Enhanced tendon healing by a tough hydrogel with an adhesive side and high drug-loading capacity.

Hydrogels that provide mechanical support and sustainably release therapeutics have been used to treat tendon injuries. However, most hydrogels are insufficiently tough, release drugs in bursts, and require cell infiltration or suturing to integrate with surrounding tissue. Here we report that a hydrogel serving as a high-capacity drug depot and combining a dissipative tough matrix on one side and a chitosan adhesive surface on the other side supports tendon gliding and strong adhesion (larger than 1,000 J m-2) to tendon on opposite surfaces of the hydrogel, as we show with porcine and human tendon preparations during cyclic-friction loadings. The hydrogel is biocompatible, strongly adheres to patellar, supraspinatus and Achilles tendons of live rats, boosted healing and reduced scar formation in a rat model of Achilles-tendon rupture, and sustainably released the corticosteroid triamcinolone acetonide in a rat model of patellar tendon injury, reducing inflammation, modulating chemokine secretion, recruiting tendon stem and progenitor cells, and promoting macrophage polarization to the M2 phenotype. Hydrogels with 'Janus' surfaces and sustained-drug-release functionality could be designed for a range of biomedical applications.

Tough Composite Hydrogels with High Loading and Local Release of Biological Drugs.

Hydrogels are under active development for controlled drug delivery, but their clinical translation is limited by low drug loading capacity, deficiencies in mechanical toughness and storage stability, and poor control over the drug release that often results in burst release and short release duration. This work reports a design of composite clay hydrogels, which simultaneously achieve a spectrum of mechanical, storage, and drug loading/releasing properties to address the critical needs from translational perspectives. The clay nanoparticles provide large surface areas to adsorb biological drugs, and assemble into microparticles that are physically trapped within and toughen hydrogel networks. The composite hydrogels demonstrate feasibility of storage, and extended release of large quantities of an insulin-like growth factor-1 mimetic protein (8 mg mL-1 ) over four weeks. The release rate is primarily governed by ionic exchange and can be upregulated by low pH, which is typical for injured tissues. A rodent model of Achilles tendon injury is used to demonstrate that the composite hydrogels allow for highly extended and localized release of biological drugs in vivo, while demonstrating biodegradation and biocompatibility. These attributes make the composite hydrogel a promising system for drug delivery and regenerative medicine.

Milling induced amorphisation and recrystallization of α-lactose monohydrate.

Preprocessing of pharmaceutical powders is a common procedure to condition the materials for a better manufacturing performance. However, such operations may induce undesired material properties modifications when conditioning particle size through milling, for example. Modification of both surface and bulk material structure will change the material properties, thus affecting the processability of the powder. Hence it is essential to control the material transformations that occur during milling. Topographical and mechanical changes in surface properties can be a preliminary indication of further material transformations. Therefore a surface evaluation of the α-lactose monohydrate after short and prolonged milling times has been performed. Unprocessed α-lactose monohydrate and spray dried lactose were evaluated in parallel to the milled samples as reference examples of the crystalline and amorphous lactose structure. Morphological differences between unprocessed α-lactose, 1 h and 20 h milled lactose and spray dried lactose were detected from SEM and AFM images. Additionally, AFM was used to simultaneously characterize particle surface amorphicity by measuring energy dissipation. Extensive surface amorphicity was detected after 1 h of milling while prolonged milling times showed only a moderate particle surface amorphisation. Bulk material characterization performed with DSC indicated a partial amorphicity for the 1 h milled lactose and a fully amorphous thermal profile for the 20 h milled lactose. The temperature profiles however, were shifted somewhat in the comparison to the amorphous reference, particularly after extended milling, suggesting a different amorphous state compared to the spray-dried material. Water loss during milling was measured with TGA, showing lower water content for the lactose amorphized through milling compared to spray dried amorphous lactose. The combined results suggest a surface-bulk propagation of the amorphicity during milling in combination with a different amorphous structural conformation to that of the amorphous spray dried lactose. The hardened surface may be due to either surface crystallization of lactose or to formation of a low-water glass transition.

AFM Colloidal Probe Measurements Implicate Capillary Condensation in Punch-Particle Surface Interactions during Tableting.

