Pei Lin Chee

Towards lignin-based functional materials in a sustainable world

In light of the incessant consumption of raw materials in the world today, the search for sustainable resources is ever pressing. Lignin, the second most naturally abundant biomass, which makes up 15% to 35% of the cell walls of terrestrial plants, has always been treated as waste and used in low-value applications such as heat and electricity generation. However, its abundance in nature could potentially solve the problem of the rapidly depleting resources if it was successfully translated into a renewable resource or valorized to higher value materials. Advanced lignin modification chemistry has generated a number of functional lignin-based polymers, which integrate both the intrinsic features of lignin and additional properties of the grafted polymers. These modified lignin and its copolymers display better miscibility with other polymeric matrices, leading to improved performance for these lignin/polymer composites. This review summarizes the progress in using such biopolymers as reinforcement fillers, antioxidants, UV adsorbents, antimicrobial agents, carbon precursors and biomaterials for tissue engineering and gene therapy. Recent developments in lignin-based smart materials are discussed as well.

Multi-functional fluorescent carbon dots with antibacterial and gene delivery properties†

Glucose is abundant in nature and can be found in various sources. In this study, we developed multifunctional carbon dots (CDs) with glucose and poly(ethyleneimine) (PEI), which were further quaternized using a facile approach. The CDs are designed to possess both anti-bacteria and gene delivery capabilities. The inherent property was characterized with TEM, NMR, FTIR and fluorescent spectroscopy. Antibacterial activity was evaluated with Broth minimum inhibitory concentration (MIC) assay on both Gram-positive and Gram-negative bacteria. The CDs showed excellent inhibitation to both bacteria. The expression of CDs condensed plasmid DNA in HEK 293T cells was investigated with luciferase expression assay. Gene transfection capability of the quaternized CDs was found to be up to 104 times efficient than naked DNA delivery.

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.

The role of hydrogen bonding in alginate/poly(acrylamide-co-dimethylacrylamide) and alginate/poly(ethylene glycol) methyl ether methacrylate-based tough hybrid hydrogels

The interpenetrating alginate-based hybrid hydrogel network is a tough yet recoverable material. This is believed to be caused by the combination of the strength of a covalent network, and the reversibility of an ionic network. However, hydrogen bonds are believed to also be responsible for the exceptional properties of these hydrogels. In this paper, the effect of varying the reactant concentrations on the mechanical properties of the hydrogels was first studied. By changing the monomer used (from polyacrylamide to polydimethylacrylamide) in the fabrication of the hydrogel, the effect of hydrogen bonding was studied. Compression test results showed that the presence of hydrogen bonds is critical for the high toughness of the hybrid hydrogel. Additionally, co-polymeric hybrid hydrogels were synthesized and shown to have improved mechanical properties over the original hybrid hydrogel, with an elastic modulus and compressive toughness of 350 kPa and 70 J m−3, respectively. The results of this experiment can be used to optimise the mechanical properties of future hybrid hydrogels.

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.

An Injectable Double-Network Hydrogel for Cell Encapsulation

Further developing on the technique originally intended for the purpose of forming tough hydrogels, we showed in this study that the double-network system can also be used to synthesize an injectable gel. The gel was made up of poly(ethylene glycol) methyl ether methacrylate, sodium alginic acid, and calcium chloride, and two networks, consisting of ionic and covalent networks, were found to co-exist in the gel. Additionally, the rheology studies showed that the mechanical properties of the gel only deteriorated under high strain, demonstrating the robustness of the gel upon injection. The results of a cell cytotoxicity test and a preliminary cell encapsulation study were promising, showing good cell compatibility and thus suggesting that the hydrogels could potentially be used for cell delivery.

CHAPTER 1:A Global Analysis of the Personal Care Market

Global trends and macroeconomic factors alike have been indicative of potential in the growth of personal care markets in the Association of Southeast Asian Nations (ASEAN). In particular, there has been an observable increase in the purchasing power of consumers, which along with a rising awareness of health and a growing interest in multifunctional products, allows for the fueling of growth and market opportunities in ASEAN regions. Furthermore, a large portion of the ASEAN personal care market is held by active ingredients, which constituted an approximate 30% of the market shares in 2013, out of which 85% was attributed to moisturizing ingredients. This market distribution is thought to be yet another contributing factor in the prediction of the growth of the ASEAN personal care market. This forecasted growth is expected to be further propelled by the regional age distribution, due to an anticipated rise in the population of the middle aged (aged 40–64), as well as the significant proportion of youths within the area, which will serve as a basis for a heightened demand for personal products targeted at the young population. Such circumstances have been predicted to drive the personal care market in ASEAN into a persisting high growth, with a CAGR of 7% between 2013 and 2017. This personal care market is currently dominated by large and growing economies such as Malaysia, Philippines, Vietnam with Indonesia and Thailand. Of this, a sizeable proportion of the market share (45% for each country), is held by Thailand and Indonesia. Other notable players in the field are the key emerging markets, which include Myanmar, Laos and Cambodia. The two most popular products are hair and skin care, which make up around 55% of the personal care markets. While technological innovation, consumer spending and greater awareness assist a company in gaining competitive advantage and greater market share, there are also numerous obstacles to the development of new active ingredients. For instance, the competition from China pressurizes global companies to cut costs, reducing the profits that could otherwise be invested for new development. The ability to invest is crucial as the main differentiation, which determines the long term gain, comes from product innovation and research and development. Another obstacle is hostile legislation. Europe and the United States are the major distributors of personal care active ingredients.