Drug release control and anti-inflammatory effect of biodegradable polymer surface modified by gas phase chemical functional reaction

The plasma technique has been widely used to modify the surfaces of materials. The purpose of this study was to evaluate the probability of controlling the prednisolone delivery velocity on a polylactic acid (PLA) surface modified by plasma surface treatment. Surface modification of PLA was performed at a low-pressure radio frequency under conditions of 100 W power, 50 mTorr chamber pressure, 100–200 sccm of flow rate, and Ar, O2, and CH4 gases. The plasma surface-modified PLA was characterized using scanning emission microscope, x-ray photoelectron spectroscopy (XPS), and contact angle measurements. In vitro evaluations were performed to determine cellular response, drug release behavior, and anti-inflammatory effects. The PLA surface morphology was changed to a porous structure (with a depth of approximately 100 μm) and the surface roughness was also significantly increased. The XPS results demonstrated higher oxygenized carbon contents than those in the non-treated PLA group. The prednisolone holding capacity increased and the release was relatively prolonged in the surface-modified PLA group compared to that in the non-treated PLA group. In addition, cell migration and proliferation significantly increased after PLA treatment alone. The activity of cytokines such as cyclooxygenase-2 (COX-2), tumor necrosis factor-a (TNF-α), interleukin (IL-1β), and IL-6 were considerably reduced in the plasma-treated and prednisolone holding group. Taken together, surface-modified PLA by plasma can provide an alternative approach to conventional physicochemical approaches for sustained anti-inflammatory drug release.


Introduction
Numerous tissue engineering studies on implantable materials for restoring or maintaining human body functions have been conducted recently, and most of these studies have focused on improving the biointerfaces between cells and materials [1].Studies on the types of materials, cell characteristics, physiologically active substances, and drug delivery have been performed [2][3][4].
The drug delivery capacity of implantable materials is an important factor in improving their performance.For effective drug delivery, the introduction of mediators such as drug carriers and hydrogels or physical methods such as creating micropores on a material surface have been investigated [5][6][7][8].In particular, to store and deliver drugs, it has been reported that micropores can be formed on the material surface using laser-based physical surface modification methods such as ion beam and femtosecond laser irradiation or chemical surface modification methods such as anodic oxidation and polishing [9][10][11][12].However, physical methods such as laser irradiation have limitations such as variations in the irradiation conditions for each material property, slow processing speed, and high cost.In addition, these methods are not easy to use because of the difficulty in resetting the conditions for each sample [13,14].Meanwhile, chemical methods such as anodic oxidation cannot easily control the desired pore size formation or uniformity, and a process for completely removing the chemicals used in the process that may cause cell toxicity is required [15].Our previous reports, including those on chemical methods such as anodization [8], physical methods such as electropolishing [12], femtosecond laser irradiation [10], and surface modification through plasma polymerization [16], suggest that only surface modification can promote cell differentiation.
The surface topology of a material is the most important factor influencing the first reaction that occurs at the cell-material interface.Cellular responses at the interface, such as receptor activation, extracellular matrix recruitment, and focal cell adhesion/avoidance, can affect the biocompatibility and function of the implanted materials.Cells are very sensitive to the physical environment of the material surface, such as surface roughness, strength, and modulus, and by recognizing these factors, the cytoskeleton, cell shape, and differentiation can be induced [17].The initial reactions of cells at the interface vary according to various factors; however, these are particularly influenced by the interaction between the biological tissue and the biomaterial surface, including the interfacial topography, wettability, and electrical properties [18].In this respect, in this study, a plasma technique that can overcome the limitations of laser irradiation or chemical methods was used to improve biocompatibility and maximize drug delivery efficacy.
Plasma technology is an optimal method for surface modification that can be applied quickly and easily with fewer external physical and chemical influences than chemical methods or laser irradiation [19,20].In this study, material surface modification was carried out through the gas-phase plasma process at atmospheric pressure, which has been used in various fields for a long time, and its safety and effectiveness have been verified [21][22][23].
Many studies on modifying polymer surfaces using plasma techniques have already been reported.Most of these studies presented results focused on surface treatment of polymers to achieve specific goals such as promoting bone regeneration [24,25].Research on controlling the drug delivery ability of polymers through plasma treatment has also been reported [26,27], but it just was presented the drug release rate and did not propose verification of drug holding ability in the polymer surface and efficacy of the drug released.Recently, research on polymers as substitutes for metals has been actively conducted for implantable materials.These studies considered the essential duration of the material's existence in the body, importance of the interface between the material and tissue, biocompatibility, and mechanical properties such as elasticity, flexibility and strength.In particular, in the case of dental or orthopedic applications, the difference in stiffness, shear stress, or elastic modulus between the implanted material and the surrounding tissue can cause the implant to fall out of the placement location or decrease its adhesion to living tissue due to physical movement or external forces.This may result in a poor prognosis.Research on the use of polymers to address the unmet needs of each clinical field in terms of mechanical properties comparable to those of metals, ease of surface modification for drug delivery, and biodegradation is being conducted continuously.For example, polyetheretherketone for orthopedic cervical cages, polylactic acid (PLA) for cardiovascular bioabsorbable stents, and polyvinyl alcohol for oral mucosal adhesive drug delivery systems have been reported [28][29][30].Among various polymers, in particular, PLA is the most commonly used biodegradable polymer in clinical applications today.Due to its advantages such as favorable biocompatibility and safe degradation products, it is used in various clinical fields such as vascular scaffolds, drug coatings, drug delivery systems, and tissue engineering.Although thrombosis is the first acute foreign reaction that occurs when a material is implanted into the body, inflammation is an important pathological phenomenon that should be noted in all lesions.This study utilized prednisolone, a steroid-based drug approved by the FDA with excellent anti-inflammatory effect and used for patient treatment.Our research group previously applied it to implantable materials and verified its efficacy [31].Studies using plasma techniques to implement sustained drug release are relatively recent, and studies focusing on inflammation and cellular responses are insufficient.Therefore, the purpose of this study was to evaluate the cellular response and prednisolone delivery rate of PLA surfaces modified using the plasma technique.

