Radical Polymerization Of 2-hydroxyethyl Methacrylate Research Articles

Porous Poly(2-hydroxyethyl methacrylate) Hydrogel Scaffolds for Tissue Engineering: Influence of Crosslinking Systems and Silk Sericin Concentration on Scaffold Properties.

Tailored porous structures of poly(2-hydroxyethyl methacrylate) (PHEMA) and silk sericin (SS) were used to create porous hydrogel scaffolds using two distinct crosslinking systems. These structures were designed to closely mimic the porous nature of the native extracellular matrix. Conventional free radical polymerization of 2-hydroxyethyl methacrylate (HEMA) was performed in the presence of different concentrations of SS (1.25, 2.50, 5.00% w/v) with two crosslinking systems. A chemical crosslinking system with N'N-methylene bisacrylamide (MBAAm) and a physical crosslinking system with dimethylurea (DMU) were used: C-PHEMA/SS (crosslinked using MBAAm) and C-PHEMA/pC-SS (crosslinked using MBAAm and DMU). The focus of this study was on investigating the impact of these crosslinking methods on various properties of the scaffolds, including pore size, pore characteristics, polymerization time, morphology, molecular interaction, in vitro degradation, thermal properties, and in vitro cytotoxicity. The various crosslinked networks were found to appreciably influence the properties of the scaffolds, especially the pore sizes, in which smaller sizes and higher numbers of pores with high regularity were seen in C-PHEMA/1.25 pC-SS (17 ± 2 μm) than in C-PHEMA/1.25 SS (34 ± 3 μm). Semi-interpenetrating networks were created by crosslinking PHEMA-MBAAm-PHEMA while incorporating free protein molecules of SS within the networks. The additional crosslinking step involving DMU occurred through hydrogen bonding of the -C=O and -N-H groups with the SS, resulting in the simultaneous incorporation of DMU and SS within the PHEMA networks. As a consequence of this process, the scaffold C-PHEMA/pC-SS exhibited smaller pore sizes compared to scaffolds without DMU crosslinking. Moreover, the incorporation of higher loadings of SS led to even smaller pore sizes. Additionally, the gelation time of C-PHEMA/pC-SS was delayed due to the presence of DMU in the crosslinking system. Both porous hydrogel scaffolds, C-PHEMA/pC-SS and PHEMA, were found to be non-cytotoxic to the normal human skin dermal fibroblast cell line (NHDF cells). This promising result indicates that these hydrogel scaffolds have potential for use in tissue engineering applications.

Preparation and Characterization of Poly(vinyl acetate-co-2-hydroxyethyl methacrylate) and In Vitro Application as Contact Lens for Acyclovir Delivery.

A series of poly(vinyl acetate-co-2-hydroxyethylmethacrylate)/acyclovir drug carrier systems (HEMAVAC) containing different acyclovir contents was prepared through bulk free radical polymerization of 2-hydroxyethyl methacrylate with vinyl acetate (VAc) in presence of acyclovir (ACVR) as the drug using a LED lamp in presence of camphorquinone as the photoinitiator. The structure of the drug carrier system was confirmed by FTIR and 1HNMR analysis, and the uniform dispersion of the drug particles in the carrier was proved by DSC and XRD analysis. The study of the physico-chemical properties of the prepared materials, such as the transparency, swelling capacity, wettability and optical refraction, was carried out by UV-visible analysis, a swelling test and measurement of the contact angle and the refractive index, respectively. The elastic modulus and the yield strength of the wet prepared materials were examined by dynamic mechanical analysis. The cytotoxicity of the prepared materials and cell adhesion on these systems were studied by LDH assay and the MTT test, respectively. The results obtained were comparable to those of standard lenses with a transparency of 76.90-89.51%, a swelling capacity of 42.23-81.80% by weight, a wettability of 75.95-89.04°, a refractive index of 1.4301-1.4526 and a modulus of elasticity of 0.67-1.50 MPa, depending on the ACVR content. It was also shown that these materials exhibit no significant cytotoxicity; on the other hand, they show significant cell adhesion. The in vitro dynamic release of ACVR in water revealed that the HEMAVAC drug carrier can consistently deliver uniformly adequate amounts of ACVR (5.04-36 wt%) over a long period (7 days) in two steps. It was also found that the solubility of ACVR obtained from the release process was improved by 1.4 times that obtained by direct solubility of the drug in powder form at the same temperature.

