Characterization of polymeric solutions as injectable vehicles for hydroxyapatite microspheres

Alginate-based Composites Microspheres: Preparations and Applications for Bone Tissue Engineering

Alginate-based biomaterials have been extensively studied for bone tissue engineering. Scaffolds, microspheres, and hydrogels can be developed using alginate, which is biocompatible, biodegradable, and able to deliver growth factors and drugs. Alginate microspheres can be produced using crosslinking, microfluidic, three-dimensional printing, extrusion, and emulsion methods. The sizes of the alginate microspheres range from 10 µm to 4 mm. This review describes the chemical characterization and mechanical assessment of alginate-based microspheres. Combinations of alginate with hydroxyapatite, chitosan, collagen, polylactic acid, polycaprolactone, and bioglass were discussed for bone tissue repair and regeneration. In addition, alginate combinations with bone morphogenetic proteins, vascular endothelial growth factor, transforming growth factor beta-3, other growth factors, cells, proteins, drugs, and osteoinductive drugs were analyzed for tissue engineering applications. Furthermore, the biocompatibility of developed alginate microspheres was discussed for different cell lines. Finally, alginate microsphere-based composites with stem cell interaction for bone tissue regeneration were presented. In the present review, we have assessed the preclinical research on in vivo models of alginate-based microspheres for bone tissue repair and regeneration. Overall, alginate-based microspheres are potential candidates for graft substitutes and the treatment of various bone-related diseases.

Design of an Emulgel for Psoriasis Focused on Patient Preferences

Adherence to topical treatments is low and is known to be influenced by the vehicle properties. Betamethasone dipropionate (BD) is an anti-inflammatory steroid, used in psoriasis treatment in the form of an ointment, cream, or solution. The aim of this work was to develop a new vehicle for BD, focusing on the preferences of patients with psoriasis as a strategy to improve treatment adherence. Two vehicles with an aqueous external phase were explored: an emulgel and a hydrogel based on a cyclodextrin inclusion complex used to improve the aqueous solubility of BD. Since BD solubilization was not fully achieved in the hydrogel, only the emulgel was selected for further characterization. This new vehicle (emulgel) is characterized by its white, shiny appearance and good spreading properties. In comparison with petrolatum, a lower residue, higher evaporation rate, lower stickiness, and reduced ability to stain polyester fabric were observed. This vehicle also showed shear thinning behavior. The impact of this new vehicle on adherence to topical treatments should be further confirmed in clinical settings.

Engineering Immunomodulatory Biomaterials for Regenerating the Infarcted Myocardium

Coronary artery disease is a severe ischemic condition characterized by the reduction of blood flow in the arteries of the heart that results in the dysfunction and death of cardiac tissue. Despite research over several decades on how to reduce long-term complications and promote angiogenesis in the infarct, the medical field has yet to define effective treatments for inducing revascularization in the ischemic tissue. With this work, we have developed functional biomaterials for the controlled release of immunomodulatory cytokines to direct immune cell fate for controlling wound healing in the ischemic myocardium. The reparative effects of colony-stimulating factor (CSF-1), and anti-inflammatory interleukins 4/6/13 (IL4/6/13) have been evaluated in vitro and in a predictive in vivo model of ischemia (the skin flap model) to optimize a new immunomodulatory biomaterial that we use for treating infarcted rat hearts. Alginate hydrogels have been produced by internal gelation with calcium carbonate (CaCO₃) as carriers for the immunomodulatory cues, and their stability, degradation, rheological properties and release kinetics have been evaluated in vitro. CD14 positive human peripheral blood monocytes treated with the immunomodulatory biomaterials show polarization into pro-healing macrophage phenotypes. Unloaded and CSF-1/IL4 loaded alginate gel formulations have been implanted in skin flap ischemic wounds to test the safety and efficacy of the delivery system in vivo. Faster wound healing is observed with the new therapeutic treatment, compared to the wounds treated with the unloaded controls at day 14. The optimized therapy has been evaluated in a rat model of myocardial infarct (ischemia/reperfusion). Macrophage polarization toward healing phenotypes and global cardiac function measured with echocardiography and immunohistochemistry at 4 and 15 days demonstrate the therapeutic potential of the proposed immunomodulatory treatment in a clinically relevant infarct model.

