Cally Owh

Recent Advances in Shape Memory Soft Materials for Biomedical Applications

Shape memory polymers (SMPs) are smart and adaptive materials able to recover their shape through an external stimulus. This functionality, combined with the good biocompatibility of polymers, has garnered much interest for biomedical applications. In this review, we discuss the design considerations critical to the successful integration of SMPs for use in vivo. We also highlight recent work on three classes of SMPs: shape memory polymers and blends, shape memory polymer composites, and shape memory hydrogels. These developments open the possibility of incorporating SMPs into device design, which can lead to vast technological improvements in the biomedical field.

Safe and efficient membrane permeabilizing polymers based on PLLA for antibacterial applications

Poly(N,N-dimethylaminoethyl methacrylate)-block-poly(L-lactic acid)-block-poly(N,N-dimethylaminoethyl methacrylate) conjugated with poly(ethylene glycol) (D-PLLA-D@PEG) copolymers were synthesized. These non-aggregating polymers showed low MIC values against Gram-negative and Gram-positive, including methicillin-resistant Staphylococcus aureus (MRSA), bacteria. The polymers exhibited minimal toxicity and are promising antibacterial agents for biomedical applications.

A thixotropic polyglycerol sebacate-based supramolecular hydrogel showing UCST behavior

Polyglycerol sebacate (PGS) is a relatively new biodegradable and elastomeric material that exhibits superior biocompatibility, a modulus that is comparable to human soft tissue, and linear biodegradation. However, the high hydrophobicity, low water uptake percentage and extreme synthesis conditions of PGS pose as a hindrance to its use in cellular biology, biomedical and other applications. We were able to modify PGS using atom transfer radical polymerization (ATRP) by synthesizing a PGS macroinitiator, allowing us to improve PGSs properties or introduce new properties to PGS. This macroinitiator would enable the building of a robust platform of PGS-based copolymers with monomers in the methacrylates, styrenes and methacrylamide families. We demonstrated the feasibility of this macroinitiator by using PEGMEMA as the monomer to synthesize PGS–PEGMEMA and created a PGS–PEGMEMA/αCD supramolecular hydrogel system. This hydrogel exhibited a tunable, low UCST of less than 90 °C, low minimum gelation concentration of 5.2%, rapid gelation and rapid self-healing ability with relatively high modulus (∼100 kPa) that is comparable to that of human soft tissue. This hydrogel system is injectable yet strong enough to provide support – features, making it a very suitable candidate as a vehicle for injectable sustained-release drug delivery, cell delivery, tissue engineering scaffold as well as for cosmetics and skincare applications.

Poly(glycerol sebacate) biomaterial: synthesis and biomedical applications

The recently developed poly(glycerol sebacate) (PGS) has been gaining attraction as a biomaterial for tissue engineering applications. Reported in 2002, a simple polycondensation method was developed to synthesize PGS for soft tissue engineering applications. It has since become a highly sought after biomaterial due to its soft, robust and flexible characteristics and it is relatively low cost compared to other biodegradable elastomers currently available in the market. We summarise in this review, the various synthetic approaches of PGS and highlight selected applications in nerve guidance, soft tissue regeneration, vascular and myocardial tissue regeneration, blood vessel reconstruction, drug delivery, and the replacement of photoreceptor cells. A critical assessment of the material is provided as a scope for future improvement. The future outlook of this material is also provided at the end of this review.

A Thixotropic Polyglycerol Sebacate-Based Supramolecular Hydrogel as an Injectable Drug Delivery Matrix

We have developed a “self-healing” polyglycerol sebacate—polyethylene glycol methyl ether methacrylate (PGS-PEGMEMA)/α-Cyclodextrin (αCD) hydrogel which could be sheared into a liquid during injection and has the potential to quickly “heal” itself back into gel post-injection. This hydrogel was shown to be biocompatible and biodegradable and therefore appropriate for use in vivo. Furthermore, the storage and loss moduli of the hydrogels could be tuned (by varying the concentration of αCD) between a fraction of a kPa to a few 100 kPa, a range that coincides with the moduli of cells and human soft tissues. This property would allow for this hydrogel to be used in vivo with maximal mechanical compatibility with human soft tissues. In vitro experiments showed that the hydrogel demonstrated a linear mass erosion profile and a biphasic drug (doxorubicin) release profile: Phase I was primarily driven by diffusion and Phase II was driven by hydrogel erosion. The diffusion mechanism was modeled with the First Order equation and the erosion mechanism with the Hopfenberg equation. This established fitting model could be used to predict releases with other drugs and estimate the composition of the hydrogel required to achieve a desired release rate.

Supramolecular cyclodextrin pseudorotaxane hydrogels: a candidate for sustained release?