Interpenetrating Polymer Network Hydrogels Formed Using Antibiotics as a Dynamic Crosslinker for Treatment of Infected Wounds.

Antibacterial hydrogels, particularly antibiotic-loaded hydrogels, are promising wound dressing materials for treatment of bacteria-infected wound. However, it is challenging to achieve sustained release of antibiotics from hydrogels through physical encapsulation of the antibiotics. Herein, an interpenetrating polymer network P(AA-co-HEMA)Gen hydrogel is reported with double crosslinking formed by free radical polymerization of 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AA), while using the antibiotic gentamicin (Gen) as the dynamic physical crosslinker. Gentamicin is incorporated into the hydrogel networks via electrostatic interaction between the carboxyl groups of poly(acrylic acid) and the amino groups of gentamicin, which leads to pH-responsive drug release and a significant increase in mechanical strength (i.e., elastic modulus, viscous modulus, and compressive modulus). More importantly, the hydrogels with optimal compositions demonstrate long-lasting antibacterial activity against both Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli) over 28 d. The in vivo studies that are conducted in an S. aureus-infected full-thickness skin wound model demonstrate that thedouble crosslinking hydrogelsloadedwith gentamicin eliminate bacteria in the wounds more effectively and significantly accelerate wound healing as compared to 3M dressing and the control without any treatment. Taken together, this antibiotic-loaded interpenetrating polymer network hydrogel is potentially a promising wound dressing material for the treatment of bacteria-infected wound.

Modified hydrogels based on poly(2-hydroxyethyl methacrylate) (pHEMA) with higher surface wettability and mechanical properties

Soft contact lenses made with poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogels modified with various comonomers such as N-vinyl pyrrolidone, methacrylic acid, glycidyl methacrylate, and glycerol monomethacrylate were prepared to investigate the effect of adding the comonomer on the water content, surface wettability, and tensile modulus. These polymers were synthesized by the free radical polymerization of 2-hydroxyethyl methacrylate (HEMA) with the comonomers in the presence of divinyl benzene used as the crosslinker and azobisisobutyronitrile as the initiator. The chemical structure and transmittance of the hydrogels were analyzed by FTIR and UV/Vis spectrophotometers. The surface wettability and tensile modulus were also studied by measuring the contact angle and tensile modulus with a universal testing machine (UTM). Regarding the properties of water in the hydrogels, the ratio between free to bound water was investigated using differential scanning calorimetry (DSC). As the concentration of crosslinker in the hydrogels increases, the tensile strength also increases, whereas the internal water content and contact angle decrease. The effect of the comonomer composition of the hydrogels was also investigated to optimize the various properties of these comonomers for soft contact lenses.

Repeatable adhesion by proton donor-acceptor interaction of polymer brushes

Polymer brushes having proton donor and acceptor type functional groups were prepared on silicon wafers by surface-initiated atom transfer radical polymerization of 2-hydroxyethyl methacrylate (HEMA), 4-hydroxystyrene (4HS), 2-vinylpyridine (2VP), and 4-vinylpyridine (4VP), respectively. Two silicon wafers, one prepared with a poly(HEMA) brush and one with a poly(4VP) brush, were jointed in a 1-cm2 contact area using 5-μL of methanol under a pressure of 120 N at room temperature and successively air-dried to form hydrogen bonds at the brush interface, yielding a lap shear adhesion strength of 337 kPa. Furthermore, poly(4HS) and poly(4VP) brushes also adhered more firmly with 5-μL of methanol to yield a lap shear adhesion strength of 843 kPa due to the phenolic OH group with a larger dipole moment compared to aliphatic OH. In addition, the adhered specimens smoothly debonded in methanol within 20 min at 298 K. The two separated substrates adhered again with a small amount of methanol. Repeatable adhesion and debonding was successfully achieved by proton donor and acceptor type polymer brushes.