PLA plasma treatment
PLA (Mw ∼60 kDa) was purchased from Sigma-Aldrich (St. Louis, MO, USA) and dissolved in chloroform (5%, w/v) with stirring at 140 • C. Completely dissolved PLA was placed in a glass dish and dried in a desiccator below 25 • C for 48 h.Prior to plasma treatment, the PLA was cut into a circular shape (150 mm in diameter and 1.0 mm in thickness) suitable for in vitro evaluation.The plasma treatment was performed with slight modifications to the conditions described in previous reports [32,33].Briefly, the PLA specimen was placed in the center of the inner stage of plasma equipment vacuum reactor and plasma treatment was performed using radio frequency (RF) discharge at 100 W of plasma power, 100-200 sccm of flow rate, and a chamber pressure of 50 mTorr (variables due to capacity due to mechanical and physical variables of equipment).The plasma gases used were CH 4 , Ar, O 2 , and N 2 for 3 min (table 1).To minimize the variables affecting the specimen, all parameters such as the  RF discharge power, gas flow rate, and RF operating pressure were identical and fixed.Thereafter, various follow-up studies on cell response, drug release, and anti-inflammatory effects were conducted (figure 1).

Surface morphology of polymer
The morphologies of the PLA surfaces were examined using scanning electron microscopy (SEM; Hitachi, Tokyo, Japan) at voltages ranging from 5 to 15 kV after sputter-coating the surfaces with platinum.To prevent melting and deformation of the polymer surface by the microscope beam, after focusing on the area around the region of interest, the angle was carefully moved to the target position and an image was taken.

Surface topology and roughness analysis
The surface topology and roughness of PLA were characterized using atomic force microscopy (AFM, XE-100, Park Systems, Suwon, Korea).The spring constant and tip radius were K = ∼42 N m −1 and <10 nm, respectively.The average roughness (Ra) was calculated using the XEI software (version 4.1.1).Representative images were obtained by scanning the region of interest at the center and edge of the specimen.The process was performed in a non-contact manner using a PPP-NCHR probe.
All experiments were independently performed three times, and the average values are presented.

X-ray photoelectron spectroscopy analysis
The PLA surface-modified by plasma was chemically analyzed using high-performance x-ray photoelectron spectroscopy (XPS, K-ALPHA+, Thermo Fisher Scientific, Waltham, MA, USA).A system equipped with a monochromatic Al Kα radiation source, a 180 • bifocal hemispherical analyzer, and a 128 channel detector was utilized.The irradiation spectra were collected in the energy range of 0-1350 eV at a resolution of 1 eV.The spectra were charge-corrected using the main lines of carbon and oxygen 1s.In this study, a narrow scan value was used to evaluate the variation in elemental combinations and the total amount of elements produced by the plasma treatment.

