Induced Cell Turnover: A Novel Therapeutic Modality for In Situ Tissue Regeneration

Induced cell turnover (ICT) is a theoretical intervention in which the targeted ablation of damaged, diseased, and/or nonfunctional cells is coupled with replacement by partially differentiated induced pluripotent stem cells in a gradual and multiphasic manner. Tissue-specific ablation can be achieved using pro-apoptotic small molecule cocktails, peptide mimetics, and/or tissue-tropic adeno-associated virus-delivered suicide genes driven by cell type-specific promoters. Replenishment with new cells can be mediated by systemic administration of cells engineered for homing, robustness, and even enhanced function and disease resistance. Otherwise, the controlled release of cells can be achieved using implanted biodegradable scaffolds, hydrogels, and polymer matrixes. In theory, ICT would enable in situ tissue regeneration without the need for surgical transplantation of organs produced ex vivo, and addresses non-transplantable tissues (such as the vasculature, lymph nodes, and the nervous system). This article outlines several complimentary strategies for overcoming barriers to ICT in an effort to stimulate further research at this promising interface of cell therapy, tissue engineering, and regenerative medicine.

Magnetically Controlled Drug Release System through Magnetomechanical Actuation

A drug release system is developed capable to modulate the drug release kinetics by the application of a magnetic field. Thus, this work reports on the production, characterization, and release kinetics of a poly(l-lactic acid) (PLLA) microporous membrane containing a zeolite (Faujasite) and a magnetic stimuli-sensitive component, magnetostrictive Terfenol-D (TD), for the release of ibuprofen (IBU) as drug model. For membranes containing IBU-loaded zeolites and TD without an applied AC magnetic field, the release kinetics is characterized by a first order release. On the other hand, the application of an AC magnetic field modifies the release profile of the membrane, leading to an increase of the release rate by more than 30%, the magnetically driven release being characterized by a super case-II within the Korsmeyer-Peppas model, indicating a release mainly driven by a swelling or erosion mechanism, induced by the magnetostrictive particles under the applied magnetic field. The increase of the TD w/w from 10% to 20% has as a consequence a decrease in the quantity of IBU released from 79% to 70%; on the contrary, increasing the H _AC intensity from 100 to 200 mT promotes an increase on the percentage of IBU released from 67% to 75%.

Adjusting inkjet printhead parameters to deposit drugs into micro-sized reservoirs

Drug delivery systems (DDS) ensure that therapeutically effective drug concentrations are delivered locally to the target site. For that reason, it is common to coat implants with a degradable polymer which contains drugs. However, the use of polymers as a drug carrier has been associated with adverse side effects. For that reason, several technologies have been developed to design polymer-free DDS. In literature it has been shown that micro-sized reservoirs can be applied as drug reservoirs. Inkjet techniques are capable of depositing drugs into these reservoirs. In this study, two different geometries of micro-sized reservoirs have been laden with a drug (ASA) using a drop-on-demand inkjet printhead. Correlations between the characteristics of the drug solution, the operating parameters of the printhead and the geometric parameters of the reservoir are shown. It is indicated that wettability of the surface play a key role for drug deposition into micro-sized reservoirs.

Development of an Experimental Drug Eluting Suprachoroidal Microstent as Glaucoma Drainage Device

PURPOSE

A novel glaucoma drainage device (GDD) with local drug delivery (LDD) system was created and characterized for safety and effectiveness after implantation into the suprachoroidal space (SCS) of rabbit eyes.

METHODS

Thin films of two different polymers, Poly(3-hydroxybutyrate) (P(3HB)) and Poly(4-hydroxybutyrate) (P(4HB)), containing the drugs mitomycin C (MitC) or paclitaxel (PTX) were attached to silicone-tubes to create LDD devices. The release kinetics of these drugs were explored in vitro using high performance liquid chromatography (HPLC).  Twenty-four New Zealand white rabbits, randomly divided into eight groups, were implanted with different kinds of microstents into SCS. The intraocular pressure (IOP) was monitored noninvasively. After 6 weeks, rabbits were sacrificed and enucleated eyes were used for anterior segment optical coherence tomography (OCT), micro magnetic resonance imaging (MRI), and histology.