In this work, PEO-α-CD pseudorotaxane hydrogels were prepared. The gels were loaded with proteins, BSA and lysozyme, representing proteins with different molecular weights. The kinetics of protein release was studied. Factors such as PEO concentration, protein concentration and exposed surface area of the gels were investigated to understand their effects on the release of the encapsulated cargo. Erosion of the gel surface appeared to be the dominant factor for release of the proteins. Fitting the data to various models supported our hypothesis that the mechanism of release was primarily erosion-driven as the data was best described by zero order, power law and Hopfenberg model. The linear relationship between the amount of mass loss and time establishes the erosion of the polymer gel matrix to be the key factor for drug release.

Biodegradable electronics: cornerstone for sustainable electronics and transient applications

Electronic devices have become ubiquitous in modern society and are prevalent in every facet of human activities. Although electronic devices have brought much convenience and value, the insatiable appetite for newer and more attractive devices has also created a growing ecological problem: managing electronic waste or e-waste. As the lifetime of electronic devices gets shorter and shorter, the pressure on e-waste management systems is mounting with no abate in sight. Therefore, an alternative to traditional electronics must be sought. Bio-degradable electronics have thus emerged as the most viable and ideal replacement to address the issue of uncontrollable e-waste. Bio-degradability will ensure that the waste generated will be at least non-toxic and even environmentally friendly. Furthermore, bio-degradable organic materials have also been shown to be biocompatible and human-friendly, being able to be metabolized safely in the body without causing adverse physiological reactions. As such, this developing class of “green” electronics is not only able to alleviate the growing e-waste problem, but also fulfils niche applications interfacing with the human body. This Review will introduce various bio-degradable organic materials that can serve as substitutes for the different components of an electronic device, highlight recent research achievements and applications in implementing such bio-degradable devices as well as present an overview of the printing technologies available that provide the low-cost and high throughput advantages of solution-processable organic materials over the traditional inorganic materials.

Bioimaging and biodetection assisted with TTA-UC materials

Upconversion of light has attracted intensive studies for biomedical research, because it enables deeper tissue analysis owing to the longer wavelength of incident light, compared with conventional downconversion fluorescent materials. Triplet-triplet annihilation (TTA), as a typical mechanism of upconversion, does not necessitate high power excitation and exhibits a higher quantum yield than rare earth upconversion owing to more sensitizer options with higher absorption coefficients. A desirable wavelength range of excitation and emission can be realized by careful selection of the combination of sensitizer and activator. Therefore, TTA-UC is worth exploring further for biorelated applications, such as bioimaging and biodetection. Recent developments are reviewed in this article.

Codelivery for Paclitaxel and Bcl‐2 Conversion Gene by PHB‐PDMAEMA Amphiphilic Cationic Copolymer for Effective Drug Resistant Cancer Therapy

Antiapoptotic Bcl-2 proteins upregulated expression is a key reason for drug resistance leading to failure of chemotherapy. In this report, a series of biocompatible amphiphilic cationic poly[(R)-3-hydroxybutyrate] (PHB)-b-poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) copolymer, comprising hydrophobic PHB block and cationic PDMAEMA block, is designed to codeliver hydrophobic chemotherapeutic paclitaxel and Bcl-2 converting gene Nur77/ΔDBD with enhanced stability, due to the micelle formation by hydrophobic PHB segment. This copolymer shows less toxicity but similar gene transfection efficiency to polyethyenimine (25k). More importantly, this codelivery approach by PHB-PDMAEMA leads to increased drug resistant HepG2/Bcl-2 cancer cell death, by increased expression of Nur77 proteins in the Bcl-2 present intracellular mitochondria. This work signifies for the first time that cationic amphiphilic PHB-b-PDMAEMA copolymers can be utilized for the drug and gene codelivery to drug resistant cancer cells with high expression of antiapoptosis Bcl-2 protein and the positive results are encouraging for the further design of codelivery platforms for combating drug resistant cancer cells.

Dual functional anti-oxidant and SPF enhancing lignin-based copolymers as additives for personal and healthcare products

The desire for protection against UV exposure has resulted in the development of an increasing number of sunscreen agents. Lignin-based polymers have potential to serve as promising sunscreen agents as they have good UV absorption and antioxidant properties contributing towards the reduction of UV-induced skin damage. In this study, a series of lignin–poly(ethylene glycol) methacrylate (PEGMA) copolymers were synthesized via atom transfer radical polymerization (ATRP) to enhance the dispersion efficiency of lignin in the commercial creams. These copolymers showed tunability in both molecular weight (10–25 kDa) and particle size (100–200 nm), as well as excellent antioxidant properties. Different amounts of such copolymers were blended into commercial creams to investigate their sunscreen performance. Results indicated that adding lignin–PEGMA copolymers into sunblock creams improved their SPF values from 15.36 ± 2.44 to 38.53 ± 0.26. In summary, such lignin-based polymers with good UV protection and antioxidant properties offer a green alternative for developing the next generation of sunscreen creams.