Adhesion of the powders to the punches is a common issue during tableting. This phenomenon is known as sticking and affects the quality of the manufactured tablets. Defective tablets increase the cost of the manufacturing process. Thus, the ability to predict the tableting performance of the formulation blend before the process is scaled-up is important. The adhesive propensity of the powder to the tableting tools is mostly governed by the surface-surface adhesive interactions. Atomic force microscopy (AFM) colloidal probe is a surface characterization technique that allows the measurement of the adhesive interactions between two materials of interest. In this study, AFM steel colloidal probe measurements were performed on ibuprofen, MCC (microcrystalline cellulose), α-lactose monohydrate, and spray-dried lactose particles as an approach to modeling the punch-particle surface interactions during tableting. The excipients (lactose and MCC) showed constant, small, attractive, and adhesive forces toward the steel surface after a repeated number of contacts. In comparison, ibuprofen displayed a much larger attractive and adhesive interaction increasing over time both in magnitude and in jump-in/jump-out separation distance. The type of interaction acting on the excipient-steel interface can be related to a van der Waals force, which is relatively weak and short-ranged. By contrast, the ibuprofen-steel interaction is described by a capillary force profile. Even though ibuprofen is not highly hydrophilic, the relatively smooth surfaces of the crystals allow "contact flooding" upon contact with the steel probe. Capillary forces increase because of the "harvesting" of moisture-due to the fast condensation kinetics-leaving a residual condensate that contributes to increase the interaction force after each consecutive contact. Local asperity contacts on the more hydrophilic surface of the excipients prevent the flooding of the contact zone, and there is no such adhesive effect under the same ambient conditions. The markedly different behavior detected by force measurements clearly shows the sticky and nonsticky propensity of the materials and allows a mechanistic description.

Determination of Interfacial Amorphicity in Functional Powders.

The nature of the surfaces of particles of pharmaceutical ingredients, food powders, and polymers is a determining factor for their performance in for example tableting, powder handling, or mixing. Changes on the surface structure of the material will impact the flow properties, dissolution rate, and tabletability of the powder blend. For crystalline materials, surface amorphization is a phenomenon which is known to impact performance. Since it is important to measure and control the level of amorphicity, several characterization techniques are available to determine the bulk amorphous content of a processed material. The possibility of characterizing the degree of amorphicity at the surface, for example by studying the mechanical properties of the particles' surface at the nanoscale, is currently only offered by atomic force microscopy (AFM). The AFM PeakForce QNM technique has been used to measure the variation in energy dissipation (eV) at the surface of the particles which sheds light on the mechanical changes occurring as a result of amorphization or recrystallization events. Two novel approaches for the characterization of amorphicity are presented here. First, since particles are heterogeneous, we present a methodology to present the results of extensive QNM analysis of multiple particles in a coherent and easily interpreted manner, by studying cumulative distributions of dissipation data with respect to a threshold value which can be used to distinguish the crystalline and amorphous states. To exemplify the approach, which is generally applicable to any material, reference materials of purely crystalline α-lactose monohydrate and completely amorphous spray dried lactose particles were compared to a partially amorphized α-lactose monohydrate sample. Dissipation data are compared to evaluations of the lactose samples with conventional AFM and SEM showing significant topographical differences. Finally, the recrystallization of the surface amorphous regions in response to humidity was followed by studying the dissipation response of a well-defined surface region over time, which confirms both that dissipation measurement is a useful measure of surface amorphicity and that significant recrystallization occurs at the surface in response to humidity.

Tablet mechanics depend on nano and micro scale adhesion, lubrication and structure.

Tablets are the most convenient form for drug administration. However, despite the ease of manufacturing problems such as powder adhesion occur during the production process. This study presents surface and structural characterization of tablets formulated with commonly used excipients (microcrystalline cellulose (MCC), lactose, mannitol, magnesium (Mg) stearate) pressed under different compaction conditions. Tablet surface analyses were performed with scanning electron microscopy (SEM), profilometry and atomic force microscopy (AFM). The mechanical properties of the tablets were evaluated with a tablet hardness test. Local adhesion detected by AFM decreased when Mg stearate was present in the formulation. Moreover, the tablet strength of plastically deformable excipients such as MCC was significantly decreased after addition of Mg stearate. Combined these facts indicate that Mg stearate affects the particle-particle bonding and thus elastic recovery. The MCC excipient also displayed the highest hardness which is characteristic for a highly cohesive material. This is discussed in the view of the relatively high adhesion found between MCC and a hydrophilic probe at the nanoscale using AFM. In contrast, the tablet strength of brittle materials like lactose and mannitol is unaffected by Mg stearate. Thus fracture occurs within the excipient particles and not at particle boundaries, creating new surfaces not previously exposed to Mg stearate. Such uncoated surfaces may well promote adhesive interactions with tools during manufacture.

