Doo Yeon Kwon

An injectable biodegradable temperature-responsive gel with an adjustable persistence window

ɛ-Caprolactone (CL) and 3-benzyloxymethyl-6-methyl-1,4-dioxane-2,5-dion (fLA), with a benzyloxymethyl group at the 3-position of the lactide, were randomly copolymerized. The methoxy polyethylene glycol (MPEG)-b-[poly(ɛ-caprolactone)-ran-poly(3-benzyloxymethyl lactide) (PCL-ran-PfLA)] diblock copolymers were designed such that the PfLA content (0-15 mol%) in the PCL segment was varied. The MPEG-b-(PCL-ran-PfLA) diblock copolymers were derivatized by introducing a pendant benzyl group (MC(x)L(y)-OBn), hydroxyl group (MC(x)L(y)-OH), or carboxylic acid group (MC(x)L(y)-COOH) at the PfLA segment. The derivatized MPEG-b-(PCL-ran-PfLA) diblock copolymer solutions exhibited sol-to-gel phase transitions upon a temperature increase. The sol-to-gel phase transition depended on both the type of functional pendant group on the PfLA and the PfLA content in the PCL segment. MC(x)L(y)-COOH diblock copolymer solutions formed gels immediately after injection into Fischer rats. The gels gradually degraded over a period of 0-6 weeks after the initial injection, and the rate of degradation increased for higher concentrations of PfLA. Immunohistochemical characterization showed that the in vivo MPEG-b-(PCL-ran-PfLA) diblock copolymer gels provoked only a modest inflammatory response. These results show that the MPEG-b-(PCL-ran-PfLA) diblock copolymer gel described here may serve as a minimally invasive therapeutic, in situ-forming gel system with an adjustable temperature-responsive and in vivo biodegradable window.

Injectable intratumoral hydrogel as 5-fluorouracil drug depot

The effectiveness of systemically administered anticancer treatments is limited by difficulties in achieving therapeutic doses within tumors, a problem that is complicated by dose-limiting side effects to normal tissue. To increase the efficacy and reduce the toxicity of systemically administered anticancer 5-fluorouracil (5-Fu) treatments in patients, intratumoral administration of an injectable hydrogel has been evaluated in the current work. The MPEG-b-(PCL-ran-PLLA) diblock copolymer (MCL) containing 5-Fu existed in an emulsion-sol state at room temperature and rapidly gelled in vivo at the body temperature. MCL acted as in vivo biodegradable drug depot over a defined experimental period. A single injection of 5-Fu-loaded MCL solution resulted in significant suppression of tumor growth, compared with repeated injection of free 5-Fu as well as saline and MCL alone. For both repeated injections of free 5-Fu and single injection of 5-Fu-loaded MCL, most of the 5-Fu was found in the tumor, indicating the maintenance of therapeutic concentrations of 5-Fu within the target tumor tissue and the prevention of systemic toxicity associated with 5-Fu in healthy normal tissues. In conclusion, this work demonstrated that intratumoral injection of 5-Fu-loaded MCL may induce significant suppression of tumor growth through effective accumulation of 5-Fu in the tumor.

Stimuli-Responsive Injectable In situ-Forming Hydrogels for Regenerative Medicines

Research on injectable in situ-forming hydrogels has been conducted in diverse biomedical applications for a long period. These hydrogels exhibit sol-to-gel phase transition in accordance with the external stimuli such as temperature change. Also, unlike the traditional surgical procedures the hydrogels have the distinct properties of easy management and minimal invasiveness via simple aqueous state injections at target sites. Currently, numerous polymer materials have been reported as potential stimulus-induced in situ–forming hydrogels. In this review, a comprehensive overview of the state-of-the-art of these rapidly developing materials has been outlined. In situ–forming hydrogels formed by electrostatic and hydrophobic interactions as well as their mechanistic characteristics and biomedical applications in regenerative medicine have also been discussed. The review concludes with perspectives on the future of stimulus-induced in situ–forming hydrogels.

