Development and applications of injectable poly(ortho esters) for pain control and periodontal treatment

In Situ Generated Medical Devices

Medical devices play a major role in all areas of modern medicine, largely contributing to the success of clinical procedures and to the health of patients worldwide. They span from simple commodity products such as gauzes and catheters, to highly advanced implants, e.g., heart valves and vascular grafts. In situ generated devices are an important family of devices that are formed at their site of clinical function that have distinct advantages. Among them, since they are formed within the body, they only require minimally invasive procedures, avoiding the pain and risks associated with open surgery. These devices also display enhanced conformability to local tissues and can reach sites that otherwise are inaccessible. This review aims at shedding light on the unique features of in situ generated devices and to underscore leading trends in the field, as they are reflected by key developments recently in the field over the last several years. Since the uniqueness of these devices stems from their in situ generation, the way they are formed is crucial. It is because of this fact that in this review, the medical devices are classified depending on whether their in situ generation entails chemical or physical phenomena.

Novel Bioactive and Therapeutic Dental Polymeric Materials to Inhibit Periodontal Pathogens and Biofilms

Periodontitis is a common infectious disease characterized by loss of tooth-supporting structures, which eventually leads to tooth loss. The heavy burden of periodontal disease and its negative consequence on the patient's quality of life indicate a strong need for developing effective therapies. According to the World Health Organization, 10⁻15% of the global population suffers from severe periodontitis. Advances in understanding the etiology, epidemiology and microbiology of periodontal pocket flora have called for antibacterial therapeutic strategies for periodontitis treatment. Currently, antimicrobial strategies combining with polymer science have attracted tremendous interest in the last decade. This review focuses on the state of the art of antibacterial polymer application against periodontal pathogens and biofilms. The first part focuses on the different polymeric materials serving as antibacterial agents, drug carriers and periodontal barrier membranes to inhibit periodontal pathogens. The second part reviews cutting-edge research on the synthesis and evaluation of a new generation of bioactive dental polymers for Class-V restorations with therapeutic effects. They possess antibacterial, acid-reduction, protein-repellent, and remineralization capabilities. In addition, the antibacterial photodynamic therapy with polymeric materials against periodontal pathogens and biofilms is also briefly described in the third part. These novel bioactive and therapeutic polymeric materials and treatment methods have great potential to inhibit periodontitis and protect tooth structures.

The Synthesis of Hydroxybutyrate-Based Block Polyurethane from Telechelic Diols with Robust Thermal and Mechanical Properties

A series of novel amphiphilic block polyurethanes (PUHE) have been successfully synthesized by solution polymerization of the derived PHB-diol and poly(ethylene glycol) with a coupling agent of 1,6-hexamethylene diisocyanate (HDI), while the PHB-diol was prepared via the transesterification of PHB and ethylene glycol. The hydroxyl contents in PHB-diols range from 1.36 to 1.99 (the molar ratio) as determined by nonaqueous titration. The molecular weight and chemical compositions of PUHE and PHB-diol were investigated by GPC,1H NMR, and FTIR in detail, which confirm the successful synthesis of PUHE. The tensile strength and elongation at break of PUHE could reach as high as 20 MPa and 210%, as the content of PHB in PUHE is 33%. TGA curves indicate that block-bonding between PHB-diol and PEG increases the thermal stability of PHB-diol. Film degradation of PUHE was studied by weight loss and scanning electron microscope (SEM). It could be concluded that degradation occurred gradually from the surface to the inside and that the degradation rate could be controlled by adjusting the PHB/PEG ratios. These properties make PUHE able to be used as a biodegradable thermoplastic elastomer.

Mechanistic analysis of PLGA/HPMC-based in-situ forming implants for periodontitis treatment

