This article was downloaded by: [The Librarian]On: 23 October 2014, At: 22:39Publisher: RoutledgeInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: MortimerHouse, 37-41 Mortimer Street, London W1T 3JH, UK

African Journal of Science, Technology, Innovationand DevelopmentPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/rajs20

A review of polymeric biomaterials research fortissue engineering and drug delivery applicationsat the Centre for Biomedical and BiomaterialsResearch, MauritiusArchana Bhaw-Luximona, Roubeena Jeetaha, Nowsheen Goonooa, Anisha Veerena, YeshmaJugdawaa & Dhanjay Jhurrya

a Centre of Excellence for Biomedical and Biomaterials Research, University of Mauritius,MSIRI Building, Réduit, MauritiusPublished online: 21 Oct 2014.

To cite this article: Archana Bhaw-Luximon, Roubeena Jeetah, Nowsheen Goonoo, Anisha Veeren, Yeshma Jugdawa &Dhanjay Jhurry (2014) A review of polymeric biomaterials research for tissue engineering and drug delivery applicationsat the Centre for Biomedical and Biomaterials Research, Mauritius, African Journal of Science, Technology, Innovation andDevelopment, 6:2, 145-157, DOI: 10.1080/20421338.2014.924270

To link to this article: http://dx.doi.org/10.1080/20421338.2014.924270

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose ofthe Content. Any opinions and views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be reliedupon and should be independently verified with primary sources of information. Taylor and Francis shallnot be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and otherliabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to orarising out of the use of the Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

African Journal of Science, Technology, Innovation and Development is co-published by Taylor & Francis and NISC (Pty) Ltd

African Journal of Science, Technology, Innovation and Development, 2014Vol. 6, No. 2, 145–157, http://dx.doi.org/10.1080/20421338.2014.924270© 2014 African Journal of Science, Technology, Innovation and Development

A review of polymeric biomaterials research for tissue engineering and drug delivery applications at the Centre for Biomedical and Biomaterials Research, Mauritius

Archana Bhaw-Luximon, Roubeena Jeetah, Nowsheen Goonoo, Anisha Veeren, Yeshma Jugdawa, Dhanjay Jhurry*

Centre of Excellence for Biomedical and Biomaterials Research, University of Mauritius, MSIRI Building, Réduit, Mauritius*Corresponding author e-mail: djhurry@uom.ac.mu

The purpose of this review article is to showcase research in the area of polymeric nanobiomaterials and nanocarriers for drug delivery, especially on the economically fast-growing African continent where research in the field of advanced polymers and nanomedicine can play an important role in addressing crucial health issues. In biomaterials research, we have developed a new family of poly(ester-ether)s and shown that poly(methyl dioxanone) (PMeDX) can efficiently assist in fine-tuning mechanical and biological properties of scaffolds for tissue engineering applications. Interestingly, degradation of scaffold films was proceeded by bulk erosion, whereas that of fibres took place by a surface erosion mechanism. In vitro cell culture studies conducted using human dermal fibroblasts showed that the electrospun polydioxanone/poly(methyl dioxanone) (PDX/PMeDX) nanofibrous scaffolds supported better cell attachment and proliferation compared to electrospun PDX. Our main focus has been on the engineering of various self-assembled nanomicelles based on a biodegradable poly(dioxanone-co-methyl dioxanone) core and hydrophilic poly(ethylene glycol) or poly(vinyl pyrolidone) or polylysine or oligoagarose shell. High drug encapsulation efficiency and prolonged drug release have been demonstrated. Adjustment of the dioxanone to methyl dioxanone ratio gives a range of copolymers whose physicochemical and biological properties can be tuned to meet specific drug delivery requirements. The efficacy of these copolymers to encapsulate and release anti-inflammatory, anti-tuberculosis drugs and anti-cancer drugs has been tested and are quite promising.

Keywords: amphiphilic block and graft copolymers, drug delivery carriers, nanobiomaterials, nanomedicine, nanomicelles

JEL classification: L60, L65, O30

IntroductionRegenerative medicine is currently a US$500 billion market with focus on biomaterials and stem-cell therapies. Three major markets for regenerative medicine products are: (1) repair and replacement of bone, cartilage and other tissues for orthopaedic applications, (2) therapies to treat cardio-vascular disease and (3) treatments able to repair and reverse neurologic damage caused by trauma or disease processes including nerve repair. The need for scaffolds with improved physicochemical, mechanical and biological properties is a key element for the development of this area.

Personalised medicine is individualised treatment and care based on personal and genetic variation. This represents globally more than a US$200 billion market with a projected annual growth of 11% per annum. To adapt to changes, strategic developments are taking place at the level of the pharmaceutical industry, which is moving from blockbuster drugs to more targeted drugs. The success of personalised and preventive medicine will depend to a large extent on access to genomic, proteomic and metabolomic information together with high-throughput technologies. Mauritius is endeavouring to develop a knowledge-based economy by encouraging the setting-up of biomedical and ocean industries.

The Centre for Biomedical and Biomaterials Research (CBBR), set up in 2011 at the University of Mauritius, aims to spearhead biomedical research and act as a bridge between the university and industry. CBBR focuses on research at the frontiers of materials science, biological sciences, and medicine and pharmacy using enabling technologies such as biotechnology and nanotechnology (Figure 1). CBBR research thrusts include (1) advanced polymer materials, biomaterials and nano-drug delivery as well as the development of value-added products from indigenous land and marine resources and (2) biopharma-ceuticals based on endemic medicinal plants, their biolog-ical activity and molecular mechanisms of action for the prevention of diabetes, cardiovascular diseases and cancer.

This paper presents a review of research undertaken at CBBR based on the use of polymeric biomaterials as scaffolds and as nanocarriers for controlled or sustained drug delivery applications.

Materials and methodsPoly(ester-ether) scaffoldsSynthesis of copolymersPoly(dioxanone-co-methyl dioxanone) [P(DX-co-MeDX)] random copolymers were synthesised by

Dow

nloa

ded

by [

The

Lib

rari

an]

at 2

2:39

23

Oct

ober

201

4

146 Bhaw-Luximon et al.— African Journal of Science, Technology, Innovation and Development 2014, Vol. 6 No. 2, pp. 145–157

procedures previously reported by Lochee et al. (2009). Diblock polycaprolactone-b-poly(dioxanone-co-methyl dioxanone) [PCL-b-P(DX-co-MeDX)] polymers were synthesised as described previously (Goonoo et al. 2012).