A computer-designed scaffold for bone regeneration within cranial defect using human dental pulp stem cells

A computer-designed, solvent-free scaffold offer several potential advantages such as ease of customized manufacture and in vivo safety. In this work, we firstly used a computer-designed, solvent-free scaffold and human dental pulp stem cells (hDPSCs) to regenerate neo-bone within cranial bone defects. The hDPSCs expressed mesenchymal stem cell markers and served as an abundant source of stem cells with a high proliferation rate. In addition, hDPSCs showed a phenotype of differentiated osteoblasts in the presence of osteogenic factors (OF). We used solid freeform fabrication (SFF) with biodegradable polyesters (MPEG-(PLLA-co-PGA-co-PCL) (PLGC)) to fabricate a computer-designed scaffold. The SFF technology gave quick and reproducible results. To assess bone tissue engineering in vivo, the computer-designed, circular PLGC scaffold was implanted into a full-thickness cranial bone defect and monitored by micro-computed tomography (CT) and histology of the in vivo tissue-engineered bone. Neo-bone formation of more than 50% in both micro-CT and histology tests was observed at only PLGC scaffold with hDPSCs/OF. Furthermore, the PLGC scaffold gradually degraded, as evidenced by the fluorescent-labeled PLGC scaffold, which provides information to tract biodegradation of implanted PLGC scaffold. In conclusion, we confirmed neo-bone formation within a cranial bone defect using hDPSCs and a computer-designed PLGC scaffold.

Injectable in situ-forming hydrogel for cartilage tissue engineering

Methoxy polyethylene glycol-poly(ε-caprolactone) (MPEG-PCL; MP) diblock copolymers undergo a solution-to-gel phase transition at body temperature and serve as ideal biomaterials for drug delivery and tissue engineering. Here, we examined the potential use of a chondrocyte-loaded MP solution as an injectable, in situ-forming hydrogel for cartilage regeneration. The chondrocyte-MP solution underwent a temperature-dependent solution-to-gel phase transition in vitro, as shown by an increase in viscosity from 1 cP at 20-30 °C to 1.6 × 105 cP at 37 °C. The chondrocytes readily attached to and proliferated on the MP hydrogel in vitro. The chondrocyte-MP solution transitioned to a hydrogel immediately after subcutaneous injection into mice, and formed an interconnected pore structure required to support the growth, proliferation, and differentiation of the chondrocytes. The chondrocyte-MP hydrogels formed cartilage in vivo, as shown by the histological and immunohistochemical staining of glycosaminoglycans, proteoglycans, and type II collagen, the major components of cartilage. Cartilage formation increased with hydrogel implantation time, and the expression of glycosaminoglycans, and type II collagen reached maximal levels at 6 weeks post-implantation. Collectively, these data suggest that in situ-forming chondrocyte-MP hydrogels have potential as non-invasive alternatives for tissue-engineered cartilage formation.

Examination of phase transition behavior of ion group functionalized MPEG-b-PCL diblock copolymers

Thermogelling block copolymers are central to a variety of biomedical applications. Here, we examined the thermal phase transition behavior of the MPEG-b-PCL diblock copolymer (MC) with carboxyl (MC–COOH) and amine (MC–NH2) groups, and their salt forms (MC–COO−Na+ and MC–NH3+Cl−) at the chain ends of the PCL segment. All MC copolymers formed an opaque emulsion sol at room temperature when prepared as 20 wt% aqueous solutions. As the temperature increased from room temperature, a sol-to-gel transition was observed for MC, MC–COOH, and MC–NH2 copolymers, although not for their salt forms (MC–COO−Na+ and MC–NH3+Cl−). Introduction of a carboxyl and an amine group into the PCL segment decreased the crystallinity and hydrophobicity of the PCL block domains, which altered the onset temperature of gelation (the gel temperature range) and the maximum viscosity. We confirmed that the sol-to-gel phase transition behavior, which indicated the formation and destruction of a structured gel network of MC copolymers, depended on the crystallinity and hydrophobicity of the PCL domains in aqueous media.

Injectable in situ-forming hydrogels for a suppression of drug burst from drug-loaded microcapsules