PHEMA-PLLA semi-interpenetrating polymer networks: A study of their swelling kinetics, mechanical properties and cellular behavior

Semi-interpenetrating polymer networks (semi-IPNs) have attracted much attention in recent years as biomaterials with a high potential in tissue engineering and controlled drug release. In this article, semi-IPNs were synthetized by free radical polymerization of 2-hydroxyethyl methacrylate (HEMA) in the presence of poly(l-lactic acid) (PLLA) with contents of 5, 10 and 20wt.% at high temperature (150°C). The study focused on the analysis of thermal and mechanical properties, wettability, swelling kinetics in buffered solutions of different pH, and biocompatibility using fibroblasts of human embryonic skin. Segregation of the components in different microdomains was verified by morphological analysis through scanning electron microscopy (SEM). Differential scanning calorimetry (DSC) results revealed that the poly(2-hydroxyethyl methacrylate) (PHEMA) network is amorphous and the PLLA is semi-crystalline. Mechanical analysis provided Young’s modulus values in the range 240–370MPa in tensile tests, and storage modulus (E′) values at 37°C, 1Hz, in the range 800–1200MPa. Equilibrium water uptake measurements displayed material dependence on composition and pH. Swelling kinetics presented good agreement with a second-order diffusion process in all media. No sample present cytotoxicity and the cell migration process occupied many semi-IPNs pores closing them and indicating good cellular recognition. In overall, these networks can be considered for their application as scaffolds for bone defects augmentation and subchondral cartilage repair.

Loose-fit polypseudorotaxanes constructed from γ-CDs and PHEMA-PPG-PEG-PPG-PHEMA.

A pentablock copolymer was prepared via the atom transfer radical polymerization of 2-hydroxyethyl methacrylate (HEMA) initiated by 2-bromoisobutyryl end-capped PPO-PEO-PPO as a macroinitiator in DMF. Attaching PHEMA blocks altered the self-assembly process of the pentablock copolymer with γ-CDs in aqueous solution. Before attaching the PHEMA, the macroinitiator was preferentially bent to pass through the inner cavity of γ-CDs to give rise to tight-fit double-chain stranded polypseudorotaxanes (PPRs). After attaching the PHEMA, the resulting pentablock copolymer was single-chain stranded into the interior of γ-CDs to form more stable, loose-fit PPRs. The results of 1H NMR, WXRD, DSC, TGA, 13C CP/MAS NMR and FTIR analyses indicated that γ-CDs can accommodate and slip over PHEMA blocks to randomly distribute along the entire pentablock copolymer chain. This results in unique, single-chain stranded PPRs showing no characteristic channel-type crystal structure.

Poly(2-hydroxyethyl methacrylate)-b-poly(L-Lysine) cationic hybrid materials for non-viral gene delivery in NIH 3T3 mouse embryonic fibroblasts.

In order to develop efficient and nontoxic gene delivery vectors, a series of biocompatible block copolymers, poly[(2-hydroxyethyl methacrylate)40 -block-(L-lysine)n ] (n = 40, 80, 120, 150), are prepared by combining an atom transfer radical polymerization of 2-hydroxyethyl methacrylate with a ring-opening polymerization of N(ϵ) -(carbobenzoxy)-L-lysine N-carboxyanhydride. The block copolymers are successfully condensed with plasmid DNA (pDNA) into nanosized (<200 nm) polyplexes. As a representative sample, p(HEMA)40 -b-p(lys)150 is utilized to confirm the effective cellular and nuclear uptake of pDNA. The polymer/pDNA polyplexes exhibit very low cytotoxicity and enhanced transfection activity by being easily taken up into mouse embryonic fibroblast cell line (NIH 3T3). Thus, the chimeric block copolymers provide a means for developing versatile nonviral gene vectors harboring the ideal requirements of low cytotoxicity, good stability, and high transfection efficiency for gene therapy.

Thermal behavior of poly(2-hydroxyethyl methacrylate-bis-[trimethoxysilylpropyl]amine) networks

Poly(HEMA-BisSi) networks were prepared by using acid-catalyzed sol-gel of bis-[trimethoxysilylpropyl]amine (BisSi) and free radical polymerization of 2-hydroxyethyl methacrylate (HEMA). The thermal properties of the poly(HEMA-BisSi) networks were investigated with differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The thermal behavior of these networks was also compared with homopolymers (The networks formed in both PHEMA and PBisSi gels were identified). The glass transition temperature (Tg) of PHEMA homopolymer was found as 103.74 °C. The thermal degradation of the poly(HEMA-BisSi) networks with different silica contents (e.g. 10, 15 and 25 wt%) were evaluated with use of DTG. It was observed that the thermal degradation temperature of poly(HEMA-BisSi) networks changed much with the BisSi content.