Preparation of blend films1,1,1,3,3,3-Hexafluoroisopropanol (HFIP) from Apollo Scientific Limited was used as received. PDX/PMeDX blend films were prepared by solvent casting at room temperature. For example, a 90/10 blend film (10% w/v) was prepared by dissolving 0.36 g PDX and 0.04 g PMeDX in 2 ml HFIP until completely homogenised. The mixture was then poured into a Teflon mould (40 mm × 10 mm × 4 mm) and the solvent allowed to evaporate in a fume hood for 24 h.

ElectrospinningBlend films were immersed in HFIP in separate vials at a concentration of 100 mg ml−1 and left overnight on a shaker plate. Polymer solutions were electrospun at a rate of 3.5 ml h−1, air-gap distance of 20 cm and a voltage of +26 kV. Continuous, non-woven fibres were collected on a rotating grounded rectangular mandrel (7.5 × 2.5 × 0.5 cm). The resulting electrospun scaffolds were

removed from the mandrel and stored in a desiccation chamber until further analysis.

Drug delivery devices

Synthesis of diblock MPEG-b-P(DX-co-MeDX) and triblock P(DX-co-MeDX)-b-PEG-b-P(DX-co-MeDX)Dioxanone (DX) and methyl dioxanone (MeDX) were synthesised in accordance with procedures previously reported (Lochee et al. 2010). Tin (II) octanoate was used as received from Aldrich. Methoxyhydroxy poly(ethylene glycol) (MPEG) of molar mass 2000, was used as received from International Laboratory, USA. Jeffamine® ED-2003 (Mw = 2000 g mol−1) was used as received from Huntsman Corporation, USA.

A range of diblock MPEG-b-P(DX-co-MeDX) and triblock P(DX-co-MeDX)-b-PEG-b-P(DX-co-MeDX) copolymers were synthesised as described previously (Jeetah et al. 2012: 1168). Briefly, MPEG-b-P(DX-co-MeDX) and P(DX-co-MeDX)-b-PEG-b-P(DX-co-MeDX) copolymers were synthesised by ring-opening polymerisation of DX and MeDX with MPEG or di-amino-terminated PEG (Jeffamine® ED-2003) as macroinitiator in the presence of tin (II) octanoate

Research areas at CBBR

Biomaterials Drug delivery systems

PDX and PmeDX blends Self-assembledAmphilic Block andGraft Copolymers

Electrospun nanofibres Solution castfilms

Nanoscaffolds Microscaffolds

Tissue engineeringapplications

Nanomicelles asdrug carriers

Oligoagarose-g-PCLPolysucrose-g-PCL

PEG-b-(DX-co-MeDX)PEG-b-P(DX-co-MeDX)2

PLys-b-PCLPVP-b-PCL

Figure 1: Research areas at the Centre for Biomedical and Biomaterials Research (CBBR), University of Mauritius (PEG: -methoxy polyethylene oxide or polyethylene oxide; DX: dioxanone; MeDX: methyl dioxanone; PLys: polylysine;PCL: polycaprolactone; PVP: polyvinylpyrrolidone)

Dow

nloa

ded

by [

The

Lib

rari

an]

at 2

2:39

23

Oct

ober

201

4

A review of polymeric biomaterials research for tissue engineering and drug delivery applications at CBBR 147

at 80 °C. Copolymers were purified by precipita-tion in diethyl ether followed by several washings with petroleum ether and dried under vacuum before use in drug loading experiments.

Synthesis of Poly(vinyl pyrrolidone)-b-Polycaprolactone [PVP-b-PCL]This synthesis was reported in a previous paper by some of us (Veeren et al. 2013). Block copolymers were prepared by atom transfer radical polymerisation (ATRP) of N-vinyl pyrrolidone (NVP) using bromo-polycap-rolactone (PCL-Br) as macroinitiator in the presence of copper (I) bromide/bipyridine (CuBr/Bpy) as a catalyst system under inert atmosphere. A typical experiment for synthesis of PVP50-b-PCL50, is here described: PCL-Br (0.1 g, 1.7 × 10−5 mol), CuBr (0.01 g, 3.4 × 10−5 mol) and Bpy (0.01 g, 6.8 × 10−5 mol) in the ratio 1:2:4 was added to a reaction tube containing NVP (91 μL) in a glove box under argon. Bulk polymerisation was performed in an oil bath at 110 °C between 24–120 h. After the required reaction time, the mixture was cooled and diluted with chloroform. The solution was then passed through a basic alumina column to remove the catalyst and the solvent evaporated to dryness. The residue was washed several times with ethanol and the product obtained was dried under vacuum and reprecipitated in diethyl ether. The remaining product was dried under vacuum for 24 h.

Drug loadingPyrazinamide (PZA) tablets were obtained from Concept Pharmaceuticals Ltd, India. Rifampicin (RIF) capsules and RIF/isoniazid (INH) capsules were obtained from Sandoz Private Limited, India. Dialysis membrane of MWCO 3500 was purchased from Spectra® Pro, Spectrum Laboratories, Inc., USA. Phosphate buffered saline (PBS) tablets (pH = 7.4) were obtained from Sigma Aldrich.

Loading and release techniques have been reported by us in previous papers (Jeetah et al. 2013; Veeren et al. 2013) and are here summarised.

Drugs (RIF, INH and PZA) were loaded into copoly-mers using an acetone volatilisation method: drug and copolymer were dissolved in acetone and stirred at room temperature. Double distilled water was added drop-wise and stirred for an additional 2–6 h. The solution was dialysed against deionised water overnight with a dialysis membrane of MWCO 3500 and freeze-dried. Drug-free nanoparticles were prepared in a similar way, but without the dialysis step.

Drug releaseFreeze-dried drug-loaded nanoparticles were suspended in PBS solution and transferred to a dialysis bag. The dialysis bag was placed in PBS at 37 °C. At predeter-mined intervals, 1 ml of PBS was taken from the external medium and replaced by fresh PBS. The drug

concentration was determined using ultraviolet (UV) spectroscopy. By comparing the amount of the released drug and total drug loading, cumulative releases were obtained.

Results and discussionPoly(ester-ethers) as scaffolds for tissue engineering applicationsThe main objective of this thrust is to engineer polymer-based scaffolds for tissue engineering applications. The major concern in the creation of extracellular matrix analogue structures lies in promoting cellular penetra-tion and not just cell proliferation on the surface of the scaffold or production of new extracellular matrix. Engineering of scaffolds is critical and tailoring of polymer properties is essential for their good performance (Goonoo et al. 2013). Scaffolds for tissue engineering applications should be biocompatible, biodegradable and porous and should possess appropriate mechanical properties.

