionotropic gelation in order to prepare tripolyphosphate (TPP)-chitosan glutamate nanoparticles suitable for the delivery of the enzyme prolidase.

METHODS

All the parameters for the preparation of TPP-chitosan nanoparticles in terms of components weight ratio, ultrasonication conditions and time-saving nanoparticles recovery conditions were optimized. The best formulation was loaded with the prolidase. All the nanoparticles were characterized in terms of morphology, size, polydispersity, zeta-potential, yield of the process and encapsulation efficiency. The in-vitro activity of the prolidase was assessed by capillary electrophoresis (CE).

RESULTS AND CONCLUSIONS

A TPP to chitosan weight ratio of 0.2:1 combined with one ultrasonication cycle (4 min using the probe-type sonifier at 75% power) obtained well-formed nanoparticles of spherical shape, mean size of approximately 365 nm (polydispersity index 0.3) and a + 17.94 mV zeta potential. A satisfactory prolidase encapsulation efficiency (43%) was obtained with a yield of the preparation process of approximately 55%. In vitro study of activity of prolidase, as free enzyme or released from chitosan nanoparticles, highlighted the ability of chitosan to stabilize the enzyme during all the steps of the preparation process and to modulate the enzyme activity up to 48 h.

Surface characterization by atomic force microscopy of sterilized PLGA microspheres

Atomic force microscopy (AFM) is recognized a suitable and powerful technique for surface and morphological analysis. Even if until now this technique has not been frequently used in the pharmaceutical field, it can contribute to an accurate morphologic characterization of microspheres and nanospheres. In this work, atomic force microscopy has been used to perform the surface characterization of sterilized microspheres. The aim is to investigate the morphologic modifications induced by gamma irradiation on poly(lactide-co-glycolide) microspheres loaded with ovalbumin and to compare the results obtained by AFM to those obtained by scanning electron microscopy (SEM). The results obtained show that, with respect to SEM, AFM can give some additional information regarding the modifications induced by gamma-irradiation on microspheres surface morphology. The significant changes in surface roughness after irradiation are indicative of damage due to gamma-irradiation. The unchanged surface roughness values calculated for microspheres containing PEG in their matrix, suggest that this polymer exerts a protective effect towards gamma-irradiation.

Compression of Controlled-Release Pellets Produced by a Hot-Melt Extrusion and Spheronization Process

The purpose of this study was to investigate the physicomechanical and dissolution properties of tablets containing controlled-release pellets prepared by a hot-melt extrusion and spheronization process. A powder blend of anhydrous theophylline, Eudragit Preparation 4135 F, and functional excipients was melt-extruded, pelletized, and then spheronized. The pellets were compressed into tablets using forces of 5, 10, 15, and 20 kN. Tablet diluents included microcrystalline cellulose, a mixture of spray-dried lactose and microcrystalline cellulose, modified food starch, and soy polysaccharides. The effective porosity of the compressed pellets was measured using mercury porosimetry and helium pycnometry, while the surface area was determined using Brunauer, Emmett, and Teller (BET) analysis. The disintegration time, hardness, and friability of compacts were determined. Drug release studies were performed according to USP 27 Apparatus 3 guidelines in 250 mL of medium (pH 1.0, 3.0, 5.0, 6.8, and 7.4) 37 degrees C and 20 dpm. Samples were analyzed by high pressure-liquid chromatography (HPLC). Effective porosity and surface area determinations of the melt-extruded pellets were not influenced by compression. The percent of theophylline released from rapidly disintegrating tablets was not affected by compression force or excipient selection, but tablets with prolonged disintegration times exhibited delayed drug release in acidic media. However, dissolution profiles of uncompressed pellets and all compacts were identical after transition from 0.1 N HCl to media increasing in pH from 3.0 to 7.4. Furthermore, pellet to filler excipient ratio and filler excipient selection did not influence the rate of drug release from compacts.

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.