Ultrasensitive non-chemically amplified low-contrast negative electron beam lithography resist with dual-tone behaviour

A non-chemically amplified negative-tone electron-beam resist with an extremely high sensitivity is presented in this work. The resist, poly(2-hydroxyethyl methacrylate-co-2-methacrylamidoethyl methacrylate) (P(HEMA-co-MAAEMA)), has been synthesized using free radical polymerization of 2-hydroxyethyl methacrylate and 2-aminoethyl methacrylate, and exhibits a crosslinking threshold dose as low as 0.5 μC cm−2. Exposed resist patterns show good adherence to silicon substrates without the assistance of adhesion promoters or thermal treatments and are shown to be adequate for use as a mask for both wet and dry etching of Si. A low contrast value of 1.2 has been measured, indicating that the synthesized polymeric mixture is particularly suitable for achieving grey (3D) lithography. Other relevant properties of the new e-beam resist are optical transparency, visible photoluminescence when crosslinked at low electronic doses, and dose-dependent dual-tone behaviour.

Biocompatible bacterial cellulose-poly(2-hydroxyethyl methacrylate) nanocomposite films.

A series of bacterial cellulose-poly(2-hydroxyethyl methacrylate) nanocomposite films was prepared by in situ radical polymerization of 2-hydroxyethyl methacrylate (HEMA), using variable amounts of poly(ethylene glycol) diacrylate (PEGDA) as cross-linker. Thin films were obtained, and their physical, chemical, thermal, and mechanical properties were evaluated. The films showed improved translucency compared to BC and enhanced thermal stability and mechanical performance when compared to poly(2-hydroxyethyl methacrylate) (PHEMA). Finally, BC/PHEMA nanocomposites proved to be nontoxic to human adipose-derived mesenchymal stem cells (ADSCs) and thus are pointed as potential dry dressings for biomedical applications.

Thiol-terminated hydroxy-functional polymer as a transtab toward polymer latex particles

Hydroxy-functional macrodisulfides have been synthesized by atom transfer radical polymerization of 2-hydroxyethyl methacrylate or 2-hydroxypropyl methacrylate in 2-propanol. Mean degrees of polymerization of the polymer chains beside the disulfide were fixed at 30, 60, and 90; since ATRP has reasonably good living character, the molecular weight distribution is relatively narrow. Furthermore, the macrodisulfides were reduced to synthesize corresponding thiol-terminated polymers with relatively narrow molecular weight distributions. 1H nuclear magnetic resonance and gel permeation chromatography were used to characterize the macrodisulfides and thiol-terminated polymers in terms of their chemical structure, molecular weight, and polydispersity, respectively. Dispersion polymerizations of styrene using the thiol-terminated hydroxy-functional polymers as a transtab (chain transfer agent + colloidal stabilizer) in ethanol resulted in colloidally stable submicrometer-sized polystyrene latex particles. Scanning electron microscopy, Fourier transform infrared spectroscopy, and elemental microanalysis were used to characterize the particles in terms of their morphologies, particle sizes and their distributions, and chemical compositions.

Generation of Functional Coatings on Hydrophobic Surfaces through Deposition of Denatured Proteins Followed by Grafting from Polymerization

Hydrophilic coatings were produced on flat hydrophobic substrates featuring n-octadecyltrichlorosilane (ODTS) and synthetic polypropylene (PP) nonwoven surfaces through the adsorption of denatured proteins. Specifically, physisorption from aqueous solutions of α-lactalbumin, lysozyme, fibrinogen, and two soy globulin proteins (glycinin and β-conglycinin) after chemical (urea) and thermal denaturation endowed the hydrophobic surfaces with amino and hydroxyl functionalities, yielding enhanced wettability. Proteins adsorbed strongly onto ODTS and PP through nonspecific interactions. The thickness of adsorbed heat-denatured proteins was adjusted by varying the pH, protein concentration in solution, and adsorption time. In addition, the stability of the immobilized protein layer was improved significantly after interfacial cross-linking with glutaraldehyde in the presence of sodium borohydride. The amino and hydroxyl groups present on the protein-modified surfaces served as reactive sites for the attachment of polymerization initiators from which polymer brushes were grown by surface-initiated atom-transfer radical polymerization of 2-hydroxyethyl methacrylate. Protein denaturation and adsorption as well as the grafting of polymeric brushes were characterized by circular dichroism, ellipsometry, contact angle, and Fourier transform infrared spectroscopy in the attenuated total reflection mode.