In-situ forming implant formulations based on poly(lactic-co-glycolic acid) (PLGA), acetyltributyl citrate (ATBC), minocycline HCl, N-methyl pyrrolidone (NMP) and optionally hydroxypropyl methylcellulose (HPMC) were prepared and thoroughly characterized in vitro. This includes electron paramagnetic resonance (EPR), nuclear magnetic resonance ((1)H NMR), mass change and drug release measurements under different conditions, optical microscopy, size exclusion chromatography (SEC) as well as antibacterial activity tests using gingival crevicular fluid samples from periodontal pockets of periodontitis patients. Based on these results, deeper insight into the physico-chemical phenomena involved in implant formation and the control of drug release could be gained. For instance, the effects of adding HPMC to the formulations, resulting in improved implant adherence and reduced swelling, could be explained. Importantly, the in-situ formed implants effectively hindered the growth of bacteria present in the patients' periodontal pockets. Interestingly, the systems were more effectively hindering the growth of pathogenic bacterial strains (e.g., Fusobacterium nucleatum) than that of strains with a lower pathogenic potential (e.g., Streptococcus salivarius). In vivo, such a preferential action against the pathogenic bacteria can be expected to give a chance to the healthy flora to re-colonize the periodontal pockets.

A mini-review on novel intraperiodontal pocket drug delivery materials for the treatment of periodontal diseases

Periodontal disease is defined as chronic inflammatory condition characterized by the destruction of the periodontal tissues causing loss of connective tissue attachment, loss of alveolar bone, and the formation of pathological pockets around the diseased teeth. The use of systemic antibiotics has been advocated for its treatment, but concerns emerged with respect to adverse drug reactions and its contribution to bacterial resistance. Thus local drug delivery devices have been developed that aim to deliver a high concentration of antimicrobial drugs directly to the affected site, while minimizing drug's systemic exposure. A burst release of antimicrobial agent from carrier, resulting in a short and inadequate exposure of bacteria residing in periodontal pocket to the agent, remains the main challenge of current local delivery systems for the treatment of periodontal disease. This review aims to investigate and compare different local antimicrobial delivery systems with regard to the treatment of periodontal disease.

In-situ forming composite implants for periodontitis treatment: How the formulation determines system performance

Periodontitis is the primary cause of tooth loss in adults and a very wide-spread disease. Recently, composite implants, based on a drug release rate controlling polymer and an adhesive polymer, have been proposed for an efficient local drug treatment. However, the processes involved in implant formation and the control of drug release in these composite systems are complex and the relationships between the systems' composition and the implants' performance are yet unclear. In this study, advanced characterization techniques (e.g., electron paramagnetic resonance, EPR) were applied to better understand the in-situ forming implants based on: (i) different types of poly(lactic-co-glycolic acid) (PLGA) as drug release rate controlling polymers; (ii) hydroxypropyl methylcellulose (HPMC) as adhesive polymer; and (iii) doxycycline or metronidazole as drugs. Interestingly, HPMC addition to shorter chain PLGA slightly slows down drug release, whereas in the case of longer chain PLGA the release rate substantially increases. This opposite impact on drug release was rather surprising, since the only difference in the formulations was the polymer molecular weight of the PLGA. Based on the physico-chemical analyses, the underlying mechanisms could be explained as follows: since longer chain PLGA is more hydrophobic than shorter chain PLGA, the addition of HPMC leads to a much more pronounced facilitation of water penetration into the system (as evidenced by EPR). This and the higher polymer lipophilicity result in more rapid PLGA precipitation and a more porous inner implant structure. Consequently, drug release is accelerated. In contrast, water penetration into formulations based on shorter chain PLGA is rather similar in the presence and absence of HPMC and the resulting implants are much less porous than those based on longer chain PLGA.

In situ forming implants for periodontitis treatment with improved adhesive properties

Novel in situ forming implants are presented showing a promising potential to overcome one of the major practical hurdles associated with local periodontitis treatment: limited adhesion to the surrounding tissue, resulting in accidental expulsion of at least parts of the implants from the patients' pockets. This leads to high uncertainties in the systems' residence times at the site of action and in the resulting drug exposure. In the present study, the addition of different types and amounts of plasticizers (acetyltributyl citrate and dibutyl sebacate) as well as of adhesive polymers (e.g., cellulose derivatives such as hydroxypropyl methylcellulose) is shown to allow for a significant increase in the stickiness of poly(lactic-co-glycolic acid)-based implants. The systems are formed in situ from N-methyl pyrrolidone-based liquid formulations. Importantly, at the same time, good plastic deformability of the implants can be provided and desired drug release patterns can be fine-tuned using several formulation tools. The antimicrobial activity of this new type of in situ forming implants, loaded with doxycycline hyclate, was demonstrated using the agar well diffusion method and multiple Streptococcus strains isolated from the oral microflora of patients suffering from periodontitis.