Wettability of surface-modified polymer
After plasma treatment of the PLA surface for 0.5, 1.0, 1.5, 2.5, and 3.0 min, the contact angles were measured using a GSX equipment (Surfacetech, Gwangju, Korea) to confirm the surface wettability.After dropping 7 µl of deionized water onto the PLA surface, the contact angles were automatically measured after 4 s.The acquired images were interpreted using the Surfacetech software (version 1.1.5.6).Experiments were performed independently three times to calculate the mean values.

Quantification of surface drug content and release rate
The prednisolone dissolved in tetrahydrofuran (THF, 200 µl, 5 wt/%) was loaded onto the PLA surface and gently shaken and allowed to stand for 24 h to ensure that it was uniformly loaded and instilled on the PLA surface.After gently washing the PLA surface with deionized water to remove the slightly physically adsorbed prednisolone from the PLA surface, the PLA specimens were lyophilized as described previously [34].To measure the total amount of prednisolone instilled onto the PLA surface, the specimens were immersed in a THF solution with gentle shaking.
The THF solution was collected and analyzed using an ultraviolet-visible (UV-vis) spectrophotometer (Multiskan EX; Thermo Fisher Scientific, Waltham, MA, USA).To determine the release rate of prednisolone from the PLA surface, the lyophilized PLA specimen was placed in a phosphate-buffered saline (pH 7.2) solution, and the solution was harvested at designated time points to measure the absorbance using a UV-vis spectrophotometer.Readings were recorded continuously until the UV value reached zero.The concentration of prednisolone released from the PLA surface was calculated by comparison with the drug standard curve and expressed as the cumulative amount relative to the total amount of prednisolone at the initial phase on the PLA surface.

2.7.
Cell culture RAW264.7 macrophage were cultured in Dulbecco's modified Eagle medium supplemented with 10% heat-inactivated fetal bovine serum and 1% penicillin at 37 • C in a 5% CO 2 atmosphere.The medium was changed every three days until the cells reached 90% confluence.

Cell migration
The scratch test was performed to assess cell migration.As reported previously [12], cells (1 × 10 4 cells cm 2 ) were seeded in cell culture dishes (25 mm in diameter).After 24 h of incubation, a 50 µm thick line was created by scraping the center of the cell monolayer with a sterile tip (approximately 12.0 ± 1.05 mm 2 ).After an additional 24 h of incubation, the regions of interest in the scratches were randomly selected for imaging [35].Cell migration was calculated as 100 × {[initial scratched area − scratched area remaining after 24 h of incubation]/initial scratched area}.

Cell proliferation
Cell proliferation was examined at designated time points after cell seeding in pristine plasma-treated PLA and plasma-treated PLA with prednisolone.The degree of cell proliferation was evaluated by WST-1 assay using an EZ-Cytox Cell Viability Assay Kit (Daeil Lab Service Co., Seoul, Korea).Briefly, 40 µl of the EZ-Cytox reagent was added to a 24 well culture dish.The amount of formazan dye metabolized by mitochondrial dehydrogenase was spectrophotometrically measured at an absorbance of 450 nm using a microplate reader (BioTek Instruments, Winooski, VT, USA).The amount of formazan salt formed corresponded to the number of viable cells per well.

Western blotting
To investigate the anti-inflammatory effects of the prednisolone released from the PLA surface, western blot analysis of RAW264.7 cells was performed.
To measure the activity of various inflammatory markers, RAW264.7 cells were stimulated with lipopolysaccharide (LPS, 1 µg ml −1 ) for 1 h.After incubating the cells for 1 h, they were lysed with RIPA lysis buffer (Cell Signaling, Beverly, MA, USA).
After measuring the protein concentration using the bicinchoninic acid (BCA) Protein Assay Kit, the protein (20 µg) was subjected to a 10% sodium dodecyl sulfate-polyacrylamide gel and transferred to a polyvinylidene fluoride membrane (Millipore, Bedford, MA).The membrane was blocked with 5% bovine serum albumin (BSA) for 1 h and then a blot was incubated with primary antibodies (1:1000 in 1.5% BSA) at 4 • C.This was followed by incubation for 1 h with horseradish peroxidase-conjugated secondary antibodies (all 1:3000).Immunoreactivity was detected using enhanced chemiluminescence (GE Healthcare Biosciences).The intensity of the band was quantified using Gel-Pro software, and protein amounts were normalized to the intensity of the control.

