*3.1. Materials*

2,2'-azobisisobutyronitrile (AIBN) and pentaerythritol tetrakis(3-mercaptopropionate) (PETMP) was purchased from Sigma-Aldrich Co. LLC. (St. Louis, MO, USA). Dipentaerythritol hexakis(3-mercaptopropionate) (DPEHMP) was purchased from TCI America (Montgomeryville, PA, USA). Methacryloxyethyl thiocarbamoyl rhodamine B was purchased from Polysciences (Warrington, PA, USA). Trifluoroacetic acid (TFA) and solvents were purchased from Thermo Fisher Scientific, Inc. (Waltham, MA, USA). *tert*-Butyl acrylate, methyl acrylate, and methyl mercaptopropionate (MMP) were purchased from Acros Organics (Morris County, NJ, USA). The inhibitors of these monomers were removed by passing through alumina before use. Other chemicals and solvents were used without further purification. 1H NMR was performed using a Varian MR400 (400 MHz, Agilent Scientific Instruments, Santa Clara, CA, USA) and analyzed using VNMRJ 3.2 (Agilent Scientific Instruments, Santa Clara, CA, USA) and MestReNova. Gel permeation chromatography (GPC) analysis was performed using a Waters 1515 HPLC instrument (Milford, MA, USA) using THF as an eluent, equipped with Waters Styragel (7.8 × 300 mm) HR 0.5, HR 1, and HR 4 columns in sequence and detected by a differential refractometer (RI). Sintered HAP discs (0.5 cm in diameter) were purchased from Himed, Inc. (Old Bethpage, NY, USA).

#### *3.2. Synthesis of tBu PAA Homopolymers*

*tert*-Butyl acrylate (t-BuA), AIBN, and chain transfer agen<sup>t</sup> (CTA) (MMP, PETMP, or DPEHMP) in acetonitrile were mixed in a flask (See Table S1 for the polymerization conditions). The oxygen of the reaction mixture was removed by bubbling nitrogen gas for 10 min, and the reaction solution was stirred at 70 ◦C for 16 h. The reaction was cooled to room temperature. The solvent was removed by evaporation under reduced pressure. The resultant residue was dissolved in diethyl ether, and the polymer was isolated by precipitation in a methanol:water [50:50 (v/v)] mixture. The yield of purification was >90% for most cases. The polymer arm length (DP) was calculated by comparing the integrated peaks of -OCH2- group of chain transfer agen<sup>t</sup> to the -CH- polymer backbone. The number average molecular weight (Mn) was calculated using the DP and molecular weights of monomers and

CTAs. Gel permeation chromatography molecular mass results were determined using a calibration curve based on the standard samples of polystyrene. 1H NMR (CDCl3, 400 MHz) δ: 4.21–4.06 (s, 2H, –OCH2– of PETMP), 2.85–2.51 (brs, 4H, –SCH2CH2–), 2.37-2.07 (brs, 1H, –CH–,), 1.97–1.14 (brs, 11H, –CH3 and –CH2–).

The tBu groups of polymers were then removed by the addition of trifluoroacetic acid (TFA) (5 mL to 1 g of polymer). After stirring for 30 min, TFA was removed by blowing with nitrogen gas in a closed container, and the gas was passed through a base (NaOH) aqueous solution to trap TFA. The residue was dissolved in methanol, and deprotected polymers were isolated by precipitating in excess diethyl ether. Subsequently, the precipitate was dissolved in distilled water and lyophilized to yield a powdery product. 1H NMR (DMSO, 400 MHz) 2.4-2.0 (brs, 1H, –CH–,), 1.8-1.2 (brs, 2H, –CH2–).

#### *3.3. Synthesis of Random Copolymers with MA*

The PAA random copolymers with methacrylate (MA) were synthesized by the same method with the tBu PAA homopolymers as described above. See Table S2 in Supporting Information for the monomer feed compositions and reaction conditions.

#### *3.4. Synthesis of Rhodamine B-Labeled Polymers*

The rhodamine B-labeled copolymers were synthesized using methacryloxyethyl thiocarbamoyl rhodamine B (0.1 mol.% to the total amount of monomers) by the same method as described above with the tBu PAA homopolymers. See Supporting Information for the detailed procedure, polymerization conditions, and monomer feed compositions (Tables S3–S6). The Mayo plots showed linear correlations, and the Ctr values of each thiol group of linear and 4-arm polymers are 0.91 and 0.97 (Figure S2 and Table S11).