Polymer Brushes on Carbon Nanotubes by Thiol-Lactam Initiated Radical Polymerization of 2-Hydroxyethyl Methacrylate

Water-soluble polymer brushes with multi-walled carbon nanotubes (MWNTs) as backbones were synthesized by grafting 2-hydroxyethyl methacrylate (HEMA) from surface functionalized MWNTs via in situ surface thiol-lactam initiated radical polymerization. MWNTs were functionalized with 2-mercaptoethanol and used as initiators in the polymerization of HEMA in the presence of butyrolactam. FT-IR, XPS, 1H NMR, GPC and TGA were used to determine chemical structure and the grafted polymer quantities of the resulting product. The covalent bonding of PHEMA to the MWNTs dramatically improved the water dispersibility of MWNTs. The average thicknesses of the polymer brushes in the functionalized MWNTs were detected with electron microscopy (SEM and TEM) and images indicated that the nanotubes were coated with polymer layer.

Homogeneous radical polymerization of 2-hydroxyethyl methacrylate mediated by cyclometalated cationic Ruthenium(II) complexes with PF6 − and Cl− in protic media

Cationic coordinatively saturated complexes of ruthenium(II), [Ru(o-C6H4-2-py)(phen)(MeCN)2]+, bearing different counterions of PF6− and Cl− have been used in the radical polymerization of 2-hydroxyethyl methacrylate in protic media and acetone under homogeneous conditions. Exchange of PF6− by Cl− increases the solubility of the complex in water. Both complexes led to the fast polymerization under mild conditions, but control was achieved only in methanol and acetone and was better for the complex with Cl−. The polymerization accelerated in aqueous media and proceeded to a high conversion even with a monomer/catalyst = 2000/1, but without control. Polymerization mediated by complex bearing Cl− was slower in protic solvents but faster in acetone and always resulted in lower molecular weight polymers. Thus, the nature of the anion strongly affected the catalytic activity of the complexes and may serve as way of fine-tuning the catalytic properties. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Dispersion polymerization using hydroxy-functional macroazoinitiators as an inistab

Hydroxy-functional macroazoinitiators with central azo unit have been synthesized by atom transfer radical polymerization of 2-hydroxyethyl methacrylate or 2-hydroxypropyl methacrylate in methanol. The mean degrees of polymerization of the polymer chains beside the azo group were fixed at 30 and 60. Proton nuclear magnetic resonance (1H NMR) and gel permeation chromatography were used to characterize the macroazoinitiators in terms of their chemical structure, molecular weight, and polydispersity, respectively. Dispersion polymerizations of styrene using the hydroxy-functional macroazoinitiators as an inistab (initiator + colloidal stabilizer) in 2-propanol or 2-propanol/water media resulted in submicrometer-sized polystyrene latex particles with hydroxy-functional polymer hair. Electron microscopies, Fourier transform infrared spectrometer, thin layer chromatography, and 1H NMR were used to characterize the particles in terms of their morphologies, particle sizes, and their distributions and chemical compositions. The synthesized particles behaved as an effective particulate emulsifier for the stabilization of oil-in-water emulsions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Novel Scaffolds Based on Poly(2-hydroxyethyl methacrylate) Superporous Hydrogels for Bone Tissue Engineering