Statistical analysis
Statistical analyses were performed using the commercially available software SPSS version 15 (SPSS, Armonk, NY, US).Data are presented as the mean ± SD.The unpaired Student's t-test was used to compare data from different groups.Values of p < 0.05 were considered statistically significant.

Surface morphologies of PLA surface
The surface morphologies and pore formation patterns of the PLA surfaces before and after the plasma treatment were examined using SEM.The surface morphology of PLA without plasma treatment was generally smooth, whereas pores were formed on the surface of the specimen treated with plasma (figure 2).The variation in surface roughness of the plasma-modified PLA was analyzed using AFM.
The roughness dramatically increased in the plasmatreated PLA group compared to that in the nontreated PLA group (figure 3

Surface chemistry of PLA surface
XPS was performed to investigate the changes in the chemical composition of the PLA surface before and after plasma treatment.The results revealed that the introduction of carbon and oxygen was significantly increased by the plasma gases (CH 4 /O 2 and CH 4 /Ar).Plasma treatment of the PLA surface made it more accessible for better binding of various chemical agents.The plasma changed the chemical surface structure of PLA, enabling the deposition of active species layers, such as COO − , C=O, and C-O, on the polymer surface (figure 4).

Contact angle measurement
The cellular response to an implanted material surface is strongly influenced by wettability.To verify the effects of plasma on PLA, its hydro-properties were measured based on the contact angles.It was visually confirmed that the contact angles of the PLA surface after the plasma treatment were significantly reduced (by 49.8% within 30 s of plasma treatment).
As the plasma treatment time increased, the contact angle decreased (figure 5, n = 3, p < 0.05).It is clear that the hydrophilicity of the specimens significantly improved after the plasma treatment.

Drug holding capacity and release velocity
The effect of the polymer surface modified by plasma on the drug-holding capacity and release velocity was investigated as described in the Materials and Methods section.The drug holding capacity increased in the plasma-treated PLA group (38.1%, n = 3, p < 0.05) compared to that in the nontreated PLA group (figure 6(a)).During the initial phase of drug release (after four days of incubation), a burst release pattern was observed in the plasma non-treated group (94.2% of the total amount of drug held), whereas the drug release was relatively prolonged in the plasma-treated PLA group (74.0% of the total amount of drug held) (figure 6(b), n = 3, p < 0.05).

Cell migration and proliferation assay
Cell migration, which is an early event in the cellular response to the material, and cell proliferation, which progresses over a long period of time, were evaluated.As described in the Materials and Methods section, the middle region of the cell monolayer on the culture dish was scratched and the cells were further cultured for 24 h (figure 7(a)).The cell migration rate increased in the plasma-treated PLA group (144.3% of the control, n = 3, p < 0.05) compared to that in the non-treated PLA group (figure 7(b)).The cell migration rate in the plasma-treated PLA group containing prednisolone was not statistically significant compared to that of the prednisolone-free plasmatreated PLA group (p = ns).This result is consistent with that of our previous study, which showed that prednisolone alone did not affect cell migration and proliferation [31].To investigate the effects of cellular responses that occur in a relatively early phase within one day, such as cell adhesion and migration, on cell proliferation and differentiation, which are long-term cellular responses, an XTT assay was performed as described in the Materials and Methods section.
Cell proliferation was significantly increased in both plasma-treated PLA groups, with and without prednisolone, compared to that in the plasma non-treated group until the seventh day of cultivation (n = 3, p < 0.05, figure 7(c)).However, after 14 d of cultivation, there was no difference in proliferation patterns between the groups.The prednisolone did not affect cell proliferation, as the proliferation pattern of the plasma-treated group with prednisolone was similar to that of the plasma-treated group without prednisolone.

Anti-inflammatory effect
Western blot analysis was performed to investigate the anti-inflammatory effects of plasma treatment and prednisolone on the PLA surface.Various markers for inflammation such as cyclooxygenase-2 (COX-2), tumor necrosis factor-a (TNF-α), interleukin (IL-1β), and IL-6 were investigated as mentioned above.Treatment of RAW264.7 cells with LPS resulted in a significant increase in cytokine production compared to the control group (figure 8(a)).However, the activities of COX-2 and TNF-α were reduced only by plasma treatment.In contrast, the activities of all the markers were considerably reduced in the prednisolone-holding group (figure 8(b)).