To this end, several natural and synthetic polymers have been investigated. However, these materials do not meet all criteria in terms of mechanical and degradation behaviours. Copolymerisation and blending are often considered to improve their processability or alteration of mechanical and biological properties. Biopolymers were found to favour cell adhesion and proliferation due to the presence of cell recognition sites, but they lack the appropriate mechanical strength for tissue engineering applications. Synthetic polymers, on the other hand, possess excellent mechanical properties but because of their hydrophobic character, cell affi nities towards them are usually poor, which leads to complement activation and liver accumulation.

The ideal biomaterial is yet to be designed and attention is focused on copolymers and blends to adjust the physicochemical, mechanical and biological properties. The most commonly investigated synthetic biocompatible polymers as biomaterials remain the poly(lactide-glycolide)s (PLGAs). Poly(dioxanone), a biodegradable poly(ester-ether), is also an interesting material. The latter was introduced by Ethicon in 1981 and marketed as US Food and Drug Administration approved monofi lament suture. More recently, a few applications have been developed where PDX is used in the elaboration of cardiac valves or drug delivery devices. New materials based on combinations of PDX with other biodegradable polymers such as PCL have been elaborated by a few groups. However, the development of that family of polymers has remained almost a virgin area.

Inspired by the PLGA family, our group reported on the synthesis and homopolymerisation of a dioxanone analogue, namely MeDX (Lochee et al. 2009, 2010) and its copolymerisation with dioxanone to produce a range of random copolymers (Wolfe et al. 2011). Figure 2 gives

Dow

nloa

ded

by [

The

Lib

rari

an]

at 2

2:39

23

Oct

ober

201

4

148 Bhaw-Luximon et al.— African Journal of Science, Technology, Innovation and Development 2014, Vol. 6 No. 2, pp. 145–157

the structures of 1,4-dioxan-2-one and 3-methyl-1,4-di-oxan-2-one. D,L-3-methyl-1,4-dioxan-2-one (MeDX) has been copolymerised with dioxanone or its homopolymer (PMeDX) blended with PDX to produce either fi lms or electrospun nanofi bres, thus opening up new perspectives for these materials.

Random P(DX-co-MeDX) copolymers and diblock copolymers consisting of PCL and P(DX-co-MeDX) have been synthesised through ring-opening polymeri-sation of DX and MeDX and used to produce nanofi -brous mats (Goonoo et al. 2012). Structures of the random and diblock copolymers are given in Figure 3. Poor miscibility of PCL and P(DX-co-MeDX) segments in the diblock copolymers was confi rmed by thermal analysis data and scanning electron microscopy (SEM). Copolymers exhibited only one crystallisation exotherm, which decreased as the MeDX content in the copolymer increased, thereby showing increasing miscibility of PCL and P(DX-co-MeDX) segments. The activation energies of thermal degradation were found to decrease with increasing MeDX content of the copolymer. Overall, increasing MeDX content infl uenced both thermal proper-ties and degradation kinetics through phase mixing of segments in the copolymers. Hydrolytic degradation studies indicated that degradation occurred via bulk erosion and that the copolymers with higher mole % of MeDX degraded faster.

Blend fi lms of semi-crystalline PDX and amorphous PMeDX have also been prepared and their mechan-ical performance, thermal and degradation behaviour

assessed (Goonoo et al. 2014a). Interaction parame-ters from viscometric analysis indicated immiscibility of the blends, which was further confi rmed by surface morphology images (SEM and atomic force microscopy [AFM]). Low amounts of PMeDX, within 15 wt %, could act as a plasticiser to high molar-mass-PDX as evidenced by a signifi cant drop in melting temperatures. Beyond this composition, phase separation of PDX and PMeDX occurred and blends were immiscible. Thermal analysis and surface morphology assessment showed that low molar-mass-PMeDX had a greater plasticising effect on PDX. Increasing PMeDX content led to reduced mechanical performance due to a decrease in crystal-linity (Figure 4). However, blends with low PMeDX content (2–15 wt %) exhibited higher Young’s modulus as compared to PDX homopolymer probably because of an increased plasticising effect. Blend fi lms with higher PMeDX contents degraded at faster rates with mass loss profi les differing from PDX. Although a drop in mechan-ical properties was observed upon blending of PDX with PMeDX due to polymer immiscibility, degradability of the blends could be tuned depending on PMeDX content and such materials could be very interesting candidates for drug delivery applications.

Non-woven electrospun nanofi brous mats of PDX/PMeDX blends were fabricated in varying weight ratios of the two components (Goonoo et al. 2014b). AFM images of the electrospun scaffolds confirmed the three-dimensionality of the PDX/PMeDX scaffolds, which also possessed large voids with height differ-ences greater than 4 μm (Figure 5). Electrospun fi bres exhibited a melting transition at 109 °C independently of the PMeDX content, which corresponded to the melting of PDX nanofi bres. Contrary to blend fi lms, the O

O

O O

O

O

(a) (b)

CH3

Figure 2: Structure of (a) 1,4-dioxan-2-one and (b) 3-methyl-1,4-dioxan-2-one

(A)

(B)

Figure 3: Structure of (a) P(DX-co-MeDX) and (b) PCL-b-P(DX-co-MeDX)

PDX film

98/2 film

85/15 film

PDX nanofibrous mat

98/2 nanofibrous mat

0.5

1

1.5

2

2.5

3

3.5

0 10 20 30 40 50

TEN

SIL

E S

TRE

SS

(MP

a)

TENSILE STRAIN (%)

Figure 4: Stress-strain curves for PDX/PMeDX 100/0, 98/2, 85/15 blend films (thickness ~0.5 mm) and their corresponding electrospun mats (thickness ~0.127 mm)

Dow

nloa

ded

by [

The

Lib

rari

an]

at 2

2:39

23

Oct

ober

201

4

A review of polymeric biomaterials research for tissue engineering and drug delivery applications at CBBR 149

presence of PMeDX in the electrospun fi bres does not affect PDX melting transition. As a result of the drawing process, PMeDX had reduced plasticising effect in the fi bres compared to fi lms. In general, it was observed that, overall, crystallinity of the fi bres decreased from 53% to 36% with increasing PMeDX content and this impacted on their mechanical properties. The Young’s moduli decreased as the PMeDX content of the fi bres increased (Figure 4). However, an increase in strain at break and peak stress were noted as a result of a decrease in the fi bre diameter. AFM images of electro-spun fi bres showed an increasing degree of morpho-logical heterogeneity with increasing PMeDX content.