Critical evaluation of biodegradable polymers used in nanodrugs

Use of biodegradable polymers for biomedical applications has increased in recent decades due to their biocompatibility, biodegradability, flexibility, and minimal side effects. Applications of these materials include creation of skin, blood vessels, cartilage scaffolds, and nanosystems for drug delivery. These biodegradable polymeric nanoparticles enhance properties such as bioavailability and stability, and provide controlled release of bioactive compounds. This review evaluates the classification, synthesis, degradation mechanisms, and biological applications of the biodegradable polymers currently being studied as drug delivery carriers. In addition, the use of nanosystems to solve current drug delivery problems are reviewed.

Biodegradable thermogelling poly[(R)-3-hydroxybutyrate]-based block copolymers: micellization, gelation, and cytotoxicity and cell culture studies

A series of biodegradable multiblock poly(ester urethane)s having poly[(R)-3-hydroxybutyrate] (PHB), poly(ethylene glycol) (PEG), and poly(propylene glycol) (PPG) segments was prepared. The critical micellization concentration (CMCs) of these water-soluble poly(ester urethane)s were determined at different temperatures in order to calculate the thermodynamic parameters for the process of micelle formation. The process for micelle formation was found to be entropy-driven. The thermogelling behavior of the aqueous polymer solution was studied by (1)H and (13)C NMR spectroscopy at different temperatures. We obtained valuable molecular level information regarding the state of the copolymer in solution based on the variation of the peak widths. Cytotoxicity studies performed on the extracts of the copolymer gel indicate good cell compatibility. Cells attach on the surface of the gel much better than on the commercially available PEG-PPG-PEG triblock copolymer. These studies indicate a potential for the copolymer gel to be used for tissue engineering applications.

Pharmaceutical organogels prepared from aromatic amino acid derivatives

Organogels are semi-solid systems in which an organic liquid phase is immobilized by a 3-dimensional network composed of self-assembled gelator molecules. Although there is a large variety of organogel systems, relatively few have been investigated in the field of drug delivery, owing mostly to the lack of information on their biocompatibility and toxicity. In this work, organogelator-biocompatible structures based on aromatic amino acids, namely, tyrosine, tryptophan, and phenylalanine were synthesized by derivatization with aliphatic chains. Their ability to gel an injectable vegetable oil (i.e. safflower oil) and to sustain the release of a model anti-Alzheimer drug (i.e. rivastigmine) was then evaluated. Organogels and molecular packing were characterized by differential scanning calorimetry, rheology analysis, Fourier-transform infrared spectroscopy and X-ray crystallography. The amino acid derivatives were able to gel safflower oil through van der Waals interactions and H-bonds. Tyrosine-derivatives produced the strongest gels while tryptophan was associated with poor gelling properties. The superior gelling ability of tyrosine derivatives could be explained by their well-structured 2-dimensional packing in the network. The addition of an optimal N-methyl-2-pyrrolidone amount to tyrosine gels fluidized the network and allowed their injection through conventional needles. Upon contact with an aqueous medium, the gels formed in situ and released entrapped rivastigmine in a sustained fashion.

Hydrolytic degradation and protein release studies of thermogelling polyurethane copolymers consisting of poly[(R)-3-hydroxybutyrate], poly(ethylene glycol), and poly(propylene glycol)

This paper reports the hydrolytic degradation and protein release studies for a series of newly synthesized thermogelling tri-component multi-block poly(ether ester urethane)s consisting of poly[(R)-3-hydroxybutyrate] (PHB), poly(propylene glycol) (PPG), and poly(ethylene glycol) (PEG). The poly(PEG/PPG/PHB urethane) copolymer hydrogels were hydrolytically degraded in phosphate buffer at pH 7.4 and 37 degrees C for a period of up to 6 months. The mass loss profiles of the copolymer hydrogels were obtained. The hydrogel residues at different time periods of hydrolysis were visualized by scanning electron microscopy, which exhibited increasing porosity with time of hydrolysis. The degradation products in the buffer were characterized by GPC, (1)H NMR, MALDI-TOF, and TGA. The results showed that the ester backbone bonds of the PHB segments were broken by random chain scission, resulting in a decrease in the molecular weight. In addition, the constituents of degradation products were found to be 3-hydroxybutyric acid monomer and oligomers of various lengths (n=1-5). The protein release profiles of the copolymer hydrogels were obtained using BSA as model protein. The results showed that the release rate was controllable by varying the composition of the poly(ether ester urethane)s or by adjusting the concentration of the copolymer in the hydrogels. Finally, we studied the correlation between the protein release characteristics of the hydrogels and their hydrolytic degradation. This is the first example that such a correlation has been attempted for a biodegradable thermogelling copolymer system.