Discussion
Recently, studies on the biocompatibility, resistance to bacterial infection or physical stress [36], material composition for biological functions [37], surface roughness [38], modulus of elasticity [39], and surface topology/morphology [40] have been conducted to improve the function of implantable materials.In addition to these mechanical and physical functions, drug-holding and delivery capabilities are considered important parameters for predicting biological effects.In this study, plasma technology, which is widely used in various fields owing to its advantages, such as ease of access and reliability of effect, was applied to PLA, the most representative implantable polymer, to verify drug delivery control and anti-inflammatory effects (figure 1).Plasma technology has been widely used to impart chemical functional groups [41,42] to the surfaces of materials or for surface modification [43,44].In this study, a plasma protocol that has been reported several times by our research group [45,46] was applied, and its consistency with previously reported studies was investigated.Plasma treatment was able to modulate the PLA surface morphology inducing surface nanostructure (figure 2).The result is consistent with our previous report that the topology of the material surface can be controlled by plasma (etching effect) [45].The surface roughness also improved (figure 3), and the wettability results were consistent with our previous report in that the hydrophilicity of the roughened surface improved (figure 5) [45].
The hydrophilic nature of the scaffold surface allows water to spread evenly over itself, maximizing the contact area between the material and the organic .In this study, surface modification and elemental changes in the material by plasma treatment as well as previous reports on drug holding and release control were investigated for their potential [52].Even if the drug is held on the surface of the implantable material during the implant procedure, it can easily cause washout and burst release, such as drug dropout due to external force, drug loss due to blood pressure and muscle movement, and dilution due to body fluids.To develop implantable materials for drug delivery, many methods for inducing chemical bonding between drug and material's surface [53] or forming pores on the surface [54] have been proposed.A covalent bond, such as an imine bond or a carboxyl bond, forms a very strong bond between a material and a drug; thus, it is difficult to break this bond in the body, making it difficult for the drug to be delivered into cells.Therefore, in the case of drugs that are incorporated into cells, such as anti-inflammatory drugs, and exert their efficacy by influencing cytokines through signaling pathways, this method of inducing chemical bonding is not suitable.Therefore, the results of this study suggest that, as a drug delivery method for anti-inflammatory effects, a physicochemical method through a barrier or drug-holding effect is more appropriate than such a strong chemical bond (figure 6).The effects of the plasma surface-modified PLA on drug retention and cellular responses, including anti-inflammatory effects, were investigated.As a result of cell migration, an initial event occurring at the interface between cells and materials, plasma treatment alone significantly increased cell migration, and the effect of prednisolone on cell migration was not significant (figures 7(a) and (b)).Although the proliferation pattern was saturated after a certain period of time (after 14 d in this study), cell proliferation, which is a late cell response, continued effectively until the 7th day of cultivation owing to the increase in cell migration (figure 7(c)).Because inflammatory cytokine analysis was conducted within a very short time of 2 h of cultivation, the initial cellular response is important.As LPS can strongly activate macrophages and induce various pro-inflammatory mediators [55], the effect of plasma treatment or prednisolone on the surface of activated proteins was confirmed by western blot analysis.The activities of COX-2 and TNF-α were reduced only by plasma treatment, and the activities of all the investigated proteins, such as COX-2, TNF-α, IL-1β, and IL-6, were reduced by prednisolone (figure 8).Macrophages (RAW264.7 cells in this study) produce various cytokines during inflammatory response [56].Depending on the differences in the activities of various types of macrophages, these cells can be classified as M1 or M2 macrophages.M1 macrophages (or pro-inflammatory macrophages) are known as classically activated by interferon (IFN-γ) or LPS and produce proinflammatory cytokines (e.g.TNF-α and IL-6) and express inflammation-related enzymes (e.g.COX-2).Meanwhile, alternatively activated macrophages, M2 (or anti-inflammatory macrophages), are activated by exposure to cytokines, such as IL-4, IL-13, or IL-10 [57].The terms M1 and M2, which are widely used to describe inflammation, may not be appropriate for describing the specific and dynamic inflammatory conditions that occur in an organism's inflammatory environment [58].Nevertheless, considering the types of cytokines inhibited, plasma treatment and prednisolone on the surface of the material are related to M1 macrophages rather than to M2 macrophages.However, these results may vary depending on the plasma technology protocol used, characteristics of the material, and cell type.As the results may vary depending on cell-oriented variables such as the shape and size of the cells, role of the filopodium (e.g.dendritic cells or endothelial cells), and surface area to which the cells attach (e.g.macrophages or osteoclasts), as well as material-oriented variables such as elasticity, roughness, shape, and strength, the effect of these variables on the cellular response requires further investigation.