Electrospun mats were thermally more stable than blend fi lms. Hydrolytic degradation of the electrospun mats conducted in phosphate buffer solution at 37 °C showed that the degradation followed a surface erosion mechanism as opposed to bulk degradation observed for blend fi lms. Moreover, degradation of blend fi lms showed a dependency on PMeDX content, whereas that of fi bres appeared to be more affected by fi bre diameter. In vitro cell culture studies conducted using human dermal fi broblasts showed that the electrospun PDX/PMeDX scaffolds supported cell attachment and prolifer-ation (Figures 6 and 7). Compared to electrospun PDX, a greater density of viable cells was observed on the PDX/PMeDX scaffolds, showing the potential of these electro-spun poly(ester-ether) blend nanofi brous scaffold for tissue engineering applications.

These poly(ester-ether) materials – copolymers, blend fi lms and blend nanofi bres – are interesting candidates for tissue engineering or drug delivery applications. This research has been the object of a thesis in our group (Goonoo 2014).

Drug delivery systems: novel amphiphilic self-assembled block and graft copolymersNanoparticle sustained drug delivery systems offer several advantages over conventional delivery such as maintenance of optimum therapeutic concentra-tion of drug in the blood or cell, elimination of frequent dosing and better patient compliance. Consequently, they are good candidates for more efficient drug release devices. As block copolymer micelles attract increased interest as drug nanocarriers, there is a growing need for tailor-made biodegradable polymers whose size and surface properties can be intelligently designed not

1.0

0

1

1

2

2

3

30

μm

μm4

0.5

0

0.5

1.0

Figure 5: Atomic force microscopic phase image of electrospun 85/15 PDX/PMeDX scaffold

(a) (b)

Figure 6: Scanning electron micrographs (300×) of human dermal fibroblasts cultured on (a) PDX and (b) 98/2 PDX/PMeDX mat after 7 days

Dow

nloa

ded

by [

The

Lib

rari

an]

at 2

2:39

23

Oct

ober

201

4

150 Bhaw-Luximon et al.— African Journal of Science, Technology, Innovation and Development 2014, Vol. 6 No. 2, pp. 145–157

only to achieve long circulation times in the blood and site-specific drug delivery but also to exploit physio-logical or biochemical features of infectious diseases. Most polymeric self-assembled nanocarrier systems are based on amphiphilic block copolymers (ABCs) with a hydrophilic PEG shell and a biodegradable hydrophobic core such as polycaprolactone or polylactide. A vast majority of systems in clinical trials or on the market are thus PEG-based targeting mainly cancer (Table 1).

Our group has focused on engineering novel amphiphilic block copolymers based on biodegradable synthetic polymers or biopolymers.

PEG-b-poly(dioxanone-co-methyl dioxanone) copolymers Our novelty in this area has been the develop-ment of a novel class of poly(ester-ether)s, namely PEG-b-poly(dioxanone-co-methyl dioxanone) copoly-mers, i.e. MPEG-b-P(DX-co-MeDX) and P(DX-co-MeDX)-b-PEG-b-P(DX-co-MeDX). The synthesis of

200 μm

Figure 7: Fluorescence microscopic image of human dermal fibroblasts on electrospun PDX/PMeDX scaffolds after 7 days. The left side of each cross-section corresponds to the scaffold surface seeded with cells

Table 1. Examples of nanomicelle-based polymer therapeutics in the market and clinical development

Subclass Examples Composition StatusBlock copolymer micelles SP1049C Doxorubicin block copolymer micelle Phase I/II

NK 105 Paclitaxel block copolymer micelle Phase IINK-6004 Cisplatin block copolymer micelle Phase II

Self-assembled polymer conjugate nanoparticles

IT-101 Polymer conjugated-cyclodextrin nanoparticle-camptothecin Phase IICALAA 01 Polymer-conjugated cyclodextrin-nanoparticle-siRNA Phase II

OH

x

OO

OO

OH

O O

x m n

OO

O

x y z

OO

OO

HO O

HN

OO

OO

HOOm n m n

O

O O

O

O O

+

Jeffamine® ED-2003

MPEG-b-P(DX-co-MeDX)

MPEG

P(DX-co-MeDX)-b-PEG-b-P(DX-co-MeDX)

DX MeDX

H3CO

H3CO

H2N

HN

NH2

Sn(Oct)2

Sn(Oct)2

Figure 8: Synthesis of diblock MPEG-b-P(DX-co-MeDX) and triblock P(DX-co-MeDX)-b-PEG-b-P(DX-co-MeDX)

Dow

nloa

ded

by [

The

Lib

rari

an]

at 2

2:39

23

Oct

ober

201

4

A review of polymeric biomaterials research for tissue engineering and drug delivery applications at CBBR 151

the copolymers is depicted in Figure 8. Adjustment of the dioxanone to methyl dioxanone ratio gives a range of copolymers whose properties (physicochemical and biological) can be tuned to meet specific biomed-ical requirements. The efficacy of these copolymers to encapsulate and release anti-inflammatory drugs (Jeetah et al. 2012) or anti-tuberculosis (anti-TB) drugs (Jeetah et al. 2013) or anti-cancer drugs (Jeetah et al. 2014) has been tested. Tuberculosis remains a major plague of the African continent. However, only a few studies report on the use of block copolymer micelles to encapsulate anti-TB drugs.

The block copolymers self-assembled in aqueous solutions with diameters in the range of 120–300 nm and with critical micelle concentration (CMC) values of the order of 10−4 M. The drug-free copolymer micelles were found to be non-hemolytic and showed no erythro-cyte agglutination between concentration ranges of 0.125 mg ml−1 to 1 mg ml−1. Biocompatibility of the micelles was determined using brine shrimp lethality assay. The copolymer micelles were highly safe, fully biocompatible and had no toxicity profi le at 200 μg ml−1 (<50% mortality) (Jeetah et al. 2013).