Biophysical properties of chitosan/siRNA polyplexes: profiling the polymer/siRNA interactions and bioactivity.

Chitosans are naturally occurring polymers widely used in life science to mediate intracellular uptake of nucleic acids such as siRNA. Four chitosans of fungal origin (Agaricus bisporus; molecular weights MW=44, 63, 93 and 143 kDa) were used in this study and profiled for size, viscosity and hydrodynamic radius using gel permeation chromatography (GPC). Polyplexes made of these chitosans and siRNA were developed and optimized for transfection efficacy in vitro. The characteristics of these polyplexes were low chitosan:siRNA ratios (4-8; N:P) similar positive zeta potential (20-30 mV) and comparable particle sizes (about 150 nm). Endogenous luciferase reporter gene down-regulation in human epithelial H1299 cells at nanomolar concentrations (37.5-150 nM) was significantly stronger for the lower molecular weight chitosans. The impact of these low N:P polyplexes on the cellular viability was minimal also at 150 nM. To help develop an understanding of these differences, an energetic profile of the molecular interactions and polyplex formation was established by isothermal titration calorimetry (ITC). The four polyplexes exhibited strong binding enthalpies delta H(bind)(-84 to -102 kcal/mol) resulting in nanomolar dissociation constants. Intracellular trafficking studies using rhodamine labeled siRNA revealed that polyplexes made from smaller MW chitosans exhibited faster cellular uptake kinetics than their higher MW counterpart. Transmission electron microscopy and small angle X-ray scattering studies (SAXS) revealed that the 44 kDa derived polyplexes exhibited regular spherical structure, whereas the 143 kDa chitosan polyplex was rather irregularly shaped. With regards to adverse effects these low N:P chitosan/siRNA formulations represent an interesting alternative to so far reported chitosan polyplexes that used vast N:P excess to achieve similar bioactivity.

Polymer swelling, drug mobilization and drug recrystallization in hydrating solid dispersion tablets studied by multinuclear NMR microimaging and spectroscopy.

Despite the advantages offered by solid dispersions, the marketed products based on this technology are few. The most frequent concern is the stability of the amorphous drug. The state of the drug in solid dispersions is, in general, poorly characterized as the number of characterization techniques available to monitor nanometer-sized drug particles embedded in a matrix are limited. Here we present a combination of localized NMR spectroscopic and NMR imaging techniques which allow in situ monitoring of the state of the drug during tablet disintegration and dissolution. (19)F NMR relaxation is shown to be sensitive to both the crystalline/amorphous state and the size of the model nanoparticles made of the drug substance flutamide. The time course of drug mobilization and recrystallization is detected with spatial resolution within swelling solid dispersion tablets. Comparing results from spatially resolved (19)F, (2)H and (1)H NMR experiments, recrystallization is related to its enabling factors such as local hydration level and local mobility of the polymer matrix. The initially amorphous drug may recrystallize either by nanoparticle coalescence or by ripening of crystalline grains.

Relationships between solid dispersion preparation process, particle size and drug release--an NMR and NMR microimaging study.

Solid dispersion tablets prepared by either spray drying or rotoevaporation and exhibiting different grain and pore sizes were investigated under the process of hydration-swelling-gelation. (2)H and (1)H NMR microimaging experiments were used to selectively follow water penetration and polymer mobilization kinetics, respectively, while the drug release kinetics was followed by (1)H NMR spectroscopy. The obtained data, in combination with morphological information by scanning electron microscopy (SEM), reveal a complex process that ultimately leads to release of the drug into the aqueous phase. We find that the rate of water ingress has no direct influence on release kinetics, which also renders air in the tablets a secondary factor. On the other hand, drug release is directly correlated with the polymer mobilization kinetics. Water diffusion into the originally dry polymer grains determines the rate of grain swelling and the hydration within the grains varies strongly with grain size. We propose that this sets the stage for creating homogeneous gels for small grain sizes and heterogeneous gels for large grain sizes. Fast diffusion through water-rich sections of the inhomogeneous gels that exhibit a large mesh size is the factor which yields a faster drug release from tablets prepared by rotoevaporation.