Conclusion
Plasma treatment dramatically improved the biocompatibility of the PLA surface, including cell migration and proliferation, and ultimately enhanced the antiinflammatory effect by improving the drug-holding capacity.In conclusion, plasma-modified porousstructured PLA can provide a novel and alternative approach beyond conventional physicochemical approaches for controllable and sustainable drug release systems with anti-inflammatory effects.

Figure 1 .
Figure 1.Schematic of plasma treatment and verification contents of the modified polymer surface in this study.

Figure 2 .
Figure 2. SEM images of untreated PLA and plasma-treated PLA.The morphologies of the PLA surface were modified by the plasma treatment in the pore size visualization.

Figure 4 .
Figure 4. Narrow scans of the XPS spectra focused on the selected elements of carbon and oxygen peak before and after the plasma treatment.

Figure 5 .
Figure 5. Surface wettability measurements.Images of the PLA surface static contact angles were acquired and analyzed quantitatively.The indicated values are means ± SD (n = 3), * p < 0.05.

Figure 6 .
Figure 6.Drug holding capacity and release velocity.Amount of total prednisolone held in the PLA surface (a) and its cumulative release velocities from the PLA surfaces (b) before and after plasma treatment.The indicated values represent the mean ± SD (n = 3), * p < 0.05.

Figure 7 .
Figure 7. Representative images of cell migrations in the range of 0-24 h of cultivation post-scratch (a), quantitative analysis (b), and RAW264.7 macrophage proliferation (c).An image analysis of the cell migration rate was performed by 100 × [(initial scratched area − remaining scratched area at 24 h of cultivation)/initial scratched area].The indicated values are means ± SD (n = 3), * p < 0.05.

Figure 8 .
Figure 8.Western blot analyses of inflammation markers.Western blots were used to assess the expression levels of several markers of inflammation such as COX-2, TNF-α, IL-1β, and IL-6 (a).The intensities of the bands were quantified using Gel-Pro software, and the protein amounts were normalized to the intensity of the control (b).β-actin was processed in parallel as an internal control for protein loading.The quantitative data indicating mean protein levels are the ± mean SD (n = 3), * p < 0.05 vs. the LPS-non-treated control, † p < 0.05 vs. the LPS-treated cells.‡ p < 0.05 vs. the LPS + plasma-treated groups.
matter.Ultimately, it improves biocompatibility by increasing cellular responses, including cell adhesion, migration, and proliferation[47, 48].Additionally, hydroxyl groups (negative charge) existing on hydrophilic surfaces inhibit bacterial attachment due to electrostatic repulsion[49].Plasma treatment causes the material surface to oxidize and form hydroxyl groups.Because these hydroxyl groups are polar, they attract water, which can ultimately improve the wettability of the PLA surface[50].Changes in PLA surface properties according to the type of injected gases were confirmed through contact angle measurement.As a result of the experiment, no change in contact angle was observed when CH 4 was injected alone, but the contact angle was decreased with plasma treatment time when CH 4 was injected at a 1:1 ratio with Ar, O 2 , or N 2 gases (data not shown).The XPS results showed that the contents of oxygenized carbon was increased (figure4), indicating that oxygenation of carbon to states OH-, CO-and COO-etc.due to plasma treatment.An increase in the peak intensity in the XPS analysis indicated the appearance of carbon-and oxygen-containing functional groups, as in the plasma-treated PLA surface.For the nonplasma treated sample, the peak 284.7 eV corresponds to the CC/CH bond, the peak 286.4 eV corresponds to the CO bond, and finally the peak 288.7 eV appears due to the presence of O=CO groups in the chain.When examining the deconvolution of the plasma treated group, changes in peak intensity found in the untreated sample were observed.Peaks associated with O=C-O and C-O groups increased in intensity, while C-C and C-H groups decreased.The functionalized PLA surface, which may act as an effective barrier to drugs, appears to correspond to crosslinking due to the effects of functional plasmaactive species[51]

Table 1 .
Conditions for plasma process by various gases.