Anti-tubercular drugs RIF, INH and PZA were encapsulated into the amphiphilic diblock/triblock copoly-mers. Rifampicin was found to have the highest binding constant with our nanomicellar systems and it achieved a higher encapsulation in single or dual loading with the other drugs. The drug loading achieved was 45–74% for single-loaded RIF micelles, 42–79% for dual-loaded RIF–INH micelles, 26–28% for PZA and 17–25% for INH. Transmission electron micrographs (Figure 9) confi rmed the encapsulation of drugs within the hydrophobic core of the micelle. The drug-containing nanoparticles gave rise to sustained release profi les that could be tuned by

modifying the MeDX content in the copolymers (Figure 10). Sustained release was observed for 9 days for RIF, 5 days for PZA and 4 days for INH. The drug-loaded micelles were stable up to two months when the lyophi-lised micelles were reconstituted in dextrose solution. Single-loaded micelles were found to be more stable than dual-loaded micelles (Jeetah et al. 2013).

Next, encapsulation of anti-cancer drugs paclitaxel (PTX) and doxorubicin (DOX) into the diblock or triblock copolymer micelles has been carried out (Jeetah et al. 2014). Preliminary studies are presented in Table 2. The encapsulation effi ciency ranged between 16% and 62% for DOX and remained almost constant at about 53% for PTX for both diblock and triblock copolymer micelles. The size of the drug-loaded micelles ranged between 177 and 300 nm.

The next step is the preclinical evaluation of the drug-free and the drug-loaded micelles, i.e. hemolysis assays and in vitro cytotoxicity assays, which is currently underway.

Figure 9:. Transmission electron micrograph of MPEG-b-P(DX-co-MeDX) (%DX:%MeDX = 70:30) RIF/INH-loaded micelles in water

100/0 RIF (Single)

40/60 RIF (Single)

100/0 RIF (Dual)

40/60 RIF (Dual)

0

10

20

30

40

50

60

70

80

90

0 50 100 150 200

CU

MU

LATI

VE

RE

LEA

SE

(%)

TIME (hours)

Figure 10: Rifampicin release profiles from diblock MPEG-b-P(DX-co-MeDX) micelles, %DX:%MeDX = 100:0, 40:60 (single loading) and %DX:%MeDX = 100:0, 40:60 (dual loading) in PBS at 37 °C

Table 2. Loading of diblock and triblock copolymer micelles with paclitaxel (PTX) and doxorubicin (DOX). EE = Encapsulation efficiency

% DX:MeDXPTX DOX

EE (%) Diameter (nm) EE (%) Diameter (nm)MPEG-b-PDX 54 282 16 230P(DX-co-MeDX)-b-PEG-b-P(DX-co-MeDX)92:8 53 229 62 17743:57 53 273 33 300

Dow

nloa

ded

by [

The

Lib

rari

an]

at 2

2:39

23

Oct

ober

201

4

152 Bhaw-Luximon et al.— African Journal of Science, Technology, Innovation and Development 2014, Vol. 6 No. 2, pp. 145–157

PEG replacement in copolymersPolymer–drug–cell interaction and polymer–drug compatibility play crucial roles in increasing efficacy of drugs. The chemical structure of PEG offers limited possibilities of modification to increase efficacy or drug compatibility. Hydrophilic bio-based polymers could offer interesting alternatives to PEG due to their biocom-patibility and availability of functional groups for drug interaction and chemical modification.

PolyLysine-b-polycaprolactone copolymersAs a replacement of PEG, we have prepared polyLy-sine-b-polycaprolactone (PolyLys-b-PCL) copoly-mers, another type of ABC (Figure 11) (Veeren et al. 2012). The amino groups of lysine can be interesting for targeting or drug-conjugation. Various novel di- or tri-block copolymers with hydrophilic PEG and/or polylysine in association with hydrophobic polycap-rolactone segments, namely PEG-b-PolyLys and PEG-b-PolyLys-b-PCL, have been synthesised and characterised. Poly(Lys-g-Glu)-b-PCL has been success-fully synthesised where D-gluconolactone was grafted

on the NH2 group of PolyLys. These copolymers self-assemble in water to form micelles in the size range 165–365 nm and CMC from 0.1 mg ml−1 to 2 mg ml−1. Both micelle size and CMC showed a strong dependency on the hydrophobic chain length. The encapsulation of ketoprofen and RIF in the different copolymer families was assessed and encapsulation efficiency determined using UV spectroscopy. The percentage drug loaded was found to depend on the interaction between drug and copolymer system. Both drugs showed chemical conjuga-tion with the PolyLys segment and physical entrapment in the PCL hydrophobic core. Higher encapsulation efficiency was obtained with RIF (17–70%).

PVP-based copolymersA range of amphiphilic poly(vinyl pyrrolidone)-b-polycaprolactone (PVP-b-PCL) diblock copolymers were synthesised by ATRP using PCL-Br as macroinitiator and a CuBr/Bpy catalytic system (Veeren et al. 2013)(Figure 12). The copolymers self-assembled in solution into core-shell micelles within the size range 150–205 nm and critical micelle concentration in the range 10−5 to 10−6 M.

Anti-TB drugs (RIF, INH and PZA) were success-fully loaded either singly or in dual combination into the PVP-b-PCL nanoparticles. The percentage drug loading varied in the order RIF ˃ PZA > INH increasing as the hydrophobic chain length increases and decreasing as the hydrophilic chain length increases (Veeren et al. 2013).

The release profi les of both single and dual drug-loaded micelles (phosphate buffer solution, pH = 7.4, 37 °C) show sustained release of the anti-TB drugs and close to zero-order kinetics was achieved over a period of 11 days for both single and dual loaded micelles. A higher drug release resulted with increasing hydrophilic chain length. As depicted in Figure 13a, the percentage drug release decreases with increase in hydrophobic chain length. For singly loaded micelles, PZA was found to be released at

HN

O

R

OO

n

H2NHN

NH

O

OR

R

NH2

n-1

O

O

m12 h

HN

NH

HN

O

R O

R OO

H

n-1 m

HN

NH

HN

O

R` O

R OO

H

n-1 m

O

OHOH

OOH

NH

HN

NH

OH

O O

NHO

OHHO

OHHO

HO

NH2

x y m

R= (CH2)4NHCOOBn

/SnOct2, 110°C,

TFA, CHCl3HBr / Acetic Acid

R`: (CH2)4NH3+Br DMF, Et3N

CH2OH

(CH2)4

(CH2)4

O

x + y = n

DMF, 50°C

Figure 11: Synthesis of di-block Poly(Lys-g-Glu)-b-PCL

1.Sn(Oct)2O O

OO

OO

O

OO

OO

O

N

NCuBr/Bpy

110°C

CH3

CH3

CH3

CH3

CH2 CH

C C

C C

Br

BIBB/ RT

(n=50-100)

(m= 50-100)Hm

m

m n

2.ppted in MeOH,dried under vaccum

Figure 12: Synthesis of PVP-b-PCL copolymers using bromo-polycaprolactone (PCL-Br) as macroinitiator (reproduced from Veeren et al. 2013)

Dow

nloa

ded

by [

The

Lib

rari

an]

at 2

2:39

23

Oct

ober

201

4

A review of polymeric biomaterials research for tissue engineering and drug delivery applications at CBBR 153

a slightly faster rate than RIF, whereas in dual combina-tion INH was released faster than RIF. The release rate of RIF was independent of single or dual combination (Figure 13b).