Mechanical Properties of Topical Anti-Psoriatic Medicines: Implications for Patient Satisfaction with Treatment

Different types of topical preparations are available as anti-psoriatic medicines, semisolid formulations being the preferred dosage forms for the treatment of body lesions. The mechanical characterization of these semisolid formulations is seldom reported, although mechanical features have been recognized to play an important role in treatment acceptability and adherence. The aim of this study was to characterize the mechanical properties of semisolid topical formulations commercially available for psoriasis treatment. One complementary aim was to evaluate patient satisfaction with topical treatment and discuss the results according to the mechanical features of the dosage form. Eight ointments (O 1-8), five creams (C 1-5), one oleogel (G1), and one excipient (E1-petrolatum) were characterized for textural properties (spreadability and penetration tests) and flow behavior. Power law model was fitted to the results. A questionnaire for the assessment of satisfaction with topical medicines used for psoriasis treatment over 6 months was developed and applied to 79 psoriasis patients. All the tested formulations presented a shear-thinning behavior with power law indexes (n) lower than 1. Ointments were distinct from the other dosage forms, since they presented higher consistency coefficients (K), firmness, and adhesiveness and this was evidenced by hierarchical cluster analysis, which identified two clusters based on the mechanical properties. Cluster 1 included the ointments and petrolatum and the cluster 2 enclosed the creams and the gel. The clusters were associated with several attributes classified by patients as analyzed with Fisher's exact test. In all cases, higher satisfaction was observed for cluster 2. The knowledge obtained regarding the influence of the dosage form on the degree of satisfaction with the treatment could be helpful in supporting the selection of the dosage form in clinical practice and thus improve treatment adherence and clinical outcomes. The differences observed between the mechanical properties of the formulations studied may be also relevant to the industry, as guidance to the development of new medicines.

Rheological properties, biocompatibility and in vivo performance of new hydrogel-based bone fillers

Three different heterologous substitutes for bone regeneration, manufactured with equine-derived cortical powder, cancellous chips and demineralized bone matrix granules, were compared in vitro and in vivo.

In situ gelation of PEG-PLGA-PEG hydrogels containing high loading of hydroxyapatite: in vitro and in vivo characteristics

Thermosensitive hydrogels are renowned carriers that are used to deliver a variety of drugs with the aim of combating diseases. In this study, the injectability of thermosensitive hydrogels comprised of poly(ethylene glycol)-poly(lactic acid-co-glycolic acid)-poly(ethylene glycol) (PEG-PLGA-PEG, PELGE) and hydroxyapatite (HA) were examined for their ability to deliver bone morphological protein 2 (BMP-2). The physicochemical characteristics of PELGE, HA, and PELGE/HA hydrogel composites were investigated by (1)H NMR, GPC, FTIR, XRD, SEM, and TEM. The rheological properties, injectability, in vitro degradation, and in vivo biocompatibility were investigated. The hydrogel with a weight ratio of 4:6 of polymer to HA was found to be resistant to auto-catalyzed degradation of acidic monomers (LA, GA) for a period of 70 days owing to the presence of alkaline HA. Injectability was quantitatively determined by the ejected weight of the hydrogel composite at room temperature and was a close match to the weight amount predetermined by the syringe pump. The results not only revealed that the PELGE/HA hydrogel composite presented a minor tissue response in the subcutis of ICR mice at eight weeks, but they also indicated an acceptable tolerance of the hydrogel composite in animals. Thus, PELGE/HA hydrogel composite is expected to be a promising injectable orthopedic substitute because of its desirable thermosensitivity and injectability.

Biological evaluation of alginate-based hydrogels, with antimicrobial features by Ce(III) incorporation, as vehicles for a bone substitute

A novel hydrogel, based on an alginate/hyaluronate mixture and Ce(III) ions, with effective bioactive and antimicrobial ability was developed to be used as vehicle of a synthetic bone substitute producing an injectable substitute (IBS). Firstly, three different IBSs were prepared using three developed alginate-based hydrogels, the hydrogel Alg composed by alginate, the hydrogel Alg/Ch composed by an alginate/chitosan mixture and the hydrogel Alg/HA composed by an alginate/hyaluronate mixture. MG63 cells viability on the IBSs was evaluated, being observed a significantly higher cell viability on the Alg/HA_IBS at all time points, which indicates a better cell adaptation to the material, increasing their predisposition to produce extracellular matrix and thus allowing a better bone regeneration. Moreover, SEM analysis showed evident filopodia and a spreader shape of MG63 cells when seeded on Alg/HA_IBS. This way, based upon the in vitro results, the hydrogel Alg/HA was chosen to the in vivo study by subcutaneous implantation in an animal model, promoting a slight irritating tissue response and visible tissue repairing. The next step was to grant antimicrobial properties to the hydrogel that showed the best biological behavior by incorporation of Ce(III) ions into the Alg/HA, producing the hydrogel Alg/HA2. The antimicrobial activity of these hyaluronate-based hydrogels was evaluated against Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa and Candida albicans. Results showed that Ce(III) ions can significantly enhance the hydrogel antimicrobial ability without compromising the osteoconductivity improvement promoted by the vehicle association to the synthetic bone substitute.

Hydrogels in calcium phosphate moldable and injectable bone substitutes: Sticky excipients or advanced 3-D carriers?

The combination of hydrogels and calcium phosphate particles is emerging as a well-established trend for bone substitutes. Besides acting as binders for the inorganic phase, hydrogels within these hybrid materials can modulate cell colonization physically and biologically. The influence of hydrogels on the healing process can also be exploited through their capability to deliver drugs and cells for tissue engineering approaches. The aim of this review is to collect some recent progress in this field, with an emphasis on design aspects and possible future directions.