Polymer-drug interactions and wetting of solid dispersions.

We demonstrate the ability of drugs to influence the wetting of solid dispersion tablets in unexpected ways. Five model drugs of different water solubility and ability to interact with the involved polymers were incorporated in hydrophilic polymer matrices, made of either hydroxypropyl methylcellulose (HPMC) or polyvinyl pyrrolidone (PVP). The physical mixtures of all combinations of drug and polymer presented surface hydrophobicities, as measured by the equilibrium advancing contact angle of water, which are expected for materials that do not influence the interactions of each other with water. However, the solid dispersions containing HPMC deviated from this regular behaviour and displayed contact angles below those of the pure compounds involved, either drug or polymer. This behaviour is explained by changed surface exposure of HPMC side groups, as a result of changes in intermolecular hydrogen bonds. In addition to water contact angle measurements, we employed NMR imaging to monitor the time course of water ingress and swelling.

Surface composition and contact angle relationships for differently prepared solid dispersions.

Solid dispersions are promising drug delivery forms which offer the possibility to disperse a hydrophobic drug in a hydrophilic matrix and thereby improve the dissolution behavior and the bioavailability of the drug. One important aspect and a prerequisite in understanding the drug dissolution mechanism from solid dispersions is a better analytical monitoring of the solid dispersion surface properties, such as powder surface composition and water adsorption properties. In this paper, we have considered chemical and structural surface analysis data for solid dispersions processed by spray drying or roto-evaporation and compared these data with information obtained by contact angle measurements. Firstly, we establish the usefulness and suitability of X-ray photoelectron spectroscopy (XPS) for determination of surface chemical composition and scanning electron microscopy (SEM) for determining the structure of solid dispersions composed of different types of carriers, drugs and drug concentrations. Secondly, we measure contact angles of solid dispersions to describe wettability, to finally establish a link between the surface chemical composition, the powder structure and the wetting behavior. These experimental methods offer a rapid screening tool for the selection of carrier, drug concentration and/or process in early development. In addition, they provide a useful tool for investigating structural aspects of solid dispersions which have intrinsic relevance for drug dissolution and stability.

Polymer mobilization and drug release during tablet swelling. A 1H NMR and NMR microimaging study.

The objective of this study was to investigate the swelling characteristics of a hydroxypropyl methylcellulose (HPMC) matrix incorporating the hydrophilic drug antipyrine. We have used this matrix to introduce a novel analytical method, which allows us to obtain within one experimental setup information about the molecular processes of the polymer carrier and its impact on drug release. Nuclear magnetic resonance (NMR) imaging revealed in situ the swelling behavior of tablets when exposed to water. By using deuterated water, the spatial distribution and molecular dynamics of HPMC and their kinetics during swelling could be observed selectively. In parallel, NMR spectroscopy provided the concentration of the drug released into the aqueous phase. We find that both swelling and release are diffusion controlled. The ability of monitoring those two processes using the same experimental setup enables mapping their interconnection, which points on the importance and potential of this analytical technique for further application in other drug delivery forms.

Predictive stress tests to study the influence of processing procedures on long term stability of supersaturated pharmaceutical o/w creams.

Partial coalescence in emulsions is a destabilization mechanism whereby the droplets retain their individual identity but there is a molecular contact between their content. This process can occur under fluctuating temperatures and/or shear stress, which effects the stability and quality of emulsions. In the case of topical drug delivery systems, in particular supersaturated oil-in-water (o/w) creams, the molecular exchange of dissolved drug from one droplet to the other is a critical issue because it can induce drug crystallization and enhance crystal growth. In this work two approaches to address the problem are reported: the stability of the emulsion in relation to (i) shear exposure and (ii) temperature cycling. Some ideas on how this approach can be used to identify critical process parameters and predict long term stability of supersaturated emulsions are discussed.

Pore size distributions of biodegradable polymer microparticles in aqueous environments measured by NMR cryoporometry.

NMR cryoporometry is a unique method permitting the investigation of pores in the microporous and mesoporous regimes for samples in aqueous environments. Here, we apply the technique to porous biodegradable polymer microparticles designed as devices for drug delivery in depot formulations. The results indicate that structural features too small to be captured in surface and fracture images obtained by SEM are able to be accessed using the technique, and that the evolution of pore structure can be studied for several days as the particles swell and degrade in the aqueous environment.