Comparison between PEG and PVP drug loaded systems We have attempted to quantify the drug interaction with the micellar hydrophobic core of polymeric nanomicelles by calculating a physical parameter, the binding constant using UV spectroscopy and the Benesi–Hildebrand

equation. The determination of this parameter could help to predict the release of the drug from the micelle. It is expected that the stronger the drug–polymer interac-tion, the higher would be the binding constant and the slower would be its release from the micelle. A compar-ison of loading of front-line anti-TB drugs into diblock PEG-b-poly(dioxanone-co-methyl dioxanone) with diblock PVP-b-PCL amphiphilic copolymer micelles was carried out as well as an assessment of the in vitro release efficiencies of the drugs. Thus, we could show that RIF

M/I 50M/I 75M/I 100

RIF(Single)RIF(Dual)

00

5

10

15

20

25

2 4 6 8 10 0 2 4 6 8 10

PE

RC

EN

TAG

E R

ELE

AS

E (%

)

TIME (days)

(a) (b)

Figure 13: Plot of percentage release of (a) rifampicin (single loading) against time (days), PVP50-b-PCL50,75,100 and (b) rifampicin (single and dual loading) against time (days), PVP50-b-PCL50 (partly reproduced from Veeren et al. 2013)

100

INH-loaded

INH-loadedRIF-loaded

RIF-loaded

0

10

20

30

40

50

60

70

80

90

0 50 100 150 200

CU

MU

LATI

VE

RE

LEA

SE

(%)

TIME (hours)250

Figure 14: Release profiles of rifampicin (RIF) and isoniazid (INH) from MPEG-P(DX-co-MeDX), %DX:%MeDX = 40/60, RIF-loaded, INH-loaded and PVP-PCL, %VP:%CL = 50/50, RIF-loaded, INH-loaded

Dow

nloa

ded

by [

The

Lib

rari

an]

at 2

2:39

23

Oct

ober

201

4

154 Bhaw-Luximon et al.— African Journal of Science, Technology, Innovation and Development 2014, Vol. 6 No. 2, pp. 145–157

binds more strongly to the hydrophobic core than INH for both MPEG-b-P(DX-co-MeDX) and PVP-b-PCL micelles, but was released at a slower rate in a sustained manner (Figure 14).

Oligoagarose-g-polycaprolactone copolymersWe have also engineered graft copolymers based on marine polysaccharides. Our oligoagarose-g-polycaprolactone copolymers (HO-OligoAga-g-PCL) organise into spherical micelles and we have success-fully loaded different drugs into the hydrophobic core (Bhaw-Luximon et al. 2011). Agarose-based systems present the unique advantage of having galactose end groups, which can play a key role in cell targeting. Well-defined oligoagarose-g-polycaprolactone copoly-mers of varying PCL chain lengths have been synthe-sised using protection/deprotection chemistry. The graft copolymers showed amphiphilic behaviour with spherical micelles in the size range 10–20 nm. Ketoprofen was loaded into the core of the micelles (Figure 15). The drug loading efficiency was shown to increase with the length of the hydrophobic PCL chain: 2% for PCL10 and 5.5% for PCL15. Sustained drug release was observed over a period of 72 h and was faster with shorter PCL chains.

Poly(sucrose)-g-polycaprolactone copolymersCBBR recently filed a patent on a method of prepara-tion of bio-amphiphilic polymers from sucrose that self-assemble into core shell micelles (Jhurry and Bhaw-Luximon 2013). The invention describes the preparation of novel amphiphilic graft copolymers consisting of sucrose-ether polycondensates onto which biodegradable polymer chains such as polyesters, poly(ester-ether)s or polypeptides have been covalently grafted (Figure 16). This invention also includes the application of the prepared amphiphilic sucrose-ether polycondensates for drug or protein encapsulation and release. Anti-inflammatory, anti-TB and anti-cancer drugs have been tested but this invention encompasses all Biopharmaceutics Classification System Class II and IV drugs that are hydrophobic and require surfactants for their transport. The sucrose-based polymeric micelles here disclosed allow a better solubility, enhanced bioavailability of the drug when adminis-tered, a prolonged circulation and a prolonged delivery. Anti-inflammatory (ketoprofen) and anti-TB drugs (RIF and PZA) have been encapsulated with loading efficien-cies up to 50% (Table 3).

Opiate sustained release systems based on polydioxanoneOpioid dependence is considered to be a lifelong, chronic relapsing disorder, which requires substantial therapeutic efforts to keep patients drug free (McLellan et al. 2000). Medically supervised treatment is often necessary as opiates have a high rate of relapse. Presently, the most efficient and well-scrutinised treatment for opioid dependence is agonist replacement therapy such as naltrexone hydrochloride (NTX) and flumazenil (FMZ).

Oral NTX is one of the foremost pharmacotherapies employed to assist opiate-dependant patients to manage their drug addiction. Oral NTX maintenance has been reported effective in the treatment of heroin dependence in previous studies (Callahan et al. 1980). However, maintenance therapy with oral NTX endures high early dropout rates and patient compliance with regular dosing has hindered its effi cacy owing to its poor bioavailability (40%). Other drugs such as oral FMZ, an imidazobenzo-diazepine derivative, antagonise the actions of benzodi-azepines on the central nervous system (O’Neil 2012). Correspondingly, its low bio-availability has discouraged its use. These disadvantages have bound scientists to fi nd new approaches to cope with these diffi culties.