Here, we describe the preparation of microcapsule formulations using in situ-forming hydrogels to achieve desired therapeutic levels over a specific period. Bovine serum albumin (BSA)-fluorescein isothiocyanate (FITC)-loaded microcapsules were prepared using a mono-axial nozzle ultrasonic atomizer with an encapsulation efficiency of approximately 65% and a particle size of approximately 60 μm. Injectable formulations were prepared by mixing BSA-FITC-loaded microcapsules (Cap) and chitosan (CH), Pluronic (PL), or methoxy poly(ethylene glycol)-b-poly(e-caprolactone) (MPEG-b-PCL) solution (MP). All formulations were prepared as solutions and became gelatinous drug depot implants after injection into the subcutaneous tissue of Sprague-Dawley (SD) rats. While monitoring in vivo BSA release, we found that the initial burst release of BSA was retarded by in situ-forming hydrogels. The Tmax and Cmax values for each formulation were significantly higher and lower, respectively, than those of the BSA-FITC-solution alone. The absolute bioavailability of BSA-FITC from each formulation depended on the viscosities of the in situ-forming hydrogels. The viscosities of the in situ-forming hydrogels were considered to be an important factor influencing the initial burst and duration of BSA release over a period of several weeks. One conclusion that might be drawn from this work is that the initial burst and sustained entire release profile depend on the hydrogel properties. In conclusion, we believe the results of the present study provide potential new insights into sustained pharmacological performance and represent a useful experimental platform using in situ-forming hydrogels for future protein delivery research.

Biodegradable poly(lactide-co-glycolide-co-ε-caprolactone) block copolymers – evaluation as drug carriers for a localized and sustained delivery system

To develop an appropriate drug carrier for drug delivery systems, we prepared random poly(lactide-co-glycolide-co-ε-caprolactone) (PLGC) copolymers in comparison to commercial poly(lactic acid-co-glycolic acid) (PLGA) grades. The molecular weights of PLGC copolymers varied from 20k to 90k g mol-1 in the total polyester segments, when poly-l-lactic acid (PLLA), polyglycolic acid (PGA), and polycaprolactone (PCL) compositions were kept constant. The lengths of PLGC copolymers varied from 10 : 10 : 80 to 40 : 40 : 20 in the PLLA : PGA : PCL segments, when the molecular weights of the total polyester segments were kept constant. The crystalline properties of the PLGA copolymers can be changed to amorphous by the incorporation of PCL segments. In vitro and in vivo degradation behavior can be easily tuned from a few days to a few weeks by changing the chemical composition of the PLGC copolymers. The in vivo inflammation associated with the PLGC implants was less pronounced than that associated with PLGA. In this study, as drug delivery carriers for locally implantable paclitaxel (Ptx) dosages, Ptx-loaded PLGC and PLGA films showed in vitro and in vivo Ptx release for 35 days. The orders of Ptx release showed profiles similar to those of in vitro and in vivo degradation of PLGC. Using near-infrared (NIR) fluorescence imaging, we confirmed the sustained release of NIR over an extended period from IR-780-loaded PLGC and PLGA implanted in live animals. In conclusion, we confirmed that compared to PLGA, PLGC effectively acts as a drug carrier for drug delivery systems.

Preparation of three-dimensional scaffolds by using solid freeform fabrication and feasibility study of the scaffolds

To adapt biomaterials for solid freeform fabrication (SFF), methoxy polyethylene glycol (MPEG)-(PLLA-co-PCL) (LxCy) block copolymers were prepared using MPEG as the initiator to precisely control the molecular weight of PLLA and PCL. The LxCy block copolymers were designed such that the PLLA and PCL content varied and their molecular weights were within 200-1000 kDa. The cylindrical LxCy scaffolds were prepared by using LxCy block copolymers in SFF. The feasibility of using LxCy block copolymers was examined in terms of flowability from the micronozzle and solidification at room temperature after scaffold printing. The flowability and solidification of LxCy block copolymers mainly depend on the proportions of PLLA and PCL. Fabrication of the cylindrical LxCy scaffolds by using SFF was rapid and showed high reproducibility. In in vivo implantation, the cylindrical LxCy scaffolds exhibited biocompatibility and gradual biodegradation on a 16 week timescale. Immunohistochemical characterization showed that the in vivo LxCy scaffolds elicit only a modest inflammatory response. Taken together, these results show that LxCy block copolymers may serve as suitable biomaterials for the fabrication of well-defined three-dimensional scaffolds by using SFF.

Preparation and characterization of polymeric micelles consisting of poly(propylene glycol) and poly(caprolactone) as a drug carrier

we describe the synthesis and solution properties of PCL-b-PPG-b-PCL triblock copolymers via ring-opening polymerization (ROP) of ε-caprolactone (CL) monomer initiated at the hydroxyl end group of poly(propylene glycol) (PPG) using HCl-Et2O as a monomer activator.