RESULTS

In vitro, faster drug release from both polymers was observed for MitC compared to PTX. Comparing polymers, the release from P(3HB) matrix was slower for both drugs. MRI and OCT showed all implants maintained a proper location. An effective IOP reduction was observed for up to 6 weeks in eyes with microstents combined with a drug-releasing LDD system. Overall, the surrounding tissue revealed mild-to-moderate inflammation. No pronounced fibrosis was observed in any of the groups. However, both drugs caused damage to the neighboring retina.

CONCLUSIONS

The suprachoroidal microstent reduced IOP with mild inflammation in rabbit eyes. To avoid negative effects on the retina, it is necessary to identify novel drugs with less cytotoxicity. Future studies are needed to explore the fibrotic process over the long-term.

TRANSLATIONAL RELEVANCE

The presented data serve as a proof of principle study for the concept of a suprachoroidal drug eluting microstent. Future device improvements will be focused on the design of LDD systems and the use of specific anti-inflammatory or antifibrotic agents with less cytotoxicity compared to MitC or PTX. Long-term animal studies using a reliable glaucoma model will be a further step towards clinical application and improvement of surgical glaucoma therapy.

MEMS: Enabled Drug Delivery Systems

Drug delivery systems play a crucial role in the treatment and management of medical conditions. Microelectromechanical systems (MEMS) technologies have allowed the development of advanced miniaturized devices for medical and biological applications. This Review presents the use of MEMS technologies to produce drug delivery devices detailing the delivery mechanisms, device formats employed, and various biomedical applications. The integration of dosing control systems, examples of commercially available microtechnology-enabled drug delivery devices, remaining challenges, and future outlook are also discussed.

VEGF-releasing suture material for enhancement of vascularization: development, in vitro and in vivo study

As it has been demonstrated that bioactive substances can be delivered locally using coated surgical suture materials, the authors developed a vascular endothelial growth factor (VEGF)-releasing suture material that should promote vascularization and potentially wound healing. In this context, the study focused on the characterization of the developed suture material and the verification of its biological activity, as well as establishing a coating process that allows reproducible and stable coating of a commercially available polydioxanone suture material with poly(l-lactide) (PLLA) and 0.1μg and 1.0μg VEGF. The in vitro VEGF release kinetics was studied using a Sandwich ELISA. The biological activity of the released VEGF was investigated in vitro using human umbilical vein endothelial cells. The potential of the VEGF-releasing suture material was also studied in vivo 5days after implantation in the hind limb of Wistar rats, when the histological findings were analyzed. The essential results, enhanced cell viability in vitro as well as significantly increased vascularization in vivo, were achieved using PLLA/1.0μg VEGF-coated suture material. Furthermore, ELISA measurements revealed a high reproducibility of the VEGF release behavior. Based on the results achieved regarding the dose-effect relationship of VEGF, the stability during its processing and the release behavior, it can be predicted that a bioactive suture material would be successful in later in vivo studies. Therefore, this knowledge could be the basis for future studies, where bioactive substances with different modes of action are combined for targeted, overall enhancement of wound healing.

Small molecules and small molecule drugs in regenerative medicine

Regenerative medicine is an emerging, multidisciplinary science that aims to replace or regenerate human cells, tissues or organs, to restore or establish normal function. Research on small molecules and small molecule drugs in regenerative medicine is currently increasing. In this review, we discuss the potential applications of small molecules and small molecule drugs in regenerative medicine. These include enabling novel cell therapy approaches and augmentation of endogenous cells for tissue regeneration, facilitating the generation of target cells for cell therapy, improving the interactions between cells and biomatrices for tissue engineering, and enhancing endogenous stem cell function for tissue regeneration. We also discuss the potential challenges for small molecule drugs in regenerative medicine.