Figure 15: Transmission electron micrograph of ketoprofen loaded HO-OligoAga-g-PCL15

Table 3: Loading of polysucrose-g-PCL with ketoprofen, rifampicin and pyrazinamide. EE = Encapsulation efficiency

DrugPolysucrose-g-PCL [CL]/

[polysucrose]=30Polysucrose-g-PCL

[CL]/[polysucrose]=50Polysucrose-g-PCL [CL]/

[polysucrose]=75EE (%) Diameter (nm) EE (%) Diameter (nm) EE (%) Diameter (nm)

Ketoprofen 50 208 11 194 10 172Rifampicin 27 184 15 267 16 168Pyrazinamide 15 135 5 100 8 177

Dow

nloa

ded

by [

The

Lib

rari

an]

at 2

2:39

23

Oct

ober

201

4

A review of polymeric biomaterials research for tissue engineering and drug delivery applications at CBBR 155

The development of a long-term controlled-release system for the delivery of NTX and FMZ has been sought to overcome the problems mentioned above. Latest clinical data on commercially available injectable and implantable NTX-sustained release systems as well as their safety and tolerability aspects have been discussed in our recently published review article (Goonoo et al. 2014c). Currently, there are two main types of sustained release technologies for NTX release: inject-able intramuscular suspension and surgical implantable pellets. Such delivery systems offer various advantages compared to conventional dosage forms including improved effi cacy, reduced toxicity, improved patient compliance and convenience. The implants fabricated by Go Medical Industries in Australia are made by integrating NTX in a matrix of biodegradable poly (D,L-lactide) (PDLA) microspheres. Clinical studies show that the existing NTX implants seem to be more effi cient than oral NTX for assisting heroin-dependent individuals (Waal et al. 2006; Ngo et al. 2008).

Recently, Hulse et al. (2013) reported on the in vitro and in vivo studies of FMZ sustained release depot. An implant was designed using FMZ loaded PDLA microspheres and compressed into tablets and either coated (long acting) or non-coated (short acting) with

a PDLA (Hulse et al. 2013). FMZ active agent may be released transcutaneously across the skin, such as via a patch or cream. The active agent may also be delivered sustainably in a bolus dose across the nasal membrane (O’Neil 2012).

We have recently developed microparticles with a matrix structure of PDX incorporating NTX by an encapsulation method based on the formation of water-in-oil-in-water (double) emulsion under controlled stirring (Hulse et al. 2008). This part of our research is being performed in collaboration with Prof. G. Hulse of the University of Western Australia. The advantage of using PDX, other than being biodegradable, is its non-antige-nicity and negligible tissue reactivity during the tissue absorption process. Microspheres with average size 5 m were obtained with narrow polydispersity index. The release studies are still under investigation.

As highlighted in our review, nanodrug delivery systems are considered as promising sustainable drug carriers for the treatment of opiate dependence (Goonoo et al. 2014c). Existing micellar systems such as PEG–Polyester, PEG–Polypeptide or PVP–Polyester need to be tested for NTX encapsulation and delivery. In addition, covalent binding of specific ligands to target opiate receptors could lead to more effective delivery.

Figure 16: Bio-amphiphilic copolymers from sucrose

O

OO

O

HOO

OH

OH

OH

O

O

CH2CH

OH

CH2 OOCH2

CH

OH

CH2Suc

Sucm

O

CH2O

HO

OCH2H

5

5

n

n

Sucrose

polysucrose-g-polyester

Chemical modification

Hydrophobic block

Hydrophilic block

CMC

Dow

nloa

ded

by [

The

Lib

rari

an]

at 2

2:39

23

Oct

ober

201

4

156 Bhaw-Luximon et al.— African Journal of Science, Technology, Innovation and Development 2014, Vol. 6 No. 2, pp. 145–157

ConclusionWe have presented in this article an overview of the main research thrusts and findings in the areas of biomate-rials and drug delivery at CBBR. In the field of biomate-rials, we have developed a new class of biodegradable polymeric scaffolds based on poly(ester-ether)s, namely PDX and PMeDX. The novel electrospun PDX/PMeDX nanofibrous scaffolds showed good mechanical perfor-mance and their biodegradability profiles could be tuned as a function of fibre properties. The electrospun mats did not show illicit response and demonstrated excellent human fibroblast cell attachment and proliferation.

In the fi eld of drug delivery, our focus is on the engineering of self-assembled polymeric micelles for use as drug nanocarriers. A range of amphiphilic block and graft copolymer micelles based on PEG, PolyLysine, PVP, oligoagarose or polysucrose as a hydrophilic block coupled with PDX and PMeDX or PCL as a biodegrad-able hydrophobic block have been successfully prepared. The drug-free copolymer micelles were found to be non-hemolytic and showed no erythrocyte agglutination. Biocompatibility tests of the micelles presented a highly safe and fully biocompatible profile. Anti-tubercular drugs rifampicin, pyrazinamide and isoniazid were successfully encapsulated within the micellar cores, either individually (rifampicin or pyrazinamide) or in dual combination (rifampicin and isoniazid) and were released in vitro in a sustained manner. Promising results were also obtained with the anti-cancer drugs paclitaxel and doxorubicin. In vivo testing of our scaffolds and drug delivery systems is a next objective of our research.

AcknowledgementsWe thank the Tertiary Education Commission, Mauritius, for PhD fellowships to Roubeena Jeetah, Nowsheen Goonoo, Anisha Veeren and Yeshma Jugdawa. We are most grateful to our international collaborators Prof. Gary L. Bowlin (University of Memphis, USA), Prof. David Kaplan (Tufts University, USA), Prof. Viness Pillay (University of the Witwatersrand, South Africa), Dr Daniel Wesner and Prof. Holger Schönherr (University of Siegen, Germany) for their assistance with analytical techniques not available at CBBR.

ReferencesBhaw-Luximon, A., Meeram, L.M., Jugdawa, Y., Helbert, W.

and Jhurry, D. (2011), ‘Oligoagarose-g-polycaprolactone Loaded Nanoparticles for Drug Delivery Applications’, in Polymer Chemistry, 2(1): 77–79.

Callahan, E.J., Rawson, R.A., McCleave, B., Arias, R., Glazer, M. and Liberman, R.P. (1980), ‘The Treatment of Heroin Addiction: Naltrexone Alone and with Behavior Therapy’, in International Journal of Addiction, 15(6): 795–807.

Goonoo, N. (2014), ‘Studies into New Poly(ester-ether)-based Materials and Evaluation of Their Performance for Tissue Engineering Scaffold Applications’, Unpublished Doctoral Dissertation, Department of Chemistry, CBBR, University of Mauritius, Mauritius.