Effect of particle size and charge on the network properties of microsphere-based hydrogels

This work describes the tailorability of the network properties of self-assembling hydrogels, based on ionic crosslinking between dextran microspheres. Copolymerization of hydroxyethyl methacrylate-derivatized dextran (dex-HEMA), emulsified in an aqueous poly(ethylene glycol) (PEG) solution, with methacrylic acid (MAA) or dimethylaminoethyl methacrylate (DMAEMA) resulted in negatively or positively charged microspheres, respectively, at physiological pH. The monomer/HEMA ratio ranged between 6 and 57, resulting in microspheres with zeta (zeta)-potentials from -6 to -34mV and +3 to +23mV, for the monomers MAA and DMAEMA, respectively. By altering the emulsification procedure, microsphere batches with various sizes and size distributions were obtained. The aim of the research was to assess the effect of particle size (distribution) and charge on the network properties of the macroscopic hydrogels. The ability to tailor the mechanical properties such as strength and elasticity increases the potential of the hydrogels to be used in a variety of pharmaceutical applications. Additionally, the injectability of these self-assembling hydrogels was investigated. Injectability is an important feature of drug delivery systems, since it allows avoiding surgery. Rheological analysis showed that an increasing surface charge of the microspheres led to stronger hydrogels. Relatively small microspheres (7microm) with a narrow size distribution (99% smaller than 14microm) gave rise to stronger hydrogels when compared to larger microspheres of 20microm with a broad distribution (99% smaller than 50microm). When small microspheres were combined with large microspheres of opposite charge, it was found that the strongest gels were obtained with 75% small and 25% large microspheres, instead of equal amounts (50/50) of positively and negatively charged microspheres. Computer modeling confirmed these findings and showed that the most favorable composition, related to the lowest potential energy, comprised of 75% small microspheres. Taking both charge and size effects into account, the storage moduli (G') of the almost fully elastic hydrogels could be tailored from 400 to 30,000Pa. Injectability tests showed that hydrogels (G' up to 4000Pa) composed of equal amounts of oppositely charged microspheres (-7 and +6mV, average particle size 7microm) could be injected through 25G needles using a static load of 15N, an ISO accepted value. In conclusion, a variety of options to control the network properties of macroscopic hydrogels are provided, related to the charge and particle size of the composing dextran microspheres. Furthermore, it is shown that the hydrogels are injectable, making them attractive candidates for a diversity of pharmaceutical applications.

PLGA nanoparticles for oral delivery of hydrophobic drugs: influence of organic solvent on nanoparticle formation and release behavior in vitro and in vivo using estradiol as a model drug

The aim of present investigation was to screen different solvents for optimizing nanoparticle preparation in terms of particle size, entrapment efficiency, and finally, release behavior using a model drug estradiol. Nanoparticles were prepared following emulsion-diffusion-evaporation method using didodecyldimethyl ammonium bromide (DMAB) or polyvinyl alcohol (PVA) as stabilizers. Ethyl acetate (EA), acetone (ACE), chloroform (CHL), and dichloromethane (DCM) were used as organic solvents either individually or in combinations. DMAB when used as surfactant led to smaller particle size as compared to PVA irrespective of the solvents and combinations used, but on the other hand, PVA produced particles with higher entrapment when combinations of solvents used. DCM in combination with EA resulted in highest entrapment with both the stabilizers. All the formulations exhibited similar in vitro release profile (Zero order) irrespective of stabilizer (DMAB or PVA) used, however, the average release per day was higher in case of DCM formulations due to greater entrapment. In situ uptake studies suggest that smaller the particle size better is the uptake. The bioavailability from nanoparticles was assessed in male Sprague Dawley (SD) rats at a dose of 1 mg drug/rat. EA/DMAB (size 116.0 +/- 2.6 nm) and DCM:EA 70:30/DMAB (size 253.0 +/- 5.5 nm) showed the release for 9 and 5 days, respectively, whereas EA/PVA (size 279.3 +/- 2.5 nm) released the drug over the periods of 3 days suggesting that particle size has significant role in determining the fate of nanoparticles in vivo. Histopathological examination revealed absence of any inflammatory response with the formulations under the studied period.