Polymers as biomaterials for tissue engineering and controlled drug delivery

The advent of biodegradable polymers has significantly influenced the development and rapid growth of various technologies in modern medicine. Biodegradable polymers are mainly used where the transient existence of materials is required and they find applications as sutures, scaffolds for tissue regeneration, tissue adhesives, hemostats, and transient barriers for tissue adhesion, as well as drug delivery systems. Each of these applications demands materials with unique physical, chemical, biological, and biomechanical properties to provide efficient therapy. Consequently, a wide range of degradable polymers, both natural and synthetic, have been investigated for these applications. Furthermore, recent advances in molecular and cellular biology, coupled with the development of novel biotechnological drugs, necessitate the modification of existing polymers or synthesis of novel polymers for specific applications. This review highlights various biodegradable polymeric materials currently investigated for use in two key medical applications: drug delivery and tissue engineering.

In situ forming parenteral drug delivery systems: an overview

Biodegradable injectable in situ forming drug delivery systems represent an attractive alternative to microspheres and implants as parenteral depot systems. Their importance will grow as numerous proteins will lose their patent protection in the near future. These devices may offer attractive opportunities for protein delivery and could possibly extend the patent life of protein drugs. The controlled release of bioactive macromolecules via (semi-) solid in situ forming systems has a number of advantages, such as ease of administration, less complicated fabrication, and less stressful manufacturing conditions for sensitive drug molecules. For these reasons, a number of polymeric drug delivery systems with the ability to form a drug reservoir at the injection site are under investigation. Here, we review various strategies used for the preparation of in situ forming parenteral drug depots and their potential benefits/draw-backs, especially with regard to the delivery of protein drug candidates.

Poly(ortho esters): synthesis, characterization, properties and uses

Over the last 30 years, poly(ortho esters) have evolved through four families, designated as POE I, POE II, POE III and POE IV. Of these, only POE IV has been shown to have all the necessary attributes to allow commercialization, and such efforts are currently underway. Dominant among these attributes is synthesis versatility that allows the facile and reproducible production of polymers having the desired mechanical and thermal properties as well as desired erosion rates and drug release rates that can be varied from a few days to many months. Further, the polymer is stable at room temperature when stored under anhydrous conditions and undergoes an erosion process confined predominantly to the surface layers. Important consequences of surface erosion are controlled and concomitant drug release as well as the maintenance of an essentially neutral pH in the interior of the matrix because acidic hydrolysis products diffuse away from the device. Two physical forms of such polymers are under development. One form, solid materials, can be fabricated into shapes such as wafers, strands, or microspheres. The other form are injectable semi-solid materials that allow drug incorporation by a simple mixing at room temperature and without the use of solvents. GMP toxicology studies on one family of POE IV polymers has been concluded, an IND filed and Phase I clinical trials are in progress. Important applications under development are treatment of post-surgical pain, osteoarthritis and ophthalmic diseases as well as the delivery of proteins, including DNA. Block copolymers of poly(ortho ester) and poly(ethylene glycol) have been prepared and their use as a matrix for drug delivery and as micelles, primarily for tumor targeting, are being explored.

Post surgical pain management with poly(ortho esters)

Poly(ortho esters), POE, are synthetic bioerodible polymers that can be prepared as solid materials, or as viscous, injectable polymers. These materials have evolved through a number of families, and the latest member of this family, POE IV, is particularly well suited to drug delivery since latent acid is integrated into the polymer backbone, thereby, modulating surface erosion. POE IV predominantly undergoes surface erosion and is able to moderate drug release over periods from days to many months. One indication in which the POE IV polymer is currently being investigated is in sustained post-surgical pain management. The local anesthetic agent, mepivacaine, has been incorporated into a viscous, injectable POE IV and its potential to provide longer-acting anesthesia has been explored in non-clinical models.