#### *3.5. Analysis of Polymerization Process*

In general, *DParm* of polymer prepared in the presence of thiol groups as a CTA may be presented by the Mayo equation [38]:

$$\frac{1}{\frac{1}{DP\_{arm}}} = \frac{1}{DP\_0} + \mathbb{C}\_{tr}\frac{[SH]}{[Monomer]}\tag{2}$$

where *DP*0, *Ctr*, [CTA] and [Monomer] represent the *DP* of each polymer arm in the absence of CTA, chain transfer coe fficient, initial mole concentration of thiol groups, and mole concentration of monomers, respectively. According to the Mayo equation, the plot of 1/DP would be proportional to [SH]/[Monomer], and the slop presents *Ctr*.

#### *3.6. HAP Binding Assay*

Fluorescence spectroscopy was used to evaluate the binding capacity of rhodamine-labeled polymers onto HAP powder. The polymer solutions in 10 mM phosphate bu ffer with 150 mM NaCl with di fferent concentrations (pH = 7, adjusted by NaOH aq., 0.5 mL, 0.04, 0.08, 0.16, 0.31, 0.63, and 1.25 g/L) were mixed with HAP (30 mg/mL) in a 1.5 mL tube. The solution was gently shaken using a mechanical shaker for 2 h at room temperature and then centrifuged at 10,000 rpm for 10 min. The fluorescence emission intensities of the supernatant were measured (excitation wavelength = 553 nm, emission wavelength = 627 nm) and compared with those for samples with same concentration of polymers without HAP.

#### *3.7. Anti-Bacterial Adhesion Assay*

HAP coated MBECTM lids were treated by polymer solutions in MilliQ water (1 wt.%, pH 6.5 adjusted with NaOH or HCl) and allowed to shake in the incubator at 37 ◦C for 1 h. Following treatment, excess polymer solution was removed from the MBECTM lids by submerging in Trypticase soy broth (TSB) for 10–15 s for three cycles, replacing the TSB broth for each new cycle. The MBECTM lids were

then incubated with freshly prepared overnight cultures of mixed *Actinomyces viscosus* (ATCC#43146, American Type Culture Collection, Manassas, VA, USA) and *Streptococcus oralis*(ATCC#35037, American Type Culture Collection, Manassas, VA, USA) for 3 h at 37 ◦C. After incubation the MBECTM lids were submerged in TSB and sonicated two times for 2 min each time in order to detach the HAP-bound bacteria into the TSB. The BacTiter-Glo Microbial Cell Viability Assay was utilized on the re-suspended TSB to determine the percent reduction in the cell viability. The percent reduction was calculated by the following equation based on the luminescent output of bacteria removed from untreated surfaces and polymer-treated surfaces: % reduction = 100 × (bacteria attached on untreated surface—bacteria attached on polymer-treated surface)/bacteria on untreated surface.

Bartlett's test (*p* = 0.265) suggested that any variations are not significant, and the samples have equal variances. Therefore one-way analysis of variance (ANOVA) was used to assess the treatment effect and determine the statistical differences between the various sets. A Tukey multiple comparison test was used to assess pairwise treatment differences. A *p* < 0.05 was used to indicate significant statistical differences.

#### *3.8. Contact Angle Measurements*

Contact angle was performed on an Attension Theta instrument from Biolin Scientific (Stockholm, Sweden). Data was analyzed using One Attension software v 2.9. Briefly, 1.0 wt.% polymer solutions in MilliQ water were prepared, and their pH adjusted to 6.5 with concentrated NaOH or HCl. Because of the immediate absorption of solution droplets into hydroxyapatite, surface modification was required prior to treatment with polymer solutions in order to obtain stable droplets for comparison. Sintered HAP was first treated with modified artificial saliva [39] for 1 h (see Supporting Information). After this time, the discs were soaked in 2 mL of polymer solution for three hours on an orbital shaker. The discs were removed and rinsed slightly to remove excess or loosely bound material, and then dried overnight. Contact angle measurements of a 3 μL droplet on four separate HAP discs were collected and averaged to provide statistical significance.