Principles of encapsulating hydrophobic drugs in PLA/PLGA microparticles

Injectable biodegradable and biocompatible copolymers of lactic and glycolic acid (PLGA) are an important advanced delivery system for week-to-month controlled release of hydrophobic drugs (e.g., from biopharmaceutical classification system class IV), which often display poor oral bioavailability. The basic principles and considerations to develop such microparticle formulations is reviewed here based on a comprehensive study of papers and patents from the beginnings of hydrophobic drug encapsulation in polylactic acid and PLGA up through the very recent literature. Challenges with the diversity of drug properties, microencapsulation methods, and organic solvents are evaluated in light of the precedence of commercialized formulations and with a focus on decreasing the time to lab-scale encapsulation of water-insoluble drug candidates in the early stage of drug development. The influence of key formulation variables on final microparticle characteristics, and how best to avoid undesired microparticle properties, is analyzed mechanistically. Finally, concepts are developed to manage the common issues of maintaining sink conditions for in vitro drug release assays of hydrophobic compounds. Overall, against the backdrop of an increasing number of new, poorly orally available drug entities entering development, microparticle delivery systems may be a viable strategy to rescue an otherwise undeliverable substance.

Bioengineering approaches to controlled protein delivery

Proteins are of crucial importance in all biologic organisms, in terms of both structure and function. Their deficits play central roles in many pathologic states, and their potential as powerful therapeutic agents has been widely recognized. Many issues, however, exist in delivery of biologically active proteins to target tissues and organs. Recent advances in biomedical engineering have lead to development of advanced techniques for controlled delivery of peptides and proteins, paving the way for their efficient use in treating human injury and disease. With a particular emphasis on most recent advances, this review discusses currently available techniques for controlled delivery of proteins and considers future research directions.

Development and characterization of polymeric microspheres for controlled release protein loaded drug delivery system

The aim of the present work was to investigate the preparation of microspheres as potential drug carriers for proteins, intended for controlled release formulation. The hydrophilic bovine serum albumin was chosen as a model protein to be encapsulated within poly(D,L-lactide-co-glycolide) (50:50) microspheres using a w/o/w double emulsion solvent evaporation method. Different parameters influencing the particle size, entrapment efficiency and in vitro release profiles were investigated. The microspheres prepared with different molecular weight and hydrophilicity of poly(D,L-lactide-co-glycolide) polymers were non porous, smooth surfaced and spherical in structure under scanning electron microscope with a mean particle size ranging from 3.98 to 8.74 mum. The protein loading efficiency varied from 40 to 71% of the theoretical amount incorporated. The in vitro release profile of bovine serum albumin from microspheres presented two phases, initial burst release phase due to the protein adsorbed on the microsphere surface, followed by slower and continuous release phase corresponding to the protein entrapped in polymer matrix. The release rate was fairly constant after an initial burst release. Consequently, these microspheres can be proposed as new controlled release protein delivery system.

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.

A Preliminary Assessment of Silver Nanoparticle Inhibition of Monkeypox Virus Plaque Formation

The use of nanotechnology and nanomaterials in medical research is growing. Silver-containing nanoparticles have previously demonstrated antimicrobial efficacy against bacteria and viral particles. This preliminary study utilized an in vitro approach to evaluate the ability of silver-based nanoparticles to inhibit infectivity of the biological select agent, monkeypox virus (MPV). Nanoparticles (10–80 nm, with or without polysaccharide coating), or silver nitrate (AgNO₃) at concentrations of 100, 50, 25, and 12.5 μg/mL were evaluated for efficacy using a plaque reduction assay. Both Ag-PS-25 (polysaccharide-coated, 25 nm) and Ag-NP-55 (non-coated, 55 nm) exhibited a significant (P ≤ 0.05) dose-dependent effect of test compound concentration on the mean number of plaque-forming units (PFU). All concentrations of silver nitrate (except 100 μg/mL) and Ag-PS-10 promoted significant (P ≤ 0.05) decreases in the number of observed PFU compared to untreated controls. Some nanoparticle treatments led to increased MPV PFU ranging from 1.04- to 1.8-fold above controls. No cytotoxicity (Vero cell monolayer sloughing) was caused by any test compound, except 100 μg/mL AgNO₃. These results demonstrate that silver-based nanoparticles of approximately 10 nm inhibit MPV infection in vitro, supporting their potential use as an anti-viral therapeutic.