In this study, poly(2-hydroxyethyl methacrylate) (pHEMA)-based superporous hydrogels were synthesized by radical polymerization of 2-hydroxyethyl methacrylate (HEMA) in the presence of a gas blowing agent, sodium bicarbonate. These hydrogels are: pHEMA, pHEMA–gelatin, glycerol phosphate (GP) cross-linked pHEMA–gelatin, glutaraldehyde (GA) cross-linked pHEMA–gelatin superporous hydrogels (SPHs) and pHEMA–hydroxyapatite (HA) superporous hydrogel composites (SPHCs). The hydrogels have a structure of interconnected pores with pore sizes of approx. 500 μm. Although the extent of swelling decreased when gelatin and HA were incorporated to the pHEMA structure, the time to reach the equilibrium swelling (approx. 20 s) was not affected so much. In the presence of gelatin and cross-linkers, mechanical properties significantly improved when compared with pHEMA SPH. Among all the synthesized hydrogels, pHEMA–HA SPHC showed great improvement in mechanical strength and its elastic modulus value was 0.027±0.002 N/mm2. Osteogenic activities of pHEMA-based scaffolds were examined by preosteoblastic MC3T3-E1 cell-culture studies. The mitochondrial activity test (MTT) showed that gelatin-containing scaffolds stimulated cell proliferation compared with other scaffolds, while alkaline phosphatase levels (ALP) and mineralization were found highest for the GP cross-linked pHEMA–gelatin SPH. However, pHEMA SPH and pHEMA–HA SPHC did not support cell proliferation and also differentiation. In conclusion, pHEMA–gelatin SPH and GP cross-linked pHEMA–gelatin SPH can be considered as potential scaffolds for bone tissue-engineering applications.

Biofunctional and Biomimetic Polymer Brushes Prepared via Surface-Initiated Atom Transfer Radical Polymerization

Surface-initiated controlled radical polymerization is a powerful strategy to tailor the chemical and physical surface properties of materials. This article highlights recent work from the author's laboratory in which surface-initiated atom transfer radical polymerization is used to generate biofunctional and biomimetic surface coatings. Three examples will be discussed. The first two examples are based on the surface-initiated atom transfer radical polymerization of 2-hydroxyethyl methacrylate and (polyethylene glycol) methacrylate, which generates a polymer brush that suppresses non-specific adhesion of proteins and cells. These non-fouling brushes have been used to generate protein microarrays and to produce coatings that can promote endothelialization of implantable biomaterials. The third example describes the use of polyelectrolyte brushes as matrices to direct the mineralization of calcium carbonate.

Superporous poly(2-hydroxyethyl methacrylate) based scaffolds: Preparation and characterization

Superporous poly(2-hydroxyethyl methacrylate) (PHEMA) scaffolds with pore size from 101 to 102μm range were prepared by radical polymerization of 2-hydroxyethyl methacrylate (HEMA) with 2wt.% ethylene dimethacrylate (EDMA) with the aim to obtain a support for cell cultivation. Superpores were formed by salt-leaching technique using NaCl or (NH4)2SO4 as a porogen. Addition of liquid porogen (cyclohexanol/dodecan-1-ol (CyOH/DOH)=9/1 w/w) to the polymerization mixture did not substantially affect the formation of meso- and macropores. The prepared slabs were characterized by several methods including water and cyclohexane regain by centrifugation, water regain by suction, scanning electron microscopy (SEM), mercury porosimetry and dynamic desorption of nitrogen. High-vacuum scanning electron microscopy (HVSEM) confirmed permeability of hydrogel slabs to 8-μm microspheres, whereas low-vacuum scanning electron microscopy (LVSEM) at cryo-conditions showed the undeformed structure of the frozen slabs. Interconnection of pores in the PHEMA slabs was proved. Water regain estimated by centrifugation method did not include volume of large superpores (imprints of porogen crystals), in contrast to water regain by suction method. The porosities of the slabs ranging from 81 to 91% were proportional to the volume of porogen in the feed.

Characterization of poly(2-hydroxyethyl methacrylate-silica) hybrid materials with different silica contents

Poly(2-hydroxyethyl methacrylate-silica) hybrid materials with significantly lower volume shrinkage were synthesized by using acid-catalyzed sol–gel reactions of tetraethyl orthosilicate and free radical polymerization of 2-hydroxyethyl methacrylate (HEMA). The mechanical, thermal, and optical properties and internal porosities of the poly(HEMA-silica) hybrids with different silica contents (e.g., 15, 25 and 30 wt%) were evaluated with the use of nanoindentation, microscratch, thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis, UV–vis spectrophotometer and N 2 adsorption–desorption method. A silica percolation threshold was found at around 20–25 wt%, beyond which a marked increase in the poly(HEMA-silica) hybrid hardness and modulus was observed as compared to pure poly(HEMA). Nanoindentation and scratch testing measurements also for the first time were introduced in characterizing poly(HEMA-silica) hybrid materials.