A novel bio-safe phase separation process for preparing open-pore biodegradable polycaprolactone microparticles

New Generation of Osteoinductive and Antimicrobial Polycaprolactone-Based Scaffolds in Bone Tissue Engineering: A Review

With respect to other fields, bone tissue engineering has significantly expanded in recent years, leading not only to relevant advances in biomedical applications but also to innovative perspectives. Polycaprolactone (PCL), produced in the beginning of the 1930s, is a biocompatible and biodegradable polymer. Due to its mechanical and physicochemical features, as well as being easily shapeable, PCL-based constructs can be produced with different shapes and degradation kinetics. Moreover, due to various development processes, PCL can be made as 3D scaffolds or fibres for bone tissue regeneration applications. This outstanding biopolymer is versatile because it can be modified by adding agents with antimicrobial properties, not only antibiotics/antifungals, but also metal ions or natural compounds. In addition, to ameliorate its osteoproliferative features, it can be blended with calcium phosphates. This review is an overview of the current state of our recent investigation into PCL modifications designed to impair microbial adhesive capability and, in parallel, to allow eukaryotic cell viability and integration, in comparison with previous reviews and excellent research papers. Our recent results demonstrated that the developed 3D constructs had a high interconnected porosity, and the addition of biphasic calcium phosphate improved human cell attachment and proliferation. The incorporation of alternative antimicrobials-for instance, silver and essential oils-at tuneable concentrations counteracted microbial growth and biofilm formation, without affecting eukaryotic cells' viability. Notably, this challenging research area needs the multidisciplinary work of material scientists, biologists, and orthopaedic surgeons to determine the most suitable modifications on biomaterials to design favourable 3D scaffolds based on PCL for the targeted healing of damaged bone tissue.

Microporous drug-eluting large silk particles through cryo-granulation

A facile method for the preparation of large, microporous, drug-loaded particles is presented. High shear bollus injections of silk with cross-linker and drug colloids into super-cooled hexane were utilized to trigger phase separation of silk droplets, followed by immediate freezing at -60°C. A subsequent -20°C freeze-thaw of the frozen droplets resulted in self-assembly (crystallization) of the silk. The silk particles developed an internal interconnected microporous morphology with 0.1-10 µm in diameter pores. The silk particles ranged in diameter from 100 to 1,300 µm, with particle mean diameter and polydispersity controlled by the starting concentration of the cross-linking agent and silk, the rheology of the reaction mixture, and the injection pressure (80 - 300kPa). Cryogranulation provided a one-step process to produce microporous meso-scale silk particles with encapsulated drugs, such as doxorubicin chloride (DoxR), tobramycin sulfate (TS), kanamycin sulfate (KS) or gentamicin sulfate (GS). Almost 100% drug encapsulation efficiency was achieved in the process, and subsequent release profiles depended on the starting concentration of both the drug, silk, and pH of the elution medium. Kirby-Bauer tests and bioluminescent imaging confirmed the retention of anti-bacterial potency of the antibiotics pre-encapsulated in the cryo-particles, and macroparticles cytocompatibility towards human fibroblast and kidney cells.

Polymer Bioprocessing to Fabricate 3D Scaffolds for Tissue Engineering

Traditional methods for polymer processing involve the use of hazardous organic solvents which may compromise the biological function of scaffolds in tissue engineering. Indeed, the toxic effect of them on biological microenvironment has a tremendous impact on cell fate so altering the main activities involved in in vitro tissue formation. To date, extensive researches focus on seeking newer methods for bio-safely processing polymeric biomaterials to be implanted in the human body. Here, we aim at over viewing two approaches based on solvent free or green solvent based processes in order to identify alternative solutions to fabricate bio-inspired scaffolds to be successfully used in regenerative and degenerative medicine.

Bio-safe processing of polylactic-co-caprolactone and polylactic acid blends to fabricate fibrous porous scaffolds for in vitro mesenchymal stem cells adhesion and proliferation

In this study, the design and fabrication of porous scaffolds, made of blends of polylactic-co-caprolactone (PLC) and polylactic acid (PLA) polymers, for tissue engineering applications is reported. The scaffolds are prepared by means of a bio-safe thermally induced phase separation (TIPS) approach with or without the addition of NaCl particles used as particulate porogen. The scaffolds are characterized to assess their crystalline structure, morphology and mechanical properties, and the texture of the pores and the pore size distribution. Moreover, in vitro human mesenchymal stem cells (hMSCs) culture tests have been carried out to demonstrate the biocompatibility of the scaffolds. The results of this study demonstrate that all of the scaffold materials processed by means of TIPS process are semi-crystalline. Furthermore, the blend composition affected polymer crystallization and, in turn, the nano and macro-structural properties of the scaffolds. Indeed, neat PLC and neat PLA crystallize into globular and randomly arranged sub micro-size scale fibrous conformations, respectively. Concomitantly, the addition of NaCl particles during the fabrication route allows for the creation of an interconnected network of large pores inside the primary structure while resulted in a significant decrease of scaffolds mechanical response. Finally, the results of cell culture tests demonstrate that both the micro and macro-structure of the scaffold affect the in vitro hMSCs adhesion and proliferation.

Dewetting based fabrication of fibrous micro-scaffolds as potential injectable cell carriers

Although regenerative medicine utilizing tissue scaffolds has made enormous strides in recent years, many constraints still hamper their effectiveness. A limitation of many scaffolds is that they form surface patches, which are not particularly effective for some types of "wounds" that are deep within tissues, e.g., stroke and myocardial infarction. In this study, we reported the generation of fibrous micro-scaffolds feasible for delivering cells by injection into the tissue parenchyma. The micro-scaffolds (widths<100μm) were made by dewetting of poly(lactic-co-glycolic acid) thin films containing parallel strips, and cells were seeded to form cell/polymer micro-constructs during or post the micro-scaffold fabrication process. Five types of cells including rat induced vascular progenitor cells were assessed for the formation of the micro-constructs. Critical factors in forming fibrous micro-scaffolds via dewetting of polymer thin films were found to be properties of polymers and supporting substrates, temperature, and proteins in the culture medium. Also, the ability of cells to attach to the micro-scaffolds was essential in forming cell/polymer micro-constructs. Both in vitro and in vivo assessments of injecting these micro-scaffolding constructs showed, as compared to free cells, enhanced cell retention at the injected site, which could lead to improved tissue engineering and regeneration.