Goonoo, N., Bhaw-Luximon, A., Bowlin, G.L. and Jhurry, D. (2012), ‘Diblock Poly(ester)-Poly(ester-ether) Copolymers: I. Synthesis, Thermal Properties, and Degradation Kinetics’, in Industrial and Engineering Chemistry Research, 51(37): 12031–12040.

Goonoo, N., Bhaw-Luximon, A., Bowlin, G.L. and Jhurry, D. (2013), ‘An Assessment of Biopolymer- and Synthetic Polymer-Based Scaffolds for Bone and Vascular Tissue Engineering’, in Polymer International, 62(4): 523–533.

Goonoo, N., Bhaw-Luximon, A., Rodriguez, I.A., Bowlin, G.L. and Jhurry, D. (2014a), ‘Poly(ester-ether)s: I. Investigation of the Properties of Blend Films of Polydioxanone and Poly(methyl dioxanone)’, in International Journal of Polymeric Materials and Polymeric Biomaterials, 63(10): 527–537.

Goonoo, N., Bhaw-Luximon, A., Rodriguez, I.A., Wesner, D., Schönherr, H., Bowlin, G.L. and Jhurry, D. (2014b), ‘Poly(ester-ether)s: II. Properties of Electrospun Nanofibres from Polydioxanone and Poly(methyl dioxanone) Blends and Human Fibroblast Cellular Proliferation’, in Biomaterials Science, 2(3): 339–351.

Goonoo, N., Bhaw-Luximon, A., Ujoodha, R., Jhugroo, A., Hulse, G.K. and Jhurry, D. (2014c), ‘Naltrexone: a Review of Existing Sustained Drug Delivery Systems and Emerging Nano-based Systems’, in Journal of Controlled Release, 183: 154–166.

Hulse, G., O’Neil, G., Morris, N., Bennett, K., Norman, A. and Hood, S. (2013), ‘Withdrawal and Psychological Sequelae, and Patient Satisfaction Associated with Subcutaneous Flumazenil Infusion for the Management of Benzodiazepine Withdrawal: a Case Series’, in Journal of Psychopharmacology, 27(2): 222–227.

Hulse, G.K., Low, V.H., Stalenberg, V., Morris, N., Thompson, R.I., Tait, R.J., Phan, C.T., Ngo, H.T. and Arnold-Reed, D.E. (2008), ‘Biodegradability of Naltrexone-poly (DL) Lactide Implants in vivo Assessed under Ultrasound in Humans’, in Addiction Biology, 13(3–4): 364–372.

Jeetah, R., Bhaw-Luximon, A. and Jhurry, D. (2012), ‘New Amphiphilic PEG-b-P(ester–ether) Micelles as Potential Drug Nanocarriers’, in Journal of Nanoparticle Research, 14(10): 1168.

Jeetah, R., Bhaw-Luximon, A. and Jhurry, D. (2013), ‘Dual Encapsulation and Controlled Delivery of Anti-TB Drugs from PEG-block-Poly(ester-ether) Nanomicelles’, in Journal of Nanopharmaceutics and Drug Delivery, 1(3): 240–257.

Jeetah, R., Bhaw-Luximon, A. and Jhurry, D. (2014), ‘Polymeric Nanomicelles for Sustained Delivery of Anti-cancer Drugs’, in Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis, DOI: 10:1016/j.mrfmmm.2014.04.009.

Jhurry, D. and Bhaw-Luximon A. (2013), ‘A Method of Preparing an Amphiphilic Graft Copolymer’, SA Patent 2013/00961 .

Lochee, Y., Bhaw-Luximon, A., Jhurry, D. and Kalangos, A. (2009), ‘Novel Biodegradable Poly(ester−ethers): Copolymers from 1,4-Dioxan-2-one and D,L-3-Methyl-1,4-dioxan-2-one’, in Macromolecules, 42(19): 7285–7291.

Lochee, Y., Jhurry, D., Bhaw-Luximon, A. and Kalangos, A. (2010), ‘Biodegradable Poly(ester-ether)s: Ring-opening Polymerization of D,L-3-Methyl-1,4-dioxan-2-one Using Various Initiator Systems’, in Polymer International, 59(9): 1310–1318.

Dow

nloa

ded

by [

The

Lib

rari

an]

at 2

2:39

23

Oct

ober

201

4

A review of polymeric biomaterials research for tissue engineering and drug delivery applications at CBBR 157

McLellan, T., Lewis, D.C., O’Brien, C.P. and Kleber, H.D. (2000), ‘Drug Dependence, a Chronic Medical Illness: Implications for Treatment, Insurance, and Outcomes Evaluation’, in Journal of the American Medical Association, 284 (13): 1689–1695.

Ngo, H.T.T., Arnold-Reed, D.E., Hansson, R.C., Tait, R.J. and Hulse, G.K. (2008), ‘Blood Naltrexone Levels Over Time Following Naltrexone Implants’ in Progress in Neuro-Psychopharmacology and Biological Psychiatry, 32(1): 23–28.

O’Neil, A.G.B. (2012), ‘Pharmaceutical Preparation and Delivery System’, US Patent Application 20120122851.

Veeren, A. and Bhaw-Luximon, A. (2012), ‘Polymer-drug encapsulation using various PEG- and polypeptide-based block copolymer micelles’, in Macromolecular Symposia, 313–314: 59–68.

Veeren, A., Bhaw-Luximon, A. and Jhurry, D. (2013), ‘Polyvinylpyrrolidone–polycaprolactone Block Copolymer Micelles as Nanocarriers of Anti-TB Drugs’, in European Polymer Journal, 49(10): 3034–3045.

Waal, H., Frogopsahl, G., Olsen, L., Christophersen, A.S. and Mørland, J. (2006), ‘Naltrexone implants – duration, tolerability and clinical usefulness’, in European Addiction Research, 12(3): 138–144.

Wolfe, P.S., Lochee, Y., Jhurry, D., Bhaw-Luximon, A. and Bowlin, G.L. (2011), ‘Characterization of Electrospun Novel Poly(ester-ether) Copolymers: 1,4-Dioxan-2-one and D,L-3-Methyl-1,4- dioxan-2-one’, in Journal of Engineered Fibers and Fabrics, 6(4): 60–69.

Dow

nloa

ded

by [

The

Lib

rari

an]

at 2

2:39

23

Oct

ober

201

4

Dow

nloa

ded

by [

The

Lib

rari

an]

at 2

2:39

23

Oct

ober

201

4